# PaCkAgE DaTaStReAm pcre 1 6657 # end of header 07070100038274000081a40000000000000000000000014f79239d000000fe000000b500010002ffffffffffffffff0000000d00000000pcre/pkginfoPKG=pcre NAME=pcre 8.30 i86pc Solaris 10 VERSION=8.30 PSTAMP=2nd April 2012 VENDOR=The PCRE Project EMAIL=http://www.pcre.org/ DESC=Perl Compatible Regular Expressions ARCH=i386 CATEGORY=utility CLASSES=none BASEDIR=/ ISTATES=S s 1 2 3 RSTATES=S s 1 2 3 07070100038273000081a40000000000000000000000014f79239d0000380d000000b500010002ffffffffffffffff0000000c00000000pcre/pkgmap: 1 6657 1 d none /usr ? ? ? 1 d none /usr/local ? ? ? 1 d none /usr/local/bin 0755 root root 1 f none /usr/local/bin/pcre-config 0755 root root 2174 23821 1333332030 1 f none /usr/local/bin/pcregrep 0755 root root 38556 46593 1333332030 1 f none /usr/local/bin/pcretest 0755 root root 68440 29516 1333332030 1 d none /usr/local/include 0755 root root 1 f none /usr/local/include/pcre.h 0644 root root 23188 30325 1333332030 1 f none 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62225 1333332030 1 f none /usr/local/share/man/man3/pcreunicode.3 0644 root root 9597 56924 1333332030 1 i checkinstall 790 2504 1333339037 1 i pkginfo 254 19389 1333339037 07070100000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000b00000000TRAILER!!!07070100038274000081a40000000000000000000000014f79239d000000fe000000b500010002ffffffffffffffff0000000800000000pkginfoPKG=pcre NAME=pcre 8.30 i86pc Solaris 10 VERSION=8.30 PSTAMP=2nd April 2012 VENDOR=The PCRE Project EMAIL=http://www.pcre.org/ DESC=Perl Compatible Regular Expressions ARCH=i386 CATEGORY=utility CLASSES=none BASEDIR=/ ISTATES=S s 1 2 3 RSTATES=S s 1 2 3 07070100038273000081a40000000000000000000000014f79239d0000380d000000b500010002ffffffffffffffff0000000700000000pkgmap: 1 6657 1 d none /usr ? ? ? 1 d none /usr/local ? ? ? 1 d none /usr/local/bin 0755 root root 1 f none /usr/local/bin/pcre-config 0755 root root 2174 23821 1333332030 1 f none /usr/local/bin/pcregrep 0755 root root 38556 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760 1333332030 1 f none /usr/local/share/man/man3/pcresyntax.3 0644 root root 11967 62225 1333332030 1 f none /usr/local/share/man/man3/pcreunicode.3 0644 root root 9597 56924 1333332030 1 i checkinstall 790 2504 1333339037 1 i pkginfo 254 19389 1333339037 07070100038485000041ed0000000000000000000000024f79239d00000000000000b500010002ffffffffffffffff0000000800000000install07070100038487000081ed0000000000000000000000014f79239d00000316000000b500010002ffffffffffffffff0000001500000000install/checkinstall#!/bin/sh # expected_bits="64" expected_release="5.10" expected_platform="i386" # release=`uname -r` platform=`uname -p` bits=`isainfo -b` # if [ ${platform} != ${expected_platform} ]; then echo "\n\n\n\tThis package must be installed on a ${expected_platform} architecture\n" echo "\tAborting installation.\n\n\n" exit 1 fi if [ ${release} != ${expected_release} ]; then echo "\n\n\n\tThis package must be installed on a ${expected_release} machine\n" echo "\tAborting installation.\n\n\n" exit 1 fi #if [ ${bits} != ${expected_bits} ]; then # echo "\n\n\n\tThis package must be installed on a ${expected_bits} bit machine\n" # echo "\tYour machine is running a ${bits} bit O.S. currently\n" # echo "\tAborting installation.\n\n\n" # exit 1 #fi exit 0 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 LICENCE Please see the file LICENCE in the PCRE distribution for licensing details. End 070701000382a7000041ed0000000000000000000000024f79239d00000000000000b500010002ffffffffffffffff0000002300000000root/usr/local/share/doc/pcre/html070701000382c9000081a40000000000000000000000014f79083e0001d74c000000b500010002ffffffffffffffff0000003000000000root/usr/local/share/doc/pcre/html/pcreapi.html pcreapi specification

pcreapi man page

Return to the PCRE index page.

This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

#include <pcre.h>


PCRE NATIVE API BASIC FUNCTIONS

pcre *pcre_compile(const char *pattern, int options, const char **errptr, int *erroffset, const unsigned char *tableptr);

pcre *pcre_compile2(const char *pattern, int options, int *errorcodeptr, const char **errptr, int *erroffset, const unsigned char *tableptr);

pcre_extra *pcre_study(const pcre *code, int options, const char **errptr);

void pcre_free_study(pcre_extra *extra);

int pcre_exec(const pcre *code, const pcre_extra *extra, const char *subject, int length, int startoffset, int options, int *ovector, int ovecsize);

int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, const char *subject, int length, int startoffset, int options, int *ovector, int ovecsize, int *workspace, int wscount);


PCRE NATIVE API STRING EXTRACTION FUNCTIONS

int pcre_copy_named_substring(const pcre *code, const char *subject, int *ovector, int stringcount, const char *stringname, char *buffer, int buffersize);

int pcre_copy_substring(const char *subject, int *ovector, int stringcount, int stringnumber, char *buffer, int buffersize);

int pcre_get_named_substring(const pcre *code, const char *subject, int *ovector, int stringcount, const char *stringname, const char **stringptr);

int pcre_get_stringnumber(const pcre *code, const char *name);

int pcre_get_stringtable_entries(const pcre *code, const char *name, char **first, char **last);

int pcre_get_substring(const char *subject, int *ovector, int stringcount, int stringnumber, const char **stringptr);

int pcre_get_substring_list(const char *subject, int *ovector, int stringcount, const char ***listptr);

void pcre_free_substring(const char *stringptr);

void pcre_free_substring_list(const char **stringptr);


PCRE NATIVE API AUXILIARY FUNCTIONS

pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

void pcre_jit_stack_free(pcre_jit_stack *stack);

void pcre_assign_jit_stack(pcre_extra *extra, pcre_jit_callback callback, void *data);

const unsigned char *pcre_maketables(void);

int pcre_fullinfo(const pcre *code, const pcre_extra *extra, int what, void *where);

int pcre_refcount(pcre *code, int adjust);

int pcre_config(int what, void *where);

const char *pcre_version(void);

int pcre_pattern_to_host_byte_order(pcre *code, pcre_extra *extra, const unsigned char *tables);


PCRE NATIVE API INDIRECTED FUNCTIONS

void *(*pcre_malloc)(size_t);

void (*pcre_free)(void *);

void *(*pcre_stack_malloc)(size_t);

void (*pcre_stack_free)(void *);

int (*pcre_callout)(pcre_callout_block *);


PCRE 8-BIT AND 16-BIT LIBRARIES

From release 8.30, PCRE can be compiled as a library for handling 16-bit character strings as well as, or instead of, the original library that handles 8-bit character strings. To avoid too much complication, this document describes the 8-bit versions of the functions, with only occasional references to the 16-bit library.

The 16-bit functions operate in the same way as their 8-bit counterparts; they just use different data types for their arguments and results, and their names start with pcre16_ instead of pcre_. For every option that has UTF8 in its name (for example, PCRE_UTF8), there is a corresponding 16-bit name with UTF8 replaced by UTF16. This facility is in fact just cosmetic; the 16-bit option names define the same bit values.

References to bytes and UTF-8 in this document should be read as references to 16-bit data quantities and UTF-16 when using the 16-bit library, unless specified otherwise. More details of the specific differences for the 16-bit library are given in the pcre16 page.


PCRE API OVERVIEW

PCRE has its own native API, which is described in this document. There are also some wrapper functions (for the 8-bit library only) that correspond to the POSIX regular expression API, but they do not give access to all the functionality. They are described in the pcreposix documentation. Both of these APIs define a set of C function calls. A C++ wrapper (again for the 8-bit library only) is also distributed with PCRE. It is documented in the pcrecpp page.

The native API C function prototypes are defined in the header file pcre.h, and on Unix-like systems the (8-bit) library itself is called libpcre. It can normally be accessed by adding -lpcre to the command for linking an application that uses PCRE. The header file defines the macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release numbers for the library. Applications can use these to include support for different releases of PCRE.

In a Windows environment, if you want to statically link an application program against a non-dll pcre.a file, you must define PCRE_STATIC before including pcre.h or pcrecpp.h, because otherwise the pcre_malloc() and pcre_free() exported functions will be declared __declspec(dllimport), with unwanted results.

The functions pcre_compile(), pcre_compile2(), pcre_study(), and pcre_exec() are used for compiling and matching regular expressions in a Perl-compatible manner. A sample program that demonstrates the simplest way of using them is provided in the file called pcredemo.c in the PCRE source distribution. A listing of this program is given in the pcredemo documentation, and the pcresample documentation describes how to compile and run it.

Just-in-time compiler support is an optional feature of PCRE that can be built in appropriate hardware environments. It greatly speeds up the matching performance of many patterns. Simple programs can easily request that it be used if available, by setting an option that is ignored when it is not relevant. More complicated programs might need to make use of the functions pcre_jit_stack_alloc(), pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control the JIT code's memory usage. These functions are discussed in the pcrejit documentation.

A second matching function, pcre_dfa_exec(), which is not Perl-compatible, is also provided. This uses a different algorithm for the matching. The alternative algorithm finds all possible matches (at a given point in the subject), and scans the subject just once (unless there are lookbehind assertions). However, this algorithm does not return captured substrings. A description of the two matching algorithms and their advantages and disadvantages is given in the pcrematching documentation.

In addition to the main compiling and matching functions, there are convenience functions for extracting captured substrings from a subject string that is matched by pcre_exec(). They are:

  pcre_copy_substring()
  pcre_copy_named_substring()
  pcre_get_substring()
  pcre_get_named_substring()
  pcre_get_substring_list()
  pcre_get_stringnumber()
  pcre_get_stringtable_entries()
pcre_free_substring() and pcre_free_substring_list() are also provided, to free the memory used for extracted strings.

The function pcre_maketables() is used to build a set of character tables in the current locale for passing to pcre_compile(), pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is provided for specialist use. Most commonly, no special tables are passed, in which case internal tables that are generated when PCRE is built are used.

The function pcre_fullinfo() is used to find out information about a compiled pattern. The function pcre_version() returns a pointer to a string containing the version of PCRE and its date of release.

The function pcre_refcount() maintains a reference count in a data block containing a compiled pattern. This is provided for the benefit of object-oriented applications.

The global variables pcre_malloc and pcre_free initially contain the entry points of the standard malloc() and free() functions, respectively. PCRE calls the memory management functions via these variables, so a calling program can replace them if it wishes to intercept the calls. This should be done before calling any PCRE functions.

The global variables pcre_stack_malloc and pcre_stack_free are also indirections to memory management functions. These special functions are used only when PCRE is compiled to use the heap for remembering data, instead of recursive function calls, when running the pcre_exec() function. See the pcrebuild documentation for details of how to do this. It is a non-standard way of building PCRE, for use in environments that have limited stacks. Because of the greater use of memory management, it runs more slowly. Separate functions are provided so that special-purpose external code can be used for this case. When used, these functions are always called in a stack-like manner (last obtained, first freed), and always for memory blocks of the same size. There is a discussion about PCRE's stack usage in the pcrestack documentation.

The global variable pcre_callout initially contains NULL. It can be set by the caller to a "callout" function, which PCRE will then call at specified points during a matching operation. Details are given in the pcrecallout documentation.


NEWLINES

PCRE supports five different conventions for indicating line breaks in strings: a single CR (carriage return) character, a single LF (linefeed) character, the two-character sequence CRLF, any of the three preceding, or any Unicode newline sequence. The Unicode newline sequences are the three just mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029).

Each of the first three conventions is used by at least one operating system as its standard newline sequence. When PCRE is built, a default can be specified. The default default is LF, which is the Unix standard. When PCRE is run, the default can be overridden, either when a pattern is compiled, or when it is matched.

At compile time, the newline convention can be specified by the options argument of pcre_compile(), or it can be specified by special text at the start of the pattern itself; this overrides any other settings. See the pcrepattern page for details of the special character sequences.

In the PCRE documentation the word "newline" is used to mean "the character or pair of characters that indicate a line break". The choice of newline convention affects the handling of the dot, circumflex, and dollar metacharacters, the handling of #-comments in /x mode, and, when CRLF is a recognized line ending sequence, the match position advancement for a non-anchored pattern. There is more detail about this in the section on pcre_exec() options below.

The choice of newline convention does not affect the interpretation of the \n or \r escape sequences, nor does it affect what \R matches, which is controlled in a similar way, but by separate options.


MULTITHREADING

The PCRE functions can be used in multi-threading applications, with the proviso that the memory management functions pointed to by pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the callout function pointed to by pcre_callout, are shared by all threads.

The compiled form of a regular expression is not altered during matching, so the same compiled pattern can safely be used by several threads at once.

If the just-in-time optimization feature is being used, it needs separate memory stack areas for each thread. See the pcrejit documentation for more details.


SAVING PRECOMPILED PATTERNS FOR LATER USE

The compiled form of a regular expression can be saved and re-used at a later time, possibly by a different program, and even on a host other than the one on which it was compiled. Details are given in the pcreprecompile documentation, which includes a description of the pcre_pattern_to_host_byte_order() function. However, compiling a regular expression with one version of PCRE for use with a different version is not guaranteed to work and may cause crashes.


CHECKING BUILD-TIME OPTIONS

int pcre_config(int what, void *where);

The function pcre_config() makes it possible for a PCRE client to discover which optional features have been compiled into the PCRE library. The pcrebuild documentation has more details about these optional features.

The first argument for pcre_config() is an integer, specifying which information is required; the second argument is a pointer to a variable into which the information is placed. The returned value is zero on success, or the negative error code PCRE_ERROR_BADOPTION if the value in the first argument is not recognized. The following information is available:

  PCRE_CONFIG_UTF8
The output is an integer that is set to one if UTF-8 support is available; otherwise it is set to zero. If this option is given to the 16-bit version of this function, pcre16_config(), the result is PCRE_ERROR_BADOPTION.
  PCRE_CONFIG_UTF16
The output is an integer that is set to one if UTF-16 support is available; otherwise it is set to zero. This value should normally be given to the 16-bit version of this function, pcre16_config(). If it is given to the 8-bit version of this function, the result is PCRE_ERROR_BADOPTION.
  PCRE_CONFIG_UNICODE_PROPERTIES
The output is an integer that is set to one if support for Unicode character properties is available; otherwise it is set to zero.
  PCRE_CONFIG_JIT
The output is an integer that is set to one if support for just-in-time compiling is available; otherwise it is set to zero.
  PCRE_CONFIG_JITTARGET
The output is a pointer to a zero-terminated "const char *" string. If JIT support is available, the string contains the name of the architecture for which the JIT compiler is configured, for example "x86 32bit (little endian + unaligned)". If JIT support is not available, the result is NULL.
  PCRE_CONFIG_NEWLINE
The output is an integer whose value specifies the default character sequence that is recognized as meaning "newline". The four values that are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY. Though they are derived from ASCII, the same values are returned in EBCDIC environments. The default should normally correspond to the standard sequence for your operating system.
  PCRE_CONFIG_BSR
The output is an integer whose value indicates what character sequences the \R escape sequence matches by default. A value of 0 means that \R matches any Unicode line ending sequence; a value of 1 means that \R matches only CR, LF, or CRLF. The default can be overridden when a pattern is compiled or matched.
  PCRE_CONFIG_LINK_SIZE
The output is an integer that contains the number of bytes used for internal linkage in compiled regular expressions. For the 8-bit library, the value can be 2, 3, or 4. For the 16-bit library, the value is either 2 or 4 and is still a number of bytes. The default value of 2 is sufficient for all but the most massive patterns, since it allows the compiled pattern to be up to 64K in size. Larger values allow larger regular expressions to be compiled, at the expense of slower matching.
  PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
The output is an integer that contains the threshold above which the POSIX interface uses malloc() for output vectors. Further details are given in the pcreposix documentation.
  PCRE_CONFIG_MATCH_LIMIT
The output is a long integer that gives the default limit for the number of internal matching function calls in a pcre_exec() execution. Further details are given with pcre_exec() below.
  PCRE_CONFIG_MATCH_LIMIT_RECURSION
The output is a long integer that gives the default limit for the depth of recursion when calling the internal matching function in a pcre_exec() execution. Further details are given with pcre_exec() below.
  PCRE_CONFIG_STACKRECURSE
The output is an integer that is set to one if internal recursion when running pcre_exec() is implemented by recursive function calls that use the stack to remember their state. This is the usual way that PCRE is compiled. The output is zero if PCRE was compiled to use blocks of data on the heap instead of recursive function calls. In this case, pcre_stack_malloc and pcre_stack_free are called to manage memory blocks on the heap, thus avoiding the use of the stack.


COMPILING A PATTERN

pcre *pcre_compile(const char *pattern, int options, const char **errptr, int *erroffset, const unsigned char *tableptr); pcre *pcre_compile2(const char *pattern, int options, int *errorcodeptr, const char **errptr, int *erroffset, const unsigned char *tableptr);

Either of the functions pcre_compile() or pcre_compile2() can be called to compile a pattern into an internal form. The only difference between the two interfaces is that pcre_compile2() has an additional argument, errorcodeptr, via which a numerical error code can be returned. To avoid too much repetition, we refer just to pcre_compile() below, but the information applies equally to pcre_compile2().

The pattern is a C string terminated by a binary zero, and is passed in the pattern argument. A pointer to a single block of memory that is obtained via pcre_malloc is returned. This contains the compiled code and related data. The pcre type is defined for the returned block; this is a typedef for a structure whose contents are not externally defined. It is up to the caller to free the memory (via pcre_free) when it is no longer required.

Although the compiled code of a PCRE regex is relocatable, that is, it does not depend on memory location, the complete pcre data block is not fully relocatable, because it may contain a copy of the tableptr argument, which is an address (see below).

The options argument contains various bit settings that affect the compilation. It should be zero if no options are required. The available options are described below. Some of them (in particular, those that are compatible with Perl, but some others as well) can also be set and unset from within the pattern (see the detailed description in the pcrepattern documentation). For those options that can be different in different parts of the pattern, the contents of the options argument specifies their settings at the start of compilation and execution. The PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and PCRE_NO_START_OPT options can be set at the time of matching as well as at compile time.

If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise, if compilation of a pattern fails, pcre_compile() returns NULL, and sets the variable pointed to by errptr to point to a textual error message. This is a static string that is part of the library. You must not try to free it. Normally, the offset from the start of the pattern to the byte that was being processed when the error was discovered is placed in the variable pointed to by erroffset, which must not be NULL (if it is, an immediate error is given). However, for an invalid UTF-8 string, the offset is that of the first byte of the failing character.

Some errors are not detected until the whole pattern has been scanned; in these cases, the offset passed back is the length of the pattern. Note that the offset is in bytes, not characters, even in UTF-8 mode. It may sometimes point into the middle of a UTF-8 character.

If pcre_compile2() is used instead of pcre_compile(), and the errorcodeptr argument is not NULL, a non-zero error code number is returned via this argument in the event of an error. This is in addition to the textual error message. Error codes and messages are listed below.

If the final argument, tableptr, is NULL, PCRE uses a default set of character tables that are built when PCRE is compiled, using the default C locale. Otherwise, tableptr must be an address that is the result of a call to pcre_maketables(). This value is stored with the compiled pattern, and used again by pcre_exec(), unless another table pointer is passed to it. For more discussion, see the section on locale support below.

This code fragment shows a typical straightforward call to pcre_compile():

  pcre *re;
  const char *error;
  int erroffset;
  re = pcre_compile(
    "^A.*Z",          /* the pattern */
    0,                /* default options */
    &error,           /* for error message */
    &erroffset,       /* for error offset */
    NULL);            /* use default character tables */
The following names for option bits are defined in the pcre.h header file:
  PCRE_ANCHORED
If this bit is set, the pattern is forced to be "anchored", that is, it is constrained to match only at the first matching point in the string that is being searched (the "subject string"). This effect can also be achieved by appropriate constructs in the pattern itself, which is the only way to do it in Perl.
  PCRE_AUTO_CALLOUT
If this bit is set, pcre_compile() automatically inserts callout items, all with number 255, before each pattern item. For discussion of the callout facility, see the pcrecallout documentation.
  PCRE_BSR_ANYCRLF
  PCRE_BSR_UNICODE
These options (which are mutually exclusive) control what the \R escape sequence matches. The choice is either to match only CR, LF, or CRLF, or to match any Unicode newline sequence. The default is specified when PCRE is built. It can be overridden from within the pattern, or by setting an option when a compiled pattern is matched.
  PCRE_CASELESS
If this bit is set, letters in the pattern match both upper and lower case letters. It is equivalent to Perl's /i option, and it can be changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the concept of case for characters whose values are less than 128, so caseless matching is always possible. For characters with higher values, the concept of case is supported if PCRE is compiled with Unicode property support, but not otherwise. If you want to use caseless matching for characters 128 and above, you must ensure that PCRE is compiled with Unicode property support as well as with UTF-8 support.
  PCRE_DOLLAR_ENDONLY
If this bit is set, a dollar metacharacter in the pattern matches only at the end of the subject string. Without this option, a dollar also matches immediately before a newline at the end of the string (but not before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set. There is no equivalent to this option in Perl, and no way to set it within a pattern.
  PCRE_DOTALL
If this bit is set, a dot metacharacter in the pattern matches a character of any value, including one that indicates a newline. However, it only ever matches one character, even if newlines are coded as CRLF. Without this option, a dot does not match when the current position is at a newline. This option is equivalent to Perl's /s option, and it can be changed within a pattern by a (?s) option setting. A negative class such as [^a] always matches newline characters, independent of the setting of this option.
  PCRE_DUPNAMES
If this bit is set, names used to identify capturing subpatterns need not be unique. This can be helpful for certain types of pattern when it is known that only one instance of the named subpattern can ever be matched. There are more details of named subpatterns below; see also the pcrepattern documentation.
  PCRE_EXTENDED
If this bit is set, whitespace data characters in the pattern are totally ignored except when escaped or inside a character class. Whitespace does not include the VT character (code 11). In addition, characters between an unescaped # outside a character class and the next newline, inclusive, are also ignored. This is equivalent to Perl's /x option, and it can be changed within a pattern by a (?x) option setting.

Which characters are interpreted as newlines is controlled by the options passed to pcre_compile() or by a special sequence at the start of the pattern, as described in the section entitled "Newline conventions" in the pcrepattern documentation. Note that the end of this type of comment is a literal newline sequence in the pattern; escape sequences that happen to represent a newline do not count.

This option makes it possible to include comments inside complicated patterns. Note, however, that this applies only to data characters. Whitespace characters may never appear within special character sequences in a pattern, for example within the sequence (?( that introduces a conditional subpattern.

  PCRE_EXTRA
This option was invented in order to turn on additional functionality of PCRE that is incompatible with Perl, but it is currently of very little use. When set, any backslash in a pattern that is followed by a letter that has no special meaning causes an error, thus reserving these combinations for future expansion. By default, as in Perl, a backslash followed by a letter with no special meaning is treated as a literal. (Perl can, however, be persuaded to give an error for this, by running it with the -w option.) There are at present no other features controlled by this option. It can also be set by a (?X) option setting within a pattern.
  PCRE_FIRSTLINE
If this option is set, an unanchored pattern is required to match before or at the first newline in the subject string, though the matched text may continue over the newline.
  PCRE_JAVASCRIPT_COMPAT
If this option is set, PCRE's behaviour is changed in some ways so that it is compatible with JavaScript rather than Perl. The changes are as follows:

(1) A lone closing square bracket in a pattern causes a compile-time error, because this is illegal in JavaScript (by default it is treated as a data character). Thus, the pattern AB]CD becomes illegal when this option is set.

(2) At run time, a back reference to an unset subpattern group matches an empty string (by default this causes the current matching alternative to fail). A pattern such as (\1)(a) succeeds when this option is set (assuming it can find an "a" in the subject), whereas it fails by default, for Perl compatibility.

(3) \U matches an upper case "U" character; by default \U causes a compile time error (Perl uses \U to upper case subsequent characters).

(4) \u matches a lower case "u" character unless it is followed by four hexadecimal digits, in which case the hexadecimal number defines the code point to match. By default, \u causes a compile time error (Perl uses it to upper case the following character).

(5) \x matches a lower case "x" character unless it is followed by two hexadecimal digits, in which case the hexadecimal number defines the code point to match. By default, as in Perl, a hexadecimal number is always expected after \x, but it may have zero, one, or two digits (so, for example, \xz matches a binary zero character followed by z).

  PCRE_MULTILINE
By default, PCRE treats the subject string as consisting of a single line of characters (even if it actually contains newlines). The "start of line" metacharacter (^) matches only at the start of the string, while the "end of line" metacharacter ($) matches only at the end of the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.

When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs match immediately following or immediately before internal newlines in the subject string, respectively, as well as at the very start and end. This is equivalent to Perl's /m option, and it can be changed within a pattern by a (?m) option setting. If there are no newlines in a subject string, or no occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.

  PCRE_NEWLINE_CR
  PCRE_NEWLINE_LF
  PCRE_NEWLINE_CRLF
  PCRE_NEWLINE_ANYCRLF
  PCRE_NEWLINE_ANY
These options override the default newline definition that was chosen when PCRE was built. Setting the first or the second specifies that a newline is indicated by a single character (CR or LF, respectively). Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be recognized. The Unicode newline sequences are the three just mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit library, the last two are recognized only in UTF-8 mode.

The newline setting in the options word uses three bits that are treated as a number, giving eight possibilities. Currently only six are used (default plus the five values above). This means that if you set more than one newline option, the combination may or may not be sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and cause an error.

The only time that a line break in a pattern is specially recognized when compiling is when PCRE_EXTENDED is set. CR and LF are whitespace characters, and so are ignored in this mode. Also, an unescaped # outside a character class indicates a comment that lasts until after the next line break sequence. In other circumstances, line break sequences in patterns are treated as literal data.

The newline option that is set at compile time becomes the default that is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.

  PCRE_NO_AUTO_CAPTURE
If this option is set, it disables the use of numbered capturing parentheses in the pattern. Any opening parenthesis that is not followed by ? behaves as if it were followed by ?: but named parentheses can still be used for capturing (and they acquire numbers in the usual way). There is no equivalent of this option in Perl.
  NO_START_OPTIMIZE
This is an option that acts at matching time; that is, it is really an option for pcre_exec() or pcre_dfa_exec(). If it is set at compile time, it is remembered with the compiled pattern and assumed at matching time. For details see the discussion of PCRE_NO_START_OPTIMIZE below.
  PCRE_UCP
This option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W, \w, and some of the POSIX character classes. By default, only ASCII characters are recognized, but if PCRE_UCP is set, Unicode properties are used instead to classify characters. More details are given in the section on generic character types in the pcrepattern page. If you set PCRE_UCP, matching one of the items it affects takes much longer. The option is available only if PCRE has been compiled with Unicode property support.
  PCRE_UNGREEDY
This option inverts the "greediness" of the quantifiers so that they are not greedy by default, but become greedy if followed by "?". It is not compatible with Perl. It can also be set by a (?U) option setting within the pattern.
  PCRE_UTF8
This option causes PCRE to regard both the pattern and the subject as strings of UTF-8 characters instead of single-byte strings. However, it is available only when PCRE is built to include UTF support. If not, the use of this option provokes an error. Details of how this option changes the behaviour of PCRE are given in the pcreunicode page.
  PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is automatically checked. There is a discussion about the validity of UTF-8 strings in the pcreunicode page. If an invalid UTF-8 sequence is found, pcre_compile() returns an error. If you already know that your pattern is valid, and you want to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid UTF-8 string as a pattern is undefined. It may cause your program to crash. Note that this option can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity checking of subject strings.


COMPILATION ERROR CODES

The following table lists the error codes than may be returned by pcre_compile2(), along with the error messages that may be returned by both compiling functions. Note that error messages are always 8-bit ASCII strings, even in 16-bit mode. As PCRE has developed, some error codes have fallen out of use. To avoid confusion, they have not been re-used.

   0  no error
   1  \ at end of pattern
   2  \c at end of pattern
   3  unrecognized character follows \
   4  numbers out of order in {} quantifier
   5  number too big in {} quantifier
   6  missing terminating ] for character class
   7  invalid escape sequence in character class
   8  range out of order in character class
   9  nothing to repeat
  10  [this code is not in use]
  11  internal error: unexpected repeat
  12  unrecognized character after (? or (?-
  13  POSIX named classes are supported only within a class
  14  missing )
  15  reference to non-existent subpattern
  16  erroffset passed as NULL
  17  unknown option bit(s) set
  18  missing ) after comment
  19  [this code is not in use]
  20  regular expression is too large
  21  failed to get memory
  22  unmatched parentheses
  23  internal error: code overflow
  24  unrecognized character after (?<
  25  lookbehind assertion is not fixed length
  26  malformed number or name after (?(
  27  conditional group contains more than two branches
  28  assertion expected after (?(
  29  (?R or (?[+-]digits must be followed by )
  30  unknown POSIX class name
  31  POSIX collating elements are not supported
  32  this version of PCRE is compiled without UTF support
  33  [this code is not in use]
  34  character value in \x{...} sequence is too large
  35  invalid condition (?(0)
  36  \C not allowed in lookbehind assertion
  37  PCRE does not support \L, \l, \N{name}, \U, or \u
  38  number after (?C is > 255
  39  closing ) for (?C expected
  40  recursive call could loop indefinitely
  41  unrecognized character after (?P
  42  syntax error in subpattern name (missing terminator)
  43  two named subpatterns have the same name
  44  invalid UTF-8 string (specifically UTF-8)
  45  support for \P, \p, and \X has not been compiled
  46  malformed \P or \p sequence
  47  unknown property name after \P or \p
  48  subpattern name is too long (maximum 32 characters)
  49  too many named subpatterns (maximum 10000)
  50  [this code is not in use]
  51  octal value is greater than \377 in 8-bit non-UTF-8 mode
  52  internal error: overran compiling workspace
  53  internal error: previously-checked referenced subpattern
        not found
  54  DEFINE group contains more than one branch
  55  repeating a DEFINE group is not allowed
  56  inconsistent NEWLINE options
  57  \g is not followed by a braced, angle-bracketed, or quoted
        name/number or by a plain number
  58  a numbered reference must not be zero
  59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
  60  (*VERB) not recognized
  61  number is too big
  62  subpattern name expected
  63  digit expected after (?+
  64  ] is an invalid data character in JavaScript compatibility mode
  65  different names for subpatterns of the same number are
        not allowed
  66  (*MARK) must have an argument
  67  this version of PCRE is not compiled with Unicode property
        support
  68  \c must be followed by an ASCII character
  69  \k is not followed by a braced, angle-bracketed, or quoted name
  70  internal error: unknown opcode in find_fixedlength()
  71  \N is not supported in a class
  72  too many forward references
  73  disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
  74  invalid UTF-16 string (specifically UTF-16)
The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may be used if the limits were changed when PCRE was built.


STUDYING A PATTERN

pcre_extra *pcre_study(const pcre *code, int options const char **errptr);

If a compiled pattern is going to be used several times, it is worth spending more time analyzing it in order to speed up the time taken for matching. The function pcre_study() takes a pointer to a compiled pattern as its first argument. If studying the pattern produces additional information that will help speed up matching, pcre_study() returns a pointer to a pcre_extra block, in which the study_data field points to the results of the study.

The returned value from pcre_study() can be passed directly to pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also contains other fields that can be set by the caller before the block is passed; these are described below in the section on matching a pattern.

If studying the pattern does not produce any useful information, pcre_study() returns NULL. In that circumstance, if the calling program wants to pass any of the other fields to pcre_exec() or pcre_dfa_exec(), it must set up its own pcre_extra block.

The second argument of pcre_study() contains option bits. There is only one option: PCRE_STUDY_JIT_COMPILE. If this is set, and the just-in-time compiler is available, the pattern is further compiled into machine code that executes much faster than the pcre_exec() matching function. If the just-in-time compiler is not available, this option is ignored. All other bits in the options argument must be zero.

JIT compilation is a heavyweight optimization. It can take some time for patterns to be analyzed, and for one-off matches and simple patterns the benefit of faster execution might be offset by a much slower study time. Not all patterns can be optimized by the JIT compiler. For those that cannot be handled, matching automatically falls back to the pcre_exec() interpreter. For more details, see the pcrejit documentation.

The third argument for pcre_study() is a pointer for an error message. If studying succeeds (even if no data is returned), the variable it points to is set to NULL. Otherwise it is set to point to a textual error message. This is a static string that is part of the library. You must not try to free it. You should test the error pointer for NULL after calling pcre_study(), to be sure that it has run successfully.

When you are finished with a pattern, you can free the memory used for the study data by calling pcre_free_study(). This function was added to the API for release 8.20. For earlier versions, the memory could be freed with pcre_free(), just like the pattern itself. This will still work in cases where PCRE_STUDY_JIT_COMPILE is not used, but it is advisable to change to the new function when convenient.

This is a typical way in which pcre_study() is used (except that in a real application there should be tests for errors):

  int rc;
  pcre *re;
  pcre_extra *sd;
  re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
  sd = pcre_study(
    re,             /* result of pcre_compile() */
    0,              /* no options */
    &error);        /* set to NULL or points to a message */
  rc = pcre_exec(   /* see below for details of pcre_exec() options */
    re, sd, "subject", 7, 0, 0, ovector, 30);
  ...
  pcre_free_study(sd);
  pcre_free(re);
Studying a pattern does two things: first, a lower bound for the length of subject string that is needed to match the pattern is computed. This does not mean that there are any strings of that length that match, but it does guarantee that no shorter strings match. The value is used by pcre_exec() and pcre_dfa_exec() to avoid wasting time by trying to match strings that are shorter than the lower bound. You can find out the value in a calling program via the pcre_fullinfo() function.

Studying a pattern is also useful for non-anchored patterns that do not have a single fixed starting character. A bitmap of possible starting bytes is created. This speeds up finding a position in the subject at which to start matching. (In 16-bit mode, the bitmap is used for 16-bit values less than 256.)

These two optimizations apply to both pcre_exec() and pcre_dfa_exec(). However, they are not used by pcre_exec() if pcre_study() is called with the PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling is successful. The optimizations can be disabled by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_exec() or pcre_dfa_exec(). You might want to do this if your pattern contains callouts or (*MARK) (which cannot be handled by the JIT compiler), and you want to make use of these facilities in cases where matching fails. See the discussion of PCRE_NO_START_OPTIMIZE below.


LOCALE SUPPORT

PCRE handles caseless matching, and determines whether characters are letters, digits, or whatever, by reference to a set of tables, indexed by character value. When running in UTF-8 mode, this applies only to characters with codes less than 128. By default, higher-valued codes never match escapes such as \w or \d, but they can be tested with \p if PCRE is built with Unicode character property support. Alternatively, the PCRE_UCP option can be set at compile time; this causes \w and friends to use Unicode property support instead of built-in tables. The use of locales with Unicode is discouraged. If you are handling characters with codes greater than 128, you should either use UTF-8 and Unicode, or use locales, but not try to mix the two.

PCRE contains an internal set of tables that are used when the final argument of pcre_compile() is NULL. These are sufficient for many applications. Normally, the internal tables recognize only ASCII characters. However, when PCRE is built, it is possible to cause the internal tables to be rebuilt in the default "C" locale of the local system, which may cause them to be different.

The internal tables can always be overridden by tables supplied by the application that calls PCRE. These may be created in a different locale from the default. As more and more applications change to using Unicode, the need for this locale support is expected to die away.

External tables are built by calling the pcre_maketables() function, which has no arguments, in the relevant locale. The result can then be passed to pcre_compile() or pcre_exec() as often as necessary. For example, to build and use tables that are appropriate for the French locale (where accented characters with values greater than 128 are treated as letters), the following code could be used:

  setlocale(LC_CTYPE, "fr_FR");
  tables = pcre_maketables();
  re = pcre_compile(..., tables);
The locale name "fr_FR" is used on Linux and other Unix-like systems; if you are using Windows, the name for the French locale is "french".

When pcre_maketables() runs, the tables are built in memory that is obtained via pcre_malloc. It is the caller's responsibility to ensure that the memory containing the tables remains available for as long as it is needed.

The pointer that is passed to pcre_compile() is saved with the compiled pattern, and the same tables are used via this pointer by pcre_study() and normally also by pcre_exec(). Thus, by default, for any single pattern, compilation, studying and matching all happen in the same locale, but different patterns can be compiled in different locales.

It is possible to pass a table pointer or NULL (indicating the use of the internal tables) to pcre_exec(). Although not intended for this purpose, this facility could be used to match a pattern in a different locale from the one in which it was compiled. Passing table pointers at run time is discussed below in the section on matching a pattern.


INFORMATION ABOUT A PATTERN

int pcre_fullinfo(const pcre *code, const pcre_extra *extra, int what, void *where);

The pcre_fullinfo() function returns information about a compiled pattern. It replaces the pcre_info() function, which was removed from the library at version 8.30, after more than 10 years of obsolescence.

The first argument for pcre_fullinfo() is a pointer to the compiled pattern. The second argument is the result of pcre_study(), or NULL if the pattern was not studied. The third argument specifies which piece of information is required, and the fourth argument is a pointer to a variable to receive the data. The yield of the function is zero for success, or one of the following negative numbers:

  PCRE_ERROR_NULL           the argument code was NULL
                            the argument where was NULL
  PCRE_ERROR_BADMAGIC       the "magic number" was not found
  PCRE_ERROR_BADENDIANNESS  the pattern was compiled with different
                            endianness
  PCRE_ERROR_BADOPTION      the value of what was invalid
The "magic number" is placed at the start of each compiled pattern as an simple check against passing an arbitrary memory pointer. The endianness error can occur if a compiled pattern is saved and reloaded on a different host. Here is a typical call of pcre_fullinfo(), to obtain the length of the compiled pattern:
  int rc;
  size_t length;
  rc = pcre_fullinfo(
    re,               /* result of pcre_compile() */
    sd,               /* result of pcre_study(), or NULL */
    PCRE_INFO_SIZE,   /* what is required */
    &length);         /* where to put the data */
The possible values for the third argument are defined in pcre.h, and are as follows:
  PCRE_INFO_BACKREFMAX
Return the number of the highest back reference in the pattern. The fourth argument should point to an int variable. Zero is returned if there are no back references.
  PCRE_INFO_CAPTURECOUNT
Return the number of capturing subpatterns in the pattern. The fourth argument should point to an int variable.
  PCRE_INFO_DEFAULT_TABLES
Return a pointer to the internal default character tables within PCRE. The fourth argument should point to an unsigned char * variable. This information call is provided for internal use by the pcre_study() function. External callers can cause PCRE to use its internal tables by passing a NULL table pointer.
  PCRE_INFO_FIRSTBYTE
Return information about the first data unit of any matched string, for a non-anchored pattern. (The name of this option refers to the 8-bit library, where data units are bytes.) The fourth argument should point to an int variable.

If there is a fixed first value, for example, the letter "c" from a pattern such as (cat|cow|coyote), its value is returned. In the 8-bit library, the value is always less than 256; in the 16-bit library the value can be up to 0xffff.

If there is no fixed first value, and if either

(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch starts with "^", or

(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set (if it were set, the pattern would be anchored),

-1 is returned, indicating that the pattern matches only at the start of a subject string or after any newline within the string. Otherwise -2 is returned. For anchored patterns, -2 is returned.

  PCRE_INFO_FIRSTTABLE
If the pattern was studied, and this resulted in the construction of a 256-bit table indicating a fixed set of values for the first data unit in any matching string, a pointer to the table is returned. Otherwise NULL is returned. The fourth argument should point to an unsigned char * variable.
  PCRE_INFO_HASCRORLF
Return 1 if the pattern contains any explicit matches for CR or LF characters, otherwise 0. The fourth argument should point to an int variable. An explicit match is either a literal CR or LF character, or \r or \n.
  PCRE_INFO_JCHANGED
Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise 0. The fourth argument should point to an int variable. (?J) and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
  PCRE_INFO_JIT
Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was successful. The fourth argument should point to an int variable. A return value of 0 means that JIT support is not available in this version of PCRE, or that the pattern was not studied with the PCRE_STUDY_JIT_COMPILE option, or that the JIT compiler could not handle this particular pattern. See the pcrejit documentation for details of what can and cannot be handled.
  PCRE_INFO_JITSIZE
If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option, return the size of the JIT compiled code, otherwise return zero. The fourth argument should point to a size_t variable.
  PCRE_INFO_LASTLITERAL
Return the value of the rightmost literal data unit that must exist in any matched string, other than at its start, if such a value has been recorded. The fourth argument should point to an int variable. If there is no such value, -1 is returned. For anchored patterns, a last literal value is recorded only if it follows something of variable length. For example, for the pattern /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value is -1.
  PCRE_INFO_MINLENGTH
If the pattern was studied and a minimum length for matching subject strings was computed, its value is returned. Otherwise the returned value is -1. The value is a number of characters, which in UTF-8 mode may be different from the number of bytes. The fourth argument should point to an int variable. A non-negative value is a lower bound to the length of any matching string. There may not be any strings of that length that do actually match, but every string that does match is at least that long.
  PCRE_INFO_NAMECOUNT
  PCRE_INFO_NAMEENTRYSIZE
  PCRE_INFO_NAMETABLE
PCRE supports the use of named as well as numbered capturing parentheses. The names are just an additional way of identifying the parentheses, which still acquire numbers. Several convenience functions such as pcre_get_named_substring() are provided for extracting captured substrings by name. It is also possible to extract the data directly, by first converting the name to a number in order to access the correct pointers in the output vector (described with pcre_exec() below). To do the conversion, you need to use the name-to-number map, which is described by these three values.

The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each entry; both of these return an int value. The entry size depends on the length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first entry of the table. This is a pointer to char in the 8-bit library, where the first two bytes of each entry are the number of the capturing parenthesis, most significant byte first. In the 16-bit library, the pointer points to 16-bit data units, the first of which contains the parenthesis number. The rest of the entry is the corresponding name, zero terminated.

The names are in alphabetical order. Duplicate names may appear if (?| is used to create multiple groups with the same number, as described in the section on duplicate subpattern numbers in the pcrepattern page. Duplicate names for subpatterns with different numbers are permitted only if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the table in the order in which they were found in the pattern. In the absence of (?| this is the order of increasing number; when (?| is used this is not necessarily the case because later subpatterns may have lower numbers.

As a simple example of the name/number table, consider the following pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is set, so white space - including newlines - is ignored):

  (?<date> (?<year>(\d\d)?\d\d) - (?<month>\d\d) - (?<day>\d\d) )
There are four named subpatterns, so the table has four entries, and each entry in the table is eight bytes long. The table is as follows, with non-printing bytes shows in hexadecimal, and undefined bytes shown as ??:
  00 01 d  a  t  e  00 ??
  00 05 d  a  y  00 ?? ??
  00 04 m  o  n  t  h  00
  00 02 y  e  a  r  00 ??
When writing code to extract data from named subpatterns using the name-to-number map, remember that the length of the entries is likely to be different for each compiled pattern.
  PCRE_INFO_OKPARTIAL
Return 1 if the pattern can be used for partial matching with pcre_exec(), otherwise 0. The fourth argument should point to an int variable. From release 8.00, this always returns 1, because the restrictions that previously applied to partial matching have been lifted. The pcrepartial documentation gives details of partial matching.
  PCRE_INFO_OPTIONS
Return a copy of the options with which the pattern was compiled. The fourth argument should point to an unsigned long int variable. These option bits are those specified in the call to pcre_compile(), modified by any top-level option settings at the start of the pattern itself. In other words, they are the options that will be in force when matching starts. For example, if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.

A pattern is automatically anchored by PCRE if all of its top-level alternatives begin with one of the following:

  ^     unless PCRE_MULTILINE is set
  \A    always
  \G    always
  .*    if PCRE_DOTALL is set and there are no back references to the subpattern in which .* appears
For such patterns, the PCRE_ANCHORED bit is set in the options returned by pcre_fullinfo().
  PCRE_INFO_SIZE
Return the size of the compiled pattern in bytes (for both libraries). The fourth argument should point to a size_t variable. This value does not include the size of the pcre structure that is returned by pcre_compile(). The value that is passed as the argument to pcre_malloc() when pcre_compile() is getting memory in which to place the compiled data is the value returned by this option plus the size of the pcre structure. Studying a compiled pattern, with or without JIT, does not alter the value returned by this option.
  PCRE_INFO_STUDYSIZE
Return the size in bytes of the data block pointed to by the study_data field in a pcre_extra block. If pcre_extra is NULL, or there is no study data, zero is returned. The fourth argument should point to a size_t variable. The study_data field is set by pcre_study() to record information that will speed up matching (see the section entitled "Studying a pattern" above). The format of the study_data block is private, but its length is made available via this option so that it can be saved and restored (see the pcreprecompile documentation for details).


REFERENCE COUNTS

int pcre_refcount(pcre *code, int adjust);

The pcre_refcount() function is used to maintain a reference count in the data block that contains a compiled pattern. It is provided for the benefit of applications that operate in an object-oriented manner, where different parts of the application may be using the same compiled pattern, but you want to free the block when they are all done.

When a pattern is compiled, the reference count field is initialized to zero. It is changed only by calling this function, whose action is to add the adjust value (which may be positive or negative) to it. The yield of the function is the new value. However, the value of the count is constrained to lie between 0 and 65535, inclusive. If the new value is outside these limits, it is forced to the appropriate limit value.

Except when it is zero, the reference count is not correctly preserved if a pattern is compiled on one host and then transferred to a host whose byte-order is different. (This seems a highly unlikely scenario.)


MATCHING A PATTERN: THE TRADITIONAL FUNCTION

int pcre_exec(const pcre *code, const pcre_extra *extra, const char *subject, int length, int startoffset, int options, int *ovector, int ovecsize);

The function pcre_exec() is called to match a subject string against a compiled pattern, which is passed in the code argument. If the pattern was studied, the result of the study should be passed in the extra argument. You can call pcre_exec() with the same code and extra arguments as many times as you like, in order to match different subject strings with the same pattern.

This function is the main matching facility of the library, and it operates in a Perl-like manner. For specialist use there is also an alternative matching function, which is described below in the section about the pcre_dfa_exec() function.

In most applications, the pattern will have been compiled (and optionally studied) in the same process that calls pcre_exec(). However, it is possible to save compiled patterns and study data, and then use them later in different processes, possibly even on different hosts. For a discussion about this, see the pcreprecompile documentation.

Here is an example of a simple call to pcre_exec():

  int rc;
  int ovector[30];
  rc = pcre_exec(
    re,             /* result of pcre_compile() */
    NULL,           /* we didn't study the pattern */
    "some string",  /* the subject string */
    11,             /* the length of the subject string */
    0,              /* start at offset 0 in the subject */
    0,              /* default options */
    ovector,        /* vector of integers for substring information */
    30);            /* number of elements (NOT size in bytes) */


Extra data for pcre_exec()

If the extra argument is not NULL, it must point to a pcre_extra data block. The pcre_study() function returns such a block (when it doesn't return NULL), but you can also create one for yourself, and pass additional information in it. The pcre_extra block contains the following fields (not necessarily in this order):

  unsigned long int flags;
  void *study_data;
  void *executable_jit;
  unsigned long int match_limit;
  unsigned long int match_limit_recursion;
  void *callout_data;
  const unsigned char *tables;
  unsigned char **mark;
In the 16-bit version of this structure, the mark field has type "PCRE_UCHAR16 **".

The flags field is a bitmap that specifies which of the other fields are set. The flag bits are:

  PCRE_EXTRA_STUDY_DATA
  PCRE_EXTRA_EXECUTABLE_JIT
  PCRE_EXTRA_MATCH_LIMIT
  PCRE_EXTRA_MATCH_LIMIT_RECURSION
  PCRE_EXTRA_CALLOUT_DATA
  PCRE_EXTRA_TABLES
  PCRE_EXTRA_MARK
Other flag bits should be set to zero. The study_data field and sometimes the executable_jit field are set in the pcre_extra block that is returned by pcre_study(), together with the appropriate flag bits. You should not set these yourself, but you may add to the block by setting the other fields and their corresponding flag bits.

The match_limit field provides a means of preventing PCRE from using up a vast amount of resources when running patterns that are not going to match, but which have a very large number of possibilities in their search trees. The classic example is a pattern that uses nested unlimited repeats.

Internally, pcre_exec() uses a function called match(), which it calls repeatedly (sometimes recursively). The limit set by match_limit is imposed on the number of times this function is called during a match, which has the effect of limiting the amount of backtracking that can take place. For patterns that are not anchored, the count restarts from zero for each position in the subject string.

When pcre_exec() is called with a pattern that was successfully studied with the PCRE_STUDY_JIT_COMPILE option, the way that the matching is executed is entirely different. However, there is still the possibility of runaway matching that goes on for a very long time, and so the match_limit value is also used in this case (but in a different way) to limit how long the matching can continue.

The default value for the limit can be set when PCRE is built; the default default is 10 million, which handles all but the most extreme cases. You can override the default by suppling pcre_exec() with a pcre_extra block in which match_limit is set, and PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.

The match_limit_recursion field is similar to match_limit, but instead of limiting the total number of times that match() is called, it limits the depth of recursion. The recursion depth is a smaller number than the total number of calls, because not all calls to match() are recursive. This limit is of use only if it is set smaller than match_limit.

Limiting the recursion depth limits the amount of machine stack that can be used, or, when PCRE has been compiled to use memory on the heap instead of the stack, the amount of heap memory that can be used. This limit is not relevant, and is ignored, if the pattern was successfully studied with PCRE_STUDY_JIT_COMPILE.

The default value for match_limit_recursion can be set when PCRE is built; the default default is the same value as the default for match_limit. You can override the default by suppling pcre_exec() with a pcre_extra block in which match_limit_recursion is set, and PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.

The callout_data field is used in conjunction with the "callout" feature, and is described in the pcrecallout documentation.

The tables field is used to pass a character tables pointer to pcre_exec(); this overrides the value that is stored with the compiled pattern. A non-NULL value is stored with the compiled pattern only if custom tables were supplied to pcre_compile() via its tableptr argument. If NULL is passed to pcre_exec() using this mechanism, it forces PCRE's internal tables to be used. This facility is helpful when re-using patterns that have been saved after compiling with an external set of tables, because the external tables might be at a different address when pcre_exec() is called. See the pcreprecompile documentation for a discussion of saving compiled patterns for later use.

If PCRE_EXTRA_MARK is set in the flags field, the mark field must be set to point to a suitable variable. If the pattern contains any backtracking control verbs such as (*MARK:NAME), and the execution ends up with a name to pass back, a pointer to the name string (zero terminated) is placed in the variable pointed to by the mark field. The names are within the compiled pattern; if you wish to retain such a name you must copy it before freeing the memory of a compiled pattern. If there is no name to pass back, the variable pointed to by the mark field is set to NULL. For details of the backtracking control verbs, see the section entitled "Backtracking control" in the pcrepattern documentation.


Option bits for pcre_exec()

The unused bits of the options argument for pcre_exec() must be zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and PCRE_PARTIAL_HARD.

If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option, the only supported options for JIT execution are PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not supported. If an unsupported option is used, JIT execution is disabled and the normal interpretive code in pcre_exec() is run.

  PCRE_ANCHORED
The PCRE_ANCHORED option limits pcre_exec() to matching at the first matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out to be anchored by virtue of its contents, it cannot be made unachored at matching time.
  PCRE_BSR_ANYCRLF
  PCRE_BSR_UNICODE
These options (which are mutually exclusive) control what the \R escape sequence matches. The choice is either to match only CR, LF, or CRLF, or to match any Unicode newline sequence. These options override the choice that was made or defaulted when the pattern was compiled.
  PCRE_NEWLINE_CR
  PCRE_NEWLINE_LF
  PCRE_NEWLINE_CRLF
  PCRE_NEWLINE_ANYCRLF
  PCRE_NEWLINE_ANY
These options override the newline definition that was chosen or defaulted when the pattern was compiled. For details, see the description of pcre_compile() above. During matching, the newline choice affects the behaviour of the dot, circumflex, and dollar metacharacters. It may also alter the way the match position is advanced after a match failure for an unanchored pattern.

When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a match attempt for an unanchored pattern fails when the current position is at a CRLF sequence, and the pattern contains no explicit matches for CR or LF characters, the match position is advanced by two characters instead of one, in other words, to after the CRLF.

The above rule is a compromise that makes the most common cases work as expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not set), it does not match the string "\r\nA" because, after failing at the start, it skips both the CR and the LF before retrying. However, the pattern [\r\n]A does match that string, because it contains an explicit CR or LF reference, and so advances only by one character after the first failure.

An explicit match for CR of LF is either a literal appearance of one of those characters, or one of the \r or \n escape sequences. Implicit matches such as [^X] do not count, nor does \s (which includes CR and LF in the characters that it matches).

Notwithstanding the above, anomalous effects may still occur when CRLF is a valid newline sequence and explicit \r or \n escapes appear in the pattern.

  PCRE_NOTBOL
This option specifies that first character of the subject string is not the beginning of a line, so the circumflex metacharacter should not match before it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex never to match. This option affects only the behaviour of the circumflex metacharacter. It does not affect \A.
  PCRE_NOTEOL
This option specifies that the end of the subject string is not the end of a line, so the dollar metacharacter should not match it nor (except in multiline mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never to match. This option affects only the behaviour of the dollar metacharacter. It does not affect \Z or \z.
  PCRE_NOTEMPTY
An empty string is not considered to be a valid match if this option is set. If there are alternatives in the pattern, they are tried. If all the alternatives match the empty string, the entire match fails. For example, if the pattern
  a?b?
is applied to a string not beginning with "a" or "b", it matches an empty string at the start of the subject. With PCRE_NOTEMPTY set, this match is not valid, so PCRE searches further into the string for occurrences of "a" or "b".
  PCRE_NOTEMPTY_ATSTART
This is like PCRE_NOTEMPTY, except that an empty string match that is not at the start of the subject is permitted. If the pattern is anchored, such a match can occur only if the pattern contains \K.

Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it does make a special case of a pattern match of the empty string within its split() function, and when using the /g modifier. It is possible to emulate Perl's behaviour after matching a null string by first trying the match again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that fails, by advancing the starting offset (see below) and trying an ordinary match again. There is some code that demonstrates how to do this in the pcredemo sample program. In the most general case, you have to check to see if the newline convention recognizes CRLF as a newline, and if so, and the current character is CR followed by LF, advance the starting offset by two characters instead of one.

  PCRE_NO_START_OPTIMIZE
There are a number of optimizations that pcre_exec() uses at the start of a match, in order to speed up the process. For example, if it is known that an unanchored match must start with a specific character, it searches the subject for that character, and fails immediately if it cannot find it, without actually running the main matching function. This means that a special item such as (*COMMIT) at the start of a pattern is not considered until after a suitable starting point for the match has been found. When callouts or (*MARK) items are in use, these "start-up" optimizations can cause them to be skipped if the pattern is never actually used. The start-up optimizations are in effect a pre-scan of the subject that takes place before the pattern is run.

The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly causing performance to suffer, but ensuring that in cases where the result is "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK) are considered at every possible starting position in the subject string. If PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching time.

Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation. Consider the pattern

  (*COMMIT)ABC
When this is compiled, PCRE records the fact that a match must start with the character "A". Suppose the subject string is "DEFABC". The start-up optimization scans along the subject, finds "A" and runs the first match attempt from there. The (*COMMIT) item means that the pattern must match the current starting position, which in this case, it does. However, if the same match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the subject string does not happen. The first match attempt is run starting from "D" and when this fails, (*COMMIT) prevents any further matches being tried, so the overall result is "no match". If the pattern is studied, more start-up optimizations may be used. For example, a minimum length for the subject may be recorded. Consider the pattern
  (*MARK:A)(X|Y)
The minimum length for a match is one character. If the subject is "ABC", there will be attempts to match "ABC", "BC", "C", and then finally an empty string. If the pattern is studied, the final attempt does not take place, because PCRE knows that the subject is too short, and so the (*MARK) is never encountered. In this case, studying the pattern does not affect the overall match result, which is still "no match", but it does affect the auxiliary information that is returned.
  PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8 string is automatically checked when pcre_exec() is subsequently called. The value of startoffset is also checked to ensure that it points to the start of a UTF-8 character. There is a discussion about the validity of UTF-8 strings in the pcreunicode page. If an invalid sequence of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In both cases, information about the precise nature of the error may also be returned (see the descriptions of these errors in the section entitled \fIError return values from\fP pcre_exec() below). If startoffset contains a value that does not point to the start of a UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.

If you already know that your subject is valid, and you want to skip these checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to do this for the second and subsequent calls to pcre_exec() if you are making repeated calls to find all the matches in a single subject string. However, you should be sure that the value of startoffset points to the start of a character (or the end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a subject or an invalid value of startoffset is undefined. Your program may crash.

  PCRE_PARTIAL_HARD
  PCRE_PARTIAL_SOFT
These options turn on the partial matching feature. For backwards compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match occurs if the end of the subject string is reached successfully, but there are not enough subject characters to complete the match. If this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by testing any remaining alternatives. Only if no complete match can be found is PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match, but only if no complete match can be found.

If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a partial match is found, pcre_exec() immediately returns PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words, when PCRE_PARTIAL_HARD is set, a partial match is considered to be more important that an alternative complete match.

In both cases, the portion of the string that was inspected when the partial match was found is set as the first matching string. There is a more detailed discussion of partial and multi-segment matching, with examples, in the pcrepartial documentation.


The string to be matched by pcre_exec()

The subject string is passed to pcre_exec() as a pointer in subject, a length in bytes in length, and a starting byte offset in startoffset. If this is negative or greater than the length of the subject, pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is zero, the search for a match starts at the beginning of the subject, and this is by far the most common case. In UTF-8 mode, the byte offset must point to the start of a UTF-8 character (or the end of the subject). Unlike the pattern string, the subject may contain binary zero bytes.

A non-zero starting offset is useful when searching for another match in the same subject by calling pcre_exec() again after a previous success. Setting startoffset differs from just passing over a shortened string and setting PCRE_NOTBOL in the case of a pattern that begins with any kind of lookbehind. For example, consider the pattern

  \Biss\B
which finds occurrences of "iss" in the middle of words. (\B matches only if the current position in the subject is not a word boundary.) When applied to the string "Mississipi" the first call to pcre_exec() finds the first occurrence. If pcre_exec() is called again with just the remainder of the subject, namely "issipi", it does not match, because \B is always false at the start of the subject, which is deemed to be a word boundary. However, if pcre_exec() is passed the entire string again, but with startoffset set to 4, it finds the second occurrence of "iss" because it is able to look behind the starting point to discover that it is preceded by a letter.

Finding all the matches in a subject is tricky when the pattern can match an empty string. It is possible to emulate Perl's /g behaviour by first trying the match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED options, and then if that fails, advancing the starting offset and trying an ordinary match again. There is some code that demonstrates how to do this in the pcredemo sample program. In the most general case, you have to check to see if the newline convention recognizes CRLF as a newline, and if so, and the current character is CR followed by LF, advance the starting offset by two characters instead of one.

If a non-zero starting offset is passed when the pattern is anchored, one attempt to match at the given offset is made. This can only succeed if the pattern does not require the match to be at the start of the subject.


How pcre_exec() returns captured substrings

In general, a pattern matches a certain portion of the subject, and in addition, further substrings from the subject may be picked out by parts of the pattern. Following the usage in Jeffrey Friedl's book, this is called "capturing" in what follows, and the phrase "capturing subpattern" is used for a fragment of a pattern that picks out a substring. PCRE supports several other kinds of parenthesized subpattern that do not cause substrings to be captured.

Captured substrings are returned to the caller via a vector of integers whose address is passed in ovector. The number of elements in the vector is passed in ovecsize, which must be a non-negative number. Note: this argument is NOT the size of ovector in bytes.

The first two-thirds of the vector is used to pass back captured substrings, each substring using a pair of integers. The remaining third of the vector is used as workspace by pcre_exec() while matching capturing subpatterns, and is not available for passing back information. The number passed in ovecsize should always be a multiple of three. If it is not, it is rounded down.

When a match is successful, information about captured substrings is returned in pairs of integers, starting at the beginning of ovector, and continuing up to two-thirds of its length at the most. The first element of each pair is set to the byte offset of the first character in a substring, and the second is set to the byte offset of the first character after the end of a substring. Note: these values are always byte offsets, even in UTF-8 mode. They are not character counts.

The first pair of integers, ovector[0] and ovector[1], identify the portion of the subject string matched by the entire pattern. The next pair is used for the first capturing subpattern, and so on. The value returned by pcre_exec() is one more than the highest numbered pair that has been set. For example, if two substrings have been captured, the returned value is 3. If there are no capturing subpatterns, the return value from a successful match is 1, indicating that just the first pair of offsets has been set.

If a capturing subpattern is matched repeatedly, it is the last portion of the string that it matched that is returned.

If the vector is too small to hold all the captured substring offsets, it is used as far as possible (up to two-thirds of its length), and the function returns a value of zero. If neither the actual string matched not any captured substrings are of interest, pcre_exec() may be called with ovector passed as NULL and ovecsize as zero. However, if the pattern contains back references and the ovector is not big enough to remember the related substrings, PCRE has to get additional memory for use during matching. Thus it is usually advisable to supply an ovector of reasonable size.

There are some cases where zero is returned (indicating vector overflow) when in fact the vector is exactly the right size for the final match. For example, consider the pattern

  (a)(?:(b)c|bd)
If a vector of 6 elements (allowing for only 1 captured substring) is given with subject string "abd", pcre_exec() will try to set the second captured string, thereby recording a vector overflow, before failing to match "c" and backing up to try the second alternative. The zero return, however, does correctly indicate that the maximum number of slots (namely 2) have been filled. In similar cases where there is temporary overflow, but the final number of used slots is actually less than the maximum, a non-zero value is returned.

The pcre_fullinfo() function can be used to find out how many capturing subpatterns there are in a compiled pattern. The smallest size for ovector that will allow for n captured substrings, in addition to the offsets of the substring matched by the whole pattern, is (n+1)*3.

It is possible for capturing subpattern number n+1 to match some part of the subject when subpattern n has not been used at all. For example, if the string "abc" is matched against the pattern (a|(z))(bc) the return from the function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this happens, both values in the offset pairs corresponding to unused subpatterns are set to -1.

Offset values that correspond to unused subpatterns at the end of the expression are also set to -1. For example, if the string "abc" is matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The return from the function is 2, because the highest used capturing subpattern number is 1, and the offsets for for the second and third capturing subpatterns (assuming the vector is large enough, of course) are set to -1.

Note: Elements in the first two-thirds of ovector that do not correspond to capturing parentheses in the pattern are never changed. That is, if a pattern contains n capturing parentheses, no more than ovector[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in the first two-thirds) retain whatever values they previously had.

Some convenience functions are provided for extracting the captured substrings as separate strings. These are described below.


Error return values from pcre_exec()

If pcre_exec() fails, it returns a negative number. The following are defined in the header file:

  PCRE_ERROR_NOMATCH        (-1)
The subject string did not match the pattern.
  PCRE_ERROR_NULL           (-2)
Either code or subject was passed as NULL, or ovector was NULL and ovecsize was not zero.
  PCRE_ERROR_BADOPTION      (-3)
An unrecognized bit was set in the options argument.
  PCRE_ERROR_BADMAGIC       (-4)
PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch the case when it is passed a junk pointer and to detect when a pattern that was compiled in an environment of one endianness is run in an environment with the other endianness. This is the error that PCRE gives when the magic number is not present.
  PCRE_ERROR_UNKNOWN_OPCODE (-5)
While running the pattern match, an unknown item was encountered in the compiled pattern. This error could be caused by a bug in PCRE or by overwriting of the compiled pattern.
  PCRE_ERROR_NOMEMORY       (-6)
If a pattern contains back references, but the ovector that is passed to pcre_exec() is not big enough to remember the referenced substrings, PCRE gets a block of memory at the start of matching to use for this purpose. If the call via pcre_malloc() fails, this error is given. The memory is automatically freed at the end of matching.

This error is also given if pcre_stack_malloc() fails in pcre_exec(). This can happen only when PCRE has been compiled with --disable-stack-for-recursion.

  PCRE_ERROR_NOSUBSTRING    (-7)
This error is used by the pcre_copy_substring(), pcre_get_substring(), and pcre_get_substring_list() functions (see below). It is never returned by pcre_exec().
  PCRE_ERROR_MATCHLIMIT     (-8)
The backtracking limit, as specified by the match_limit field in a pcre_extra structure (or defaulted) was reached. See the description above.
  PCRE_ERROR_CALLOUT        (-9)
This error is never generated by pcre_exec() itself. It is provided for use by callout functions that want to yield a distinctive error code. See the pcrecallout documentation for details.
  PCRE_ERROR_BADUTF8        (-10)
A string that contains an invalid UTF-8 byte sequence was passed as a subject, and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector (ovecsize) is at least 2, the byte offset to the start of the the invalid UTF-8 character is placed in the first element, and a reason code is placed in the second element. The reason codes are listed in the following section. For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 character at the end of the subject (reason codes 1 to 5), PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
  PCRE_ERROR_BADUTF8_OFFSET (-11)
The UTF-8 byte sequence that was passed as a subject was checked and found to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of startoffset did not point to the beginning of a UTF-8 character or the end of the subject.
  PCRE_ERROR_PARTIAL        (-12)
The subject string did not match, but it did match partially. See the pcrepartial documentation for details of partial matching.
  PCRE_ERROR_BADPARTIAL     (-13)
This code is no longer in use. It was formerly returned when the PCRE_PARTIAL option was used with a compiled pattern containing items that were not supported for partial matching. From release 8.00 onwards, there are no restrictions on partial matching.
  PCRE_ERROR_INTERNAL       (-14)
An unexpected internal error has occurred. This error could be caused by a bug in PCRE or by overwriting of the compiled pattern.
  PCRE_ERROR_BADCOUNT       (-15)
This error is given if the value of the ovecsize argument is negative.
  PCRE_ERROR_RECURSIONLIMIT (-21)
The internal recursion limit, as specified by the match_limit_recursion field in a pcre_extra structure (or defaulted) was reached. See the description above.
  PCRE_ERROR_BADNEWLINE     (-23)
An invalid combination of PCRE_NEWLINE_xxx options was given.
  PCRE_ERROR_BADOFFSET      (-24)
The value of startoffset was negative or greater than the length of the subject, that is, the value in length.
  PCRE_ERROR_SHORTUTF8      (-25)
This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set. Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this case, but this special error code for PCRE_PARTIAL_HARD precedes the implementation of returned information; it is retained for backwards compatibility.
  PCRE_ERROR_RECURSELOOP    (-26)
This error is returned when pcre_exec() detects a recursion loop within the pattern. Specifically, it means that either the whole pattern or a subpattern has been called recursively for the second time at the same position in the subject string. Some simple patterns that might do this are detected and faulted at compile time, but more complicated cases, in particular mutual recursions between two different subpatterns, cannot be detected until run time.
  PCRE_ERROR_JIT_STACKLIMIT (-27)
This error is returned when a pattern that was successfully studied using the PCRE_STUDY_JIT_COMPILE option is being matched, but the memory available for the just-in-time processing stack is not large enough. See the pcrejit documentation for more details.
  PCRE_ERROR_BADMODE (-28)
This error is given if a pattern that was compiled by the 8-bit library is passed to a 16-bit library function, or vice versa.
  PCRE_ERROR_BADENDIANNESS (-29)
This error is given if a pattern that was compiled and saved is reloaded on a host with different endianness. The utility function pcre_pattern_to_host_byte_order() can be used to convert such a pattern so that it runs on the new host.

Error numbers -16 to -20 and -22 are not used by pcre_exec().


Reason codes for invalid UTF-8 strings

This section applies only to the 8-bit library. The corresponding information for the 16-bit library is given in the pcre16 page.

When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORTUTF8, and the size of the output vector (ovecsize) is at least 2, the offset of the start of the invalid UTF-8 character is placed in the first output vector element (ovector[0]) and a reason code is placed in the second element (ovector[1]). The reason codes are given names in the pcre.h header file:

  PCRE_UTF8_ERR1
  PCRE_UTF8_ERR2
  PCRE_UTF8_ERR3
  PCRE_UTF8_ERR4
  PCRE_UTF8_ERR5
The string ends with a truncated UTF-8 character; the code specifies how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279) allows for up to 6 bytes, and this is checked first; hence the possibility of 4 or 5 missing bytes.
  PCRE_UTF8_ERR6
  PCRE_UTF8_ERR7
  PCRE_UTF8_ERR8
  PCRE_UTF8_ERR9
  PCRE_UTF8_ERR10
The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the character do not have the binary value 0b10 (that is, either the most significant bit is 0, or the next bit is 1).
  PCRE_UTF8_ERR11
  PCRE_UTF8_ERR12
A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long; these code points are excluded by RFC 3629.
  PCRE_UTF8_ERR13
A 4-byte character has a value greater than 0x10fff; these code points are excluded by RFC 3629.
  PCRE_UTF8_ERR14
A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of code points are reserved by RFC 3629 for use with UTF-16, and so are excluded from UTF-8.
  PCRE_UTF8_ERR15
  PCRE_UTF8_ERR16
  PCRE_UTF8_ERR17
  PCRE_UTF8_ERR18
  PCRE_UTF8_ERR19
A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a value that can be represented by fewer bytes, which is invalid. For example, the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just one byte.
  PCRE_UTF8_ERR20
The two most significant bits of the first byte of a character have the binary value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a byte can only validly occur as the second or subsequent byte of a multi-byte character.
  PCRE_UTF8_ERR21
The first byte of a character has the value 0xfe or 0xff. These values can never occur in a valid UTF-8 string.


EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

int pcre_copy_substring(const char *subject, int *ovector, int stringcount, int stringnumber, char *buffer, int buffersize);

int pcre_get_substring(const char *subject, int *ovector, int stringcount, int stringnumber, const char **stringptr);

int pcre_get_substring_list(const char *subject, int *ovector, int stringcount, const char ***listptr);

Captured substrings can be accessed directly by using the offsets returned by pcre_exec() in ovector. For convenience, the functions pcre_copy_substring(), pcre_get_substring(), and pcre_get_substring_list() are provided for extracting captured substrings as new, separate, zero-terminated strings. These functions identify substrings by number. The next section describes functions for extracting named substrings.

A substring that contains a binary zero is correctly extracted and has a further zero added on the end, but the result is not, of course, a C string. However, you can process such a string by referring to the length that is returned by pcre_copy_substring() and pcre_get_substring(). Unfortunately, the interface to pcre_get_substring_list() is not adequate for handling strings containing binary zeros, because the end of the final string is not independently indicated.

The first three arguments are the same for all three of these functions: subject is the subject string that has just been successfully matched, ovector is a pointer to the vector of integer offsets that was passed to pcre_exec(), and stringcount is the number of substrings that were captured by the match, including the substring that matched the entire regular expression. This is the value returned by pcre_exec() if it is greater than zero. If pcre_exec() returned zero, indicating that it ran out of space in ovector, the value passed as stringcount should be the number of elements in the vector divided by three.

The functions pcre_copy_substring() and pcre_get_substring() extract a single substring, whose number is given as stringnumber. A value of zero extracts the substring that matched the entire pattern, whereas higher values extract the captured substrings. For pcre_copy_substring(), the string is placed in buffer, whose length is given by buffersize, while for pcre_get_substring() a new block of memory is obtained via pcre_malloc, and its address is returned via stringptr. The yield of the function is the length of the string, not including the terminating zero, or one of these error codes:

  PCRE_ERROR_NOMEMORY       (-6)
The buffer was too small for pcre_copy_substring(), or the attempt to get memory failed for pcre_get_substring().
  PCRE_ERROR_NOSUBSTRING    (-7)
There is no substring whose number is stringnumber.

The pcre_get_substring_list() function extracts all available substrings and builds a list of pointers to them. All this is done in a single block of memory that is obtained via pcre_malloc. The address of the memory block is returned via listptr, which is also the start of the list of string pointers. The end of the list is marked by a NULL pointer. The yield of the function is zero if all went well, or the error code

  PCRE_ERROR_NOMEMORY       (-6)
if the attempt to get the memory block failed.

When any of these functions encounter a substring that is unset, which can happen when capturing subpattern number n+1 matches some part of the subject, but subpattern n has not been used at all, they return an empty string. This can be distinguished from a genuine zero-length substring by inspecting the appropriate offset in ovector, which is negative for unset substrings.

The two convenience functions pcre_free_substring() and pcre_free_substring_list() can be used to free the memory returned by a previous call of pcre_get_substring() or pcre_get_substring_list(), respectively. They do nothing more than call the function pointed to by pcre_free, which of course could be called directly from a C program. However, PCRE is used in some situations where it is linked via a special interface to another programming language that cannot use pcre_free directly; it is for these cases that the functions are provided.


EXTRACTING CAPTURED SUBSTRINGS BY NAME

int pcre_get_stringnumber(const pcre *code, const char *name);

int pcre_copy_named_substring(const pcre *code, const char *subject, int *ovector, int stringcount, const char *stringname, char *buffer, int buffersize);

int pcre_get_named_substring(const pcre *code, const char *subject, int *ovector, int stringcount, const char *stringname, const char **stringptr);

To extract a substring by name, you first have to find associated number. For example, for this pattern

  (a+)b(?<xxx>\d+)...
the number of the subpattern called "xxx" is 2. If the name is known to be unique (PCRE_DUPNAMES was not set), you can find the number from the name by calling pcre_get_stringnumber(). The first argument is the compiled pattern, and the second is the name. The yield of the function is the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of that name.

Given the number, you can extract the substring directly, or use one of the functions described in the previous section. For convenience, there are also two functions that do the whole job.

Most of the arguments of pcre_copy_named_substring() and pcre_get_named_substring() are the same as those for the similarly named functions that extract by number. As these are described in the previous section, they are not re-described here. There are just two differences:

First, instead of a substring number, a substring name is given. Second, there is an extra argument, given at the start, which is a pointer to the compiled pattern. This is needed in order to gain access to the name-to-number translation table.

These functions call pcre_get_stringnumber(), and if it succeeds, they then call pcre_copy_substring() or pcre_get_substring(), as appropriate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the behaviour may not be what you want (see the next section).

Warning: If the pattern uses the (?| feature to set up multiple subpatterns with the same number, as described in the section on duplicate subpattern numbers in the pcrepattern page, you cannot use names to distinguish the different subpatterns, because names are not included in the compiled code. The matching process uses only numbers. For this reason, the use of different names for subpatterns of the same number causes an error at compile time.


DUPLICATE SUBPATTERN NAMES

int pcre_get_stringtable_entries(const pcre *code, const char *name, char **first, char **last);

When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns are not required to be unique. (Duplicate names are always allowed for subpatterns with the same number, created by using the (?| feature. Indeed, if such subpatterns are named, they are required to use the same names.)

Normally, patterns with duplicate names are such that in any one match, only one of the named subpatterns participates. An example is shown in the pcrepattern documentation.

When duplicates are present, pcre_copy_named_substring() and pcre_get_named_substring() return the first substring corresponding to the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is returned; no data is returned. The pcre_get_stringnumber() function returns one of the numbers that are associated with the name, but it is not defined which it is.

If you want to get full details of all captured substrings for a given name, you must use the pcre_get_stringtable_entries() function. The first argument is the compiled pattern, and the second is the name. The third and fourth are pointers to variables which are updated by the function. After it has run, they point to the first and last entries in the name-to-number table for the given name. The function itself returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is described above in the section entitled Information about a pattern above. Given all the relevant entries for the name, you can extract each of their numbers, and hence the captured data, if any.


FINDING ALL POSSIBLE MATCHES

The traditional matching function uses a similar algorithm to Perl, which stops when it finds the first match, starting at a given point in the subject. If you want to find all possible matches, or the longest possible match, consider using the alternative matching function (see below) instead. If you cannot use the alternative function, but still need to find all possible matches, you can kludge it up by making use of the callout facility, which is described in the pcrecallout documentation.

What you have to do is to insert a callout right at the end of the pattern. When your callout function is called, extract and save the current matched substring. Then return 1, which forces pcre_exec() to backtrack and try other alternatives. Ultimately, when it runs out of matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.


OBTAINING AN ESTIMATE OF STACK USAGE

Matching certain patterns using pcre_exec() can use a lot of process stack, which in certain environments can be rather limited in size. Some users find it helpful to have an estimate of the amount of stack that is used by pcre_exec(), to help them set recursion limits, as described in the pcrestack documentation. The estimate that is output by pcretest when called with the -m and -C options is obtained by calling pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its first five arguments.

Normally, if its first argument is NULL, pcre_exec() immediately returns the negative error code PCRE_ERROR_NULL, but with this special combination of arguments, it returns instead a negative number whose absolute value is the approximate stack frame size in bytes. (A negative number is used so that it is clear that no match has happened.) The value is approximate because in some cases, recursive calls to pcre_exec() occur when there are one or two additional variables on the stack.

If PCRE has been compiled to use the heap instead of the stack for recursion, the value returned is the size of each block that is obtained from the heap.


MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, const char *subject, int length, int startoffset, int options, int *ovector, int ovecsize, int *workspace, int wscount);

The function pcre_dfa_exec() is called to match a subject string against a compiled pattern, using a matching algorithm that scans the subject string just once, and does not backtrack. This has different characteristics to the normal algorithm, and is not compatible with Perl. Some of the features of PCRE patterns are not supported. Nevertheless, there are times when this kind of matching can be useful. For a discussion of the two matching algorithms, and a list of features that pcre_dfa_exec() does not support, see the pcrematching documentation.

The arguments for the pcre_dfa_exec() function are the same as for pcre_exec(), plus two extras. The ovector argument is used in a different way, and this is described below. The other common arguments are used in the same way as for pcre_exec(), so their description is not repeated here.

The two additional arguments provide workspace for the function. The workspace vector should contain at least 20 elements. It is used for keeping track of multiple paths through the pattern tree. More workspace will be needed for patterns and subjects where there are a lot of potential matches.

Here is an example of a simple call to pcre_dfa_exec():

  int rc;
  int ovector[10];
  int wspace[20];
  rc = pcre_dfa_exec(
    re,             /* result of pcre_compile() */
    NULL,           /* we didn't study the pattern */
    "some string",  /* the subject string */
    11,             /* the length of the subject string */
    0,              /* start at offset 0 in the subject */
    0,              /* default options */
    ovector,        /* vector of integers for substring information */
    10,             /* number of elements (NOT size in bytes) */
    wspace,         /* working space vector */
    20);            /* number of elements (NOT size in bytes) */


Option bits for pcre_dfa_exec()

The unused bits of the options argument for pcre_dfa_exec() must be zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last four of these are exactly the same as for pcre_exec(), so their description is not repeated here.

  PCRE_PARTIAL_HARD
  PCRE_PARTIAL_SOFT
These have the same general effect as they do for pcre_exec(), but the details are slightly different. When PCRE_PARTIAL_HARD is set for pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the subject is reached and there is still at least one matching possibility that requires additional characters. This happens even if some complete matches have also been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached, there have been no complete matches, but there is still at least one matching possibility. The portion of the string that was inspected when the longest partial match was found is set as the first matching string in both cases. There is a more detailed discussion of partial and multi-segment matching, with examples, in the pcrepartial documentation.
  PCRE_DFA_SHORTEST
Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as soon as it has found one match. Because of the way the alternative algorithm works, this is necessarily the shortest possible match at the first possible matching point in the subject string.
  PCRE_DFA_RESTART
When pcre_dfa_exec() returns a partial match, it is possible to call it again, with additional subject characters, and have it continue with the same match. The PCRE_DFA_RESTART option requests this action; when it is set, the workspace and wscount options must reference the same vector as before because data about the match so far is left in them after a partial match. There is more discussion of this facility in the pcrepartial documentation.


Successful returns from pcre_dfa_exec()

When pcre_dfa_exec() succeeds, it may have matched more than one substring in the subject. Note, however, that all the matches from one run of the function start at the same point in the subject. The shorter matches are all initial substrings of the longer matches. For example, if the pattern

  <.*>
is matched against the string
  This is <something> <something else> <something further> no more
the three matched strings are
  <something>
  <something> <something else>
  <something> <something else> <something further>
On success, the yield of the function is a number greater than zero, which is the number of matched substrings. The substrings themselves are returned in ovector. Each string uses two elements; the first is the offset to the start, and the second is the offset to the end. In fact, all the strings have the same start offset. (Space could have been saved by giving this only once, but it was decided to retain some compatibility with the way pcre_exec() returns data, even though the meaning of the strings is different.)

The strings are returned in reverse order of length; that is, the longest matching string is given first. If there were too many matches to fit into ovector, the yield of the function is zero, and the vector is filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() can use the entire ovector for returning matched strings.


Error returns from pcre_dfa_exec()

The pcre_dfa_exec() function returns a negative number when it fails. Many of the errors are the same as for pcre_exec(), and these are described above. There are in addition the following errors that are specific to pcre_dfa_exec():

  PCRE_ERROR_DFA_UITEM      (-16)
This return is given if pcre_dfa_exec() encounters an item in the pattern that it does not support, for instance, the use of \C or a back reference.
  PCRE_ERROR_DFA_UCOND      (-17)
This return is given if pcre_dfa_exec() encounters a condition item that uses a back reference for the condition, or a test for recursion in a specific group. These are not supported.
  PCRE_ERROR_DFA_UMLIMIT    (-18)
This return is given if pcre_dfa_exec() is called with an extra block that contains a setting of the match_limit or match_limit_recursion fields. This is not supported (these fields are meaningless for DFA matching).
  PCRE_ERROR_DFA_WSSIZE     (-19)
This return is given if pcre_dfa_exec() runs out of space in the workspace vector.
  PCRE_ERROR_DFA_RECURSE    (-20)
When a recursive subpattern is processed, the matching function calls itself recursively, using private vectors for ovector and workspace. This error is given if the output vector is not large enough. This should be extremely rare, as a vector of size 1000 is used.


SEE ALSO

pcre16(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 21 January 2012
Copyright © 1997-2012 University of Cambridge.

Return to the PCRE index page.

070701000382b9000081a40000000000000000000000014f79083e0000087a000000b500010002ffffffffffffffff0000004100000000root/usr/local/share/doc/pcre/html/pcre_get_named_substring.html pcre_get_named_substring specification

pcre_get_named_substring man page

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This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

SYNOPSIS

#include <pcre.h>

int pcre_get_named_substring(const pcre *code, const char *subject, int *ovector, int stringcount, const char *stringname, const char **stringptr);

int pcre16_get_named_substring(const pcre16 *code, PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 stringname, PCRE_SPTR16 *stringptr);


DESCRIPTION

This is a convenience function for extracting a captured substring by name. The arguments are:

  code          Compiled pattern
  subject       Subject that has been successfully matched
  ovector       Offset vector that pcre[16]_exec() used
  stringcount   Value returned by pcre[16]_exec()
  stringname    Name of the required substring
  stringptr     Where to put the string pointer
The memory in which the substring is placed is obtained by calling pcre[16]_malloc(). The convenience function pcre[16]_free_substring() can be used to free it when it is no longer needed. The yield of the function is the length of the extracted substring, PCRE_ERROR_NOMEMORY if sufficient memory could not be obtained, or PCRE_ERROR_NOSUBSTRING if the string name is invalid.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

Return to the PCRE index page.

070701000382bb000081a40000000000000000000000014f79083e00000752000000b500010002ffffffffffffffff0000004500000000root/usr/local/share/doc/pcre/html/pcre_get_stringtable_entries.html pcre_get_stringtable_entries specification

pcre_get_stringtable_entries man page

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SYNOPSIS

#include <pcre.h>

int pcre_get_stringtable_entries(const pcre *code, const char *name, char **first, char **last);

int pcre16_get_stringtable_entries(const pcre16 *code, PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last);


DESCRIPTION

This convenience function finds, for a compiled pattern, the first and last entries for a given name in the table that translates capturing parenthesis names into numbers. When names are required to be unique (PCRE_DUPNAMES is not set), it is usually easier to use pcre[16]_get_stringnumber() instead.

  code    Compiled regular expression
  name    Name whose entries required
  first   Where to return a pointer to the first entry
  last    Where to return a pointer to the last entry
The yield of the function is the length of each entry, or PCRE_ERROR_NOSUBSTRING if none are found.

There is a complete description of the PCRE native API, including the format of the table entries, in the pcreapi page, and a description of the POSIX API in the pcreposix page.

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070701000382c1000081a40000000000000000000000014f79083e00000531000000b500010002ffffffffffffffff0000003800000000root/usr/local/share/doc/pcre/html/pcre_maketables.html pcre_maketables specification

pcre_maketables man page

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SYNOPSIS

#include <pcre.h>

const unsigned char *pcre_maketables(void);

const unsigned char *pcre16_maketables(void);


DESCRIPTION

This function builds a set of character tables for character values less than 256. These can be passed to pcre[16]_compile() to override PCRE's internal, built-in tables (which were made by pcre[16]_maketables() when PCRE was compiled). You might want to do this if you are using a non-standard locale. The function yields a pointer to the tables.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382ae000081a40000000000000000000000014f79083e00001074000000b500010002ffffffffffffffff0000003600000000root/usr/local/share/doc/pcre/html/pcre_compile2.html pcre_compile2 specification

pcre_compile2 man page

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SYNOPSIS

#include <pcre.h>

pcre *pcre_compile2(const char *pattern, int options, int *errorcodeptr, const char **errptr, int *erroffset, const unsigned char *tableptr);

pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options, int *errorcodeptr, const char **errptr, int *erroffset, const unsigned char *tableptr);


DESCRIPTION

This function compiles a regular expression into an internal form. It is the same as pcre[16]_compile(), except for the addition of the errorcodeptr argument. The arguments are:

  pattern       A zero-terminated string containing the
                  regular expression to be compiled
  options       Zero or more option bits
  errorcodeptr  Where to put an error code
  errptr        Where to put an error message
  erroffset     Offset in pattern where error was found
  tableptr      Pointer to character tables, or NULL to
                  use the built-in default
The option bits are:
  PCRE_ANCHORED           Force pattern anchoring
  PCRE_AUTO_CALLOUT       Compile automatic callouts
  PCRE_BSR_ANYCRLF        \R matches only CR, LF, or CRLF
  PCRE_BSR_UNICODE        \R matches all Unicode line endings
  PCRE_CASELESS           Do caseless matching
  PCRE_DOLLAR_ENDONLY     $ not to match newline at end
  PCRE_DOTALL             . matches anything including NL
  PCRE_DUPNAMES           Allow duplicate names for subpatterns
  PCRE_EXTENDED           Ignore whitespace and # comments
  PCRE_EXTRA              PCRE extra features
                            (not much use currently)
  PCRE_FIRSTLINE          Force matching to be before newline
  PCRE_JAVASCRIPT_COMPAT  JavaScript compatibility
  PCRE_MULTILINE          ^ and $ match newlines within data
  PCRE_NEWLINE_ANY        Recognize any Unicode newline sequence
  PCRE_NEWLINE_ANYCRLF    Recognize CR, LF, and CRLF as newline
                            sequences
  PCRE_NEWLINE_CR         Set CR as the newline sequence
  PCRE_NEWLINE_CRLF       Set CRLF as the newline sequence
  PCRE_NEWLINE_LF         Set LF as the newline sequence
  PCRE_NO_AUTO_CAPTURE    Disable numbered capturing paren-
                            theses (named ones available)
  PCRE_NO_UTF16_CHECK     Do not check the pattern for UTF-16
                            validity (only relevant if
                            PCRE_UTF16 is set)
  PCRE_NO_UTF8_CHECK      Do not check the pattern for UTF-8
                            validity (only relevant if
                            PCRE_UTF8 is set)
  PCRE_UCP                Use Unicode properties for \d, \w, etc.
  PCRE_UNGREEDY           Invert greediness of quantifiers
  PCRE_UTF16              Run pcre16_compile() in UTF-16 mode
  PCRE_UTF8               Run pcre_compile() in UTF-8 mode
PCRE must be built with UTF support in order to use PCRE_UTF8/16 and PCRE_NO_UTF8/16_CHECK, and with UCP support if PCRE_UCP is used.

The yield of the function is a pointer to a private data structure that contains the compiled pattern, or NULL if an error was detected. Note that compiling regular expressions with one version of PCRE for use with a different version is not guaranteed to work and may cause crashes.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

Return to the PCRE index page.

070701000382bd000081a40000000000000000000000014f79083e000007dc000000b500010002ffffffffffffffff0000004000000000root/usr/local/share/doc/pcre/html/pcre_get_substring_list.html pcre_get_substring_list specification

pcre_get_substring_list man page

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SYNOPSIS

#include <pcre.h>

int pcre_get_substring_list(const char *subject, int *ovector, int stringcount, const char ***listptr);

int pcre16_get_substring_list(PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 **listptr);


DESCRIPTION

This is a convenience function for extracting a list of all the captured substrings. The arguments are:

  subject       Subject that has been successfully matched
  ovector       Offset vector that pcre[16]_exec used
  stringcount   Value returned by pcre[16]_exec
  listptr       Where to put a pointer to the list
The memory in which the substrings and the list are placed is obtained by calling pcre[16]_malloc(). The convenience function pcre[16]_free_substring_list() can be used to free it when it is no longer needed. A pointer to a list of pointers is put in the variable whose address is in listptr. The list is terminated by a NULL pointer. The yield of the function is zero on success or PCRE_ERROR_NOMEMORY if sufficient memory could not be obtained.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

Return to the PCRE index page.

070701000382b2000081a40000000000000000000000014f79083e000014b5000000b500010002ffffffffffffffff0000003600000000root/usr/local/share/doc/pcre/html/pcre_dfa_exec.html pcre_dfa_exec specification

pcre_dfa_exec man page

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SYNOPSIS

#include <pcre.h>

int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, const char *subject, int length, int startoffset, int options, int *ovector, int ovecsize, int *workspace, int wscount);

int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra, PCRE_SPTR16 subject, int length, int startoffset, int options, int *ovector, int ovecsize, int *workspace, int wscount);


DESCRIPTION

This function matches a compiled regular expression against a given subject string, using an alternative matching algorithm that scans the subject string just once (not Perl-compatible). Note that the main, Perl-compatible, matching function is pcre[16]_exec(). The arguments for this function are:

  code         Points to the compiled pattern
  extra        Points to an associated pcre[16]_extra structure,
                 or is NULL
  subject      Points to the subject string
  length       Length of the subject string, in bytes
  startoffset  Offset in bytes in the subject at which to
                 start matching
  options      Option bits
  ovector      Points to a vector of ints for result offsets
  ovecsize     Number of elements in the vector
  workspace    Points to a vector of ints used as working space
  wscount      Number of elements in the vector
The options are:
  PCRE_ANCHORED          Match only at the first position
  PCRE_BSR_ANYCRLF       \R matches only CR, LF, or CRLF
  PCRE_BSR_UNICODE       \R matches all Unicode line endings
  PCRE_NEWLINE_ANY       Recognize any Unicode newline sequence
  PCRE_NEWLINE_ANYCRLF   Recognize CR, LF, & CRLF as newline sequences
  PCRE_NEWLINE_CR        Recognize CR as the only newline sequence
  PCRE_NEWLINE_CRLF      Recognize CRLF as the only newline sequence
  PCRE_NEWLINE_LF        Recognize LF as the only newline sequence
  PCRE_NOTBOL            Subject is not the beginning of a line
  PCRE_NOTEOL            Subject is not the end of a line
  PCRE_NOTEMPTY          An empty string is not a valid match
  PCRE_NOTEMPTY_ATSTART  An empty string at the start of the subject
                           is not a valid match
  PCRE_NO_START_OPTIMIZE Do not do "start-match" optimizations
  PCRE_NO_UTF16_CHECK    Do not check the subject for UTF-16
                           validity (only relevant if PCRE_UTF16
                           was set at compile time)
  PCRE_NO_UTF8_CHECK     Do not check the subject for UTF-8
                           validity (only relevant if PCRE_UTF8
                           was set at compile time)
  PCRE_PARTIAL           ) Return PCRE_ERROR_PARTIAL for a partial
  PCRE_PARTIAL_SOFT      )   match if no full matches are found
  PCRE_PARTIAL_HARD      Return PCRE_ERROR_PARTIAL for a partial match
                           even if there is a full match as well
  PCRE_DFA_SHORTEST      Return only the shortest match
  PCRE_DFA_RESTART       Restart after a partial match
There are restrictions on what may appear in a pattern when using this matching function. Details are given in the pcrematching documentation. For details of partial matching, see the pcrepartial page.

A pcre[16]_extra structure contains the following fields:

  flags            Bits indicating which fields are set
  study_data       Opaque data from pcre[16]_study()
  match_limit      Limit on internal resource use
  match_limit_recursion  Limit on internal recursion depth
  callout_data     Opaque data passed back to callouts
  tables           Points to character tables or is NULL
  mark             For passing back a *MARK pointer
  executable_jit   Opaque data from JIT compilation
The flag bits are PCRE_EXTRA_STUDY_DATA, PCRE_EXTRA_MATCH_LIMIT, PCRE_EXTRA_MATCH_LIMIT_RECURSION, PCRE_EXTRA_CALLOUT_DATA, PCRE_EXTRA_TABLES, PCRE_EXTRA_MARK and PCRE_EXTRA_EXECUTABLE_JIT. For this matching function, the match_limit and match_limit_recursion fields are not used, and must not be set. The PCRE_EXTRA_EXECUTABLE_JIT flag and the corresponding variable are ignored.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

Return to the PCRE index page.

070701000382af000081a40000000000000000000000014f79083e00000d82000000b500010002ffffffffffffffff0000003400000000root/usr/local/share/doc/pcre/html/pcre_config.html pcre_config specification

pcre_config man page

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This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

SYNOPSIS

#include <pcre.h>

int pcre_config(int what, void *where);

int pcre16_config(int what, void *where);


DESCRIPTION

This function makes it possible for a client program to find out which optional features are available in the version of the PCRE library it is using. The arguments are as follows:

  what     A code specifying what information is required
  where    Points to where to put the data
The where argument must point to an integer variable, except for PCRE_CONFIG_MATCH_LIMIT and PCRE_CONFIG_MATCH_LIMIT_RECURSION, when it must point to an unsigned long integer. The available codes are:
  PCRE_CONFIG_JIT           Availability of just-in-time compiler
                              support (1=yes 0=no)
  PCRE_CONFIG_JITTARGET     String containing information about the
                              target architecture for the JIT compiler,
                              or NULL if there is no JIT support
  PCRE_CONFIG_LINK_SIZE     Internal link size: 2, 3, or 4
  PCRE_CONFIG_MATCH_LIMIT   Internal resource limit
  PCRE_CONFIG_MATCH_LIMIT_RECURSION
                            Internal recursion depth limit
  PCRE_CONFIG_NEWLINE       Value of the default newline sequence:
                                13 (0x000d)    for CR
                                10 (0x000a)    for LF
                              3338 (0x0d0a)    for CRLF
                                -2             for ANYCRLF
                                -1             for ANY
  PCRE_CONFIG_BSR           Indicates what \R matches by default:
                                 0             all Unicode line endings
                                 1             CR, LF, or CRLF only
  PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
                            Threshold of return slots, above which
                              malloc() is used by the POSIX API
  PCRE_CONFIG_STACKRECURSE  Recursion implementation (1=stack 0=heap)
  PCRE_CONFIG_UTF16         Availability of UTF-16 support (1=yes
                               0=no); option for pcre16_config()
  PCRE_CONFIG_UTF8          Availability of UTF-8 support (1=yes 0=no);
                              option for pcre_config()
  PCRE_CONFIG_UNICODE_PROPERTIES
                            Availability of Unicode property support
                              (1=yes 0=no)
The function yields 0 on success or PCRE_ERROR_BADOPTION otherwise. That error is also given if PCRE_CONFIG_UTF16 is passed to pcre_config() or if PCRE_CONFIG_UTF8 is passed to pcre16_config().

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

Return to the PCRE index page.

070701000382db000081a40000000000000000000000014f79083e0000a3e1000000b500010002ffffffffffffffff0000003100000000root/usr/local/share/doc/pcre/html/pcretest.html pcretest specification

pcretest man page

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SYNOPSIS

pcretest [options] [input file [output file]]

pcretest was written as a test program for the PCRE regular expression library itself, but it can also be used for experimenting with regular expressions. This document describes the features of the test program; for details of the regular expressions themselves, see the pcrepattern documentation. For details of the PCRE library function calls and their options, see the pcreapi and pcre16 documentation. The input for pcretest is a sequence of regular expression patterns and strings to be matched, as described below. The output shows the result of each match. Options on the command line and the patterns control PCRE options and exactly what is output.


PCRE's 8-BIT and 16-BIT LIBRARIES

From release 8.30, two separate PCRE libraries can be built. The original one supports 8-bit character strings, whereas the newer 16-bit library supports character strings encoded in 16-bit units. The pcretest program can be used to test both libraries. However, it is itself still an 8-bit program, reading 8-bit input and writing 8-bit output. When testing the 16-bit library, the patterns and data strings are converted to 16-bit format before being passed to the PCRE library functions. Results are converted to 8-bit for output.

References to functions and structures of the form pcre[16]_xx below mean "pcre_xx when using the 8-bit library or pcre16_xx when using the 16-bit library".


COMMAND LINE OPTIONS

-16 If both the 8-bit and the 16-bit libraries have been built, this option causes the 16-bit library to be used. If only the 16-bit library has been built, this is the default (so has no effect). If only the 8-bit library has been built, this option causes an error.

-b Behave as if each pattern has the /B (show byte code) modifier; the internal form is output after compilation.

-C Output the version number of the PCRE library, and all available information about the optional features that are included, and then exit. All other options are ignored.

-C option Output information about a specific build-time option, then exit. This functionality is intended for use in scripts such as RunTest. The following options output the value indicated:

  linksize   the internal link size (2, 3, or 4)
  newline    the default newline setting:
               CR, LF, CRLF, ANYCRLF, or ANY
The following options output 1 for true or zero for false:
  jit        just-in-time support is available
  pcre16     the 16-bit library was built
  pcre8      the 8-bit library was built
  ucp        Unicode property support is available
  utf        UTF-8 and/or UTF-16 support is available

-d Behave as if each pattern has the /D (debug) modifier; the internal form and information about the compiled pattern is output after compilation; -d is equivalent to -b -i.

-dfa Behave as if each data line contains the \D escape sequence; this causes the alternative matching function, pcre[16]_dfa_exec(), to be used instead of the standard pcre[16]_exec() function (more detail is given below).

-help Output a brief summary these options and then exit.

-i Behave as if each pattern has the /I modifier; information about the compiled pattern is given after compilation.

-M Behave as if each data line contains the \M escape sequence; this causes PCRE to discover the minimum MATCH_LIMIT and MATCH_LIMIT_RECURSION settings by calling pcre[16]_exec() repeatedly with different limits.

-m Output the size of each compiled pattern after it has been compiled. This is equivalent to adding /M to each regular expression. The size is given in bytes for both libraries.

-o osize Set the number of elements in the output vector that is used when calling pcre[16]_exec() or pcre[16]_dfa_exec() to be osize. The default value is 45, which is enough for 14 capturing subexpressions for pcre[16]_exec() or 22 different matches for pcre[16]_dfa_exec(). The vector size can be changed for individual matching calls by including \O in the data line (see below).

-p Behave as if each pattern has the /P modifier; the POSIX wrapper API is used to call PCRE. None of the other options has any effect when -p is set. This option can be used only with the 8-bit library.

-q Do not output the version number of pcretest at the start of execution.

-S size On Unix-like systems, set the size of the run-time stack to size megabytes.

-s or -s+ Behave as if each pattern has the /S modifier; in other words, force each pattern to be studied. If -s+ is used, the PCRE_STUDY_JIT_COMPILE flag is passed to pcre[16]_study(), causing just-in-time optimization to be set up if it is available. If the /I or /D option is present on a pattern (requesting output about the compiled pattern), information about the result of studying is not included when studying is caused only by -s and neither -i nor -d is present on the command line. This behaviour means that the output from tests that are run with and without -s should be identical, except when options that output information about the actual running of a match are set.

The -M, -t, and -tm options, which give information about resources used, are likely to produce different output with and without -s. Output may also differ if the /C option is present on an individual pattern. This uses callouts to trace the the matching process, and this may be different between studied and non-studied patterns. If the pattern contains (*MARK) items there may also be differences, for the same reason. The -s command line option can be overridden for specific patterns that should never be studied (see the /S pattern modifier below).

-t Run each compile, study, and match many times with a timer, and output resulting time per compile or match (in milliseconds). Do not set -m with -t, because you will then get the size output a zillion times, and the timing will be distorted. You can control the number of iterations that are used for timing by following -t with a number (as a separate item on the command line). For example, "-t 1000" would iterate 1000 times. The default is to iterate 500000 times.

-tm This is like -t except that it times only the matching phase, not the compile or study phases.


DESCRIPTION

If pcretest is given two filename arguments, it reads from the first and writes to the second. If it is given only one filename argument, it reads from that file and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and prompts for each line of input, using "re>" to prompt for regular expressions, and "data>" to prompt for data lines.

When pcretest is built, a configuration option can specify that it should be linked with the libreadline library. When this is done, if the input is from a terminal, it is read using the readline() function. This provides line-editing and history facilities. The output from the -help option states whether or not readline() will be used.

The program handles any number of sets of input on a single input file. Each set starts with a regular expression, and continues with any number of data lines to be matched against the pattern.

Each data line is matched separately and independently. If you want to do multi-line matches, you have to use the \n escape sequence (or \r or \r\n, etc., depending on the newline setting) in a single line of input to encode the newline sequences. There is no limit on the length of data lines; the input buffer is automatically extended if it is too small.

An empty line signals the end of the data lines, at which point a new regular expression is read. The regular expressions are given enclosed in any non-alphanumeric delimiters other than backslash, for example:

  /(a|bc)x+yz/
White space before the initial delimiter is ignored. A regular expression may be continued over several input lines, in which case the newline characters are included within it. It is possible to include the delimiter within the pattern by escaping it, for example
  /abc\/def/
If you do so, the escape and the delimiter form part of the pattern, but since delimiters are always non-alphanumeric, this does not affect its interpretation. If the terminating delimiter is immediately followed by a backslash, for example,
  /abc/\
then a backslash is added to the end of the pattern. This is done to provide a way of testing the error condition that arises if a pattern finishes with a backslash, because
  /abc\/
is interpreted as the first line of a pattern that starts with "abc/", causing pcretest to read the next line as a continuation of the regular expression.


PATTERN MODIFIERS

A pattern may be followed by any number of modifiers, which are mostly single characters. Following Perl usage, these are referred to below as, for example, "the /i modifier", even though the delimiter of the pattern need not always be a slash, and no slash is used when writing modifiers. White space may appear between the final pattern delimiter and the first modifier, and between the modifiers themselves.

The /i, /m, /s, and /x modifiers set the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively, when pcre[16]_compile() is called. These four modifier letters have the same effect as they do in Perl. For example:

  /caseless/i
The following table shows additional modifiers for setting PCRE compile-time options that do not correspond to anything in Perl:
  /8              PCRE_UTF8           ) when using the 8-bit
  /?              PCRE_NO_UTF8_CHECK  )   library

  /8              PCRE_UTF16          ) when using the 16-bit
  /?              PCRE_NO_UTF16_CHECK )   library

  /A              PCRE_ANCHORED
  /C              PCRE_AUTO_CALLOUT
  /E              PCRE_DOLLAR_ENDONLY
  /f              PCRE_FIRSTLINE
  /J              PCRE_DUPNAMES
  /N              PCRE_NO_AUTO_CAPTURE
  /U              PCRE_UNGREEDY
  /W              PCRE_UCP
  /X              PCRE_EXTRA
  /Y              PCRE_NO_START_OPTIMIZE
  /<JS>           PCRE_JAVASCRIPT_COMPAT
  /<cr>           PCRE_NEWLINE_CR
  /<lf>           PCRE_NEWLINE_LF
  /<crlf>         PCRE_NEWLINE_CRLF
  /<anycrlf>      PCRE_NEWLINE_ANYCRLF
  /<any>          PCRE_NEWLINE_ANY
  /<bsr_anycrlf>  PCRE_BSR_ANYCRLF
  /<bsr_unicode>  PCRE_BSR_UNICODE
The modifiers that are enclosed in angle brackets are literal strings as shown, including the angle brackets, but the letters within can be in either case. This example sets multiline matching with CRLF as the line ending sequence:
  /^abc/m<CRLF>
As well as turning on the PCRE_UTF8/16 option, the /8 modifier causes all non-printing characters in output strings to be printed using the \x{hh...} notation. Otherwise, those less than 0x100 are output in hex without the curly brackets.

Full details of the PCRE options are given in the pcreapi documentation.


Finding all matches in a string

Searching for all possible matches within each subject string can be requested by the /g or /G modifier. After finding a match, PCRE is called again to search the remainder of the subject string. The difference between /g and /G is that the former uses the startoffset argument to pcre[16]_exec() to start searching at a new point within the entire string (which is in effect what Perl does), whereas the latter passes over a shortened substring. This makes a difference to the matching process if the pattern begins with a lookbehind assertion (including \b or \B).

If any call to pcre[16]_exec() in a /g or /G sequence matches an empty string, the next call is done with the PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED flags set in order to search for another, non-empty, match at the same point. If this second match fails, the start offset is advanced, and the normal match is retried. This imitates the way Perl handles such cases when using the /g modifier or the split() function. Normally, the start offset is advanced by one character, but if the newline convention recognizes CRLF as a newline, and the current character is CR followed by LF, an advance of two is used.


Other modifiers

There are yet more modifiers for controlling the way pcretest operates.

The /+ modifier requests that as well as outputting the substring that matched the entire pattern, pcretest should in addition output the remainder of the subject string. This is useful for tests where the subject contains multiple copies of the same substring. If the + modifier appears twice, the same action is taken for captured substrings. In each case the remainder is output on the following line with a plus character following the capture number. Note that this modifier must not immediately follow the /S modifier because /S+ has another meaning.

The /= modifier requests that the values of all potential captured parentheses be output after a match. By default, only those up to the highest one actually used in the match are output (corresponding to the return code from pcre[16]_exec()). Values in the offsets vector corresponding to higher numbers should be set to -1, and these are output as "<unset>". This modifier gives a way of checking that this is happening.

The /B modifier is a debugging feature. It requests that pcretest output a representation of the compiled code after compilation. Normally this information contains length and offset values; however, if /Z is also present, this data is replaced by spaces. This is a special feature for use in the automatic test scripts; it ensures that the same output is generated for different internal link sizes.

The /D modifier is a PCRE debugging feature, and is equivalent to /BI, that is, both the /B and the /I modifiers.

The /F modifier causes pcretest to flip the byte order of the 2-byte and 4-byte fields in the compiled pattern. This facility is for testing the feature in PCRE that allows it to execute patterns that were compiled on a host with a different endianness. This feature is not available when the POSIX interface to PCRE is being used, that is, when the /P pattern modifier is specified. See also the section about saving and reloading compiled patterns below.

The /I modifier requests that pcretest output information about the compiled pattern (whether it is anchored, has a fixed first character, and so on). It does this by calling pcre[16]_fullinfo() after compiling a pattern. If the pattern is studied, the results of that are also output.

The /K modifier requests pcretest to show names from backtracking control verbs that are returned from calls to pcre[16]_exec(). It causes pcretest to create a pcre[16]_extra block if one has not already been created by a call to pcre[16]_study(), and to set the PCRE_EXTRA_MARK flag and the mark field within it, every time that pcre[16]_exec() is called. If the variable that the mark field points to is non-NULL for a match, non-match, or partial match, pcretest prints the string to which it points. For a match, this is shown on a line by itself, tagged with "MK:". For a non-match it is added to the message.

The /L modifier must be followed directly by the name of a locale, for example,

  /pattern/Lfr_FR
For this reason, it must be the last modifier. The given locale is set, pcre[16]_maketables() is called to build a set of character tables for the locale, and this is then passed to pcre[16]_compile() when compiling the regular expression. Without an /L (or /T) modifier, NULL is passed as the tables pointer; that is, /L applies only to the expression on which it appears.

The /M modifier causes the size in bytes of the memory block used to hold the compiled pattern to be output. This does not include the size of the pcre[16] block; it is just the actual compiled data. If the pattern is successfully studied with the PCRE_STUDY_JIT_COMPILE option, the size of the JIT compiled code is also output.

If the /S modifier appears once, it causes pcre[16]_study() to be called after the expression has been compiled, and the results used when the expression is matched. If /S appears twice, it suppresses studying, even if it was requested externally by the -s command line option. This makes it possible to specify that certain patterns are always studied, and others are never studied, independently of -s. This feature is used in the test files in a few cases where the output is different when the pattern is studied.

If the /S modifier is immediately followed by a + character, the call to pcre[16]_study() is made with the PCRE_STUDY_JIT_COMPILE option, requesting just-in-time optimization support if it is available. Note that there is also a /+ modifier; it must not be given immediately after /S because this will be misinterpreted. If JIT studying is successful, it will automatically be used when pcre[16]_exec() is run, except when incompatible run-time options are specified. These include the partial matching options; a complete list is given in the pcrejit documentation. See also the \J escape sequence below for a way of setting the size of the JIT stack.

The /T modifier must be followed by a single digit. It causes a specific set of built-in character tables to be passed to pcre[16]_compile(). It is used in the standard PCRE tests to check behaviour with different character tables. The digit specifies the tables as follows:

  0   the default ASCII tables, as distributed in
        pcre_chartables.c.dist
  1   a set of tables defining ISO 8859 characters
In table 1, some characters whose codes are greater than 128 are identified as letters, digits, spaces, etc.


Using the POSIX wrapper API

The /P modifier causes pcretest to call PCRE via the POSIX wrapper API rather than its native API. This supports only the 8-bit library. When /P is set, the following modifiers set options for the regcomp() function:

  /i    REG_ICASE
  /m    REG_NEWLINE
  /N    REG_NOSUB
  /s    REG_DOTALL     )
  /U    REG_UNGREEDY   ) These options are not part of
  /W    REG_UCP        )   the POSIX standard
  /8    REG_UTF8       )
The /+ modifier works as described above. All other modifiers are ignored.


DATA LINES

Before each data line is passed to pcre[16]_exec(), leading and trailing white space is removed, and it is then scanned for \ escapes. Some of these are pretty esoteric features, intended for checking out some of the more complicated features of PCRE. If you are just testing "ordinary" regular expressions, you probably don't need any of these. The following escapes are recognized:

  \a         alarm (BEL, \x07)
  \b         backspace (\x08)
  \e         escape (\x27)
  \f         form feed (\x0c)
  \n         newline (\x0a)
  \qdd       set the PCRE_MATCH_LIMIT limit to dd (any number of digits)
  \r         carriage return (\x0d)
  \t         tab (\x09)
  \v         vertical tab (\x0b)
  \nnn       octal character (up to 3 octal digits); always
               a byte unless > 255 in UTF-8 or 16-bit mode
  \xhh       hexadecimal byte (up to 2 hex digits)
  \x{hh...}  hexadecimal character (any number of hex digits)
  \A         pass the PCRE_ANCHORED option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \B         pass the PCRE_NOTBOL option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \Cdd       call pcre[16]_copy_substring() for substring dd after a successful match (number less than 32)
  \Cname     call pcre[16]_copy_named_substring() for substring "name" after a successful match (name termin-
               ated by next non alphanumeric character)
  \C+        show the current captured substrings at callout time
  \C-        do not supply a callout function
  \C!n       return 1 instead of 0 when callout number n is reached
  \C!n!m     return 1 instead of 0 when callout number n is reached for the nth time
  \C*n       pass the number n (may be negative) as callout data; this is used as the callout return value
  \D         use the pcre[16]_dfa_exec() match function
  \F         only shortest match for pcre[16]_dfa_exec()
  \Gdd       call pcre[16]_get_substring() for substring dd after a successful match (number less than 32)
  \Gname     call pcre[16]_get_named_substring() for substring "name" after a successful match (name termin-
               ated by next non-alphanumeric character)
  \Jdd       set up a JIT stack of dd kilobytes maximum (any number of digits)
  \L         call pcre[16]_get_substringlist() after a successful match
  \M         discover the minimum MATCH_LIMIT and MATCH_LIMIT_RECURSION settings
  \N         pass the PCRE_NOTEMPTY option to pcre[16]_exec() or pcre[16]_dfa_exec(); if used twice, pass the
               PCRE_NOTEMPTY_ATSTART option
  \Odd       set the size of the output vector passed to pcre[16]_exec() to dd (any number of digits)
  \P         pass the PCRE_PARTIAL_SOFT option to pcre[16]_exec() or pcre[16]_dfa_exec(); if used twice, pass the
               PCRE_PARTIAL_HARD option
  \Qdd       set the PCRE_MATCH_LIMIT_RECURSION limit to dd (any number of digits)
  \R         pass the PCRE_DFA_RESTART option to pcre[16]_dfa_exec()
  \S         output details of memory get/free calls during matching
  \Y         pass the PCRE_NO_START_OPTIMIZE option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \Z         pass the PCRE_NOTEOL option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \?         pass the PCRE_NO_UTF[8|16]_CHECK option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \>dd       start the match at offset dd (optional "-"; then any number of digits); this sets the startoffset
               argument for pcre[16]_exec() or pcre[16]_dfa_exec()
  \<cr>      pass the PCRE_NEWLINE_CR option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \<lf>      pass the PCRE_NEWLINE_LF option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \<crlf>    pass the PCRE_NEWLINE_CRLF option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \<anycrlf> pass the PCRE_NEWLINE_ANYCRLF option to pcre[16]_exec() or pcre[16]_dfa_exec()
  \<any>     pass the PCRE_NEWLINE_ANY option to pcre[16]_exec() or pcre[16]_dfa_exec()
The use of \x{hh...} is not dependent on the use of the /8 modifier on the pattern. It is recognized always. There may be any number of hexadecimal digits inside the braces; invalid values provoke error messages.

Note that \xhh specifies one byte rather than one character in UTF-8 mode; this makes it possible to construct invalid UTF-8 sequences for testing purposes. On the other hand, \x{hh} is interpreted as a UTF-8 character in UTF-8 mode, generating more than one byte if the value is greater than 127. When testing the 8-bit library not in UTF-8 mode, \x{hh} generates one byte for values less than 256, and causes an error for greater values.

In UTF-16 mode, all 4-digit \x{hhhh} values are accepted. This makes it possible to construct invalid UTF-16 sequences for testing purposes.

The escapes that specify line ending sequences are literal strings, exactly as shown. No more than one newline setting should be present in any data line.

A backslash followed by anything else just escapes the anything else. If the very last character is a backslash, it is ignored. This gives a way of passing an empty line as data, since a real empty line terminates the data input.

The \J escape provides a way of setting the maximum stack size that is used by the just-in-time optimization code. It is ignored if JIT optimization is not being used. Providing a stack that is larger than the default 32K is necessary only for very complicated patterns.

If \M is present, pcretest calls pcre[16]_exec() several times, with different values in the match_limit and match_limit_recursion fields of the pcre[16]_extra data structure, until it finds the minimum numbers for each parameter that allow pcre[16]_exec() to complete without error. Because this is testing a specific feature of the normal interpretive pcre[16]_exec() execution, the use of any JIT optimization that might have been set up by the /S+ qualifier of -s+ option is disabled.

The match_limit number is a measure of the amount of backtracking that takes place, and checking it out can be instructive. For most simple matches, the number is quite small, but for patterns with very large numbers of matching possibilities, it can become large very quickly with increasing length of subject string. The match_limit_recursion number is a measure of how much stack (or, if PCRE is compiled with NO_RECURSE, how much heap) memory is needed to complete the match attempt.

When \O is used, the value specified may be higher or lower than the size set by the -O command line option (or defaulted to 45); \O applies only to the call of pcre[16]_exec() for the line in which it appears.

If the /P modifier was present on the pattern, causing the POSIX wrapper API to be used, the only option-setting sequences that have any effect are \B, \N, and \Z, causing REG_NOTBOL, REG_NOTEMPTY, and REG_NOTEOL, respectively, to be passed to regexec().


THE ALTERNATIVE MATCHING FUNCTION

By default, pcretest uses the standard PCRE matching function, pcre[16]_exec() to match each data line. PCRE also supports an alternative matching function, pcre[16]_dfa_test(), which operates in a different way, and has some restrictions. The differences between the two functions are described in the pcrematching documentation.

If a data line contains the \D escape sequence, or if the command line contains the -dfa option, the alternative matching function is used. This function finds all possible matches at a given point. If, however, the \F escape sequence is present in the data line, it stops after the first match is found. This is always the shortest possible match.


DEFAULT OUTPUT FROM PCRETEST

This section describes the output when the normal matching function, pcre[16]_exec(), is being used.

When a match succeeds, pcretest outputs the list of captured substrings that pcre[16]_exec() returns, starting with number 0 for the string that matched the whole pattern. Otherwise, it outputs "No match" when the return is PCRE_ERROR_NOMATCH, and "Partial match:" followed by the partially matching substring when pcre[16]_exec() returns PCRE_ERROR_PARTIAL. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \K, \b, or \B was involved.) For any other return, pcretest outputs the PCRE negative error number and a short descriptive phrase. If the error is a failed UTF string check, the offset of the start of the failing character and the reason code are also output, provided that the size of the output vector is at least two. Here is an example of an interactive pcretest run.

  $ pcretest
  PCRE version 8.13 2011-04-30

    re> /^abc(\d+)/
  data> abc123
   0: abc123
   1: 123
  data> xyz
  No match
Unset capturing substrings that are not followed by one that is set are not returned by pcre[16]_exec(), and are not shown by pcretest. In the following example, there are two capturing substrings, but when the first data line is matched, the second, unset substring is not shown. An "internal" unset substring is shown as "<unset>", as for the second data line.
    re> /(a)|(b)/
  data> a
   0: a
   1: a
  data> b
   0: b
   1: <unset>
   2: b
If the strings contain any non-printing characters, they are output as \xhh escapes if the value is less than 256 and UTF mode is not set. Otherwise they are output as \x{hh...} escapes. See below for the definition of non-printing characters. If the pattern has the /+ modifier, the output for substring 0 is followed by the the rest of the subject string, identified by "0+" like this:
    re> /cat/+
  data> cataract
   0: cat
   0+ aract
If the pattern has the /g or /G modifier, the results of successive matching attempts are output in sequence, like this:
    re> /\Bi(\w\w)/g
  data> Mississippi
   0: iss
   1: ss
   0: iss
   1: ss
   0: ipp
   1: pp
"No match" is output only if the first match attempt fails. Here is an example of a failure message (the offset 4 that is specified by \>4 is past the end of the subject string):
    re> /xyz/
  data> xyz\>4
  Error -24 (bad offset value)

If any of the sequences \C, \G, or \L are present in a data line that is successfully matched, the substrings extracted by the convenience functions are output with C, G, or L after the string number instead of a colon. This is in addition to the normal full list. The string length (that is, the return from the extraction function) is given in parentheses after each string for \C and \G.

Note that whereas patterns can be continued over several lines (a plain ">" prompt is used for continuations), data lines may not. However newlines can be included in data by means of the \n escape (or \r, \r\n, etc., depending on the newline sequence setting).


OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION

When the alternative matching function, pcre[16]_dfa_exec(), is used (by means of the \D escape sequence or the -dfa command line option), the output consists of a list of all the matches that start at the first point in the subject where there is at least one match. For example:

    re> /(tang|tangerine|tan)/
  data> yellow tangerine\D
   0: tangerine
   1: tang
   2: tan
(Using the normal matching function on this data finds only "tang".) The longest matching string is always given first (and numbered zero). After a PCRE_ERROR_PARTIAL return, the output is "Partial match:", followed by the partially matching substring. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \K, \b, or \B was involved.)

If /g is present on the pattern, the search for further matches resumes at the end of the longest match. For example:

    re> /(tang|tangerine|tan)/g
  data> yellow tangerine and tangy sultana\D
   0: tangerine
   1: tang
   2: tan
   0: tang
   1: tan
   0: tan
Since the matching function does not support substring capture, the escape sequences that are concerned with captured substrings are not relevant.


RESTARTING AFTER A PARTIAL MATCH

When the alternative matching function has given the PCRE_ERROR_PARTIAL return, indicating that the subject partially matched the pattern, you can restart the match with additional subject data by means of the \R escape sequence. For example:

    re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
  data> 23ja\P\D
  Partial match: 23ja
  data> n05\R\D
   0: n05
For further information about partial matching, see the pcrepartial documentation.


CALLOUTS

If the pattern contains any callout requests, pcretest's callout function is called during matching. This works with both matching functions. By default, the called function displays the callout number, the start and current positions in the text at the callout time, and the next pattern item to be tested. For example:

  --->pqrabcdef
    0    ^  ^     \d
This output indicates that callout number 0 occurred for a match attempt starting at the fourth character of the subject string, when the pointer was at the seventh character of the data, and when the next pattern item was \d. Just one circumflex is output if the start and current positions are the same.

Callouts numbered 255 are assumed to be automatic callouts, inserted as a result of the /C pattern modifier. In this case, instead of showing the callout number, the offset in the pattern, preceded by a plus, is output. For example:

    re> /\d?[A-E]\*/C
  data> E*
  --->E*
   +0 ^      \d?
   +3 ^      [A-E]
   +8 ^^     \*
  +10 ^ ^
   0: E*
If a pattern contains (*MARK) items, an additional line is output whenever a change of latest mark is passed to the callout function. For example:
    re> /a(*MARK:X)bc/C
  data> abc
  --->abc
   +0 ^       a
   +1 ^^      (*MARK:X)
  +10 ^^      b
  Latest Mark: X
  +11 ^ ^     c
  +12 ^  ^
   0: abc
The mark changes between matching "a" and "b", but stays the same for the rest of the match, so nothing more is output. If, as a result of backtracking, the mark reverts to being unset, the text "<unset>" is output.

The callout function in pcretest returns zero (carry on matching) by default, but you can use a \C item in a data line (as described above) to change this and other parameters of the callout.

Inserting callouts can be helpful when using pcretest to check complicated regular expressions. For further information about callouts, see the pcrecallout documentation.


NON-PRINTING CHARACTERS

When pcretest is outputting text in the compiled version of a pattern, bytes other than 32-126 are always treated as non-printing characters are are therefore shown as hex escapes.

When pcretest is outputting text that is a matched part of a subject string, it behaves in the same way, unless a different locale has been set for the pattern (using the /L modifier). In this case, the isprint() function to distinguish printing and non-printing characters.


SAVING AND RELOADING COMPILED PATTERNS

The facilities described in this section are not available when the POSIX interface to PCRE is being used, that is, when the /P pattern modifier is specified.

When the POSIX interface is not in use, you can cause pcretest to write a compiled pattern to a file, by following the modifiers with > and a file name. For example:

  /pattern/im >/some/file
See the pcreprecompile documentation for a discussion about saving and re-using compiled patterns. Note that if the pattern was successfully studied with JIT optimization, the JIT data cannot be saved.

The data that is written is binary. The first eight bytes are the length of the compiled pattern data followed by the length of the optional study data, each written as four bytes in big-endian order (most significant byte first). If there is no study data (either the pattern was not studied, or studying did not return any data), the second length is zero. The lengths are followed by an exact copy of the compiled pattern. If there is additional study data, this (excluding any JIT data) follows immediately after the compiled pattern. After writing the file, pcretest expects to read a new pattern.

A saved pattern can be reloaded into pcretest by specifying < and a file name instead of a pattern. The name of the file must not contain a < character, as otherwise pcretest will interpret the line as a pattern delimited by < characters. For example:

   re> </some/file
  Compiled pattern loaded from /some/file
  No study data
If the pattern was previously studied with the JIT optimization, the JIT information cannot be saved and restored, and so is lost. When the pattern has been loaded, pcretest proceeds to read data lines in the usual way.

You can copy a file written by pcretest to a different host and reload it there, even if the new host has opposite endianness to the one on which the pattern was compiled. For example, you can compile on an i86 machine and run on a SPARC machine. When a pattern is reloaded on a host with different endianness, the confirmation message is changed to:

  Compiled pattern (byte-inverted) loaded from /some/file
The test suite contains some saved pre-compiled patterns with different endianness. These are reloaded using "<!" instead of just "<". This suppresses the "(byte-inverted)" text so that the output is the same on all hosts. It also forces debugging output once the pattern has been reloaded.

File names for saving and reloading can be absolute or relative, but note that the shell facility of expanding a file name that starts with a tilde (~) is not available.

The ability to save and reload files in pcretest is intended for testing and experimentation. It is not intended for production use because only a single pattern can be written to a file. Furthermore, there is no facility for supplying custom character tables for use with a reloaded pattern. If the original pattern was compiled with custom tables, an attempt to match a subject string using a reloaded pattern is likely to cause pcretest to crash. Finally, if you attempt to load a file that is not in the correct format, the result is undefined.


SEE ALSO

pcre(3), pcre16(3), pcreapi(3), pcrecallout(3), pcrejit, pcrematching(3), pcrepartial(d), pcrepattern(3), pcreprecompile(3).


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 14 January 2012
Copyright © 1997-2012 University of Cambridge.

Return to the PCRE index page.

070701000382ab000081a40000000000000000000000014f79083e00003d59000000b500010002ffffffffffffffff0000002f00000000root/usr/local/share/doc/pcre/html/pcre16.html pcre16 specification

pcre16 man page

Return to the PCRE index page.

This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

#include <pcre.h>


PCRE 16-BIT API BASIC FUNCTIONS

pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options, const char **errptr, int *erroffset, const unsigned char *tableptr);

pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options, int *errorcodeptr, const char **errptr, int *erroffset, const unsigned char *tableptr);

pcre16_extra *pcre16_study(const pcre16 *code, int options, const char **errptr);

void pcre16_free_study(pcre16_extra *extra);

int pcre16_exec(const pcre16 *code, const pcre16_extra *extra, PCRE_SPTR16 subject, int length, int startoffset, int options, int *ovector, int ovecsize);

int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra, PCRE_SPTR16 subject, int length, int startoffset, int options, int *ovector, int ovecsize, int *workspace, int wscount);


PCRE 16-BIT API STRING EXTRACTION FUNCTIONS

int pcre16_copy_named_substring(const pcre16 *code, PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 stringname, PCRE_UCHAR16 *buffer, int buffersize);

int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector, int stringcount, int stringnumber, PCRE_UCHAR16 *buffer, int buffersize);

int pcre16_get_named_substring(const pcre16 *code, PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 stringname, PCRE_SPTR16 *stringptr);

int pcre16_get_stringnumber(const pcre16 *code, PCRE_SPTR16 name);

int pcre16_get_stringtable_entries(const pcre16 *code, PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last);

int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector, int stringcount, int stringnumber, PCRE_SPTR16 *stringptr);

int pcre16_get_substring_list(PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 **listptr);

void pcre16_free_substring(PCRE_SPTR16 stringptr);

void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);


PCRE 16-BIT API AUXILIARY FUNCTIONS

pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);

void pcre16_jit_stack_free(pcre16_jit_stack *stack);

void pcre16_assign_jit_stack(pcre16_extra *extra, pcre16_jit_callback callback, void *data);

const unsigned char *pcre16_maketables(void);

int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra, int what, void *where);

int pcre16_refcount(pcre16 *code, int adjust);

int pcre16_config(int what, void *where);

const char *pcre16_version(void);

int pcre16_pattern_to_host_byte_order(pcre16 *code, pcre16_extra *extra, const unsigned char *tables);


PCRE 16-BIT API INDIRECTED FUNCTIONS

void *(*pcre16_malloc)(size_t);

void (*pcre16_free)(void *);

void *(*pcre16_stack_malloc)(size_t);

void (*pcre16_stack_free)(void *);

int (*pcre16_callout)(pcre16_callout_block *);


PCRE 16-BIT API 16-BIT-ONLY FUNCTION

int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output, PCRE_SPTR16 input, int length, int *byte_order, int keep_boms);


THE PCRE 16-BIT LIBRARY

Starting with release 8.30, it is possible to compile a PCRE library that supports 16-bit character strings, including UTF-16 strings, as well as or instead of the original 8-bit library. The majority of the work to make this possible was done by Zoltan Herczeg. The two libraries contain identical sets of functions, used in exactly the same way. Only the names of the functions and the data types of their arguments and results are different. To avoid over-complication and reduce the documentation maintenance load, most of the PCRE documentation describes the 8-bit library, with only occasional references to the 16-bit library. This page describes what is different when you use the 16-bit library.

WARNING: A single application can be linked with both libraries, but you must take care when processing any particular pattern to use functions from just one library. For example, if you want to study a pattern that was compiled with pcre16_compile(), you must do so with pcre16_study(), not pcre_study(), and you must free the study data with pcre16_free_study().


THE HEADER FILE

There is only one header file, pcre.h. It contains prototypes for all the functions in both libraries, as well as definitions of flags, structures, error codes, etc.


THE LIBRARY NAME

In Unix-like systems, the 16-bit library is called libpcre16, and can normally be accesss by adding -lpcre16 to the command for linking an application that uses PCRE.


STRING TYPES

In the 8-bit library, strings are passed to PCRE library functions as vectors of bytes with the C type "char *". In the 16-bit library, strings are passed as vectors of unsigned 16-bit quantities. The macro PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is defined as "const PCRE_UCHAR16 *". In very many environments, "short int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16 as "short int", but checks that it really is a 16-bit data type. If it is not, the build fails with an error message telling the maintainer to modify the definition appropriately.


STRUCTURE TYPES

The types of the opaque structures that are used for compiled 16-bit patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively. The type of the user-accessible structure that is returned by pcre16_study() is pcre16_extra, and the type of the structure that is used for passing data to a callout function is pcre16_callout_block. These structures contain the same fields, with the same names, as their 8-bit counterparts. The only difference is that pointers to character strings are 16-bit instead of 8-bit types.


16-BIT FUNCTIONS

For every function in the 8-bit library there is a corresponding function in the 16-bit library with a name that starts with pcre16_ instead of pcre_. The prototypes are listed above. In addition, there is one extra function, pcre16_utf16_to_host_byte_order(). This is a utility function that converts a UTF-16 character string to host byte order if necessary. The other 16-bit functions expect the strings they are passed to be in host byte order.

The input and output arguments of pcre16_utf16_to_host_byte_order() may point to the same address, that is, conversion in place is supported. The output buffer must be at least as long as the input.

The length argument specifies the number of 16-bit data units in the input string; a negative value specifies a zero-terminated string.

If byte_order is NULL, it is assumed that the string starts off in host byte order. This may be changed by byte-order marks (BOMs) anywhere in the string (commonly as the first character).

If byte_order is not NULL, a non-zero value of the integer to which it points means that the input starts off in host byte order, otherwise the opposite order is assumed. Again, BOMs in the string can change this. The final byte order is passed back at the end of processing.

If keep_boms is not zero, byte-order mark characters (0xfeff) are copied into the output string. Otherwise they are discarded.

The result of the function is the number of 16-bit units placed into the output buffer, including the zero terminator if the string was zero-terminated.


SUBJECT STRING OFFSETS

The offsets within subject strings that are returned by the matching functions are in 16-bit units rather than bytes.


NAMED SUBPATTERNS

The name-to-number translation table that is maintained for named subpatterns uses 16-bit characters. The pcre16_get_stringtable_entries() function returns the length of each entry in the table as the number of 16-bit data units.


OPTION NAMES

There are two new general option names, PCRE_UTF16 and PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options define the same bits in the options word.

For the pcre16_config() function there is an option PCRE_CONFIG_UTF16 that returns 1 if UTF-16 support is configured, otherwise 0. If this option is given to pcre_config(), or if the PCRE_CONFIG_UTF8 option is given to pcre16_config(), the result is the PCRE_ERROR_BADOPTION error.


CHARACTER CODES

In 16-bit mode, when PCRE_UTF16 is not set, character values are treated in the same way as in 8-bit, non UTF-8 mode, except, of course, that they can range from 0 to 0xffff instead of 0 to 0xff. Character types for characters less than 0xff can therefore be influenced by the locale in the same way as before. Characters greater than 0xff have only one case, and no "type" (such as letter or digit).

In UTF-16 mode, the character code is Unicode, in the range 0 to 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff because those are "surrogate" values that are used in pairs to encode values greater than 0xffff.

A UTF-16 string can indicate its endianness by special code knows as a byte-order mark (BOM). The PCRE functions do not handle this, expecting strings to be in host byte order. A utility function called pcre16_utf16_to_host_byte_order() is provided to help with this (see above).


ERROR NAMES

The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 correspond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed to a function that processes patterns in the other mode, for example, if a pattern compiled with pcre_compile() is passed to pcre16_exec().

There are new error codes whose names begin with PCRE_UTF16_ERR for invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for UTF-8 strings that are described in the section entitled "Reason codes for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors are:

  PCRE_UTF16_ERR1  Missing low surrogate at end of string
  PCRE_UTF16_ERR2  Invalid low surrogate follows high surrogate
  PCRE_UTF16_ERR3  Isolated low surrogate
  PCRE_UTF16_ERR4  Invalid character 0xfffe


ERROR TEXTS

If there is an error while compiling a pattern, the error text that is passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit character string, zero-terminated.


CALLOUTS

The subject and mark fields in the callout block that is passed to a callout function point to 16-bit vectors.


TESTING

The pcretest program continues to operate with 8-bit input and output files, but it can be used for testing the 16-bit library. If it is run with the command line option -16, patterns and subject strings are converted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit library functions are used instead of the 8-bit ones. Returned 16-bit strings are converted to 8-bit for output. If the 8-bit library was not compiled, pcretest defaults to 16-bit and the -16 option is ignored.

When PCRE is being built, the RunTest script that is called by "make check" uses the pcretest -C option to discover which of the 8-bit and 16-bit libraries has been built, and runs the tests appropriately.


NOT SUPPORTED IN 16-BIT MODE

Not all the features of the 8-bit library are available with the 16-bit library. The C++ and POSIX wrapper functions support only the 8-bit library, and the pcregrep program is at present 8-bit only.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 08 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382a8000081a40000000000000000000000014f79083e00001bbe000000b500010002ffffffffffffffff0000002e00000000root/usr/local/share/doc/pcre/html/index.html PCRE specification

Perl-compatible Regular Expressions (PCRE)

The HTML documentation for PCRE comprises the following pages:

pcre   Introductory page
pcre16   Discussion of the 16-bit PCRE library
pcre-config   Information about the installation configuration
pcreapi   PCRE's native API
pcrebuild   Options for building PCRE
pcrecallout   The callout facility
pcrecompat   Compability with Perl
pcrecpp   The C++ wrapper for the PCRE library
pcredemo   A demonstration C program that uses the PCRE library
pcregrep   The pcregrep command
pcrejit   Discussion of the just-in-time optimization support
pcrelimits   Details of size and other limits
pcrematching   Discussion of the two matching algorithms
pcrepartial   Using PCRE for partial matching
pcrepattern   Specification of the regular expressions supported by PCRE
pcreperform   Some comments on performance
pcreposix   The POSIX API to the PCRE library
pcreprecompile   How to save and re-use compiled patterns
pcresample   Discussion of the pcredemo program
pcrestack   Discussion of PCRE's stack usage
pcresyntax   Syntax quick-reference summary
pcretest   The pcretest command for testing PCRE
pcreunicode   Discussion of Unicode and UTF-8 support

There are also individual pages that summarize the interface for each function in the library. There is a single page for each pair of 8-bit/16-bit functions.

pcre_assign_jit_stack   Assign stack for JIT matching
pcre_compile   Compile a regular expression
pcre_compile2   Compile a regular expression (alternate interface)
pcre_config   Show build-time configuration options
pcre_copy_named_substring   Extract named substring into given buffer
pcre_copy_substring   Extract numbered substring into given buffer
pcre_dfa_exec   Match a compiled pattern to a subject string (DFA algorithm; not Perl compatible)
pcre_free_study   Free study data
pcre_exec   Match a compiled pattern to a subject string (Perl compatible)
pcre_free_substring   Free extracted substring
pcre_free_substring_list   Free list of extracted substrings
pcre_fullinfo   Extract information about a pattern
pcre_get_named_substring   Extract named substring into new memory
pcre_get_stringnumber   Convert captured string name to number
pcre_get_substring   Extract numbered substring into new memory
pcre_get_substring_list   Extract all substrings into new memory
pcre_info   Obsolete information extraction function
pcre_jit_stack_alloc   Create a stack for JIT matching
pcre_jit_stack_free   Free a JIT matching stack
pcre_maketables   Build character tables in current locale
pcre_pattern_to_host_byte_order   Convert compiled pattern to host byte order if necessary
pcre_refcount   Maintain reference count in compiled pattern
pcre_study   Study a compiled pattern
pcre_utf16_to_host_byte_order   Convert UTF-16 string to host byte order if necessary
pcre_version   Return PCRE version and release date
070701000382b4000081a40000000000000000000000014f79083e00000488000000b500010002ffffffffffffffff0000003800000000root/usr/local/share/doc/pcre/html/pcre_free_study.html pcre_free_study specification

pcre_free_study man page

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This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

SYNOPSIS

#include <pcre.h>

void pcre_free_study(pcre_extra *extra);

void pcre16_free_study(pcre16_extra *extra);


DESCRIPTION

This function is used to free the memory used for the data generated by a call to pcre[16]_study() when it is no longer needed. The argument must be the result of such a call.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382cd000081a40000000000000000000000014f79083e00003831000000b500010002ffffffffffffffff0000003000000000root/usr/local/share/doc/pcre/html/pcrecpp.html pcrecpp specification

pcrecpp man page

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SYNOPSIS OF C++ WRAPPER

#include <pcrecpp.h>


DESCRIPTION

The C++ wrapper for PCRE was provided by Google Inc. Some additional functionality was added by Giuseppe Maxia. This brief man page was constructed from the notes in the pcrecpp.h file, which should be consulted for further details. Note that the C++ wrapper supports only the original 8-bit PCRE library. There is no 16-bit support at present.


MATCHING INTERFACE

The "FullMatch" operation checks that supplied text matches a supplied pattern exactly. If pointer arguments are supplied, it copies matched sub-strings that match sub-patterns into them.

  Example: successful match
     pcrecpp::RE re("h.*o");
     re.FullMatch("hello");

  Example: unsuccessful match (requires full match):
     pcrecpp::RE re("e");
     !re.FullMatch("hello");

  Example: creating a temporary RE object:
     pcrecpp::RE("h.*o").FullMatch("hello");
You can pass in a "const char*" or a "string" for "text". The examples below tend to use a const char*. You can, as in the different examples above, store the RE object explicitly in a variable or use a temporary RE object. The examples below use one mode or the other arbitrarily. Either could correctly be used for any of these examples.

You must supply extra pointer arguments to extract matched subpieces.

  Example: extracts "ruby" into "s" and 1234 into "i"
     int i;
     string s;
     pcrecpp::RE re("(\\w+):(\\d+)");
     re.FullMatch("ruby:1234", &s, &i);

  Example: does not try to extract any extra sub-patterns
     re.FullMatch("ruby:1234", &s);

  Example: does not try to extract into NULL
     re.FullMatch("ruby:1234", NULL, &i);

  Example: integer overflow causes failure
     !re.FullMatch("ruby:1234567891234", NULL, &i);

  Example: fails because there aren't enough sub-patterns:
     !pcrecpp::RE("\\w+:\\d+").FullMatch("ruby:1234", &s);

  Example: fails because string cannot be stored in integer
     !pcrecpp::RE("(.*)").FullMatch("ruby", &i);
The provided pointer arguments can be pointers to any scalar numeric type, or one of:
   string        (matched piece is copied to string)
   StringPiece   (StringPiece is mutated to point to matched piece)
   T             (where "bool T::ParseFrom(const char*, int)" exists)
   NULL          (the corresponding matched sub-pattern is not copied)
The function returns true iff all of the following conditions are satisfied:
  a. "text" matches "pattern" exactly;

  b. The number of matched sub-patterns is >= number of supplied
     pointers;

  c. The "i"th argument has a suitable type for holding the
     string captured as the "i"th sub-pattern. If you pass in
     void * NULL for the "i"th argument, or a non-void * NULL
     of the correct type, or pass fewer arguments than the
     number of sub-patterns, "i"th captured sub-pattern is
     ignored.
CAVEAT: An optional sub-pattern that does not exist in the matched string is assigned the empty string. Therefore, the following will return false (because the empty string is not a valid number):
   int number;
   pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number);
The matching interface supports at most 16 arguments per call. If you need more, consider using the more general interface pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch.

NOTE: Do not use no_arg, which is used internally to mark the end of a list of optional arguments, as a placeholder for missing arguments, as this can lead to segfaults.


QUOTING METACHARACTERS

You can use the "QuoteMeta" operation to insert backslashes before all potentially meaningful characters in a string. The returned string, used as a regular expression, will exactly match the original string.

  Example:
     string quoted = RE::QuoteMeta(unquoted);
Note that it's legal to escape a character even if it has no special meaning in a regular expression -- so this function does that. (This also makes it identical to the perl function of the same name; see "perldoc -f quotemeta".) For example, "1.5-2.0?" becomes "1\.5\-2\.0\?".


PARTIAL MATCHES

You can use the "PartialMatch" operation when you want the pattern to match any substring of the text.

  Example: simple search for a string:
     pcrecpp::RE("ell").PartialMatch("hello");

  Example: find first number in a string:
     int number;
     pcrecpp::RE re("(\\d+)");
     re.PartialMatch("x*100 + 20", &number);
     assert(number == 100);


UTF-8 AND THE MATCHING INTERFACE

By default, pattern and text are plain text, one byte per character. The UTF8 flag, passed to the constructor, causes both pattern and string to be treated as UTF-8 text, still a byte stream but potentially multiple bytes per character. In practice, the text is likelier to be UTF-8 than the pattern, but the match returned may depend on the UTF8 flag, so always use it when matching UTF8 text. For example, "." will match one byte normally but with UTF8 set may match up to three bytes of a multi-byte character.

  Example:
     pcrecpp::RE_Options options;
     options.set_utf8();
     pcrecpp::RE re(utf8_pattern, options);
     re.FullMatch(utf8_string);

  Example: using the convenience function UTF8():
     pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8());
     re.FullMatch(utf8_string);
NOTE: The UTF8 flag is ignored if pcre was not configured with the
      --enable-utf8 flag.


PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE

PCRE defines some modifiers to change the behavior of the regular expression engine. The C++ wrapper defines an auxiliary class, RE_Options, as a vehicle to pass such modifiers to a RE class. Currently, the following modifiers are supported:

   modifier              description               Perl corresponding

   PCRE_CASELESS         case insensitive match      /i
   PCRE_MULTILINE        multiple lines match        /m
   PCRE_DOTALL           dot matches newlines        /s
   PCRE_DOLLAR_ENDONLY   $ matches only at end       N/A
   PCRE_EXTRA            strict escape parsing       N/A
   PCRE_EXTENDED         ignore whitespaces          /x
   PCRE_UTF8             handles UTF8 chars          built-in
   PCRE_UNGREEDY         reverses * and *?           N/A
   PCRE_NO_AUTO_CAPTURE  disables capturing parens   N/A (*)
(*) Both Perl and PCRE allow non capturing parentheses by means of the "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not capture, while (ab|cd) does.

For a full account on how each modifier works, please check the PCRE API reference page.

For each modifier, there are two member functions whose name is made out of the modifier in lowercase, without the "PCRE_" prefix. For instance, PCRE_CASELESS is handled by

  bool caseless()
which returns true if the modifier is set, and
  RE_Options & set_caseless(bool)
which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can be accessed through the set_match_limit() and match_limit() member functions. Setting match_limit to a non-zero value will limit the execution of pcre to keep it from doing bad things like blowing the stack or taking an eternity to return a result. A value of 5000 is good enough to stop stack blowup in a 2MB thread stack. Setting match_limit to zero disables match limiting. Alternatively, you can call match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to limit how much PCRE recurses. match_limit() limits the number of matches PCRE does; match_limit_recursion() limits the depth of internal recursion, and therefore the amount of stack that is used.

Normally, to pass one or more modifiers to a RE class, you declare a RE_Options object, set the appropriate options, and pass this object to a RE constructor. Example:

   RE_Options opt;
   opt.set_caseless(true);
   if (RE("HELLO", opt).PartialMatch("hello world")) ...
RE_options has two constructors. The default constructor takes no arguments and creates a set of flags that are off by default. The optional parameter option_flags is to facilitate transfer of legacy code from C programs. This lets you do
   RE(pattern,
     RE_Options(PCRE_CASELESS|PCRE_MULTILINE)).PartialMatch(str);
However, new code is better off doing
   RE(pattern,
     RE_Options().set_caseless(true).set_multiline(true))
       .PartialMatch(str);
If you are going to pass one of the most used modifiers, there are some convenience functions that return a RE_Options class with the appropriate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(), and EXTENDED().

If you need to set several options at once, and you don't want to go through the pains of declaring a RE_Options object and setting several options, there is a parallel method that give you such ability on the fly. You can concatenate several set_xxxxx() member functions, since each of them returns a reference to its class object. For example, to pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one statement, you may write:

   RE(" ^ xyz \\s+ .* blah$",
     RE_Options()
       .set_caseless(true)
       .set_extended(true)
       .set_multiline(true)).PartialMatch(sometext);


SCANNING TEXT INCREMENTALLY

The "Consume" operation may be useful if you want to repeatedly match regular expressions at the front of a string and skip over them as they match. This requires use of the "StringPiece" type, which represents a sub-range of a real string. Like RE, StringPiece is defined in the pcrecpp namespace.

  Example: read lines of the form "var = value" from a string.
     string contents = ...;                 // Fill string somehow
     pcrecpp::StringPiece input(contents);  // Wrap in a StringPiece

     string var;
     int value;
     pcrecpp::RE re("(\\w+) = (\\d+)\n");
     while (re.Consume(&input, &var, &value)) {
       ...;
     }
Each successful call to "Consume" will set "var/value", and also advance "input" so it points past the matched text.

The "FindAndConsume" operation is similar to "Consume" but does not anchor your match at the beginning of the string. For example, you could extract all words from a string by repeatedly calling

  pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word)


PARSING HEX/OCTAL/C-RADIX NUMBERS

By default, if you pass a pointer to a numeric value, the corresponding text is interpreted as a base-10 number. You can instead wrap the pointer with a call to one of the operators Hex(), Octal(), or CRadix() to interpret the text in another base. The CRadix operator interprets C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to base-10.

  Example:
    int a, b, c, d;
    pcrecpp::RE re("(.*) (.*) (.*) (.*)");
    re.FullMatch("100 40 0100 0x40",
                 pcrecpp::Octal(&a), pcrecpp::Hex(&b),
                 pcrecpp::CRadix(&c), pcrecpp::CRadix(&d));
will leave 64 in a, b, c, and d.


REPLACING PARTS OF STRINGS

You can replace the first match of "pattern" in "str" with "rewrite". Within "rewrite", backslash-escaped digits (\1 to \9) can be used to insert text matching corresponding parenthesized group from the pattern. \0 in "rewrite" refers to the entire matching text. For example:

  string s = "yabba dabba doo";
  pcrecpp::RE("b+").Replace("d", &s);
will leave "s" containing "yada dabba doo". The result is true if the pattern matches and a replacement occurs, false otherwise.

GlobalReplace is like Replace except that it replaces all occurrences of the pattern in the string with the rewrite. Replacements are not subject to re-matching. For example:

  string s = "yabba dabba doo";
  pcrecpp::RE("b+").GlobalReplace("d", &s);
will leave "s" containing "yada dada doo". It returns the number of replacements made.

Extract is like Replace, except that if the pattern matches, "rewrite" is copied into "out" (an additional argument) with substitutions. The non-matching portions of "text" are ignored. Returns true iff a match occurred and the extraction happened successfully; if no match occurs, the string is left unaffected.


AUTHOR

The C++ wrapper was contributed by Google Inc.
Copyright © 2007 Google Inc.


REVISION

Last updated: 08 January 2012

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070701000382ce000081a40000000000000000000000014f79083e00003f40000000b500010002ffffffffffffffff0000003100000000root/usr/local/share/doc/pcre/html/pcredemo.html pcredemo specification

pcredemo man page

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This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

/*************************************************
*           PCRE DEMONSTRATION PROGRAM           *
*************************************************/

/* This is a demonstration program to illustrate the most straightforward ways
of calling the PCRE regular expression library from a C program. See the
pcresample documentation for a short discussion ("man pcresample" if you have
the PCRE man pages installed).

In Unix-like environments, if PCRE is installed in your standard system
libraries, you should be able to compile this program using this command:

gcc -Wall pcredemo.c -lpcre -o pcredemo

If PCRE is not installed in a standard place, it is likely to be installed with
support for the pkg-config mechanism. If you have pkg-config, you can compile
this program using this command:

gcc -Wall pcredemo.c `pkg-config --cflags --libs libpcre` -o pcredemo

If you do not have pkg-config, you may have to use this:

gcc -Wall pcredemo.c -I/usr/local/include -L/usr/local/lib \
  -R/usr/local/lib -lpcre -o pcredemo

Replace "/usr/local/include" and "/usr/local/lib" with wherever the include and
library files for PCRE are installed on your system. Only some operating
systems (e.g. Solaris) use the -R option.

Building under Windows:

If you want to statically link this program against a non-dll .a file, you must
define PCRE_STATIC before including pcre.h, otherwise the pcre_malloc() and
pcre_free() exported functions will be declared __declspec(dllimport), with
unwanted results. So in this environment, uncomment the following line. */

/* #define PCRE_STATIC */

#include <stdio.h>
#include <string.h>
#include <pcre.h>

#define OVECCOUNT 30    /* should be a multiple of 3 */


int main(int argc, char **argv)
{
pcre *re;
const char *error;
char *pattern;
char *subject;
unsigned char *name_table;
unsigned int option_bits;
int erroffset;
int find_all;
int crlf_is_newline;
int namecount;
int name_entry_size;
int ovector[OVECCOUNT];
int subject_length;
int rc, i;
int utf8;


/**************************************************************************
* First, sort out the command line. There is only one possible option at  *
* the moment, "-g" to request repeated matching to find all occurrences,  *
* like Perl's /g option. We set the variable find_all to a non-zero value *
* if the -g option is present. Apart from that, there must be exactly two *
* arguments.                                                              *
**************************************************************************/

find_all = 0;
for (i = 1; i < argc; i++)
  {
  if (strcmp(argv[i], "-g") == 0) find_all = 1;
    else break;
  }

/* After the options, we require exactly two arguments, which are the pattern,
and the subject string. */

if (argc - i != 2)
  {
  printf("Two arguments required: a regex and a subject string\n");
  return 1;
  }

pattern = argv[i];
subject = argv[i+1];
subject_length = (int)strlen(subject);


/*************************************************************************
* Now we are going to compile the regular expression pattern, and handle *
* and errors that are detected.                                          *
*************************************************************************/

re = pcre_compile(
  pattern,              /* the pattern */
  0,                    /* default options */
  &error,               /* for error message */
  &erroffset,           /* for error offset */
  NULL);                /* use default character tables */

/* Compilation failed: print the error message and exit */

if (re == NULL)
  {
  printf("PCRE compilation failed at offset %d: %s\n", erroffset, error);
  return 1;
  }


/*************************************************************************
* If the compilation succeeded, we call PCRE again, in order to do a     *
* pattern match against the subject string. This does just ONE match. If *
* further matching is needed, it will be done below.                     *
*************************************************************************/

rc = pcre_exec(
  re,                   /* the compiled pattern */
  NULL,                 /* no extra data - we didn't study the pattern */
  subject,              /* the subject string */
  subject_length,       /* the length of the subject */
  0,                    /* start at offset 0 in the subject */
  0,                    /* default options */
  ovector,              /* output vector for substring information */
  OVECCOUNT);           /* number of elements in the output vector */

/* Matching failed: handle error cases */

if (rc < 0)
  {
  switch(rc)
    {
    case PCRE_ERROR_NOMATCH: printf("No match\n"); break;
    /*
    Handle other special cases if you like
    */
    default: printf("Matching error %d\n", rc); break;
    }
  pcre_free(re);     /* Release memory used for the compiled pattern */
  return 1;
  }

/* Match succeded */

printf("\nMatch succeeded at offset %d\n", ovector[0]);


/*************************************************************************
* We have found the first match within the subject string. If the output *
* vector wasn't big enough, say so. Then output any substrings that were *
* captured.                                                              *
*************************************************************************/

/* The output vector wasn't big enough */

if (rc == 0)
  {
  rc = OVECCOUNT/3;
  printf("ovector only has room for %d captured substrings\n", rc - 1);
  }

/* Show substrings stored in the output vector by number. Obviously, in a real
application you might want to do things other than print them. */

for (i = 0; i < rc; i++)
  {
  char *substring_start = subject + ovector[2*i];
  int substring_length = ovector[2*i+1] - ovector[2*i];
  printf("%2d: %.*s\n", i, substring_length, substring_start);
  }


/**************************************************************************
* That concludes the basic part of this demonstration program. We have    *
* compiled a pattern, and performed a single match. The code that follows *
* shows first how to access named substrings, and then how to code for    *
* repeated matches on the same subject.                                   *
**************************************************************************/

/* See if there are any named substrings, and if so, show them by name. First
we have to extract the count of named parentheses from the pattern. */

(void)pcre_fullinfo(
  re,                   /* the compiled pattern */
  NULL,                 /* no extra data - we didn't study the pattern */
  PCRE_INFO_NAMECOUNT,  /* number of named substrings */
  &namecount);          /* where to put the answer */

if (namecount <= 0) printf("No named substrings\n"); else
  {
  unsigned char *tabptr;
  printf("Named substrings\n");

  /* Before we can access the substrings, we must extract the table for
  translating names to numbers, and the size of each entry in the table. */

  (void)pcre_fullinfo(
    re,                       /* the compiled pattern */
    NULL,                     /* no extra data - we didn't study the pattern */
    PCRE_INFO_NAMETABLE,      /* address of the table */
    &name_table);             /* where to put the answer */

  (void)pcre_fullinfo(
    re,                       /* the compiled pattern */
    NULL,                     /* no extra data - we didn't study the pattern */
    PCRE_INFO_NAMEENTRYSIZE,  /* size of each entry in the table */
    &name_entry_size);        /* where to put the answer */

  /* Now we can scan the table and, for each entry, print the number, the name,
  and the substring itself. */

  tabptr = name_table;
  for (i = 0; i < namecount; i++)
    {
    int n = (tabptr[0] << 8) | tabptr[1];
    printf("(%d) %*s: %.*s\n", n, name_entry_size - 3, tabptr + 2,
      ovector[2*n+1] - ovector[2*n], subject + ovector[2*n]);
    tabptr += name_entry_size;
    }
  }


/*************************************************************************
* If the "-g" option was given on the command line, we want to continue  *
* to search for additional matches in the subject string, in a similar   *
* way to the /g option in Perl. This turns out to be trickier than you   *
* might think because of the possibility of matching an empty string.    *
* What happens is as follows:                                            *
*                                                                        *
* If the previous match was NOT for an empty string, we can just start   *
* the next match at the end of the previous one.                         *
*                                                                        *
* If the previous match WAS for an empty string, we can't do that, as it *
* would lead to an infinite loop. Instead, a special call of pcre_exec() *
* is made with the PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED flags set.    *
* The first of these tells PCRE that an empty string at the start of the *
* subject is not a valid match; other possibilities must be tried. The   *
* second flag restricts PCRE to one match attempt at the initial string  *
* position. If this match succeeds, an alternative to the empty string   *
* match has been found, and we can print it and proceed round the loop,  *
* advancing by the length of whatever was found. If this match does not  *
* succeed, we still stay in the loop, advancing by just one character.   *
* In UTF-8 mode, which can be set by (*UTF8) in the pattern, this may be *
* more than one byte.                                                    *
*                                                                        *
* However, there is a complication concerned with newlines. When the     *
* newline convention is such that CRLF is a valid newline, we want must  *
* advance by two characters rather than one. The newline convention can  *
* be set in the regex by (*CR), etc.; if not, we must find the default.  *
*************************************************************************/

if (!find_all)     /* Check for -g */
  {
  pcre_free(re);   /* Release the memory used for the compiled pattern */
  return 0;        /* Finish unless -g was given */
  }

/* Before running the loop, check for UTF-8 and whether CRLF is a valid newline
sequence. First, find the options with which the regex was compiled; extract
the UTF-8 state, and mask off all but the newline options. */

(void)pcre_fullinfo(re, NULL, PCRE_INFO_OPTIONS, &option_bits);
utf8 = option_bits & PCRE_UTF8;
option_bits &= PCRE_NEWLINE_CR|PCRE_NEWLINE_LF|PCRE_NEWLINE_CRLF|
               PCRE_NEWLINE_ANY|PCRE_NEWLINE_ANYCRLF;

/* If no newline options were set, find the default newline convention from the
build configuration. */

if (option_bits == 0)
  {
  int d;
  (void)pcre_config(PCRE_CONFIG_NEWLINE, &d);
  /* Note that these values are always the ASCII ones, even in
  EBCDIC environments. CR = 13, NL = 10. */
  option_bits = (d == 13)? PCRE_NEWLINE_CR :
          (d == 10)? PCRE_NEWLINE_LF :
          (d == (13<<8 | 10))? PCRE_NEWLINE_CRLF :
          (d == -2)? PCRE_NEWLINE_ANYCRLF :
          (d == -1)? PCRE_NEWLINE_ANY : 0;
  }

/* See if CRLF is a valid newline sequence. */

crlf_is_newline =
     option_bits == PCRE_NEWLINE_ANY ||
     option_bits == PCRE_NEWLINE_CRLF ||
     option_bits == PCRE_NEWLINE_ANYCRLF;

/* Loop for second and subsequent matches */

for (;;)
  {
  int options = 0;                 /* Normally no options */
  int start_offset = ovector[1];   /* Start at end of previous match */

  /* If the previous match was for an empty string, we are finished if we are
  at the end of the subject. Otherwise, arrange to run another match at the
  same point to see if a non-empty match can be found. */

  if (ovector[0] == ovector[1])
    {
    if (ovector[0] == subject_length) break;
    options = PCRE_NOTEMPTY_ATSTART | PCRE_ANCHORED;
    }

  /* Run the next matching operation */

  rc = pcre_exec(
    re,                   /* the compiled pattern */
    NULL,                 /* no extra data - we didn't study the pattern */
    subject,              /* the subject string */
    subject_length,       /* the length of the subject */
    start_offset,         /* starting offset in the subject */
    options,              /* options */
    ovector,              /* output vector for substring information */
    OVECCOUNT);           /* number of elements in the output vector */

  /* This time, a result of NOMATCH isn't an error. If the value in "options"
  is zero, it just means we have found all possible matches, so the loop ends.
  Otherwise, it means we have failed to find a non-empty-string match at a
  point where there was a previous empty-string match. In this case, we do what
  Perl does: advance the matching position by one character, and continue. We
  do this by setting the "end of previous match" offset, because that is picked
  up at the top of the loop as the point at which to start again.

  There are two complications: (a) When CRLF is a valid newline sequence, and
  the current position is just before it, advance by an extra byte. (b)
  Otherwise we must ensure that we skip an entire UTF-8 character if we are in
  UTF-8 mode. */

  if (rc == PCRE_ERROR_NOMATCH)
    {
    if (options == 0) break;                    /* All matches found */
    ovector[1] = start_offset + 1;              /* Advance one byte */
    if (crlf_is_newline &&                      /* If CRLF is newline & */
        start_offset < subject_length - 1 &&    /* we are at CRLF, */
        subject[start_offset] == '\r' &&
        subject[start_offset + 1] == '\n')
      ovector[1] += 1;                          /* Advance by one more. */
    else if (utf8)                              /* Otherwise, ensure we */
      {                                         /* advance a whole UTF-8 */
      while (ovector[1] < subject_length)       /* character. */
        {
        if ((subject[ovector[1]] & 0xc0) != 0x80) break;
        ovector[1] += 1;
        }
      }
    continue;    /* Go round the loop again */
    }

  /* Other matching errors are not recoverable. */

  if (rc < 0)
    {
    printf("Matching error %d\n", rc);
    pcre_free(re);    /* Release memory used for the compiled pattern */
    return 1;
    }

  /* Match succeded */

  printf("\nMatch succeeded again at offset %d\n", ovector[0]);

  /* The match succeeded, but the output vector wasn't big enough. */

  if (rc == 0)
    {
    rc = OVECCOUNT/3;
    printf("ovector only has room for %d captured substrings\n", rc - 1);
    }

  /* As before, show substrings stored in the output vector by number, and then
  also any named substrings. */

  for (i = 0; i < rc; i++)
    {
    char *substring_start = subject + ovector[2*i];
    int substring_length = ovector[2*i+1] - ovector[2*i];
    printf("%2d: %.*s\n", i, substring_length, substring_start);
    }

  if (namecount <= 0) printf("No named substrings\n"); else
    {
    unsigned char *tabptr = name_table;
    printf("Named substrings\n");
    for (i = 0; i < namecount; i++)
      {
      int n = (tabptr[0] << 8) | tabptr[1];
      printf("(%d) %*s: %.*s\n", n, name_entry_size - 3, tabptr + 2,
        ovector[2*n+1] - ovector[2*n], subject + ovector[2*n]);
      tabptr += name_entry_size;
      }
    }
  }      /* End of loop to find second and subsequent matches */

printf("\n");
pcre_free(re);       /* Release memory used for the compiled pattern */
return 0;
}

/* End of pcredemo.c */

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070701000382c5000081a40000000000000000000000014f79083e000007ca000000b500010002ffffffffffffffff0000003300000000root/usr/local/share/doc/pcre/html/pcre_study.html pcre_study specification

pcre_study man page

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SYNOPSIS

#include <pcre.h>

pcre_extra *pcre_study(const pcre *code, int options, const char **errptr);

pcre16_extra *pcre16_study(const pcre16 *code, int options, const char **errptr);


DESCRIPTION

This function studies a compiled pattern, to see if additional information can be extracted that might speed up matching. Its arguments are:

  code       A compiled regular expression
  options    Options for pcre[16]_study()
  errptr     Where to put an error message
If the function succeeds, it returns a value that can be passed to pcre[16]_exec() or pcre[16]_dfa_exec() via their extra arguments.

If the function returns NULL, either it could not find any additional information, or there was an error. You can tell the difference by looking at the error value. It is NULL in first case.

The only option is PCRE_STUDY_JIT_COMPILE. It requests just-in-time compilation if possible. If PCRE has been compiled without JIT support, this option is ignored. See the pcrejit page for further details.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382ad000081a40000000000000000000000014f79083e00000ffc000000b500010002ffffffffffffffff0000003500000000root/usr/local/share/doc/pcre/html/pcre_compile.html pcre_compile specification

pcre_compile man page

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SYNOPSIS

#include <pcre.h>

pcre *pcre_compile(const char *pattern, int options, const char **errptr, int *erroffset, const unsigned char *tableptr);

pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options, const char **errptr, int *erroffset, const unsigned char *tableptr);


DESCRIPTION

This function compiles a regular expression into an internal form. It is the same as pcre[16]_compile2(), except for the absence of the errorcodeptr argument. Its arguments are:

  pattern       A zero-terminated string containing the
                  regular expression to be compiled
  options       Zero or more option bits
  errptr        Where to put an error message
  erroffset     Offset in pattern where error was found
  tableptr      Pointer to character tables, or NULL to
                  use the built-in default
The option bits are:
  PCRE_ANCHORED           Force pattern anchoring
  PCRE_AUTO_CALLOUT       Compile automatic callouts
  PCRE_BSR_ANYCRLF        \R matches only CR, LF, or CRLF
  PCRE_BSR_UNICODE        \R matches all Unicode line endings
  PCRE_CASELESS           Do caseless matching
  PCRE_DOLLAR_ENDONLY     $ not to match newline at end
  PCRE_DOTALL             . matches anything including NL
  PCRE_DUPNAMES           Allow duplicate names for subpatterns
  PCRE_EXTENDED           Ignore whitespace and # comments
  PCRE_EXTRA              PCRE extra features
                            (not much use currently)
  PCRE_FIRSTLINE          Force matching to be before newline
  PCRE_JAVASCRIPT_COMPAT  JavaScript compatibility
  PCRE_MULTILINE          ^ and $ match newlines within data
  PCRE_NEWLINE_ANY        Recognize any Unicode newline sequence
  PCRE_NEWLINE_ANYCRLF    Recognize CR, LF, and CRLF as newline
                            sequences
  PCRE_NEWLINE_CR         Set CR as the newline sequence
  PCRE_NEWLINE_CRLF       Set CRLF as the newline sequence
  PCRE_NEWLINE_LF         Set LF as the newline sequence
  PCRE_NO_AUTO_CAPTURE    Disable numbered capturing paren-
                            theses (named ones available)
  PCRE_NO_UTF16_CHECK     Do not check the pattern for UTF-16
                            validity (only relevant if
                            PCRE_UTF16 is set)
  PCRE_NO_UTF8_CHECK      Do not check the pattern for UTF-8
                            validity (only relevant if
                            PCRE_UTF8 is set)
  PCRE_UCP                Use Unicode properties for \d, \w, etc.
  PCRE_UNGREEDY           Invert greediness of quantifiers
  PCRE_UTF16              Run in pcre16_compile() UTF-16 mode
  PCRE_UTF8               Run in pcre_compile() UTF-8 mode
PCRE must be built with UTF support in order to use PCRE_UTF8/16 and PCRE_NO_UTF8/16_CHECK, and with UCP support if PCRE_UCP is used.

The yield of the function is a pointer to a private data structure that contains the compiled pattern, or NULL if an error was detected. Note that compiling regular expressions with one version of PCRE for use with a different version is not guaranteed to work and may cause crashes.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382dc000081a40000000000000000000000014f79083e000027fa000000b500010002ffffffffffffffff0000003400000000root/usr/local/share/doc/pcre/html/pcreunicode.html pcreunicode specification

pcreunicode man page

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UTF-8, UTF-16, AND UNICODE PROPERTY SUPPORT

From Release 8.30, in addition to its previous UTF-8 support, PCRE also supports UTF-16 by means of a separate 16-bit library. This can be built as well as, or instead of, the 8-bit library.


UTF-8 SUPPORT

In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF support, and, in addition, you must call pcre_compile() with the PCRE_UTF8 option flag, or the pattern must start with the sequence (*UTF8). When either of these is the case, both the pattern and any subject strings that are matched against it are treated as UTF-8 strings instead of strings of 1-byte characters.


UTF-16 SUPPORT

In order process UTF-16 strings, you must build PCRE's 16-bit library with UTF support, and, in addition, you must call pcre16_compile() with the PCRE_UTF16 option flag, or the pattern must start with the sequence (*UTF16). When either of these is the case, both the pattern and any subject strings that are matched against it are treated as UTF-16 strings instead of strings of 16-bit characters.


UTF SUPPORT OVERHEAD

If you compile PCRE with UTF support, but do not use it at run time, the library will be a bit bigger, but the additional run time overhead is limited to testing the PCRE_UTF8/16 flag occasionally, so should not be very big.


UNICODE PROPERTY SUPPORT

If PCRE is built with Unicode character property support (which implies UTF support), the escape sequences \p{..}, \P{..}, and \X can be used. The available properties that can be tested are limited to the general category properties such as Lu for an upper case letter or Nd for a decimal number, the Unicode script names such as Arabic or Han, and the derived properties Any and L&. A full list is given in the pcrepattern documentation. Only the short names for properties are supported. For example, \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported. Furthermore, in Perl, many properties may optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE does not support this.


Validity of UTF-8 strings

When you set the PCRE_UTF8 flag, the byte strings passed as patterns and subjects are (by default) checked for validity on entry to the relevant functions. From release 7.3 of PCRE, the check is according the rules of RFC 3629, which are themselves derived from the Unicode specification. Earlier releases of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0 to U+10FFFF, excluding U+D800 to U+DFFF.

The excluded code points are the "Surrogate Area" of Unicode. They are reserved for use by UTF-16, where they are used in pairs to encode codepoints with values greater than 0xFFFF. The code points that are encoded by UTF-16 pairs are available independently in the UTF-8 encoding. (In other words, the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)

If an invalid UTF-8 string is passed to PCRE, an error return is given. At compile time, the only additional information is the offset to the first byte of the failing character. The runtime functions pcre_exec() and pcre_dfa_exec() also pass back this information, as well as a more detailed reason code if the caller has provided memory in which to do this.

In some situations, you may already know that your strings are valid, and therefore want to skip these checks in order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE assumes that the pattern or subject it is given (respectively) contains only valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 string.

If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what happens depends on why the string is invalid. If the string conforms to the "old" definition of UTF-8 (RFC 2279), it is processed as a string of characters in the range 0 to 0x7FFFFFFF by pcre_dfa_exec() and the interpreted version of pcre_exec(). In other words, apart from the initial validity test, these functions (when in UTF-8 mode) handle strings according to the more liberal rules of RFC 2279. However, the just-in-time (JIT) optimization for pcre_exec() supports only RFC 3629. If you are using JIT optimization, or if the string does not even conform to RFC 2279, the result is undefined. Your program may crash.

If you want to process strings of values in the full range 0 to 0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you can set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this situation, you will have to apply your own validity check, and avoid the use of JIT optimization.


Validity of UTF-16 strings

When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are passed as patterns and subjects are (by default) checked for validity on entry to the relevant functions. Values other than those in the surrogate range U+D800 to U+DFFF are independent code points. Values in the surrogate range must be used in pairs in the correct manner.

If an invalid UTF-16 string is passed to PCRE, an error return is given. At compile time, the only additional information is the offset to the first data unit of the failing character. The runtime functions pcre16_exec() and pcre16_dfa_exec() also pass back this information, as well as a more detailed reason code if the caller has provided memory in which to do this.

In some situations, you may already know that your strings are valid, and therefore want to skip these checks in order to improve performance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that the pattern or subject it is given (respectively) contains only valid UTF-16 sequences. In this case, it does not diagnose an invalid UTF-16 string.


General comments about UTF modes

1. Codepoints less than 256 can be specified by either braced or unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). Larger values have to use braced sequences.

2. Octal numbers up to \777 are recognized, and in UTF-8 mode, they match two-byte characters for values greater than \177.

3. Repeat quantifiers apply to complete UTF characters, not to individual data units, for example: \x{100}{3}.

4. The dot metacharacter matches one UTF character instead of a single data unit.

5. The escape sequence \C can be used to match a single byte in UTF-8 mode, or a single 16-bit data unit in UTF-16 mode, but its use can lead to some strange effects because it breaks up multi-unit characters (see the description of \C in the pcrepattern documentation). The use of \C is not supported in the alternative matching function pcre[16]_dfa_exec(), nor is it supported in UTF mode by the JIT optimization of pcre[16]_exec(). If JIT optimization is requested for a UTF pattern that contains \C, it will not succeed, and so the matching will be carried out by the normal interpretive function.

6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly test characters of any code value, but, by default, the characters that PCRE recognizes as digits, spaces, or word characters remain the same set as in non-UTF mode, all with values less than 256. This remains true even when PCRE is built to include Unicode property support, because to do otherwise would slow down PCRE in many common cases. Note in particular that this applies to \b and \B, because they are defined in terms of \w and \W. If you really want to test for a wider sense of, say, "digit", you can use explicit Unicode property tests such as \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the character escapes work is changed so that Unicode properties are used to determine which characters match. There are more details in the section on generic character types in the pcrepattern documentation.

7. Similarly, characters that match the POSIX named character classes are all low-valued characters, unless the PCRE_UCP option is set.

8. However, the horizontal and vertical whitespace matching escapes (\h, \H, \v, and \V) do match all the appropriate Unicode characters, whether or not PCRE_UCP is set.

9. Case-insensitive matching applies only to characters whose values are less than 128, unless PCRE is built with Unicode property support. Even when Unicode property support is available, PCRE still uses its own character tables when checking the case of low-valued characters, so as not to degrade performance. The Unicode property information is used only for characters with higher values. Furthermore, PCRE supports case-insensitive matching only when there is a one-to-one mapping between a letter's cases. There are a small number of many-to-one mappings in Unicode; these are not supported by PCRE.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 13 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382d0000081a40000000000000000000000014f79083e00004013000000b500010002ffffffffffffffff0000003000000000root/usr/local/share/doc/pcre/html/pcrejit.html pcrejit specification

pcrejit man page

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PCRE JUST-IN-TIME COMPILER SUPPORT

Just-in-time compiling is a heavyweight optimization that can greatly speed up pattern matching. However, it comes at the cost of extra processing before the match is performed. Therefore, it is of most benefit when the same pattern is going to be matched many times. This does not necessarily mean many calls of a matching function; if the pattern is not anchored, matching attempts may take place many times at various positions in the subject, even for a single call. Therefore, if the subject string is very long, it may still pay to use JIT for one-off matches.

JIT support applies only to the traditional Perl-compatible matching function. It does not apply when the DFA matching function is being used. The code for this support was written by Zoltan Herczeg.


8-BIT and 16-BIT SUPPORT

JIT support is available for both the 8-bit and 16-bit PCRE libraries. To keep this documentation simple, only the 8-bit interface is described in what follows. If you are using the 16-bit library, substitute the 16-bit functions and 16-bit structures (for example, pcre16_jit_stack instead of pcre_jit_stack).


AVAILABILITY OF JIT SUPPORT

JIT support is an optional feature of PCRE. The "configure" option --enable-jit (or equivalent CMake option) must be set when PCRE is built if you want to use JIT. The support is limited to the following hardware platforms:

  ARM v5, v7, and Thumb2
  Intel x86 32-bit and 64-bit
  MIPS 32-bit
  Power PC 32-bit and 64-bit
The Power PC support is designated as experimental because it has not been fully tested. If --enable-jit is set on an unsupported platform, compilation fails.

A program that is linked with PCRE 8.20 or later can tell if JIT support is available by calling pcre_config() with the PCRE_CONFIG_JIT option. The result is 1 when JIT is available, and 0 otherwise. However, a simple program does not need to check this in order to use JIT. The API is implemented in a way that falls back to the ordinary PCRE code if JIT is not available.

If your program may sometimes be linked with versions of PCRE that are older than 8.20, but you want to use JIT when it is available, you can test the values of PCRE_MAJOR and PCRE_MINOR, or the existence of a JIT macro such as PCRE_CONFIG_JIT, for compile-time control of your code.


SIMPLE USE OF JIT

You have to do two things to make use of the JIT support in the simplest way:

  (1) Call pcre_study() with the PCRE_STUDY_JIT_COMPILE option for
      each compiled pattern, and pass the resulting pcre_extra block to
      pcre_exec().

  (2) Use pcre_free_study() to free the pcre_extra block when it is
      no longer needed instead of just freeing it yourself. This
      ensures that any JIT data is also freed.
For a program that may be linked with pre-8.20 versions of PCRE, you can insert
  #ifndef PCRE_STUDY_JIT_COMPILE
  #define PCRE_STUDY_JIT_COMPILE 0
  #endif
so that no option is passed to pcre_study(), and then use something like this to free the study data:
  #ifdef PCRE_CONFIG_JIT
      pcre_free_study(study_ptr);
  #else
      pcre_free(study_ptr);
  #endif
In some circumstances you may need to call additional functions. These are described in the section entitled "Controlling the JIT stack" below.

If JIT support is not available, PCRE_STUDY_JIT_COMPILE is ignored, and no JIT data is set up. Otherwise, the compiled pattern is passed to the JIT compiler, which turns it into machine code that executes much faster than the normal interpretive code. When pcre_exec() is passed a pcre_extra block containing a pointer to JIT code, it obeys that instead of the normal code. The result is identical, but the code runs much faster.

There are some pcre_exec() options that are not supported for JIT execution. There are also some pattern items that JIT cannot handle. Details are given below. In both cases, execution automatically falls back to the interpretive code.

If the JIT compiler finds an unsupported item, no JIT data is generated. You can find out if JIT execution is available after studying a pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A result of 1 means that JIT compilation was successful. A result of 0 means that JIT support is not available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE, or the JIT compiler was not able to handle the pattern.

Once a pattern has been studied, with or without JIT, it can be used as many times as you like for matching different subject strings.


UNSUPPORTED OPTIONS AND PATTERN ITEMS

The only pcre_exec() options that are supported for JIT execution are PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not supported.

The unsupported pattern items are:

  \C             match a single byte; not supported in UTF-8 mode
  (?Cn)          callouts
  (*COMMIT)      )
  (*MARK)        )
  (*PRUNE)       ) the backtracking control verbs
  (*SKIP)        )
  (*THEN)        )
Support for some of these may be added in future.


RETURN VALUES FROM JIT EXECUTION

When a pattern is matched using JIT execution, the return values are the same as those given by the interpretive pcre_exec() code, with the addition of one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means that the memory used for the JIT stack was insufficient. See "Controlling the JIT stack" below for a discussion of JIT stack usage. For compatibility with the interpretive pcre_exec() code, no more than two-thirds of the ovector argument is used for passing back captured substrings.

The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if searching a very large pattern tree goes on for too long, as it is in the same circumstance when JIT is not used, but the details of exactly what is counted are not the same. The PCRE_ERROR_RECURSIONLIMIT error code is never returned by JIT execution.


SAVING AND RESTORING COMPILED PATTERNS

The code that is generated by the JIT compiler is architecture-specific, and is also position dependent. For those reasons it cannot be saved (in a file or database) and restored later like the bytecode and other data of a compiled pattern. Saving and restoring compiled patterns is not something many people do. More detail about this facility is given in the pcreprecompile documentation. It should be possible to run pcre_study() on a saved and restored pattern, and thereby recreate the JIT data, but because JIT compilation uses significant resources, it is probably not worth doing this; you might as well recompile the original pattern.


CONTROLLING THE JIT STACK

When the compiled JIT code runs, it needs a block of memory to use as a stack. By default, it uses 32K on the machine stack. However, some large or complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT is given when there is not enough stack. Three functions are provided for managing blocks of memory for use as JIT stacks. There is further discussion about the use of JIT stacks in the section entitled "JIT stack FAQ" below.

The pcre_jit_stack_alloc() function creates a JIT stack. Its arguments are a starting size and a maximum size, and it returns a pointer to an opaque structure of type pcre_jit_stack, or NULL if there is an error. The pcre_jit_stack_free() function can be used to free a stack that is no longer needed. (For the technically minded: the address space is allocated by mmap or VirtualAlloc.)

JIT uses far less memory for recursion than the interpretive code, and a maximum stack size of 512K to 1M should be more than enough for any pattern.

The pcre_assign_jit_stack() function specifies which stack JIT code should use. Its arguments are as follows:

  pcre_extra         *extra
  pcre_jit_callback  callback
  void               *data
The extra argument must be the result of studying a pattern with PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the other two options:
  (1) If callback is NULL and data is NULL, an internal 32K block
      on the machine stack is used.

  (2) If callback is NULL and data is not NULL, data must be
      a valid JIT stack, the result of calling pcre_jit_stack_alloc().

  (3) If callback not NULL, it must point to a function that is called
      with data as an argument at the start of matching, in order to
      set up a JIT stack. If the result is NULL, the internal 32K stack
      is used; otherwise the return value must be a valid JIT stack,
      the result of calling pcre_jit_stack_alloc().
You may safely assign the same JIT stack to more than one pattern, as long as they are all matched sequentially in the same thread. In a multithread application, each thread must use its own JIT stack.

Strictly speaking, even more is allowed. You can assign the same stack to any number of patterns as long as they are not used for matching by multiple threads at the same time. For example, you can assign the same stack to all compiled patterns, and use a global mutex in the callback to wait until the stack is available for use. However, this is an inefficient solution, and not recommended.

This is a suggestion for how a typical multithreaded program might operate:

  During thread initalization
    thread_local_var = pcre_jit_stack_alloc(...)

  During thread exit
    pcre_jit_stack_free(thread_local_var)

  Use a one-line callback function
    return thread_local_var
All the functions described in this section do nothing if JIT is not available, and pcre_assign_jit_stack() does nothing unless the extra argument is non-NULL and points to a pcre_extra block that is the result of a successful study with PCRE_STUDY_JIT_COMPILE.


JIT STACK FAQ

(1) Why do we need JIT stacks?

PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack where the local data of the current node is pushed before checking its child nodes. Allocating real machine stack on some platforms is difficult. For example, the stack chain needs to be updated every time if we extend the stack on PowerPC. Although it is possible, its updating time overhead decreases performance. So we do the recursion in memory.

(2) Why don't we simply allocate blocks of memory with malloc()?

Modern operating systems have a nice feature: they can reserve an address space instead of allocating memory. We can safely allocate memory pages inside this address space, so the stack could grow without moving memory data (this is important because of pointers). Thus we can allocate 1M address space, and use only a single memory page (usually 4K) if that is enough. However, we can still grow up to 1M anytime if needed.

(3) Who "owns" a JIT stack?

The owner of the stack is the user program, not the JIT studied pattern or anything else. The user program must ensure that if a stack is used by pcre_exec(), (that is, it is assigned to the pattern currently running), that stack must not be used by any other threads (to avoid overwriting the same memory area). The best practice for multithreaded programs is to allocate a stack for each thread, and return this stack through the JIT callback function.

(4) When should a JIT stack be freed?

You can free a JIT stack at any time, as long as it will not be used by pcre_exec() again. When you assign the stack to a pattern, only a pointer is set. There is no reference counting or any other magic. You can free the patterns and stacks in any order, anytime. Just do not call pcre_exec() with a pattern pointing to an already freed stack, as that will cause SEGFAULT. (Also, do not free a stack currently used by pcre_exec() in another thread). You can also replace the stack for a pattern at any time. You can even free the previous stack before assigning a replacement.

(5) Should I allocate/free a stack every time before/after calling pcre_exec()?

No, because this is too costly in terms of resources. However, you could implement some clever idea which release the stack if it is not used in let's say two minutes. The JIT callback can help to achive this without keeping a list of the currently JIT studied patterns.

(6) OK, the stack is for long term memory allocation. But what happens if a pattern causes stack overflow with a stack of 1M? Is that 1M kept until the stack is freed?

Especially on embedded sytems, it might be a good idea to release memory sometimes without freeing the stack. There is no API for this at the moment. Probably a function call which returns with the currently allocated memory for any stack and another which allows releasing memory (shrinking the stack) would be a good idea if someone needs this.

(7) This is too much of a headache. Isn't there any better solution for JIT stack handling?

No, thanks to Windows. If POSIX threads were used everywhere, we could throw out this complicated API.


EXAMPLE CODE

This is a single-threaded example that specifies a JIT stack without using a callback.

  int rc;
  int ovector[30];
  pcre *re;
  pcre_extra *extra;
  pcre_jit_stack *jit_stack;

  re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
  /* Check for errors */
  extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
  jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024);
  /* Check for error (NULL) */
  pcre_assign_jit_stack(extra, NULL, jit_stack);
  rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
  /* Check results */
  pcre_free(re);
  pcre_free_study(extra);
  pcre_jit_stack_free(jit_stack);


SEE ALSO

pcreapi(3)


AUTHOR

Philip Hazel (FAQ by Zoltan Herczeg)
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 08 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382d6000081a40000000000000000000000014f79083e00002f6d000000b500010002ffffffffffffffff0000003200000000root/usr/local/share/doc/pcre/html/pcreposix.html pcreposix specification

pcreposix man page

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SYNOPSIS OF POSIX API

#include <pcreposix.h>

int regcomp(regex_t *preg, const char *pattern, int cflags);

int regexec(regex_t *preg, const char *string, size_t nmatch, regmatch_t pmatch[], int eflags);

size_t regerror(int errcode, const regex_t *preg, char *errbuf, size_t errbuf_size);

void regfree(regex_t *preg);


DESCRIPTION

This set of functions provides a POSIX-style API for the PCRE regular expression 8-bit library. See the pcreapi documentation for a description of PCRE's native API, which contains much additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit library.

The functions described here are just wrapper functions that ultimately call the PCRE native API. Their prototypes are defined in the pcreposix.h header file, and on Unix systems the library itself is called pcreposix.a, so can be accessed by adding -lpcreposix to the command for linking an application that uses them. Because the POSIX functions call the native ones, it is also necessary to add -lpcre.

I have implemented only those POSIX option bits that can be reasonably mapped to PCRE native options. In addition, the option REG_EXTENDED is defined with the value zero. This has no effect, but since programs that are written to the POSIX interface often use it, this makes it easier to slot in PCRE as a replacement library. Other POSIX options are not even defined.

There are also some other options that are not defined by POSIX. These have been added at the request of users who want to make use of certain PCRE-specific features via the POSIX calling interface.

When PCRE is called via these functions, it is only the API that is POSIX-like in style. The syntax and semantics of the regular expressions themselves are still those of Perl, subject to the setting of various PCRE options, as described below. "POSIX-like in style" means that the API approximates to the POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding domains it is probably even less compatible.

The header for these functions is supplied as pcreposix.h to avoid any potential clash with other POSIX libraries. It can, of course, be renamed or aliased as regex.h, which is the "correct" name. It provides two structure types, regex_t for compiled internal forms, and regmatch_t for returning captured substrings. It also defines some constants whose names start with "REG_"; these are used for setting options and identifying error codes.


COMPILING A PATTERN

The function regcomp() is called to compile a pattern into an internal form. The pattern is a C string terminated by a binary zero, and is passed in the argument pattern. The preg argument is a pointer to a regex_t structure that is used as a base for storing information about the compiled regular expression.

The argument cflags is either zero, or contains one or more of the bits defined by the following macros:

  REG_DOTALL
The PCRE_DOTALL option is set when the regular expression is passed for compilation to the native function. Note that REG_DOTALL is not part of the POSIX standard.
  REG_ICASE
The PCRE_CASELESS option is set when the regular expression is passed for compilation to the native function.
  REG_NEWLINE
The PCRE_MULTILINE option is set when the regular expression is passed for compilation to the native function. Note that this does not mimic the defined POSIX behaviour for REG_NEWLINE (see the following section).
  REG_NOSUB
The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed for compilation to the native function. In addition, when a pattern that is compiled with this flag is passed to regexec() for matching, the nmatch and pmatch arguments are ignored, and no captured strings are returned.
  REG_UCP
The PCRE_UCP option is set when the regular expression is passed for compilation to the native function. This causes PCRE to use Unicode properties when matchine \d, \w, etc., instead of just recognizing ASCII values. Note that REG_UTF8 is not part of the POSIX standard.
  REG_UNGREEDY
The PCRE_UNGREEDY option is set when the regular expression is passed for compilation to the native function. Note that REG_UNGREEDY is not part of the POSIX standard.
  REG_UTF8
The PCRE_UTF8 option is set when the regular expression is passed for compilation to the native function. This causes the pattern itself and all data strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8 is not part of the POSIX standard.

In the absence of these flags, no options are passed to the native function. This means the the regex is compiled with PCRE default semantics. In particular, the way it handles newline characters in the subject string is the Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. It does not affect the way newlines are matched by . (they are not) or by a negative class such as [^a] (they are).

The yield of regcomp() is zero on success, and non-zero otherwise. The preg structure is filled in on success, and one member of the structure is public: re_nsub contains the number of capturing subpatterns in the regular expression. Various error codes are defined in the header file.

NOTE: If the yield of regcomp() is non-zero, you must not attempt to use the contents of the preg structure. If, for example, you pass it to regexec(), the result is undefined and your program is likely to crash.


MATCHING NEWLINE CHARACTERS

This area is not simple, because POSIX and Perl take different views of things. It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never intended to be a POSIX engine. The following table lists the different possibilities for matching newline characters in PCRE:

                          Default   Change with

  . matches newline          no     PCRE_DOTALL
  newline matches [^a]       yes    not changeable
  $ matches \n at end        yes    PCRE_DOLLARENDONLY
  $ matches \n in middle     no     PCRE_MULTILINE
  ^ matches \n in middle     no     PCRE_MULTILINE
This is the equivalent table for POSIX:
                          Default   Change with

  . matches newline          yes    REG_NEWLINE
  newline matches [^a]       yes    REG_NEWLINE
  $ matches \n at end        no     REG_NEWLINE
  $ matches \n in middle     no     REG_NEWLINE
  ^ matches \n in middle     no     REG_NEWLINE
PCRE's behaviour is the same as Perl's, except that there is no equivalent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop newline from matching [^a].

The default POSIX newline handling can be obtained by setting PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the REG_NEWLINE action.


MATCHING A PATTERN

The function regexec() is called to match a compiled pattern preg against a given string, which is by default terminated by a zero byte (but see REG_STARTEND below), subject to the options in eflags. These can be:

  REG_NOTBOL
The PCRE_NOTBOL option is set when calling the underlying PCRE matching function.
  REG_NOTEMPTY
The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching function. Note that REG_NOTEMPTY is not part of the POSIX standard. However, setting this option can give more POSIX-like behaviour in some situations.
  REG_NOTEOL
The PCRE_NOTEOL option is set when calling the underlying PCRE matching function.
  REG_STARTEND
The string is considered to start at string + pmatch[0].rm_so and to have a terminating NUL located at string + pmatch[0].rm_eo (there need not actually be a NUL at that location), regardless of the value of nmatch. This is a BSD extension, compatible with but not specified by IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software intended to be portable to other systems. Note that a non-zero rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not how it is matched.

If the pattern was compiled with the REG_NOSUB flag, no data about any matched strings is returned. The nmatch and pmatch arguments of regexec() are ignored.

If the value of nmatch is zero, or if the value pmatch is NULL, no data about any matched strings is returned.

Otherwise,the portion of the string that was matched, and also any captured substrings, are returned via the pmatch argument, which points to an array of nmatch structures of type regmatch_t, containing the members rm_so and rm_eo. These contain the offset to the first character of each substring and the offset to the first character after the end of each substring, respectively. The 0th element of the vector relates to the entire portion of string that was matched; subsequent elements relate to the capturing subpatterns of the regular expression. Unused entries in the array have both structure members set to -1.

A successful match yields a zero return; various error codes are defined in the header file, of which REG_NOMATCH is the "expected" failure code.


ERROR MESSAGES

The regerror() function maps a non-zero errorcode from either regcomp() or regexec() to a printable message. If preg is not NULL, the error should have arisen from the use of that structure. A message terminated by a binary zero is placed in errbuf. The length of the message, including the zero, is limited to errbuf_size. The yield of the function is the size of buffer needed to hold the whole message.


MEMORY USAGE

Compiling a regular expression causes memory to be allocated and associated with the preg structure. The function regfree() frees all such memory, after which preg may no longer be used as a compiled expression.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 09 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382bc000081a40000000000000000000000014f79083e000007de000000b500010002ffffffffffffffff0000003b00000000root/usr/local/share/doc/pcre/html/pcre_get_substring.html pcre_get_substring specification

pcre_get_substring man page

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SYNOPSIS

#include <pcre.h>

int pcre_get_substring(const char *subject, int *ovector, int stringcount, int stringnumber, const char **stringptr);

int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector, int stringcount, int stringnumber, PCRE_SPTR16 *stringptr);


DESCRIPTION

This is a convenience function for extracting a captured substring. The arguments are:

  subject       Subject that has been successfully matched
  ovector       Offset vector that pcre[16]_exec() used
  stringcount   Value returned by pcre[16]_exec()
  stringnumber  Number of the required substring
  stringptr     Where to put the string pointer
The memory in which the substring is placed is obtained by calling pcre[16]_malloc(). The convenience function pcre[16]_free_substring() can be used to free it when it is no longer needed. The yield of the function is the length of the substring, PCRE_ERROR_NOMEMORY if sufficient memory could not be obtained, or PCRE_ERROR_NOSUBSTRING if the string number is invalid.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382ac000081a40000000000000000000000014f79083e00000946000000b500010002ffffffffffffffff0000003e00000000root/usr/local/share/doc/pcre/html/pcre_assign_jit_stack.html pcre_assign_jit_stack specification

pcre_assign_jit_stack man page

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SYNOPSIS

#include <pcre.h>

void pcre_assign_jit_stack(pcre_extra *extra, pcre_jit_callback callback, void *data);

void pcre16_assign_jit_stack(pcre16_extra *extra, pcre16_jit_callback callback, void *data);


DESCRIPTION

This function provides control over the memory used as a stack at runtime by a call to pcre[16]_exec() with a pattern that has been successfully compiled with JIT optimization. The arguments are:

  extra     the data pointer returned by pcre[16]_study()
  callback  a callback function
  data      a JIT stack or a value to be passed to the callback
              function

If callback is NULL and data is NULL, an internal 32K block on the machine stack is used.

If callback is NULL and data is not NULL, data must be a valid JIT stack, the result of calling pcre[16]_jit_stack_alloc().

If callback not NULL, it is called with data as an argument at the start of matching, in order to set up a JIT stack. If the result is NULL, the internal 32K stack is used; otherwise the return value must be a valid JIT stack, the result of calling pcre[16]_jit_stack_alloc().

You may safely assign the same JIT stack to multiple patterns, as long as they are all matched in the same thread. In a multithread application, each thread must use its own JIT stack. For more details, see the pcrejit page.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382c0000081a40000000000000000000000014f79083e000004b0000000b500010002ffffffffffffffff0000003c00000000root/usr/local/share/doc/pcre/html/pcre_jit_stack_free.html pcre_jit_stack_free specification

pcre_jit_stack_free man page

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SYNOPSIS

#include <pcre.h>

void pcre_jit_stack_free(pcre_jit_stack *stack);

void pcre16_jit_stack_free(pcre16_jit_stack *stack);


DESCRIPTION

This function is used to free a JIT stack that was created by pcre[16]_jit_stack_alloc() when it is no longer needed. For more details, see the pcrejit page.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382a9000081a40000000000000000000000014f79083e00000d7e000000b500010002ffffffffffffffff0000003400000000root/usr/local/share/doc/pcre/html/pcre-config.html pcre-config specification

pcre-config man page

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SYNOPSIS

pcre-config [--prefix] [--exec-prefix] [--version] [--libs] [--libs16] [--libs-cpp] [--libs-posix] [--cflags] [--cflags-posix]


DESCRIPTION

pcre-config returns the configuration of the installed PCRE libraries and the options required to compile a program to use them. Some of the options apply only to the 8-bit or 16-bit libraries, respectively, and are not available if only one of those libraries has been built. If an unavailable option is encountered, the "usage" information is output.


OPTIONS

--prefix Writes the directory prefix used in the PCRE installation for architecture independent files (/usr on many systems, /usr/local on some systems) to the standard output.

--exec-prefix Writes the directory prefix used in the PCRE installation for architecture dependent files (normally the same as --prefix) to the standard output.

--version Writes the version number of the installed PCRE libraries to the standard output.

--libs Writes to the standard output the command line options required to link with the 8-bit PCRE library (-lpcre on many systems).

--libs16 Writes to the standard output the command line options required to link with the 16-bit PCRE library (-lpcre16 on many systems).

--libs-cpp Writes to the standard output the command line options required to link with PCRE's C++ wrapper library (-lpcrecpp -lpcre on many systems).

--libs-posix Writes to the standard output the command line options required to link with PCRE's POSIX API wrapper library (-lpcreposix -lpcre on many systems).

--cflags Writes to the standard output the command line options required to compile files that use PCRE (this may include some -I options, but is blank on many systems).

--cflags-posix Writes to the standard output the command line options required to compile files that use PCRE's POSIX API wrapper library (this may include some -I options, but is blank on many systems).


SEE ALSO

pcre(3)


AUTHOR

This manual page was originally written by Mark Baker for the Debian GNU/Linux system. It has been subsequently revised as a generic PCRE man page.


REVISION

Last updated: 01 January 2012

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070701000382d8000081a40000000000000000000000014f79083e00000ec8000000b500010002ffffffffffffffff0000003300000000root/usr/local/share/doc/pcre/html/pcresample.html pcresample specification

pcresample man page

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PCRE SAMPLE PROGRAM

A simple, complete demonstration program, to get you started with using PCRE, is supplied in the file pcredemo.c in the PCRE distribution. A listing of this program is given in the pcredemo documentation. If you do not have a copy of the PCRE distribution, you can save this listing to re-create pcredemo.c.

The demonstration program, which uses the original PCRE 8-bit library, compiles the regular expression that is its first argument, and matches it against the subject string in its second argument. No PCRE options are set, and default character tables are used. If matching succeeds, the program outputs the portion of the subject that matched, together with the contents of any captured substrings.

If the -g option is given on the command line, the program then goes on to check for further matches of the same regular expression in the same subject string. The logic is a little bit tricky because of the possibility of matching an empty string. Comments in the code explain what is going on.

If PCRE is installed in the standard include and library directories for your operating system, you should be able to compile the demonstration program using this command:

  gcc -o pcredemo pcredemo.c -lpcre
If PCRE is installed elsewhere, you may need to add additional options to the command line. For example, on a Unix-like system that has PCRE installed in /usr/local, you can compile the demonstration program using a command like this:
  gcc -o pcredemo -I/usr/local/include pcredemo.c -L/usr/local/lib -lpcre
In a Windows environment, if you want to statically link the program against a non-dll pcre.a file, you must uncomment the line that defines PCRE_STATIC before including pcre.h, because otherwise the pcre_malloc() and pcre_free() exported functions will be declared __declspec(dllimport), with unwanted results.

Once you have compiled and linked the demonstration program, you can run simple tests like this:

  ./pcredemo 'cat|dog' 'the cat sat on the mat'
  ./pcredemo -g 'cat|dog' 'the dog sat on the cat'
Note that there is a much more comprehensive test program, called pcretest, which supports many more facilities for testing regular expressions and both PCRE libraries. The pcredemo program is provided as a simple coding example.

If you try to run pcredemo when PCRE is not installed in the standard library directory, you may get an error like this on some operating systems (e.g. Solaris):

  ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or directory
This is caused by the way shared library support works on those systems. You need to add
  -R/usr/local/lib
(for example) to the compile command to get round this problem.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 10 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382d4000081a40000000000000000000000014f79083e0001e3b4000000b500010002ffffffffffffffff0000003400000000root/usr/local/share/doc/pcre/html/pcrepattern.html pcrepattern specification

pcrepattern man page

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PCRE REGULAR EXPRESSION DETAILS

The syntax and semantics of the regular expressions that are supported by PCRE are described in detail below. There is a quick-reference syntax summary in the pcresyntax page. PCRE tries to match Perl syntax and semantics as closely as it can. PCRE also supports some alternative regular expression syntax (which does not conflict with the Perl syntax) in order to provide some compatibility with regular expressions in Python, .NET, and Oniguruma.

Perl's regular expressions are described in its own documentation, and regular expressions in general are covered in a number of books, some of which have copious examples. Jeffrey Friedl's "Mastering Regular Expressions", published by O'Reilly, covers regular expressions in great detail. This description of PCRE's regular expressions is intended as reference material.

The original operation of PCRE was on strings of one-byte characters. However, there is now also support for UTF-8 strings in the original library, and a second library that supports 16-bit and UTF-16 character strings. To use these features, PCRE must be built to include appropriate support. When using UTF strings you must either call the compiling function with the PCRE_UTF8 or PCRE_UTF16 option, or the pattern must start with one of these special sequences:

  (*UTF8)
  (*UTF16)
Starting a pattern with such a sequence is equivalent to setting the relevant option. This feature is not Perl-compatible. How setting a UTF mode affects pattern matching is mentioned in several places below. There is also a summary of features in the pcreunicode page.

Another special sequence that may appear at the start of a pattern or in combination with (*UTF8) or (*UTF16) is:

  (*UCP)
This has the same effect as setting the PCRE_UCP option: it causes sequences such as \d and \w to use Unicode properties to determine character types, instead of recognizing only characters with codes less than 128 via a lookup table.

If a pattern starts with (*NO_START_OPT), it has the same effect as setting the PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are also some more of these special sequences that are concerned with the handling of newlines; they are described below.

The remainder of this document discusses the patterns that are supported by PCRE when one its main matching functions, pcre_exec() (8-bit) or pcre16_exec() (16-bit), is used. PCRE also has alternative matching functions, pcre_dfa_exec() and pcre16_dfa_exec(), which match using a different algorithm that is not Perl-compatible. Some of the features discussed below are not available when DFA matching is used. The advantages and disadvantages of the alternative functions, and how they differ from the normal functions, are discussed in the pcrematching page.


NEWLINE CONVENTIONS

PCRE supports five different conventions for indicating line breaks in strings: a single CR (carriage return) character, a single LF (linefeed) character, the two-character sequence CRLF, any of the three preceding, or any Unicode newline sequence. The pcreapi page has further discussion about newlines, and shows how to set the newline convention in the options arguments for the compiling and matching functions.

It is also possible to specify a newline convention by starting a pattern string with one of the following five sequences:

  (*CR)        carriage return
  (*LF)        linefeed
  (*CRLF)      carriage return, followed by linefeed
  (*ANYCRLF)   any of the three above
  (*ANY)       all Unicode newline sequences
These override the default and the options given to the compiling function. For example, on a Unix system where LF is the default newline sequence, the pattern
  (*CR)a.b
changes the convention to CR. That pattern matches "a\nb" because LF is no longer a newline. Note that these special settings, which are not Perl-compatible, are recognized only at the very start of a pattern, and that they must be in upper case. If more than one of them is present, the last one is used.

The newline convention affects the interpretation of the dot metacharacter when PCRE_DOTALL is not set, and also the behaviour of \N. However, it does not affect what the \R escape sequence matches. By default, this is any Unicode newline sequence, for Perl compatibility. However, this can be changed; see the description of \R in the section entitled "Newline sequences" below. A change of \R setting can be combined with a change of newline convention.


CHARACTERS AND METACHARACTERS

A regular expression is a pattern that is matched against a subject string from left to right. Most characters stand for themselves in a pattern, and match the corresponding characters in the subject. As a trivial example, the pattern

  The quick brown fox
matches a portion of a subject string that is identical to itself. When caseless matching is specified (the PCRE_CASELESS option), letters are matched independently of case. In a UTF mode, PCRE always understands the concept of case for characters whose values are less than 128, so caseless matching is always possible. For characters with higher values, the concept of case is supported if PCRE is compiled with Unicode property support, but not otherwise. If you want to use caseless matching for characters 128 and above, you must ensure that PCRE is compiled with Unicode property support as well as with UTF support.

The power of regular expressions comes from the ability to include alternatives and repetitions in the pattern. These are encoded in the pattern by the use of metacharacters, which do not stand for themselves but instead are interpreted in some special way.

There are two different sets of metacharacters: those that are recognized anywhere in the pattern except within square brackets, and those that are recognized within square brackets. Outside square brackets, the metacharacters are as follows:

  \      general escape character with several uses
  ^      assert start of string (or line, in multiline mode)
  $      assert end of string (or line, in multiline mode)
  .      match any character except newline (by default)
  [      start character class definition
  |      start of alternative branch
  (      start subpattern
  )      end subpattern
  ?      extends the meaning of (
         also 0 or 1 quantifier
         also quantifier minimizer
  *      0 or more quantifier
  +      1 or more quantifier
         also "possessive quantifier"
  {      start min/max quantifier
Part of a pattern that is in square brackets is called a "character class". In a character class the only metacharacters are:
  \      general escape character
  ^      negate the class, but only if the first character
  -      indicates character range
  [      POSIX character class (only if followed by POSIX syntax)
  ]      terminates the character class
The following sections describe the use of each of the metacharacters.


BACKSLASH

The backslash character has several uses. Firstly, if it is followed by a character that is not a number or a letter, it takes away any special meaning that character may have. This use of backslash as an escape character applies both inside and outside character classes.

For example, if you want to match a * character, you write \* in the pattern. This escaping action applies whether or not the following character would otherwise be interpreted as a metacharacter, so it is always safe to precede a non-alphanumeric with backslash to specify that it stands for itself. In particular, if you want to match a backslash, you write \\.

In a UTF mode, only ASCII numbers and letters have any special meaning after a backslash. All other characters (in particular, those whose codepoints are greater than 127) are treated as literals.

If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the pattern (other than in a character class) and characters between a # outside a character class and the next newline are ignored. An escaping backslash can be used to include a whitespace or # character as part of the pattern.

If you want to remove the special meaning from a sequence of characters, you can do so by putting them between \Q and \E. This is different from Perl in that $ and @ are handled as literals in \Q...\E sequences in PCRE, whereas in Perl, $ and @ cause variable interpolation. Note the following examples:

  Pattern            PCRE matches   Perl matches

  \Qabc$xyz\E        abc$xyz        abc followed by the contents of $xyz
  \Qabc\$xyz\E       abc\$xyz       abc\$xyz
  \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
The \Q...\E sequence is recognized both inside and outside character classes. An isolated \E that is not preceded by \Q is ignored. If \Q is not followed by \E later in the pattern, the literal interpretation continues to the end of the pattern (that is, \E is assumed at the end). If the isolated \Q is inside a character class, this causes an error, because the character class is not terminated.


Non-printing characters

A second use of backslash provides a way of encoding non-printing characters in patterns in a visible manner. There is no restriction on the appearance of non-printing characters, apart from the binary zero that terminates a pattern, but when a pattern is being prepared by text editing, it is often easier to use one of the following escape sequences than the binary character it represents:

  \a        alarm, that is, the BEL character (hex 07)
  \cx       "control-x", where x is any ASCII character
  \e        escape (hex 1B)
  \f        formfeed (hex 0C)
  \n        linefeed (hex 0A)
  \r        carriage return (hex 0D)
  \t        tab (hex 09)
  \ddd      character with octal code ddd, or back reference
  \xhh      character with hex code hh
  \x{hhh..} character with hex code hhh.. (non-JavaScript mode)
  \uhhhh    character with hex code hhhh (JavaScript mode only)
The precise effect of \cx is as follows: if x is a lower case letter, it is converted to upper case. Then bit 6 of the character (hex 40) is inverted. Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({ is 7B), while \c; becomes hex 7B (; is 3B). If the byte following \c has a value greater than 127, a compile-time error occurs. This locks out non-ASCII characters in all modes. (When PCRE is compiled in EBCDIC mode, all byte values are valid. A lower case letter is converted to upper case, and then the 0xc0 bits are flipped.)

By default, after \x, from zero to two hexadecimal digits are read (letters can be in upper or lower case). Any number of hexadecimal digits may appear between \x{ and }, but the character code is constrained as follows:

  8-bit non-UTF mode    less than 0x100
  8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
  16-bit non-UTF mode   less than 0x10000
  16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called "surrogate" codepoints).

If characters other than hexadecimal digits appear between \x{ and }, or if there is no terminating }, this form of escape is not recognized. Instead, the initial \x will be interpreted as a basic hexadecimal escape, with no following digits, giving a character whose value is zero.

If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x is as just described only when it is followed by two hexadecimal digits. Otherwise, it matches a literal "x" character. In JavaScript mode, support for code points greater than 256 is provided by \u, which must be followed by four hexadecimal digits; otherwise it matches a literal "u" character.

Characters whose value is less than 256 can be defined by either of the two syntaxes for \x (or by \u in JavaScript mode). There is no difference in the way they are handled. For example, \xdc is exactly the same as \x{dc} (or \u00dc in JavaScript mode).

After \0 up to two further octal digits are read. If there are fewer than two digits, just those that are present are used. Thus the sequence \0\x\07 specifies two binary zeros followed by a BEL character (code value 7). Make sure you supply two digits after the initial zero if the pattern character that follows is itself an octal digit.

The handling of a backslash followed by a digit other than 0 is complicated. Outside a character class, PCRE reads it and any following digits as a decimal number. If the number is less than 10, or if there have been at least that many previous capturing left parentheses in the expression, the entire sequence is taken as a back reference. A description of how this works is given later, following the discussion of parenthesized subpatterns.

Inside a character class, or if the decimal number is greater than 9 and there have not been that many capturing subpatterns, PCRE re-reads up to three octal digits following the backslash, and uses them to generate a data character. Any subsequent digits stand for themselves. The value of the character is constrained in the same way as characters specified in hexadecimal. For example:

  \040   is another way of writing a space
  \40    is the same, provided there are fewer than 40 previous capturing subpatterns
  \7     is always a back reference
  \11    might be a back reference, or another way of writing a tab
  \011   is always a tab
  \0113  is a tab followed by the character "3"
  \113   might be a back reference, otherwise the character with octal code 113
  \377   might be a back reference, otherwise the value 255 (decimal)
  \81    is either a back reference, or a binary zero followed by the two characters "8" and "1"
Note that octal values of 100 or greater must not be introduced by a leading zero, because no more than three octal digits are ever read.

All the sequences that define a single character value can be used both inside and outside character classes. In addition, inside a character class, \b is interpreted as the backspace character (hex 08).

\N is not allowed in a character class. \B, \R, and \X are not special inside a character class. Like other unrecognized escape sequences, they are treated as the literal characters "B", "R", and "X" by default, but cause an error if the PCRE_EXTRA option is set. Outside a character class, these sequences have different meanings.


Unsupported escape sequences

In Perl, the sequences \l, \L, \u, and \U are recognized by its string handler and used to modify the case of following characters. By default, PCRE does not support these escape sequences. However, if the PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and \u can be used to define a character by code point, as described in the previous section.


Absolute and relative back references

The sequence \g followed by an unsigned or a negative number, optionally enclosed in braces, is an absolute or relative back reference. A named back reference can be coded as \g{name}. Back references are discussed later, following the discussion of parenthesized subpatterns.


Absolute and relative subroutine calls

For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is an alternative syntax for referencing a subpattern as a "subroutine". Details are discussed later. Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not synonymous. The former is a back reference; the latter is a subroutine call.


Generic character types

Another use of backslash is for specifying generic character types:

  \d     any decimal digit
  \D     any character that is not a decimal digit
  \h     any horizontal whitespace character
  \H     any character that is not a horizontal whitespace character
  \s     any whitespace character
  \S     any character that is not a whitespace character
  \v     any vertical whitespace character
  \V     any character that is not a vertical whitespace character
  \w     any "word" character
  \W     any "non-word" character
There is also the single sequence \N, which matches a non-newline character. This is the same as the "." metacharacter when PCRE_DOTALL is not set. Perl also uses \N to match characters by name; PCRE does not support this.

Each pair of lower and upper case escape sequences partitions the complete set of characters into two disjoint sets. Any given character matches one, and only one, of each pair. The sequences can appear both inside and outside character classes. They each match one character of the appropriate type. If the current matching point is at the end of the subject string, all of them fail, because there is no character to match.

For compatibility with Perl, \s does not match the VT character (code 11). This makes it different from the the POSIX "space" class. The \s characters are HT (9), LF (10), FF (12), CR (13), and space (32). If "use locale;" is included in a Perl script, \s may match the VT character. In PCRE, it never does.

A "word" character is an underscore or any character that is a letter or digit. By default, the definition of letters and digits is controlled by PCRE's low-valued character tables, and may vary if locale-specific matching is taking place (see "Locale support" in the pcreapi page). For example, in a French locale such as "fr_FR" in Unix-like systems, or "french" in Windows, some character codes greater than 128 are used for accented letters, and these are then matched by \w. The use of locales with Unicode is discouraged.

By default, in a UTF mode, characters with values greater than 128 never match \d, \s, or \w, and always match \D, \S, and \W. These sequences retain their original meanings from before UTF support was available, mainly for efficiency reasons. However, if PCRE is compiled with Unicode property support, and the PCRE_UCP option is set, the behaviour is changed so that Unicode properties are used to determine character types, as follows:

  \d  any character that \p{Nd} matches (decimal digit)
  \s  any character that \p{Z} matches, plus HT, LF, FF, CR
  \w  any character that \p{L} or \p{N} matches, plus underscore
The upper case escapes match the inverse sets of characters. Note that \d matches only decimal digits, whereas \w matches any Unicode digit, as well as any Unicode letter, and underscore. Note also that PCRE_UCP affects \b, and \B because they are defined in terms of \w and \W. Matching these sequences is noticeably slower when PCRE_UCP is set.

The sequences \h, \H, \v, and \V are features that were added to Perl at release 5.10. In contrast to the other sequences, which match only ASCII characters by default, these always match certain high-valued codepoints, whether or not PCRE_UCP is set. The horizontal space characters are:

  U+0009     Horizontal tab
  U+0020     Space
  U+00A0     Non-break space
  U+1680     Ogham space mark
  U+180E     Mongolian vowel separator
  U+2000     En quad
  U+2001     Em quad
  U+2002     En space
  U+2003     Em space
  U+2004     Three-per-em space
  U+2005     Four-per-em space
  U+2006     Six-per-em space
  U+2007     Figure space
  U+2008     Punctuation space
  U+2009     Thin space
  U+200A     Hair space
  U+202F     Narrow no-break space
  U+205F     Medium mathematical space
  U+3000     Ideographic space
The vertical space characters are:
  U+000A     Linefeed
  U+000B     Vertical tab
  U+000C     Formfeed
  U+000D     Carriage return
  U+0085     Next line
  U+2028     Line separator
  U+2029     Paragraph separator
In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are relevant.


Newline sequences

Outside a character class, by default, the escape sequence \R matches any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent to the following:

  (?>\r\n|\n|\x0b|\f|\r|\x85)
This is an example of an "atomic group", details of which are given below. This particular group matches either the two-character sequence CR followed by LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage return, U+000D), or NEL (next line, U+0085). The two-character sequence is treated as a single unit that cannot be split.

In other modes, two additional characters whose codepoints are greater than 255 are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029). Unicode character property support is not needed for these characters to be recognized.

It is possible to restrict \R to match only CR, LF, or CRLF (instead of the complete set of Unicode line endings) by setting the option PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched. (BSR is an abbrevation for "backslash R".) This can be made the default when PCRE is built; if this is the case, the other behaviour can be requested via the PCRE_BSR_UNICODE option. It is also possible to specify these settings by starting a pattern string with one of the following sequences:

  (*BSR_ANYCRLF)   CR, LF, or CRLF only
  (*BSR_UNICODE)   any Unicode newline sequence
These override the default and the options given to the compiling function, but they can themselves be overridden by options given to a matching function. Note that these special settings, which are not Perl-compatible, are recognized only at the very start of a pattern, and that they must be in upper case. If more than one of them is present, the last one is used. They can be combined with a change of newline convention; for example, a pattern can start with:
  (*ANY)(*BSR_ANYCRLF)
They can also be combined with the (*UTF8), (*UTF16), or (*UCP) special sequences. Inside a character class, \R is treated as an unrecognized escape sequence, and so matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.


Unicode character properties

When PCRE is built with Unicode character property support, three additional escape sequences that match characters with specific properties are available. When in 8-bit non-UTF-8 mode, these sequences are of course limited to testing characters whose codepoints are less than 256, but they do work in this mode. The extra escape sequences are:

  \p{xx}   a character with the xx property
  \P{xx}   a character without the xx property
  \X       an extended Unicode sequence
The property names represented by xx above are limited to the Unicode script names, the general category properties, "Any", which matches any character (including newline), and some special PCRE properties (described in the next section). Other Perl properties such as "InMusicalSymbols" are not currently supported by PCRE. Note that \P{Any} does not match any characters, so always causes a match failure.

Sets of Unicode characters are defined as belonging to certain scripts. A character from one of these sets can be matched using a script name. For example:

  \p{Greek}
  \P{Han}
Those that are not part of an identified script are lumped together as "Common". The current list of scripts is:

Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, Yi.

Each character has exactly one Unicode general category property, specified by a two-letter abbreviation. For compatibility with Perl, negation can be specified by including a circumflex between the opening brace and the property name. For example, \p{^Lu} is the same as \P{Lu}.

If only one letter is specified with \p or \P, it includes all the general category properties that start with that letter. In this case, in the absence of negation, the curly brackets in the escape sequence are optional; these two examples have the same effect:

  \p{L}
  \pL
The following general category property codes are supported:
  C     Other
  Cc    Control
  Cf    Format
  Cn    Unassigned
  Co    Private use
  Cs    Surrogate

  L     Letter
  Ll    Lower case letter
  Lm    Modifier letter
  Lo    Other letter
  Lt    Title case letter
  Lu    Upper case letter

  M     Mark
  Mc    Spacing mark
  Me    Enclosing mark
  Mn    Non-spacing mark

  N     Number
  Nd    Decimal number
  Nl    Letter number
  No    Other number

  P     Punctuation
  Pc    Connector punctuation
  Pd    Dash punctuation
  Pe    Close punctuation
  Pf    Final punctuation
  Pi    Initial punctuation
  Po    Other punctuation
  Ps    Open punctuation

  S     Symbol
  Sc    Currency symbol
  Sk    Modifier symbol
  Sm    Mathematical symbol
  So    Other symbol

  Z     Separator
  Zl    Line separator
  Zp    Paragraph separator
  Zs    Space separator
The special property L& is also supported: it matches a character that has the Lu, Ll, or Lt property, in other words, a letter that is not classified as a modifier or "other".

The Cs (Surrogate) property applies only to characters in the range U+D800 to U+DFFF. Such characters are not valid in Unicode strings and so cannot be tested by PCRE, unless UTF validity checking has been turned off (see the discussion of PCRE_NO_UTF8_CHECK and PCRE_NO_UTF16_CHECK in the pcreapi page). Perl does not support the Cs property.

The long synonyms for property names that Perl supports (such as \p{Letter}) are not supported by PCRE, nor is it permitted to prefix any of these properties with "Is".

No character that is in the Unicode table has the Cn (unassigned) property. Instead, this property is assumed for any code point that is not in the Unicode table.

Specifying caseless matching does not affect these escape sequences. For example, \p{Lu} always matches only upper case letters.

The \X escape matches any number of Unicode characters that form an extended Unicode sequence. \X is equivalent to

  (?>\PM\pM*)
That is, it matches a character without the "mark" property, followed by zero or more characters with the "mark" property, and treats the sequence as an atomic group (see below). Characters with the "mark" property are typically accents that affect the preceding character. None of them have codepoints less than 256, so in 8-bit non-UTF-8 mode \X matches any one character.

Note that recent versions of Perl have changed \X to match what Unicode calls an "extended grapheme cluster", which has a more complicated definition.

Matching characters by Unicode property is not fast, because PCRE has to search a structure that contains data for over fifteen thousand characters. That is why the traditional escape sequences such as \d and \w do not use Unicode properties in PCRE by default, though you can make them do so by setting the PCRE_UCP option or by starting the pattern with (*UCP).


PCRE's additional properties

As well as the standard Unicode properties described in the previous section, PCRE supports four more that make it possible to convert traditional escape sequences such as \w and \s and POSIX character classes to use Unicode properties. PCRE uses these non-standard, non-Perl properties internally when PCRE_UCP is set. They are:

  Xan   Any alphanumeric character
  Xps   Any POSIX space character
  Xsp   Any Perl space character
  Xwd   Any Perl "word" character
Xan matches characters that have either the L (letter) or the N (number) property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or carriage return, and any other character that has the Z (separator) property. Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the same characters as Xan, plus underscore.


Resetting the match start

The escape sequence \K causes any previously matched characters not to be included in the final matched sequence. For example, the pattern:

  foo\Kbar
matches "foobar", but reports that it has matched "bar". This feature is similar to a lookbehind assertion (described below). However, in this case, the part of the subject before the real match does not have to be of fixed length, as lookbehind assertions do. The use of \K does not interfere with the setting of captured substrings. For example, when the pattern
  (foo)\Kbar
matches "foobar", the first substring is still set to "foo".

Perl documents that the use of \K within assertions is "not well defined". In PCRE, \K is acted upon when it occurs inside positive assertions, but is ignored in negative assertions.


Simple assertions

The final use of backslash is for certain simple assertions. An assertion specifies a condition that has to be met at a particular point in a match, without consuming any characters from the subject string. The use of subpatterns for more complicated assertions is described below. The backslashed assertions are:

  \b     matches at a word boundary
  \B     matches when not at a word boundary
  \A     matches at the start of the subject
  \Z     matches at the end of the subject
          also matches before a newline at the end of the subject
  \z     matches only at the end of the subject
  \G     matches at the first matching position in the subject
Inside a character class, \b has a different meaning; it matches the backspace character. If any other of these assertions appears in a character class, by default it matches the corresponding literal character (for example, \B matches the letter B). However, if the PCRE_EXTRA option is set, an "invalid escape sequence" error is generated instead.

A word boundary is a position in the subject string where the current character and the previous character do not both match \w or \W (i.e. one matches \w and the other matches \W), or the start or end of the string if the first or last character matches \w, respectively. In a UTF mode, the meanings of \w and \W can be changed by setting the PCRE_UCP option. When this is done, it also affects \b and \B. Neither PCRE nor Perl has a separate "start of word" or "end of word" metasequence. However, whatever follows \b normally determines which it is. For example, the fragment \ba matches "a" at the start of a word.

The \A, \Z, and \z assertions differ from the traditional circumflex and dollar (described in the next section) in that they only ever match at the very start and end of the subject string, whatever options are set. Thus, they are independent of multiline mode. These three assertions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which affect only the behaviour of the circumflex and dollar metacharacters. However, if the startoffset argument of pcre_exec() is non-zero, indicating that matching is to start at a point other than the beginning of the subject, \A can never match. The difference between \Z and \z is that \Z matches before a newline at the end of the string as well as at the very end, whereas \z matches only at the end.

The \G assertion is true only when the current matching position is at the start point of the match, as specified by the startoffset argument of pcre_exec(). It differs from \A when the value of startoffset is non-zero. By calling pcre_exec() multiple times with appropriate arguments, you can mimic Perl's /g option, and it is in this kind of implementation where \G can be useful.

Note, however, that PCRE's interpretation of \G, as the start of the current match, is subtly different from Perl's, which defines it as the end of the previous match. In Perl, these can be different when the previously matched string was empty. Because PCRE does just one match at a time, it cannot reproduce this behaviour.

If all the alternatives of a pattern begin with \G, the expression is anchored to the starting match position, and the "anchored" flag is set in the compiled regular expression.


CIRCUMFLEX AND DOLLAR

Outside a character class, in the default matching mode, the circumflex character is an assertion that is true only if the current matching point is at the start of the subject string. If the startoffset argument of pcre_exec() is non-zero, circumflex can never match if the PCRE_MULTILINE option is unset. Inside a character class, circumflex has an entirely different meaning (see below).

Circumflex need not be the first character of the pattern if a number of alternatives are involved, but it should be the first thing in each alternative in which it appears if the pattern is ever to match that branch. If all possible alternatives start with a circumflex, that is, if the pattern is constrained to match only at the start of the subject, it is said to be an "anchored" pattern. (There are also other constructs that can cause a pattern to be anchored.)

A dollar character is an assertion that is true only if the current matching point is at the end of the subject string, or immediately before a newline at the end of the string (by default). Dollar need not be the last character of the pattern if a number of alternatives are involved, but it should be the last item in any branch in which it appears. Dollar has no special meaning in a character class.

The meaning of dollar can be changed so that it matches only at the very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at compile time. This does not affect the \Z assertion.

The meanings of the circumflex and dollar characters are changed if the PCRE_MULTILINE option is set. When this is the case, a circumflex matches immediately after internal newlines as well as at the start of the subject string. It does not match after a newline that ends the string. A dollar matches before any newlines in the string, as well as at the very end, when PCRE_MULTILINE is set. When newline is specified as the two-character sequence CRLF, isolated CR and LF characters do not indicate newlines.

For example, the pattern /^abc$/ matches the subject string "def\nabc" (where \n represents a newline) in multiline mode, but not otherwise. Consequently, patterns that are anchored in single line mode because all branches start with ^ are not anchored in multiline mode, and a match for circumflex is possible when the startoffset argument of pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.

Note that the sequences \A, \Z, and \z can be used to match the start and end of the subject in both modes, and if all branches of a pattern start with \A it is always anchored, whether or not PCRE_MULTILINE is set.


FULL STOP (PERIOD, DOT) AND \N

Outside a character class, a dot in the pattern matches any one character in the subject string except (by default) a character that signifies the end of a line.

When a line ending is defined as a single character, dot never matches that character; when the two-character sequence CRLF is used, dot does not match CR if it is immediately followed by LF, but otherwise it matches all characters (including isolated CRs and LFs). When any Unicode line endings are being recognized, dot does not match CR or LF or any of the other line ending characters.

The behaviour of dot with regard to newlines can be changed. If the PCRE_DOTALL option is set, a dot matches any one character, without exception. If the two-character sequence CRLF is present in the subject string, it takes two dots to match it.

The handling of dot is entirely independent of the handling of circumflex and dollar, the only relationship being that they both involve newlines. Dot has no special meaning in a character class.

The escape sequence \N behaves like a dot, except that it is not affected by the PCRE_DOTALL option. In other words, it matches any character except one that signifies the end of a line. Perl also uses \N to match characters by name; PCRE does not support this.


MATCHING A SINGLE DATA UNIT

Outside a character class, the escape sequence \C matches any one data unit, whether or not a UTF mode is set. In the 8-bit library, one data unit is one byte; in the 16-bit library it is a 16-bit unit. Unlike a dot, \C always matches line-ending characters. The feature is provided in Perl in order to match individual bytes in UTF-8 mode, but it is unclear how it can usefully be used. Because \C breaks up characters into individual data units, matching one unit with \C in a UTF mode means that the rest of the string may start with a malformed UTF character. This has undefined results, because PCRE assumes that it is dealing with valid UTF strings (and by default it checks this at the start of processing unless the PCRE_NO_UTF8_CHECK option is used).

PCRE does not allow \C to appear in lookbehind assertions (described below) in a UTF mode, because this would make it impossible to calculate the length of the lookbehind.

In general, the \C escape sequence is best avoided. However, one way of using it that avoids the problem of malformed UTF characters is to use a lookahead to check the length of the next character, as in this pattern, which could be used with a UTF-8 string (ignore white space and line breaks):

  (?| (?=[\x00-\x7f])(\C) |
      (?=[\x80-\x{7ff}])(\C)(\C) |
      (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) |
      (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))
A group that starts with (?| resets the capturing parentheses numbers in each alternative (see "Duplicate Subpattern Numbers" below). The assertions at the start of each branch check the next UTF-8 character for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The character's individual bytes are then captured by the appropriate number of groups.


SQUARE BRACKETS AND CHARACTER CLASSES

An opening square bracket introduces a character class, terminated by a closing square bracket. A closing square bracket on its own is not special by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, a lone closing square bracket causes a compile-time error. If a closing square bracket is required as a member of the class, it should be the first data character in the class (after an initial circumflex, if present) or escaped with a backslash.

A character class matches a single character in the subject. In a UTF mode, the character may be more than one data unit long. A matched character must be in the set of characters defined by the class, unless the first character in the class definition is a circumflex, in which case the subject character must not be in the set defined by the class. If a circumflex is actually required as a member of the class, ensure it is not the first character, or escape it with a backslash.

For example, the character class [aeiou] matches any lower case vowel, while [^aeiou] matches any character that is not a lower case vowel. Note that a circumflex is just a convenient notation for specifying the characters that are in the class by enumerating those that are not. A class that starts with a circumflex is not an assertion; it still consumes a character from the subject string, and therefore it fails if the current pointer is at the end of the string.

In UTF-8 (UTF-16) mode, characters with values greater than 255 (0xffff) can be included in a class as a literal string of data units, or by using the \x{ escaping mechanism.

When caseless matching is set, any letters in a class represent both their upper case and lower case versions, so for example, a caseless [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a caseful version would. In a UTF mode, PCRE always understands the concept of case for characters whose values are less than 128, so caseless matching is always possible. For characters with higher values, the concept of case is supported if PCRE is compiled with Unicode property support, but not otherwise. If you want to use caseless matching in a UTF mode for characters 128 and above, you must ensure that PCRE is compiled with Unicode property support as well as with UTF support.

Characters that might indicate line breaks are never treated in any special way when matching character classes, whatever line-ending sequence is in use, and whatever setting of the PCRE_DOTALL and PCRE_MULTILINE options is used. A class such as [^a] always matches one of these characters.

The minus (hyphen) character can be used to specify a range of characters in a character class. For example, [d-m] matches any letter between d and m, inclusive. If a minus character is required in a class, it must be escaped with a backslash or appear in a position where it cannot be interpreted as indicating a range, typically as the first or last character in the class.

It is not possible to have the literal character "]" as the end character of a range. A pattern such as [W-]46] is interpreted as a class of two characters ("W" and "-") followed by a literal string "46]", so it would match "W46]" or "-46]". However, if the "]" is escaped with a backslash it is interpreted as the end of range, so [W-\]46] is interpreted as a class containing a range followed by two other characters. The octal or hexadecimal representation of "]" can also be used to end a range.

Ranges operate in the collating sequence of character values. They can also be used for characters specified numerically, for example [\000-\037]. Ranges can include any characters that are valid for the current mode.

If a range that includes letters is used when caseless matching is set, it matches the letters in either case. For example, [W-c] is equivalent to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if character tables for a French locale are in use, [\xc8-\xcb] matches accented E characters in both cases. In UTF modes, PCRE supports the concept of case for characters with values greater than 128 only when it is compiled with Unicode property support.

The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, \w, and \W may appear in a character class, and add the characters that they match to the class. For example, [\dABCDEF] matches any hexadecimal digit. In UTF modes, the PCRE_UCP option affects the meanings of \d, \s, \w and their upper case partners, just as it does when they appear outside a character class, as described in the section entitled "Generic character types" above. The escape sequence \b has a different meaning inside a character class; it matches the backspace character. The sequences \B, \N, \R, and \X are not special inside a character class. Like any other unrecognized escape sequences, they are treated as the literal characters "B", "N", "R", and "X" by default, but cause an error if the PCRE_EXTRA option is set.

A circumflex can conveniently be used with the upper case character types to specify a more restricted set of characters than the matching lower case type. For example, the class [^\W_] matches any letter or digit, but not underscore, whereas [\w] includes underscore. A positive character class should be read as "something OR something OR ..." and a negative class as "NOT something AND NOT something AND NOT ...".

The only metacharacters that are recognized in character classes are backslash, hyphen (only where it can be interpreted as specifying a range), circumflex (only at the start), opening square bracket (only when it can be interpreted as introducing a POSIX class name - see the next section), and the terminating closing square bracket. However, escaping other non-alphanumeric characters does no harm.


POSIX CHARACTER CLASSES

Perl supports the POSIX notation for character classes. This uses names enclosed by [: and :] within the enclosing square brackets. PCRE also supports this notation. For example,

  [01[:alpha:]%]
matches "0", "1", any alphabetic character, or "%". The supported class names are:
  alnum    letters and digits
  alpha    letters
  ascii    character codes 0 - 127
  blank    space or tab only
  cntrl    control characters
  digit    decimal digits (same as \d)
  graph    printing characters, excluding space
  lower    lower case letters
  print    printing characters, including space
  punct    printing characters, excluding letters and digits and space
  space    white space (not quite the same as \s)
  upper    upper case letters
  word     "word" characters (same as \w)
  xdigit   hexadecimal digits
The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), and space (32). Notice that this list includes the VT character (code 11). This makes "space" different to \s, which does not include VT (for Perl compatibility).

The name "word" is a Perl extension, and "blank" is a GNU extension from Perl 5.8. Another Perl extension is negation, which is indicated by a ^ character after the colon. For example,

  [12[:^digit:]]
matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not supported, and an error is given if they are encountered.

By default, in UTF modes, characters with values greater than 128 do not match any of the POSIX character classes. However, if the PCRE_UCP option is passed to pcre_compile(), some of the classes are changed so that Unicode character properties are used. This is achieved by replacing the POSIX classes by other sequences, as follows:

  [:alnum:]  becomes  \p{Xan}
  [:alpha:]  becomes  \p{L}
  [:blank:]  becomes  \h
  [:digit:]  becomes  \p{Nd}
  [:lower:]  becomes  \p{Ll}
  [:space:]  becomes  \p{Xps}
  [:upper:]  becomes  \p{Lu}
  [:word:]   becomes  \p{Xwd}
Negated versions, such as [:^alpha:] use \P instead of \p. The other POSIX classes are unchanged, and match only characters with code points less than 128.


VERTICAL BAR

Vertical bar characters are used to separate alternative patterns. For example, the pattern

  gilbert|sullivan
matches either "gilbert" or "sullivan". Any number of alternatives may appear, and an empty alternative is permitted (matching the empty string). The matching process tries each alternative in turn, from left to right, and the first one that succeeds is used. If the alternatives are within a subpattern (defined below), "succeeds" means matching the rest of the main pattern as well as the alternative in the subpattern.


INTERNAL OPTION SETTING

The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and PCRE_EXTENDED options (which are Perl-compatible) can be changed from within the pattern by a sequence of Perl option letters enclosed between "(?" and ")". The option letters are

  i  for PCRE_CASELESS
  m  for PCRE_MULTILINE
  s  for PCRE_DOTALL
  x  for PCRE_EXTENDED
For example, (?im) sets caseless, multiline matching. It is also possible to unset these options by preceding the letter with a hyphen, and a combined setting and unsetting such as (?im-sx), which sets PCRE_CASELESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, is also permitted. If a letter appears both before and after the hyphen, the option is unset.

The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA can be changed in the same way as the Perl-compatible options by using the characters J, U and X respectively.

When one of these option changes occurs at top level (that is, not inside subpattern parentheses), the change applies to the remainder of the pattern that follows. If the change is placed right at the start of a pattern, PCRE extracts it into the global options (and it will therefore show up in data extracted by the pcre_fullinfo() function).

An option change within a subpattern (see below for a description of subpatterns) affects only that part of the subpattern that follows it, so

  (a(?i)b)c
matches abc and aBc and no other strings (assuming PCRE_CASELESS is not used). By this means, options can be made to have different settings in different parts of the pattern. Any changes made in one alternative do carry on into subsequent branches within the same subpattern. For example,
  (a(?i)b|c)
matches "ab", "aB", "c", and "C", even though when matching "C" the first branch is abandoned before the option setting. This is because the effects of option settings happen at compile time. There would be some very weird behaviour otherwise.

Note: There are other PCRE-specific options that can be set by the application when the compiling or matching functions are called. In some cases the pattern can contain special leading sequences such as (*CRLF) to override what the application has set or what has been defaulted. Details are given in the section entitled "Newline sequences" above. There are also the (*UTF8), (*UTF16), and (*UCP) leading sequences that can be used to set UTF and Unicode property modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, and the PCRE_UCP options, respectively.


SUBPATTERNS

Subpatterns are delimited by parentheses (round brackets), which can be nested. Turning part of a pattern into a subpattern does two things:

1. It localizes a set of alternatives. For example, the pattern

  cat(aract|erpillar|)
matches "cataract", "caterpillar", or "cat". Without the parentheses, it would match "cataract", "erpillar" or an empty string.

2. It sets up the subpattern as a capturing subpattern. This means that, when the whole pattern matches, that portion of the subject string that matched the subpattern is passed back to the caller via the ovector argument of the matching function. (This applies only to the traditional matching functions; the DFA matching functions do not support capturing.)

Opening parentheses are counted from left to right (starting from 1) to obtain numbers for the capturing subpatterns. For example, if the string "the red king" is matched against the pattern

  the ((red|white) (king|queen))
the captured substrings are "red king", "red", and "king", and are numbered 1, 2, and 3, respectively.

The fact that plain parentheses fulfil two functions is not always helpful. There are often times when a grouping subpattern is required without a capturing requirement. If an opening parenthesis is followed by a question mark and a colon, the subpattern does not do any capturing, and is not counted when computing the number of any subsequent capturing subpatterns. For example, if the string "the white queen" is matched against the pattern

  the ((?:red|white) (king|queen))
the captured substrings are "white queen" and "queen", and are numbered 1 and 2. The maximum number of capturing subpatterns is 65535.

As a convenient shorthand, if any option settings are required at the start of a non-capturing subpattern, the option letters may appear between the "?" and the ":". Thus the two patterns

  (?i:saturday|sunday)
  (?:(?i)saturday|sunday)
match exactly the same set of strings. Because alternative branches are tried from left to right, and options are not reset until the end of the subpattern is reached, an option setting in one branch does affect subsequent branches, so the above patterns match "SUNDAY" as well as "Saturday".


DUPLICATE SUBPATTERN NUMBERS

Perl 5.10 introduced a feature whereby each alternative in a subpattern uses the same numbers for its capturing parentheses. Such a subpattern starts with (?| and is itself a non-capturing subpattern. For example, consider this pattern:

  (?|(Sat)ur|(Sun))day
Because the two alternatives are inside a (?| group, both sets of capturing parentheses are numbered one. Thus, when the pattern matches, you can look at captured substring number one, whichever alternative matched. This construct is useful when you want to capture part, but not all, of one of a number of alternatives. Inside a (?| group, parentheses are numbered as usual, but the number is reset at the start of each branch. The numbers of any capturing parentheses that follow the subpattern start after the highest number used in any branch. The following example is taken from the Perl documentation. The numbers underneath show in which buffer the captured content will be stored.
  # before  ---------------branch-reset----------- after
  / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
  # 1            2         2  3        2     3     4
A back reference to a numbered subpattern uses the most recent value that is set for that number by any subpattern. The following pattern matches "abcabc" or "defdef":
  /(?|(abc)|(def))\1/
In contrast, a subroutine call to a numbered subpattern always refers to the first one in the pattern with the given number. The following pattern matches "abcabc" or "defabc":
  /(?|(abc)|(def))(?1)/
If a condition test for a subpattern's having matched refers to a non-unique number, the test is true if any of the subpatterns of that number have matched.

An alternative approach to using this "branch reset" feature is to use duplicate named subpatterns, as described in the next section.


NAMED SUBPATTERNS

Identifying capturing parentheses by number is simple, but it can be very hard to keep track of the numbers in complicated regular expressions. Furthermore, if an expression is modified, the numbers may change. To help with this difficulty, PCRE supports the naming of subpatterns. This feature was not added to Perl until release 5.10. Python had the feature earlier, and PCRE introduced it at release 4.0, using the Python syntax. PCRE now supports both the Perl and the Python syntax. Perl allows identically numbered subpatterns to have different names, but PCRE does not.

In PCRE, a subpattern can be named in one of three ways: (?<name>...) or (?'name'...) as in Perl, or (?P<name>...) as in Python. References to capturing parentheses from other parts of the pattern, such as back references, recursion, and conditions, can be made by name as well as by number.

Names consist of up to 32 alphanumeric characters and underscores. Named capturing parentheses are still allocated numbers as well as names, exactly as if the names were not present. The PCRE API provides function calls for extracting the name-to-number translation table from a compiled pattern. There is also a convenience function for extracting a captured substring by name.

By default, a name must be unique within a pattern, but it is possible to relax this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate names are also always permitted for subpatterns with the same number, set up as described in the previous section.) Duplicate names can be useful for patterns where only one instance of the named parentheses can match. Suppose you want to match the name of a weekday, either as a 3-letter abbreviation or as the full name, and in both cases you want to extract the abbreviation. This pattern (ignoring the line breaks) does the job:

  (?<DN>Mon|Fri|Sun)(?:day)?|
  (?<DN>Tue)(?:sday)?|
  (?<DN>Wed)(?:nesday)?|
  (?<DN>Thu)(?:rsday)?|
  (?<DN>Sat)(?:urday)?
There are five capturing substrings, but only one is ever set after a match. (An alternative way of solving this problem is to use a "branch reset" subpattern, as described in the previous section.)

The convenience function for extracting the data by name returns the substring for the first (and in this example, the only) subpattern of that name that matched. This saves searching to find which numbered subpattern it was.

If you make a back reference to a non-unique named subpattern from elsewhere in the pattern, the one that corresponds to the first occurrence of the name is used. In the absence of duplicate numbers (see the previous section) this is the one with the lowest number. If you use a named reference in a condition test (see the section about conditions below), either to check whether a subpattern has matched, or to check for recursion, all subpatterns with the same name are tested. If the condition is true for any one of them, the overall condition is true. This is the same behaviour as testing by number. For further details of the interfaces for handling named subpatterns, see the pcreapi documentation.

Warning: You cannot use different names to distinguish between two subpatterns with the same number because PCRE uses only the numbers when matching. For this reason, an error is given at compile time if different names are given to subpatterns with the same number. However, you can give the same name to subpatterns with the same number, even when PCRE_DUPNAMES is not set.


REPETITION

Repetition is specified by quantifiers, which can follow any of the following items:

  a literal data character
  the dot metacharacter
  the \C escape sequence
  the \X escape sequence
  the \R escape sequence
  an escape such as \d or \pL that matches a single character
  a character class
  a back reference (see next section)
  a parenthesized subpattern (including assertions)
  a subroutine call to a subpattern (recursive or otherwise)
The general repetition quantifier specifies a minimum and maximum number of permitted matches, by giving the two numbers in curly brackets (braces), separated by a comma. The numbers must be less than 65536, and the first must be less than or equal to the second. For example:
  z{2,4}
matches "zz", "zzz", or "zzzz". A closing brace on its own is not a special character. If the second number is omitted, but the comma is present, there is no upper limit; if the second number and the comma are both omitted, the quantifier specifies an exact number of required matches. Thus
  [aeiou]{3,}
matches at least 3 successive vowels, but may match many more, while
  \d{8}
matches exactly 8 digits. An opening curly bracket that appears in a position where a quantifier is not allowed, or one that does not match the syntax of a quantifier, is taken as a literal character. For example, {,6} is not a quantifier, but a literal string of four characters.

In UTF modes, quantifiers apply to characters rather than to individual data units. Thus, for example, \x{100}{2} matches two characters, each of which is represented by a two-byte sequence in a UTF-8 string. Similarly, \X{3} matches three Unicode extended sequences, each of which may be several data units long (and they may be of different lengths).

The quantifier {0} is permitted, causing the expression to behave as if the previous item and the quantifier were not present. This may be useful for subpatterns that are referenced as subroutines from elsewhere in the pattern (but see also the section entitled "Defining subpatterns for use by reference only" below). Items other than subpatterns that have a {0} quantifier are omitted from the compiled pattern.

For convenience, the three most common quantifiers have single-character abbreviations:

  *    is equivalent to {0,}
  +    is equivalent to {1,}
  ?    is equivalent to {0,1}
It is possible to construct infinite loops by following a subpattern that can match no characters with a quantifier that has no upper limit, for example:
  (a?)*
Earlier versions of Perl and PCRE used to give an error at compile time for such patterns. However, because there are cases where this can be useful, such patterns are now accepted, but if any repetition of the subpattern does in fact match no characters, the loop is forcibly broken.

By default, the quantifiers are "greedy", that is, they match as much as possible (up to the maximum number of permitted times), without causing the rest of the pattern to fail. The classic example of where this gives problems is in trying to match comments in C programs. These appear between /* and */ and within the comment, individual * and / characters may appear. An attempt to match C comments by applying the pattern

  /\*.*\*/
to the string
  /* first comment */  not comment  /* second comment */
fails, because it matches the entire string owing to the greediness of the .* item.

However, if a quantifier is followed by a question mark, it ceases to be greedy, and instead matches the minimum number of times possible, so the pattern

  /\*.*?\*/
does the right thing with the C comments. The meaning of the various quantifiers is not otherwise changed, just the preferred number of matches. Do not confuse this use of question mark with its use as a quantifier in its own right. Because it has two uses, it can sometimes appear doubled, as in
  \d??\d
which matches one digit by preference, but can match two if that is the only way the rest of the pattern matches.

If the PCRE_UNGREEDY option is set (an option that is not available in Perl), the quantifiers are not greedy by default, but individual ones can be made greedy by following them with a question mark. In other words, it inverts the default behaviour.

When a parenthesized subpattern is quantified with a minimum repeat count that is greater than 1 or with a limited maximum, more memory is required for the compiled pattern, in proportion to the size of the minimum or maximum.

If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equivalent to Perl's /s) is set, thus allowing the dot to match newlines, the pattern is implicitly anchored, because whatever follows will be tried against every character position in the subject string, so there is no point in retrying the overall match at any position after the first. PCRE normally treats such a pattern as though it were preceded by \A.

In cases where it is known that the subject string contains no newlines, it is worth setting PCRE_DOTALL in order to obtain this optimization, or alternatively using ^ to indicate anchoring explicitly.

However, there is one situation where the optimization cannot be used. When .* is inside capturing parentheses that are the subject of a back reference elsewhere in the pattern, a match at the start may fail where a later one succeeds. Consider, for example:

  (.*)abc\1
If the subject is "xyz123abc123" the match point is the fourth character. For this reason, such a pattern is not implicitly anchored.

When a capturing subpattern is repeated, the value captured is the substring that matched the final iteration. For example, after

  (tweedle[dume]{3}\s*)+
has matched "tweedledum tweedledee" the value of the captured substring is "tweedledee". However, if there are nested capturing subpatterns, the corresponding captured values may have been set in previous iterations. For example, after
  /(a|(b))+/
matches "aba" the value of the second captured substring is "b".


ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS

With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") repetition, failure of what follows normally causes the repeated item to be re-evaluated to see if a different number of repeats allows the rest of the pattern to match. Sometimes it is useful to prevent this, either to change the nature of the match, or to cause it fail earlier than it otherwise might, when the author of the pattern knows there is no point in carrying on.

Consider, for example, the pattern \d+foo when applied to the subject line

  123456bar
After matching all 6 digits and then failing to match "foo", the normal action of the matcher is to try again with only 5 digits matching the \d+ item, and then with 4, and so on, before ultimately failing. "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides the means for specifying that once a subpattern has matched, it is not to be re-evaluated in this way.

If we use atomic grouping for the previous example, the matcher gives up immediately on failing to match "foo" the first time. The notation is a kind of special parenthesis, starting with (?> as in this example:

  (?>\d+)foo
This kind of parenthesis "locks up" the part of the pattern it contains once it has matched, and a failure further into the pattern is prevented from backtracking into it. Backtracking past it to previous items, however, works as normal.

An alternative description is that a subpattern of this type matches the string of characters that an identical standalone pattern would match, if anchored at the current point in the subject string.

Atomic grouping subpatterns are not capturing subpatterns. Simple cases such as the above example can be thought of as a maximizing repeat that must swallow everything it can. So, while both \d+ and \d+? are prepared to adjust the number of digits they match in order to make the rest of the pattern match, (?>\d+) can only match an entire sequence of digits.

Atomic groups in general can of course contain arbitrarily complicated subpatterns, and can be nested. However, when the subpattern for an atomic group is just a single repeated item, as in the example above, a simpler notation, called a "possessive quantifier" can be used. This consists of an additional + character following a quantifier. Using this notation, the previous example can be rewritten as

  \d++foo
Note that a possessive quantifier can be used with an entire group, for example:
  (abc|xyz){2,3}+
Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY option is ignored. They are a convenient notation for the simpler forms of atomic group. However, there is no difference in the meaning of a possessive quantifier and the equivalent atomic group, though there may be a performance difference; possessive quantifiers should be slightly faster.

The possessive quantifier syntax is an extension to the Perl 5.8 syntax. Jeffrey Friedl originated the idea (and the name) in the first edition of his book. Mike McCloskey liked it, so implemented it when he built Sun's Java package, and PCRE copied it from there. It ultimately found its way into Perl at release 5.10.

PCRE has an optimization that automatically "possessifies" certain simple pattern constructs. For example, the sequence A+B is treated as A++B because there is no point in backtracking into a sequence of A's when B must follow.

When a pattern contains an unlimited repeat inside a subpattern that can itself be repeated an unlimited number of times, the use of an atomic group is the only way to avoid some failing matches taking a very long time indeed. The pattern

  (\D+|<\d+>)*[!?]
matches an unlimited number of substrings that either consist of non-digits, or digits enclosed in <>, followed by either ! or ?. When it matches, it runs quickly. However, if it is applied to
  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
it takes a long time before reporting failure. This is because the string can be divided between the internal \D+ repeat and the external * repeat in a large number of ways, and all have to be tried. (The example uses [!?] rather than a single character at the end, because both PCRE and Perl have an optimization that allows for fast failure when a single character is used. They remember the last single character that is required for a match, and fail early if it is not present in the string.) If the pattern is changed so that it uses an atomic group, like this:
  ((?>\D+)|<\d+>)*[!?]
sequences of non-digits cannot be broken, and failure happens quickly.


BACK REFERENCES

Outside a character class, a backslash followed by a digit greater than 0 (and possibly further digits) is a back reference to a capturing subpattern earlier (that is, to its left) in the pattern, provided there have been that many previous capturing left parentheses.

However, if the decimal number following the backslash is less than 10, it is always taken as a back reference, and causes an error only if there are not that many capturing left parentheses in the entire pattern. In other words, the parentheses that are referenced need not be to the left of the reference for numbers less than 10. A "forward back reference" of this type can make sense when a repetition is involved and the subpattern to the right has participated in an earlier iteration.

It is not possible to have a numerical "forward back reference" to a subpattern whose number is 10 or more using this syntax because a sequence such as \50 is interpreted as a character defined in octal. See the subsection entitled "Non-printing characters" above for further details of the handling of digits following a backslash. There is no such problem when named parentheses are used. A back reference to any subpattern is possible using named parentheses (see below).

Another way of avoiding the ambiguity inherent in the use of digits following a backslash is to use the \g escape sequence. This escape must be followed by an unsigned number or a negative number, optionally enclosed in braces. These examples are all identical:

  (ring), \1
  (ring), \g1
  (ring), \g{1}
An unsigned number specifies an absolute reference without the ambiguity that is present in the older syntax. It is also useful when literal digits follow the reference. A negative number is a relative reference. Consider this example:
  (abc(def)ghi)\g{-1}
The sequence \g{-1} is a reference to the most recently started capturing subpattern before \g, that is, is it equivalent to \2 in this example. Similarly, \g{-2} would be equivalent to \1. The use of relative references can be helpful in long patterns, and also in patterns that are created by joining together fragments that contain references within themselves.

A back reference matches whatever actually matched the capturing subpattern in the current subject string, rather than anything matching the subpattern itself (see "Subpatterns as subroutines" below for a way of doing that). So the pattern

  (sens|respons)e and \1ibility
matches "sense and sensibility" and "response and responsibility", but not "sense and responsibility". If caseful matching is in force at the time of the back reference, the case of letters is relevant. For example,
  ((?i)rah)\s+\1
matches "rah rah" and "RAH RAH", but not "RAH rah", even though the original capturing subpattern is matched caselessly.

There are several different ways of writing back references to named subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or \k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's unified back reference syntax, in which \g can be used for both numeric and named references, is also supported. We could rewrite the above example in any of the following ways:

  (?<p1>(?i)rah)\s+\k<p1>
  (?'p1'(?i)rah)\s+\k{p1}
  (?P<p1>(?i)rah)\s+(?P=p1)
  (?<p1>(?i)rah)\s+\g{p1}
A subpattern that is referenced by name may appear in the pattern before or after the reference.

There may be more than one back reference to the same subpattern. If a subpattern has not actually been used in a particular match, any back references to it always fail by default. For example, the pattern

  (a|(bc))\2
always fails if it starts to match "a" rather than "bc". However, if the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back reference to an unset value matches an empty string.

Because there may be many capturing parentheses in a pattern, all digits following a backslash are taken as part of a potential back reference number. If the pattern continues with a digit character, some delimiter must be used to terminate the back reference. If the PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{ syntax or an empty comment (see "Comments" below) can be used.


Recursive back references

A back reference that occurs inside the parentheses to which it refers fails when the subpattern is first used, so, for example, (a\1) never matches. However, such references can be useful inside repeated subpatterns. For example, the pattern

  (a|b\1)+
matches any number of "a"s and also "aba", "ababbaa" etc. At each iteration of the subpattern, the back reference matches the character string corresponding to the previous iteration. In order for this to work, the pattern must be such that the first iteration does not need to match the back reference. This can be done using alternation, as in the example above, or by a quantifier with a minimum of zero.

Back references of this type cause the group that they reference to be treated as an atomic group. Once the whole group has been matched, a subsequent matching failure cannot cause backtracking into the middle of the group.


ASSERTIONS

An assertion is a test on the characters following or preceding the current matching point that does not actually consume any characters. The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described above.

More complicated assertions are coded as subpatterns. There are two kinds: those that look ahead of the current position in the subject string, and those that look behind it. An assertion subpattern is matched in the normal way, except that it does not cause the current matching position to be changed.

Assertion subpatterns are not capturing subpatterns. If such an assertion contains capturing subpatterns within it, these are counted for the purposes of numbering the capturing subpatterns in the whole pattern. However, substring capturing is carried out only for positive assertions, because it does not make sense for negative assertions.

For compatibility with Perl, assertion subpatterns may be repeated; though it makes no sense to assert the same thing several times, the side effect of capturing parentheses may occasionally be useful. In practice, there only three cases:

(1) If the quantifier is {0}, the assertion is never obeyed during matching. However, it may contain internal capturing parenthesized groups that are called from elsewhere via the subroutine mechanism.

(2) If quantifier is {0,n} where n is greater than zero, it is treated as if it were {0,1}. At run time, the rest of the pattern match is tried with and without the assertion, the order depending on the greediness of the quantifier.

(3) If the minimum repetition is greater than zero, the quantifier is ignored. The assertion is obeyed just once when encountered during matching.


Lookahead assertions

Lookahead assertions start with (?= for positive assertions and (?! for negative assertions. For example,

  \w+(?=;)
matches a word followed by a semicolon, but does not include the semicolon in the match, and
  foo(?!bar)
matches any occurrence of "foo" that is not followed by "bar". Note that the apparently similar pattern
  (?!foo)bar
does not find an occurrence of "bar" that is preceded by something other than "foo"; it finds any occurrence of "bar" whatsoever, because the assertion (?!foo) is always true when the next three characters are "bar". A lookbehind assertion is needed to achieve the other effect.

If you want to force a matching failure at some point in a pattern, the most convenient way to do it is with (?!) because an empty string always matches, so an assertion that requires there not to be an empty string must always fail. The backtracking control verb (*FAIL) or (*F) is a synonym for (?!).


Lookbehind assertions

Lookbehind assertions start with (?<= for positive assertions and (?<! for negative assertions. For example,

  (?<!foo)bar
does find an occurrence of "bar" that is not preceded by "foo". The contents of a lookbehind assertion are restricted such that all the strings it matches must have a fixed length. However, if there are several top-level alternatives, they do not all have to have the same fixed length. Thus
  (?<=bullock|donkey)
is permitted, but
  (?<!dogs?|cats?)
causes an error at compile time. Branches that match different length strings are permitted only at the top level of a lookbehind assertion. This is an extension compared with Perl, which requires all branches to match the same length of string. An assertion such as
  (?<=ab(c|de))
is not permitted, because its single top-level branch can match two different lengths, but it is acceptable to PCRE if rewritten to use two top-level branches:
  (?<=abc|abde)
In some cases, the escape sequence \K (see above) can be used instead of a lookbehind assertion to get round the fixed-length restriction.

The implementation of lookbehind assertions is, for each alternative, to temporarily move the current position back by the fixed length and then try to match. If there are insufficient characters before the current position, the assertion fails.

In a UTF mode, PCRE does not allow the \C escape (which matches a single data unit even in a UTF mode) to appear in lookbehind assertions, because it makes it impossible to calculate the length of the lookbehind. The \X and \R escapes, which can match different numbers of data units, are also not permitted.

"Subroutine" calls (see below) such as (?2) or (?&X) are permitted in lookbehinds, as long as the subpattern matches a fixed-length string. Recursion, however, is not supported.

Possessive quantifiers can be used in conjunction with lookbehind assertions to specify efficient matching of fixed-length strings at the end of subject strings. Consider a simple pattern such as

  abcd$
when applied to a long string that does not match. Because matching proceeds from left to right, PCRE will look for each "a" in the subject and then see if what follows matches the rest of the pattern. If the pattern is specified as
  ^.*abcd$
the initial .* matches the entire string at first, but when this fails (because there is no following "a"), it backtracks to match all but the last character, then all but the last two characters, and so on. Once again the search for "a" covers the entire string, from right to left, so we are no better off. However, if the pattern is written as
  ^.*+(?<=abcd)
there can be no backtracking for the .*+ item; it can match only the entire string. The subsequent lookbehind assertion does a single test on the last four characters. If it fails, the match fails immediately. For long strings, this approach makes a significant difference to the processing time.


Using multiple assertions

Several assertions (of any sort) may occur in succession. For example,

  (?<=\d{3})(?<!999)foo
matches "foo" preceded by three digits that are not "999". Notice that each of the assertions is applied independently at the same point in the subject string. First there is a check that the previous three characters are all digits, and then there is a check that the same three characters are not "999". This pattern does not match "foo" preceded by six characters, the first of which are digits and the last three of which are not "999". For example, it doesn't match "123abcfoo". A pattern to do that is
  (?<=\d{3}...)(?<!999)foo
This time the first assertion looks at the preceding six characters, checking that the first three are digits, and then the second assertion checks that the preceding three characters are not "999".

Assertions can be nested in any combination. For example,

  (?<=(?<!foo)bar)baz
matches an occurrence of "baz" that is preceded by "bar" which in turn is not preceded by "foo", while
  (?<=\d{3}(?!999)...)foo
is another pattern that matches "foo" preceded by three digits and any three characters that are not "999".


CONDITIONAL SUBPATTERNS

It is possible to cause the matching process to obey a subpattern conditionally or to choose between two alternative subpatterns, depending on the result of an assertion, or whether a specific capturing subpattern has already been matched. The two possible forms of conditional subpattern are:

  (?(condition)yes-pattern)
  (?(condition)yes-pattern|no-pattern)
If the condition is satisfied, the yes-pattern is used; otherwise the no-pattern (if present) is used. If there are more than two alternatives in the subpattern, a compile-time error occurs. Each of the two alternatives may itself contain nested subpatterns of any form, including conditional subpatterns; the restriction to two alternatives applies only at the level of the condition. This pattern fragment is an example where the alternatives are complex:
  (?(1) (A|B|C) | (D | (?(2)E|F) | E) )

There are four kinds of condition: references to subpatterns, references to recursion, a pseudo-condition called DEFINE, and assertions.


Checking for a used subpattern by number

If the text between the parentheses consists of a sequence of digits, the condition is true if a capturing subpattern of that number has previously matched. If there is more than one capturing subpattern with the same number (see the earlier section about duplicate subpattern numbers), the condition is true if any of them have matched. An alternative notation is to precede the digits with a plus or minus sign. In this case, the subpattern number is relative rather than absolute. The most recently opened parentheses can be referenced by (?(-1), the next most recent by (?(-2), and so on. Inside loops it can also make sense to refer to subsequent groups. The next parentheses to be opened can be referenced as (?(+1), and so on. (The value zero in any of these forms is not used; it provokes a compile-time error.)

Consider the following pattern, which contains non-significant white space to make it more readable (assume the PCRE_EXTENDED option) and to divide it into three parts for ease of discussion:

  ( \( )?    [^()]+    (?(1) \) )
The first part matches an optional opening parenthesis, and if that character is present, sets it as the first captured substring. The second part matches one or more characters that are not parentheses. The third part is a conditional subpattern that tests whether or not the first set of parentheses matched. If they did, that is, if subject started with an opening parenthesis, the condition is true, and so the yes-pattern is executed and a closing parenthesis is required. Otherwise, since no-pattern is not present, the subpattern matches nothing. In other words, this pattern matches a sequence of non-parentheses, optionally enclosed in parentheses.

If you were embedding this pattern in a larger one, you could use a relative reference:

  ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
This makes the fragment independent of the parentheses in the larger pattern.


Checking for a used subpattern by name

Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used subpattern by name. For compatibility with earlier versions of PCRE, which had this facility before Perl, the syntax (?(name)...) is also recognized. However, there is a possible ambiguity with this syntax, because subpattern names may consist entirely of digits. PCRE looks first for a named subpattern; if it cannot find one and the name consists entirely of digits, PCRE looks for a subpattern of that number, which must be greater than zero. Using subpattern names that consist entirely of digits is not recommended.

Rewriting the above example to use a named subpattern gives this:

  (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
If the name used in a condition of this kind is a duplicate, the test is applied to all subpatterns of the same name, and is true if any one of them has matched.


Checking for pattern recursion

If the condition is the string (R), and there is no subpattern with the name R, the condition is true if a recursive call to the whole pattern or any subpattern has been made. If digits or a name preceded by ampersand follow the letter R, for example:

  (?(R3)...) or (?(R&name)...)
the condition is true if the most recent recursion is into a subpattern whose number or name is given. This condition does not check the entire recursion stack. If the name used in a condition of this kind is a duplicate, the test is applied to all subpatterns of the same name, and is true if any one of them is the most recent recursion.

At "top level", all these recursion test conditions are false. The syntax for recursive patterns is described below.


Defining subpatterns for use by reference only

If the condition is the string (DEFINE), and there is no subpattern with the name DEFINE, the condition is always false. In this case, there may be only one alternative in the subpattern. It is always skipped if control reaches this point in the pattern; the idea of DEFINE is that it can be used to define subroutines that can be referenced from elsewhere. (The use of subroutines is described below.) For example, a pattern to match an IPv4 address such as "192.168.23.245" could be written like this (ignore whitespace and line breaks):

  (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
  \b (?&byte) (\.(?&byte)){3} \b
The first part of the pattern is a DEFINE group inside which a another group named "byte" is defined. This matches an individual component of an IPv4 address (a number less than 256). When matching takes place, this part of the pattern is skipped because DEFINE acts like a false condition. The rest of the pattern uses references to the named group to match the four dot-separated components of an IPv4 address, insisting on a word boundary at each end.


Assertion conditions

If the condition is not in any of the above formats, it must be an assertion. This may be a positive or negative lookahead or lookbehind assertion. Consider this pattern, again containing non-significant white space, and with the two alternatives on the second line:

  (?(?=[^a-z]*[a-z])
  \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
The condition is a positive lookahead assertion that matches an optional sequence of non-letters followed by a letter. In other words, it tests for the presence of at least one letter in the subject. If a letter is found, the subject is matched against the first alternative; otherwise it is matched against the second. This pattern matches strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits.


COMMENTS

There are two ways of including comments in patterns that are processed by PCRE. In both cases, the start of the comment must not be in a character class, nor in the middle of any other sequence of related characters such as (?: or a subpattern name or number. The characters that make up a comment play no part in the pattern matching.

The sequence (?# marks the start of a comment that continues up to the next closing parenthesis. Nested parentheses are not permitted. If the PCRE_EXTENDED option is set, an unescaped # character also introduces a comment, which in this case continues to immediately after the next newline character or character sequence in the pattern. Which characters are interpreted as newlines is controlled by the options passed to a compiling function or by a special sequence at the start of the pattern, as described in the section entitled "Newline conventions" above. Note that the end of this type of comment is a literal newline sequence in the pattern; escape sequences that happen to represent a newline do not count. For example, consider this pattern when PCRE_EXTENDED is set, and the default newline convention is in force:

  abc #comment \n still comment
On encountering the # character, pcre_compile() skips along, looking for a newline in the pattern. The sequence \n is still literal at this stage, so it does not terminate the comment. Only an actual character with the code value 0x0a (the default newline) does so.


RECURSIVE PATTERNS

Consider the problem of matching a string in parentheses, allowing for unlimited nested parentheses. Without the use of recursion, the best that can be done is to use a pattern that matches up to some fixed depth of nesting. It is not possible to handle an arbitrary nesting depth.

For some time, Perl has provided a facility that allows regular expressions to recurse (amongst other things). It does this by interpolating Perl code in the expression at run time, and the code can refer to the expression itself. A Perl pattern using code interpolation to solve the parentheses problem can be created like this:

  $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
The (?p{...}) item interpolates Perl code at run time, and in this case refers recursively to the pattern in which it appears.

Obviously, PCRE cannot support the interpolation of Perl code. Instead, it supports special syntax for recursion of the entire pattern, and also for individual subpattern recursion. After its introduction in PCRE and Python, this kind of recursion was subsequently introduced into Perl at release 5.10.

A special item that consists of (? followed by a number greater than zero and a closing parenthesis is a recursive subroutine call of the subpattern of the given number, provided that it occurs inside that subpattern. (If not, it is a non-recursive subroutine call, which is described in the next section.) The special item (?R) or (?0) is a recursive call of the entire regular expression.

This PCRE pattern solves the nested parentheses problem (assume the PCRE_EXTENDED option is set so that white space is ignored):

  \( ( [^()]++ | (?R) )* \)
First it matches an opening parenthesis. Then it matches any number of substrings which can either be a sequence of non-parentheses, or a recursive match of the pattern itself (that is, a correctly parenthesized substring). Finally there is a closing parenthesis. Note the use of a possessive quantifier to avoid backtracking into sequences of non-parentheses.

If this were part of a larger pattern, you would not want to recurse the entire pattern, so instead you could use this:

  ( \( ( [^()]++ | (?1) )* \) )
We have put the pattern into parentheses, and caused the recursion to refer to them instead of the whole pattern.

In a larger pattern, keeping track of parenthesis numbers can be tricky. This is made easier by the use of relative references. Instead of (?1) in the pattern above you can write (?-2) to refer to the second most recently opened parentheses preceding the recursion. In other words, a negative number counts capturing parentheses leftwards from the point at which it is encountered.

It is also possible to refer to subsequently opened parentheses, by writing references such as (?+2). However, these cannot be recursive because the reference is not inside the parentheses that are referenced. They are always non-recursive subroutine calls, as described in the next section.

An alternative approach is to use named parentheses instead. The Perl syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also supported. We could rewrite the above example as follows:

  (?<pn> \( ( [^()]++ | (?&pn) )* \) )
If there is more than one subpattern with the same name, the earliest one is used.

This particular example pattern that we have been looking at contains nested unlimited repeats, and so the use of a possessive quantifier for matching strings of non-parentheses is important when applying the pattern to strings that do not match. For example, when this pattern is applied to

  (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
it yields "no match" quickly. However, if a possessive quantifier is not used, the match runs for a very long time indeed because there are so many different ways the + and * repeats can carve up the subject, and all have to be tested before failure can be reported.

At the end of a match, the values of capturing parentheses are those from the outermost level. If you want to obtain intermediate values, a callout function can be used (see below and the pcrecallout documentation). If the pattern above is matched against

  (ab(cd)ef)
the value for the inner capturing parentheses (numbered 2) is "ef", which is the last value taken on at the top level. If a capturing subpattern is not matched at the top level, its final captured value is unset, even if it was (temporarily) set at a deeper level during the matching process.

If there are more than 15 capturing parentheses in a pattern, PCRE has to obtain extra memory to store data during a recursion, which it does by using pcre_malloc, freeing it via pcre_free afterwards. If no memory can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.

Do not confuse the (?R) item with the condition (R), which tests for recursion. Consider this pattern, which matches text in angle brackets, allowing for arbitrary nesting. Only digits are allowed in nested brackets (that is, when recursing), whereas any characters are permitted at the outer level.

  < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
In this pattern, (?(R) is the start of a conditional subpattern, with two different alternatives for the recursive and non-recursive cases. The (?R) item is the actual recursive call.


Differences in recursion processing between PCRE and Perl

Recursion processing in PCRE differs from Perl in two important ways. In PCRE (like Python, but unlike Perl), a recursive subpattern call is always treated as an atomic group. That is, once it has matched some of the subject string, it is never re-entered, even if it contains untried alternatives and there is a subsequent matching failure. This can be illustrated by the following pattern, which purports to match a palindromic string that contains an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"):

  ^(.|(.)(?1)\2)$
The idea is that it either matches a single character, or two identical characters surrounding a sub-palindrome. In Perl, this pattern works; in PCRE it does not if the pattern is longer than three characters. Consider the subject string "abcba":

At the top level, the first character is matched, but as it is not at the end of the string, the first alternative fails; the second alternative is taken and the recursion kicks in. The recursive call to subpattern 1 successfully matches the next character ("b"). (Note that the beginning and end of line tests are not part of the recursion).

Back at the top level, the next character ("c") is compared with what subpattern 2 matched, which was "a". This fails. Because the recursion is treated as an atomic group, there are now no backtracking points, and so the entire match fails. (Perl is able, at this point, to re-enter the recursion and try the second alternative.) However, if the pattern is written with the alternatives in the other order, things are different:

  ^((.)(?1)\2|.)$
This time, the recursing alternative is tried first, and continues to recurse until it runs out of characters, at which point the recursion fails. But this time we do have another alternative to try at the higher level. That is the big difference: in the previous case the remaining alternative is at a deeper recursion level, which PCRE cannot use.

To change the pattern so that it matches all palindromic strings, not just those with an odd number of characters, it is tempting to change the pattern to this:

  ^((.)(?1)\2|.?)$
Again, this works in Perl, but not in PCRE, and for the same reason. When a deeper recursion has matched a single character, it cannot be entered again in order to match an empty string. The solution is to separate the two cases, and write out the odd and even cases as alternatives at the higher level:
  ^(?:((.)(?1)\2|)|((.)(?3)\4|.))
If you want to match typical palindromic phrases, the pattern has to ignore all non-word characters, which can be done like this:
  ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$
If run with the PCRE_CASELESS option, this pattern matches phrases such as "A man, a plan, a canal: Panama!" and it works well in both PCRE and Perl. Note the use of the possessive quantifier *+ to avoid backtracking into sequences of non-word characters. Without this, PCRE takes a great deal longer (ten times or more) to match typical phrases, and Perl takes so long that you think it has gone into a loop.

WARNING: The palindrome-matching patterns above work only if the subject string does not start with a palindrome that is shorter than the entire string. For example, although "abcba" is correctly matched, if the subject is "ababa", PCRE finds the palindrome "aba" at the start, then fails at top level because the end of the string does not follow. Once again, it cannot jump back into the recursion to try other alternatives, so the entire match fails.

The second way in which PCRE and Perl differ in their recursion processing is in the handling of captured values. In Perl, when a subpattern is called recursively or as a subpattern (see the next section), it has no access to any values that were captured outside the recursion, whereas in PCRE these values can be referenced. Consider this pattern:

  ^(.)(\1|a(?2))
In PCRE, this pattern matches "bab". The first capturing parentheses match "b", then in the second group, when the back reference \1 fails to match "b", the second alternative matches "a" and then recurses. In the recursion, \1 does now match "b" and so the whole match succeeds. In Perl, the pattern fails to match because inside the recursive call \1 cannot access the externally set value.


SUBPATTERNS AS SUBROUTINES

If the syntax for a recursive subpattern call (either by number or by name) is used outside the parentheses to which it refers, it operates like a subroutine in a programming language. The called subpattern may be defined before or after the reference. A numbered reference can be absolute or relative, as in these examples:

  (...(absolute)...)...(?2)...
  (...(relative)...)...(?-1)...
  (...(?+1)...(relative)...
An earlier example pointed out that the pattern
  (sens|respons)e and \1ibility
matches "sense and sensibility" and "response and responsibility", but not "sense and responsibility". If instead the pattern
  (sens|respons)e and (?1)ibility
is used, it does match "sense and responsibility" as well as the other two strings. Another example is given in the discussion of DEFINE above.

All subroutine calls, whether recursive or not, are always treated as atomic groups. That is, once a subroutine has matched some of the subject string, it is never re-entered, even if it contains untried alternatives and there is a subsequent matching failure. Any capturing parentheses that are set during the subroutine call revert to their previous values afterwards.

Processing options such as case-independence are fixed when a subpattern is defined, so if it is used as a subroutine, such options cannot be changed for different calls. For example, consider this pattern:

  (abc)(?i:(?-1))
It matches "abcabc". It does not match "abcABC" because the change of processing option does not affect the called subpattern.


ONIGURUMA SUBROUTINE SYNTAX

For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is an alternative syntax for referencing a subpattern as a subroutine, possibly recursively. Here are two of the examples used above, rewritten using this syntax:

  (?<pn> \( ( (?>[^()]+) | \g<pn> )* \) )
  (sens|respons)e and \g'1'ibility
PCRE supports an extension to Oniguruma: if a number is preceded by a plus or a minus sign it is taken as a relative reference. For example:
  (abc)(?i:\g<-1>)
Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not synonymous. The former is a back reference; the latter is a subroutine call.


CALLOUTS

Perl has a feature whereby using the sequence (?{...}) causes arbitrary Perl code to be obeyed in the middle of matching a regular expression. This makes it possible, amongst other things, to extract different substrings that match the same pair of parentheses when there is a repetition.

PCRE provides a similar feature, but of course it cannot obey arbitrary Perl code. The feature is called "callout". The caller of PCRE provides an external function by putting its entry point in the global variable pcre_callout (8-bit library) or pcre16_callout (16-bit library). By default, this variable contains NULL, which disables all calling out.

Within a regular expression, (?C) indicates the points at which the external function is to be called. If you want to identify different callout points, you can put a number less than 256 after the letter C. The default value is zero. For example, this pattern has two callout points:

  (?C1)abc(?C2)def
If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, callouts are automatically installed before each item in the pattern. They are all numbered 255.

During matching, when PCRE reaches a callout point, the external function is called. It is provided with the number of the callout, the position in the pattern, and, optionally, one item of data originally supplied by the caller of the matching function. The callout function may cause matching to proceed, to backtrack, or to fail altogether. A complete description of the interface to the callout function is given in the pcrecallout documentation.


BACKTRACKING CONTROL

Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which are described in the Perl documentation as "experimental and subject to change or removal in a future version of Perl". It goes on to say: "Their usage in production code should be noted to avoid problems during upgrades." The same remarks apply to the PCRE features described in this section.

Since these verbs are specifically related to backtracking, most of them can be used only when the pattern is to be matched using one of the traditional matching functions, which use a backtracking algorithm. With the exception of (*FAIL), which behaves like a failing negative assertion, they cause an error if encountered by a DFA matching function.

If any of these verbs are used in an assertion or in a subpattern that is called as a subroutine (whether or not recursively), their effect is confined to that subpattern; it does not extend to the surrounding pattern, with one exception: the name from a *(MARK), (*PRUNE), or (*THEN) that is encountered in a successful positive assertion is passed back when a match succeeds (compare capturing parentheses in assertions). Note that such subpatterns are processed as anchored at the point where they are tested. Note also that Perl's treatment of subroutines is different in some cases.

The new verbs make use of what was previously invalid syntax: an opening parenthesis followed by an asterisk. They are generally of the form (*VERB) or (*VERB:NAME). Some may take either form, with differing behaviour, depending on whether or not an argument is present. A name is any sequence of characters that does not include a closing parenthesis. If the name is empty, that is, if the closing parenthesis immediately follows the colon, the effect is as if the colon were not there. Any number of these verbs may occur in a pattern.

PCRE contains some optimizations that are used to speed up matching by running some checks at the start of each match attempt. For example, it may know the minimum length of matching subject, or that a particular character must be present. When one of these optimizations suppresses the running of a match, any included backtracking verbs will not, of course, be processed. You can suppress the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_compile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT).

Experiments with Perl suggest that it too has similar optimizations, sometimes leading to anomalous results.


Verbs that act immediately

The following verbs act as soon as they are encountered. They may not be followed by a name.

   (*ACCEPT)
This verb causes the match to end successfully, skipping the remainder of the pattern. However, when it is inside a subpattern that is called as a subroutine, only that subpattern is ended successfully. Matching then continues at the outer level. If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For example:
  A((?:A|B(*ACCEPT)|C)D)
This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is captured by the outer parentheses.
  (*FAIL) or (*F)
This verb causes a matching failure, forcing backtracking to occur. It is equivalent to (?!) but easier to read. The Perl documentation notes that it is probably useful only when combined with (?{}) or (??{}). Those are, of course, Perl features that are not present in PCRE. The nearest equivalent is the callout feature, as for example in this pattern:
  a+(?C)(*FAIL)
A match with the string "aaaa" always fails, but the callout is taken before each backtrack happens (in this example, 10 times).


Recording which path was taken

There is one verb whose main purpose is to track how a match was arrived at, though it also has a secondary use in conjunction with advancing the match starting point (see (*SKIP) below).

  (*MARK:NAME) or (*:NAME)
A name is always required with this verb. There may be as many instances of (*MARK) as you like in a pattern, and their names do not have to be unique.

When a match succeeds, the name of the last-encountered (*MARK) on the matching path is passed back to the caller as described in the section entitled "Extra data for pcre_exec()" in the pcreapi documentation. Here is an example of pcretest output, where the /K modifier requests the retrieval and outputting of (*MARK) data:

    re> /X(*MARK:A)Y|X(*MARK:B)Z/K
  data> XY
   0: XY
  MK: A
  XZ
   0: XZ
  MK: B
The (*MARK) name is tagged with "MK:" in this output, and in this example it indicates which of the two alternatives matched. This is a more efficient way of obtaining this information than putting each alternative in its own capturing parentheses.

If (*MARK) is encountered in a positive assertion, its name is recorded and passed back if it is the last-encountered. This does not happen for negative assertions.

After a partial match or a failed match, the name of the last encountered (*MARK) in the entire match process is returned. For example:

    re> /X(*MARK:A)Y|X(*MARK:B)Z/K
  data> XP
  No match, mark = B
Note that in this unanchored example the mark is retained from the match attempt that started at the letter "X". Subsequent match attempts starting at "P" and then with an empty string do not get as far as the (*MARK) item, but nevertheless do not reset it.


Verbs that act after backtracking

The following verbs do nothing when they are encountered. Matching continues with what follows, but if there is no subsequent match, causing a backtrack to the verb, a failure is forced. That is, backtracking cannot pass to the left of the verb. However, when one of these verbs appears inside an atomic group, its effect is confined to that group, because once the group has been matched, there is never any backtracking into it. In this situation, backtracking can "jump back" to the left of the entire atomic group. (Remember also, as stated above, that this localization also applies in subroutine calls and assertions.)

These verbs differ in exactly what kind of failure occurs when backtracking reaches them.

  (*COMMIT)
This verb, which may not be followed by a name, causes the whole match to fail outright if the rest of the pattern does not match. Even if the pattern is unanchored, no further attempts to find a match by advancing the starting point take place. Once (*COMMIT) has been passed, pcre_exec() is committed to finding a match at the current starting point, or not at all. For example:
  a+(*COMMIT)b
This matches "xxaab" but not "aacaab". It can be thought of as a kind of dynamic anchor, or "I've started, so I must finish." The name of the most recently passed (*MARK) in the path is passed back when (*COMMIT) forces a match failure.

Note that (*COMMIT) at the start of a pattern is not the same as an anchor, unless PCRE's start-of-match optimizations are turned off, as shown in this pcretest example:

    re> /(*COMMIT)abc/
  data> xyzabc
   0: abc
  xyzabc\Y
  No match
PCRE knows that any match must start with "a", so the optimization skips along the subject to "a" before running the first match attempt, which succeeds. When the optimization is disabled by the \Y escape in the second subject, the match starts at "x" and so the (*COMMIT) causes it to fail without trying any other starting points.
  (*PRUNE) or (*PRUNE:NAME)
This verb causes the match to fail at the current starting position in the subject if the rest of the pattern does not match. If the pattern is unanchored, the normal "bumpalong" advance to the next starting character then happens. Backtracking can occur as usual to the left of (*PRUNE), before it is reached, or when matching to the right of (*PRUNE), but if there is no match to the right, backtracking cannot cross (*PRUNE). In simple cases, the use of (*PRUNE) is just an alternative to an atomic group or possessive quantifier, but there are some uses of (*PRUNE) that cannot be expressed in any other way. The behaviour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an anchored pattern (*PRUNE) has the same effect as (*COMMIT).
  (*SKIP)
This verb, when given without a name, is like (*PRUNE), except that if the pattern is unanchored, the "bumpalong" advance is not to the next character, but to the position in the subject where (*SKIP) was encountered. (*SKIP) signifies that whatever text was matched leading up to it cannot be part of a successful match. Consider:
  a+(*SKIP)b
If the subject is "aaaac...", after the first match attempt fails (starting at the first character in the string), the starting point skips on to start the next attempt at "c". Note that a possessive quantifer does not have the same effect as this example; although it would suppress backtracking during the first match attempt, the second attempt would start at the second character instead of skipping on to "c".
  (*SKIP:NAME)
When (*SKIP) has an associated name, its behaviour is modified. If the following pattern fails to match, the previous path through the pattern is searched for the most recent (*MARK) that has the same name. If one is found, the "bumpalong" advance is to the subject position that corresponds to that (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with a matching name is found, the (*SKIP) is ignored.
  (*THEN) or (*THEN:NAME)
This verb causes a skip to the next innermost alternative if the rest of the pattern does not match. That is, it cancels pending backtracking, but only within the current alternative. Its name comes from the observation that it can be used for a pattern-based if-then-else block:
  ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
If the COND1 pattern matches, FOO is tried (and possibly further items after the end of the group if FOO succeeds); on failure, the matcher skips to the second alternative and tries COND2, without backtracking into COND1. The behaviour of (*THEN:NAME) is exactly the same as (*MARK:NAME)(*THEN). If (*THEN) is not inside an alternation, it acts like (*PRUNE).

Note that a subpattern that does not contain a | character is just a part of the enclosing alternative; it is not a nested alternation with only one alternative. The effect of (*THEN) extends beyond such a subpattern to the enclosing alternative. Consider this pattern, where A, B, etc. are complex pattern fragments that do not contain any | characters at this level:

  A (B(*THEN)C) | D
If A and B are matched, but there is a failure in C, matching does not backtrack into A; instead it moves to the next alternative, that is, D. However, if the subpattern containing (*THEN) is given an alternative, it behaves differently:
  A (B(*THEN)C | (*FAIL)) | D
The effect of (*THEN) is now confined to the inner subpattern. After a failure in C, matching moves to (*FAIL), which causes the whole subpattern to fail because there are no more alternatives to try. In this case, matching does now backtrack into A.

Note also that a conditional subpattern is not considered as having two alternatives, because only one is ever used. In other words, the | character in a conditional subpattern has a different meaning. Ignoring white space, consider:

  ^.*? (?(?=a) a | b(*THEN)c )
If the subject is "ba", this pattern does not match. Because .*? is ungreedy, it initially matches zero characters. The condition (?=a) then fails, the character "b" is matched, but "c" is not. At this point, matching does not backtrack to .*? as might perhaps be expected from the presence of the | character. The conditional subpattern is part of the single alternative that comprises the whole pattern, and so the match fails. (If there was a backtrack into .*?, allowing it to match "b", the match would succeed.)

The verbs just described provide four different "strengths" of control when subsequent matching fails. (*THEN) is the weakest, carrying on the match at the next alternative. (*PRUNE) comes next, failing the match at the current starting position, but allowing an advance to the next character (for an unanchored pattern). (*SKIP) is similar, except that the advance may be more than one character. (*COMMIT) is the strongest, causing the entire match to fail.

If more than one such verb is present in a pattern, the "strongest" one wins. For example, consider this pattern, where A, B, etc. are complex pattern fragments:

  (A(*COMMIT)B(*THEN)C|D)
Once A has matched, PCRE is committed to this match, at the current starting position. If subsequently B matches, but C does not, the normal (*THEN) action of trying the next alternative (that is, D) does not happen because (*COMMIT) overrides.


SEE ALSO

pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3), pcre16(3).


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 09 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382ba000081a40000000000000000000000014f79083e0000066e000000b500010002ffffffffffffffff0000003e00000000root/usr/local/share/doc/pcre/html/pcre_get_stringnumber.html pcre_get_stringnumber specification

pcre_get_stringnumber man page

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SYNOPSIS

#include <pcre.h>

int pcre_get_stringnumber(const pcre *code, const char *name);

int pcre16_get_stringnumber(const pcre16 *code, PCRE_SPTR16 name);


DESCRIPTION

This convenience function finds the number of a named substring capturing parenthesis in a compiled pattern. Its arguments are:

  code    Compiled regular expression
  name    Name whose number is required
The yield of the function is the number of the parenthesis if the name is found, or PCRE_ERROR_NOSUBSTRING otherwise. When duplicate names are allowed (PCRE_DUPNAMES is set), it is not defined which of the numbers is returned by pcre[16]_get_stringnumber(). You can obtain the complete list by calling pcre[16]_get_stringtable_entries().

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382aa000081a40000000000000000000000014f79083e00001c39000000b500010002ffffffffffffffff0000002d00000000root/usr/local/share/doc/pcre/html/pcre.html pcre specification

pcre man page

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INTRODUCTION

The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl, with just a few differences. Some features that appeared in Python and PCRE before they appeared in Perl are also available using the Python syntax, there is some support for one or two .NET and Oniguruma syntax items, and there is an option for requesting some minor changes that give better JavaScript compatibility.

Starting with release 8.30, it is possible to compile two separate PCRE libraries: the original, which supports 8-bit character strings (including UTF-8 strings), and a second library that supports 16-bit character strings (including UTF-16 strings). The build process allows either one or both to be built. The majority of the work to make this possible was done by Zoltan Herczeg.

The two libraries contain identical sets of functions, except that the names in the 16-bit library start with pcre16_ instead of pcre_. To avoid over-complication and reduce the documentation maintenance load, most of the documentation describes the 8-bit library, with the differences for the 16-bit library described separately in the pcre16 page. References to functions or structures of the form pcre[16]_xxx should be read as meaning "pcre_xxx when using the 8-bit library and pcre16_xxx when using the 16-bit library".

The current implementation of PCRE corresponds approximately with Perl 5.12, including support for UTF-8/16 encoded strings and Unicode general category properties. However, UTF-8/16 and Unicode support has to be explicitly enabled; it is not the default. The Unicode tables correspond to Unicode release 6.0.0.

In addition to the Perl-compatible matching function, PCRE contains an alternative function that matches the same compiled patterns in a different way. In certain circumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the pcrematching page.

PCRE is written in C and released as a C library. A number of people have written wrappers and interfaces of various kinds. In particular, Google Inc. have provided a comprehensive C++ wrapper for the 8-bit library. This is now included as part of the PCRE distribution. The pcrecpp page has details of this interface. Other people's contributions can be found in the Contrib directory at the primary FTP site, which is: ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre

Details of exactly which Perl regular expression features are and are not supported by PCRE are given in separate documents. See the pcrepattern and pcrecompat pages. There is a syntax summary in the pcresyntax page.

Some features of PCRE can be included, excluded, or changed when the library is built. The pcre_config() function makes it possible for a client to discover which features are available. The features themselves are described in the pcrebuild page. Documentation about building PCRE for various operating systems can be found in the README and NON-UNIX-USE files in the source distribution.

The libraries contains a number of undocumented internal functions and data tables that are used by more than one of the exported external functions, but which are not intended for use by external callers. Their names all begin with "_pcre_" or "_pcre16_", which hopefully will not provoke any name clashes. In some environments, it is possible to control which external symbols are exported when a shared library is built, and in these cases the undocumented symbols are not exported.


USER DOCUMENTATION

The user documentation for PCRE comprises a number of different sections. In the "man" format, each of these is a separate "man page". In the HTML format, each is a separate page, linked from the index page. In the plain text format, all the sections, except the pcredemo section, are concatenated, for ease of searching. The sections are as follows:

  pcre              this document
  pcre16            details of the 16-bit library
  pcre-config       show PCRE installation configuration information
  pcreapi           details of PCRE's native C API
  pcrebuild         options for building PCRE
  pcrecallout       details of the callout feature
  pcrecompat        discussion of Perl compatibility
  pcrecpp           details of the C++ wrapper for the 8-bit library
  pcredemo          a demonstration C program that uses PCRE
  pcregrep          description of the pcregrep command (8-bit only)
  pcrejit           discussion of the just-in-time optimization support
  pcrelimits        details of size and other limits
  pcrematching      discussion of the two matching algorithms
  pcrepartial       details of the partial matching facility
  pcrepattern       syntax and semantics of supported regular expressions
  pcreperform       discussion of performance issues
  pcreposix         the POSIX-compatible C API for the 8-bit library
  pcreprecompile    details of saving and re-using precompiled patterns
  pcresample        discussion of the pcredemo program
  pcrestack         discussion of stack usage
  pcresyntax        quick syntax reference
  pcretest          description of the pcretest testing command
  pcreunicode       discussion of Unicode and UTF-8/16 support
In addition, in the "man" and HTML formats, there is a short page for each 8-bit C library function, listing its arguments and results.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.

Putting an actual email address here seems to have been a spam magnet, so I've taken it away. If you want to email me, use my two initials, followed by the two digits 10, at the domain cam.ac.uk.


REVISION

Last updated: 10 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382b0000081a40000000000000000000000014f79083e00000805000000b500010002ffffffffffffffff0000004200000000root/usr/local/share/doc/pcre/html/pcre_copy_named_substring.html pcre_copy_named_substring specification

pcre_copy_named_substring man page

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SYNOPSIS

#include <pcre.h>

int pcre_copy_named_substring(const pcre *code, const char *subject, int *ovector, int stringcount, const char *stringname, char *buffer, int buffersize);

int pcre16_copy_named_substring(const pcre16 *code, PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 stringname, PCRE_UCHAR16 *buffer, int buffersize);


DESCRIPTION

This is a convenience function for extracting a captured substring, identified by name, into a given buffer. The arguments are:

  code          Pattern that was successfully matched
  subject       Subject that has been successfully matched
  ovector       Offset vector that pcre[16]_exec() used
  stringcount   Value returned by pcre[16]_exec()
  stringname    Name of the required substring
  buffer        Buffer to receive the string
  buffersize    Size of buffer
The yield is the length of the substring, PCRE_ERROR_NOMEMORY if the buffer was too small, or PCRE_ERROR_NOSUBSTRING if the string name is invalid.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382b3000081a40000000000000000000000014f79083e00001172000000b500010002ffffffffffffffff0000003200000000root/usr/local/share/doc/pcre/html/pcre_exec.html pcre_exec specification

pcre_exec man page

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SYNOPSIS

#include <pcre.h>

int pcre_exec(const pcre *code, const pcre_extra *extra, const char *subject, int length, int startoffset, int options, int *ovector, int ovecsize);

int pcre16_exec(const pcre16 *code, const pcre16_extra *extra, PCRE_SPTR16 subject, int length, int startoffset, int options, int *ovector, int ovecsize);


DESCRIPTION

This function matches a compiled regular expression against a given subject string, using a matching algorithm that is similar to Perl's. It returns offsets to captured substrings. Its arguments are:

  code         Points to the compiled pattern
  extra        Points to an associated pcre[16]_extra structure,
                 or is NULL
  subject      Points to the subject string
  length       Length of the subject string, in bytes
  startoffset  Offset in bytes in the subject at which to
                 start matching
  options      Option bits
  ovector      Points to a vector of ints for result offsets
  ovecsize     Number of elements in the vector (a multiple of 3)
The options are:
  PCRE_ANCHORED          Match only at the first position
  PCRE_BSR_ANYCRLF       \R matches only CR, LF, or CRLF
  PCRE_BSR_UNICODE       \R matches all Unicode line endings
  PCRE_NEWLINE_ANY       Recognize any Unicode newline sequence
  PCRE_NEWLINE_ANYCRLF   Recognize CR, LF, & CRLF as newline sequences
  PCRE_NEWLINE_CR        Recognize CR as the only newline sequence
  PCRE_NEWLINE_CRLF      Recognize CRLF as the only newline sequence
  PCRE_NEWLINE_LF        Recognize LF as the only newline sequence
  PCRE_NOTBOL            Subject string is not the beginning of a line
  PCRE_NOTEOL            Subject string is not the end of a line
  PCRE_NOTEMPTY          An empty string is not a valid match
  PCRE_NOTEMPTY_ATSTART  An empty string at the start of the subject
                           is not a valid match
  PCRE_NO_START_OPTIMIZE Do not do "start-match" optimizations
  PCRE_NO_UTF16_CHECK    Do not check the subject for UTF-16
                           validity (only relevant if PCRE_UTF16
                           was set at compile time)
  PCRE_NO_UTF8_CHECK     Do not check the subject for UTF-8
                           validity (only relevant if PCRE_UTF8
                           was set at compile time)
  PCRE_PARTIAL           ) Return PCRE_ERROR_PARTIAL for a partial
  PCRE_PARTIAL_SOFT      )   match if no full matches are found
  PCRE_PARTIAL_HARD      Return PCRE_ERROR_PARTIAL for a partial match
                           if that is found before a full match
For details of partial matching, see the pcrepartial page. A pcre_extra structure contains the following fields:
  flags            Bits indicating which fields are set
  study_data       Opaque data from pcre[16]_study()
  match_limit      Limit on internal resource use
  match_limit_recursion  Limit on internal recursion depth
  callout_data     Opaque data passed back to callouts
  tables           Points to character tables or is NULL
  mark             For passing back a *MARK pointer
  executable_jit   Opaque data from JIT compilation
The flag bits are PCRE_EXTRA_STUDY_DATA, PCRE_EXTRA_MATCH_LIMIT, PCRE_EXTRA_MATCH_LIMIT_RECURSION, PCRE_EXTRA_CALLOUT_DATA, PCRE_EXTRA_TABLES, PCRE_EXTRA_MARK and PCRE_EXTRA_EXECUTABLE_JIT.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382c8000081a40000000000000000000000014f79083e00000455000000b500010002ffffffffffffffff0000003500000000root/usr/local/share/doc/pcre/html/pcre_version.html pcre_version specification

pcre_version man page

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SYNOPSIS

#include <pcre.h>

const char *pcre_version(void);

const char *pcre16_version(void);


DESCRIPTION

This function (even in the 16-bit library) returns a zero-terminated, 8-bit character string that gives the version number of the PCRE library and the date of its release.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382b5000081a40000000000000000000000014f79083e000004b3000000b500010002ffffffffffffffff0000003c00000000root/usr/local/share/doc/pcre/html/pcre_free_substring.html pcre_free_substring specification

pcre_free_substring man page

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SYNOPSIS

#include <pcre.h>

void pcre_free_substring(const char *stringptr);

void pcre16_free_substring(PCRE_SPTR16 stringptr);


DESCRIPTION

This is a convenience function for freeing the store obtained by a previous call to pcre[16]_get_substring() or pcre[16]_get_named_substring(). Its only argument is a pointer to the string.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382cb000081a40000000000000000000000014f79083e00002623000000b500010002ffffffffffffffff0000003400000000root/usr/local/share/doc/pcre/html/pcrecallout.html pcrecallout specification

pcrecallout man page

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PCRE CALLOUTS

int (*pcre_callout)(pcre_callout_block *);

int (*pcre16_callout)(pcre16_callout_block *);

PCRE provides a feature called "callout", which is a means of temporarily passing control to the caller of PCRE in the middle of pattern matching. The caller of PCRE provides an external function by putting its entry point in the global variable pcre_callout (pcre16_callout for the 16-bit library). By default, this variable contains NULL, which disables all calling out.

Within a regular expression, (?C) indicates the points at which the external function is to be called. Different callout points can be identified by putting a number less than 256 after the letter C. The default value is zero. For example, this pattern has two callout points:

  (?C1)abc(?C2)def
If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, PCRE automatically inserts callouts, all with number 255, before each item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the pattern
  A(\d{2}|--)
it is processed as if it were

(?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)

Notice that there is a callout before and after each parenthesis and alternation bar. Automatic callouts can be used for tracking the progress of pattern matching. The pcretest command has an option that sets automatic callouts; when it is used, the output indicates how the pattern is matched. This is useful information when you are trying to optimize the performance of a particular pattern.

The use of callouts in a pattern makes it ineligible for optimization by the just-in-time compiler. Studying such a pattern with the PCRE_STUDY_JIT_COMPILE option always fails.


MISSING CALLOUTS

You should be aware that, because of optimizations in the way PCRE matches patterns by default, callouts sometimes do not happen. For example, if the pattern is

  ab(?C4)cd
PCRE knows that any matching string must contain the letter "d". If the subject string is "abyz", the lack of "d" means that matching doesn't ever start, and the callout is never reached. However, with "abyd", though the result is still no match, the callout is obeyed.

If the pattern is studied, PCRE knows the minimum length of a matching string, and will immediately give a "no match" return without actually running a match if the subject is not long enough, or, for unanchored patterns, if it has been scanned far enough.

You can disable these optimizations by passing the PCRE_NO_START_OPTIMIZE option to the matching function, or by starting the pattern with (*NO_START_OPT). This slows down the matching process, but does ensure that callouts such as the example above are obeyed.


THE CALLOUT INTERFACE

During matching, when PCRE reaches a callout point, the external function defined by pcre_callout or pcre16_callout is called (if it is set). This applies to both normal and DFA matching. The only argument to the callout function is a pointer to a pcre_callout or pcre16_callout block. These structures contains the following fields:

  int           version;
  int           callout_number;
  int          *offset_vector;
  const char   *subject;           (8-bit version)
  PCRE_SPTR16   subject;           (16-bit version)
  int           subject_length;
  int           start_match;
  int           current_position;
  int           capture_top;
  int           capture_last;
  void         *callout_data;
  int           pattern_position;
  int           next_item_length;
  const unsigned char *mark;       (8-bit version)
  const PCRE_UCHAR16  *mark;       (16-bit version)
The version field is an integer containing the version number of the block format. The initial version was 0; the current version is 2. The version number will change again in future if additional fields are added, but the intention is never to remove any of the existing fields.

The callout_number field contains the number of the callout, as compiled into the pattern (that is, the number after ?C for manual callouts, and 255 for automatically generated callouts).

The offset_vector field is a pointer to the vector of offsets that was passed by the caller to the matching function. When pcre_exec() or pcre16_exec() is used, the contents can be inspected, in order to extract substrings that have been matched so far, in the same way as for extracting substrings after a match has completed. For the DFA matching functions, this field is not useful.

The subject and subject_length fields contain copies of the values that were passed to the matching function.

The start_match field normally contains the offset within the subject at which the current match attempt started. However, if the escape sequence \K has been encountered, this value is changed to reflect the modified starting point. If the pattern is not anchored, the callout function may be called several times from the same point in the pattern for different starting points in the subject.

The current_position field contains the offset within the subject of the current match pointer.

When the pcre_exec() or pcre16_exec() is used, the capture_top field contains one more than the number of the highest numbered captured substring so far. If no substrings have been captured, the value of capture_top is one. This is always the case when the DFA functions are used, because they do not support captured substrings.

The capture_last field contains the number of the most recently captured substring. If no substrings have been captured, its value is -1. This is always the case for the DFA matching functions.

The callout_data field contains a value that is passed to a matching function specifically so that it can be passed back in callouts. It is passed in the callout_data field of a pcre_extra or pcre16_extra data structure. If no such data was passed, the value of callout_data in a callout block is NULL. There is a description of the pcre_extra structure in the pcreapi documentation.

The pattern_position field is present from version 1 of the callout structure. It contains the offset to the next item to be matched in the pattern string.

The next_item_length field is present from version 1 of the callout structure. It contains the length of the next item to be matched in the pattern string. When the callout immediately precedes an alternation bar, a closing parenthesis, or the end of the pattern, the length is zero. When the callout precedes an opening parenthesis, the length is that of the entire subpattern.

The pattern_position and next_item_length fields are intended to help in distinguishing between different automatic callouts, which all have the same callout number. However, they are set for all callouts.

The mark field is present from version 2 of the callout structure. In callouts from pcre_exec() or pcre16_exec() it contains a pointer to the zero-terminated name of the most recently passed (*MARK), (*PRUNE), or (*THEN) item in the match, or NULL if no such items have been passed. Instances of (*PRUNE) or (*THEN) without a name do not obliterate a previous (*MARK). In callouts from the DFA matching functions this field always contains NULL.


RETURN VALUES

The external callout function returns an integer to PCRE. If the value is zero, matching proceeds as normal. If the value is greater than zero, matching fails at the current point, but the testing of other matching possibilities goes ahead, just as if a lookahead assertion had failed. If the value is less than zero, the match is abandoned, the matching function returns the negative value.

Negative values should normally be chosen from the set of PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a standard "no match" failure. The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions; it will never be used by PCRE itself.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 08 Janurary 2012
Copyright © 1997-2012 University of Cambridge.

Return to the PCRE index page.

070701000382ca000081a40000000000000000000000014f79083e000047cd000000b500010002ffffffffffffffff0000003200000000root/usr/local/share/doc/pcre/html/pcrebuild.html pcrebuild specification

pcrebuild man page

Return to the PCRE index page.

This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.


PCRE BUILD-TIME OPTIONS

This document describes the optional features of PCRE that can be selected when the library is compiled. It assumes use of the configure script, where the optional features are selected or deselected by providing options to configure before running the make command. However, the same options can be selected in both Unix-like and non-Unix-like environments using the GUI facility of cmake-gui if you are using CMake instead of configure to build PCRE.

There is a lot more information about building PCRE in non-Unix-like environments in the file called NON_UNIX_USE, which is part of the PCRE distribution. You should consult this file as well as the README file if you are building in a non-Unix-like environment.

The complete list of options for configure (which includes the standard ones such as the selection of the installation directory) can be obtained by running

  ./configure --help
The following sections include descriptions of options whose names begin with --enable or --disable. These settings specify changes to the defaults for the configure command. Because of the way that configure works, --enable and --disable always come in pairs, so the complementary option always exists as well, but as it specifies the default, it is not described.


BUILDING 8-BIT and 16-BIT LIBRARIES

By default, a library called libpcre is built, containing functions that take string arguments contained in vectors of bytes, either as single-byte characters, or interpreted as UTF-8 strings. You can also build a separate library, called libpcre16, in which strings are contained in vectors of 16-bit data units and interpreted either as single-unit characters or UTF-16 strings, by adding

  --enable-pcre16
to the configure command. If you do not want the 8-bit library, add
  --disable-pcre8
as well. At least one of the two libraries must be built. Note that the C++ and POSIX wrappers are for the 8-bit library only, and that pcregrep is an 8-bit program. None of these are built if you select only the 16-bit library.


BUILDING SHARED AND STATIC LIBRARIES

The PCRE building process uses libtool to build both shared and static Unix libraries by default. You can suppress one of these by adding one of

  --disable-shared
  --disable-static
to the configure command, as required.


C++ SUPPORT

By default, if the 8-bit library is being built, the configure script will search for a C++ compiler and C++ header files. If it finds them, it automatically builds the C++ wrapper library (which supports only 8-bit strings). You can disable this by adding

  --disable-cpp
to the configure command.


UTF-8 and UTF-16 SUPPORT

To build PCRE with support for UTF Unicode character strings, add

  --enable-utf
to the configure command. This setting applies to both libraries, adding support for UTF-8 to the 8-bit library and support for UTF-16 to the 16-bit library. There are no separate options for enabling UTF-8 and UTF-16 independently because that would allow ridiculous settings such as requesting UTF-16 support while building only the 8-bit library. It is not possible to build one library with UTF support and the other without in the same configuration. (For backwards compatibility, --enable-utf8 is a synonym of --enable-utf.)

Of itself, this setting does not make PCRE treat strings as UTF-8 or UTF-16. As well as compiling PCRE with this option, you also have have to set the PCRE_UTF8 or PCRE_UTF16 option when you call one of the pattern compiling functions.

If you set --enable-utf when compiling in an EBCDIC environment, PCRE expects its input to be either ASCII or UTF-8 (depending on the runtime option). It is not possible to support both EBCDIC and UTF-8 codes in the same version of the library. Consequently, --enable-utf and --enable-ebcdic are mutually exclusive.


UNICODE CHARACTER PROPERTY SUPPORT

UTF support allows the libraries to process character codepoints up to 0x10ffff in the strings that they handle. On its own, however, it does not provide any facilities for accessing the properties of such characters. If you want to be able to use the pattern escapes \P, \p, and \X, which refer to Unicode character properties, you must add

  --enable-unicode-properties
to the configure command. This implies UTF support, even if you have not explicitly requested it.

Including Unicode property support adds around 30K of tables to the PCRE library. Only the general category properties such as Lu and Nd are supported. Details are given in the pcrepattern documentation.


JUST-IN-TIME COMPILER SUPPORT

Just-in-time compiler support is included in the build by specifying

  --enable-jit
This support is available only for certain hardware architectures. If this option is set for an unsupported architecture, a compile time error occurs. See the pcrejit documentation for a discussion of JIT usage. When JIT support is enabled, pcregrep automatically makes use of it, unless you add
  --disable-pcregrep-jit
to the "configure" command.


CODE VALUE OF NEWLINE

By default, PCRE interprets the linefeed (LF) character as indicating the end of a line. This is the normal newline character on Unix-like systems. You can compile PCRE to use carriage return (CR) instead, by adding

  --enable-newline-is-cr
to the configure command. There is also a --enable-newline-is-lf option, which explicitly specifies linefeed as the newline character.

Alternatively, you can specify that line endings are to be indicated by the two character sequence CRLF. If you want this, add
  --enable-newline-is-crlf
to the configure command. There is a fourth option, specified by
  --enable-newline-is-anycrlf
which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as indicating a line ending. Finally, a fifth option, specified by
  --enable-newline-is-any
causes PCRE to recognize any Unicode newline sequence.

Whatever line ending convention is selected when PCRE is built can be overridden when the library functions are called. At build time it is conventional to use the standard for your operating system.


WHAT \R MATCHES

By default, the sequence \R in a pattern matches any Unicode newline sequence, whatever has been selected as the line ending sequence. If you specify

  --enable-bsr-anycrlf
the default is changed so that \R matches only CR, LF, or CRLF. Whatever is selected when PCRE is built can be overridden when the library functions are called.


POSIX MALLOC USAGE

When the 8-bit library is called through the POSIX interface (see the pcreposix documentation), additional working storage is required for holding the pointers to capturing substrings, because PCRE requires three integers per substring, whereas the POSIX interface provides only two. If the number of expected substrings is small, the wrapper function uses space on the stack, because this is faster than using malloc() for each call. The default threshold above which the stack is no longer used is 10; it can be changed by adding a setting such as

  --with-posix-malloc-threshold=20
to the configure command.


HANDLING VERY LARGE PATTERNS

Within a compiled pattern, offset values are used to point from one part to another (for example, from an opening parenthesis to an alternation metacharacter). By default, two-byte values are used for these offsets, leading to a maximum size for a compiled pattern of around 64K. This is sufficient to handle all but the most gigantic patterns. Nevertheless, some people do want to process truly enormous patterns, so it is possible to compile PCRE to use three-byte or four-byte offsets by adding a setting such as

  --with-link-size=3
to the configure command. The value given must be 2, 3, or 4. For the 16-bit library, a value of 3 is rounded up to 4. Using longer offsets slows down the operation of PCRE because it has to load additional data when handling them.


AVOIDING EXCESSIVE STACK USAGE

When matching with the pcre_exec() function, PCRE implements backtracking by making recursive calls to an internal function called match(). In environments where the size of the stack is limited, this can severely limit PCRE's operation. (The Unix environment does not usually suffer from this problem, but it may sometimes be necessary to increase the maximum stack size. There is a discussion in the pcrestack documentation.) An alternative approach to recursion that uses memory from the heap to remember data, instead of using recursive function calls, has been implemented to work round the problem of limited stack size. If you want to build a version of PCRE that works this way, add

  --disable-stack-for-recursion
to the configure command. With this configuration, PCRE will use the pcre_stack_malloc and pcre_stack_free variables to call memory management functions. By default these point to malloc() and free(), but you can replace the pointers so that your own functions are used instead.

Separate functions are provided rather than using pcre_malloc and pcre_free because the usage is very predictable: the block sizes requested are always the same, and the blocks are always freed in reverse order. A calling program might be able to implement optimized functions that perform better than malloc() and free(). PCRE runs noticeably more slowly when built in this way. This option affects only the pcre_exec() function; it is not relevant for pcre_dfa_exec().


LIMITING PCRE RESOURCE USAGE

Internally, PCRE has a function called match(), which it calls repeatedly (sometimes recursively) when matching a pattern with the pcre_exec() function. By controlling the maximum number of times this function may be called during a single matching operation, a limit can be placed on the resources used by a single call to pcre_exec(). The limit can be changed at run time, as described in the pcreapi documentation. The default is 10 million, but this can be changed by adding a setting such as

  --with-match-limit=500000
to the configure command. This setting has no effect on the pcre_dfa_exec() matching function.

In some environments it is desirable to limit the depth of recursive calls of match() more strictly than the total number of calls, in order to restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion is specified) that is used. A second limit controls this; it defaults to the value that is set for --with-match-limit, which imposes no additional constraints. However, you can set a lower limit by adding, for example,

  --with-match-limit-recursion=10000
to the configure command. This value can also be overridden at run time.


CREATING CHARACTER TABLES AT BUILD TIME

PCRE uses fixed tables for processing characters whose code values are less than 256. By default, PCRE is built with a set of tables that are distributed in the file pcre_chartables.c.dist. These tables are for ASCII codes only. If you add

  --enable-rebuild-chartables
to the configure command, the distributed tables are no longer used. Instead, a program called dftables is compiled and run. This outputs the source for new set of tables, created in the default locale of your C runtime system. (This method of replacing the tables does not work if you are cross compiling, because dftables is run on the local host. If you need to create alternative tables when cross compiling, you will have to do so "by hand".)


USING EBCDIC CODE

PCRE assumes by default that it will run in an environment where the character code is ASCII (or Unicode, which is a superset of ASCII). This is the case for most computer operating systems. PCRE can, however, be compiled to run in an EBCDIC environment by adding

  --enable-ebcdic
to the configure command. This setting implies --enable-rebuild-chartables. You should only use it if you know that you are in an EBCDIC environment (for example, an IBM mainframe operating system). The --enable-ebcdic option is incompatible with --enable-utf.


PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT

By default, pcregrep reads all files as plain text. You can build it so that it recognizes files whose names end in .gz or .bz2, and reads them with libz or libbz2, respectively, by adding one or both of

  --enable-pcregrep-libz
  --enable-pcregrep-libbz2
to the configure command. These options naturally require that the relevant libraries are installed on your system. Configuration will fail if they are not.


PCREGREP BUFFER SIZE

pcregrep uses an internal buffer to hold a "window" on the file it is scanning, in order to be able to output "before" and "after" lines when it finds a match. The size of the buffer is controlled by a parameter whose default value is 20K. The buffer itself is three times this size, but because of the way it is used for holding "before" lines, the longest line that is guaranteed to be processable is the parameter size. You can change the default parameter value by adding, for example,

  --with-pcregrep-bufsize=50K
to the configure command. The caller of \fPpcregrep\fP can, however, override this value by specifying a run-time option.


PCRETEST OPTION FOR LIBREADLINE SUPPORT

If you add

  --enable-pcretest-libreadline
to the configure command, pcretest is linked with the libreadline library, and when its input is from a terminal, it reads it using the readline() function. This provides line-editing and history facilities. Note that libreadline is GPL-licensed, so if you distribute a binary of pcretest linked in this way, there may be licensing issues.

Setting this option causes the -lreadline option to be added to the pcretest build. In many operating environments with a sytem-installed libreadline this is sufficient. However, in some environments (e.g. if an unmodified distribution version of readline is in use), some extra configuration may be necessary. The INSTALL file for libreadline says this:

  "Readline uses the termcap functions, but does not link with the
  termcap or curses library itself, allowing applications which link
  with readline the to choose an appropriate library."
If your environment has not been set up so that an appropriate library is automatically included, you may need to add something like
  LIBS="-ncurses"
immediately before the configure command.


SEE ALSO

pcreapi(3), pcre16, pcre_config(3).


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 07 January 2012
Copyright © 1997-2012 University of Cambridge.

Return to the PCRE index page.

070701000382d9000081a40000000000000000000000014f79083e00002544000000b500010002ffffffffffffffff0000003200000000root/usr/local/share/doc/pcre/html/pcrestack.html pcrestack specification

pcrestack man page

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This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

PCRE DISCUSSION OF STACK USAGE

When you call pcre[16]_exec(), it makes use of an internal function called match(). This calls itself recursively at branch points in the pattern, in order to remember the state of the match so that it can back up and try a different alternative if the first one fails. As matching proceeds deeper and deeper into the tree of possibilities, the recursion depth increases. The match() function is also called in other circumstances, for example, whenever a parenthesized sub-pattern is entered, and in certain cases of repetition.

Not all calls of match() increase the recursion depth; for an item such as a* it may be called several times at the same level, after matching different numbers of a's. Furthermore, in a number of cases where the result of the recursive call would immediately be passed back as the result of the current call (a "tail recursion"), the function is just restarted instead.

The above comments apply when pcre[16]_exec() is run in its normal interpretive manner. If the pattern was studied with the PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was successful, and the options passed to pcre[16]_exec() were not incompatible, the matching process uses the JIT-compiled code instead of the match() function. In this case, the memory requirements are handled entirely differently. See the pcrejit documentation for details.

The pcre[16]_dfa_exec() function operates in an entirely different way, and uses recursion only when there is a regular expression recursion or subroutine call in the pattern. This includes the processing of assertion and "once-only" subpatterns, which are handled like subroutine calls. Normally, these are never very deep, and the limit on the complexity of pcre[16]_dfa_exec() is controlled by the amount of workspace it is given. However, it is possible to write patterns with runaway infinite recursions; such patterns will cause pcre[16]_dfa_exec() to run out of stack. At present, there is no protection against this.

The comments that follow do NOT apply to pcre[16]_dfa_exec(); they are relevant only for pcre[16]_exec() without the JIT optimization.


Reducing pcre[16]_exec()'s stack usage

Each time that match() is actually called recursively, it uses memory from the process stack. For certain kinds of pattern and data, very large amounts of stack may be needed, despite the recognition of "tail recursion". You can often reduce the amount of recursion, and therefore the amount of stack used, by modifying the pattern that is being matched. Consider, for example, this pattern:

  ([^<]|<(?!inet))+
It matches from wherever it starts until it encounters "<inet" or the end of the data, and is the kind of pattern that might be used when processing an XML file. Each iteration of the outer parentheses matches either one character that is not "<" or a "<" that is not followed by "inet". However, each time a parenthesis is processed, a recursion occurs, so this formulation uses a stack frame for each matched character. For a long string, a lot of stack is required. Consider now this rewritten pattern, which matches exactly the same strings:
  ([^<]++|<(?!inet))+
This uses very much less stack, because runs of characters that do not contain "<" are "swallowed" in one item inside the parentheses. Recursion happens only when a "<" character that is not followed by "inet" is encountered (and we assume this is relatively rare). A possessive quantifier is used to stop any backtracking into the runs of non-"<" characters, but that is not related to stack usage.

This example shows that one way of avoiding stack problems when matching long subject strings is to write repeated parenthesized subpatterns to match more than one character whenever possible.


Compiling PCRE to use heap instead of stack for pcre[16]_exec()

In environments where stack memory is constrained, you might want to compile PCRE to use heap memory instead of stack for remembering back-up points when pcre[16]_exec() is running. This makes it run a lot more slowly, however. Details of how to do this are given in the pcrebuild documentation. When built in this way, instead of using the stack, PCRE obtains and frees memory by calling the functions that are pointed to by the pcre[16]_stack_malloc and pcre[16]_stack_free variables. By default, these point to malloc() and free(), but you can replace the pointers to cause PCRE to use your own functions. Since the block sizes are always the same, and are always freed in reverse order, it may be possible to implement customized memory handlers that are more efficient than the standard functions.


Limiting pcre[16]_exec()'s stack usage

You can set limits on the number of times that match() is called, both in total and recursively. If a limit is exceeded, pcre[16]_exec() returns an error code. Setting suitable limits should prevent it from running out of stack. The default values of the limits are very large, and unlikely ever to operate. They can be changed when PCRE is built, and they can also be set when pcre[16]_exec() is called. For details of these interfaces, see the pcrebuild documentation and the section on extra data for pcre[16]_exec() in the pcreapi documentation.

As a very rough rule of thumb, you should reckon on about 500 bytes per recursion. Thus, if you want to limit your stack usage to 8Mb, you should set the limit at 16000 recursions. A 64Mb stack, on the other hand, can support around 128000 recursions.

In Unix-like environments, the pcretest test program has a command line option (-S) that can be used to increase the size of its stack. As long as the stack is large enough, another option (-M) can be used to find the smallest limits that allow a particular pattern to match a given subject string. This is done by calling pcre[16]_exec() repeatedly with different limits.


Obtaining an estimate of stack usage

The actual amount of stack used per recursion can vary quite a lot, depending on the compiler that was used to build PCRE and the optimization or debugging options that were set for it. The rule of thumb value of 500 bytes mentioned above may be larger or smaller than what is actually needed. A better approximation can be obtained by running this command:

  pcretest -m -C
The -C option causes pcretest to output information about the options with which PCRE was compiled. When -m is also given (before -C), information about stack use is given in a line like this:
  Match recursion uses stack: approximate frame size = 640 bytes
The value is approximate because some recursions need a bit more (up to perhaps 16 more bytes).

If the above command is given when PCRE is compiled to use the heap instead of the stack for recursion, the value that is output is the size of each block that is obtained from the heap.


Changing stack size in Unix-like systems

In Unix-like environments, there is not often a problem with the stack unless very long strings are involved, though the default limit on stack size varies from system to system. Values from 8Mb to 64Mb are common. You can find your default limit by running the command:

  ulimit -s
Unfortunately, the effect of running out of stack is often SIGSEGV, though sometimes a more explicit error message is given. You can normally increase the limit on stack size by code such as this:
  struct rlimit rlim;
  getrlimit(RLIMIT_STACK, &rlim);
  rlim.rlim_cur = 100*1024*1024;
  setrlimit(RLIMIT_STACK, &rlim);
This reads the current limits (soft and hard) using getrlimit(), then attempts to increase the soft limit to 100Mb using setrlimit(). You must do this before calling pcre[16]_exec().


Changing stack size in Mac OS X

Using setrlimit(), as described above, should also work on Mac OS X. It is also possible to set a stack size when linking a program. There is a discussion about stack sizes in Mac OS X at this web site: http://developer.apple.com/qa/qa2005/qa1419.html.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 21 January 2012
Copyright © 1997-2012 University of Cambridge.

Return to the PCRE index page.

070701000382b8000081a40000000000000000000000014f79083e00000e00000000b500010002ffffffffffffffff0000003600000000root/usr/local/share/doc/pcre/html/pcre_fullinfo.html pcre_fullinfo specification

pcre_fullinfo man page

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This page is part of the PCRE HTML documentation. It was generated automatically from the original man page. If there is any nonsense in it, please consult the man page, in case the conversion went wrong.

SYNOPSIS

#include <pcre.h>

int pcre_fullinfo(const pcre *code, const pcre_extra *extra, int what, void *where);

int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra, int what, void *where);


DESCRIPTION

This function returns information about a compiled pattern. Its arguments are:

  code                      Compiled regular expression
  extra                     Result of pcre[16]_study() or NULL
  what                      What information is required
  where                     Where to put the information
The following information is available:
  PCRE_INFO_BACKREFMAX      Number of highest back reference
  PCRE_INFO_CAPTURECOUNT    Number of capturing subpatterns
  PCRE_INFO_DEFAULT_TABLES  Pointer to default tables
  PCRE_INFO_FIRSTBYTE       Fixed first data unit for a match, or
                              -1 for start of string
                                 or after newline, or
                              -2 otherwise
  PCRE_INFO_FIRSTTABLE      Table of first data units (after studying)
  PCRE_INFO_HASCRORLF       Return 1 if explicit CR or LF matches exist
  PCRE_INFO_JCHANGED        Return 1 if (?J) or (?-J) was used
  PCRE_INFO_JIT             Return 1 after successful JIT compilation
  PCRE_INFO_JITSIZE         Size of JIT compiled code
  PCRE_INFO_LASTLITERAL     Literal last data unit required
  PCRE_INFO_MINLENGTH       Lower bound length of matching strings
  PCRE_INFO_NAMECOUNT       Number of named subpatterns
  PCRE_INFO_NAMEENTRYSIZE   Size of name table entry
  PCRE_INFO_NAMETABLE       Pointer to name table
  PCRE_INFO_OKPARTIAL       Return 1 if partial matching can be tried
                              (always returns 1 after release 8.00)
  PCRE_INFO_OPTIONS         Option bits used for compilation
  PCRE_INFO_SIZE            Size of compiled pattern
  PCRE_INFO_STUDYSIZE       Size of study data
The where argument must point to an integer variable, except for the following what values:
  PCRE_INFO_DEFAULT_TABLES  const unsigned char *
  PCRE_INFO_FIRSTTABLE      const unsigned char *
  PCRE_INFO_NAMETABLE       PCRE_SPTR16           (16-bit library)
  PCRE_INFO_NAMETABLE       const unsigned char * (8-bit library)
  PCRE_INFO_OPTIONS         unsigned long int
  PCRE_INFO_SIZE            size_t
The yield of the function is zero on success or:
  PCRE_ERROR_NULL           the argument code was NULL
                            the argument where was NULL
  PCRE_ERROR_BADMAGIC       the "magic number" was not found
  PCRE_ERROR_BADOPTION      the value of what was invalid

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382c6000081a40000000000000000000000014f79083e000007e7000000b500010002ffffffffffffffff0000004600000000root/usr/local/share/doc/pcre/html/pcre_utf16_to_host_byte_order.html pcre_utf16_to_host_byte_order specification

pcre_utf16_to_host_byte_order man page

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SYNOPSIS

#include <pcre.h>

int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output, PCRE_SPTR16 input, int length, int *host_byte_order, int keep_boms);


DESCRIPTION

This function, which exists only in the 16-bit library, converts a UTF-16 string to the correct order for the current host, taking account of any byte order marks (BOMs) within the string. Its arguments are:

  output           pointer to output buffer, may be the same as input
  input            pointer to input buffer
  length           number of 16-bit units in the input, or negative for
                     a zero-terminated string
  host_byte_order  a NULL value or a non-zero value pointed to means
                     start in host byte order
  keep_boms        if non-zero, BOMs are copied to the output string
The result of the function is the number of 16-bit units placed into the output buffer, including the zero terminator if the string was zero-terminated.

If host_byte_order is not NULL, it is set to indicate the byte order that is current at the end of the string.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382cc000081a40000000000000000000000014f79083e00002188000000b500010002ffffffffffffffff0000003300000000root/usr/local/share/doc/pcre/html/pcrecompat.html pcrecompat specification

pcrecompat man page

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DIFFERENCES BETWEEN PCRE AND PERL

This document describes the differences in the ways that PCRE and Perl handle regular expressions. The differences described here are with respect to Perl versions 5.10 and above.

1. PCRE has only a subset of Perl's Unicode support. Details of what it does have are given in the pcreunicode page.

2. PCRE allows repeat quantifiers only on parenthesized assertions, but they do not mean what you might think. For example, (?!a){3} does not assert that the next three characters are not "a". It just asserts that the next character is not "a" three times (in principle: PCRE optimizes this to run the assertion just once). Perl allows repeat quantifiers on other assertions such as \b, but these do not seem to have any use.

3. Capturing subpatterns that occur inside negative lookahead assertions are counted, but their entries in the offsets vector are never set. Perl sets its numerical variables from any such patterns that are matched before the assertion fails to match something (thereby succeeding), but only if the negative lookahead assertion contains just one branch.

4. Though binary zero characters are supported in the subject string, they are not allowed in a pattern string because it is passed as a normal C string, terminated by zero. The escape sequence \0 can be used in the pattern to represent a binary zero.

5. The following Perl escape sequences are not supported: \l, \u, \L, \U, and \N when followed by a character name or Unicode value. (\N on its own, matching a non-newline character, is supported.) In fact these are implemented by Perl's general string-handling and are not part of its pattern matching engine. If any of these are encountered by PCRE, an error is generated by default. However, if the PCRE_JAVASCRIPT_COMPAT option is set, \U and \u are interpreted as JavaScript interprets them.

6. The Perl escape sequences \p, \P, and \X are supported only if PCRE is built with Unicode character property support. The properties that can be tested with \p and \P are limited to the general category properties such as Lu and Nd, script names such as Greek or Han, and the derived properties Any and L&. PCRE does support the Cs (surrogate) property, which Perl does not; the Perl documentation says "Because Perl hides the need for the user to understand the internal representation of Unicode characters, there is no need to implement the somewhat messy concept of surrogates."

7. PCRE implements a simpler version of \X than Perl, which changed to make \X match what Unicode calls an "extended grapheme cluster". This is more complicated than an extended Unicode sequence, which is what PCRE matches.

8. PCRE does support the \Q...\E escape for quoting substrings. Characters in between are treated as literals. This is slightly different from Perl in that $ and @ are also handled as literals inside the quotes. In Perl, they cause variable interpolation (but of course PCRE does not have variables). Note the following examples:

    Pattern            PCRE matches      Perl matches

    \Qabc$xyz\E        abc$xyz           abc followed by the contents of $xyz
    \Qabc\$xyz\E       abc\$xyz          abc\$xyz
    \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
The \Q...\E sequence is recognized both inside and outside character classes.

9. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) constructions. However, there is support for recursive patterns. This is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE "callout" feature allows an external function to be called during pattern matching. See the pcrecallout documentation for details.

10. Subpatterns that are called as subroutines (whether or not recursively) are always treated as atomic groups in PCRE. This is like Python, but unlike Perl. Captured values that are set outside a subroutine call can be reference from inside in PCRE, but not in Perl. There is a discussion that explains these differences in more detail in the section on recursion differences from Perl in the pcrepattern page.

11. If (*THEN) is present in a group that is called as a subroutine, its action is limited to that group, even if the group does not contain any | characters.

12. There are some differences that are concerned with the settings of captured strings when part of a pattern is repeated. For example, matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE it is set to "b".

13. PCRE's handling of duplicate subpattern numbers and duplicate subpattern names is not as general as Perl's. This is a consequence of the fact the PCRE works internally just with numbers, using an external table to translate between numbers and names. In particular, a pattern such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have the same number but different names, is not supported, and causes an error at compile time. If it were allowed, it would not be possible to distinguish which parentheses matched, because both names map to capturing subpattern number 1. To avoid this confusing situation, an error is given at compile time.

14. Perl recognizes comments in some places that PCRE does not, for example, between the ( and ? at the start of a subpattern. If the /x modifier is set, Perl allows whitespace between ( and ? but PCRE never does, even if the PCRE_EXTENDED option is set.

15. PCRE provides some extensions to the Perl regular expression facilities. Perl 5.10 includes new features that are not in earlier versions of Perl, some of which (such as named parentheses) have been in PCRE for some time. This list is with respect to Perl 5.10:

(a) Although lookbehind assertions in PCRE must match fixed length strings, each alternative branch of a lookbehind assertion can match a different length of string. Perl requires them all to have the same length.

(b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $ meta-character matches only at the very end of the string.

(c) If PCRE_EXTRA is set, a backslash followed by a letter with no special meaning is faulted. Otherwise, like Perl, the backslash is quietly ignored. (Perl can be made to issue a warning.)

(d) If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is inverted, that is, by default they are not greedy, but if followed by a question mark they are.

(e) PCRE_ANCHORED can be used at matching time to force a pattern to be tried only at the first matching position in the subject string.

(f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equivalents.

(g) The \R escape sequence can be restricted to match only CR, LF, or CRLF by the PCRE_BSR_ANYCRLF option.

(h) The callout facility is PCRE-specific.

(i) The partial matching facility is PCRE-specific.

(j) Patterns compiled by PCRE can be saved and re-used at a later time, even on different hosts that have the other endianness. However, this does not apply to optimized data created by the just-in-time compiler.

(k) The alternative matching functions (pcre_dfa_exec() and pcre16_dfa_exec()) match in a different way and are not Perl-compatible.

(l) PCRE recognizes some special sequences such as (*CR) at the start of a pattern that set overall options that cannot be changed within the pattern.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 08 Januray 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382b1000081a40000000000000000000000014f79083e0000074e000000b500010002ffffffffffffffff0000003c00000000root/usr/local/share/doc/pcre/html/pcre_copy_substring.html pcre_copy_substring specification

pcre_copy_substring man page

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SYNOPSIS

#include <pcre.h>

int pcre_copy_substring(const char *subject, int *ovector, int stringcount, int stringnumber, char *buffer, int buffersize);

int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector, int stringcount, int stringnumber, PCRE_UCHAR16 *buffer, int buffersize);


DESCRIPTION

This is a convenience function for extracting a captured substring into a given buffer. The arguments are:

  subject       Subject that has been successfully matched
  ovector       Offset vector that pcre[16]_exec() used
  stringcount   Value returned by pcre[16]_exec()
  stringnumber  Number of the required substring
  buffer        Buffer to receive the string
  buffersize    Size of buffer
The yield is the length of the string, PCRE_ERROR_NOMEMORY if the buffer was too small, or PCRE_ERROR_NOSUBSTRING if the string number is invalid.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382d7000081a40000000000000000000000014f79083e00001bdb000000b500010002ffffffffffffffff0000003700000000root/usr/local/share/doc/pcre/html/pcreprecompile.html pcreprecompile specification

pcreprecompile man page

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SAVING AND RE-USING PRECOMPILED PCRE PATTERNS

If you are running an application that uses a large number of regular expression patterns, it may be useful to store them in a precompiled form instead of having to compile them every time the application is run. If you are not using any private character tables (see the pcre_maketables() documentation), this is relatively straightforward. If you are using private tables, it is a little bit more complicated. However, if you are using the just-in-time optimization feature, it is not possible to save and reload the JIT data.

If you save compiled patterns to a file, you can copy them to a different host and run them there. If the two hosts have different endianness (byte order), you should run the pcre[16]_pattern_to_host_byte_order() function on the new host before trying to match the pattern. The matching functions return PCRE_ERROR_BADENDIANNESS if they detect a pattern with the wrong endianness.

Compiling regular expressions with one version of PCRE for use with a different version is not guaranteed to work and may cause crashes, and saving and restoring a compiled pattern loses any JIT optimization data.


SAVING A COMPILED PATTERN

The value returned by pcre[16]_compile() points to a single block of memory that holds the compiled pattern and associated data. You can find the length of this block in bytes by calling pcre[16]_fullinfo() with an argument of PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is sample code for the 8-bit library that compiles a pattern and writes it to a file. It assumes that the variable fd refers to a file that is open for output:

  int erroroffset, rc, size;
  char *error;
  pcre *re;

  re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
  if (re == NULL) { ... handle errors ... }
  rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
  if (rc < 0) { ... handle errors ... }
  rc = fwrite(re, 1, size, fd);
  if (rc != size) { ... handle errors ... }
In this example, the bytes that comprise the compiled pattern are copied exactly. Note that this is binary data that may contain any of the 256 possible byte values. On systems that make a distinction between binary and non-binary data, be sure that the file is opened for binary output.

If you want to write more than one pattern to a file, you will have to devise a way of separating them. For binary data, preceding each pattern with its length is probably the most straightforward approach. Another possibility is to write out the data in hexadecimal instead of binary, one pattern to a line.

Saving compiled patterns in a file is only one possible way of storing them for later use. They could equally well be saved in a database, or in the memory of some daemon process that passes them via sockets to the processes that want them.

If the pattern has been studied, it is also possible to save the normal study data in a similar way to the compiled pattern itself. However, if the PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is created cannot be saved because it is too dependent on the current environment. When studying generates additional information, pcre[16]_study() returns a pointer to a pcre[16]_extra data block. Its format is defined in the section on matching a pattern in the pcreapi documentation. The study_data field points to the binary study data, and this is what you must save (not the pcre[16]_extra block itself). The length of the study data can be obtained by calling pcre[16]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remember to check that pcre[16]_study() did return a non-NULL value before trying to save the study data.


RE-USING A PRECOMPILED PATTERN

Re-using a precompiled pattern is straightforward. Having reloaded it into main memory, called pcre[16]_pattern_to_host_byte_order() if necessary, you pass its pointer to pcre[16]_exec() or pcre[16]_dfa_exec() in the usual way.

However, if you passed a pointer to custom character tables when the pattern was compiled (the tableptr argument of pcre[16]_compile()), you must now pass a similar pointer to pcre[16]_exec() or pcre[16]_dfa_exec(), because the value saved with the compiled pattern will obviously be nonsense. A field in a pcre[16]_extra() block is used to pass this data, as described in the section on matching a pattern in the pcreapi documentation.

If you did not provide custom character tables when the pattern was compiled, the pointer in the compiled pattern is NULL, which causes the matching functions to use PCRE's internal tables. Thus, you do not need to take any special action at run time in this case.

If you saved study data with the compiled pattern, you need to create your own pcre[16]_extra data block and set the study_data field to point to the reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study data is present. Then pass the pcre[16]_extra block to the matching function in the usual way. If the pattern was studied for just-in-time optimization, that data cannot be saved, and so is lost by a save/restore cycle.


COMPATIBILITY WITH DIFFERENT PCRE RELEASES

In general, it is safest to recompile all saved patterns when you update to a new PCRE release, though not all updates actually require this.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 10 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382cf000081a40000000000000000000000014f79083e00007d04000000b500010002ffffffffffffffff0000003100000000root/usr/local/share/doc/pcre/html/pcregrep.html pcregrep specification

pcregrep man page

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SYNOPSIS

pcregrep [options] [long options] [pattern] [path1 path2 ...]


DESCRIPTION

pcregrep searches files for character patterns, in the same way as other grep commands do, but it uses the PCRE regular expression library to support patterns that are compatible with the regular expressions of Perl 5. See pcrepattern(3) for a full description of syntax and semantics of the regular expressions that PCRE supports.

Patterns, whether supplied on the command line or in a separate file, are given without delimiters. For example:

  pcregrep Thursday /etc/motd
If you attempt to use delimiters (for example, by surrounding a pattern with slashes, as is common in Perl scripts), they are interpreted as part of the pattern. Quotes can of course be used to delimit patterns on the command line because they are interpreted by the shell, and indeed they are required if a pattern contains white space or shell metacharacters.

The first argument that follows any option settings is treated as the single pattern to be matched when neither -e nor -f is present. Conversely, when one or both of these options are used to specify patterns, all arguments are treated as path names. At least one of -e, -f, or an argument pattern must be provided.

If no files are specified, pcregrep reads the standard input. The standard input can also be referenced by a name consisting of a single hyphen. For example:

  pcregrep some-pattern /file1 - /file3
By default, each line that matches a pattern is copied to the standard output, and if there is more than one file, the file name is output at the start of each line, followed by a colon. However, there are options that can change how pcregrep behaves. In particular, the -M option makes it possible to search for patterns that span line boundaries. What defines a line boundary is controlled by the -N (--newline) option.

The amount of memory used for buffering files that are being scanned is controlled by a parameter that can be set by the --buffer-size option. The default value for this parameter is specified when pcregrep is built, with the default default being 20K. A block of memory three times this size is used (to allow for buffering "before" and "after" lines). An error occurs if a line overflows the buffer.

Patterns are limited to 8K or BUFSIZ bytes, whichever is the greater. BUFSIZ is defined in <stdio.h>. When there is more than one pattern (specified by the use of -e and/or -f), each pattern is applied to each line in the order in which they are defined, except that all the -e patterns are tried before the -f patterns.

By default, as soon as one pattern matches (or fails to match when -v is used), no further patterns are considered. However, if --colour (or --color) is used to colour the matching substrings, or if --only-matching, --file-offsets, or --line-offsets is used to output only the part of the line that matched (either shown literally, or as an offset), scanning resumes immediately following the match, so that further matches on the same line can be found. If there are multiple patterns, they are all tried on the remainder of the line, but patterns that follow the one that matched are not tried on the earlier part of the line.

This is the same behaviour as GNU grep, but it does mean that the order in which multiple patterns are specified can affect the output when one of the above options is used.

Patterns that can match an empty string are accepted, but empty string matches are never recognized. An example is the pattern "(super)?(man)?", in which all components are optional. This pattern finds all occurrences of both "super" and "man"; the output differs from matching with "super|man" when only the matching substrings are being shown.

If the LC_ALL or LC_CTYPE environment variable is set, pcregrep uses the value to set a locale when calling the PCRE library. The --locale option can be used to override this.


SUPPORT FOR COMPRESSED FILES

It is possible to compile pcregrep so that it uses libz or libbz2 to read files whose names end in .gz or .bz2, respectively. You can find out whether your binary has support for one or both of these file types by running it with the --help option. If the appropriate support is not present, files are treated as plain text. The standard input is always so treated.


OPTIONS

The order in which some of the options appear can affect the output. For example, both the -h and -l options affect the printing of file names. Whichever comes later in the command line will be the one that takes effect. Numerical values for options may be followed by K or M, to signify multiplication by 1024 or 1024*1024 respectively.

-- This terminates the list of options. It is useful if the next item on the command line starts with a hyphen but is not an option. This allows for the processing of patterns and filenames that start with hyphens.

-A number, --after-context=number Output number lines of context after each matching line. If filenames and/or line numbers are being output, a hyphen separator is used instead of a colon for the context lines. A line containing "--" is output between each group of lines, unless they are in fact contiguous in the input file. The value of number is expected to be relatively small. However, pcregrep guarantees to have up to 8K of following text available for context output.

-B number, --before-context=number Output number lines of context before each matching line. If filenames and/or line numbers are being output, a hyphen separator is used instead of a colon for the context lines. A line containing "--" is output between each group of lines, unless they are in fact contiguous in the input file. The value of number is expected to be relatively small. However, pcregrep guarantees to have up to 8K of preceding text available for context output.

--buffer-size=number Set the parameter that controls how much memory is used for buffering files that are being scanned.

-C number, --context=number Output number lines of context both before and after each matching line. This is equivalent to setting both -A and -B to the same value.

-c, --count Do not output individual lines from the files that are being scanned; instead output the number of lines that would otherwise have been shown. If no lines are selected, the number zero is output. If several files are are being scanned, a count is output for each of them. However, if the --files-with-matches option is also used, only those files whose counts are greater than zero are listed. When -c is used, the -A, -B, and -C options are ignored.

--colour, --color If this option is given without any data, it is equivalent to "--colour=auto". If data is required, it must be given in the same shell item, separated by an equals sign.

--colour=value, --color=value This option specifies under what circumstances the parts of a line that matched a pattern should be coloured in the output. By default, the output is not coloured. The value (which is optional, see above) may be "never", "always", or "auto". In the latter case, colouring happens only if the standard output is connected to a terminal. More resources are used when colouring is enabled, because pcregrep has to search for all possible matches in a line, not just one, in order to colour them all.

The colour that is used can be specified by setting the environment variable PCREGREP_COLOUR or PCREGREP_COLOR. The value of this variable should be a string of two numbers, separated by a semicolon. They are copied directly into the control string for setting colour on a terminal, so it is your responsibility to ensure that they make sense. If neither of the environment variables is set, the default is "1;31", which gives red.

-D action, --devices=action If an input path is not a regular file or a directory, "action" specifies how it is to be processed. Valid values are "read" (the default) or "skip" (silently skip the path).

-d action, --directories=action If an input path is a directory, "action" specifies how it is to be processed. Valid values are "read" (the default), "recurse" (equivalent to the -r option), or "skip" (silently skip the path). In the default case, directories are read as if they were ordinary files. In some operating systems the effect of reading a directory like this is an immediate end-of-file.

-e pattern, --regex=pattern, --regexp=pattern Specify a pattern to be matched. This option can be used multiple times in order to specify several patterns. It can also be used as a way of specifying a single pattern that starts with a hyphen. When -e is used, no argument pattern is taken from the command line; all arguments are treated as file names. There is an overall maximum of 100 patterns. They are applied to each line in the order in which they are defined until one matches (or fails to match if -v is used). If -f is used with -e, the command line patterns are matched first, followed by the patterns from the file, independent of the order in which these options are specified. Note that multiple use of -e is not the same as a single pattern with alternatives. For example, X|Y finds the first character in a line that is X or Y, whereas if the two patterns are given separately, pcregrep finds X if it is present, even if it follows Y in the line. It finds Y only if there is no X in the line. This really matters only if you are using -o to show the part(s) of the line that matched.

--exclude=pattern When pcregrep is searching the files in a directory as a consequence of the -r (recursive search) option, any regular files whose names match the pattern are excluded. Subdirectories are not excluded by this option; they are searched recursively, subject to the --exclude-dir and --include_dir options. The pattern is a PCRE regular expression, and is matched against the final component of the file name (not the entire path). If a file name matches both --include and --exclude, it is excluded. There is no short form for this option.

--exclude-dir=pattern When pcregrep is searching the contents of a directory as a consequence of the -r (recursive search) option, any subdirectories whose names match the pattern are excluded. (Note that the \fP--exclude\fP option does not affect subdirectories.) The pattern is a PCRE regular expression, and is matched against the final component of the name (not the entire path). If a subdirectory name matches both --include-dir and --exclude-dir, it is excluded. There is no short form for this option.

-F, --fixed-strings Interpret each pattern as a list of fixed strings, separated by newlines, instead of as a regular expression. The -w (match as a word) and -x (match whole line) options can be used with -F. They apply to each of the fixed strings. A line is selected if any of the fixed strings are found in it (subject to -w or -x, if present).

-f filename, --file=filename Read a number of patterns from the file, one per line, and match them against each line of input. A data line is output if any of the patterns match it. The filename can be given as "-" to refer to the standard input. When -f is used, patterns specified on the command line using -e may also be present; they are tested before the file's patterns. However, no other pattern is taken from the command line; all arguments are treated as file names. There is an overall maximum of 100 patterns. Trailing white space is removed from each line, and blank lines are ignored. An empty file contains no patterns and therefore matches nothing. See also the comments about multiple patterns versus a single pattern with alternatives in the description of -e above.

--file-offsets Instead of showing lines or parts of lines that match, show each match as an offset from the start of the file and a length, separated by a comma. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown separately. This option is mutually exclusive with --line-offsets and --only-matching.

-H, --with-filename Force the inclusion of the filename at the start of output lines when searching a single file. By default, the filename is not shown in this case. For matching lines, the filename is followed by a colon; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name.

-h, --no-filename Suppress the output filenames when searching multiple files. By default, filenames are shown when multiple files are searched. For matching lines, the filename is followed by a colon; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name.

--help Output a help message, giving brief details of the command options and file type support, and then exit.

-i, --ignore-case Ignore upper/lower case distinctions during comparisons.

--include=pattern When pcregrep is searching the files in a directory as a consequence of the -r (recursive search) option, only those regular files whose names match the pattern are included. Subdirectories are always included and searched recursively, subject to the \fP--include-dir\fP and --exclude-dir options. The pattern is a PCRE regular expression, and is matched against the final component of the file name (not the entire path). If a file name matches both --include and --exclude, it is excluded. There is no short form for this option.

--include-dir=pattern When pcregrep is searching the contents of a directory as a consequence of the -r (recursive search) option, only those subdirectories whose names match the pattern are included. (Note that the --include option does not affect subdirectories.) The pattern is a PCRE regular expression, and is matched against the final component of the name (not the entire path). If a subdirectory name matches both --include-dir and --exclude-dir, it is excluded. There is no short form for this option.

-L, --files-without-match Instead of outputting lines from the files, just output the names of the files that do not contain any lines that would have been output. Each file name is output once, on a separate line.

-l, --files-with-matches Instead of outputting lines from the files, just output the names of the files containing lines that would have been output. Each file name is output once, on a separate line. Searching normally stops as soon as a matching line is found in a file. However, if the -c (count) option is also used, matching continues in order to obtain the correct count, and those files that have at least one match are listed along with their counts. Using this option with -c is a way of suppressing the listing of files with no matches.

--label=name This option supplies a name to be used for the standard input when file names are being output. If not supplied, "(standard input)" is used. There is no short form for this option.

--line-buffered When this option is given, input is read and processed line by line, and the output is flushed after each write. By default, input is read in large chunks, unless pcregrep can determine that it is reading from a terminal (which is currently possible only in Unix environments). Output to terminal is normally automatically flushed by the operating system. This option can be useful when the input or output is attached to a pipe and you do not want pcregrep to buffer up large amounts of data. However, its use will affect performance, and the -M (multiline) option ceases to work.

--line-offsets Instead of showing lines or parts of lines that match, show each match as a line number, the offset from the start of the line, and a length. The line number is terminated by a colon (as usual; see the -n option), and the offset and length are separated by a comma. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown separately. This option is mutually exclusive with --file-offsets and --only-matching.

--locale=locale-name This option specifies a locale to be used for pattern matching. It overrides the value in the LC_ALL or LC_CTYPE environment variables. If no locale is specified, the PCRE library's default (usually the "C" locale) is used. There is no short form for this option.

--match-limit=number Processing some regular expression patterns can require a very large amount of memory, leading in some cases to a program crash if not enough is available. Other patterns may take a very long time to search for all possible matching strings. The pcre_exec() function that is called by pcregrep to do the matching has two parameters that can limit the resources that it uses.

The --match-limit option provides a means of limiting resource usage when processing patterns that are not going to match, but which have a very large number of possibilities in their search trees. The classic example is a pattern that uses nested unlimited repeats. Internally, PCRE uses a function called match() which it calls repeatedly (sometimes recursively). The limit set by --match-limit is imposed on the number of times this function is called during a match, which has the effect of limiting the amount of backtracking that can take place.

The --recursion-limit option is similar to --match-limit, but instead of limiting the total number of times that match() is called, it limits the depth of recursive calls, which in turn limits the amount of memory that can be used. The recursion depth is a smaller number than the total number of calls, because not all calls to match() are recursive. This limit is of use only if it is set smaller than --match-limit.

There are no short forms for these options. The default settings are specified when the PCRE library is compiled, with the default default being 10 million.

-M, --multiline Allow patterns to match more than one line. When this option is given, patterns may usefully contain literal newline characters and internal occurrences of ^ and $ characters. The output for a successful match may consist of more than one line, the last of which is the one in which the match ended. If the matched string ends with a newline sequence the output ends at the end of that line.

When this option is set, the PCRE library is called in "multiline" mode. There is a limit to the number of lines that can be matched, imposed by the way that pcregrep buffers the input file as it scans it. However, pcregrep ensures that at least 8K characters or the rest of the document (whichever is the shorter) are available for forward matching, and similarly the previous 8K characters (or all the previous characters, if fewer than 8K) are guaranteed to be available for lookbehind assertions. This option does not work when input is read line by line (see \fP--line-buffered\fP.)

-N newline-type, --newline=newline-type The PCRE library supports five different conventions for indicating the ends of lines. They are the single-character sequences CR (carriage return) and LF (linefeed), the two-character sequence CRLF, an "anycrlf" convention, which recognizes any of the preceding three types, and an "any" convention, in which any Unicode line ending sequence is assumed to end a line. The Unicode sequences are the three just mentioned, plus VT (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029).

When the PCRE library is built, a default line-ending sequence is specified. This is normally the standard sequence for the operating system. Unless otherwise specified by this option, pcregrep uses the library's default. The possible values for this option are CR, LF, CRLF, ANYCRLF, or ANY. This makes it possible to use pcregrep on files that have come from other environments without having to modify their line endings. If the data that is being scanned does not agree with the convention set by this option, pcregrep may behave in strange ways.

-n, --line-number Precede each output line by its line number in the file, followed by a colon for matching lines or a hyphen for context lines. If the filename is also being output, it precedes the line number. This option is forced if --line-offsets is used.

--no-jit If the PCRE library is built with support for just-in-time compiling (which speeds up matching), pcregrep automatically makes use of this, unless it was explicitly disabled at build time. This option can be used to disable the use of JIT at run time. It is provided for testing and working round problems. It should never be needed in normal use.

-o, --only-matching Show only the part of the line that matched a pattern instead of the whole line. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown separately. If -o is combined with -v (invert the sense of the match to find non-matching lines), no output is generated, but the return code is set appropriately. If the matched portion of the line is empty, nothing is output unless the file name or line number are being printed, in which case they are shown on an otherwise empty line. This option is mutually exclusive with --file-offsets and --line-offsets.

-onumber, --only-matching=number Show only the part of the line that matched the capturing parentheses of the given number. Up to 32 capturing parentheses are supported. Because these options can be given without an argument (see above), if an argument is present, it must be given in the same shell item, for example, -o3 or --only-matching=2. The comments given for the non-argument case above also apply to this case. If the specified capturing parentheses do not exist in the pattern, or were not set in the match, nothing is output unless the file name or line number are being printed.

-q, --quiet Work quietly, that is, display nothing except error messages. The exit status indicates whether or not any matches were found.

-r, --recursive If any given path is a directory, recursively scan the files it contains, taking note of any --include and --exclude settings. By default, a directory is read as a normal file; in some operating systems this gives an immediate end-of-file. This option is a shorthand for setting the -d option to "recurse".

--recursion-limit=number See --match-limit above.

-s, --no-messages Suppress error messages about non-existent or unreadable files. Such files are quietly skipped. However, the return code is still 2, even if matches were found in other files.

-u, --utf-8 Operate in UTF-8 mode. This option is available only if PCRE has been compiled with UTF-8 support. Both patterns and subject lines must be valid strings of UTF-8 characters.

-V, --version Write the version numbers of pcregrep and the PCRE library that is being used to the standard error stream.

-v, --invert-match Invert the sense of the match, so that lines which do not match any of the patterns are the ones that are found.

-w, --word-regex, --word-regexp Force the patterns to match only whole words. This is equivalent to having \b at the start and end of the pattern.

-x, --line-regex, --line-regexp Force the patterns to be anchored (each must start matching at the beginning of a line) and in addition, require them to match entire lines. This is equivalent to having ^ and $ characters at the start and end of each alternative branch in every pattern.


ENVIRONMENT VARIABLES

The environment variables LC_ALL and LC_CTYPE are examined, in that order, for a locale. The first one that is set is used. This can be overridden by the --locale option. If no locale is set, the PCRE library's default (usually the "C" locale) is used.


NEWLINES

The -N (--newline) option allows pcregrep to scan files with different newline conventions from the default. However, the setting of this option does not affect the way in which pcregrep writes information to the standard error and output streams. It uses the string "\n" in C printf() calls to indicate newlines, relying on the C I/O library to convert this to an appropriate sequence if the output is sent to a file.


OPTIONS COMPATIBILITY

Many of the short and long forms of pcregrep's options are the same as in the GNU grep program (version 2.5.4). Any long option of the form --xxx-regexp (GNU terminology) is also available as --xxx-regex (PCRE terminology). However, the --file-offsets, --include-dir, --line-offsets, --locale, --match-limit, -M, --multiline, -N, --newline, --recursion-limit, -u, and --utf-8 options are specific to pcregrep, as is the use of the --only-matching option with a capturing parentheses number.

Although most of the common options work the same way, a few are different in pcregrep. For example, the --include option's argument is a glob for GNU grep, but a regular expression for pcregrep. If both the -c and -l options are given, GNU grep lists only file names, without counts, but pcregrep gives the counts.


OPTIONS WITH DATA

There are four different ways in which an option with data can be specified. If a short form option is used, the data may follow immediately, or (with one exception) in the next command line item. For example:

  -f/some/file
  -f /some/file
The exception is the -o option, which may appear with or without data. Because of this, if data is present, it must follow immediately in the same item, for example -o3.

If a long form option is used, the data may appear in the same command line item, separated by an equals character, or (with two exceptions) it may appear in the next command line item. For example:

  --file=/some/file
  --file /some/file
Note, however, that if you want to supply a file name beginning with ~ as data in a shell command, and have the shell expand ~ to a home directory, you must separate the file name from the option, because the shell does not treat ~ specially unless it is at the start of an item.

The exceptions to the above are the --colour (or --color) and --only-matching options, for which the data is optional. If one of these options does have data, it must be given in the first form, using an equals character. Otherwise pcregrep will assume that it has no data.


MATCHING ERRORS

It is possible to supply a regular expression that takes a very long time to fail to match certain lines. Such patterns normally involve nested indefinite repeats, for example: (a+)*\d when matched against a line of a's with no final digit. The PCRE matching function has a resource limit that causes it to abort in these circumstances. If this happens, pcregrep outputs an error message and the line that caused the problem to the standard error stream. If there are more than 20 such errors, pcregrep gives up.

The --match-limit option of pcregrep can be used to set the overall resource limit; there is a second option called --recursion-limit that sets a limit on the amount of memory (usually stack) that is used (see the discussion of these options above).


DIAGNOSTICS

Exit status is 0 if any matches were found, 1 if no matches were found, and 2 for syntax errors, overlong lines, non-existent or inaccessible files (even if matches were found in other files) or too many matching errors. Using the -s option to suppress error messages about inaccessible files does not affect the return code.


SEE ALSO

pcrepattern(3), pcretest(1).


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 06 September 2011
Copyright © 1997-2011 University of Cambridge.

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070701000382d2000081a40000000000000000000000014f79083e0000284f000000b500010002ffffffffffffffff0000003500000000root/usr/local/share/doc/pcre/html/pcrematching.html pcrematching specification

pcrematching man page

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PCRE MATCHING ALGORITHMS

This document describes the two different algorithms that are available in PCRE for matching a compiled regular expression against a given subject string. The "standard" algorithm is the one provided by the pcre_exec() and pcre16_exec() functions. These work in the same was as Perl's matching function, and provide a Perl-compatible matching operation. The just-in-time (JIT) optimization that is described in the pcrejit documentation is compatible with these functions.

An alternative algorithm is provided by the pcre_dfa_exec() and pcre16_dfa_exec() functions; they operate in a different way, and are not Perl-compatible. This alternative has advantages and disadvantages compared with the standard algorithm, and these are described below.

When there is only one possible way in which a given subject string can match a pattern, the two algorithms give the same answer. A difference arises, however, when there are multiple possibilities. For example, if the pattern

  ^<.*>
is matched against the string
  <something> <something else> <something further>
there are three possible answers. The standard algorithm finds only one of them, whereas the alternative algorithm finds all three.


REGULAR EXPRESSIONS AS TREES

The set of strings that are matched by a regular expression can be represented as a tree structure. An unlimited repetition in the pattern makes the tree of infinite size, but it is still a tree. Matching the pattern to a given subject string (from a given starting point) can be thought of as a search of the tree. There are two ways to search a tree: depth-first and breadth-first, and these correspond to the two matching algorithms provided by PCRE.


THE STANDARD MATCHING ALGORITHM

In the terminology of Jeffrey Friedl's book "Mastering Regular Expressions", the standard algorithm is an "NFA algorithm". It conducts a depth-first search of the pattern tree. That is, it proceeds along a single path through the tree, checking that the subject matches what is required. When there is a mismatch, the algorithm tries any alternatives at the current point, and if they all fail, it backs up to the previous branch point in the tree, and tries the next alternative branch at that level. This often involves backing up (moving to the left) in the subject string as well. The order in which repetition branches are tried is controlled by the greedy or ungreedy nature of the quantifier.

If a leaf node is reached, a matching string has been found, and at that point the algorithm stops. Thus, if there is more than one possible match, this algorithm returns the first one that it finds. Whether this is the shortest, the longest, or some intermediate length depends on the way the greedy and ungreedy repetition quantifiers are specified in the pattern.

Because it ends up with a single path through the tree, it is relatively straightforward for this algorithm to keep track of the substrings that are matched by portions of the pattern in parentheses. This provides support for capturing parentheses and back references.


THE ALTERNATIVE MATCHING ALGORITHM

This algorithm conducts a breadth-first search of the tree. Starting from the first matching point in the subject, it scans the subject string from left to right, once, character by character, and as it does this, it remembers all the paths through the tree that represent valid matches. In Friedl's terminology, this is a kind of "DFA algorithm", though it is not implemented as a traditional finite state machine (it keeps multiple states active simultaneously).

Although the general principle of this matching algorithm is that it scans the subject string only once, without backtracking, there is one exception: when a lookaround assertion is encountered, the characters following or preceding the current point have to be independently inspected.

The scan continues until either the end of the subject is reached, or there are no more unterminated paths. At this point, terminated paths represent the different matching possibilities (if there are none, the match has failed). Thus, if there is more than one possible match, this algorithm finds all of them, and in particular, it finds the longest. The matches are returned in decreasing order of length. There is an option to stop the algorithm after the first match (which is necessarily the shortest) is found.

Note that all the matches that are found start at the same point in the subject. If the pattern

  cat(er(pillar)?)?
is matched against the string "the caterpillar catchment", the result will be the three strings "caterpillar", "cater", and "cat" that start at the fifth character of the subject. The algorithm does not automatically move on to find matches that start at later positions.

There are a number of features of PCRE regular expressions that are not supported by the alternative matching algorithm. They are as follows:

1. Because the algorithm finds all possible matches, the greedy or ungreedy nature of repetition quantifiers is not relevant. Greedy and ungreedy quantifiers are treated in exactly the same way. However, possessive quantifiers can make a difference when what follows could also match what is quantified, for example in a pattern like this:

  ^a++\w!
This pattern matches "aaab!" but not "aaa!", which would be matched by a non-possessive quantifier. Similarly, if an atomic group is present, it is matched as if it were a standalone pattern at the current point, and the longest match is then "locked in" for the rest of the overall pattern.

2. When dealing with multiple paths through the tree simultaneously, it is not straightforward to keep track of captured substrings for the different matching possibilities, and PCRE's implementation of this algorithm does not attempt to do this. This means that no captured substrings are available.

3. Because no substrings are captured, back references within the pattern are not supported, and cause errors if encountered.

4. For the same reason, conditional expressions that use a backreference as the condition or test for a specific group recursion are not supported.

5. Because many paths through the tree may be active, the \K escape sequence, which resets the start of the match when encountered (but may be on some paths and not on others), is not supported. It causes an error if encountered.

6. Callouts are supported, but the value of the capture_top field is always 1, and the value of the capture_last field is always -1.

7. The \C escape sequence, which (in the standard algorithm) always matches a single data unit, even in UTF-8 or UTF-16 modes, is not supported in these modes, because the alternative algorithm moves through the subject string one character (not data unit) at a time, for all active paths through the tree.

8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) are not supported. (*FAIL) is supported, and behaves like a failing negative assertion.


ADVANTAGES OF THE ALTERNATIVE ALGORITHM

Using the alternative matching algorithm provides the following advantages:

1. All possible matches (at a single point in the subject) are automatically found, and in particular, the longest match is found. To find more than one match using the standard algorithm, you have to do kludgy things with callouts.

2. Because the alternative algorithm scans the subject string just once, and never needs to backtrack (except for lookbehinds), it is possible to pass very long subject strings to the matching function in several pieces, checking for partial matching each time. Although it is possible to do multi-segment matching using the standard algorithm by retaining partially matched substrings, it is more complicated. The pcrepartial documentation gives details of partial matching and discusses multi-segment matching.


DISADVANTAGES OF THE ALTERNATIVE ALGORITHM

The alternative algorithm suffers from a number of disadvantages:

1. It is substantially slower than the standard algorithm. This is partly because it has to search for all possible matches, but is also because it is less susceptible to optimization.

2. Capturing parentheses and back references are not supported.

3. Although atomic groups are supported, their use does not provide the performance advantage that it does for the standard algorithm.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 08 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382b6000081a40000000000000000000000014f79083e000004b6000000b500010002ffffffffffffffff0000004100000000root/usr/local/share/doc/pcre/html/pcre_free_substring_list.html pcre_free_substring_list specification

pcre_free_substring_list man page

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SYNOPSIS

#include <pcre.h>

void pcre_free_substring_list(const char **stringptr);

void pcre16_free_substring_list(PCRE_SPTR16 *stringptr);


DESCRIPTION

This is a convenience function for freeing the store obtained by a previous call to pcre[16]_get_substring_list(). Its only argument is a pointer to the list of string pointers.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382da000081a40000000000000000000000014f79083e00003b15000000b500010002ffffffffffffffff0000003300000000root/usr/local/share/doc/pcre/html/pcresyntax.html pcresyntax specification

pcresyntax man page

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PCRE REGULAR EXPRESSION SYNTAX SUMMARY

The full syntax and semantics of the regular expressions that are supported by PCRE are described in the pcrepattern documentation. This document contains a quick-reference summary of the syntax.


QUOTING

  \x         where x is non-alphanumeric is a literal x
  \Q...\E    treat enclosed characters as literal


CHARACTERS

  \a         alarm, that is, the BEL character (hex 07)
  \cx        "control-x", where x is any ASCII character
  \e         escape (hex 1B)
  \f         formfeed (hex 0C)
  \n         newline (hex 0A)
  \r         carriage return (hex 0D)
  \t         tab (hex 09)
  \ddd       character with octal code ddd, or backreference
  \xhh       character with hex code hh
  \x{hhh..}  character with hex code hhh..


CHARACTER TYPES

  .          any character except newline;
               in dotall mode, any character whatsoever
  \C         one data unit, even in UTF mode (best avoided)
  \d         a decimal digit
  \D         a character that is not a decimal digit
  \h         a horizontal whitespace character
  \H         a character that is not a horizontal whitespace character
  \N         a character that is not a newline
  \p{xx}     a character with the xx property
  \P{xx}     a character without the xx property
  \R         a newline sequence
  \s         a whitespace character
  \S         a character that is not a whitespace character
  \v         a vertical whitespace character
  \V         a character that is not a vertical whitespace character
  \w         a "word" character
  \W         a "non-word" character
  \X         an extended Unicode sequence
In PCRE, by default, \d, \D, \s, \S, \w, and \W recognize only ASCII characters, even in a UTF mode. However, this can be changed by setting the PCRE_UCP option.


GENERAL CATEGORY PROPERTIES FOR \p and \P

  C          Other
  Cc         Control
  Cf         Format
  Cn         Unassigned
  Co         Private use
  Cs         Surrogate

  L          Letter
  Ll         Lower case letter
  Lm         Modifier letter
  Lo         Other letter
  Lt         Title case letter
  Lu         Upper case letter
  L&         Ll, Lu, or Lt

  M          Mark
  Mc         Spacing mark
  Me         Enclosing mark
  Mn         Non-spacing mark

  N          Number
  Nd         Decimal number
  Nl         Letter number
  No         Other number

  P          Punctuation
  Pc         Connector punctuation
  Pd         Dash punctuation
  Pe         Close punctuation
  Pf         Final punctuation
  Pi         Initial punctuation
  Po         Other punctuation
  Ps         Open punctuation

  S          Symbol
  Sc         Currency symbol
  Sk         Modifier symbol
  Sm         Mathematical symbol
  So         Other symbol

  Z          Separator
  Zl         Line separator
  Zp         Paragraph separator
  Zs         Space separator


PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P

  Xan        Alphanumeric: union of properties L and N
  Xps        POSIX space: property Z or tab, NL, VT, FF, CR
  Xsp        Perl space: property Z or tab, NL, FF, CR
  Xwd        Perl word: property Xan or underscore


SCRIPT NAMES FOR \p AND \P

Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, Yi.


CHARACTER CLASSES

  [...]       positive character class
  [^...]      negative character class
  [x-y]       range (can be used for hex characters)
  [[:xxx:]]   positive POSIX named set
  [[:^xxx:]]  negative POSIX named set

  alnum       alphanumeric
  alpha       alphabetic
  ascii       0-127
  blank       space or tab
  cntrl       control character
  digit       decimal digit
  graph       printing, excluding space
  lower       lower case letter
  print       printing, including space
  punct       printing, excluding alphanumeric
  space       whitespace
  upper       upper case letter
  word        same as \w
  xdigit      hexadecimal digit
In PCRE, POSIX character set names recognize only ASCII characters by default, but some of them use Unicode properties if PCRE_UCP is set. You can use \Q...\E inside a character class.


QUANTIFIERS

  ?           0 or 1, greedy
  ?+          0 or 1, possessive
  ??          0 or 1, lazy
  *           0 or more, greedy
  *+          0 or more, possessive
  *?          0 or more, lazy
  +           1 or more, greedy
  ++          1 or more, possessive
  +?          1 or more, lazy
  {n}         exactly n
  {n,m}       at least n, no more than m, greedy
  {n,m}+      at least n, no more than m, possessive
  {n,m}?      at least n, no more than m, lazy
  {n,}        n or more, greedy
  {n,}+       n or more, possessive
  {n,}?       n or more, lazy


ANCHORS AND SIMPLE ASSERTIONS

  \b          word boundary
  \B          not a word boundary
  ^           start of subject
               also after internal newline in multiline mode
  \A          start of subject
  $           end of subject
               also before newline at end of subject
               also before internal newline in multiline mode
  \Z          end of subject
               also before newline at end of subject
  \z          end of subject
  \G          first matching position in subject


MATCH POINT RESET

  \K          reset start of match


ALTERNATION

  expr|expr|expr...


CAPTURING

  (...)           capturing group
  (?<name>...)    named capturing group (Perl)
  (?'name'...)    named capturing group (Perl)
  (?P<name>...)   named capturing group (Python)
  (?:...)         non-capturing group
  (?|...)         non-capturing group; reset group numbers for
                   capturing groups in each alternative


ATOMIC GROUPS

  (?>...)         atomic, non-capturing group


COMMENT

  (?#....)        comment (not nestable)


OPTION SETTING

  (?i)            caseless
  (?J)            allow duplicate names
  (?m)            multiline
  (?s)            single line (dotall)
  (?U)            default ungreedy (lazy)
  (?x)            extended (ignore white space)
  (?-...)         unset option(s)
The following are recognized only at the start of a pattern or after one of the newline-setting options with similar syntax:
  (*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE)
  (*UTF8)         set UTF-8 mode: 8-bit library (PCRE_UTF8)
  (*UTF16)        set UTF-16 mode: 16-bit library (PCRE_UTF16)
  (*UCP)          set PCRE_UCP (use Unicode properties for \d etc)


LOOKAHEAD AND LOOKBEHIND ASSERTIONS

  (?=...)         positive look ahead
  (?!...)         negative look ahead
  (?<=...)        positive look behind
  (?<!...)        negative look behind
Each top-level branch of a look behind must be of a fixed length.


BACKREFERENCES

  \n              reference by number (can be ambiguous)
  \gn             reference by number
  \g{n}           reference by number
  \g{-n}          relative reference by number
  \k<name>        reference by name (Perl)
  \k'name'        reference by name (Perl)
  \g{name}        reference by name (Perl)
  \k{name}        reference by name (.NET)
  (?P=name)       reference by name (Python)


SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)

  (?R)            recurse whole pattern
  (?n)            call subpattern by absolute number
  (?+n)           call subpattern by relative number
  (?-n)           call subpattern by relative number
  (?&name)        call subpattern by name (Perl)
  (?P>name)       call subpattern by name (Python)
  \g<name>        call subpattern by name (Oniguruma)
  \g'name'        call subpattern by name (Oniguruma)
  \g<n>           call subpattern by absolute number (Oniguruma)
  \g'n'           call subpattern by absolute number (Oniguruma)
  \g<+n>          call subpattern by relative number (PCRE extension)
  \g'+n'          call subpattern by relative number (PCRE extension)
  \g<-n>          call subpattern by relative number (PCRE extension)
  \g'-n'          call subpattern by relative number (PCRE extension)


CONDITIONAL PATTERNS

  (?(condition)yes-pattern)
  (?(condition)yes-pattern|no-pattern)

  (?(n)...        absolute reference condition
  (?(+n)...       relative reference condition
  (?(-n)...       relative reference condition
  (?(<name>)...   named reference condition (Perl)
  (?('name')...   named reference condition (Perl)
  (?(name)...     named reference condition (PCRE)
  (?(R)...        overall recursion condition
  (?(Rn)...       specific group recursion condition
  (?(R&name)...   specific recursion condition
  (?(DEFINE)...   define subpattern for reference
  (?(assert)...   assertion condition


BACKTRACKING CONTROL

The following act immediately they are reached:

  (*ACCEPT)       force successful match
  (*FAIL)         force backtrack; synonym (*F)
  (*MARK:NAME)    set name to be passed back; synonym (*:NAME)
The following act only when a subsequent match failure causes a backtrack to reach them. They all force a match failure, but they differ in what happens afterwards. Those that advance the start-of-match point do so only if the pattern is not anchored.
  (*COMMIT)       overall failure, no advance of starting point
  (*PRUNE)        advance to next starting character
  (*PRUNE:NAME)   equivalent to (*MARK:NAME)(*PRUNE)
  (*SKIP)         advance to current matching position
  (*SKIP:NAME)    advance to position corresponding to an earlier
                  (*MARK:NAME); if not found, the (*SKIP) is ignored
  (*THEN)         local failure, backtrack to next alternation
  (*THEN:NAME)    equivalent to (*MARK:NAME)(*THEN)


NEWLINE CONVENTIONS

These are recognized only at the very start of the pattern or after a (*BSR_...), (*UTF8), (*UTF16) or (*UCP) option.

  (*CR)           carriage return only
  (*LF)           linefeed only
  (*CRLF)         carriage return followed by linefeed
  (*ANYCRLF)      all three of the above
  (*ANY)          any Unicode newline sequence


WHAT \R MATCHES

These are recognized only at the very start of the pattern or after a (*...) option that sets the newline convention or a UTF or UCP mode.

  (*BSR_ANYCRLF)  CR, LF, or CRLF
  (*BSR_UNICODE)  any Unicode newline sequence


CALLOUTS

  (?C)      callout
  (?Cn)     callout with data n


SEE ALSO

pcrepattern(3), pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 10 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382c4000081a40000000000000000000000014f79083e00000555000000b500010002ffffffffffffffff0000003600000000root/usr/local/share/doc/pcre/html/pcre_refcount.html pcre_refcount specification

pcre_refcount man page

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SYNOPSIS

#include <pcre.h>

int pcre_refcount(pcre *code, int adjust);

int pcre16_refcount(pcre16 *code, int adjust);


DESCRIPTION

This function is used to maintain a reference count inside a data block that contains a compiled pattern. Its arguments are:

  code                      Compiled regular expression
  adjust                    Adjustment to reference value
The yield of the function is the adjusted reference value, which is constrained to lie between 0 and 65535.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382d1000081a40000000000000000000000014f79083e00000a62000000b500010002ffffffffffffffff0000003300000000root/usr/local/share/doc/pcre/html/pcrelimits.html pcrelimits specification

pcrelimits man page

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SIZE AND OTHER LIMITATIONS

There are some size limitations in PCRE but it is hoped that they will never in practice be relevant.

The maximum length of a compiled pattern is approximately 64K data units (bytes for the 8-bit library, 16-bit units for the 16-bit library) if PCRE is compiled with the default internal linkage size of 2 bytes. If you want to process regular expressions that are truly enormous, you can compile PCRE with an internal linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded up to 4). See the README file in the source distribution and the pcrebuild documentation for details. In these cases the limit is substantially larger. However, the speed of execution is slower.

All values in repeating quantifiers must be less than 65536.

There is no limit to the number of parenthesized subpatterns, but there can be no more than 65535 capturing subpatterns.

There is a limit to the number of forward references to subsequent subpatterns of around 200,000. Repeated forward references with fixed upper limits, for example, (?2){0,100} when subpattern number 2 is to the right, are included in the count. There is no limit to the number of backward references.

The maximum length of name for a named subpattern is 32 characters, and the maximum number of named subpatterns is 10000.

The maximum length of a subject string is the largest positive number that an integer variable can hold. However, when using the traditional matching function, PCRE uses recursion to handle subpatterns and indefinite repetition. This means that the available stack space may limit the size of a subject string that can be processed by certain patterns. For a discussion of stack issues, see the pcrestack documentation.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 08 January 2012
Copyright © 1997-2012 University of Cambridge.

Return to the PCRE index page.

070701000382d3000081a40000000000000000000000014f79083e00004fb1000000b500010002ffffffffffffffff0000003400000000root/usr/local/share/doc/pcre/html/pcrepartial.html pcrepartial specification

pcrepartial man page

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PARTIAL MATCHING IN PCRE

In normal use of PCRE, if the subject string that is passed to a matching function matches as far as it goes, but is too short to match the entire pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances where it might be helpful to distinguish this case from other cases in which there is no match.

Consider, for example, an application where a human is required to type in data for a field with specific formatting requirements. An example might be a date in the form ddmmmyy, defined by this pattern:

  ^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$
If the application sees the user's keystrokes one by one, and can check that what has been typed so far is potentially valid, it is able to raise an error as soon as a mistake is made, by beeping and not reflecting the character that has been typed, for example. This immediate feedback is likely to be a better user interface than a check that is delayed until the entire string has been entered. Partial matching can also be useful when the subject string is very long and is not all available at once.

PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and PCRE_PARTIAL_HARD options, which can be set when calling any of the matching functions. For backwards compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. The essential difference between the two options is whether or not a partial match is preferred to an alternative complete match, though the details differ between the two types of matching function. If both options are set, PCRE_PARTIAL_HARD takes precedence.

Setting a partial matching option disables the use of any just-in-time code that was set up by studying the compiled pattern with the PCRE_STUDY_JIT_COMPILE option. It also disables two of PCRE's standard optimizations. PCRE remembers the last literal data unit in a pattern, and abandons matching immediately if it is not present in the subject string. This optimization cannot be used for a subject string that might match only partially. If the pattern was studied, PCRE knows the minimum length of a matching string, and does not bother to run the matching function on shorter strings. This optimization is also disabled for partial matching.


PARTIAL MATCHING USING pcre_exec() OR pcre16_exec()

A partial match occurs during a call to pcre_exec() or pcre16_exec() when the end of the subject string is reached successfully, but matching cannot continue because more characters are needed. However, at least one character in the subject must have been inspected. This character need not form part of the final matched string; lookbehind assertions and the \K escape sequence provide ways of inspecting characters before the start of a matched substring. The requirement for inspecting at least one character exists because an empty string can always be matched; without such a restriction there would always be a partial match of an empty string at the end of the subject.

If there are at least two slots in the offsets vector when a partial match is returned, the first slot is set to the offset of the earliest character that was inspected. For convenience, the second offset points to the end of the subject so that a substring can easily be identified.

For the majority of patterns, the first offset identifies the start of the partially matched string. However, for patterns that contain lookbehind assertions, or \K, or begin with \b or \B, earlier characters have been inspected while carrying out the match. For example:

  /(?<=abc)123/
This pattern matches "123", but only if it is preceded by "abc". If the subject string is "xyzabc12", the offsets after a partial match are for the substring "abc12", because all these characters are needed if another match is tried with extra characters added to the subject.

What happens when a partial match is identified depends on which of the two partial matching options are set.


PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre16_exec()

If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre16_exec() identifies a partial match, the partial match is remembered, but matching continues as normal, and other alternatives in the pattern are tried. If no complete match can be found, PCRE_ERROR_PARTIAL is returned instead of PCRE_ERROR_NOMATCH.

This option is "soft" because it prefers a complete match over a partial match. All the various matching items in a pattern behave as if the subject string is potentially complete. For example, \z, \Z, and $ match at the end of the subject, as normal, and for \b and \B the end of the subject is treated as a non-alphanumeric.

If there is more than one partial match, the first one that was found provides the data that is returned. Consider this pattern:

  /123\w+X|dogY/
If this is matched against the subject string "abc123dog", both alternatives fail to match, but the end of the subject is reached during matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 and 9, identifying "123dog" as the first partial match that was found. (In this example, there are two partial matches, because "dog" on its own partially matches the second alternative.)


PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre16_exec()

If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre16_exec(), PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, without continuing to search for possible complete matches. This option is "hard" because it prefers an earlier partial match over a later complete match. For this reason, the assumption is made that the end of the supplied subject string may not be the true end of the available data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the subject, the result is PCRE_ERROR_PARTIAL, provided that at least one character in the subject has been inspected.

Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject strings are checked for validity. Normally, an invalid sequence causes the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the special case of a truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when PCRE_PARTIAL_HARD is set.


Comparing hard and soft partial matching

The difference between the two partial matching options can be illustrated by a pattern such as:

  /dog(sbody)?/
This matches either "dog" or "dogsbody", greedily (that is, it prefers the longer string if possible). If it is matched against the string "dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog". However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL. On the other hand, if the pattern is made ungreedy the result is different:
  /dog(sbody)??/
In this case the result is always a complete match because that is found first, and matching never continues after finding a complete match. It might be easier to follow this explanation by thinking of the two patterns like this:
  /dog(sbody)?/    is the same as  /dogsbody|dog/
  /dog(sbody)??/   is the same as  /dog|dogsbody/
The second pattern will never match "dogsbody", because it will always find the shorter match first.


PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec()

The DFA functions move along the subject string character by character, without backtracking, searching for all possible matches simultaneously. If the end of the subject is reached before the end of the pattern, there is the possibility of a partial match, again provided that at least one character has been inspected.

When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if there have been no complete matches. Otherwise, the complete matches are returned. However, if PCRE_PARTIAL_HARD is set, a partial match takes precedence over any complete matches. The portion of the string that was inspected when the longest partial match was found is set as the first matching string, provided there are at least two slots in the offsets vector.

Because the DFA functions always search for all possible matches, and there is no difference between greedy and ungreedy repetition, their behaviour is different from the standard functions when PCRE_PARTIAL_HARD is set. Consider the string "dog" matched against the ungreedy pattern shown above:

  /dog(sbody)??/
Whereas the standard functions stop as soon as they find the complete match for "dog", the DFA functions also find the partial match for "dogsbody", and so return that when PCRE_PARTIAL_HARD is set.


PARTIAL MATCHING AND WORD BOUNDARIES

If a pattern ends with one of sequences \b or \B, which test for word boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter-intuitive results. Consider this pattern:

  /\bcat\b/
This matches "cat", provided there is a word boundary at either end. If the subject string is "the cat", the comparison of the final "t" with a following character cannot take place, so a partial match is found. However, normal matching carries on, and \b matches at the end of the subject when the last character is a letter, so a complete match is found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because then the partial match takes precedence.


FORMERLY RESTRICTED PATTERNS

For releases of PCRE prior to 8.00, because of the way certain internal optimizations were implemented in the pcre_exec() function, the PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be used with all patterns. From release 8.00 onwards, the restrictions no longer apply, and partial matching with can be requested for any pattern.

Items that were formerly restricted were repeated single characters and repeated metasequences. If PCRE_PARTIAL was set for a pattern that did not conform to the restrictions, pcre_exec() returned the error code PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled pattern can be used for partial matching now always returns 1.


EXAMPLE OF PARTIAL MATCHING USING PCRETEST

If the escape sequence \P is present in a pcretest data line, the PCRE_PARTIAL_SOFT option is used for the match. Here is a run of pcretest that uses the date example quoted above:

    re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
  data> 25jun04\P
   0: 25jun04
   1: jun
  data> 25dec3\P
  Partial match: 23dec3
  data> 3ju\P
  Partial match: 3ju
  data> 3juj\P
  No match
  data> j\P
  No match
The first data string is matched completely, so pcretest shows the matched substrings. The remaining four strings do not match the complete pattern, but the first two are partial matches. Similar output is obtained if DFA matching is used.

If the escape sequence \P is present more than once in a pcretest data line, the PCRE_PARTIAL_HARD option is set for the match.


MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_dfa_exec()

When a partial match has been found using a DFA matching function, it is possible to continue the match by providing additional subject data and calling the function again with the same compiled regular expression, this time setting the PCRE_DFA_RESTART option. You must pass the same working space as before, because this is where details of the previous partial match are stored. Here is an example using pcretest, using the \R escape sequence to set the PCRE_DFA_RESTART option (\D specifies the use of the DFA matching function):

    re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
  data> 23ja\P\D
  Partial match: 23ja
  data> n05\R\D
   0: n05
The first call has "23ja" as the subject, and requests partial matching; the second call has "n05" as the subject for the continued (restarted) match. Notice that when the match is complete, only the last part is shown; PCRE does not retain the previously partially-matched string. It is up to the calling program to do that if it needs to.

You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with PCRE_DFA_RESTART to continue partial matching over multiple segments. This facility can be used to pass very long subject strings to the DFA matching functions.


MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec()

From release 8.00, the standard matching functions can also be used to do multi-segment matching. Unlike the DFA functions, it is not possible to restart the previous match with a new segment of data. Instead, new data must be added to the previous subject string, and the entire match re-run, starting from the point where the partial match occurred. Earlier data can be discarded.

It is best to use PCRE_PARTIAL_HARD in this situation, because it does not treat the end of a segment as the end of the subject when matching \z, \Z, \b, \B, and $. Consider an unanchored pattern that matches dates:

    re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/
  data> The date is 23ja\P\P
  Partial match: 23ja
At this stage, an application could discard the text preceding "23ja", add on text from the next segment, and call the matching function again. Unlike the DFA matching functions the entire matching string must always be available, and the complete matching process occurs for each call, so more memory and more processing time is needed.

Note: If the pattern contains lookbehind assertions, or \K, or starts with \b or \B, the string that is returned for a partial match includes characters that precede the partially matched string itself, because these must be retained when adding on more characters for a subsequent matching attempt.


ISSUES WITH MULTI-SEGMENT MATCHING

Certain types of pattern may give problems with multi-segment matching, whichever matching function is used.

1. If the pattern contains a test for the beginning of a line, you need to pass the PCRE_NOTBOL option when the subject string for any call does start at the beginning of a line. There is also a PCRE_NOTEOL option, but in practice when doing multi-segment matching you should be using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL.

2. Lookbehind assertions at the start of a pattern are catered for in the offsets that are returned for a partial match. However, in theory, a lookbehind assertion later in the pattern could require even earlier characters to be inspected, and it might not have been reached when a partial match occurs. This is probably an extremely unlikely case; you could guard against it to a certain extent by always including extra characters at the start.

3. Matching a subject string that is split into multiple segments may not always produce exactly the same result as matching over one single long string, especially when PCRE_PARTIAL_SOFT is used. The section "Partial Matching and Word Boundaries" above describes an issue that arises if the pattern ends with \b or \B. Another kind of difference may occur when there are multiple matching possibilities, because (for PCRE_PARTIAL_SOFT) a partial match result is given only when there are no completed matches. This means that as soon as the shortest match has been found, continuation to a new subject segment is no longer possible. Consider again this pcretest example:

    re> /dog(sbody)?/
  data> dogsb\P
   0: dog
  data> do\P\D
  Partial match: do
  data> gsb\R\P\D
   0: g
  data> dogsbody\D
   0: dogsbody
   1: dog
The first data line passes the string "dogsb" to a standard matching function, setting the PCRE_PARTIAL_SOFT option. Although the string is a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the shorter string "dog" is a complete match. Similarly, when the subject is presented to a DFA matching function in several parts ("do" and "gsb" being the first two) the match stops when "dog" has been found, and it is not possible to continue. On the other hand, if "dogsbody" is presented as a single string, a DFA matching function finds both matches.

Because of these problems, it is best to use PCRE_PARTIAL_HARD when matching multi-segment data. The example above then behaves differently:

    re> /dog(sbody)?/
  data> dogsb\P\P
  Partial match: dogsb
  data> do\P\D
  Partial match: do
  data> gsb\R\P\P\D
  Partial match: gsb
4. Patterns that contain alternatives at the top level which do not all start with the same pattern item may not work as expected when PCRE_DFA_RESTART is used. For example, consider this pattern:
  1234|3789
If the first part of the subject is "ABC123", a partial match of the first alternative is found at offset 3. There is no partial match for the second alternative, because such a match does not start at the same point in the subject string. Attempting to continue with the string "7890" does not yield a match because only those alternatives that match at one point in the subject are remembered. The problem arises because the start of the second alternative matches within the first alternative. There is no problem with anchored patterns or patterns such as:
  1234|ABCD
where no string can be a partial match for both alternatives. This is not a problem if a standard matching function is used, because the entire match has to be rerun each time:
    re> /1234|3789/
  data> ABC123\P\P
  Partial match: 123
  data> 1237890
   0: 3789
Of course, instead of using PCRE_DFA_RESTART, the same technique of re-running the entire match can also be used with the DFA matching functions. Another possibility is to work with two buffers. If a partial match at offset n in the first buffer is followed by "no match" when PCRE_DFA_RESTART is used on the second buffer, you can then try a new match starting at offset n+1 in the first buffer.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 21 January 2012
Copyright © 1997-2012 University of Cambridge.

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070701000382bf000081a40000000000000000000000014f79083e00000635000000b500010002ffffffffffffffff0000003d00000000root/usr/local/share/doc/pcre/html/pcre_jit_stack_alloc.html pcre_jit_stack_alloc specification

pcre_jit_stack_alloc man page

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SYNOPSIS

#include <pcre.h>

pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize);


DESCRIPTION

This function is used to create a stack for use by the code compiled by the JIT optimization of pcre[16]_study(). The arguments are a starting size for the stack, and a maximum size to which it is allowed to grow. The result can be passed to the JIT runtime code by pcre[16]_assign_jit_stack(), or that function can set up a callback for obtaining a stack. A maximum stack size of 512K to 1M should be more than enough for any pattern. For more details, see the pcrejit page.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382c2000081a40000000000000000000000014f79083e00000701000000b500010002ffffffffffffffff0000004800000000root/usr/local/share/doc/pcre/html/pcre_pattern_to_host_byte_order.html pcre_pattern_to_host_byte_order specification

pcre_pattern_to_host_byte_order man page

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SYNOPSIS

#include <pcre.h>

int pcre_pattern_to_host_byte_order(pcre *code, pcre_extra *extra, const unsigned char *tables);

int pcre16_pattern_to_host_byte_order(pcre16 *code, pcre16_extra *extra, const unsigned char *tables);


DESCRIPTION

This function ensures that the bytes in 2-byte and 4-byte values in a compiled pattern are in the correct order for the current host. It is useful when a pattern that has been compiled on one host is transferred to another that might have different endianness. The arguments are:

  code         A compiled regular expression
  extra        Points to an associated pcre[16]_extra structure,
                 or is NULL
  tables       Pointer to character tables, or NULL to
                 set the built-in default
The result is 0 for success, a negative PCRE_ERROR_xxx value otherwise.

There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.

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070701000382d5000081a40000000000000000000000014f79083e00001eb9000000b500010002ffffffffffffffff0000003400000000root/usr/local/share/doc/pcre/html/pcreperform.html pcreperform specification

pcreperform man page

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PCRE PERFORMANCE

Two aspects of performance are discussed below: memory usage and processing time. The way you express your pattern as a regular expression can affect both of them.


COMPILED PATTERN MEMORY USAGE

Patterns are compiled by PCRE into a reasonably efficient interpretive code, so that most simple patterns do not use much memory. However, there is one case where the memory usage of a compiled pattern can be unexpectedly large. If a parenthesized subpattern has a quantifier with a minimum greater than 1 and/or a limited maximum, the whole subpattern is repeated in the compiled code. For example, the pattern

  (abc|def){2,4}
is compiled as if it were
  (abc|def)(abc|def)((abc|def)(abc|def)?)?
(Technical aside: It is done this way so that backtrack points within each of the repetitions can be independently maintained.)

For regular expressions whose quantifiers use only small numbers, this is not usually a problem. However, if the numbers are large, and particularly if such repetitions are nested, the memory usage can become an embarrassment. For example, the very simple pattern

  ((ab){1,1000}c){1,3}
uses 51K bytes when compiled using the 8-bit library. When PCRE is compiled with its default internal pointer size of two bytes, the size limit on a compiled pattern is 64K data units, and this is reached with the above pattern if the outer repetition is increased from 3 to 4. PCRE can be compiled to use larger internal pointers and thus handle larger compiled patterns, but it is better to try to rewrite your pattern to use less memory if you can.

One way of reducing the memory usage for such patterns is to make use of PCRE's "subroutine" facility. Re-writing the above pattern as

  ((ab)(?2){0,999}c)(?1){0,2}
reduces the memory requirements to 18K, and indeed it remains under 20K even with the outer repetition increased to 100. However, this pattern is not exactly equivalent, because the "subroutine" calls are treated as atomic groups into which there can be no backtracking if there is a subsequent matching failure. Therefore, PCRE cannot do this kind of rewriting automatically. Furthermore, there is a noticeable loss of speed when executing the modified pattern. Nevertheless, if the atomic grouping is not a problem and the loss of speed is acceptable, this kind of rewriting will allow you to process patterns that PCRE cannot otherwise handle.


STACK USAGE AT RUN TIME

When pcre_exec() or pcre16_exec() is used for matching, certain kinds of pattern can cause it to use large amounts of the process stack. In some environments the default process stack is quite small, and if it runs out the result is often SIGSEGV. This issue is probably the most frequently raised problem with PCRE. Rewriting your pattern can often help. The pcrestack documentation discusses this issue in detail.


PROCESSING TIME

Certain items in regular expression patterns are processed more efficiently than others. It is more efficient to use a character class like [aeiou] than a set of single-character alternatives such as (a|e|i|o|u). In general, the simplest construction that provides the required behaviour is usually the most efficient. Jeffrey Friedl's book contains a lot of useful general discussion about optimizing regular expressions for efficient performance. This document contains a few observations about PCRE.

Using Unicode character properties (the \p, \P, and \X escapes) is slow, because PCRE has to scan a structure that contains data for over fifteen thousand characters whenever it needs a character's property. If you can find an alternative pattern that does not use character properties, it will probably be faster.

By default, the escape sequences \b, \d, \s, and \w, and the POSIX character classes such as [:alpha:] do not use Unicode properties, partly for backwards compatibility, and partly for performance reasons. However, you can set PCRE_UCP if you want Unicode character properties to be used. This can double the matching time for items such as \d, when matched with a traditional matching function; the performance loss is less with a DFA matching function, and in both cases there is not much difference for \b.

When a pattern begins with .* not in parentheses, or in parentheses that are not the subject of a backreference, and the PCRE_DOTALL option is set, the pattern is implicitly anchored by PCRE, since it can match only at the start of a subject string. However, if PCRE_DOTALL is not set, PCRE cannot make this optimization, because the . metacharacter does not then match a newline, and if the subject string contains newlines, the pattern may match from the character immediately following one of them instead of from the very start. For example, the pattern

  .*second
matches the subject "first\nand second" (where \n stands for a newline character), with the match starting at the seventh character. In order to do this, PCRE has to retry the match starting after every newline in the subject.

If you are using such a pattern with subject strings that do not contain newlines, the best performance is obtained by setting PCRE_DOTALL, or starting the pattern with ^.* or ^.*? to indicate explicit anchoring. That saves PCRE from having to scan along the subject looking for a newline to restart at.

Beware of patterns that contain nested indefinite repeats. These can take a long time to run when applied to a string that does not match. Consider the pattern fragment

  ^(a+)*
This can match "aaaa" in 16 different ways, and this number increases very rapidly as the string gets longer. (The * repeat can match 0, 1, 2, 3, or 4 times, and for each of those cases other than 0 or 4, the + repeats can match different numbers of times.) When the remainder of the pattern is such that the entire match is going to fail, PCRE has in principle to try every possible variation, and this can take an extremely long time, even for relatively short strings.

An optimization catches some of the more simple cases such as

  (a+)*b
where a literal character follows. Before embarking on the standard matching procedure, PCRE checks that there is a "b" later in the subject string, and if there is not, it fails the match immediately. However, when there is no following literal this optimization cannot be used. You can see the difference by comparing the behaviour of
  (a+)*\d
with the pattern above. The former gives a failure almost instantly when applied to a whole line of "a" characters, whereas the latter takes an appreciable time with strings longer than about 20 characters.

In many cases, the solution to this kind of performance issue is to use an atomic group or a possessive quantifier.


AUTHOR

Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.


REVISION

Last updated: 09 January 2012
Copyright © 1997-2012 University of Cambridge.

Return to the PCRE index page.

070701000382a1000081a40000000000000000000000014f79083e00000353000000b500010002ffffffffffffffff0000002600000000root/usr/local/share/doc/pcre/AUTHORSTHE MAIN PCRE LIBRARY --------------------- Written by: Philip Hazel Email local part: ph10 Email domain: cam.ac.uk University of Cambridge Computing Service, Cambridge, England. Copyright (c) 1997-2012 University of Cambridge All rights reserved PCRE JUST-IN-TIME COMPILATION SUPPORT ------------------------------------- Written by: Zoltan Herczeg Email local part: hzmester Emain domain: freemail.hu Copyright(c) 2010-2012 Zoltan Herczeg All rights reserved. STACK-LESS JUST-IN-TIME COMPILER -------------------------------- Written by: Zoltan Herczeg Email local part: hzmester Emain domain: freemail.hu Copyright(c) 2009-2012 Zoltan Herczeg All rights reserved. THE C++ WRAPPER LIBRARY ----------------------- Written by: Google Inc. Copyright (c) 2007-2012 Google Inc All rights reserved #### 07070100038367000081a40000000000000000000000014f79083e00008a2f000000b500010002ffffffffffffffff0000002b00000000root/usr/local/share/doc/pcre/pcregrep.txtPCREGREP(1) PCREGREP(1) NAME pcregrep - a grep with Perl-compatible regular expressions. SYNOPSIS pcregrep [options] [long options] [pattern] [path1 path2 ...] DESCRIPTION pcregrep searches files for character patterns, in the same way as other grep commands do, but it uses the PCRE regular expression library to support patterns that are compatible with the regular expressions of Perl 5. See pcrepattern(3) for a full description of syntax and seman- tics of the regular expressions that PCRE supports. Patterns, whether supplied on the command line or in a separate file, are given without delimiters. For example: pcregrep Thursday /etc/motd If you attempt to use delimiters (for example, by surrounding a pattern with slashes, as is common in Perl scripts), they are interpreted as part of the pattern. Quotes can of course be used to delimit patterns on the command line because they are interpreted by the shell, and indeed they are required if a pattern contains white space or shell metacharacters. The first argument that follows any option settings is treated as the single pattern to be matched when neither -e nor -f is present. Con- versely, when one or both of these options are used to specify pat- terns, all arguments are treated as path names. At least one of -e, -f, or an argument pattern must be provided. If no files are specified, pcregrep reads the standard input. The stan- dard input can also be referenced by a name consisting of a single hyphen. For example: pcregrep some-pattern /file1 - /file3 By default, each line that matches a pattern is copied to the standard output, and if there is more than one file, the file name is output at the start of each line, followed by a colon. However, there are options that can change how pcregrep behaves. In particular, the -M option makes it possible to search for patterns that span line boundaries. What defines a line boundary is controlled by the -N (--newline) option. The amount of memory used for buffering files that are being scanned is controlled by a parameter that can be set by the --buffer-size option. The default value for this parameter is specified when pcregrep is built, with the default default being 20K. A block of memory three times this size is used (to allow for buffering "before" and "after" lines). An error occurs if a line overflows the buffer. Patterns are limited to 8K or BUFSIZ bytes, whichever is the greater. BUFSIZ is defined in . When there is more than one pattern (specified by the use of -e and/or -f), each pattern is applied to each line in the order in which they are defined, except that all the -e patterns are tried before the -f patterns. By default, as soon as one pattern matches (or fails to match when -v is used), no further patterns are considered. However, if --colour (or --color) is used to colour the matching substrings, or if --only-match- ing, --file-offsets, or --line-offsets is used to output only the part of the line that matched (either shown literally, or as an offset), scanning resumes immediately following the match, so that further matches on the same line can be found. If there are multiple patterns, they are all tried on the remainder of the line, but patterns that fol- low the one that matched are not tried on the earlier part of the line. This is the same behaviour as GNU grep, but it does mean that the order in which multiple patterns are specified can affect the output when one of the above options is used. Patterns that can match an empty string are accepted, but empty string matches are never recognized. An example is the pattern "(super)?(man)?", in which all components are optional. This pattern finds all occurrences of both "super" and "man"; the output differs from matching with "super|man" when only the matching substrings are being shown. If the LC_ALL or LC_CTYPE environment variable is set, pcregrep uses the value to set a locale when calling the PCRE library. The --locale option can be used to override this. SUPPORT FOR COMPRESSED FILES It is possible to compile pcregrep so that it uses libz or libbz2 to read files whose names end in .gz or .bz2, respectively. You can find out whether your binary has support for one or both of these file types by running it with the --help option. If the appropriate support is not present, files are treated as plain text. The standard input is always so treated. OPTIONS The order in which some of the options appear can affect the output. For example, both the -h and -l options affect the printing of file names. Whichever comes later in the command line will be the one that takes effect. Numerical values for options may be followed by K or M, to signify multiplication by 1024 or 1024*1024 respectively. -- This terminates the list of options. It is useful if the next item on the command line starts with a hyphen but is not an option. This allows for the processing of patterns and file- names that start with hyphens. -A number, --after-context=number Output number lines of context after each matching line. If filenames and/or line numbers are being output, a hyphen sep- arator is used instead of a colon for the context lines. A line containing "--" is output between each group of lines, unless they are in fact contiguous in the input file. The value of number is expected to be relatively small. However, pcregrep guarantees to have up to 8K of following text avail- able for context output. -B number, --before-context=number Output number lines of context before each matching line. If filenames and/or line numbers are being output, a hyphen sep- arator is used instead of a colon for the context lines. A line containing "--" is output between each group of lines, unless they are in fact contiguous in the input file. The value of number is expected to be relatively small. However, pcregrep guarantees to have up to 8K of preceding text avail- able for context output. --buffer-size=number Set the parameter that controls how much memory is used for buffering files that are being scanned. -C number, --context=number Output number lines of context both before and after each matching line. This is equivalent to setting both -A and -B to the same value. -c, --count Do not output individual lines from the files that are being scanned; instead output the number of lines that would other- wise have been shown. If no lines are selected, the number zero is output. If several files are are being scanned, a count is output for each of them. However, if the --files- with-matches option is also used, only those files whose counts are greater than zero are listed. When -c is used, the -A, -B, and -C options are ignored. --colour, --color If this option is given without any data, it is equivalent to "--colour=auto". If data is required, it must be given in the same shell item, separated by an equals sign. --colour=value, --color=value This option specifies under what circumstances the parts of a line that matched a pattern should be coloured in the output. By default, the output is not coloured. The value (which is optional, see above) may be "never", "always", or "auto". In the latter case, colouring happens only if the standard out- put is connected to a terminal. More resources are used when colouring is enabled, because pcregrep has to search for all possible matches in a line, not just one, in order to colour them all. The colour that is used can be specified by setting the envi- ronment variable PCREGREP_COLOUR or PCREGREP_COLOR. The value of this variable should be a string of two numbers, separated by a semicolon. They are copied directly into the control string for setting colour on a terminal, so it is your responsibility to ensure that they make sense. If neither of the environment variables is set, the default is "1;31", which gives red. -D action, --devices=action If an input path is not a regular file or a directory, "action" specifies how it is to be processed. Valid values are "read" (the default) or "skip" (silently skip the path). -d action, --directories=action If an input path is a directory, "action" specifies how it is to be processed. Valid values are "read" (the default), "recurse" (equivalent to the -r option), or "skip" (silently skip the path). In the default case, directories are read as if they were ordinary files. In some operating systems the effect of reading a directory like this is an immediate end- of-file. -e pattern, --regex=pattern, --regexp=pattern Specify a pattern to be matched. This option can be used mul- tiple times in order to specify several patterns. It can also be used as a way of specifying a single pattern that starts with a hyphen. When -e is used, no argument pattern is taken from the command line; all arguments are treated as file names. There is an overall maximum of 100 patterns. They are applied to each line in the order in which they are defined until one matches (or fails to match if -v is used). If -f is used with -e, the command line patterns are matched first, followed by the patterns from the file, independent of the order in which these options are specified. Note that multi- ple use of -e is not the same as a single pattern with alter- natives. For example, X|Y finds the first character in a line that is X or Y, whereas if the two patterns are given sepa- rately, pcregrep finds X if it is present, even if it follows Y in the line. It finds Y only if there is no X in the line. This really matters only if you are using -o to show the part(s) of the line that matched. --exclude=pattern When pcregrep is searching the files in a directory as a con- sequence of the -r (recursive search) option, any regular files whose names match the pattern are excluded. Subdirecto- ries are not excluded by this option; they are searched recursively, subject to the --exclude-dir and --include_dir options. The pattern is a PCRE regular expression, and is matched against the final component of the file name (not the entire path). If a file name matches both --include and --exclude, it is excluded. There is no short form for this option. --exclude-dir=pattern When pcregrep is searching the contents of a directory as a consequence of the -r (recursive search) option, any subdi- rectories whose names match the pattern are excluded. (Note that the --exclude option does not affect subdirectories.) The pattern is a PCRE regular expression, and is matched against the final component of the name (not the entire path). If a subdirectory name matches both --include-dir and --exclude-dir, it is excluded. There is no short form for this option. -F, --fixed-strings Interpret each pattern as a list of fixed strings, separated by newlines, instead of as a regular expression. The -w (match as a word) and -x (match whole line) options can be used with -F. They apply to each of the fixed strings. A line is selected if any of the fixed strings are found in it (sub- ject to -w or -x, if present). -f filename, --file=filename Read a number of patterns from the file, one per line, and match them against each line of input. A data line is output if any of the patterns match it. The filename can be given as "-" to refer to the standard input. When -f is used, patterns specified on the command line using -e may also be present; they are tested before the file's patterns. However, no other pattern is taken from the command line; all arguments are treated as file names. There is an overall maximum of 100 patterns. Trailing white space is removed from each line, and blank lines are ignored. An empty file contains no patterns and therefore matches nothing. See also the comments about multiple patterns versus a single pattern with alternatives in the description of -e above. --file-offsets Instead of showing lines or parts of lines that match, show each match as an offset from the start of the file and a length, separated by a comma. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown separately. This option is mutually exclusive with --line- offsets and --only-matching. -H, --with-filename Force the inclusion of the filename at the start of output lines when searching a single file. By default, the filename is not shown in this case. For matching lines, the filename is followed by a colon; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name. -h, --no-filename Suppress the output filenames when searching multiple files. By default, filenames are shown when multiple files are searched. For matching lines, the filename is followed by a colon; for context lines, a hyphen separator is used. If a line number is also being output, it follows the file name. --help Output a help message, giving brief details of the command options and file type support, and then exit. -i, --ignore-case Ignore upper/lower case distinctions during comparisons. --include=pattern When pcregrep is searching the files in a directory as a con- sequence of the -r (recursive search) option, only those reg- ular files whose names match the pattern are included. Subdi- rectories are always included and searched recursively, sub- ject to the --include-dir and --exclude-dir options. The pat- tern is a PCRE regular expression, and is matched against the final component of the file name (not the entire path). If a file name matches both --include and --exclude, it is excluded. There is no short form for this option. --include-dir=pattern When pcregrep is searching the contents of a directory as a consequence of the -r (recursive search) option, only those subdirectories whose names match the pattern are included. (Note that the --include option does not affect subdirecto- ries.) The pattern is a PCRE regular expression, and is matched against the final component of the name (not the entire path). If a subdirectory name matches both --include- dir and --exclude-dir, it is excluded. There is no short form for this option. -L, --files-without-match Instead of outputting lines from the files, just output the names of the files that do not contain any lines that would have been output. Each file name is output once, on a sepa- rate line. -l, --files-with-matches Instead of outputting lines from the files, just output the names of the files containing lines that would have been out- put. Each file name is output once, on a separate line. Searching normally stops as soon as a matching line is found in a file. However, if the -c (count) option is also used, matching continues in order to obtain the correct count, and those files that have at least one match are listed along with their counts. Using this option with -c is a way of sup- pressing the listing of files with no matches. --label=name This option supplies a name to be used for the standard input when file names are being output. If not supplied, "(standard input)" is used. There is no short form for this option. --line-buffered When this option is given, input is read and processed line by line, and the output is flushed after each write. By default, input is read in large chunks, unless pcregrep can determine that it is reading from a terminal (which is cur- rently possible only in Unix environments). Output to termi- nal is normally automatically flushed by the operating sys- tem. This option can be useful when the input or output is attached to a pipe and you do not want pcregrep to buffer up large amounts of data. However, its use will affect perfor- mance, and the -M (multiline) option ceases to work. --line-offsets Instead of showing lines or parts of lines that match, show each match as a line number, the offset from the start of the line, and a length. The line number is terminated by a colon (as usual; see the -n option), and the offset and length are separated by a comma. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown sepa- rately. This option is mutually exclusive with --file-offsets and --only-matching. --locale=locale-name This option specifies a locale to be used for pattern match- ing. It overrides the value in the LC_ALL or LC_CTYPE envi- ronment variables. If no locale is specified, the PCRE library's default (usually the "C" locale) is used. There is no short form for this option. --match-limit=number Processing some regular expression patterns can require a very large amount of memory, leading in some cases to a pro- gram crash if not enough is available. Other patterns may take a very long time to search for all possible matching strings. The pcre_exec() function that is called by pcregrep to do the matching has two parameters that can limit the resources that it uses. The --match-limit option provides a means of limiting resource usage when processing patterns that are not going to match, but which have a very large number of possibilities in their search trees. The classic example is a pattern that uses nested unlimited repeats. Internally, PCRE uses a func- tion called match() which it calls repeatedly (sometimes recursively). The limit set by --match-limit is imposed on the number of times this function is called during a match, which has the effect of limiting the amount of backtracking that can take place. The --recursion-limit option is similar to --match-limit, but instead of limiting the total number of times that match() is called, it limits the depth of recursive calls, which in turn limits the amount of memory that can be used. The recursion depth is a smaller number than the total number of calls, because not all calls to match() are recursive. This limit is of use only if it is set smaller than --match-limit. There are no short forms for these options. The default set- tings are specified when the PCRE library is compiled, with the default default being 10 million. -M, --multiline Allow patterns to match more than one line. When this option is given, patterns may usefully contain literal newline char- acters and internal occurrences of ^ and $ characters. The output for a successful match may consist of more than one line, the last of which is the one in which the match ended. If the matched string ends with a newline sequence the output ends at the end of that line. When this option is set, the PCRE library is called in "mul- tiline" mode. There is a limit to the number of lines that can be matched, imposed by the way that pcregrep buffers the input file as it scans it. However, pcregrep ensures that at least 8K characters or the rest of the document (whichever is the shorter) are available for forward matching, and simi- larly the previous 8K characters (or all the previous charac- ters, if fewer than 8K) are guaranteed to be available for lookbehind assertions. This option does not work when input is read line by line (see --line-buffered.) -N newline-type, --newline=newline-type The PCRE library supports five different conventions for indicating the ends of lines. They are the single-character sequences CR (carriage return) and LF (linefeed), the two- character sequence CRLF, an "anycrlf" convention, which rec- ognizes any of the preceding three types, and an "any" con- vention, in which any Unicode line ending sequence is assumed to end a line. The Unicode sequences are the three just men- tioned, plus VT (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029). When the PCRE library is built, a default line-ending sequence is specified. This is normally the standard sequence for the operating system. Unless otherwise specified by this option, pcregrep uses the library's default. The possible values for this option are CR, LF, CRLF, ANYCRLF, or ANY. This makes it possible to use pcregrep on files that have come from other environments without having to modify their line endings. If the data that is being scanned does not agree with the convention set by this option, pcregrep may behave in strange ways. -n, --line-number Precede each output line by its line number in the file, fol- lowed by a colon for matching lines or a hyphen for context lines. If the filename is also being output, it precedes the line number. This option is forced if --line-offsets is used. --no-jit If the PCRE library is built with support for just-in-time compiling (which speeds up matching), pcregrep automatically makes use of this, unless it was explicitly disabled at build time. This option can be used to disable the use of JIT at run time. It is provided for testing and working round prob- lems. It should never be needed in normal use. -o, --only-matching Show only the part of the line that matched a pattern instead of the whole line. In this mode, no context is shown. That is, the -A, -B, and -C options are ignored. If there is more than one match in a line, each of them is shown separately. If -o is combined with -v (invert the sense of the match to find non-matching lines), no output is generated, but the return code is set appropriately. If the matched portion of the line is empty, nothing is output unless the file name or line number are being printed, in which case they are shown on an otherwise empty line. This option is mutually exclusive with --file-offsets and --line-offsets. -onumber, --only-matching=number Show only the part of the line that matched the capturing parentheses of the given number. Up to 32 capturing parenthe- ses are supported. Because these options can be given without an argument (see above), if an argument is present, it must be given in the same shell item, for example, -o3 or --only- matching=2. The comments given for the non-argument case above also apply to this case. If the specified capturing parentheses do not exist in the pattern, or were not set in the match, nothing is output unless the file name or line number are being printed. -q, --quiet Work quietly, that is, display nothing except error messages. The exit status indicates whether or not any matches were found. -r, --recursive If any given path is a directory, recursively scan the files it contains, taking note of any --include and --exclude set- tings. By default, a directory is read as a normal file; in some operating systems this gives an immediate end-of-file. This option is a shorthand for setting the -d option to "recurse". --recursion-limit=number See --match-limit above. -s, --no-messages Suppress error messages about non-existent or unreadable files. Such files are quietly skipped. However, the return code is still 2, even if matches were found in other files. -u, --utf-8 Operate in UTF-8 mode. This option is available only if PCRE has been compiled with UTF-8 support. Both patterns and sub- ject lines must be valid strings of UTF-8 characters. -V, --version Write the version numbers of pcregrep and the PCRE library that is being used to the standard error stream. -v, --invert-match Invert the sense of the match, so that lines which do not match any of the patterns are the ones that are found. -w, --word-regex, --word-regexp Force the patterns to match only whole words. This is equiva- lent to having \b at the start and end of the pattern. -x, --line-regex, --line-regexp Force the patterns to be anchored (each must start matching at the beginning of a line) and in addition, require them to match entire lines. This is equivalent to having ^ and $ characters at the start and end of each alternative branch in every pattern. ENVIRONMENT VARIABLES The environment variables LC_ALL and LC_CTYPE are examined, in that order, for a locale. The first one that is set is used. This can be overridden by the --locale option. If no locale is set, the PCRE library's default (usually the "C" locale) is used. NEWLINES The -N (--newline) option allows pcregrep to scan files with different newline conventions from the default. However, the setting of this option does not affect the way in which pcregrep writes information to the standard error and output streams. It uses the string "\n" in C printf() calls to indicate newlines, relying on the C I/O library to convert this to an appropriate sequence if the output is sent to a file. OPTIONS COMPATIBILITY Many of the short and long forms of pcregrep's options are the same as in the GNU grep program (version 2.5.4). Any long option of the form --xxx-regexp (GNU terminology) is also available as --xxx-regex (PCRE terminology). However, the --file-offsets, --include-dir, --line-off- sets, --locale, --match-limit, -M, --multiline, -N, --newline, --recur- sion-limit, -u, and --utf-8 options are specific to pcregrep, as is the use of the --only-matching option with a capturing parentheses number. Although most of the common options work the same way, a few are dif- ferent in pcregrep. For example, the --include option's argument is a glob for GNU grep, but a regular expression for pcregrep. If both the -c and -l options are given, GNU grep lists only file names, without counts, but pcregrep gives the counts. OPTIONS WITH DATA There are four different ways in which an option with data can be spec- ified. If a short form option is used, the data may follow immedi- ately, or (with one exception) in the next command line item. For exam- ple: -f/some/file -f /some/file The exception is the -o option, which may appear with or without data. Because of this, if data is present, it must follow immediately in the same item, for example -o3. If a long form option is used, the data may appear in the same command line item, separated by an equals character, or (with two exceptions) it may appear in the next command line item. For example: --file=/some/file --file /some/file Note, however, that if you want to supply a file name beginning with ~ as data in a shell command, and have the shell expand ~ to a home directory, you must separate the file name from the option, because the shell does not treat ~ specially unless it is at the start of an item. The exceptions to the above are the --colour (or --color) and --only- matching options, for which the data is optional. If one of these options does have data, it must be given in the first form, using an equals character. Otherwise pcregrep will assume that it has no data. MATCHING ERRORS It is possible to supply a regular expression that takes a very long time to fail to match certain lines. Such patterns normally involve nested indefinite repeats, for example: (a+)*\d when matched against a line of a's with no final digit. The PCRE matching function has a resource limit that causes it to abort in these circumstances. If this happens, pcregrep outputs an error message and the line that caused the problem to the standard error stream. If there are more than 20 such errors, pcregrep gives up. The --match-limit option of pcregrep can be used to set the overall resource limit; there is a second option called --recursion-limit that sets a limit on the amount of memory (usually stack) that is used (see the discussion of these options above). DIAGNOSTICS Exit status is 0 if any matches were found, 1 if no matches were found, and 2 for syntax errors, overlong lines, non-existent or inaccessible files (even if matches were found in other files) or too many matching errors. Using the -s option to suppress error messages about inaccessi- ble files does not affect the return code. SEE ALSO pcrepattern(3), pcretest(1). AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 06 September 2011 Copyright (c) 1997-2011 University of Cambridge. 070701000382a3000081a40000000000000000000000014f79083e00037283000000b500010002ffffffffffffffff0000002800000000root/usr/local/share/doc/pcre/ChangeLogChangeLog for PCRE ------------------ Version 8.30 04-February-2012 ----------------------------- 1. Renamed "isnumber" as "is_a_number" because in some Mac environments this name is defined in ctype.h. 2. Fixed a bug in fixed-length calculation for lookbehinds that would show up only in quite long subpatterns. 3. Removed the function pcre_info(), which has been obsolete and deprecated since it was replaced by pcre_fullinfo() in February 2000. 4. For a non-anchored pattern, if (*SKIP) was given with a name that did not match a (*MARK), and the match failed at the start of the subject, a reference to memory before the start of the subject could occur. This bug was introduced by fix 17 of release 8.21. 5. A reference to an unset group with zero minimum repetition was giving totally wrong answers (in non-JavaScript-compatibility mode). For example, /(another)?(\1?)test/ matched against "hello world test". This bug was introduced in release 8.13. 6. Add support for 16-bit character strings (a large amount of work involving many changes and refactorings). 7. RunGrepTest failed on msys because \r\n was replaced by whitespace when the command "pattern=`printf 'xxx\r\njkl'`" was run. The pattern is now taken from a file. 8. Ovector size of 2 is also supported by JIT based pcre_exec (the ovector size rounding is not applied in this particular case). 9. The invalid Unicode surrogate codepoints U+D800 to U+DFFF are now rejected if they appear, or are escaped, in patterns. 10. Get rid of a number of -Wunused-but-set-variable warnings. 11. The pattern /(?=(*:x))(q|)/ matches an empty string, and returns the mark "x". The similar pattern /(?=(*:x))((*:y)q|)/ did not return a mark at all. Oddly, Perl behaves the same way. PCRE has been fixed so that this pattern also returns the mark "x". This bug applied to capturing parentheses, non-capturing parentheses, and atomic parentheses. It also applied to some assertions. 12. Stephen Kelly's patch to CMakeLists.txt allows it to parse the version information out of configure.ac instead of relying on pcre.h.generic, which is not stored in the repository. 13. Applied Dmitry V. Levin's patch for a more portable method for linking with -lreadline. 14. ZH added PCRE_CONFIG_JITTARGET; added its output to pcretest -C. 15. Applied Graycode's patch to put the top-level frame on the stack rather than the heap when not using the stack for recursion. This gives a performance improvement in many cases when recursion is not deep. 16. Experimental code added to "pcretest -C" to output the stack frame size. Version 8.21 12-Dec-2011 ------------------------ 1. Updating the JIT compiler. 2. JIT compiler now supports OP_NCREF, OP_RREF and OP_NRREF. New test cases are added as well. 3. Fix cache-flush issue on PowerPC (It is still an experimental JIT port). PCRE_EXTRA_TABLES is not suported by JIT, and should be checked before calling _pcre_jit_exec. Some extra comments are added. 4. (*MARK) settings inside atomic groups that do not contain any capturing parentheses, for example, (?>a(*:m)), were not being passed out. This bug was introduced by change 18 for 8.20. 5. Supporting of \x, \U and \u in JavaScript compatibility mode based on the ECMA-262 standard. 6. Lookbehinds such as (?<=a{2}b) that contained a fixed repetition were erroneously being rejected as "not fixed length" if PCRE_CASELESS was set. This bug was probably introduced by change 9 of 8.13. 7. While fixing 6 above, I noticed that a number of other items were being incorrectly rejected as "not fixed length". This arose partly because newer opcodes had not been added to the fixed-length checking code. I have (a) corrected the bug and added tests for these items, and (b) arranged for an error to occur if an unknown opcode is encountered while checking for fixed length instead of just assuming "not fixed length". The items that were rejected were: (*ACCEPT), (*COMMIT), (*FAIL), (*MARK), (*PRUNE), (*SKIP), (*THEN), \h, \H, \v, \V, and single character negative classes with fixed repetitions, e.g. [^a]{3}, with and without PCRE_CASELESS. 8. A possessively repeated conditional subpattern such as (?(?=c)c|d)++ was being incorrectly compiled and would have given unpredicatble results. 9. A possessively repeated subpattern with minimum repeat count greater than one behaved incorrectly. For example, (A){2,}+ behaved as if it was (A)(A)++ which meant that, after a subsequent mismatch, backtracking into the first (A) could occur when it should not. 10. Add a cast and remove a redundant test from the code. 11. JIT should use pcre_malloc/pcre_free for allocation. 12. Updated pcre-config so that it no longer shows -L/usr/lib, which seems best practice nowadays, and helps with cross-compiling. (If the exec_prefix is anything other than /usr, -L is still shown). 13. In non-UTF-8 mode, \C is now supported in lookbehinds and DFA matching. 14. Perl does not support \N without a following name in a [] class; PCRE now also gives an error. 15. If a forward reference was repeated with an upper limit of around 2000, it caused the error "internal error: overran compiling workspace". The maximum number of forward references (including repeats) was limited by the internal workspace, and dependent on the LINK_SIZE. The code has been rewritten so that the workspace expands (via pcre_malloc) if necessary, and the default depends on LINK_SIZE. There is a new upper limit (for safety) of around 200,000 forward references. While doing this, I also speeded up the filling in of repeated forward references. 16. A repeated forward reference in a pattern such as (a)(?2){2}(.) was incorrectly expecting the subject to contain another "a" after the start. 17. When (*SKIP:name) is activated without a corresponding (*MARK:name) earlier in the match, the SKIP should be ignored. This was not happening; instead the SKIP was being treated as NOMATCH. For patterns such as /A(*MARK:A)A+(*SKIP:B)Z|AAC/ this meant that the AAC branch was never tested. 18. The behaviour of (*MARK), (*PRUNE), and (*THEN) has been reworked and is now much more compatible with Perl, in particular in cases where the result is a non-match for a non-anchored pattern. For example, if /b(*:m)f|a(*:n)w/ is matched against "abc", the non-match returns the name "m", where previously it did not return a name. A side effect of this change is that for partial matches, the last encountered mark name is returned, as for non matches. A number of tests that were previously not Perl-compatible have been moved into the Perl-compatible test files. The refactoring has had the pleasing side effect of removing one argument from the match() function, thus reducing its stack requirements. 19. If the /S+ option was used in pcretest to study a pattern using JIT, subsequent uses of /S (without +) incorrectly behaved like /S+. 21. Retrieve executable code size support for the JIT compiler and fixing some warnings. 22. A caseless match of a UTF-8 character whose other case uses fewer bytes did not work when the shorter character appeared right at the end of the subject string. 23. Added some (int) casts to non-JIT modules to reduce warnings on 64-bit systems. 24. Added PCRE_INFO_JITSIZE to pass on the value from (21) above, and also output it when the /M option is used in pcretest. 25. The CheckMan script was not being included in the distribution. Also, added an explicit "perl" to run Perl scripts from the PrepareRelease script because this is reportedly needed in Windows. 26. If study data was being save in a file and studying had not found a set of "starts with" bytes for the pattern, the data written to the file (though never used) was taken from uninitialized memory and so caused valgrind to complain. 27. Updated RunTest.bat as provided by Sheri Pierce. 28. Fixed a possible uninitialized memory bug in pcre_jit_compile.c. 29. Computation of memory usage for the table of capturing group names was giving an unnecessarily large value. Version 8.20 21-Oct-2011 ------------------------ 1. Change 37 of 8.13 broke patterns like [:a]...[b:] because it thought it had a POSIX class. After further experiments with Perl, which convinced me that Perl has bugs and confusions, a closing square bracket is no longer allowed in a POSIX name. This bug also affected patterns with classes that started with full stops. 2. If a pattern such as /(a)b|ac/ is matched against "ac", there is no captured substring, but while checking the failing first alternative, substring 1 is temporarily captured. If the output vector supplied to pcre_exec() was not big enough for this capture, the yield of the function was still zero ("insufficient space for captured substrings"). This cannot be totally fixed without adding another stack variable, which seems a lot of expense for a edge case. However, I have improved the situation in cases such as /(a)(b)x|abc/ matched against "abc", where the return code indicates that fewer than the maximum number of slots in the ovector have been set. 3. Related to (2) above: when there are more back references in a pattern than slots in the output vector, pcre_exec() uses temporary memory during matching, and copies in the captures as far as possible afterwards. It was using the entire output vector, but this conflicts with the specification that only 2/3 is used for passing back captured substrings. Now it uses only the first 2/3, for compatibility. This is, of course, another edge case. 4. Zoltan Herczeg's just-in-time compiler support has been integrated into the main code base, and can be used by building with --enable-jit. When this is done, pcregrep automatically uses it unless --disable-pcregrep-jit or the runtime --no-jit option is given. 5. When the number of matches in a pcre_dfa_exec() run exactly filled the ovector, the return from the function was zero, implying that there were other matches that did not fit. The correct "exactly full" value is now returned. 6. If a subpattern that was called recursively or as a subroutine contained (*PRUNE) or any other control that caused it to give a non-standard return, invalid errors such as "Error -26 (nested recursion at the same subject position)" or even infinite loops could occur. 7. If a pattern such as /a(*SKIP)c|b(*ACCEPT)|/ was studied, it stopped computing the minimum length on reaching *ACCEPT, and so ended up with the wrong value of 1 rather than 0. Further investigation indicates that computing a minimum subject length in the presence of *ACCEPT is difficult (think back references, subroutine calls), and so I have changed the code so that no minimum is registered for a pattern that contains *ACCEPT. 8. If (*THEN) was present in the first (true) branch of a conditional group, it was not handled as intended. [But see 16 below.] 9. Replaced RunTest.bat and CMakeLists.txt with improved versions provided by Sheri Pierce. 10. A pathological pattern such as /(*ACCEPT)a/ was miscompiled, thinking that the first byte in a match must be "a". 11. Change 17 for 8.13 increased the recursion depth for patterns like /a(?:.)*?a/ drastically. I've improved things by remembering whether a pattern contains any instances of (*THEN). If it does not, the old optimizations are restored. It would be nice to do this on a per-group basis, but at the moment that is not feasible. 12. In some environments, the output of pcretest -C is CRLF terminated. This broke RunTest's code that checks for the link size. A single white space character after the value is now allowed for. 13. RunTest now checks for the "fr" locale as well as for "fr_FR" and "french". For "fr", it uses the Windows-specific input and output files. 14. If (*THEN) appeared in a group that was called recursively or as a subroutine, it did not work as intended. [But see next item.] 15. Consider the pattern /A (B(*THEN)C) | D/ where A, B, C, and D are complex pattern fragments (but not containing any | characters). If A and B are matched, but there is a failure in C so that it backtracks to (*THEN), PCRE was behaving differently to Perl. PCRE backtracked into A, but Perl goes to D. In other words, Perl considers parentheses that do not contain any | characters to be part of a surrounding alternative, whereas PCRE was treading (B(*THEN)C) the same as (B(*THEN)C|(*FAIL)) -- which Perl handles differently. PCRE now behaves in the same way as Perl, except in the case of subroutine/recursion calls such as (?1) which have in any case always been different (but PCRE had them first :-). 16. Related to 15 above: Perl does not treat the | in a conditional group as creating alternatives. Such a group is treated in the same way as an ordinary group without any | characters when processing (*THEN). PCRE has been changed to match Perl's behaviour. 17. If a user had set PCREGREP_COLO(U)R to something other than 1:31, the RunGrepTest script failed. 18. Change 22 for version 13 caused atomic groups to use more stack. This is inevitable for groups that contain captures, but it can lead to a lot of stack use in large patterns. The old behaviour has been restored for atomic groups that do not contain any capturing parentheses. 19. If the PCRE_NO_START_OPTIMIZE option was set for pcre_compile(), it did not suppress the check for a minimum subject length at run time. (If it was given to pcre_exec() or pcre_dfa_exec() it did work.) 20. Fixed an ASCII-dependent infelicity in pcretest that would have made it fail to work when decoding hex characters in data strings in EBCDIC environments. 21. It appears that in at least one Mac OS environment, the isxdigit() function is implemented as a macro that evaluates to its argument more than once, contravening the C 90 Standard (I haven't checked a later standard). There was an instance in pcretest which caused it to go wrong when processing \x{...} escapes in subject strings. The has been rewritten to avoid using things like p++ in the argument of isxdigit(). Version 8.13 16-Aug-2011 ------------------------ 1. The Unicode data tables have been updated to Unicode 6.0.0. 2. Two minor typos in pcre_internal.h have been fixed. 3. Added #include to pcre_scanner_unittest.cc, pcrecpp.cc, and pcrecpp_unittest.cc. They are needed for strcmp(), memset(), and strchr() in some environments (e.g. Solaris 10/SPARC using Sun Studio 12U2). 4. There were a number of related bugs in the code for matching backrefences caselessly in UTF-8 mode when codes for the characters concerned were different numbers of bytes. For example, U+023A and U+2C65 are an upper and lower case pair, using 2 and 3 bytes, respectively. The main bugs were: (a) A reference to 3 copies of a 2-byte code matched only 2 of a 3-byte code. (b) A reference to 2 copies of a 3-byte code would not match 2 of a 2-byte code at the end of the subject (it thought there wasn't enough data left). 5. Comprehensive information about what went wrong is now returned by pcre_exec() and pcre_dfa_exec() when the UTF-8 string check fails, as long as the output vector has at least 2 elements. The offset of the start of the failing character and a reason code are placed in the vector. 6. When the UTF-8 string check fails for pcre_compile(), the offset that is now returned is for the first byte of the failing character, instead of the last byte inspected. This is an incompatible change, but I hope it is small enough not to be a problem. It makes the returned offset consistent with pcre_exec() and pcre_dfa_exec(). 7. pcretest now gives a text phrase as well as the error number when pcre_exec() or pcre_dfa_exec() fails; if the error is a UTF-8 check failure, the offset and reason code are output. 8. When \R was used with a maximizing quantifier it failed to skip backwards over a \r\n pair if the subsequent match failed. Instead, it just skipped back over a single character (\n). This seems wrong (because it treated the two characters as a single entity when going forwards), conflicts with the documentation that \R is equivalent to (?>\r\n|\n|...etc), and makes the behaviour of \R* different to (\R)*, which also seems wrong. The behaviour has been changed. 9. Some internal refactoring has changed the processing so that the handling of the PCRE_CASELESS and PCRE_MULTILINE options is done entirely at compile time (the PCRE_DOTALL option was changed this way some time ago: version 7.7 change 16). This has made it possible to abolish the OP_OPT op code, which was always a bit of a fudge. It also means that there is one less argument for the match() function, which reduces its stack requirements slightly. This change also fixes an incompatibility with Perl: the pattern (?i:([^b]))(?1) should not match "ab", but previously PCRE gave a match. 10. More internal refactoring has drastically reduced the number of recursive calls to match() for possessively repeated groups such as (abc)++ when using pcre_exec(). 11. While implementing 10, a number of bugs in the handling of groups were discovered and fixed: (?<=(a)+) was not diagnosed as invalid (non-fixed-length lookbehind). (a|)*(?1) gave a compile-time internal error. ((a|)+)+ did not notice that the outer group could match an empty string. (^a|^)+ was not marked as anchored. (.*a|.*)+ was not marked as matching at start or after a newline. 12. Yet more internal refactoring has removed another argument from the match() function. Special calls to this function are now indicated by setting a value in a variable in the "match data" data block. 13. Be more explicit in pcre_study() instead of relying on "default" for opcodes that mean there is no starting character; this means that when new ones are added and accidentally left out of pcre_study(), testing should pick them up. 14. The -s option of pcretest has been documented for ages as being an old synonym of -m (show memory usage). I have changed it to mean "force study for every regex", that is, assume /S for every regex. This is similar to -i and -d etc. It's slightly incompatible, but I'm hoping nobody is still using it. It makes it easier to run collections of tests with and without study enabled, and thereby test pcre_study() more easily. All the standard tests are now run with and without -s (but some patterns can be marked as "never study" - see 20 below). 15. When (*ACCEPT) was used in a subpattern that was called recursively, the restoration of the capturing data to the outer values was not happening correctly. 16. If a recursively called subpattern ended with (*ACCEPT) and matched an empty string, and PCRE_NOTEMPTY was set, pcre_exec() thought the whole pattern had matched an empty string, and so incorrectly returned a no match. 17. There was optimizing code for the last branch of non-capturing parentheses, and also for the obeyed branch of a conditional subexpression, which used tail recursion to cut down on stack usage. Unfortunately, now that there is the possibility of (*THEN) occurring in these branches, tail recursion is no longer possible because the return has to be checked for (*THEN). These two optimizations have therefore been removed. [But see 8.20/11 above.] 18. If a pattern containing \R was studied, it was assumed that \R always matched two bytes, thus causing the minimum subject length to be incorrectly computed because \R can also match just one byte. 19. If a pattern containing (*ACCEPT) was studied, the minimum subject length was incorrectly computed. 20. If /S is present twice on a test pattern in pcretest input, it now *disables* studying, thereby overriding the use of -s on the command line (see 14 above). This is necessary for one or two tests to keep the output identical in both cases. 21. When (*ACCEPT) was used in an assertion that matched an empty string and PCRE_NOTEMPTY was set, PCRE applied the non-empty test to the assertion. 22. When an atomic group that contained a capturing parenthesis was successfully matched, but the branch in which it appeared failed, the capturing was not being forgotten if a higher numbered group was later captured. For example, /(?>(a))b|(a)c/ when matching "ac" set capturing group 1 to "a", when in fact it should be unset. This applied to multi- branched capturing and non-capturing groups, repeated or not, and also to positive assertions (capturing in negative assertions does not happen in PCRE) and also to nested atomic groups. 23. Add the ++ qualifier feature to pcretest, to show the remainder of the subject after a captured substring, to make it easier to tell which of a number of identical substrings has been captured. 24. The way atomic groups are processed by pcre_exec() has been changed so that if they are repeated, backtracking one repetition now resets captured values correctly. For example, if ((?>(a+)b)+aabab) is matched against "aaaabaaabaabab" the value of captured group 2 is now correctly recorded as "aaa". Previously, it would have been "a". As part of this code refactoring, the way recursive calls are handled has also been changed. 25. If an assertion condition captured any substrings, they were not passed back unless some other capturing happened later. For example, if (?(?=(a))a) was matched against "a", no capturing was returned. 26. When studying a pattern that contained subroutine calls or assertions, the code for finding the minimum length of a possible match was handling direct recursions such as (xxx(?1)|yyy) but not mutual recursions (where group 1 called group 2 while simultaneously a separate group 2 called group 1). A stack overflow occurred in this case. I have fixed this by limiting the recursion depth to 10. 27. Updated RunTest.bat in the distribution to the version supplied by Tom Fortmann. This supports explicit test numbers on the command line, and has argument validation and error reporting. 28. An instance of \X with an unlimited repeat could fail if at any point the first character it looked at was a mark character. 29. Some minor code refactoring concerning Unicode properties and scripts should reduce the stack requirement of match() slightly. 30. Added the '=' option to pcretest to check the setting of unused capturing slots at the end of the pattern, which are documented as being -1, but are not included in the return count. 31. If \k was not followed by a braced, angle-bracketed, or quoted name, PCRE compiled something random. Now it gives a compile-time error (as does Perl). 32. A *MARK encountered during the processing of a positive assertion is now recorded and passed back (compatible with Perl). 33. If --only-matching or --colour was set on a pcregrep call whose pattern had alternative anchored branches, the search for a second match in a line was done as if at the line start. Thus, for example, /^01|^02/ incorrectly matched the line "0102" twice. The same bug affected patterns that started with a backwards assertion. For example /\b01|\b02/ also matched "0102" twice. 34. Previously, PCRE did not allow quantification of assertions. However, Perl does, and because of capturing effects, quantifying parenthesized assertions may at times be useful. Quantifiers are now allowed for parenthesized assertions. 35. A minor code tidy in pcre_compile() when checking options for \R usage. 36. \g was being checked for fancy things in a character class, when it should just be a literal "g". 37. PCRE was rejecting [:a[:digit:]] whereas Perl was not. It seems that the appearance of a nested POSIX class supersedes an apparent external class. For example, [:a[:digit:]b:] matches "a", "b", ":", or a digit. Also, unescaped square brackets may also appear as part of class names. For example, [:a[:abc]b:] gives unknown class "[:abc]b:]". PCRE now behaves more like Perl. (But see 8.20/1 above.) 38. PCRE was giving an error for \N with a braced quantifier such as {1,} (this was because it thought it was \N{name}, which is not supported). 39. Add minix to OS list not supporting the -S option in pcretest. 40. PCRE tries to detect cases of infinite recursion at compile time, but it cannot analyze patterns in sufficient detail to catch mutual recursions such as ((?1))((?2)). There is now a runtime test that gives an error if a subgroup is called recursively as a subpattern for a second time at the same position in the subject string. In previous releases this might have been caught by the recursion limit, or it might have run out of stack. 41. A pattern such as /(?(R)a+|(?R)b)/ is quite safe, as the recursion can happen only once. PCRE was, however incorrectly giving a compile time error "recursive call could loop indefinitely" because it cannot analyze the pattern in sufficient detail. The compile time test no longer happens when PCRE is compiling a conditional subpattern, but actual runaway loops are now caught at runtime (see 40 above). 42. It seems that Perl allows any characters other than a closing parenthesis to be part of the NAME in (*MARK:NAME) and other backtracking verbs. PCRE has been changed to be the same. 43. Updated configure.ac to put in more quoting round AC_LANG_PROGRAM etc. so as not to get warnings when autogen.sh is called. Also changed AC_PROG_LIBTOOL (deprecated) to LT_INIT (the current macro). 44. To help people who use pcregrep to scan files containing exceedingly long lines, the following changes have been made: (a) The default value of the buffer size parameter has been increased from 8K to 20K. (The actual buffer used is three times this size.) (b) The default can be changed by ./configure --with-pcregrep-bufsize when PCRE is built. (c) A --buffer-size=n option has been added to pcregrep, to allow the size to be set at run time. (d) Numerical values in pcregrep options can be followed by K or M, for example --buffer-size=50K. (e) If a line being scanned overflows pcregrep's buffer, an error is now given and the return code is set to 2. 45. Add a pointer to the latest mark to the callout data block. 46. The pattern /.(*F)/, when applied to "abc" with PCRE_PARTIAL_HARD, gave a partial match of an empty string instead of no match. This was specific to the use of ".". 47. The pattern /f.*/8s, when applied to "for" with PCRE_PARTIAL_HARD, gave a complete match instead of a partial match. This bug was dependent on both the PCRE_UTF8 and PCRE_DOTALL options being set. 48. For a pattern such as /\babc|\bdef/ pcre_study() was failing to set up the starting byte set, because \b was not being ignored. Version 8.12 15-Jan-2011 ------------------------ 1. Fixed some typos in the markup of the man pages, and wrote a script that checks for such things as part of the documentation building process. 2. On a big-endian 64-bit system, pcregrep did not correctly process the --match-limit and --recursion-limit options (added for 8.11). In particular, this made one of the standard tests fail. (The integer value went into the wrong half of a long int.) 3. If the --colour option was given to pcregrep with -v (invert match), it did strange things, either producing crazy output, or crashing. It should, of course, ignore a request for colour when reporting lines that do not match. 4. Another pcregrep bug caused similar problems if --colour was specified with -M (multiline) and the pattern match finished with a line ending. 5. In pcregrep, when a pattern that ended with a literal newline sequence was matched in multiline mode, the following line was shown as part of the match. This seems wrong, so I have changed it. 6. Another pcregrep bug in multiline mode, when --colour was specified, caused the check for further matches in the same line (so they could be coloured) to overrun the end of the current line. If another match was found, it was incorrectly shown (and then shown again when found in the next line). 7. If pcregrep was compiled under Windows, there was a reference to the function pcregrep_exit() before it was defined. I am assuming this was the cause of the "error C2371: 'pcregrep_exit' : redefinition;" that was reported by a user. I've moved the definition above the reference. Version 8.11 10-Dec-2010 ------------------------ 1. (*THEN) was not working properly if there were untried alternatives prior to it in the current branch. For example, in ((a|b)(*THEN)(*F)|c..) it backtracked to try for "b" instead of moving to the next alternative branch at the same level (in this case, to look for "c"). The Perl documentation is clear that when (*THEN) is backtracked onto, it goes to the "next alternative in the innermost enclosing group". 2. (*COMMIT) was not overriding (*THEN), as it does in Perl. In a pattern such as (A(*COMMIT)B(*THEN)C|D) any failure after matching A should result in overall failure. Similarly, (*COMMIT) now overrides (*PRUNE) and (*SKIP), (*SKIP) overrides (*PRUNE) and (*THEN), and (*PRUNE) overrides (*THEN). 3. If \s appeared in a character class, it removed the VT character from the class, even if it had been included by some previous item, for example in [\x00-\xff\s]. (This was a bug related to the fact that VT is not part of \s, but is part of the POSIX "space" class.) 4. A partial match never returns an empty string (because you can always match an empty string at the end of the subject); however the checking for an empty string was starting at the "start of match" point. This has been changed to the "earliest inspected character" point, because the returned data for a partial match starts at this character. This means that, for example, /(?<=abc)def/ gives a partial match for the subject "abc" (previously it gave "no match"). 5. Changes have been made to the way PCRE_PARTIAL_HARD affects the matching of $, \z, \Z, \b, and \B. If the match point is at the end of the string, previously a full match would be given. However, setting PCRE_PARTIAL_HARD has an implication that the given string is incomplete (because a partial match is preferred over a full match). For this reason, these items now give a partial match in this situation. [Aside: previously, the one case /t\b/ matched against "cat" with PCRE_PARTIAL_HARD set did return a partial match rather than a full match, which was wrong by the old rules, but is now correct.] 6. There was a bug in the handling of #-introduced comments, recognized when PCRE_EXTENDED is set, when PCRE_NEWLINE_ANY and PCRE_UTF8 were also set. If a UTF-8 multi-byte character included the byte 0x85 (e.g. +U0445, whose UTF-8 encoding is 0xd1,0x85), this was misinterpreted as a newline when scanning for the end of the comment. (*Character* 0x85 is an "any" newline, but *byte* 0x85 is not, in UTF-8 mode). This bug was present in several places in pcre_compile(). 7. Related to (6) above, when pcre_compile() was skipping #-introduced comments when looking ahead for named forward references to subpatterns, the only newline sequence it recognized was NL. It now handles newlines according to the set newline convention. 8. SunOS4 doesn't have strerror() or strtoul(); pcregrep dealt with the former, but used strtoul(), whereas pcretest avoided strtoul() but did not cater for a lack of strerror(). These oversights have been fixed. 9. Added --match-limit and --recursion-limit to pcregrep. 10. Added two casts needed to build with Visual Studio when NO_RECURSE is set. 11. When the -o option was used, pcregrep was setting a return code of 1, even when matches were found, and --line-buffered was not being honoured. 12. Added an optional parentheses number to the -o and --only-matching options of pcregrep. 13. Imitating Perl's /g action for multiple matches is tricky when the pattern can match an empty string. The code to do it in pcretest and pcredemo needed fixing: (a) When the newline convention was "crlf", pcretest got it wrong, skipping only one byte after an empty string match just before CRLF (this case just got forgotten; "any" and "anycrlf" were OK). (b) The pcretest code also had a bug, causing it to loop forever in UTF-8 mode when an empty string match preceded an ASCII character followed by a non-ASCII character. (The code for advancing by one character rather than one byte was nonsense.) (c) The pcredemo.c sample program did not have any code at all to handle the cases when CRLF is a valid newline sequence. 14. Neither pcre_exec() nor pcre_dfa_exec() was checking that the value given as a starting offset was within the subject string. There is now a new error, PCRE_ERROR_BADOFFSET, which is returned if the starting offset is negative or greater than the length of the string. In order to test this, pcretest is extended to allow the setting of negative starting offsets. 15. In both pcre_exec() and pcre_dfa_exec() the code for checking that the starting offset points to the beginning of a UTF-8 character was unnecessarily clumsy. I tidied it up. 16. Added PCRE_ERROR_SHORTUTF8 to make it possible to distinguish between a bad UTF-8 sequence and one that is incomplete when using PCRE_PARTIAL_HARD. 17. Nobody had reported that the --include_dir option, which was added in release 7.7 should have been called --include-dir (hyphen, not underscore) for compatibility with GNU grep. I have changed it to --include-dir, but left --include_dir as an undocumented synonym, and the same for --exclude-dir, though that is not available in GNU grep, at least as of release 2.5.4. 18. At a user's suggestion, the macros GETCHAR and friends (which pick up UTF-8 characters from a string of bytes) have been redefined so as not to use loops, in order to improve performance in some environments. At the same time, I abstracted some of the common code into auxiliary macros to save repetition (this should not affect the compiled code). 19. If \c was followed by a multibyte UTF-8 character, bad things happened. A compile-time error is now given if \c is not followed by an ASCII character, that is, a byte less than 128. (In EBCDIC mode, the code is different, and any byte value is allowed.) 20. Recognize (*NO_START_OPT) at the start of a pattern to set the PCRE_NO_ START_OPTIMIZE option, which is now allowed at compile time - but just passed through to pcre_exec() or pcre_dfa_exec(). This makes it available to pcregrep and other applications that have no direct access to PCRE options. The new /Y option in pcretest sets this option when calling pcre_compile(). 21. Change 18 of release 8.01 broke the use of named subpatterns for recursive back references. Groups containing recursive back references were forced to be atomic by that change, but in the case of named groups, the amount of memory required was incorrectly computed, leading to "Failed: internal error: code overflow". This has been fixed. 22. Some patches to pcre_stringpiece.h, pcre_stringpiece_unittest.cc, and pcretest.c, to avoid build problems in some Borland environments. Version 8.10 25-Jun-2010 ------------------------ 1. Added support for (*MARK:ARG) and for ARG additions to PRUNE, SKIP, and THEN. 2. (*ACCEPT) was not working when inside an atomic group. 3. Inside a character class, \B is treated as a literal by default, but faulted if PCRE_EXTRA is set. This mimics Perl's behaviour (the -w option causes the error). The code is unchanged, but I tidied the documentation. 4. Inside a character class, PCRE always treated \R and \X as literals, whereas Perl faults them if its -w option is set. I have changed PCRE so that it faults them when PCRE_EXTRA is set. 5. Added support for \N, which always matches any character other than newline. (It is the same as "." when PCRE_DOTALL is not set.) 6. When compiling pcregrep with newer versions of gcc which may have FORTIFY_SOURCE set, several warnings "ignoring return value of 'fwrite', declared with attribute warn_unused_result" were given. Just casting the result to (void) does not stop the warnings; a more elaborate fudge is needed. I've used a macro to implement this. 7. Minor change to pcretest.c to avoid a compiler warning. 8. Added four artifical Unicode properties to help with an option to make \s etc use properties (see next item). The new properties are: Xan (alphanumeric), Xsp (Perl space), Xps (POSIX space), and Xwd (word). 9. Added PCRE_UCP to make \b, \d, \s, \w, and certain POSIX character classes use Unicode properties. (*UCP) at the start of a pattern can be used to set this option. Modified pcretest to add /W to test this facility. Added REG_UCP to make it available via the POSIX interface. 10. Added --line-buffered to pcregrep. 11. In UTF-8 mode, if a pattern that was compiled with PCRE_CASELESS was studied, and the match started with a letter with a code point greater than 127 whose first byte was different to the first byte of the other case of the letter, the other case of this starting letter was not recognized (#976). 12. If a pattern that was studied started with a repeated Unicode property test, for example, \p{Nd}+, there was the theoretical possibility of setting up an incorrect bitmap of starting bytes, but fortunately it could not have actually happened in practice until change 8 above was made (it added property types that matched character-matching opcodes). 13. pcre_study() now recognizes \h, \v, and \R when constructing a bit map of possible starting bytes for non-anchored patterns. 14. Extended the "auto-possessify" feature of pcre_compile(). It now recognizes \R, and also a number of cases that involve Unicode properties, both explicit and implicit when PCRE_UCP is set. 15. If a repeated Unicode property match (e.g. \p{Lu}*) was used with non-UTF-8 input, it could crash or give wrong results if characters with values greater than 0xc0 were present in the subject string. (Detail: it assumed UTF-8 input when processing these items.) 16. Added a lot of (int) casts to avoid compiler warnings in systems where size_t is 64-bit (#991). 17. Added a check for running out of memory when PCRE is compiled with --disable-stack-for-recursion (#990). 18. If the last data line in a file for pcretest does not have a newline on the end, a newline was missing in the output. 19. The default pcre_chartables.c file recognizes only ASCII characters (values less than 128) in its various bitmaps. However, there is a facility for generating tables according to the current locale when PCRE is compiled. It turns out that in some environments, 0x85 and 0xa0, which are Unicode space characters, are recognized by isspace() and therefore were getting set in these tables, and indeed these tables seem to approximate to ISO 8859. This caused a problem in UTF-8 mode when pcre_study() was used to create a list of bytes that can start a match. For \s, it was including 0x85 and 0xa0, which of course cannot start UTF-8 characters. I have changed the code so that only real ASCII characters (less than 128) and the correct starting bytes for UTF-8 encodings are set for characters greater than 127 when in UTF-8 mode. (When PCRE_UCP is set - see 9 above - the code is different altogether.) 20. Added the /T option to pcretest so as to be able to run tests with non- standard character tables, thus making it possible to include the tests used for 19 above in the standard set of tests. 21. A pattern such as (?&t)(?#()(?(DEFINE)(?a)) which has a forward reference to a subpattern the other side of a comment that contains an opening parenthesis caused either an internal compiling error, or a reference to the wrong subpattern. Version 8.02 19-Mar-2010 ------------------------ 1. The Unicode data tables have been updated to Unicode 5.2.0. 2. Added the option --libs-cpp to pcre-config, but only when C++ support is configured. 3. Updated the licensing terms in the pcregexp.pas file, as agreed with the original author of that file, following a query about its status. 4. On systems that do not have stdint.h (e.g. Solaris), check for and include inttypes.h instead. This fixes a bug that was introduced by change 8.01/8. 5. A pattern such as (?&t)*+(?(DEFINE)(?.)) which has a possessive quantifier applied to a forward-referencing subroutine call, could compile incorrect code or give the error "internal error: previously-checked referenced subpattern not found". 6. Both MS Visual Studio and Symbian OS have problems with initializing variables to point to external functions. For these systems, therefore, pcre_malloc etc. are now initialized to local functions that call the relevant global functions. 7. There were two entries missing in the vectors called coptable and poptable in pcre_dfa_exec.c. This could lead to memory accesses outsize the vectors. I've fixed the data, and added a kludgy way of testing at compile time that the lengths are correct (equal to the number of opcodes). 8. Following on from 7, I added a similar kludge to check the length of the eint vector in pcreposix.c. 9. Error texts for pcre_compile() are held as one long string to avoid too much relocation at load time. To find a text, the string is searched, counting zeros. There was no check for running off the end of the string, which could happen if a new error number was added without updating the string. 10. \K gave a compile-time error if it appeared in a lookbehind assersion. 11. \K was not working if it appeared in an atomic group or in a group that was called as a "subroutine", or in an assertion. Perl 5.11 documents that \K is "not well defined" if used in an assertion. PCRE now accepts it if the assertion is positive, but not if it is negative. 12. Change 11 fortuitously reduced the size of the stack frame used in the "match()" function of pcre_exec.c by one pointer. Forthcoming implementation of support for (*MARK) will need an extra pointer on the stack; I have reserved it now, so that the stack frame size does not decrease. 13. A pattern such as (?P(?P0)|(?P>L2)(?P>L1)) in which the only other item in branch that calls a recursion is a subroutine call - as in the second branch in the above example - was incorrectly given the compile- time error "recursive call could loop indefinitely" because pcre_compile() was not correctly checking the subroutine for matching a non-empty string. 14. The checks for overrunning compiling workspace could trigger after an overrun had occurred. This is a "should never occur" error, but it can be triggered by pathological patterns such as hundreds of nested parentheses. The checks now trigger 100 bytes before the end of the workspace. 15. Fix typo in configure.ac: "srtoq" should be "strtoq". Version 8.01 19-Jan-2010 ------------------------ 1. If a pattern contained a conditional subpattern with only one branch (in particular, this includes all (*DEFINE) patterns), a call to pcre_study() computed the wrong minimum data length (which is of course zero for such subpatterns). This could cause incorrect "no match" results. 2. For patterns such as (?i)a(?-i)b|c where an option setting at the start of the pattern is reset in the first branch, pcre_compile() failed with "internal error: code overflow at offset...". This happened only when the reset was to the original external option setting. (An optimization abstracts leading options settings into an external setting, which was the cause of this.) 3. A pattern such as ^(?!a(*SKIP)b) where a negative assertion contained one of the verbs SKIP, PRUNE, or COMMIT, did not work correctly. When the assertion pattern did not match (meaning that the assertion was true), it was incorrectly treated as false if the SKIP had been reached during the matching. This also applied to assertions used as conditions. 4. If an item that is not supported by pcre_dfa_exec() was encountered in an assertion subpattern, including such a pattern used as a condition, unpredictable results occurred, instead of the error return PCRE_ERROR_DFA_UITEM. 5. The C++ GlobalReplace function was not working like Perl for the special situation when an empty string is matched. It now does the fancy magic stuff that is necessary. 6. In pcre_internal.h, obsolete includes to setjmp.h and stdarg.h have been removed. (These were left over from very, very early versions of PCRE.) 7. Some cosmetic changes to the code to make life easier when compiling it as part of something else: (a) Change DEBUG to PCRE_DEBUG. (b) In pcre_compile(), rename the member of the "branch_chain" structure called "current" as "current_branch", to prevent a collision with the Linux macro when compiled as a kernel module. (c) In pcre_study(), rename the function set_bit() as set_table_bit(), to prevent a collision with the Linux macro when compiled as a kernel module. 8. In pcre_compile() there are some checks for integer overflows that used to cast potentially large values to (double). This has been changed to that when building, a check for int64_t is made, and if it is found, it is used instead, thus avoiding the use of floating point arithmetic. (There is no other use of FP in PCRE.) If int64_t is not found, the fallback is to double. 9. Added two casts to avoid signed/unsigned warnings from VS Studio Express 2005 (difference between two addresses compared to an unsigned value). 10. Change the standard AC_CHECK_LIB test for libbz2 in configure.ac to a custom one, because of the following reported problem in Windows: - libbz2 uses the Pascal calling convention (WINAPI) for the functions under Win32. - The standard autoconf AC_CHECK_LIB fails to include "bzlib.h", therefore missing the function definition. - The compiler thus generates a "C" signature for the test function. - The linker fails to find the "C" function. - PCRE fails to configure if asked to do so against libbz2. 11. When running libtoolize from libtool-2.2.6b as part of autogen.sh, these messages were output: Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and rerunning libtoolize, to keep the correct libtool macros in-tree. Consider adding `-I m4' to ACLOCAL_AMFLAGS in Makefile.am. I have done both of these things. 12. Although pcre_dfa_exec() does not use nearly as much stack as pcre_exec() most of the time, it *can* run out if it is given a pattern that contains a runaway infinite recursion. I updated the discussion in the pcrestack man page. 13. Now that we have gone to the x.xx style of version numbers, the minor version may start with zero. Using 08 or 09 is a bad idea because users might check the value of PCRE_MINOR in their code, and 08 or 09 may be interpreted as invalid octal numbers. I've updated the previous comment in configure.ac, and also added a check that gives an error if 08 or 09 are used. 14. Change 8.00/11 was not quite complete: code had been accidentally omitted, causing partial matching to fail when the end of the subject matched \W in a UTF-8 pattern where \W was quantified with a minimum of 3. 15. There were some discrepancies between the declarations in pcre_internal.h of _pcre_is_newline(), _pcre_was_newline(), and _pcre_valid_utf8() and their definitions. The declarations used "const uschar *" and the definitions used USPTR. Even though USPTR is normally defined as "const unsigned char *" (and uschar is typedeffed as "unsigned char"), it was reported that: "This difference in casting confuses some C++ compilers, for example, SunCC recognizes above declarations as different functions and generates broken code for hbpcre." I have changed the declarations to use USPTR. 16. GNU libtool is named differently on some systems. The autogen.sh script now tries several variants such as glibtoolize (MacOSX) and libtoolize1x (FreeBSD). 17. Applied Craig's patch that fixes an HP aCC compile error in pcre 8.00 (strtoXX undefined when compiling pcrecpp.cc). The patch contains this comment: "Figure out how to create a longlong from a string: strtoll and equivalent. It's not enough to call AC_CHECK_FUNCS: hpux has a strtoll, for instance, but it only takes 2 args instead of 3!" 18. A subtle bug concerned with back references has been fixed by a change of specification, with a corresponding code fix. A pattern such as ^(xa|=?\1a)+$ which contains a back reference inside the group to which it refers, was giving matches when it shouldn't. For example, xa=xaaa would match that pattern. Interestingly, Perl (at least up to 5.11.3) has the same bug. Such groups have to be quantified to be useful, or contained inside another quantified group. (If there's no repetition, the reference can never match.) The problem arises because, having left the group and moved on to the rest of the pattern, a later failure that backtracks into the group uses the captured value from the final iteration of the group rather than the correct earlier one. I have fixed this in PCRE by forcing any group that contains a reference to itself to be an atomic group; that is, there cannot be any backtracking into it once it has completed. This is similar to recursive and subroutine calls. Version 8.00 19-Oct-09 ---------------------- 1. The table for translating pcre_compile() error codes into POSIX error codes was out-of-date, and there was no check on the pcre_compile() error code being within the table. This could lead to an OK return being given in error. 2. Changed the call to open a subject file in pcregrep from fopen(pathname, "r") to fopen(pathname, "rb"), which fixed a problem with some of the tests in a Windows environment. 3. The pcregrep --count option prints the count for each file even when it is zero, as does GNU grep. However, pcregrep was also printing all files when --files-with-matches was added. Now, when both options are given, it prints counts only for those files that have at least one match. (GNU grep just prints the file name in this circumstance, but including the count seems more useful - otherwise, why use --count?) Also ensured that the combination -clh just lists non-zero counts, with no names. 4. The long form of the pcregrep -F option was incorrectly implemented as --fixed_strings instead of --fixed-strings. This is an incompatible change, but it seems right to fix it, and I didn't think it was worth preserving the old behaviour. 5. The command line items --regex=pattern and --regexp=pattern were not recognized by pcregrep, which required --regex pattern or --regexp pattern (with a space rather than an '='). The man page documented the '=' forms, which are compatible with GNU grep; these now work. 6. No libpcreposix.pc file was created for pkg-config; there was just libpcre.pc and libpcrecpp.pc. The omission has been rectified. 7. Added #ifndef SUPPORT_UCP into the pcre_ucd.c module, to reduce its size when UCP support is not needed, by modifying the Python script that generates it from Unicode data files. This should not matter if the module is correctly used as a library, but I received one complaint about 50K of unwanted data. My guess is that the person linked everything into his program rather than using a library. Anyway, it does no harm. 8. A pattern such as /\x{123}{2,2}+/8 was incorrectly compiled; the trigger was a minimum greater than 1 for a wide character in a possessive repetition. The same bug could also affect patterns like /(\x{ff}{0,2})*/8 which had an unlimited repeat of a nested, fixed maximum repeat of a wide character. Chaos in the form of incorrect output or a compiling loop could result. 9. The restrictions on what a pattern can contain when partial matching is requested for pcre_exec() have been removed. All patterns can now be partially matched by this function. In addition, if there are at least two slots in the offset vector, the offset of the earliest inspected character for the match and the offset of the end of the subject are set in them when PCRE_ERROR_PARTIAL is returned. 10. Partial matching has been split into two forms: PCRE_PARTIAL_SOFT, which is synonymous with PCRE_PARTIAL, for backwards compatibility, and PCRE_PARTIAL_HARD, which causes a partial match to supersede a full match, and may be more useful for multi-segment matching. 11. Partial matching with pcre_exec() is now more intuitive. A partial match used to be given if ever the end of the subject was reached; now it is given only if matching could not proceed because another character was needed. This makes a difference in some odd cases such as Z(*FAIL) with the string "Z", which now yields "no match" instead of "partial match". In the case of pcre_dfa_exec(), "no match" is given if every matching path for the final character ended with (*FAIL). 12. Restarting a match using pcre_dfa_exec() after a partial match did not work if the pattern had a "must contain" character that was already found in the earlier partial match, unless partial matching was again requested. For example, with the pattern /dog.(body)?/, the "must contain" character is "g". If the first part-match was for the string "dog", restarting with "sbody" failed. This bug has been fixed. 13. The string returned by pcre_dfa_exec() after a partial match has been changed so that it starts at the first inspected character rather than the first character of the match. This makes a difference only if the pattern starts with a lookbehind assertion or \b or \B (\K is not supported by pcre_dfa_exec()). It's an incompatible change, but it makes the two matching functions compatible, and I think it's the right thing to do. 14. Added a pcredemo man page, created automatically from the pcredemo.c file, so that the demonstration program is easily available in environments where PCRE has not been installed from source. 15. Arranged to add -DPCRE_STATIC to cflags in libpcre.pc, libpcreposix.cp, libpcrecpp.pc and pcre-config when PCRE is not compiled as a shared library. 16. Added REG_UNGREEDY to the pcreposix interface, at the request of a user. It maps to PCRE_UNGREEDY. It is not, of course, POSIX-compatible, but it is not the first non-POSIX option to be added. Clearly some people find these options useful. 17. If a caller to the POSIX matching function regexec() passes a non-zero value for nmatch with a NULL value for pmatch, the value of nmatch is forced to zero. 18. RunGrepTest did not have a test for the availability of the -u option of the diff command, as RunTest does. It now checks in the same way as RunTest, and also checks for the -b option. 19. If an odd number of negated classes containing just a single character interposed, within parentheses, between a forward reference to a named subpattern and the definition of the subpattern, compilation crashed with an internal error, complaining that it could not find the referenced subpattern. An example of a crashing pattern is /(?&A)(([^m])(?))/. [The bug was that it was starting one character too far in when skipping over the character class, thus treating the ] as data rather than terminating the class. This meant it could skip too much.] 20. Added PCRE_NOTEMPTY_ATSTART in order to be able to correctly implement the /g option in pcretest when the pattern contains \K, which makes it possible to have an empty string match not at the start, even when the pattern is anchored. Updated pcretest and pcredemo to use this option. 21. If the maximum number of capturing subpatterns in a recursion was greater than the maximum at the outer level, the higher number was returned, but with unset values at the outer level. The correct (outer level) value is now given. 22. If (*ACCEPT) appeared inside capturing parentheses, previous releases of PCRE did not set those parentheses (unlike Perl). I have now found a way to make it do so. The string so far is captured, making this feature compatible with Perl. 23. The tests have been re-organized, adding tests 11 and 12, to make it possible to check the Perl 5.10 features against Perl 5.10. 24. Perl 5.10 allows subroutine calls in lookbehinds, as long as the subroutine pattern matches a fixed length string. PCRE did not allow this; now it does. Neither allows recursion. 25. I finally figured out how to implement a request to provide the minimum length of subject string that was needed in order to match a given pattern. (It was back references and recursion that I had previously got hung up on.) This code has now been added to pcre_study(); it finds a lower bound to the length of subject needed. It is not necessarily the greatest lower bound, but using it to avoid searching strings that are too short does give some useful speed-ups. The value is available to calling programs via pcre_fullinfo(). 26. While implementing 25, I discovered to my embarrassment that pcretest had not been passing the result of pcre_study() to pcre_dfa_exec(), so the study optimizations had never been tested with that matching function. Oops. What is worse, even when it was passed study data, there was a bug in pcre_dfa_exec() that meant it never actually used it. Double oops. There were also very few tests of studied patterns with pcre_dfa_exec(). 27. If (?| is used to create subpatterns with duplicate numbers, they are now allowed to have the same name, even if PCRE_DUPNAMES is not set. However, on the other side of the coin, they are no longer allowed to have different names, because these cannot be distinguished in PCRE, and this has caused confusion. (This is a difference from Perl.) 28. When duplicate subpattern names are present (necessarily with different numbers, as required by 27 above), and a test is made by name in a conditional pattern, either for a subpattern having been matched, or for recursion in such a pattern, all the associated numbered subpatterns are tested, and the overall condition is true if the condition is true for any one of them. This is the way Perl works, and is also more like the way testing by number works. Version 7.9 11-Apr-09 --------------------- 1. When building with support for bzlib/zlib (pcregrep) and/or readline (pcretest), all targets were linked against these libraries. This included libpcre, libpcreposix, and libpcrecpp, even though they do not use these libraries. This caused unwanted dependencies to be created. This problem has been fixed, and now only pcregrep is linked with bzlib/zlib and only pcretest is linked with readline. 2. The "typedef int BOOL" in pcre_internal.h that was included inside the "#ifndef FALSE" condition by an earlier change (probably 7.8/18) has been moved outside it again, because FALSE and TRUE are already defined in AIX, but BOOL is not. 3. The pcre_config() function was treating the PCRE_MATCH_LIMIT and PCRE_MATCH_LIMIT_RECURSION values as ints, when they should be long ints. 4. The pcregrep documentation said spaces were inserted as well as colons (or hyphens) following file names and line numbers when outputting matching lines. This is not true; no spaces are inserted. I have also clarified the wording for the --colour (or --color) option. 5. In pcregrep, when --colour was used with -o, the list of matching strings was not coloured; this is different to GNU grep, so I have changed it to be the same. 6. When --colo(u)r was used in pcregrep, only the first matching substring in each matching line was coloured. Now it goes on to look for further matches of any of the test patterns, which is the same behaviour as GNU grep. 7. A pattern that could match an empty string could cause pcregrep to loop; it doesn't make sense to accept an empty string match in pcregrep, so I have locked it out (using PCRE's PCRE_NOTEMPTY option). By experiment, this seems to be how GNU grep behaves. 8. The pattern (?(?=.*b)b|^) was incorrectly compiled as "match must be at start or after a newline", because the conditional assertion was not being correctly handled. The rule now is that both the assertion and what follows in the first alternative must satisfy the test. 9. If auto-callout was enabled in a pattern with a conditional group whose condition was an assertion, PCRE could crash during matching, both with pcre_exec() and pcre_dfa_exec(). 10. The PCRE_DOLLAR_ENDONLY option was not working when pcre_dfa_exec() was used for matching. 11. Unicode property support in character classes was not working for characters (bytes) greater than 127 when not in UTF-8 mode. 12. Added the -M command line option to pcretest. 14. Added the non-standard REG_NOTEMPTY option to the POSIX interface. 15. Added the PCRE_NO_START_OPTIMIZE match-time option. 16. Added comments and documentation about mis-use of no_arg in the C++ wrapper. 17. Implemented support for UTF-8 encoding in EBCDIC environments, a patch from Martin Jerabek that uses macro names for all relevant character and string constants. 18. Added to pcre_internal.h two configuration checks: (a) If both EBCDIC and SUPPORT_UTF8 are set, give an error; (b) If SUPPORT_UCP is set without SUPPORT_UTF8, define SUPPORT_UTF8. The "configure" script handles both of these, but not everybody uses configure. 19. A conditional group that had only one branch was not being correctly recognized as an item that could match an empty string. This meant that an enclosing group might also not be so recognized, causing infinite looping (and probably a segfault) for patterns such as ^"((?(?=[a])[^"])|b)*"$ with the subject "ab", where knowledge that the repeated group can match nothing is needed in order to break the loop. 20. If a pattern that was compiled with callouts was matched using pcre_dfa_ exec(), but without supplying a callout function, matching went wrong. 21. If PCRE_ERROR_MATCHLIMIT occurred during a recursion, there was a memory leak if the size of the offset vector was greater than 30. When the vector is smaller, the saved offsets during recursion go onto a local stack vector, but for larger vectors malloc() is used. It was failing to free when the recursion yielded PCRE_ERROR_MATCH_LIMIT (or any other "abnormal" error, in fact). 22. There was a missing #ifdef SUPPORT_UTF8 round one of the variables in the heapframe that is used only when UTF-8 support is enabled. This caused no problem, but was untidy. 23. Steven Van Ingelgem's patch to CMakeLists.txt to change the name CMAKE_BINARY_DIR to PROJECT_BINARY_DIR so that it works when PCRE is included within another project. 24. Steven Van Ingelgem's patches to add more options to the CMake support, slightly modified by me: (a) PCRE_BUILD_TESTS can be set OFF not to build the tests, including not building pcregrep. (b) PCRE_BUILD_PCREGREP can be see OFF not to build pcregrep, but only if PCRE_BUILD_TESTS is also set OFF, because the tests use pcregrep. 25. Forward references, both numeric and by name, in patterns that made use of duplicate group numbers, could behave incorrectly or give incorrect errors, because when scanning forward to find the reference group, PCRE was not taking into account the duplicate group numbers. A pattern such as ^X(?3)(a)(?|(b)|(q))(Y) is an example. 26. Changed a few more instances of "const unsigned char *" to USPTR, making the feature of a custom pointer more persuasive (as requested by a user). 27. Wrapped the definitions of fileno and isatty for Windows, which appear in pcretest.c, inside #ifndefs, because it seems they are sometimes already pre-defined. 28. Added support for (*UTF8) at the start of a pattern. 29. Arrange for flags added by the "release type" setting in CMake to be shown in the configuration summary. Version 7.8 05-Sep-08 --------------------- 1. Replaced UCP searching code with optimized version as implemented for Ad Muncher (http://www.admuncher.com/) by Peter Kankowski. This uses a two- stage table and inline lookup instead of a function, giving speed ups of 2 to 5 times on some simple patterns that I tested. Permission was given to distribute the MultiStage2.py script that generates the tables (it's not in the tarball, but is in the Subversion repository). 2. Updated the Unicode datatables to Unicode 5.1.0. This adds yet more scripts. 3. Change 12 for 7.7 introduced a bug in pcre_study() when a pattern contained a group with a zero qualifier. The result of the study could be incorrect, or the function might crash, depending on the pattern. 4. Caseless matching was not working for non-ASCII characters in back references. For example, /(\x{de})\1/8i was not matching \x{de}\x{fe}. It now works when Unicode Property Support is available. 5. In pcretest, an escape such as \x{de} in the data was always generating a UTF-8 string, even in non-UTF-8 mode. Now it generates a single byte in non-UTF-8 mode. If the value is greater than 255, it gives a warning about truncation. 6. Minor bugfix in pcrecpp.cc (change "" == ... to NULL == ...). 7. Added two (int) casts to pcregrep when printing the difference of two pointers, in case they are 64-bit values. 8. Added comments about Mac OS X stack usage to the pcrestack man page and to test 2 if it fails. 9. Added PCRE_CALL_CONVENTION just before the names of all exported functions, and a #define of that name to empty if it is not externally set. This is to allow users of MSVC to set it if necessary. 10. The PCRE_EXP_DEFN macro which precedes exported functions was missing from the convenience functions in the pcre_get.c source file. 11. An option change at the start of a pattern that had top-level alternatives could cause overwriting and/or a crash. This command provoked a crash in some environments: printf "/(?i)[\xc3\xa9\xc3\xbd]|[\xc3\xa9\xc3\xbdA]/8\n" | pcretest This potential security problem was recorded as CVE-2008-2371. 12. For a pattern where the match had to start at the beginning or immediately after a newline (e.g /.*anything/ without the DOTALL flag), pcre_exec() and pcre_dfa_exec() could read past the end of the passed subject if there was no match. To help with detecting such bugs (e.g. with valgrind), I modified pcretest so that it places the subject at the end of its malloc-ed buffer. 13. The change to pcretest in 12 above threw up a couple more cases when pcre_ exec() might read past the end of the data buffer in UTF-8 mode. 14. A similar bug to 7.3/2 existed when the PCRE_FIRSTLINE option was set and the data contained the byte 0x85 as part of a UTF-8 character within its first line. This applied both to normal and DFA matching. 15. Lazy qualifiers were not working in some cases in UTF-8 mode. For example, /^[^d]*?$/8 failed to match "abc". 16. Added a missing copyright notice to pcrecpp_internal.h. 17. Make it more clear in the documentation that values returned from pcre_exec() in ovector are byte offsets, not character counts. 18. Tidied a few places to stop certain compilers from issuing warnings. 19. Updated the Virtual Pascal + BCC files to compile the latest v7.7, as supplied by Stefan Weber. I made a further small update for 7.8 because there is a change of source arrangements: the pcre_searchfuncs.c module is replaced by pcre_ucd.c. Version 7.7 07-May-08 --------------------- 1. Applied Craig's patch to sort out a long long problem: "If we can't convert a string to a long long, pretend we don't even have a long long." This is done by checking for the strtoq, strtoll, and _strtoi64 functions. 2. Applied Craig's patch to pcrecpp.cc to restore ABI compatibility with pre-7.6 versions, which defined a global no_arg variable instead of putting it in the RE class. (See also #8 below.) 3. Remove a line of dead code, identified by coverity and reported by Nuno Lopes. 4. Fixed two related pcregrep bugs involving -r with --include or --exclude: (1) The include/exclude patterns were being applied to the whole pathnames of files, instead of just to the final components. (2) If there was more than one level of directory, the subdirectories were skipped unless they satisfied the include/exclude conditions. This is inconsistent with GNU grep (and could even be seen as contrary to the pcregrep specification - which I improved to make it absolutely clear). The action now is always to scan all levels of directory, and just apply the include/exclude patterns to regular files. 5. Added the --include_dir and --exclude_dir patterns to pcregrep, and used --exclude_dir in the tests to avoid scanning .svn directories. 6. Applied Craig's patch to the QuoteMeta function so that it escapes the NUL character as backslash + 0 rather than backslash + NUL, because PCRE doesn't support NULs in patterns. 7. Added some missing "const"s to declarations of static tables in pcre_compile.c and pcre_dfa_exec.c. 8. Applied Craig's patch to pcrecpp.cc to fix a problem in OS X that was caused by fix #2 above. (Subsequently also a second patch to fix the first patch. And a third patch - this was a messy problem.) 9. Applied Craig's patch to remove the use of push_back(). 10. Applied Alan Lehotsky's patch to add REG_STARTEND support to the POSIX matching function regexec(). 11. Added support for the Oniguruma syntax \g, \g, \g'name', \g'n', which, however, unlike Perl's \g{...}, are subroutine calls, not back references. PCRE supports relative numbers with this syntax (I don't think Oniguruma does). 12. Previously, a group with a zero repeat such as (...){0} was completely omitted from the compiled regex. However, this means that if the group was called as a subroutine from elsewhere in the pattern, things went wrong (an internal error was given). Such groups are now left in the compiled pattern, with a new opcode that causes them to be skipped at execution time. 13. Added the PCRE_JAVASCRIPT_COMPAT option. This makes the following changes to the way PCRE behaves: (a) A lone ] character is dis-allowed (Perl treats it as data). (b) A back reference to an unmatched subpattern matches an empty string (Perl fails the current match path). (c) A data ] in a character class must be notated as \] because if the first data character in a class is ], it defines an empty class. (In Perl it is not possible to have an empty class.) The empty class [] never matches; it forces failure and is equivalent to (*FAIL) or (?!). The negative empty class [^] matches any one character, independently of the DOTALL setting. 14. A pattern such as /(?2)[]a()b](abc)/ which had a forward reference to a non-existent subpattern following a character class starting with ']' and containing () gave an internal compiling error instead of "reference to non-existent subpattern". Fortunately, when the pattern did exist, the compiled code was correct. (When scanning forwards to check for the existencd of the subpattern, it was treating the data ']' as terminating the class, so got the count wrong. When actually compiling, the reference was subsequently set up correctly.) 15. The "always fail" assertion (?!) is optimzed to (*FAIL) by pcre_compile; it was being rejected as not supported by pcre_dfa_exec(), even though other assertions are supported. I have made pcre_dfa_exec() support (*FAIL). 16. The implementation of 13c above involved the invention of a new opcode, OP_ALLANY, which is like OP_ANY but doesn't check the /s flag. Since /s cannot be changed at match time, I realized I could make a small improvement to matching performance by compiling OP_ALLANY instead of OP_ANY for "." when DOTALL was set, and then removing the runtime tests on the OP_ANY path. 17. Compiling pcretest on Windows with readline support failed without the following two fixes: (1) Make the unistd.h include conditional on HAVE_UNISTD_H; (2) #define isatty and fileno as _isatty and _fileno. 18. Changed CMakeLists.txt and cmake/FindReadline.cmake to arrange for the ncurses library to be included for pcretest when ReadLine support is requested, but also to allow for it to be overridden. This patch came from Daniel Bergström. 19. There was a typo in the file ucpinternal.h where f0_rangeflag was defined as 0x00f00000 instead of 0x00800000. Luckily, this would not have caused any errors with the current Unicode tables. Thanks to Peter Kankowski for spotting this. Version 7.6 28-Jan-08 --------------------- 1. A character class containing a very large number of characters with codepoints greater than 255 (in UTF-8 mode, of course) caused a buffer overflow. 2. Patch to cut out the "long long" test in pcrecpp_unittest when HAVE_LONG_LONG is not defined. 3. Applied Christian Ehrlicher's patch to update the CMake build files to bring them up to date and include new features. This patch includes: - Fixed PH's badly added libz and libbz2 support. - Fixed a problem with static linking. - Added pcredemo. [But later removed - see 7 below.] - Fixed dftables problem and added an option. - Added a number of HAVE_XXX tests, including HAVE_WINDOWS_H and HAVE_LONG_LONG. - Added readline support for pcretest. - Added an listing of the option settings after cmake has run. 4. A user submitted a patch to Makefile that makes it easy to create "pcre.dll" under mingw when using Configure/Make. I added stuff to Makefile.am that cause it to include this special target, without affecting anything else. Note that the same mingw target plus all the other distribution libraries and programs are now supported when configuring with CMake (see 6 below) instead of with Configure/Make. 5. Applied Craig's patch that moves no_arg into the RE class in the C++ code. This is an attempt to solve the reported problem "pcrecpp::no_arg is not exported in the Windows port". It has not yet been confirmed that the patch solves the problem, but it does no harm. 6. Applied Sheri's patch to CMakeLists.txt to add NON_STANDARD_LIB_PREFIX and NON_STANDARD_LIB_SUFFIX for dll names built with mingw when configured with CMake, and also correct the comment about stack recursion. 7. Remove the automatic building of pcredemo from the ./configure system and from CMakeLists.txt. The whole idea of pcredemo.c is that it is an example of a program that users should build themselves after PCRE is installed, so building it automatically is not really right. What is more, it gave trouble in some build environments. 8. Further tidies to CMakeLists.txt from Sheri and Christian. Version 7.5 10-Jan-08 --------------------- 1. Applied a patch from Craig: "This patch makes it possible to 'ignore' values in parens when parsing an RE using the C++ wrapper." 2. Negative specials like \S did not work in character classes in UTF-8 mode. Characters greater than 255 were excluded from the class instead of being included. 3. The same bug as (2) above applied to negated POSIX classes such as [:^space:]. 4. PCRECPP_STATIC was referenced in pcrecpp_internal.h, but nowhere was it defined or documented. It seems to have been a typo for PCRE_STATIC, so I have changed it. 5. The construct (?&) was not diagnosed as a syntax error (it referenced the first named subpattern) and a construct such as (?&a) would reference the first named subpattern whose name started with "a" (in other words, the length check was missing). Both these problems are fixed. "Subpattern name expected" is now given for (?&) (a zero-length name), and this patch also makes it give the same error for \k'' (previously it complained that that was a reference to a non-existent subpattern). 6. The erroneous patterns (?+-a) and (?-+a) give different error messages; this is right because (?- can be followed by option settings as well as by digits. I have, however, made the messages clearer. 7. Patterns such as (?(1)a|b) (a pattern that contains fewer subpatterns than the number used in the conditional) now cause a compile-time error. This is actually not compatible with Perl, which accepts such patterns, but treats the conditional as always being FALSE (as PCRE used to), but it seems to me that giving a diagnostic is better. 8. Change "alphameric" to the more common word "alphanumeric" in comments and messages. 9. Fix two occurrences of "backslash" in comments that should have been "backspace". 10. Remove two redundant lines of code that can never be obeyed (their function was moved elsewhere). 11. The program that makes PCRE's Unicode character property table had a bug which caused it to generate incorrect table entries for sequences of characters that have the same character type, but are in different scripts. It amalgamated them into a single range, with the script of the first of them. In other words, some characters were in the wrong script. There were thirteen such cases, affecting characters in the following ranges: U+002b0 - U+002c1 U+0060c - U+0060d U+0061e - U+00612 U+0064b - U+0065e U+0074d - U+0076d U+01800 - U+01805 U+01d00 - U+01d77 U+01d9b - U+01dbf U+0200b - U+0200f U+030fc - U+030fe U+03260 - U+0327f U+0fb46 - U+0fbb1 U+10450 - U+1049d 12. The -o option (show only the matching part of a line) for pcregrep was not compatible with GNU grep in that, if there was more than one match in a line, it showed only the first of them. It now behaves in the same way as GNU grep. 13. If the -o and -v options were combined for pcregrep, it printed a blank line for every non-matching line. GNU grep prints nothing, and pcregrep now does the same. The return code can be used to tell if there were any non-matching lines. 14. Added --file-offsets and --line-offsets to pcregrep. 15. The pattern (?=something)(?R) was not being diagnosed as a potentially infinitely looping recursion. The bug was that positive lookaheads were not being skipped when checking for a possible empty match (negative lookaheads and both kinds of lookbehind were skipped). 16. Fixed two typos in the Windows-only code in pcregrep.c, and moved the inclusion of to before rather than after the definition of INVALID_FILE_ATTRIBUTES (patch from David Byron). 17. Specifying a possessive quantifier with a specific limit for a Unicode character property caused pcre_compile() to compile bad code, which led at runtime to PCRE_ERROR_INTERNAL (-14). Examples of patterns that caused this are: /\p{Zl}{2,3}+/8 and /\p{Cc}{2}+/8. It was the possessive "+" that caused the error; without that there was no problem. 18. Added --enable-pcregrep-libz and --enable-pcregrep-libbz2. 19. Added --enable-pcretest-libreadline. 20. In pcrecpp.cc, the variable 'count' was incremented twice in RE::GlobalReplace(). As a result, the number of replacements returned was double what it should be. I removed one of the increments, but Craig sent a later patch that removed the other one (the right fix) and added unit tests that check the return values (which was not done before). 21. Several CMake things: (1) Arranged that, when cmake is used on Unix, the libraries end up with the names libpcre and libpcreposix, not just pcre and pcreposix. (2) The above change means that pcretest and pcregrep are now correctly linked with the newly-built libraries, not previously installed ones. (3) Added PCRE_SUPPORT_LIBREADLINE, PCRE_SUPPORT_LIBZ, PCRE_SUPPORT_LIBBZ2. 22. In UTF-8 mode, with newline set to "any", a pattern such as .*a.*=.b.* crashed when matching a string such as a\x{2029}b (note that \x{2029} is a UTF-8 newline character). The key issue is that the pattern starts .*; this means that the match must be either at the beginning, or after a newline. The bug was in the code for advancing after a failed match and checking that the new position followed a newline. It was not taking account of UTF-8 characters correctly. 23. PCRE was behaving differently from Perl in the way it recognized POSIX character classes. PCRE was not treating the sequence [:...:] as a character class unless the ... were all letters. Perl, however, seems to allow any characters between [: and :], though of course it rejects as unknown any "names" that contain non-letters, because all the known class names consist only of letters. Thus, Perl gives an error for [[:1234:]], for example, whereas PCRE did not - it did not recognize a POSIX character class. This seemed a bit dangerous, so the code has been changed to be closer to Perl. The behaviour is not identical to Perl, because PCRE will diagnose an unknown class for, for example, [[:l\ower:]] where Perl will treat it as [[:lower:]]. However, PCRE does now give "unknown" errors where Perl does, and where it didn't before. 24. Rewrite so as to remove the single use of %n from pcregrep because in some Windows environments %n is disabled by default. Version 7.4 21-Sep-07 --------------------- 1. Change 7.3/28 was implemented for classes by looking at the bitmap. This means that a class such as [\s] counted as "explicit reference to CR or LF". That isn't really right - the whole point of the change was to try to help when there was an actual mention of one of the two characters. So now the change happens only if \r or \n (or a literal CR or LF) character is encountered. 2. The 32-bit options word was also used for 6 internal flags, but the numbers of both had grown to the point where there were only 3 bits left. Fortunately, there was spare space in the data structure, and so I have moved the internal flags into a new 16-bit field to free up more option bits. 3. The appearance of (?J) at the start of a pattern set the DUPNAMES option, but did not set the internal JCHANGED flag - either of these is enough to control the way the "get" function works - but the PCRE_INFO_JCHANGED facility is supposed to tell if (?J) was ever used, so now (?J) at the start sets both bits. 4. Added options (at build time, compile time, exec time) to change \R from matching any Unicode line ending sequence to just matching CR, LF, or CRLF. 5. doc/pcresyntax.html was missing from the distribution. 6. Put back the definition of PCRE_ERROR_NULLWSLIMIT, for backward compatibility, even though it is no longer used. 7. Added macro for snprintf to pcrecpp_unittest.cc and also for strtoll and strtoull to pcrecpp.cc to select the available functions in WIN32 when the windows.h file is present (where different names are used). [This was reversed later after testing - see 16 below.] 8. Changed all #include to #include "config.h". There were also some further cases that I changed to "pcre.h". 9. When pcregrep was used with the --colour option, it missed the line ending sequence off the lines that it output. 10. It was pointed out to me that arrays of string pointers cause lots of relocations when a shared library is dynamically loaded. A technique of using a single long string with a table of offsets can drastically reduce these. I have refactored PCRE in four places to do this. The result is dramatic: Originally: 290 After changing UCP table: 187 After changing error message table: 43 After changing table of "verbs" 36 After changing table of Posix names 22 Thanks to the folks working on Gregex for glib for this insight. 11. --disable-stack-for-recursion caused compiling to fail unless -enable- unicode-properties was also set. 12. Updated the tests so that they work when \R is defaulted to ANYCRLF. 13. Added checks for ANY and ANYCRLF to pcrecpp.cc where it previously checked only for CRLF. 14. Added casts to pcretest.c to avoid compiler warnings. 15. Added Craig's patch to various pcrecpp modules to avoid compiler warnings. 16. Added Craig's patch to remove the WINDOWS_H tests, that were not working, and instead check for _strtoi64 explicitly, and avoid the use of snprintf() entirely. This removes changes made in 7 above. 17. The CMake files have been updated, and there is now more information about building with CMake in the NON-UNIX-USE document. Version 7.3 28-Aug-07 --------------------- 1. In the rejigging of the build system that eventually resulted in 7.1, the line "#include " was included in pcre_internal.h. The use of angle brackets there is not right, since it causes compilers to look for an installed pcre.h, not the version that is in the source that is being compiled (which of course may be different). I have changed it back to: #include "pcre.h" I have a vague recollection that the change was concerned with compiling in different directories, but in the new build system, that is taken care of by the VPATH setting the Makefile. 2. The pattern .*$ when run in not-DOTALL UTF-8 mode with newline=any failed when the subject happened to end in the byte 0x85 (e.g. if the last character was \x{1ec5}). *Character* 0x85 is one of the "any" newline characters but of course it shouldn't be taken as a newline when it is part of another character. The bug was that, for an unlimited repeat of . in not-DOTALL UTF-8 mode, PCRE was advancing by bytes rather than by characters when looking for a newline. 3. A small performance improvement in the DOTALL UTF-8 mode .* case. 4. Debugging: adjusted the names of opcodes for different kinds of parentheses in debug output. 5. Arrange to use "%I64d" instead of "%lld" and "%I64u" instead of "%llu" for long printing in the pcrecpp unittest when running under MinGW. 6. ESC_K was left out of the EBCDIC table. 7. Change 7.0/38 introduced a new limit on the number of nested non-capturing parentheses; I made it 1000, which seemed large enough. Unfortunately, the limit also applies to "virtual nesting" when a pattern is recursive, and in this case 1000 isn't so big. I have been able to remove this limit at the expense of backing off one optimization in certain circumstances. Normally, when pcre_exec() would call its internal match() function recursively and immediately return the result unconditionally, it uses a "tail recursion" feature to save stack. However, when a subpattern that can match an empty string has an unlimited repetition quantifier, it no longer makes this optimization. That gives it a stack frame in which to save the data for checking that an empty string has been matched. Previously this was taken from the 1000-entry workspace that had been reserved. So now there is no explicit limit, but more stack is used. 8. Applied Daniel's patches to solve problems with the import/export magic syntax that is required for Windows, and which was going wrong for the pcreposix and pcrecpp parts of the library. These were overlooked when this problem was solved for the main library. 9. There were some crude static tests to avoid integer overflow when computing the size of patterns that contain repeated groups with explicit upper limits. As the maximum quantifier is 65535, the maximum group length was set at 30,000 so that the product of these two numbers did not overflow a 32-bit integer. However, it turns out that people want to use groups that are longer than 30,000 bytes (though not repeat them that many times). Change 7.0/17 (the refactoring of the way the pattern size is computed) has made it possible to implement the integer overflow checks in a much more dynamic way, which I have now done. The artificial limitation on group length has been removed - we now have only the limit on the total length of the compiled pattern, which depends on the LINK_SIZE setting. 10. Fixed a bug in the documentation for get/copy named substring when duplicate names are permitted. If none of the named substrings are set, the functions return PCRE_ERROR_NOSUBSTRING (7); the doc said they returned an empty string. 11. Because Perl interprets \Q...\E at a high level, and ignores orphan \E instances, patterns such as [\Q\E] or [\E] or even [^\E] cause an error, because the ] is interpreted as the first data character and the terminating ] is not found. PCRE has been made compatible with Perl in this regard. Previously, it interpreted [\Q\E] as an empty class, and [\E] could cause memory overwriting. 10. Like Perl, PCRE automatically breaks an unlimited repeat after an empty string has been matched (to stop an infinite loop). It was not recognizing a conditional subpattern that could match an empty string if that subpattern was within another subpattern. For example, it looped when trying to match (((?(1)X|))*) but it was OK with ((?(1)X|)*) where the condition was not nested. This bug has been fixed. 12. A pattern like \X?\d or \P{L}?\d in non-UTF-8 mode could cause a backtrack past the start of the subject in the presence of bytes with the top bit set, for example "\x8aBCD". 13. Added Perl 5.10 experimental backtracking controls (*FAIL), (*F), (*PRUNE), (*SKIP), (*THEN), (*COMMIT), and (*ACCEPT). 14. Optimized (?!) to (*FAIL). 15. Updated the test for a valid UTF-8 string to conform to the later RFC 3629. This restricts code points to be within the range 0 to 0x10FFFF, excluding the "low surrogate" sequence 0xD800 to 0xDFFF. Previously, PCRE allowed the full range 0 to 0x7FFFFFFF, as defined by RFC 2279. Internally, it still does: it's just the validity check that is more restrictive. 16. Inserted checks for integer overflows during escape sequence (backslash) processing, and also fixed erroneous offset values for syntax errors during backslash processing. 17. Fixed another case of looking too far back in non-UTF-8 mode (cf 12 above) for patterns like [\PPP\x8a]{1,}\x80 with the subject "A\x80". 18. An unterminated class in a pattern like (?1)\c[ with a "forward reference" caused an overrun. 19. A pattern like (?:[\PPa*]*){8,} which had an "extended class" (one with something other than just ASCII characters) inside a group that had an unlimited repeat caused a loop at compile time (while checking to see whether the group could match an empty string). 20. Debugging a pattern containing \p or \P could cause a crash. For example, [\P{Any}] did so. (Error in the code for printing property names.) 21. An orphan \E inside a character class could cause a crash. 22. A repeated capturing bracket such as (A)? could cause a wild memory reference during compilation. 23. There are several functions in pcre_compile() that scan along a compiled expression for various reasons (e.g. to see if it's fixed length for look behind). There were bugs in these functions when a repeated \p or \P was present in the pattern. These operators have additional parameters compared with \d, etc, and these were not being taken into account when moving along the compiled data. Specifically: (a) A item such as \p{Yi}{3} in a lookbehind was not treated as fixed length. (b) An item such as \pL+ within a repeated group could cause crashes or loops. (c) A pattern such as \p{Yi}+(\P{Yi}+)(?1) could give an incorrect "reference to non-existent subpattern" error. (d) A pattern like (\P{Yi}{2}\277)? could loop at compile time. 24. A repeated \S or \W in UTF-8 mode could give wrong answers when multibyte characters were involved (for example /\S{2}/8g with "A\x{a3}BC"). 25. Using pcregrep in multiline, inverted mode (-Mv) caused it to loop. 26. Patterns such as [\P{Yi}A] which include \p or \P and just one other character were causing crashes (broken optimization). 27. Patterns such as (\P{Yi}*\277)* (group with possible zero repeat containing \p or \P) caused a compile-time loop. 28. More problems have arisen in unanchored patterns when CRLF is a valid line break. For example, the unstudied pattern [\r\n]A does not match the string "\r\nA" because change 7.0/46 below moves the current point on by two characters after failing to match at the start. However, the pattern \nA *does* match, because it doesn't start till \n, and if [\r\n]A is studied, the same is true. There doesn't seem any very clean way out of this, but what I have chosen to do makes the common cases work: PCRE now takes note of whether there can be an explicit match for \r or \n anywhere in the pattern, and if so, 7.0/46 no longer applies. As part of this change, there's a new PCRE_INFO_HASCRORLF option for finding out whether a compiled pattern has explicit CR or LF references. 29. Added (*CR) etc for changing newline setting at start of pattern. Version 7.2 19-Jun-07 --------------------- 1. If the fr_FR locale cannot be found for test 3, try the "french" locale, which is apparently normally available under Windows. 2. Re-jig the pcregrep tests with different newline settings in an attempt to make them independent of the local environment's newline setting. 3. Add code to configure.ac to remove -g from the CFLAGS default settings. 4. Some of the "internals" tests were previously cut out when the link size was not 2, because the output contained actual offsets. The recent new "Z" feature of pcretest means that these can be cut out, making the tests usable with all link sizes. 5. Implemented Stan Switzer's goto replacement for longjmp() when not using stack recursion. This gives a massive performance boost under BSD, but just a small improvement under Linux. However, it saves one field in the frame in all cases. 6. Added more features from the forthcoming Perl 5.10: (a) (?-n) (where n is a string of digits) is a relative subroutine or recursion call. It refers to the nth most recently opened parentheses. (b) (?+n) is also a relative subroutine call; it refers to the nth next to be opened parentheses. (c) Conditions that refer to capturing parentheses can be specified relatively, for example, (?(-2)... or (?(+3)... (d) \K resets the start of the current match so that everything before is not part of it. (e) \k{name} is synonymous with \k and \k'name' (.NET compatible). (f) \g{name} is another synonym - part of Perl 5.10's unification of reference syntax. (g) (?| introduces a group in which the numbering of parentheses in each alternative starts with the same number. (h) \h, \H, \v, and \V match horizontal and vertical whitespace. 7. Added two new calls to pcre_fullinfo(): PCRE_INFO_OKPARTIAL and PCRE_INFO_JCHANGED. 8. A pattern such as (.*(.)?)* caused pcre_exec() to fail by either not terminating or by crashing. Diagnosed by Viktor Griph; it was in the code for detecting groups that can match an empty string. 9. A pattern with a very large number of alternatives (more than several hundred) was running out of internal workspace during the pre-compile phase, where pcre_compile() figures out how much memory will be needed. A bit of new cunning has reduced the workspace needed for groups with alternatives. The 1000-alternative test pattern now uses 12 bytes of workspace instead of running out of the 4096 that are available. 10. Inserted some missing (unsigned int) casts to get rid of compiler warnings. 11. Applied patch from Google to remove an optimization that didn't quite work. The report of the bug said: pcrecpp::RE("a*").FullMatch("aaa") matches, while pcrecpp::RE("a*?").FullMatch("aaa") does not, and pcrecpp::RE("a*?\\z").FullMatch("aaa") does again. 12. If \p or \P was used in non-UTF-8 mode on a character greater than 127 it matched the wrong number of bytes. Version 7.1 24-Apr-07 --------------------- 1. Applied Bob Rossi and Daniel G's patches to convert the build system to one that is more "standard", making use of automake and other Autotools. There is some re-arrangement of the files and adjustment of comments consequent on this. 2. Part of the patch fixed a problem with the pcregrep tests. The test of -r for recursive directory scanning broke on some systems because the files are not scanned in any specific order and on different systems the order was different. A call to "sort" has been inserted into RunGrepTest for the approprate test as a short-term fix. In the longer term there may be an alternative. 3. I had an email from Eric Raymond about problems translating some of PCRE's man pages to HTML (despite the fact that I distribute HTML pages, some people do their own conversions for various reasons). The problems concerned the use of low-level troff macros .br and .in. I have therefore removed all such uses from the man pages (some were redundant, some could be replaced by .nf/.fi pairs). The 132html script that I use to generate HTML has been updated to handle .nf/.fi and to complain if it encounters .br or .in. 4. Updated comments in configure.ac that get placed in config.h.in and also arranged for config.h to be included in the distribution, with the name config.h.generic, for the benefit of those who have to compile without Autotools (compare pcre.h, which is now distributed as pcre.h.generic). 5. Updated the support (such as it is) for Virtual Pascal, thanks to Stefan Weber: (1) pcre_internal.h was missing some function renames; (2) updated makevp.bat for the current PCRE, using the additional files makevp_c.txt, makevp_l.txt, and pcregexp.pas. 6. A Windows user reported a minor discrepancy with test 2, which turned out to be caused by a trailing space on an input line that had got lost in his copy. The trailing space was an accident, so I've just removed it. 7. Add -Wl,-R... flags in pcre-config.in for *BSD* systems, as I'm told that is needed. 8. Mark ucp_table (in ucptable.h) and ucp_gentype (in pcre_ucp_searchfuncs.c) as "const" (a) because they are and (b) because it helps the PHP maintainers who have recently made a script to detect big data structures in the php code that should be moved to the .rodata section. I remembered to update Builducptable as well, so it won't revert if ucptable.h is ever re-created. 9. Added some extra #ifdef SUPPORT_UTF8 conditionals into pcretest.c, pcre_printint.src, pcre_compile.c, pcre_study.c, and pcre_tables.c, in order to be able to cut out the UTF-8 tables in the latter when UTF-8 support is not required. This saves 1.5-2K of code, which is important in some applications. Later: more #ifdefs are needed in pcre_ord2utf8.c and pcre_valid_utf8.c so as not to refer to the tables, even though these functions will never be called when UTF-8 support is disabled. Otherwise there are problems with a shared library. 10. Fixed two bugs in the emulated memmove() function in pcre_internal.h: (a) It was defining its arguments as char * instead of void *. (b) It was assuming that all moves were upwards in memory; this was true a long time ago when I wrote it, but is no longer the case. The emulated memove() is provided for those environments that have neither memmove() nor bcopy(). I didn't think anyone used it these days, but that is clearly not the case, as these two bugs were recently reported. 11. The script PrepareRelease is now distributed: it calls 132html, CleanTxt, and Detrail to create the HTML documentation, the .txt form of the man pages, and it removes trailing spaces from listed files. It also creates pcre.h.generic and config.h.generic from pcre.h and config.h. In the latter case, it wraps all the #defines with #ifndefs. This script should be run before "make dist". 12. Fixed two fairly obscure bugs concerned with quantified caseless matching with Unicode property support. (a) For a maximizing quantifier, if the two different cases of the character were of different lengths in their UTF-8 codings (there are some cases like this - I found 11), and the matching function had to back up over a mixture of the two cases, it incorrectly assumed they were both the same length. (b) When PCRE was configured to use the heap rather than the stack for recursion during matching, it was not correctly preserving the data for the other case of a UTF-8 character when checking ahead for a match while processing a minimizing repeat. If the check also involved matching a wide character, but failed, corruption could cause an erroneous result when trying to check for a repeat of the original character. 13. Some tidying changes to the testing mechanism: (a) The RunTest script now detects the internal link size and whether there is UTF-8 and UCP support by running ./pcretest -C instead of relying on values substituted by "configure". (The RunGrepTest script already did this for UTF-8.) The configure.ac script no longer substitutes the relevant variables. (b) The debugging options /B and /D in pcretest show the compiled bytecode with length and offset values. This means that the output is different for different internal link sizes. Test 2 is skipped for link sizes other than 2 because of this, bypassing the problem. Unfortunately, there was also a test in test 3 (the locale tests) that used /B and failed for link sizes other than 2. Rather than cut the whole test out, I have added a new /Z option to pcretest that replaces the length and offset values with spaces. This is now used to make test 3 independent of link size. (Test 2 will be tidied up later.) 14. If erroroffset was passed as NULL to pcre_compile, it provoked a segmentation fault instead of returning the appropriate error message. 15. In multiline mode when the newline sequence was set to "any", the pattern ^$ would give a match between the \r and \n of a subject such as "A\r\nB". This doesn't seem right; it now treats the CRLF combination as the line ending, and so does not match in that case. It's only a pattern such as ^$ that would hit this one: something like ^ABC$ would have failed after \r and then tried again after \r\n. 16. Changed the comparison command for RunGrepTest from "diff -u" to "diff -ub" in an attempt to make files that differ only in their line terminators compare equal. This works on Linux. 17. Under certain error circumstances pcregrep might try to free random memory as it exited. This is now fixed, thanks to valgrind. 19. In pcretest, if the pattern /(?m)^$/g was matched against the string "abc\r\n\r\n", it found an unwanted second match after the second \r. This was because its rules for how to advance for /g after matching an empty string at the end of a line did not allow for this case. They now check for it specially. 20. pcretest is supposed to handle patterns and data of any length, by extending its buffers when necessary. It was getting this wrong when the buffer for a data line had to be extended. 21. Added PCRE_NEWLINE_ANYCRLF which is like ANY, but matches only CR, LF, or CRLF as a newline sequence. 22. Code for handling Unicode properties in pcre_dfa_exec() wasn't being cut out by #ifdef SUPPORT_UCP. This did no harm, as it could never be used, but I have nevertheless tidied it up. 23. Added some casts to kill warnings from HP-UX ia64 compiler. 24. Added a man page for pcre-config. Version 7.0 19-Dec-06 --------------------- 1. Fixed a signed/unsigned compiler warning in pcre_compile.c, shown up by moving to gcc 4.1.1. 2. The -S option for pcretest uses setrlimit(); I had omitted to #include sys/time.h, which is documented as needed for this function. It doesn't seem to matter on Linux, but it showed up on some releases of OS X. 3. It seems that there are systems where bytes whose values are greater than 127 match isprint() in the "C" locale. The "C" locale should be the default when a C program starts up. In most systems, only ASCII printing characters match isprint(). This difference caused the output from pcretest to vary, making some of the tests fail. I have changed pcretest so that: (a) When it is outputting text in the compiled version of a pattern, bytes other than 32-126 are always shown as hex escapes. (b) When it is outputting text that is a matched part of a subject string, it does the same, unless a different locale has been set for the match (using the /L modifier). In this case, it uses isprint() to decide. 4. Fixed a major bug that caused incorrect computation of the amount of memory required for a compiled pattern when options that changed within the pattern affected the logic of the preliminary scan that determines the length. The relevant options are -x, and -i in UTF-8 mode. The result was that the computed length was too small. The symptoms of this bug were either the PCRE error "internal error: code overflow" from pcre_compile(), or a glibc crash with a message such as "pcretest: free(): invalid next size (fast)". Examples of patterns that provoked this bug (shown in pcretest format) are: /(?-x: )/x /(?x)(?-x: \s*#\s*)/ /((?i)[\x{c0}])/8 /(?i:[\x{c0}])/8 HOWEVER: Change 17 below makes this fix obsolete as the memory computation is now done differently. 5. Applied patches from Google to: (a) add a QuoteMeta function to the C++ wrapper classes; (b) implement a new function in the C++ scanner that is more efficient than the old way of doing things because it avoids levels of recursion in the regex matching; (c) add a paragraph to the documentation for the FullMatch() function. 6. The escape sequence \n was being treated as whatever was defined as "newline". Not only was this contrary to the documentation, which states that \n is character 10 (hex 0A), but it also went horribly wrong when "newline" was defined as CRLF. This has been fixed. 7. In pcre_dfa_exec.c the value of an unsigned integer (the variable called c) was being set to -1 for the "end of line" case (supposedly a value that no character can have). Though this value is never used (the check for end of line is "zero bytes in current character"), it caused compiler complaints. I've changed it to 0xffffffff. 8. In pcre_version.c, the version string was being built by a sequence of C macros that, in the event of PCRE_PRERELEASE being defined as an empty string (as it is for production releases) called a macro with an empty argument. The C standard says the result of this is undefined. The gcc compiler treats it as an empty string (which was what was wanted) but it is reported that Visual C gives an error. The source has been hacked around to avoid this problem. 9. On the advice of a Windows user, included and in Windows builds of pcretest, and changed the call to _setmode() to use _O_BINARY instead of 0x8000. Made all the #ifdefs test both _WIN32 and WIN32 (not all of them did). 10. Originally, pcretest opened its input and output without "b"; then I was told that "b" was needed in some environments, so it was added for release 5.0 to both the input and output. (It makes no difference on Unix-like systems.) Later I was told that it is wrong for the input on Windows. I've now abstracted the modes into two macros, to make it easier to fiddle with them, and removed "b" from the input mode under Windows. 11. Added pkgconfig support for the C++ wrapper library, libpcrecpp. 12. Added -help and --help to pcretest as an official way of being reminded of the options. 13. Removed some redundant semicolons after macro calls in pcrecpparg.h.in and pcrecpp.cc because they annoy compilers at high warning levels. 14. A bit of tidying/refactoring in pcre_exec.c in the main bumpalong loop. 15. Fixed an occurrence of == in configure.ac that should have been = (shell scripts are not C programs :-) and which was not noticed because it works on Linux. 16. pcretest is supposed to handle any length of pattern and data line (as one line or as a continued sequence of lines) by extending its input buffer if necessary. This feature was broken for very long pattern lines, leading to a string of junk being passed to pcre_compile() if the pattern was longer than about 50K. 17. I have done a major re-factoring of the way pcre_compile() computes the amount of memory needed for a compiled pattern. Previously, there was code that made a preliminary scan of the pattern in order to do this. That was OK when PCRE was new, but as the facilities have expanded, it has become harder and harder to keep it in step with the real compile phase, and there have been a number of bugs (see for example, 4 above). I have now found a cunning way of running the real compile function in a "fake" mode that enables it to compute how much memory it would need, while actually only ever using a few hundred bytes of working memory and without too many tests of the mode. This should make future maintenance and development easier. A side effect of this work is that the limit of 200 on the nesting depth of parentheses has been removed (though this was never a serious limitation, I suspect). However, there is a downside: pcre_compile() now runs more slowly than before (30% or more, depending on the pattern). I hope this isn't a big issue. There is no effect on runtime performance. 18. Fixed a minor bug in pcretest: if a pattern line was not terminated by a newline (only possible for the last line of a file) and it was a pattern that set a locale (followed by /Lsomething), pcretest crashed. 19. Added additional timing features to pcretest. (1) The -tm option now times matching only, not compiling. (2) Both -t and -tm can be followed, as a separate command line item, by a number that specifies the number of repeats to use when timing. The default is 50000; this gives better precision, but takes uncomfortably long for very large patterns. 20. Extended pcre_study() to be more clever in cases where a branch of a subpattern has no definite first character. For example, (a*|b*)[cd] would previously give no result from pcre_study(). Now it recognizes that the first character must be a, b, c, or d. 21. There was an incorrect error "recursive call could loop indefinitely" if a subpattern (or the entire pattern) that was being tested for matching an empty string contained only one non-empty item after a nested subpattern. For example, the pattern (?>\x{100}*)\d(?R) provoked this error incorrectly, because the \d was being skipped in the check. 22. The pcretest program now has a new pattern option /B and a command line option -b, which is equivalent to adding /B to every pattern. This causes it to show the compiled bytecode, without the additional information that -d shows. The effect of -d is now the same as -b with -i (and similarly, /D is the same as /B/I). 23. A new optimization is now able automatically to treat some sequences such as a*b as a*+b. More specifically, if something simple (such as a character or a simple class like \d) has an unlimited quantifier, and is followed by something that cannot possibly match the quantified thing, the quantifier is automatically "possessified". 24. A recursive reference to a subpattern whose number was greater than 39 went wrong under certain circumstances in UTF-8 mode. This bug could also have affected the operation of pcre_study(). 25. Realized that a little bit of performance could be had by replacing (c & 0xc0) == 0xc0 with c >= 0xc0 when processing UTF-8 characters. 26. Timing data from pcretest is now shown to 4 decimal places instead of 3. 27. Possessive quantifiers such as a++ were previously implemented by turning them into atomic groups such as ($>a+). Now they have their own opcodes, which improves performance. This includes the automatically created ones from 23 above. 28. A pattern such as (?=(\w+))\1: which simulates an atomic group using a lookahead was broken if it was not anchored. PCRE was mistakenly expecting the first matched character to be a colon. This applied both to named and numbered groups. 29. The ucpinternal.h header file was missing its idempotency #ifdef. 30. I was sent a "project" file called libpcre.a.dev which I understand makes building PCRE on Windows easier, so I have included it in the distribution. 31. There is now a check in pcretest against a ridiculously large number being returned by pcre_exec() or pcre_dfa_exec(). If this happens in a /g or /G loop, the loop is abandoned. 32. Forward references to subpatterns in conditions such as (?(2)...) where subpattern 2 is defined later cause pcre_compile() to search forwards in the pattern for the relevant set of parentheses. This search went wrong when there were unescaped parentheses in a character class, parentheses escaped with \Q...\E, or parentheses in a #-comment in /x mode. 33. "Subroutine" calls and backreferences were previously restricted to referencing subpatterns earlier in the regex. This restriction has now been removed. 34. Added a number of extra features that are going to be in Perl 5.10. On the whole, these are just syntactic alternatives for features that PCRE had previously implemented using the Python syntax or my own invention. The other formats are all retained for compatibility. (a) Named groups can now be defined as (?...) or (?'name'...) as well as (?P...). The new forms, as well as being in Perl 5.10, are also .NET compatible. (b) A recursion or subroutine call to a named group can now be defined as (?&name) as well as (?P>name). (c) A backreference to a named group can now be defined as \k or \k'name' as well as (?P=name). The new forms, as well as being in Perl 5.10, are also .NET compatible. (d) A conditional reference to a named group can now use the syntax (?() or (?('name') as well as (?(name). (e) A "conditional group" of the form (?(DEFINE)...) can be used to define groups (named and numbered) that are never evaluated inline, but can be called as "subroutines" from elsewhere. In effect, the DEFINE condition is always false. There may be only one alternative in such a group. (f) A test for recursion can be given as (?(R1).. or (?(R&name)... as well as the simple (?(R). The condition is true only if the most recent recursion is that of the given number or name. It does not search out through the entire recursion stack. (g) The escape \gN or \g{N} has been added, where N is a positive or negative number, specifying an absolute or relative reference. 35. Tidied to get rid of some further signed/unsigned compiler warnings and some "unreachable code" warnings. 36. Updated the Unicode property tables to Unicode version 5.0.0. Amongst other things, this adds five new scripts. 37. Perl ignores orphaned \E escapes completely. PCRE now does the same. There were also incompatibilities regarding the handling of \Q..\E inside character classes, for example with patterns like [\Qa\E-\Qz\E] where the hyphen was adjacent to \Q or \E. I hope I've cleared all this up now. 38. Like Perl, PCRE detects when an indefinitely repeated parenthesized group matches an empty string, and forcibly breaks the loop. There were bugs in this code in non-simple cases. For a pattern such as ^(a()*)* matched against aaaa the result was just "a" rather than "aaaa", for example. Two separate and independent bugs (that affected different cases) have been fixed. 39. Refactored the code to abolish the use of different opcodes for small capturing bracket numbers. This is a tidy that I avoided doing when I removed the limit on the number of capturing brackets for 3.5 back in 2001. The new approach is not only tidier, it makes it possible to reduce the memory needed to fix the previous bug (38). 40. Implemented PCRE_NEWLINE_ANY to recognize any of the Unicode newline sequences (http://unicode.org/unicode/reports/tr18/) as "newline" when processing dot, circumflex, or dollar metacharacters, or #-comments in /x mode. 41. Add \R to match any Unicode newline sequence, as suggested in the Unicode report. 42. Applied patch, originally from Ari Pollak, modified by Google, to allow copy construction and assignment in the C++ wrapper. 43. Updated pcregrep to support "--newline=any". In the process, I fixed a couple of bugs that could have given wrong results in the "--newline=crlf" case. 44. Added a number of casts and did some reorganization of signed/unsigned int variables following suggestions from Dair Grant. Also renamed the variable "this" as "item" because it is a C++ keyword. 45. Arranged for dftables to add #include "pcre_internal.h" to pcre_chartables.c because without it, gcc 4.x may remove the array definition from the final binary if PCRE is built into a static library and dead code stripping is activated. 46. For an unanchored pattern, if a match attempt fails at the start of a newline sequence, and the newline setting is CRLF or ANY, and the next two characters are CRLF, advance by two characters instead of one. Version 6.7 04-Jul-06 --------------------- 1. In order to handle tests when input lines are enormously long, pcretest has been re-factored so that it automatically extends its buffers when necessary. The code is crude, but this _is_ just a test program. The default size has been increased from 32K to 50K. 2. The code in pcre_study() was using the value of the re argument before testing it for NULL. (Of course, in any sensible call of the function, it won't be NULL.) 3. The memmove() emulation function in pcre_internal.h, which is used on systems that lack both memmove() and bcopy() - that is, hardly ever - was missing a "static" storage class specifier. 4. When UTF-8 mode was not set, PCRE looped when compiling certain patterns containing an extended class (one that cannot be represented by a bitmap because it contains high-valued characters or Unicode property items, e.g. [\pZ]). Almost always one would set UTF-8 mode when processing such a pattern, but PCRE should not loop if you do not (it no longer does). [Detail: two cases were found: (a) a repeated subpattern containing an extended class; (b) a recursive reference to a subpattern that followed a previous extended class. It wasn't skipping over the extended class correctly when UTF-8 mode was not set.] 5. A negated single-character class was not being recognized as fixed-length in lookbehind assertions such as (?<=[^f]), leading to an incorrect compile error "lookbehind assertion is not fixed length". 6. The RunPerlTest auxiliary script was showing an unexpected difference between PCRE and Perl for UTF-8 tests. It turns out that it is hard to write a Perl script that can interpret lines of an input file either as byte characters or as UTF-8, which is what "perltest" was being required to do for the non-UTF-8 and UTF-8 tests, respectively. Essentially what you can't do is switch easily at run time between having the "use utf8;" pragma or not. In the end, I fudged it by using the RunPerlTest script to insert "use utf8;" explicitly for the UTF-8 tests. 7. In multiline (/m) mode, PCRE was matching ^ after a terminating newline at the end of the subject string, contrary to the documentation and to what Perl does. This was true of both matching functions. Now it matches only at the start of the subject and immediately after *internal* newlines. 8. A call of pcre_fullinfo() from pcretest to get the option bits was passing a pointer to an int instead of a pointer to an unsigned long int. This caused problems on 64-bit systems. 9. Applied a patch from the folks at Google to pcrecpp.cc, to fix "another instance of the 'standard' template library not being so standard". 10. There was no check on the number of named subpatterns nor the maximum length of a subpattern name. The product of these values is used to compute the size of the memory block for a compiled pattern. By supplying a very long subpattern name and a large number of named subpatterns, the size computation could be caused to overflow. This is now prevented by limiting the length of names to 32 characters, and the number of named subpatterns to 10,000. 11. Subpatterns that are repeated with specific counts have to be replicated in the compiled pattern. The size of memory for this was computed from the length of the subpattern and the repeat count. The latter is limited to 65535, but there was no limit on the former, meaning that integer overflow could in principle occur. The compiled length of a repeated subpattern is now limited to 30,000 bytes in order to prevent this. 12. Added the optional facility to have named substrings with the same name. 13. Added the ability to use a named substring as a condition, using the Python syntax: (?(name)yes|no). This overloads (?(R)... and names that are numbers (not recommended). Forward references are permitted. 14. Added forward references in named backreferences (if you see what I mean). 15. In UTF-8 mode, with the PCRE_DOTALL option set, a quantified dot in the pattern could run off the end of the subject. For example, the pattern "(?s)(.{1,5})"8 did this with the subject "ab". 16. If PCRE_DOTALL or PCRE_MULTILINE were set, pcre_dfa_exec() behaved as if PCRE_CASELESS was set when matching characters that were quantified with ? or *. 17. A character class other than a single negated character that had a minimum but no maximum quantifier - for example [ab]{6,} - was not handled correctly by pce_dfa_exec(). It would match only one character. 18. A valid (though odd) pattern that looked like a POSIX character class but used an invalid character after [ (for example [[,abc,]]) caused pcre_compile() to give the error "Failed: internal error: code overflow" or in some cases to crash with a glibc free() error. This could even happen if the pattern terminated after [[ but there just happened to be a sequence of letters, a binary zero, and a closing ] in the memory that followed. 19. Perl's treatment of octal escapes in the range \400 to \777 has changed over the years. Originally (before any Unicode support), just the bottom 8 bits were taken. Thus, for example, \500 really meant \100. Nowadays the output from "man perlunicode" includes this: The regular expression compiler produces polymorphic opcodes. That is, the pattern adapts to the data and automatically switches to the Unicode character scheme when presented with Unicode data--or instead uses a traditional byte scheme when presented with byte data. Sadly, a wide octal escape does not cause a switch, and in a string with no other multibyte characters, these octal escapes are treated as before. Thus, in Perl, the pattern /\500/ actually matches \100 but the pattern /\500|\x{1ff}/ matches \500 or \777 because the whole thing is treated as a Unicode string. I have not perpetrated such confusion in PCRE. Up till now, it took just the bottom 8 bits, as in old Perl. I have now made octal escapes with values greater than \377 illegal in non-UTF-8 mode. In UTF-8 mode they translate to the appropriate multibyte character. 29. Applied some refactoring to reduce the number of warnings from Microsoft and Borland compilers. This has included removing the fudge introduced seven years ago for the OS/2 compiler (see 2.02/2 below) because it caused a warning about an unused variable. 21. PCRE has not included VT (character 0x0b) in the set of whitespace characters since release 4.0, because Perl (from release 5.004) does not. [Or at least, is documented not to: some releases seem to be in conflict with the documentation.] However, when a pattern was studied with pcre_study() and all its branches started with \s, PCRE still included VT as a possible starting character. Of course, this did no harm; it just caused an unnecessary match attempt. 22. Removed a now-redundant internal flag bit that recorded the fact that case dependency changed within the pattern. This was once needed for "required byte" processing, but is no longer used. This recovers a now-scarce options bit. Also moved the least significant internal flag bit to the most- significant bit of the word, which was not previously used (hangover from the days when it was an int rather than a uint) to free up another bit for the future. 23. Added support for CRLF line endings as well as CR and LF. As well as the default being selectable at build time, it can now be changed at runtime via the PCRE_NEWLINE_xxx flags. There are now options for pcregrep to specify that it is scanning data with non-default line endings. 24. Changed the definition of CXXLINK to make it agree with the definition of LINK in the Makefile, by replacing LDFLAGS to CXXFLAGS. 25. Applied Ian Taylor's patches to avoid using another stack frame for tail recursions. This makes a big different to stack usage for some patterns. 26. If a subpattern containing a named recursion or subroutine reference such as (?P>B) was quantified, for example (xxx(?P>B)){3}, the calculation of the space required for the compiled pattern went wrong and gave too small a value. Depending on the environment, this could lead to "Failed: internal error: code overflow at offset 49" or "glibc detected double free or corruption" errors. 27. Applied patches from Google (a) to support the new newline modes and (b) to advance over multibyte UTF-8 characters in GlobalReplace. 28. Change free() to pcre_free() in pcredemo.c. Apparently this makes a difference for some implementation of PCRE in some Windows version. 29. Added some extra testing facilities to pcretest: \q in a data line sets the "match limit" value \Q in a data line sets the "match recursion limt" value -S sets the stack size, where is in megabytes The -S option isn't available for Windows. Version 6.6 06-Feb-06 --------------------- 1. Change 16(a) for 6.5 broke things, because PCRE_DATA_SCOPE was not defined in pcreposix.h. I have copied the definition from pcre.h. 2. Change 25 for 6.5 broke compilation in a build directory out-of-tree because pcre.h is no longer a built file. 3. Added Jeff Friedl's additional debugging patches to pcregrep. These are not normally included in the compiled code. Version 6.5 01-Feb-06 --------------------- 1. When using the partial match feature with pcre_dfa_exec(), it was not anchoring the second and subsequent partial matches at the new starting point. This could lead to incorrect results. For example, with the pattern /1234/, partially matching against "123" and then "a4" gave a match. 2. Changes to pcregrep: (a) All non-match returns from pcre_exec() were being treated as failures to match the line. Now, unless the error is PCRE_ERROR_NOMATCH, an error message is output. Some extra information is given for the PCRE_ERROR_MATCHLIMIT and PCRE_ERROR_RECURSIONLIMIT errors, which are probably the only errors that are likely to be caused by users (by specifying a regex that has nested indefinite repeats, for instance). If there are more than 20 of these errors, pcregrep is abandoned. (b) A binary zero was treated as data while matching, but terminated the output line if it was written out. This has been fixed: binary zeroes are now no different to any other data bytes. (c) Whichever of the LC_ALL or LC_CTYPE environment variables is set is used to set a locale for matching. The --locale=xxxx long option has been added (no short equivalent) to specify a locale explicitly on the pcregrep command, overriding the environment variables. (d) When -B was used with -n, some line numbers in the output were one less than they should have been. (e) Added the -o (--only-matching) option. (f) If -A or -C was used with -c (count only), some lines of context were accidentally printed for the final match. (g) Added the -H (--with-filename) option. (h) The combination of options -rh failed to suppress file names for files that were found from directory arguments. (i) Added the -D (--devices) and -d (--directories) options. (j) Added the -F (--fixed-strings) option. (k) Allow "-" to be used as a file name for -f as well as for a data file. (l) Added the --colo(u)r option. (m) Added Jeffrey Friedl's -S testing option, but within #ifdefs so that it is not present by default. 3. A nasty bug was discovered in the handling of recursive patterns, that is, items such as (?R) or (?1), when the recursion could match a number of alternatives. If it matched one of the alternatives, but subsequently, outside the recursion, there was a failure, the code tried to back up into the recursion. However, because of the way PCRE is implemented, this is not possible, and the result was an incorrect result from the match. In order to prevent this happening, the specification of recursion has been changed so that all such subpatterns are automatically treated as atomic groups. Thus, for example, (?R) is treated as if it were (?>(?R)). 4. I had overlooked the fact that, in some locales, there are characters for which isalpha() is true but neither isupper() nor islower() are true. In the fr_FR locale, for instance, the \xAA and \xBA characters (ordmasculine and ordfeminine) are like this. This affected the treatment of \w and \W when they appeared in character classes, but not when they appeared outside a character class. The bit map for "word" characters is now created separately from the results of isalnum() instead of just taking it from the upper, lower, and digit maps. (Plus the underscore character, of course.) 5. The above bug also affected the handling of POSIX character classes such as [[:alpha:]] and [[:alnum:]]. These do not have their own bit maps in PCRE's permanent tables. Instead, the bit maps for such a class were previously created as the appropriate unions of the upper, lower, and digit bitmaps. Now they are created by subtraction from the [[:word:]] class, which has its own bitmap. 6. The [[:blank:]] character class matches horizontal, but not vertical space. It is created by subtracting the vertical space characters (\x09, \x0a, \x0b, \x0c) from the [[:space:]] bitmap. Previously, however, the subtraction was done in the overall bitmap for a character class, meaning that a class such as [\x0c[:blank:]] was incorrect because \x0c would not be recognized. This bug has been fixed. 7. Patches from the folks at Google: (a) pcrecpp.cc: "to handle a corner case that may or may not happen in real life, but is still worth protecting against". (b) pcrecpp.cc: "corrects a bug when negative radixes are used with regular expressions". (c) pcre_scanner.cc: avoid use of std::count() because not all systems have it. (d) Split off pcrecpparg.h from pcrecpp.h and had the former built by "configure" and the latter not, in order to fix a problem somebody had with compiling the Arg class on HP-UX. (e) Improve the error-handling of the C++ wrapper a little bit. (f) New tests for checking recursion limiting. 8. The pcre_memmove() function, which is used only if the environment does not have a standard memmove() function (and is therefore rarely compiled), contained two bugs: (a) use of int instead of size_t, and (b) it was not returning a result (though PCRE never actually uses the result). 9. In the POSIX regexec() interface, if nmatch is specified as a ridiculously large number - greater than INT_MAX/(3*sizeof(int)) - REG_ESPACE is returned instead of calling malloc() with an overflowing number that would most likely cause subsequent chaos. 10. The debugging option of pcretest was not showing the NO_AUTO_CAPTURE flag. 11. The POSIX flag REG_NOSUB is now supported. When a pattern that was compiled with this option is matched, the nmatch and pmatch options of regexec() are ignored. 12. Added REG_UTF8 to the POSIX interface. This is not defined by POSIX, but is provided in case anyone wants to the the POSIX interface with UTF-8 strings. 13. Added CXXLDFLAGS to the Makefile parameters to provide settings only on the C++ linking (needed for some HP-UX environments). 14. Avoid compiler warnings in get_ucpname() when compiled without UCP support (unused parameter) and in the pcre_printint() function (omitted "default" switch label when the default is to do nothing). 15. Added some code to make it possible, when PCRE is compiled as a C++ library, to replace subject pointers for pcre_exec() with a smart pointer class, thus making it possible to process discontinuous strings. 16. The two macros PCRE_EXPORT and PCRE_DATA_SCOPE are confusing, and perform much the same function. They were added by different people who were trying to make PCRE easy to compile on non-Unix systems. It has been suggested that PCRE_EXPORT be abolished now that there is more automatic apparatus for compiling on Windows systems. I have therefore replaced it with PCRE_DATA_SCOPE. This is set automatically for Windows; if not set it defaults to "extern" for C or "extern C" for C++, which works fine on Unix-like systems. It is now possible to override the value of PCRE_DATA_ SCOPE with something explicit in config.h. In addition: (a) pcreposix.h still had just "extern" instead of either of these macros; I have replaced it with PCRE_DATA_SCOPE. (b) Functions such as _pcre_xclass(), which are internal to the library, but external in the C sense, all had PCRE_EXPORT in their definitions. This is apparently wrong for the Windows case, so I have removed it. (It makes no difference on Unix-like systems.) 17. Added a new limit, MATCH_LIMIT_RECURSION, which limits the depth of nesting of recursive calls to match(). This is different to MATCH_LIMIT because that limits the total number of calls to match(), not all of which increase the depth of recursion. Limiting the recursion depth limits the amount of stack (or heap if NO_RECURSE is set) that is used. The default can be set when PCRE is compiled, and changed at run time. A patch from Google adds this functionality to the C++ interface. 18. Changes to the handling of Unicode character properties: (a) Updated the table to Unicode 4.1.0. (b) Recognize characters that are not in the table as "Cn" (undefined). (c) I revised the way the table is implemented to a much improved format which includes recognition of ranges. It now supports the ranges that are defined in UnicodeData.txt, and it also amalgamates other characters into ranges. This has reduced the number of entries in the table from around 16,000 to around 3,000, thus reducing its size considerably. I realized I did not need to use a tree structure after all - a binary chop search is just as efficient. Having reduced the number of entries, I extended their size from 6 bytes to 8 bytes to allow for more data. (d) Added support for Unicode script names via properties such as \p{Han}. 19. In UTF-8 mode, a backslash followed by a non-Ascii character was not matching that character. 20. When matching a repeated Unicode property with a minimum greater than zero, (for example \pL{2,}), PCRE could look past the end of the subject if it reached it while seeking the minimum number of characters. This could happen only if some of the characters were more than one byte long, because there is a check for at least the minimum number of bytes. 21. Refactored the implementation of \p and \P so as to be more general, to allow for more different types of property in future. This has changed the compiled form incompatibly. Anybody with saved compiled patterns that use \p or \P will have to recompile them. 22. Added "Any" and "L&" to the supported property types. 23. Recognize \x{...} as a code point specifier, even when not in UTF-8 mode, but give a compile time error if the value is greater than 0xff. 24. The man pages for pcrepartial, pcreprecompile, and pcre_compile2 were accidentally not being installed or uninstalled. 25. The pcre.h file was built from pcre.h.in, but the only changes that were made were to insert the current release number. This seemed silly, because it made things harder for people building PCRE on systems that don't run "configure". I have turned pcre.h into a distributed file, no longer built by "configure", with the version identification directly included. There is no longer a pcre.h.in file. However, this change necessitated a change to the pcre-config script as well. It is built from pcre-config.in, and one of the substitutions was the release number. I have updated configure.ac so that ./configure now finds the release number by grepping pcre.h. 26. Added the ability to run the tests under valgrind. Version 6.4 05-Sep-05 --------------------- 1. Change 6.0/10/(l) to pcregrep introduced a bug that caused separator lines "--" to be printed when multiple files were scanned, even when none of the -A, -B, or -C options were used. This is not compatible with Gnu grep, so I consider it to be a bug, and have restored the previous behaviour. 2. A couple of code tidies to get rid of compiler warnings. 3. The pcretest program used to cheat by referring to symbols in the library whose names begin with _pcre_. These are internal symbols that are not really supposed to be visible externally, and in some environments it is possible to suppress them. The cheating is now confined to including certain files from the library's source, which is a bit cleaner. 4. Renamed pcre.in as pcre.h.in to go with pcrecpp.h.in; it also makes the file's purpose clearer. 5. Reorganized pcre_ucp_findchar(). Version 6.3 15-Aug-05 --------------------- 1. The file libpcre.pc.in did not have general read permission in the tarball. 2. There were some problems when building without C++ support: (a) If C++ support was not built, "make install" and "make test" still tried to test it. (b) There were problems when the value of CXX was explicitly set. Some changes have been made to try to fix these, and ... (c) --disable-cpp can now be used to explicitly disable C++ support. (d) The use of @CPP_OBJ@ directly caused a blank line preceded by a backslash in a target when C++ was disabled. This confuses some versions of "make", apparently. Using an intermediate variable solves this. (Same for CPP_LOBJ.) 3. $(LINK_FOR_BUILD) now includes $(CFLAGS_FOR_BUILD) and $(LINK) (non-Windows) now includes $(CFLAGS) because these flags are sometimes necessary on certain architectures. 4. Added a setting of -export-symbols-regex to the link command to remove those symbols that are exported in the C sense, but actually are local within the library, and not documented. Their names all begin with "_pcre_". This is not a perfect job, because (a) we have to except some symbols that pcretest ("illegally") uses, and (b) the facility isn't always available (and never for static libraries). I have made a note to try to find a way round (a) in the future. Version 6.2 01-Aug-05 --------------------- 1. There was no test for integer overflow of quantifier values. A construction such as {1111111111111111} would give undefined results. What is worse, if a minimum quantifier for a parenthesized subpattern overflowed and became negative, the calculation of the memory size went wrong. This could have led to memory overwriting. 2. Building PCRE using VPATH was broken. Hopefully it is now fixed. 3. Added "b" to the 2nd argument of fopen() in dftables.c, for non-Unix-like operating environments where this matters. 4. Applied Giuseppe Maxia's patch to add additional features for controlling PCRE options from within the C++ wrapper. 5. Named capturing subpatterns were not being correctly counted when a pattern was compiled. This caused two problems: (a) If there were more than 100 such subpatterns, the calculation of the memory needed for the whole compiled pattern went wrong, leading to an overflow error. (b) Numerical back references of the form \12, where the number was greater than 9, were not recognized as back references, even though there were sufficient previous subpatterns. 6. Two minor patches to pcrecpp.cc in order to allow it to compile on older versions of gcc, e.g. 2.95.4. Version 6.1 21-Jun-05 --------------------- 1. There was one reference to the variable "posix" in pcretest.c that was not surrounded by "#if !defined NOPOSIX". 2. Make it possible to compile pcretest without DFA support, UTF8 support, or the cross-check on the old pcre_info() function, for the benefit of the cut-down version of PCRE that is currently imported into Exim. 3. A (silly) pattern starting with (?i)(?-i) caused an internal space allocation error. I've done the easy fix, which wastes 2 bytes for sensible patterns that start (?i) but I don't think that matters. The use of (?i) is just an example; this all applies to the other options as well. 4. Since libtool seems to echo the compile commands it is issuing, the output from "make" can be reduced a bit by putting "@" in front of each libtool compile command. 5. Patch from the folks at Google for configure.in to be a bit more thorough in checking for a suitable C++ installation before trying to compile the C++ stuff. This should fix a reported problem when a compiler was present, but no suitable headers. 6. The man pages all had just "PCRE" as their title. I have changed them to be the relevant file name. I have also arranged that these names are retained in the file doc/pcre.txt, which is a concatenation in text format of all the man pages except the little individual ones for each function. 7. The NON-UNIX-USE file had not been updated for the different set of source files that come with release 6. I also added a few comments about the C++ wrapper. Version 6.0 07-Jun-05 --------------------- 1. Some minor internal re-organization to help with my DFA experiments. 2. Some missing #ifdef SUPPORT_UCP conditionals in pcretest and printint that didn't matter for the library itself when fully configured, but did matter when compiling without UCP support, or within Exim, where the ucp files are not imported. 3. Refactoring of the library code to split up the various functions into different source modules. The addition of the new DFA matching code (see below) to a single monolithic source would have made it really too unwieldy, quite apart from causing all the code to be include in a statically linked application, when only some functions are used. This is relevant even without the DFA addition now that patterns can be compiled in one application and matched in another. The downside of splitting up is that there have to be some external functions and data tables that are used internally in different modules of the library but which are not part of the API. These have all had their names changed to start with "_pcre_" so that they are unlikely to clash with other external names. 4. Added an alternate matching function, pcre_dfa_exec(), which matches using a different (DFA) algorithm. Although it is slower than the original function, it does have some advantages for certain types of matching problem. 5. Upgrades to pcretest in order to test the features of pcre_dfa_exec(), including restarting after a partial match. 6. A patch for pcregrep that defines INVALID_FILE_ATTRIBUTES if it is not defined when compiling for Windows was sent to me. I have put it into the code, though I have no means of testing or verifying it. 7. Added the pcre_refcount() auxiliary function. 8. Added the PCRE_FIRSTLINE option. This constrains an unanchored pattern to match before or at the first newline in the subject string. In pcretest, the /f option on a pattern can be used to set this. 9. A repeated \w when used in UTF-8 mode with characters greater than 256 would behave wrongly. This has been present in PCRE since release 4.0. 10. A number of changes to the pcregrep command: (a) Refactored how -x works; insert ^(...)$ instead of setting PCRE_ANCHORED and checking the length, in preparation for adding something similar for -w. (b) Added the -w (match as a word) option. (c) Refactored the way lines are read and buffered so as to have more than one at a time available. (d) Implemented a pcregrep test script. (e) Added the -M (multiline match) option. This allows patterns to match over several lines of the subject. The buffering ensures that at least 8K, or the rest of the document (whichever is the shorter) is available for matching (and similarly the previous 8K for lookbehind assertions). (f) Changed the --help output so that it now says -w, --word-regex(p) instead of two lines, one with "regex" and the other with "regexp" because that confused at least one person since the short forms are the same. (This required a bit of code, as the output is generated automatically from a table. It wasn't just a text change.) (g) -- can be used to terminate pcregrep options if the next thing isn't an option but starts with a hyphen. Could be a pattern or a path name starting with a hyphen, for instance. (h) "-" can be given as a file name to represent stdin. (i) When file names are being printed, "(standard input)" is used for the standard input, for compatibility with GNU grep. Previously "" was used. (j) The option --label=xxx can be used to supply a name to be used for stdin when file names are being printed. There is no short form. (k) Re-factored the options decoding logic because we are going to add two more options that take data. Such options can now be given in four different ways, e.g. "-fname", "-f name", "--file=name", "--file name". (l) Added the -A, -B, and -C options for requesting that lines of context around matches be printed. (m) Added the -L option to print the names of files that do not contain any matching lines, that is, the complement of -l. (n) The return code is 2 if any file cannot be opened, but pcregrep does continue to scan other files. (o) The -s option was incorrectly implemented. For compatibility with other greps, it now suppresses the error message for a non-existent or non- accessible file (but not the return code). There is a new option called -q that suppresses the output of matching lines, which was what -s was previously doing. (p) Added --include and --exclude options to specify files for inclusion and exclusion when recursing. 11. The Makefile was not using the Autoconf-supported LDFLAGS macro properly. Hopefully, it now does. 12. Missing cast in pcre_study(). 13. Added an "uninstall" target to the makefile. 14. Replaced "extern" in the function prototypes in Makefile.in with "PCRE_DATA_SCOPE", which defaults to 'extern' or 'extern "C"' in the Unix world, but is set differently for Windows. 15. Added a second compiling function called pcre_compile2(). The only difference is that it has an extra argument, which is a pointer to an integer error code. When there is a compile-time failure, this is set non-zero, in addition to the error test pointer being set to point to an error message. The new argument may be NULL if no error number is required (but then you may as well call pcre_compile(), which is now just a wrapper). This facility is provided because some applications need a numeric error indication, but it has also enabled me to tidy up the way compile-time errors are handled in the POSIX wrapper. 16. Added VPATH=.libs to the makefile; this should help when building with one prefix path and installing with another. (Or so I'm told by someone who knows more about this stuff than I do.) 17. Added a new option, REG_DOTALL, to the POSIX function regcomp(). This passes PCRE_DOTALL to the pcre_compile() function, making the "." character match everything, including newlines. This is not POSIX-compatible, but somebody wanted the feature. From pcretest it can be activated by using both the P and the s flags. 18. AC_PROG_LIBTOOL appeared twice in Makefile.in. Removed one. 19. libpcre.pc was being incorrectly installed as executable. 20. A couple of places in pcretest check for end-of-line by looking for '\n'; it now also looks for '\r' so that it will work unmodified on Windows. 21. Added Google's contributed C++ wrapper to the distribution. 22. Added some untidy missing memory free() calls in pcretest, to keep Electric Fence happy when testing. Version 5.0 13-Sep-04 --------------------- 1. Internal change: literal characters are no longer packed up into items containing multiple characters in a single byte-string. Each character is now matched using a separate opcode. However, there may be more than one byte in the character in UTF-8 mode. 2. The pcre_callout_block structure has two new fields: pattern_position and next_item_length. These contain the offset in the pattern to the next match item, and its length, respectively. 3. The PCRE_AUTO_CALLOUT option for pcre_compile() requests the automatic insertion of callouts before each pattern item. Added the /C option to pcretest to make use of this. 4. On the advice of a Windows user, the lines #if defined(_WIN32) || defined(WIN32) _setmode( _fileno( stdout ), 0x8000 ); #endif /* defined(_WIN32) || defined(WIN32) */ have been added to the source of pcretest. This apparently does useful magic in relation to line terminators. 5. Changed "r" and "w" in the calls to fopen() in pcretest to "rb" and "wb" for the benefit of those environments where the "b" makes a difference. 6. The icc compiler has the same options as gcc, but "configure" doesn't seem to know about it. I have put a hack into configure.in that adds in code to set GCC=yes if CC=icc. This seems to end up at a point in the generated configure script that is early enough to affect the setting of compiler options, which is what is needed, but I have no means of testing whether it really works. (The user who reported this had patched the generated configure script, which of course I cannot do.) LATER: After change 22 below (new libtool files), the configure script seems to know about icc (and also ecc). Therefore, I have commented out this hack in configure.in. 7. Added support for pkg-config (2 patches were sent in). 8. Negated POSIX character classes that used a combination of internal tables were completely broken. These were [[:^alpha:]], [[:^alnum:]], and [[:^ascii]]. Typically, they would match almost any characters. The other POSIX classes were not broken in this way. 9. Matching the pattern "\b.*?" against "ab cd", starting at offset 1, failed to find the match, as PCRE was deluded into thinking that the match had to start at the start point or following a newline. The same bug applied to patterns with negative forward assertions or any backward assertions preceding ".*" at the start, unless the pattern required a fixed first character. This was a failing pattern: "(?!.bcd).*". The bug is now fixed. 10. In UTF-8 mode, when moving forwards in the subject after a failed match starting at the last subject character, bytes beyond the end of the subject string were read. 11. Renamed the variable "class" as "classbits" to make life easier for C++ users. (Previously there was a macro definition, but it apparently wasn't enough.) 12. Added the new field "tables" to the extra data so that tables can be passed in at exec time, or the internal tables can be re-selected. This allows a compiled regex to be saved and re-used at a later time by a different program that might have everything at different addresses. 13. Modified the pcre-config script so that, when run on Solaris, it shows a -R library as well as a -L library. 14. The debugging options of pcretest (-d on the command line or D on a pattern) showed incorrect output for anything following an extended class that contained multibyte characters and which was followed by a quantifier. 15. Added optional support for general category Unicode character properties via the \p, \P, and \X escapes. Unicode property support implies UTF-8 support. It adds about 90K to the size of the library. The meanings of the inbuilt class escapes such as \d and \s have NOT been changed. 16. Updated pcredemo.c to include calls to free() to release the memory for the compiled pattern. 17. The generated file chartables.c was being created in the source directory instead of in the building directory. This caused the build to fail if the source directory was different from the building directory, and was read-only. 18. Added some sample Win commands from Mark Tetrode into the NON-UNIX-USE file. No doubt somebody will tell me if they don't make sense... Also added Dan Mooney's comments about building on OpenVMS. 19. Added support for partial matching via the PCRE_PARTIAL option for pcre_exec() and the \P data escape in pcretest. 20. Extended pcretest with 3 new pattern features: (i) A pattern option of the form ">rest-of-line" causes pcretest to write the compiled pattern to the file whose name is "rest-of-line". This is a straight binary dump of the data, with the saved pointer to the character tables forced to be NULL. The study data, if any, is written too. After writing, pcretest reads a new pattern. (ii) If, instead of a pattern, ": new target : new target : use native compiler : use native linker : handle Windows platform correctly : ditto : ditto copy DLL to top builddir before testing As part of these changes, -no-undefined was removed again. This was reported to give trouble on HP-UX 11.0, so getting rid of it seems like a good idea in any case. 3. Some tidies to get rid of compiler warnings: . In the match_data structure, match_limit was an unsigned long int, whereas match_call_count was an int. I've made them both unsigned long ints. . In pcretest the fact that a const uschar * doesn't automatically cast to a void * provoked a warning. . Turning on some more compiler warnings threw up some "shadow" variables and a few more missing casts. 4. If PCRE was complied with UTF-8 support, but called without the PCRE_UTF8 option, a class that contained a single character with a value between 128 and 255 (e.g. /[\xFF]/) caused PCRE to crash. 5. If PCRE was compiled with UTF-8 support, but called without the PCRE_UTF8 option, a class that contained several characters, but with at least one whose value was between 128 and 255 caused PCRE to crash. Version 4.1 12-Mar-03 --------------------- 1. Compiling with gcc -pedantic found a couple of places where casts were needed, and a string in dftables.c that was longer than standard compilers are required to support. 2. Compiling with Sun's compiler found a few more places where the code could be tidied up in order to avoid warnings. 3. The variables for cross-compiling were called HOST_CC and HOST_CFLAGS; the first of these names is deprecated in the latest Autoconf in favour of the name CC_FOR_BUILD, because "host" is typically used to mean the system on which the compiled code will be run. I can't find a reference for HOST_CFLAGS, but by analogy I have changed it to CFLAGS_FOR_BUILD. 4. Added -no-undefined to the linking command in the Makefile, because this is apparently helpful for Windows. To make it work, also added "-L. -lpcre" to the linking step for the pcreposix library. 5. PCRE was failing to diagnose the case of two named groups with the same name. 6. A problem with one of PCRE's optimizations was discovered. PCRE remembers a literal character that is needed in the subject for a match, and scans along to ensure that it is present before embarking on the full matching process. This saves time in cases of nested unlimited repeats that are never going to match. Problem: the scan can take a lot of time if the subject is very long (e.g. megabytes), thus penalizing straightforward matches. It is now done only if the amount of subject to be scanned is less than 1000 bytes. 7. A lesser problem with the same optimization is that it was recording the first character of an anchored pattern as "needed", thus provoking a search right along the subject, even when the first match of the pattern was going to fail. The "needed" character is now not set for anchored patterns, unless it follows something in the pattern that is of non-fixed length. Thus, it still fulfils its original purpose of finding quick non-matches in cases of nested unlimited repeats, but isn't used for simple anchored patterns such as /^abc/. Version 4.0 17-Feb-03 --------------------- 1. If a comment in an extended regex that started immediately after a meta-item extended to the end of string, PCRE compiled incorrect data. This could lead to all kinds of weird effects. Example: /#/ was bad; /()#/ was bad; /a#/ was not. 2. Moved to autoconf 2.53 and libtool 1.4.2. 3. Perl 5.8 no longer needs "use utf8" for doing UTF-8 things. Consequently, the special perltest8 script is no longer needed - all the tests can be run from a single perltest script. 4. From 5.004, Perl has not included the VT character (0x0b) in the set defined by \s. It has now been removed in PCRE. This means it isn't recognized as whitespace in /x regexes too, which is the same as Perl. Note that the POSIX class [:space:] *does* include VT, thereby creating a mess. 5. Added the class [:blank:] (a GNU extension from Perl 5.8) to match only space and tab. 6. Perl 5.005 was a long time ago. It's time to amalgamate the tests that use its new features into the main test script, reducing the number of scripts. 7. Perl 5.8 has changed the meaning of patterns like /a(?i)b/. Earlier versions were backward compatible, and made the (?i) apply to the whole pattern, as if /i were given. Now it behaves more logically, and applies the option setting only to what follows. PCRE has been changed to follow suit. However, if it finds options settings right at the start of the pattern, it extracts them into the global options, as before. Thus, they show up in the info data. 8. Added support for the \Q...\E escape sequence. Characters in between are treated as literals. This is slightly different from Perl in that $ and @ are also handled as literals inside the quotes. In Perl, they will cause variable interpolation. Note the following examples: Pattern PCRE matches Perl matches \Qabc$xyz\E abc$xyz abc followed by the contents of $xyz \Qabc\$xyz\E abc\$xyz abc\$xyz \Qabc\E\$\Qxyz\E abc$xyz abc$xyz For compatibility with Perl, \Q...\E sequences are recognized inside character classes as well as outside them. 9. Re-organized 3 code statements in pcretest to avoid "overflow in floating-point constant arithmetic" warnings from a Microsoft compiler. Added a (size_t) cast to one statement in pcretest and one in pcreposix to avoid signed/unsigned warnings. 10. SunOS4 doesn't have strtoul(). This was used only for unpicking the -o option for pcretest, so I've replaced it by a simple function that does just that job. 11. pcregrep was ending with code 0 instead of 2 for the commands "pcregrep" or "pcregrep -". 12. Added "possessive quantifiers" ?+, *+, ++, and {,}+ which come from Sun's Java package. This provides some syntactic sugar for simple cases of what my documentation calls "once-only subpatterns". A pattern such as x*+ is the same as (?>x*). In other words, if what is inside (?>...) is just a single repeated item, you can use this simplified notation. Note that only makes sense with greedy quantifiers. Consequently, the use of the possessive quantifier forces greediness, whatever the setting of the PCRE_UNGREEDY option. 13. A change of greediness default within a pattern was not taking effect at the current level for patterns like /(b+(?U)a+)/. It did apply to parenthesized subpatterns that followed. Patterns like /b+(?U)a+/ worked because the option was abstracted outside. 14. PCRE now supports the \G assertion. It is true when the current matching position is at the start point of the match. This differs from \A when the starting offset is non-zero. Used with the /g option of pcretest (or similar code), it works in the same way as it does for Perl's /g option. If all alternatives of a regex begin with \G, the expression is anchored to the start match position, and the "anchored" flag is set in the compiled expression. 15. Some bugs concerning the handling of certain option changes within patterns have been fixed. These applied to options other than (?ims). For example, "a(?x: b c )d" did not match "XabcdY" but did match "Xa b c dY". It should have been the other way round. Some of this was related to change 7 above. 16. PCRE now gives errors for /[.x.]/ and /[=x=]/ as unsupported POSIX features, as Perl does. Previously, PCRE gave the warnings only for /[[.x.]]/ and /[[=x=]]/. PCRE now also gives an error for /[:name:]/ because it supports POSIX classes only within a class (e.g. /[[:alpha:]]/). 17. Added support for Perl's \C escape. This matches one byte, even in UTF8 mode. Unlike ".", it always matches newline, whatever the setting of PCRE_DOTALL. However, PCRE does not permit \C to appear in lookbehind assertions. Perl allows it, but it doesn't (in general) work because it can't calculate the length of the lookbehind. At least, that's the case for Perl 5.8.0 - I've been told they are going to document that it doesn't work in future. 18. Added an error diagnosis for escapes that PCRE does not support: these are \L, \l, \N, \P, \p, \U, \u, and \X. 19. Although correctly diagnosing a missing ']' in a character class, PCRE was reading past the end of the pattern in cases such as /[abcd/. 20. PCRE was getting more memory than necessary for patterns with classes that contained both POSIX named classes and other characters, e.g. /[[:space:]abc/. 21. Added some code, conditional on #ifdef VPCOMPAT, to make life easier for compiling PCRE for use with Virtual Pascal. 22. Small fix to the Makefile to make it work properly if the build is done outside the source tree. 23. Added a new extension: a condition to go with recursion. If a conditional subpattern starts with (?(R) the "true" branch is used if recursion has happened, whereas the "false" branch is used only at the top level. 24. When there was a very long string of literal characters (over 255 bytes without UTF support, over 250 bytes with UTF support), the computation of how much memory was required could be incorrect, leading to segfaults or other strange effects. 25. PCRE was incorrectly assuming anchoring (either to start of subject or to start of line for a non-DOTALL pattern) when a pattern started with (.*) and there was a subsequent back reference to those brackets. This meant that, for example, /(.*)\d+\1/ failed to match "abc123bc". Unfortunately, it isn't possible to check for precisely this case. All we can do is abandon the optimization if .* occurs inside capturing brackets when there are any back references whatsoever. (See below for a better fix that came later.) 26. The handling of the optimization for finding the first character of a non-anchored pattern, and for finding a character that is required later in the match were failing in some cases. This didn't break the matching; it just failed to optimize when it could. The way this is done has been re-implemented. 27. Fixed typo in error message for invalid (?R item (it said "(?p"). 28. Added a new feature that provides some of the functionality that Perl provides with (?{...}). The facility is termed a "callout". The way it is done in PCRE is for the caller to provide an optional function, by setting pcre_callout to its entry point. Like pcre_malloc and pcre_free, this is a global variable. By default it is unset, which disables all calling out. To get the function called, the regex must include (?C) at appropriate points. This is, in fact, equivalent to (?C0), and any number <= 255 may be given with (?C). This provides a means of identifying different callout points. When PCRE reaches such a point in the regex, if pcre_callout has been set, the external function is called. It is provided with data in a structure called pcre_callout_block, which is defined in pcre.h. If the function returns 0, matching continues; if it returns a non-zero value, the match at the current point fails. However, backtracking will occur if possible. [This was changed later and other features added - see item 49 below.] 29. pcretest is upgraded to test the callout functionality. It provides a callout function that displays information. By default, it shows the start of the match and the current position in the text. There are some new data escapes to vary what happens: \C+ in addition, show current contents of captured substrings \C- do not supply a callout function \C!n return 1 when callout number n is reached \C!n!m return 1 when callout number n is reached for the mth time 30. If pcregrep was called with the -l option and just a single file name, it output "" if a match was found, instead of the file name. 31. Improve the efficiency of the POSIX API to PCRE. If the number of capturing slots is less than POSIX_MALLOC_THRESHOLD, use a block on the stack to pass to pcre_exec(). This saves a malloc/free per call. The default value of POSIX_MALLOC_THRESHOLD is 10; it can be changed by --with-posix-malloc-threshold when configuring. 32. The default maximum size of a compiled pattern is 64K. There have been a few cases of people hitting this limit. The code now uses macros to handle the storing of links as offsets within the compiled pattern. It defaults to 2-byte links, but this can be changed to 3 or 4 bytes by --with-link-size when configuring. Tests 2 and 5 work only with 2-byte links because they output debugging information about compiled patterns. 33. Internal code re-arrangements: (a) Moved the debugging function for printing out a compiled regex into its own source file (printint.c) and used #include to pull it into pcretest.c and, when DEBUG is defined, into pcre.c, instead of having two separate copies. (b) Defined the list of op-code names for debugging as a macro in internal.h so that it is next to the definition of the opcodes. (c) Defined a table of op-code lengths for simpler skipping along compiled code. This is again a macro in internal.h so that it is next to the definition of the opcodes. 34. Added support for recursive calls to individual subpatterns, along the lines of Robin Houston's patch (but implemented somewhat differently). 35. Further mods to the Makefile to help Win32. Also, added code to pcregrep to allow it to read and process whole directories in Win32. This code was contributed by Lionel Fourquaux; it has not been tested by me. 36. Added support for named subpatterns. The Python syntax (?P...) is used to name a group. Names consist of alphanumerics and underscores, and must be unique. Back references use the syntax (?P=name) and recursive calls use (?P>name) which is a PCRE extension to the Python extension. Groups still have numbers. The function pcre_fullinfo() can be used after compilation to extract a name/number map. There are three relevant calls: PCRE_INFO_NAMEENTRYSIZE yields the size of each entry in the map PCRE_INFO_NAMECOUNT yields the number of entries PCRE_INFO_NAMETABLE yields a pointer to the map. The map is a vector of fixed-size entries. The size of each entry depends on the length of the longest name used. The first two bytes of each entry are the group number, most significant byte first. There follows the corresponding name, zero terminated. The names are in alphabetical order. 37. Make the maximum literal string in the compiled code 250 for the non-UTF-8 case instead of 255. Making it the same both with and without UTF-8 support means that the same test output works with both. 38. There was a case of malloc(0) in the POSIX testing code in pcretest. Avoid calling malloc() with a zero argument. 39. Change 25 above had to resort to a heavy-handed test for the .* anchoring optimization. I've improved things by keeping a bitmap of backreferences with numbers 1-31 so that if .* occurs inside capturing brackets that are not in fact referenced, the optimization can be applied. It is unlikely that a relevant occurrence of .* (i.e. one which might indicate anchoring or forcing the match to follow \n) will appear inside brackets with a number greater than 31, but if it does, any back reference > 31 suppresses the optimization. 40. Added a new compile-time option PCRE_NO_AUTO_CAPTURE. This has the effect of disabling numbered capturing parentheses. Any opening parenthesis that is not followed by ? behaves as if it were followed by ?: but named parentheses can still be used for capturing (and they will acquire numbers in the usual way). 41. Redesigned the return codes from the match() function into yes/no/error so that errors can be passed back from deep inside the nested calls. A malloc failure while inside a recursive subpattern call now causes the PCRE_ERROR_NOMEMORY return instead of quietly going wrong. 42. It is now possible to set a limit on the number of times the match() function is called in a call to pcre_exec(). This facility makes it possible to limit the amount of recursion and backtracking, though not in a directly obvious way, because the match() function is used in a number of different circumstances. The count starts from zero for each position in the subject string (for non-anchored patterns). The default limit is, for compatibility, a large number, namely 10 000 000. You can change this in two ways: (a) When configuring PCRE before making, you can use --with-match-limit=n to set a default value for the compiled library. (b) For each call to pcre_exec(), you can pass a pcre_extra block in which a different value is set. See 45 below. If the limit is exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT. 43. Added a new function pcre_config(int, void *) to enable run-time extraction of things that can be changed at compile time. The first argument specifies what is wanted and the second points to where the information is to be placed. The current list of available information is: PCRE_CONFIG_UTF8 The output is an integer that is set to one if UTF-8 support is available; otherwise it is set to zero. PCRE_CONFIG_NEWLINE The output is an integer that it set to the value of the code that is used for newline. It is either LF (10) or CR (13). PCRE_CONFIG_LINK_SIZE The output is an integer that contains the number of bytes used for internal linkage in compiled expressions. The value is 2, 3, or 4. See item 32 above. PCRE_CONFIG_POSIX_MALLOC_THRESHOLD The output is an integer that contains the threshold above which the POSIX interface uses malloc() for output vectors. See item 31 above. PCRE_CONFIG_MATCH_LIMIT The output is an unsigned integer that contains the default limit of the number of match() calls in a pcre_exec() execution. See 42 above. 44. pcretest has been upgraded by the addition of the -C option. This causes it to extract all the available output from the new pcre_config() function, and to output it. The program then exits immediately. 45. A need has arisen to pass over additional data with calls to pcre_exec() in order to support additional features. One way would have been to define pcre_exec2() (for example) with extra arguments, but this would not have been extensible, and would also have required all calls to the original function to be mapped to the new one. Instead, I have chosen to extend the mechanism that is used for passing in "extra" data from pcre_study(). The pcre_extra structure is now exposed and defined in pcre.h. It currently contains the following fields: flags a bitmap indicating which of the following fields are set study_data opaque data from pcre_study() match_limit a way of specifying a limit on match() calls for a specific call to pcre_exec() callout_data data for callouts (see 49 below) The flag bits are also defined in pcre.h, and are PCRE_EXTRA_STUDY_DATA PCRE_EXTRA_MATCH_LIMIT PCRE_EXTRA_CALLOUT_DATA The pcre_study() function now returns one of these new pcre_extra blocks, with the actual study data pointed to by the study_data field, and the PCRE_EXTRA_STUDY_DATA flag set. This can be passed directly to pcre_exec() as before. That is, this change is entirely upwards-compatible and requires no change to existing code. If you want to pass in additional data to pcre_exec(), you can either place it in a pcre_extra block provided by pcre_study(), or create your own pcre_extra block. 46. pcretest has been extended to test the PCRE_EXTRA_MATCH_LIMIT feature. If a data string contains the escape sequence \M, pcretest calls pcre_exec() several times with different match limits, until it finds the minimum value needed for pcre_exec() to complete. The value is then output. This can be instructive; for most simple matches the number is quite small, but for pathological cases it gets very large very quickly. 47. There's a new option for pcre_fullinfo() called PCRE_INFO_STUDYSIZE. It returns the size of the data block pointed to by the study_data field in a pcre_extra block, that is, the value that was passed as the argument to pcre_malloc() when PCRE was getting memory in which to place the information created by pcre_study(). The fourth argument should point to a size_t variable. pcretest has been extended so that this information is shown after a successful pcre_study() call when information about the compiled regex is being displayed. 48. Cosmetic change to Makefile: there's no need to have / after $(DESTDIR) because what follows is always an absolute path. (Later: it turns out that this is more than cosmetic for MinGW, because it doesn't like empty path components.) 49. Some changes have been made to the callout feature (see 28 above): (i) A callout function now has three choices for what it returns: 0 => success, carry on matching > 0 => failure at this point, but backtrack if possible < 0 => serious error, return this value from pcre_exec() Negative values should normally be chosen from the set of PCRE_ERROR_xxx values. In particular, returning PCRE_ERROR_NOMATCH forces a standard "match failed" error. The error number PCRE_ERROR_CALLOUT is reserved for use by callout functions. It will never be used by PCRE itself. (ii) The pcre_extra structure (see 45 above) has a void * field called callout_data, with corresponding flag bit PCRE_EXTRA_CALLOUT_DATA. The pcre_callout_block structure has a field of the same name. The contents of the field passed in the pcre_extra structure are passed to the callout function in the corresponding field in the callout block. This makes it easier to use the same callout-containing regex from multiple threads. For testing, the pcretest program has a new data escape \C*n pass the number n (may be negative) as callout_data If the callout function in pcretest receives a non-zero value as callout_data, it returns that value. 50. Makefile wasn't handling CFLAGS properly when compiling dftables. Also, there were some redundant $(CFLAGS) in commands that are now specified as $(LINK), which already includes $(CFLAGS). 51. Extensions to UTF-8 support are listed below. These all apply when (a) PCRE has been compiled with UTF-8 support *and* pcre_compile() has been compiled with the PCRE_UTF8 flag. Patterns that are compiled without that flag assume one-byte characters throughout. Note that case-insensitive matching applies only to characters whose values are less than 256. PCRE doesn't support the notion of cases for higher-valued characters. (i) A character class whose characters are all within 0-255 is handled as a bit map, and the map is inverted for negative classes. Previously, a character > 255 always failed to match such a class; however it should match if the class was a negative one (e.g. [^ab]). This has been fixed. (ii) A negated character class with a single character < 255 is coded as "not this character" (OP_NOT). This wasn't working properly when the test character was multibyte, either singly or repeated. (iii) Repeats of multibyte characters are now handled correctly in UTF-8 mode, for example: \x{100}{2,3}. (iv) The character escapes \b, \B, \d, \D, \s, \S, \w, and \W (either singly or repeated) now correctly test multibyte characters. However, PCRE doesn't recognize any characters with values greater than 255 as digits, spaces, or word characters. Such characters always match \D, \S, and \W, and never match \d, \s, or \w. (v) Classes may now contain characters and character ranges with values greater than 255. For example: [ab\x{100}-\x{400}]. (vi) pcregrep now has a --utf-8 option (synonym -u) which makes it call PCRE in UTF-8 mode. 52. The info request value PCRE_INFO_FIRSTCHAR has been renamed PCRE_INFO_FIRSTBYTE because it is a byte value. However, the old name is retained for backwards compatibility. (Note that LASTLITERAL is also a byte value.) 53. The single man page has become too large. I have therefore split it up into a number of separate man pages. These also give rise to individual HTML pages; these are now put in a separate directory, and there is an index.html page that lists them all. Some hyperlinking between the pages has been installed. 54. Added convenience functions for handling named capturing parentheses. 55. Unknown escapes inside character classes (e.g. [\M]) and escapes that aren't interpreted therein (e.g. [\C]) are literals in Perl. This is now also true in PCRE, except when the PCRE_EXTENDED option is set, in which case they are faulted. 56. Introduced HOST_CC and HOST_CFLAGS which can be set in the environment when calling configure. These values are used when compiling the dftables.c program which is run to generate the source of the default character tables. They default to the values of CC and CFLAGS. If you are cross-compiling PCRE, you will need to set these values. 57. Updated the building process for Windows DLL, as provided by Fred Cox. Version 3.9 02-Jan-02 --------------------- 1. A bit of extraneous text had somehow crept into the pcregrep documentation. 2. If --disable-static was given, the building process failed when trying to build pcretest and pcregrep. (For some reason it was using libtool to compile them, which is not right, as they aren't part of the library.) Version 3.8 18-Dec-01 --------------------- 1. The experimental UTF-8 code was completely screwed up. It was packing the bytes in the wrong order. How dumb can you get? Version 3.7 29-Oct-01 --------------------- 1. In updating pcretest to check change 1 of version 3.6, I screwed up. This caused pcretest, when used on the test data, to segfault. Unfortunately, this didn't happen under Solaris 8, where I normally test things. 2. The Makefile had to be changed to make it work on BSD systems, where 'make' doesn't seem to recognize that ./xxx and xxx are the same file. (This entry isn't in ChangeLog distributed with 3.7 because I forgot when I hastily made this fix an hour or so after the initial 3.7 release.) Version 3.6 23-Oct-01 --------------------- 1. Crashed with /(sens|respons)e and \1ibility/ and "sense and sensibility" if offsets passed as NULL with zero offset count. 2. The config.guess and config.sub files had not been updated when I moved to the latest autoconf. Version 3.5 15-Aug-01 --------------------- 1. Added some missing #if !defined NOPOSIX conditionals in pcretest.c that had been forgotten. 2. By using declared but undefined structures, we can avoid using "void" definitions in pcre.h while keeping the internal definitions of the structures private. 3. The distribution is now built using autoconf 2.50 and libtool 1.4. From a user point of view, this means that both static and shared libraries are built by default, but this can be individually controlled. More of the work of handling this static/shared cases is now inside libtool instead of PCRE's make file. 4. The pcretest utility is now installed along with pcregrep because it is useful for users (to test regexs) and by doing this, it automatically gets relinked by libtool. The documentation has been turned into a man page, so there are now .1, .txt, and .html versions in /doc. 5. Upgrades to pcregrep: (i) Added long-form option names like gnu grep. (ii) Added --help to list all options with an explanatory phrase. (iii) Added -r, --recursive to recurse into sub-directories. (iv) Added -f, --file to read patterns from a file. 6. pcre_exec() was referring to its "code" argument before testing that argument for NULL (and giving an error if it was NULL). 7. Upgraded Makefile.in to allow for compiling in a different directory from the source directory. 8. Tiny buglet in pcretest: when pcre_fullinfo() was called to retrieve the options bits, the pointer it was passed was to an int instead of to an unsigned long int. This mattered only on 64-bit systems. 9. Fixed typo (3.4/1) in pcre.h again. Sigh. I had changed pcre.h (which is generated) instead of pcre.in, which it its source. Also made the same change in several of the .c files. 10. A new release of gcc defines printf() as a macro, which broke pcretest because it had an ifdef in the middle of a string argument for printf(). Fixed by using separate calls to printf(). 11. Added --enable-newline-is-cr and --enable-newline-is-lf to the configure script, to force use of CR or LF instead of \n in the source. On non-Unix systems, the value can be set in config.h. 12. The limit of 200 on non-capturing parentheses is a _nesting_ limit, not an absolute limit. Changed the text of the error message to make this clear, and likewise updated the man page. 13. The limit of 99 on the number of capturing subpatterns has been removed. The new limit is 65535, which I hope will not be a "real" limit. Version 3.4 22-Aug-00 --------------------- 1. Fixed typo in pcre.h: unsigned const char * changed to const unsigned char *. 2. Diagnose condition (?(0) as an error instead of crashing on matching. Version 3.3 01-Aug-00 --------------------- 1. If an octal character was given, but the value was greater than \377, it was not getting masked to the least significant bits, as documented. This could lead to crashes in some systems. 2. Perl 5.6 (if not earlier versions) accepts classes like [a-\d] and treats the hyphen as a literal. PCRE used to give an error; it now behaves like Perl. 3. Added the functions pcre_free_substring() and pcre_free_substring_list(). These just pass their arguments on to (pcre_free)(), but they are provided because some uses of PCRE bind it to non-C systems that can call its functions, but cannot call free() or pcre_free() directly. 4. Add "make test" as a synonym for "make check". Corrected some comments in the Makefile. 5. Add $(DESTDIR)/ in front of all the paths in the "install" target in the Makefile. 6. Changed the name of pgrep to pcregrep, because Solaris has introduced a command called pgrep for grepping around the active processes. 7. Added the beginnings of support for UTF-8 character strings. 8. Arranged for the Makefile to pass over the settings of CC, CFLAGS, and RANLIB to ./ltconfig so that they are used by libtool. I think these are all the relevant ones. (AR is not passed because ./ltconfig does its own figuring out for the ar command.) Version 3.2 12-May-00 --------------------- This is purely a bug fixing release. 1. If the pattern /((Z)+|A)*/ was matched agained ZABCDEFG it matched Z instead of ZA. This was just one example of several cases that could provoke this bug, which was introduced by change 9 of version 2.00. The code for breaking infinite loops after an iteration that matches an empty string was't working correctly. 2. The pcretest program was not imitating Perl correctly for the pattern /a*/g when matched against abbab (for example). After matching an empty string, it wasn't forcing anchoring when setting PCRE_NOTEMPTY for the next attempt; this caused it to match further down the string than it should. 3. The code contained an inclusion of sys/types.h. It isn't clear why this was there because it doesn't seem to be needed, and it causes trouble on some systems, as it is not a Standard C header. It has been removed. 4. Made 4 silly changes to the source to avoid stupid compiler warnings that were reported on the Macintosh. The changes were from while ((c = *(++ptr)) != 0 && c != '\n'); to while ((c = *(++ptr)) != 0 && c != '\n') ; Totally extraordinary, but if that's what it takes... 5. PCRE is being used in one environment where neither memmove() nor bcopy() is available. Added HAVE_BCOPY and an autoconf test for it; if neither HAVE_MEMMOVE nor HAVE_BCOPY is set, use a built-in emulation function which assumes the way PCRE uses memmove() (always moving upwards). 6. PCRE is being used in one environment where strchr() is not available. There was only one use in pcre.c, and writing it out to avoid strchr() probably gives faster code anyway. Version 3.1 09-Feb-00 --------------------- The only change in this release is the fixing of some bugs in Makefile.in for the "install" target: (1) It was failing to install pcreposix.h. (2) It was overwriting the pcre.3 man page with the pcreposix.3 man page. Version 3.0 01-Feb-00 --------------------- 1. Add support for the /+ modifier to perltest (to output $` like it does in pcretest). 2. Add support for the /g modifier to perltest. 3. Fix pcretest so that it behaves even more like Perl for /g when the pattern matches null strings. 4. Fix perltest so that it doesn't do unwanted things when fed an empty pattern. Perl treats empty patterns specially - it reuses the most recent pattern, which is not what we want. Replace // by /(?#)/ in order to avoid this effect. 5. The POSIX interface was broken in that it was just handing over the POSIX captured string vector to pcre_exec(), but (since release 2.00) PCRE has required a bigger vector, with some working space on the end. This means that the POSIX wrapper now has to get and free some memory, and copy the results. 6. Added some simple autoconf support, placing the test data and the documentation in separate directories, re-organizing some of the information files, and making it build pcre-config (a GNU standard). Also added libtool support for building PCRE as a shared library, which is now the default. 7. Got rid of the leading zero in the definition of PCRE_MINOR because 08 and 09 are not valid octal constants. Single digits will be used for minor values less than 10. 8. Defined REG_EXTENDED and REG_NOSUB as zero in the POSIX header, so that existing programs that set these in the POSIX interface can use PCRE without modification. 9. Added a new function, pcre_fullinfo() with an extensible interface. It can return all that pcre_info() returns, plus additional data. The pcre_info() function is retained for compatibility, but is considered to be obsolete. 10. Added experimental recursion feature (?R) to handle one common case that Perl 5.6 will be able to do with (?p{...}). 11. Added support for POSIX character classes like [:alpha:], which Perl is adopting. Version 2.08 31-Aug-99 ---------------------- 1. When startoffset was not zero and the pattern began with ".*", PCRE was not trying to match at the startoffset position, but instead was moving forward to the next newline as if a previous match had failed. 2. pcretest was not making use of PCRE_NOTEMPTY when repeating for /g and /G, and could get into a loop if a null string was matched other than at the start of the subject. 3. Added definitions of PCRE_MAJOR and PCRE_MINOR to pcre.h so the version can be distinguished at compile time, and for completeness also added PCRE_DATE. 5. Added Paul Sokolovsky's minor changes to make it easy to compile a Win32 DLL in GnuWin32 environments. Version 2.07 29-Jul-99 ---------------------- 1. The documentation is now supplied in plain text form and HTML as well as in the form of man page sources. 2. C++ compilers don't like assigning (void *) values to other pointer types. In particular this affects malloc(). Although there is no problem in Standard C, I've put in casts to keep C++ compilers happy. 3. Typo on pcretest.c; a cast of (unsigned char *) in the POSIX regexec() call should be (const char *). 4. If NOPOSIX is defined, pcretest.c compiles without POSIX support. This may be useful for non-Unix systems who don't want to bother with the POSIX stuff. However, I haven't made this a standard facility. The documentation doesn't mention it, and the Makefile doesn't support it. 5. The Makefile now contains an "install" target, with editable destinations at the top of the file. The pcretest program is not installed. 6. pgrep -V now gives the PCRE version number and date. 7. Fixed bug: a zero repetition after a literal string (e.g. /abcde{0}/) was causing the entire string to be ignored, instead of just the last character. 8. If a pattern like /"([^\\"]+|\\.)*"/ is applied in the normal way to a non-matching string, it can take a very, very long time, even for strings of quite modest length, because of the nested recursion. PCRE now does better in some of these cases. It does this by remembering the last required literal character in the pattern, and pre-searching the subject to ensure it is present before running the real match. In other words, it applies a heuristic to detect some types of certain failure quickly, and in the above example, if presented with a string that has no trailing " it gives "no match" very quickly. 9. A new runtime option PCRE_NOTEMPTY causes null string matches to be ignored; other alternatives are tried instead. Version 2.06 09-Jun-99 ---------------------- 1. Change pcretest's output for amount of store used to show just the code space, because the remainder (the data block) varies in size between 32-bit and 64-bit systems. 2. Added an extra argument to pcre_exec() to supply an offset in the subject to start matching at. This allows lookbehinds to work when searching for multiple occurrences in a string. 3. Added additional options to pcretest for testing multiple occurrences: /+ outputs the rest of the string that follows a match /g loops for multiple occurrences, using the new startoffset argument /G loops for multiple occurrences by passing an incremented pointer 4. PCRE wasn't doing the "first character" optimization for patterns starting with \b or \B, though it was doing it for other lookbehind assertions. That is, it wasn't noticing that a match for a pattern such as /\bxyz/ has to start with the letter 'x'. On long subject strings, this gives a significant speed-up. Version 2.05 21-Apr-99 ---------------------- 1. Changed the type of magic_number from int to long int so that it works properly on 16-bit systems. 2. Fixed a bug which caused patterns starting with .* not to work correctly when the subject string contained newline characters. PCRE was assuming anchoring for such patterns in all cases, which is not correct because .* will not pass a newline unless PCRE_DOTALL is set. It now assumes anchoring only if DOTALL is set at top level; otherwise it knows that patterns starting with .* must be retried after every newline in the subject. Version 2.04 18-Feb-99 ---------------------- 1. For parenthesized subpatterns with repeats whose minimum was zero, the computation of the store needed to hold the pattern was incorrect (too large). If such patterns were nested a few deep, this could multiply and become a real problem. 2. Added /M option to pcretest to show the memory requirement of a specific pattern. Made -m a synonym of -s (which does this globally) for compatibility. 3. Subpatterns of the form (regex){n,m} (i.e. limited maximum) were being compiled in such a way that the backtracking after subsequent failure was pessimal. Something like (a){0,3} was compiled as (a)?(a)?(a)? instead of ((a)((a)(a)?)?)? with disastrous performance if the maximum was of any size. Version 2.03 02-Feb-99 ---------------------- 1. Fixed typo and small mistake in man page. 2. Added 4th condition (GPL supersedes if conflict) and created separate LICENCE file containing the conditions. 3. Updated pcretest so that patterns such as /abc\/def/ work like they do in Perl, that is the internal \ allows the delimiter to be included in the pattern. Locked out the use of \ as a delimiter. If \ immediately follows the final delimiter, add \ to the end of the pattern (to test the error). 4. Added the convenience functions for extracting substrings after a successful match. Updated pcretest to make it able to test these functions. Version 2.02 14-Jan-99 ---------------------- 1. Initialized the working variables associated with each extraction so that their saving and restoring doesn't refer to uninitialized store. 2. Put dummy code into study.c in order to trick the optimizer of the IBM C compiler for OS/2 into generating correct code. Apparently IBM isn't going to fix the problem. 3. Pcretest: the timing code wasn't using LOOPREPEAT for timing execution calls, and wasn't printing the correct value for compiling calls. Increased the default value of LOOPREPEAT, and the number of significant figures in the times. 4. Changed "/bin/rm" in the Makefile to "-rm" so it works on Windows NT. 5. Renamed "deftables" as "dftables" to get it down to 8 characters, to avoid a building problem on Windows NT with a FAT file system. Version 2.01 21-Oct-98 ---------------------- 1. Changed the API for pcre_compile() to allow for the provision of a pointer to character tables built by pcre_maketables() in the current locale. If NULL is passed, the default tables are used. Version 2.00 24-Sep-98 ---------------------- 1. Since the (>?) facility is in Perl 5.005, don't require PCRE_EXTRA to enable it any more. 2. Allow quantification of (?>) groups, and make it work correctly. 3. The first character computation wasn't working for (?>) groups. 4. Correct the implementation of \Z (it is permitted to match on the \n at the end of the subject) and add 5.005's \z, which really does match only at the very end of the subject. 5. Remove the \X "cut" facility; Perl doesn't have it, and (?> is neater. 6. Remove the ability to specify CASELESS, MULTILINE, DOTALL, and DOLLAR_END_ONLY at runtime, to make it possible to implement the Perl 5.005 localized options. All options to pcre_study() were also removed. 7. Add other new features from 5.005: $(?<= positive lookbehind $(?a*))*/ (a PCRE_EXTRA facility). Version 1.00 18-Nov-97 ---------------------- 1. Added compile-time macros to support systems such as SunOS4 which don't have memmove() or strerror() but have other things that can be used instead. 2. Arranged that "make clean" removes the executables. Version 0.99 27-Oct-97 ---------------------- 1. Fixed bug in code for optimizing classes with only one character. It was initializing a 32-byte map regardless, which could cause it to run off the end of the memory it had got. 2. Added, conditional on PCRE_EXTRA, the proposed (?>REGEX) construction. Version 0.98 22-Oct-97 ---------------------- 1. Fixed bug in code for handling temporary memory usage when there are more back references than supplied space in the ovector. This could cause segfaults. Version 0.97 21-Oct-97 ---------------------- 1. Added the \X "cut" facility, conditional on PCRE_EXTRA. 2. Optimized negated single characters not to use a bit map. 3. Brought error texts together as macro definitions; clarified some of them; fixed one that was wrong - it said "range out of order" when it meant "invalid escape sequence". 4. Changed some char * arguments to const char *. 5. Added PCRE_NOTBOL and PCRE_NOTEOL (from POSIX). 6. Added the POSIX-style API wrapper in pcreposix.a and testing facilities in pcretest. Version 0.96 16-Oct-97 ---------------------- 1. Added a simple "pgrep" utility to the distribution. 2. Fixed an incompatibility with Perl: "{" is now treated as a normal character unless it appears in one of the precise forms "{ddd}", "{ddd,}", or "{ddd,ddd}" where "ddd" means "one or more decimal digits". 3. Fixed serious bug. If a pattern had a back reference, but the call to pcre_exec() didn't supply a large enough ovector to record the related identifying subpattern, the match always failed. PCRE now remembers the number of the largest back reference, and gets some temporary memory in which to save the offsets during matching if necessary, in order to ensure that backreferences always work. 4. Increased the compatibility with Perl in a number of ways: (a) . no longer matches \n by default; an option PCRE_DOTALL is provided to request this handling. The option can be set at compile or exec time. (b) $ matches before a terminating newline by default; an option PCRE_DOLLAR_ENDONLY is provided to override this (but not in multiline mode). The option can be set at compile or exec time. (c) The handling of \ followed by a digit other than 0 is now supposed to be the same as Perl's. If the decimal number it represents is less than 10 or there aren't that many previous left capturing parentheses, an octal escape is read. Inside a character class, it's always an octal escape, even if it is a single digit. (d) An escaped but undefined alphabetic character is taken as a literal, unless PCRE_EXTRA is set. Currently this just reserves the remaining escapes. (e) {0} is now permitted. (The previous item is removed from the compiled pattern). 5. Changed all the names of code files so that the basic parts are no longer than 10 characters, and abolished the teeny "globals.c" file. 6. Changed the handling of character classes; they are now done with a 32-byte bit map always. 7. Added the -d and /D options to pcretest to make it possible to look at the internals of compilation without having to recompile pcre. Version 0.95 23-Sep-97 ---------------------- 1. Fixed bug in pre-pass concerning escaped "normal" characters such as \x5c or \x20 at the start of a run of normal characters. These were being treated as real characters, instead of the source characters being re-checked. Version 0.94 18-Sep-97 ---------------------- 1. The functions are now thread-safe, with the caveat that the global variables containing pointers to malloc() and free() or alternative functions are the same for all threads. 2. Get pcre_study() to generate a bitmap of initial characters for non- anchored patterns when this is possible, and use it if passed to pcre_exec(). Version 0.93 15-Sep-97 ---------------------- 1. /(b)|(:+)/ was computing an incorrect first character. 2. Add pcre_study() to the API and the passing of pcre_extra to pcre_exec(), but not actually doing anything yet. 3. Treat "-" characters in classes that cannot be part of ranges as literals, as Perl does (e.g. [-az] or [az-]). 4. Set the anchored flag if a branch starts with .* or .*? because that tests all possible positions. 5. Split up into different modules to avoid including unneeded functions in a compiled binary. However, compile and exec are still in one module. The "study" function is split off. 6. The character tables are now in a separate module whose source is generated by an auxiliary program - but can then be edited by hand if required. There are now no calls to isalnum(), isspace(), isdigit(), isxdigit(), tolower() or toupper() in the code. 7. Turn the malloc/free funtions variables into pcre_malloc and pcre_free and make them global. Abolish the function for setting them, as the caller can now set them directly. Version 0.92 11-Sep-97 ---------------------- 1. A repeat with a fixed maximum and a minimum of 1 for an ordinary character (e.g. /a{1,3}/) was broken (I mis-optimized it). 2. Caseless matching was not working in character classes if the characters in the pattern were in upper case. 3. Make ranges like [W-c] work in the same way as Perl for caseless matching. 4. Make PCRE_ANCHORED public and accept as a compile option. 5. Add an options word to pcre_exec() and accept PCRE_ANCHORED and PCRE_CASELESS at run time. Add escapes \A and \I to pcretest to cause it to pass them. 6. Give an error if bad option bits passed at compile or run time. 7. Add PCRE_MULTILINE at compile and exec time, and (?m) as well. Add \M to pcretest to cause it to pass that flag. 8. Add pcre_info(), to get the number of identifying subpatterns, the stored options, and the first character, if set. 9. Recognize C+ or C{n,m} where n >= 1 as providing a fixed starting character. Version 0.91 10-Sep-97 ---------------------- 1. PCRE was failing to diagnose unlimited repeats of subpatterns that could match the empty string as in /(a*)*/. It was looping and ultimately crashing. 2. PCRE was looping on encountering an indefinitely repeated back reference to a subpattern that had matched an empty string, e.g. /(a|)\1*/. It now does what Perl does - treats the match as successful. **** 070701000382a6000081a40000000000000000000000014f79083e00009ed0000000b500010002ffffffffffffffff0000002500000000root/usr/local/share/doc/pcre/READMEREADME file for PCRE (Perl-compatible regular expression library) ----------------------------------------------------------------- The latest release of PCRE is always available in three alternative formats from: ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-xxx.tar.gz ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-xxx.tar.bz2 ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-xxx.zip There is a mailing list for discussion about the development of PCRE at pcre-dev@exim.org Please read the NEWS file if you are upgrading from a previous release. The contents of this README file are: The PCRE APIs Documentation for PCRE Contributions by users of PCRE Building PCRE on non-Unix systems Building PCRE on Unix-like systems Retrieving configuration information on Unix-like systems Shared libraries on Unix-like systems Cross-compiling on Unix-like systems Using HP's ANSI C++ compiler (aCC) Using PCRE from MySQL Making new tarballs Testing PCRE Character tables File manifest The PCRE APIs ------------- PCRE is written in C, and it has its own API. There are two sets of functions, one for the 8-bit library, which processes strings of bytes, and one for the 16-bit library, which processes strings of 16-bit values. The distribution also includes a set of C++ wrapper functions (see the pcrecpp man page for details), courtesy of Google Inc., which can be used to call the 8-bit PCRE library from C++. In addition, there is a set of C wrapper functions (again, just for the 8-bit library) that are based on the POSIX regular expression API (see the pcreposix man page). These end up in the library called libpcreposix. Note that this just provides a POSIX calling interface to PCRE; the regular expressions themselves still follow Perl syntax and semantics. The POSIX API is restricted, and does not give full access to all of PCRE's facilities. The header file for the POSIX-style functions is called pcreposix.h. The official POSIX name is regex.h, but I did not want to risk possible problems with existing files of that name by distributing it that way. To use PCRE with an existing program that uses the POSIX API, pcreposix.h will have to be renamed or pointed at by a link. If you are using the POSIX interface to PCRE and there is already a POSIX regex library installed on your system, as well as worrying about the regex.h header file (as mentioned above), you must also take care when linking programs to ensure that they link with PCRE's libpcreposix library. Otherwise they may pick up the POSIX functions of the same name from the other library. One way of avoiding this confusion is to compile PCRE with the addition of -Dregcomp=PCREregcomp (and similarly for the other POSIX functions) to the compiler flags (CFLAGS if you are using "configure" -- see below). This has the effect of renaming the functions so that the names no longer clash. Of course, you have to do the same thing for your applications, or write them using the new names. Documentation for PCRE ---------------------- If you install PCRE in the normal way on a Unix-like system, you will end up with a set of man pages whose names all start with "pcre". The one that is just called "pcre" lists all the others. In addition to these man pages, the PCRE documentation is supplied in two other forms: 1. There are files called doc/pcre.txt, doc/pcregrep.txt, and doc/pcretest.txt in the source distribution. The first of these is a concatenation of the text forms of all the section 3 man pages except those that summarize individual functions. The other two are the text forms of the section 1 man pages for the pcregrep and pcretest commands. These text forms are provided for ease of scanning with text editors or similar tools. They are installed in /share/doc/pcre, where is the installation prefix (defaulting to /usr/local). 2. A set of files containing all the documentation in HTML form, hyperlinked in various ways, and rooted in a file called index.html, is distributed in doc/html and installed in /share/doc/pcre/html. Users of PCRE have contributed files containing the documentation for various releases in CHM format. These can be found in the Contrib directory of the FTP site (see next section). Contributions by users of PCRE ------------------------------ You can find contributions from PCRE users in the directory ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/Contrib There is a README file giving brief descriptions of what they are. Some are complete in themselves; others are pointers to URLs containing relevant files. Some of this material is likely to be well out-of-date. Several of the earlier contributions provided support for compiling PCRE on various flavours of Windows (I myself do not use Windows). Nowadays there is more Windows support in the standard distribution, so these contibutions have been archived. Building PCRE on non-Unix systems --------------------------------- For a non-Unix system, please read the comments in the file NON-UNIX-USE, though if your system supports the use of "configure" and "make" you may be able to build PCRE in the same way as for Unix-like systems. PCRE can also be configured in many platform environments using the GUI facility provided by CMake's cmake-gui command. This creates Makefiles, solution files, etc. PCRE has been compiled on many different operating systems. It should be straightforward to build PCRE on any system that has a Standard C compiler and library, because it uses only Standard C functions. Building PCRE on Unix-like systems ---------------------------------- If you are using HP's ANSI C++ compiler (aCC), please see the special note in the section entitled "Using HP's ANSI C++ compiler (aCC)" below. The following instructions assume the use of the widely used "configure, make, make install" process. There is also support for CMake in the PCRE distribution; there are some comments about using CMake in the NON-UNIX-USE file, though it can also be used in Unix-like systems. To build PCRE on a Unix-like system, first run the "configure" command from the PCRE distribution directory, with your current directory set to the directory where you want the files to be created. This command is a standard GNU "autoconf" configuration script, for which generic instructions are supplied in the file INSTALL. Most commonly, people build PCRE within its own distribution directory, and in this case, on many systems, just running "./configure" is sufficient. However, the usual methods of changing standard defaults are available. For example: CFLAGS='-O2 -Wall' ./configure --prefix=/opt/local This command specifies that the C compiler should be run with the flags '-O2 -Wall' instead of the default, and that "make install" should install PCRE under /opt/local instead of the default /usr/local. If you want to build in a different directory, just run "configure" with that directory as current. For example, suppose you have unpacked the PCRE source into /source/pcre/pcre-xxx, but you want to build it in /build/pcre/pcre-xxx: cd /build/pcre/pcre-xxx /source/pcre/pcre-xxx/configure PCRE is written in C and is normally compiled as a C library. However, it is possible to build it as a C++ library, though the provided building apparatus does not have any features to support this. There are some optional features that can be included or omitted from the PCRE library. They are also documented in the pcrebuild man page. . By default, both shared and static libraries are built. You can change this by adding one of these options to the "configure" command: --disable-shared --disable-static (See also "Shared libraries on Unix-like systems" below.) . By default, only the 8-bit library is built. If you add --enable-pcre16 to the "configure" command, the 16-bit library is also built. If you want only the 16-bit library, use "./configure --enable-pcre16 --disable-pcre8". . If you are building the 8-bit library and want to suppress the building of the C++ wrapper library, you can add --disable-cpp to the "configure" command. Otherwise, when "configure" is run without --disable-pcre8, it will try to find a C++ compiler and C++ header files, and if it succeeds, it will try to build the C++ wrapper. . If you want to include support for just-in-time compiling, which can give large performance improvements on certain platforms, add --enable-jit to the "configure" command. This support is available only for certain hardware architectures. If you try to enable it on an unsupported architecture, there will be a compile time error. . When JIT support is enabled, pcregrep automatically makes use of it, unless you add --disable-pcregrep-jit to the "configure" command. . If you want to make use of the support for UTF-8 Unicode character strings in the 8-bit library, or UTF-16 Unicode character strings in the 16-bit library, you must add --enable-utf to the "configure" command. Without it, the code for handling UTF-8 and UTF-16 is not included in the relevant library. Even when --enable-utf is included, the use of a UTF encoding still has to be enabled by an option at run time. When PCRE is compiled with this option, its input can only either be ASCII or UTF-8/16, even when running on EBCDIC platforms. It is not possible to use both --enable-utf and --enable-ebcdic at the same time. . There are no separate options for enabling UTF-8 and UTF-16 independently because that would allow ridiculous settings such as requesting UTF-16 support while building only the 8-bit library. However, the option --enable-utf8 is retained for backwards compatibility with earlier releases that did not support 16-bit character strings. It is synonymous with --enable-utf. It is not possible to configure one library with UTF support and the other without in the same configuration. . If, in addition to support for UTF-8/16 character strings, you want to include support for the \P, \p, and \X sequences that recognize Unicode character properties, you must add --enable-unicode-properties to the "configure" command. This adds about 30K to the size of the library (in the form of a property table); only the basic two-letter properties such as Lu are supported. . You can build PCRE to recognize either CR or LF or the sequence CRLF or any of the preceding, or any of the Unicode newline sequences as indicating the end of a line. Whatever you specify at build time is the default; the caller of PCRE can change the selection at run time. The default newline indicator is a single LF character (the Unix standard). You can specify the default newline indicator by adding --enable-newline-is-cr or --enable-newline-is-lf or --enable-newline-is-crlf or --enable-newline-is-anycrlf or --enable-newline-is-any to the "configure" command, respectively. If you specify --enable-newline-is-cr or --enable-newline-is-crlf, some of the standard tests will fail, because the lines in the test files end with LF. Even if the files are edited to change the line endings, there are likely to be some failures. With --enable-newline-is-anycrlf or --enable-newline-is-any, many tests should succeed, but there may be some failures. . By default, the sequence \R in a pattern matches any Unicode line ending sequence. This is independent of the option specifying what PCRE considers to be the end of a line (see above). However, the caller of PCRE can restrict \R to match only CR, LF, or CRLF. You can make this the default by adding --enable-bsr-anycrlf to the "configure" command (bsr = "backslash R"). . When called via the POSIX interface, PCRE uses malloc() to get additional storage for processing capturing parentheses if there are more than 10 of them in a pattern. You can increase this threshold by setting, for example, --with-posix-malloc-threshold=20 on the "configure" command. . PCRE has a counter that can be set to limit the amount of resources it uses. If the limit is exceeded during a match, the match fails. The default is ten million. You can change the default by setting, for example, --with-match-limit=500000 on the "configure" command. This is just the default; individual calls to pcre_exec() can supply their own value. There is more discussion on the pcreapi man page. . There is a separate counter that limits the depth of recursive function calls during a matching process. This also has a default of ten million, which is essentially "unlimited". You can change the default by setting, for example, --with-match-limit-recursion=500000 Recursive function calls use up the runtime stack; running out of stack can cause programs to crash in strange ways. There is a discussion about stack sizes in the pcrestack man page. . The default maximum compiled pattern size is around 64K. You can increase this by adding --with-link-size=3 to the "configure" command. In the 8-bit library, PCRE then uses three bytes instead of two for offsets to different parts of the compiled pattern. In the 16-bit library, --with-link-size=3 is the same as --with-link-size=4, which (in both libraries) uses four-byte offsets. Increasing the internal link size reduces performance. . You can build PCRE so that its internal match() function that is called from pcre_exec() does not call itself recursively. Instead, it uses memory blocks obtained from the heap via the special functions pcre_stack_malloc() and pcre_stack_free() to save data that would otherwise be saved on the stack. To build PCRE like this, use --disable-stack-for-recursion on the "configure" command. PCRE runs more slowly in this mode, but it may be necessary in environments with limited stack sizes. This applies only to the normal execution of the pcre_exec() function; if JIT support is being successfully used, it is not relevant. Equally, it does not apply to pcre_dfa_exec(), which does not use deeply nested recursion. There is a discussion about stack sizes in the pcrestack man page. . For speed, PCRE uses four tables for manipulating and identifying characters whose code point values are less than 256. By default, it uses a set of tables for ASCII encoding that is part of the distribution. If you specify --enable-rebuild-chartables a program called dftables is compiled and run in the default C locale when you obey "make". It builds a source file called pcre_chartables.c. If you do not specify this option, pcre_chartables.c is created as a copy of pcre_chartables.c.dist. See "Character tables" below for further information. . It is possible to compile PCRE for use on systems that use EBCDIC as their character code (as opposed to ASCII) by specifying --enable-ebcdic This automatically implies --enable-rebuild-chartables (see above). However, when PCRE is built this way, it always operates in EBCDIC. It cannot support both EBCDIC and UTF-8/16. . The pcregrep program currently supports only 8-bit data files, and so requires the 8-bit PCRE library. It is possible to compile pcregrep to use libz and/or libbz2, in order to read .gz and .bz2 files (respectively), by specifying one or both of --enable-pcregrep-libz --enable-pcregrep-libbz2 Of course, the relevant libraries must be installed on your system. . The default size of internal buffer used by pcregrep can be set by, for example: --with-pcregrep-bufsize=50K The default value is 20K. . It is possible to compile pcretest so that it links with the libreadline library, by specifying --enable-pcretest-libreadline If this is done, when pcretest's input is from a terminal, it reads it using the readline() function. This provides line-editing and history facilities. Note that libreadline is GPL-licenced, so if you distribute a binary of pcretest linked in this way, there may be licensing issues. Setting this option causes the -lreadline option to be added to the pcretest build. In many operating environments with a sytem-installed readline library this is sufficient. However, in some environments (e.g. if an unmodified distribution version of readline is in use), it may be necessary to specify something like LIBS="-lncurses" as well. This is because, to quote the readline INSTALL, "Readline uses the termcap functions, but does not link with the termcap or curses library itself, allowing applications which link with readline the to choose an appropriate library." If you get error messages about missing functions tgetstr, tgetent, tputs, tgetflag, or tgoto, this is the problem, and linking with the ncurses library should fix it. The "configure" script builds the following files for the basic C library: . Makefile the makefile that builds the library . config.h build-time configuration options for the library . pcre.h the public PCRE header file . pcre-config script that shows the building settings such as CFLAGS that were set for "configure" . libpcre.pc ) data for the pkg-config command . libpcre16.pc ) . libpcreposix.pc ) . libtool script that builds shared and/or static libraries . RunTest script for running tests on the basic C library . RunGrepTest script for running tests on the pcregrep command Versions of config.h and pcre.h are distributed in the PCRE tarballs under the names config.h.generic and pcre.h.generic. These are provided for those who have to built PCRE without using "configure" or CMake. If you use "configure" or CMake, the .generic versions are not used. When building the 8-bit library, if a C++ compiler is found, the following files are also built: . libpcrecpp.pc data for the pkg-config command . pcrecpparg.h header file for calling PCRE via the C++ wrapper . pcre_stringpiece.h header for the C++ "stringpiece" functions The "configure" script also creates config.status, which is an executable script that can be run to recreate the configuration, and config.log, which contains compiler output from tests that "configure" runs. Once "configure" has run, you can run "make". This builds either or both of the libraries libpcre and libpcre16, and a test program called pcretest. If you enabled JIT support with --enable-jit, a test program called pcre_jit_test is built as well. If the 8-bit library is built, libpcreposix and the pcregrep command are also built, and if a C++ compiler was found on your system, and you did not disable it with --disable-cpp, "make" builds the C++ wrapper library, which is called libpcrecpp, as well as some test programs called pcrecpp_unittest, pcre_scanner_unittest, and pcre_stringpiece_unittest. The command "make check" runs all the appropriate tests. Details of the PCRE tests are given below in a separate section of this document. You can use "make install" to install PCRE into live directories on your system. The following are installed (file names are all relative to the that is set when "configure" is run): Commands (bin): pcretest pcregrep (if 8-bit support is enabled) pcre-config Libraries (lib): libpcre16 (if 16-bit support is enabled) libpcre (if 8-bit support is enabled) libpcreposix (if 8-bit support is enabled) libpcrecpp (if 8-bit and C++ support is enabled) Configuration information (lib/pkgconfig): libpcre16.pc libpcre.pc libpcreposix.pc libpcrecpp.pc (if C++ support is enabled) Header files (include): pcre.h pcreposix.h pcre_scanner.h ) pcre_stringpiece.h ) if C++ support is enabled pcrecpp.h ) pcrecpparg.h ) Man pages (share/man/man{1,3}): pcregrep.1 pcretest.1 pcre-config.1 pcre.3 pcre*.3 (lots more pages, all starting "pcre") HTML documentation (share/doc/pcre/html): index.html *.html (lots more pages, hyperlinked from index.html) Text file documentation (share/doc/pcre): AUTHORS COPYING ChangeLog LICENCE NEWS README pcre.txt (a concatenation of the man(3) pages) pcretest.txt the pcretest man page pcregrep.txt the pcregrep man page pcre-config.txt the pcre-config man page If you want to remove PCRE from your system, you can run "make uninstall". This removes all the files that "make install" installed. However, it does not remove any directories, because these are often shared with other programs. Retrieving configuration information on Unix-like systems --------------------------------------------------------- Running "make install" installs the command pcre-config, which can be used to recall information about the PCRE configuration and installation. For example: pcre-config --version prints the version number, and pcre-config --libs outputs information about where the library is installed. This command can be included in makefiles for programs that use PCRE, saving the programmer from having to remember too many details. The pkg-config command is another system for saving and retrieving information about installed libraries. Instead of separate commands for each library, a single command is used. For example: pkg-config --cflags pcre The data is held in *.pc files that are installed in a directory called /lib/pkgconfig. Shared libraries on Unix-like systems ------------------------------------- The default distribution builds PCRE as shared libraries and static libraries, as long as the operating system supports shared libraries. Shared library support relies on the "libtool" script which is built as part of the "configure" process. The libtool script is used to compile and link both shared and static libraries. They are placed in a subdirectory called .libs when they are newly built. The programs pcretest and pcregrep are built to use these uninstalled libraries (by means of wrapper scripts in the case of shared libraries). When you use "make install" to install shared libraries, pcregrep and pcretest are automatically re-built to use the newly installed shared libraries before being installed themselves. However, the versions left in the build directory still use the uninstalled libraries. To build PCRE using static libraries only you must use --disable-shared when configuring it. For example: ./configure --prefix=/usr/gnu --disable-shared Then run "make" in the usual way. Similarly, you can use --disable-static to build only shared libraries. Cross-compiling on Unix-like systems ------------------------------------ You can specify CC and CFLAGS in the normal way to the "configure" command, in order to cross-compile PCRE for some other host. However, you should NOT specify --enable-rebuild-chartables, because if you do, the dftables.c source file is compiled and run on the local host, in order to generate the inbuilt character tables (the pcre_chartables.c file). This will probably not work, because dftables.c needs to be compiled with the local compiler, not the cross compiler. When --enable-rebuild-chartables is not specified, pcre_chartables.c is created by making a copy of pcre_chartables.c.dist, which is a default set of tables that assumes ASCII code. Cross-compiling with the default tables should not be a problem. If you need to modify the character tables when cross-compiling, you should move pcre_chartables.c.dist out of the way, then compile dftables.c by hand and run it on the local host to make a new version of pcre_chartables.c.dist. Then when you cross-compile PCRE this new version of the tables will be used. Using HP's ANSI C++ compiler (aCC) ---------------------------------- Unless C++ support is disabled by specifying the "--disable-cpp" option of the "configure" script, you must include the "-AA" option in the CXXFLAGS environment variable in order for the C++ components to compile correctly. Also, note that the aCC compiler on PA-RISC platforms may have a defect whereby needed libraries fail to get included when specifying the "-AA" compiler option. If you experience unresolved symbols when linking the C++ programs, use the workaround of specifying the following environment variable prior to running the "configure" script: CXXLDFLAGS="-lstd_v2 -lCsup_v2" Using Sun's compilers for Solaris --------------------------------- A user reports that the following configurations work on Solaris 9 sparcv9 and Solaris 9 x86 (32-bit): Solaris 9 sparcv9: ./configure --disable-cpp CC=/bin/cc CFLAGS="-m64 -g" Solaris 9 x86: ./configure --disable-cpp CC=/bin/cc CFLAGS="-g" Using PCRE from MySQL --------------------- On systems where both PCRE and MySQL are installed, it is possible to make use of PCRE from within MySQL, as an alternative to the built-in pattern matching. There is a web page that tells you how to do this: http://www.mysqludf.org/lib_mysqludf_preg/index.php Making new tarballs ------------------- The command "make dist" creates three PCRE tarballs, in tar.gz, tar.bz2, and zip formats. The command "make distcheck" does the same, but then does a trial build of the new distribution to ensure that it works. If you have modified any of the man page sources in the doc directory, you should first run the PrepareRelease script before making a distribution. This script creates the .txt and HTML forms of the documentation from the man pages. Testing PCRE ------------ To test the basic PCRE library on a Unix system, run the RunTest script that is created by the configuring process. There is also a script called RunGrepTest that tests the options of the pcregrep command. If the C++ wrapper library is built, three test programs called pcrecpp_unittest, pcre_scanner_unittest, and pcre_stringpiece_unittest are also built. When JIT support is enabled, another test program called pcre_jit_test is built. Both the scripts and all the program tests are run if you obey "make check" or "make test". For other systems, see the instructions in NON-UNIX-USE. The RunTest script runs the pcretest test program (which is documented in its own man page) on each of the relevant testinput files in the testdata directory, and compares the output with the contents of the corresponding testoutput files. Some tests are relevant only when certain build-time options were selected. For example, the tests for UTF-8/16 support are run only if --enable-utf was used. RunTest outputs a comment when it skips a test. Many of the tests that are not skipped are run up to three times. The second run forces pcre_study() to be called for all patterns except for a few in some tests that are marked "never study" (see the pcretest program for how this is done). If JIT support is available, the non-DFA tests are run a third time, this time with a forced pcre_study() with the PCRE_STUDY_JIT_COMPILE option. When both 8-bit and 16-bit support is enabled, the entire set of tests is run twice, once for each library. If you want to run just one set of tests, call RunTest with either the -8 or -16 option. RunTest uses a file called testtry to hold the main output from pcretest. Other files whose names begin with "test" are used as working files in some tests. To run pcretest on just one or more specific test files, give their numbers as arguments to RunTest, for example: RunTest 2 7 11 The first test file can be fed directly into the perltest.pl script to check that Perl gives the same results. The only difference you should see is in the first few lines, where the Perl version is given instead of the PCRE version. The second set of tests check pcre_fullinfo(), pcre_study(), pcre_copy_substring(), pcre_get_substring(), pcre_get_substring_list(), error detection, and run-time flags that are specific to PCRE, as well as the POSIX wrapper API. It also uses the debugging flags to check some of the internals of pcre_compile(). If you build PCRE with a locale setting that is not the standard C locale, the character tables may be different (see next paragraph). In some cases, this may cause failures in the second set of tests. For example, in a locale where the isprint() function yields TRUE for characters in the range 128-255, the use of [:isascii:] inside a character class defines a different set of characters, and this shows up in this test as a difference in the compiled code, which is being listed for checking. Where the comparison test output contains [\x00-\x7f] the test will contain [\x00-\xff], and similarly in some other cases. This is not a bug in PCRE. The third set of tests checks pcre_maketables(), the facility for building a set of character tables for a specific locale and using them instead of the default tables. The tests make use of the "fr_FR" (French) locale. Before running the test, the script checks for the presence of this locale by running the "locale" command. If that command fails, or if it doesn't include "fr_FR" in the list of available locales, the third test cannot be run, and a comment is output to say why. If running this test produces instances of the error ** Failed to set locale "fr_FR" in the comparison output, it means that locale is not available on your system, despite being listed by "locale". This does not mean that PCRE is broken. [If you are trying to run this test on Windows, you may be able to get it to work by changing "fr_FR" to "french" everywhere it occurs. Alternatively, use RunTest.bat. The version of RunTest.bat included with PCRE 7.4 and above uses Windows versions of test 2. More info on using RunTest.bat is included in the document entitled NON-UNIX-USE.] The fourth and fifth tests check the UTF-8/16 support and error handling and internal UTF features of PCRE that are not relevant to Perl, respectively. The sixth and seventh tests do the same for Unicode character properties support. The eighth, ninth, and tenth tests check the pcre_dfa_exec() alternative matching function, in non-UTF-8/16 mode, UTF-8/16 mode, and UTF-8/16 mode with Unicode property support, respectively. The eleventh test checks some internal offsets and code size features; it is run only when the default "link size" of 2 is set (in other cases the sizes change) and when Unicode property support is enabled. The twelfth test is run only when JIT support is available, and the thirteenth test is run only when JIT support is not available. They test some JIT-specific features such as information output from pcretest about JIT compilation. The fourteenth, fifteenth, and sixteenth tests are run only in 8-bit mode, and the seventeenth, eighteenth, and nineteenth tests are run only in 16-bit mode. These are tests that generate different output in the two modes. They are for general cases, UTF-8/16 support, and Unicode property support, respectively. The twentieth test is run only in 16-bit mode. It tests some specific 16-bit features of the DFA matching engine. The twenty-first and twenty-second tests are run only in 16-bit mode, when the link size is set to 2. They test reloading pre-compiled patterns. Character tables ---------------- For speed, PCRE uses four tables for manipulating and identifying characters whose code point values are less than 256. The final argument of the pcre_compile() function is a pointer to a block of memory containing the concatenated tables. A call to pcre_maketables() can be used to generate a set of tables in the current locale. If the final argument for pcre_compile() is passed as NULL, a set of default tables that is built into the binary is used. The source file called pcre_chartables.c contains the default set of tables. By default, this is created as a copy of pcre_chartables.c.dist, which contains tables for ASCII coding. However, if --enable-rebuild-chartables is specified for ./configure, a different version of pcre_chartables.c is built by the program dftables (compiled from dftables.c), which uses the ANSI C character handling functions such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table sources. This means that the default C locale which is set for your system will control the contents of these default tables. You can change the default tables by editing pcre_chartables.c and then re-building PCRE. If you do this, you should take care to ensure that the file does not get automatically re-generated. The best way to do this is to move pcre_chartables.c.dist out of the way and replace it with your customized tables. When the dftables program is run as a result of --enable-rebuild-chartables, it uses the default C locale that is set on your system. It does not pay attention to the LC_xxx environment variables. In other words, it uses the system's default locale rather than whatever the compiling user happens to have set. If you really do want to build a source set of character tables in a locale that is specified by the LC_xxx variables, you can run the dftables program by hand with the -L option. For example: ./dftables -L pcre_chartables.c.special The first two 256-byte tables provide lower casing and case flipping functions, respectively. The next table consists of three 32-byte bit maps which identify digits, "word" characters, and white space, respectively. These are used when building 32-byte bit maps that represent character classes for code points less than 256. The final 256-byte table has bits indicating various character types, as follows: 1 white space character 2 letter 4 decimal digit 8 hexadecimal digit 16 alphanumeric or '_' 128 regular expression metacharacter or binary zero You should not alter the set of characters that contain the 128 bit, as that will cause PCRE to malfunction. File manifest ------------- The distribution should contain the files listed below. Where a file name is given as pcre[16]_xxx it means that there are two files, one with the name pcre_xxx and the other with the name pcre16_xxx. (A) Source files of the PCRE library functions and their headers: dftables.c auxiliary program for building pcre_chartables.c when --enable-rebuild-chartables is specified pcre_chartables.c.dist a default set of character tables that assume ASCII coding; used, unless --enable-rebuild-chartables is specified, by copying to pcre[16]_chartables.c pcreposix.c ) pcre[16]_byte_order.c ) pcre[16]_compile.c ) pcre[16]_config.c ) pcre[16]_dfa_exec.c ) pcre[16]_exec.c ) pcre[16]_fullinfo.c ) pcre[16]_get.c ) sources for the functions in the library, pcre[16]_globals.c ) and some internal functions that they use pcre[16]_jit_compile.c ) pcre[16]_maketables.c ) pcre[16]_newline.c ) pcre[16]_refcount.c ) pcre[16]_string_utils.c ) pcre[16]_study.c ) pcre[16]_tables.c ) pcre[16]_ucd.c ) pcre[16]_version.c ) pcre[16]_xclass.c ) pcre_ord2utf8.c ) pcre_valid_utf8.c ) pcre16_ord2utf16.c ) pcre16_utf16_utils.c ) pcre16_valid_utf16.c ) pcre[16]_printint.c ) debugging function that is used by pcretest, ) and can also be #included in pcre_compile() pcre.h.in template for pcre.h when built by "configure" pcreposix.h header for the external POSIX wrapper API pcre_internal.h header for internal use sljit/* 16 files that make up the JIT compiler ucp.h header for Unicode property handling config.h.in template for config.h, which is built by "configure" pcrecpp.h public header file for the C++ wrapper pcrecpparg.h.in template for another C++ header file pcre_scanner.h public header file for C++ scanner functions pcrecpp.cc ) pcre_scanner.cc ) source for the C++ wrapper library pcre_stringpiece.h.in template for pcre_stringpiece.h, the header for the C++ stringpiece functions pcre_stringpiece.cc source for the C++ stringpiece functions (B) Source files for programs that use PCRE: pcredemo.c simple demonstration of coding calls to PCRE pcregrep.c source of a grep utility that uses PCRE pcretest.c comprehensive test program (C) Auxiliary files: 132html script to turn "man" pages into HTML AUTHORS information about the author of PCRE ChangeLog log of changes to the code CleanTxt script to clean nroff output for txt man pages Detrail script to remove trailing spaces HACKING some notes about the internals of PCRE INSTALL generic installation instructions LICENCE conditions for the use of PCRE COPYING the same, using GNU's standard name Makefile.in ) template for Unix Makefile, which is built by ) "configure" Makefile.am ) the automake input that was used to create ) Makefile.in NEWS important changes in this release NON-UNIX-USE notes on building PCRE on non-Unix systems PrepareRelease script to make preparations for "make dist" README this file RunTest a Unix shell script for running tests RunGrepTest a Unix shell script for pcregrep tests aclocal.m4 m4 macros (generated by "aclocal") config.guess ) files used by libtool, config.sub ) used only when building a shared library configure a configuring shell script (built by autoconf) configure.ac ) the autoconf input that was used to build ) "configure" and config.h depcomp ) script to find program dependencies, generated by ) automake doc/*.3 man page sources for PCRE doc/*.1 man page sources for pcregrep and pcretest doc/index.html.src the base HTML page doc/html/* HTML documentation doc/pcre.txt plain text version of the man pages doc/pcretest.txt plain text documentation of test program doc/perltest.txt plain text documentation of Perl test program install-sh a shell script for installing files libpcre16.pc.in template for libpcre16.pc for pkg-config libpcre.pc.in template for libpcre.pc for pkg-config libpcreposix.pc.in template for libpcreposix.pc for pkg-config libpcrecpp.pc.in template for libpcrecpp.pc for pkg-config ltmain.sh file used to build a libtool script missing ) common stub for a few missing GNU programs while ) installing, generated by automake mkinstalldirs script for making install directories perltest.pl Perl test program pcre-config.in source of script which retains PCRE information pcre_jit_test.c test program for the JIT compiler pcrecpp_unittest.cc ) pcre_scanner_unittest.cc ) test programs for the C++ wrapper pcre_stringpiece_unittest.cc ) testdata/testinput* test data for main library tests testdata/testoutput* expected test results testdata/grep* input and output for pcregrep tests testdata/* other supporting test files (D) Auxiliary files for cmake support cmake/COPYING-CMAKE-SCRIPTS cmake/FindPackageHandleStandardArgs.cmake cmake/FindReadline.cmake CMakeLists.txt config-cmake.h.in (E) Auxiliary files for VPASCAL makevp.bat makevp_c.txt makevp_l.txt pcregexp.pas (F) Auxiliary files for building PCRE "by hand" pcre.h.generic ) a version of the public PCRE header file ) for use in non-"configure" environments config.h.generic ) a version of config.h for use in non-"configure" ) environments (F) Miscellaneous RunTest.bat a script for running tests under Windows Philip Hazel Email local part: ph10 Email domain: cam.ac.uk Last updated: 20 January 2012 07070100038368000081a40000000000000000000000014f79083e0000a992000000b500010002ffffffffffffffff0000002b00000000root/usr/local/share/doc/pcre/pcretest.txtPCRETEST(1) PCRETEST(1) NAME pcretest - a program for testing Perl-compatible regular expressions. SYNOPSIS pcretest [options] [input file [output file]] pcretest was written as a test program for the PCRE regular expression library itself, but it can also be used for experimenting with regular expressions. This document describes the features of the test program; for details of the regular expressions themselves, see the pcrepattern documentation. For details of the PCRE library function calls and their options, see the pcreapi and pcre16 documentation. The input for pcretest is a sequence of regular expression patterns and strings to be matched, as described below. The output shows the result of each match. Options on the command line and the patterns control PCRE options and exactly what is output. PCRE's 8-BIT and 16-BIT LIBRARIES From release 8.30, two separate PCRE libraries can be built. The origi- nal one supports 8-bit character strings, whereas the newer 16-bit library supports character strings encoded in 16-bit units. The pcretest program can be used to test both libraries. However, it is itself still an 8-bit program, reading 8-bit input and writing 8-bit output. When testing the 16-bit library, the patterns and data strings are converted to 16-bit format before being passed to the PCRE library functions. Results are converted to 8-bit for output. References to functions and structures of the form pcre[16]_xx below mean "pcre_xx when using the 8-bit library or pcre16_xx when using the 16-bit library". COMMAND LINE OPTIONS -16 If both the 8-bit and the 16-bit libraries have been built, this option causes the 16-bit library to be used. If only the 16-bit library has been built, this is the default (so has no effect). If only the 8-bit library has been built, this option causes an error. -b Behave as if each pattern has the /B (show byte code) modi- fier; the internal form is output after compilation. -C Output the version number of the PCRE library, and all avail- able information about the optional features that are included, and then exit. All other options are ignored. -C option Output information about a specific build-time option, then exit. This functionality is intended for use in scripts such as RunTest. The following options output the value indicated: linksize the internal link size (2, 3, or 4) newline the default newline setting: CR, LF, CRLF, ANYCRLF, or ANY The following options output 1 for true or zero for false: jit just-in-time support is available pcre16 the 16-bit library was built pcre8 the 8-bit library was built ucp Unicode property support is available utf UTF-8 and/or UTF-16 support is available -d Behave as if each pattern has the /D (debug) modifier; the internal form and information about the compiled pattern is output after compilation; -d is equivalent to -b -i. -dfa Behave as if each data line contains the \D escape sequence; this causes the alternative matching function, pcre[16]_dfa_exec(), to be used instead of the standard pcre[16]_exec() function (more detail is given below). -help Output a brief summary these options and then exit. -i Behave as if each pattern has the /I modifier; information about the compiled pattern is given after compilation. -M Behave as if each data line contains the \M escape sequence; this causes PCRE to discover the minimum MATCH_LIMIT and MATCH_LIMIT_RECURSION settings by calling pcre[16]_exec() repeatedly with different limits. -m Output the size of each compiled pattern after it has been compiled. This is equivalent to adding /M to each regular expression. The size is given in bytes for both libraries. -o osize Set the number of elements in the output vector that is used when calling pcre[16]_exec() or pcre[16]_dfa_exec() to be osize. The default value is 45, which is enough for 14 cap- turing subexpressions for pcre[16]_exec() or 22 different matches for pcre[16]_dfa_exec(). The vector size can be changed for individual matching calls by including \O in the data line (see below). -p Behave as if each pattern has the /P modifier; the POSIX wrapper API is used to call PCRE. None of the other options has any effect when -p is set. This option can be used only with the 8-bit library. -q Do not output the version number of pcretest at the start of execution. -S size On Unix-like systems, set the size of the run-time stack to size megabytes. -s or -s+ Behave as if each pattern has the /S modifier; in other words, force each pattern to be studied. If -s+ is used, the PCRE_STUDY_JIT_COMPILE flag is passed to pcre[16]_study(), causing just-in-time optimization to be set up if it is available. If the /I or /D option is present on a pattern (requesting output about the compiled pattern), information about the result of studying is not included when studying is caused only by -s and neither -i nor -d is present on the command line. This behaviour means that the output from tests that are run with and without -s should be identical, except when options that output information about the actual running of a match are set. The -M, -t, and -tm options, which give information about resources used, are likely to produce different output with and without -s. Output may also differ if the /C option is present on an individual pattern. This uses callouts to trace the the matching process, and this may be different between studied and non-studied patterns. If the pattern contains (*MARK) items there may also be differences, for the same reason. The -s command line option can be overridden for spe- cific patterns that should never be studied (see the /S pat- tern modifier below). -t Run each compile, study, and match many times with a timer, and output resulting time per compile or match (in millisec- onds). Do not set -m with -t, because you will then get the size output a zillion times, and the timing will be dis- torted. You can control the number of iterations that are used for timing by following -t with a number (as a separate item on the command line). For example, "-t 1000" would iter- ate 1000 times. The default is to iterate 500000 times. -tm This is like -t except that it times only the matching phase, not the compile or study phases. DESCRIPTION If pcretest is given two filename arguments, it reads from the first and writes to the second. If it is given only one filename argument, it reads from that file and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and prompts for each line of input, using "re>" to prompt for regular expressions, and "data>" to prompt for data lines. When pcretest is built, a configuration option can specify that it should be linked with the libreadline library. When this is done, if the input is from a terminal, it is read using the readline() function. This provides line-editing and history facilities. The output from the -help option states whether or not readline() will be used. The program handles any number of sets of input on a single input file. Each set starts with a regular expression, and continues with any num- ber of data lines to be matched against the pattern. Each data line is matched separately and independently. If you want to do multi-line matches, you have to use the \n escape sequence (or \r or \r\n, etc., depending on the newline setting) in a single line of input to encode the newline sequences. There is no limit on the length of data lines; the input buffer is automatically extended if it is too small. An empty line signals the end of the data lines, at which point a new regular expression is read. The regular expressions are given enclosed in any non-alphanumeric delimiters other than backslash, for example: /(a|bc)x+yz/ White space before the initial delimiter is ignored. A regular expres- sion may be continued over several input lines, in which case the new- line characters are included within it. It is possible to include the delimiter within the pattern by escaping it, for example /abc\/def/ If you do so, the escape and the delimiter form part of the pattern, but since delimiters are always non-alphanumeric, this does not affect its interpretation. If the terminating delimiter is immediately fol- lowed by a backslash, for example, /abc/\ then a backslash is added to the end of the pattern. This is done to provide a way of testing the error condition that arises if a pattern finishes with a backslash, because /abc\/ is interpreted as the first line of a pattern that starts with "abc/", causing pcretest to read the next line as a continuation of the regular expression. PATTERN MODIFIERS A pattern may be followed by any number of modifiers, which are mostly single characters. Following Perl usage, these are referred to below as, for example, "the /i modifier", even though the delimiter of the pattern need not always be a slash, and no slash is used when writing modifiers. White space may appear between the final pattern delimiter and the first modifier, and between the modifiers themselves. The /i, /m, /s, and /x modifiers set the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively, when pcre[16]_com- pile() is called. These four modifier letters have the same effect as they do in Perl. For example: /caseless/i The following table shows additional modifiers for setting PCRE com- pile-time options that do not correspond to anything in Perl: /8 PCRE_UTF8 ) when using the 8-bit /? PCRE_NO_UTF8_CHECK ) library /8 PCRE_UTF16 ) when using the 16-bit /? PCRE_NO_UTF16_CHECK ) library /A PCRE_ANCHORED /C PCRE_AUTO_CALLOUT /E PCRE_DOLLAR_ENDONLY /f PCRE_FIRSTLINE /J PCRE_DUPNAMES /N PCRE_NO_AUTO_CAPTURE /U PCRE_UNGREEDY /W PCRE_UCP /X PCRE_EXTRA /Y PCRE_NO_START_OPTIMIZE / PCRE_JAVASCRIPT_COMPAT / PCRE_NEWLINE_CR / PCRE_NEWLINE_LF / PCRE_NEWLINE_CRLF / PCRE_NEWLINE_ANYCRLF / PCRE_NEWLINE_ANY / PCRE_BSR_ANYCRLF / PCRE_BSR_UNICODE The modifiers that are enclosed in angle brackets are literal strings as shown, including the angle brackets, but the letters within can be in either case. This example sets multiline matching with CRLF as the line ending sequence: /^abc/m As well as turning on the PCRE_UTF8/16 option, the /8 modifier causes all non-printing characters in output strings to be printed using the \x{hh...} notation. Otherwise, those less than 0x100 are output in hex without the curly brackets. Full details of the PCRE options are given in the pcreapi documenta- tion. Finding all matches in a string Searching for all possible matches within each subject string can be requested by the /g or /G modifier. After finding a match, PCRE is called again to search the remainder of the subject string. The differ- ence between /g and /G is that the former uses the startoffset argument to pcre[16]_exec() to start searching at a new point within the entire string (which is in effect what Perl does), whereas the latter passes over a shortened substring. This makes a difference to the matching process if the pattern begins with a lookbehind assertion (including \b or \B). If any call to pcre[16]_exec() in a /g or /G sequence matches an empty string, the next call is done with the PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED flags set in order to search for another, non-empty, match at the same point. If this second match fails, the start offset is advanced, and the normal match is retried. This imitates the way Perl handles such cases when using the /g modifier or the split() func- tion. Normally, the start offset is advanced by one character, but if the newline convention recognizes CRLF as a newline, and the current character is CR followed by LF, an advance of two is used. Other modifiers There are yet more modifiers for controlling the way pcretest operates. The /+ modifier requests that as well as outputting the substring that matched the entire pattern, pcretest should in addition output the remainder of the subject string. This is useful for tests where the subject contains multiple copies of the same substring. If the + modi- fier appears twice, the same action is taken for captured substrings. In each case the remainder is output on the following line with a plus character following the capture number. Note that this modifier must not immediately follow the /S modifier because /S+ has another meaning. The /= modifier requests that the values of all potential captured parentheses be output after a match. By default, only those up to the highest one actually used in the match are output (corresponding to the return code from pcre[16]_exec()). Values in the offsets vector corre- sponding to higher numbers should be set to -1, and these are output as "". This modifier gives a way of checking that this is happen- ing. The /B modifier is a debugging feature. It requests that pcretest out- put a representation of the compiled code after compilation. Normally this information contains length and offset values; however, if /Z is also present, this data is replaced by spaces. This is a special fea- ture for use in the automatic test scripts; it ensures that the same output is generated for different internal link sizes. The /D modifier is a PCRE debugging feature, and is equivalent to /BI, that is, both the /B and the /I modifiers. The /F modifier causes pcretest to flip the byte order of the 2-byte and 4-byte fields in the compiled pattern. This facility is for testing the feature in PCRE that allows it to execute patterns that were com- piled on a host with a different endianness. This feature is not avail- able when the POSIX interface to PCRE is being used, that is, when the /P pattern modifier is specified. See also the section about saving and reloading compiled patterns below. The /I modifier requests that pcretest output information about the compiled pattern (whether it is anchored, has a fixed first character, and so on). It does this by calling pcre[16]_fullinfo() after compiling a pattern. If the pattern is studied, the results of that are also out- put. The /K modifier requests pcretest to show names from backtracking con- trol verbs that are returned from calls to pcre[16]_exec(). It causes pcretest to create a pcre[16]_extra block if one has not already been created by a call to pcre[16]_study(), and to set the PCRE_EXTRA_MARK flag and the mark field within it, every time that pcre[16]_exec() is called. If the variable that the mark field points to is non-NULL for a match, non-match, or partial match, pcretest prints the string to which it points. For a match, this is shown on a line by itself, tagged with "MK:". For a non-match it is added to the message. The /L modifier must be followed directly by the name of a locale, for example, /pattern/Lfr_FR For this reason, it must be the last modifier. The given locale is set, pcre[16]_maketables() is called to build a set of character tables for the locale, and this is then passed to pcre[16]_compile() when compil- ing the regular expression. Without an /L (or /T) modifier, NULL is passed as the tables pointer; that is, /L applies only to the expres- sion on which it appears. The /M modifier causes the size in bytes of the memory block used to hold the compiled pattern to be output. This does not include the size of the pcre[16] block; it is just the actual compiled data. If the pat- tern is successfully studied with the PCRE_STUDY_JIT_COMPILE option, the size of the JIT compiled code is also output. If the /S modifier appears once, it causes pcre[16]_study() to be called after the expression has been compiled, and the results used when the expression is matched. If /S appears twice, it suppresses studying, even if it was requested externally by the -s command line option. This makes it possible to specify that certain patterns are always studied, and others are never studied, independently of -s. This feature is used in the test files in a few cases where the output is different when the pattern is studied. If the /S modifier is immediately followed by a + character, the call to pcre[16]_study() is made with the PCRE_STUDY_JIT_COMPILE option, requesting just-in-time optimization support if it is available. Note that there is also a /+ modifier; it must not be given immediately after /S because this will be misinterpreted. If JIT studying is suc- cessful, it will automatically be used when pcre[16]_exec() is run, except when incompatible run-time options are specified. These include the partial matching options; a complete list is given in the pcrejit documentation. See also the \J escape sequence below for a way of set- ting the size of the JIT stack. The /T modifier must be followed by a single digit. It causes a spe- cific set of built-in character tables to be passed to pcre[16]_com- pile(). It is used in the standard PCRE tests to check behaviour with different character tables. The digit specifies the tables as follows: 0 the default ASCII tables, as distributed in pcre_chartables.c.dist 1 a set of tables defining ISO 8859 characters In table 1, some characters whose codes are greater than 128 are iden- tified as letters, digits, spaces, etc. Using the POSIX wrapper API The /P modifier causes pcretest to call PCRE via the POSIX wrapper API rather than its native API. This supports only the 8-bit library. When /P is set, the following modifiers set options for the regcomp() func- tion: /i REG_ICASE /m REG_NEWLINE /N REG_NOSUB /s REG_DOTALL ) /U REG_UNGREEDY ) These options are not part of /W REG_UCP ) the POSIX standard /8 REG_UTF8 ) The /+ modifier works as described above. All other modifiers are ignored. DATA LINES Before each data line is passed to pcre[16]_exec(), leading and trail- ing white space is removed, and it is then scanned for \ escapes. Some of these are pretty esoteric features, intended for checking out some of the more complicated features of PCRE. If you are just testing "ordinary" regular expressions, you probably don't need any of these. The following escapes are recognized: \a alarm (BEL, \x07) \b backspace (\x08) \e escape (\x27) \f form feed (\x0c) \n newline (\x0a) \qdd set the PCRE_MATCH_LIMIT limit to dd (any number of digits) \r carriage return (\x0d) \t tab (\x09) \v vertical tab (\x0b) \nnn octal character (up to 3 octal digits); always a byte unless > 255 in UTF-8 or 16-bit mode \xhh hexadecimal byte (up to 2 hex digits) \x{hh...} hexadecimal character (any number of hex digits) \A pass the PCRE_ANCHORED option to pcre[16]_exec() or pcre[16]_dfa_exec() \B pass the PCRE_NOTBOL option to pcre[16]_exec() or pcre[16]_dfa_exec() \Cdd call pcre[16]_copy_substring() for substring dd after a successful match (number less than 32) \Cname call pcre[16]_copy_named_substring() for substring "name" after a successful match (name termin- ated by next non alphanumeric character) \C+ show the current captured substrings at callout time \C- do not supply a callout function \C!n return 1 instead of 0 when callout number n is reached \C!n!m return 1 instead of 0 when callout number n is reached for the nth time \C*n pass the number n (may be negative) as callout data; this is used as the callout return value \D use the pcre[16]_dfa_exec() match function \F only shortest match for pcre[16]_dfa_exec() \Gdd call pcre[16]_get_substring() for substring dd after a successful match (number less than 32) \Gname call pcre[16]_get_named_substring() for substring "name" after a successful match (name termin- ated by next non-alphanumeric character) \Jdd set up a JIT stack of dd kilobytes maximum (any number of digits) \L call pcre[16]_get_substringlist() after a successful match \M discover the minimum MATCH_LIMIT and MATCH_LIMIT_RECURSION settings \N pass the PCRE_NOTEMPTY option to pcre[16]_exec() or pcre[16]_dfa_exec(); if used twice, pass the PCRE_NOTEMPTY_ATSTART option \Odd set the size of the output vector passed to pcre[16]_exec() to dd (any number of digits) \P pass the PCRE_PARTIAL_SOFT option to pcre[16]_exec() or pcre[16]_dfa_exec(); if used twice, pass the PCRE_PARTIAL_HARD option \Qdd set the PCRE_MATCH_LIMIT_RECURSION limit to dd (any number of digits) \R pass the PCRE_DFA_RESTART option to pcre[16]_dfa_exec() \S output details of memory get/free calls during matching \Y pass the PCRE_NO_START_OPTIMIZE option to pcre[16]_exec() or pcre[16]_dfa_exec() \Z pass the PCRE_NOTEOL option to pcre[16]_exec() or pcre[16]_dfa_exec() \? pass the PCRE_NO_UTF[8|16]_CHECK option to pcre[16]_exec() or pcre[16]_dfa_exec() \>dd start the match at offset dd (optional "-"; then any number of digits); this sets the startoffset argument for pcre[16]_exec() or pcre[16]_dfa_exec() \ pass the PCRE_NEWLINE_CR option to pcre[16]_exec() or pcre[16]_dfa_exec() \ pass the PCRE_NEWLINE_LF option to pcre[16]_exec() or pcre[16]_dfa_exec() \ pass the PCRE_NEWLINE_CRLF option to pcre[16]_exec() or pcre[16]_dfa_exec() \ pass the PCRE_NEWLINE_ANYCRLF option to pcre[16]_exec() or pcre[16]_dfa_exec() \ pass the PCRE_NEWLINE_ANY option to pcre[16]_exec() or pcre[16]_dfa_exec() The use of \x{hh...} is not dependent on the use of the /8 modifier on the pattern. It is recognized always. There may be any number of hexa- decimal digits inside the braces; invalid values provoke error mes- sages. Note that \xhh specifies one byte rather than one character in UTF-8 mode; this makes it possible to construct invalid UTF-8 sequences for testing purposes. On the other hand, \x{hh} is interpreted as a UTF-8 character in UTF-8 mode, generating more than one byte if the value is greater than 127. When testing the 8-bit library not in UTF-8 mode, \x{hh} generates one byte for values less than 256, and causes an error for greater values. In UTF-16 mode, all 4-digit \x{hhhh} values are accepted. This makes it possible to construct invalid UTF-16 sequences for testing purposes. The escapes that specify line ending sequences are literal strings, exactly as shown. No more than one newline setting should be present in any data line. A backslash followed by anything else just escapes the anything else. If the very last character is a backslash, it is ignored. This gives a way of passing an empty line as data, since a real empty line termi- nates the data input. The \J escape provides a way of setting the maximum stack size that is used by the just-in-time optimization code. It is ignored if JIT opti- mization is not being used. Providing a stack that is larger than the default 32K is necessary only for very complicated patterns. If \M is present, pcretest calls pcre[16]_exec() several times, with different values in the match_limit and match_limit_recursion fields of the pcre[16]_extra data structure, until it finds the minimum numbers for each parameter that allow pcre[16]_exec() to complete without error. Because this is testing a specific feature of the normal inter- pretive pcre[16]_exec() execution, the use of any JIT optimization that might have been set up by the /S+ qualifier of -s+ option is disabled. The match_limit number is a measure of the amount of backtracking that takes place, and checking it out can be instructive. For most simple matches, the number is quite small, but for patterns with very large numbers of matching possibilities, it can become large very quickly with increasing length of subject string. The match_limit_recursion number is a measure of how much stack (or, if PCRE is compiled with NO_RECURSE, how much heap) memory is needed to complete the match attempt. When \O is used, the value specified may be higher or lower than the size set by the -O command line option (or defaulted to 45); \O applies only to the call of pcre[16]_exec() for the line in which it appears. If the /P modifier was present on the pattern, causing the POSIX wrap- per API to be used, the only option-setting sequences that have any effect are \B, \N, and \Z, causing REG_NOTBOL, REG_NOTEMPTY, and REG_NOTEOL, respectively, to be passed to regexec(). THE ALTERNATIVE MATCHING FUNCTION By default, pcretest uses the standard PCRE matching function, pcre[16]_exec() to match each data line. PCRE also supports an alterna- tive matching function, pcre[16]_dfa_test(), which operates in a dif- ferent way, and has some restrictions. The differences between the two functions are described in the pcrematching documentation. If a data line contains the \D escape sequence, or if the command line contains the -dfa option, the alternative matching function is used. This function finds all possible matches at a given point. If, however, the \F escape sequence is present in the data line, it stops after the first match is found. This is always the shortest possible match. DEFAULT OUTPUT FROM PCRETEST This section describes the output when the normal matching function, pcre[16]_exec(), is being used. When a match succeeds, pcretest outputs the list of captured substrings that pcre[16]_exec() returns, starting with number 0 for the string that matched the whole pattern. Otherwise, it outputs "No match" when the return is PCRE_ERROR_NOMATCH, and "Partial match:" followed by the partially matching substring when pcre[16]_exec() returns PCRE_ERROR_PARTIAL. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \K, \b, or \B was involved.) For any other return, pcretest outputs the PCRE negative error number and a short descriptive phrase. If the error is a failed UTF string check, the offset of the start of the failing character and the reason code are also output, provided that the size of the output vector is at least two. Here is an example of an interactive pcretest run. $ pcretest PCRE version 8.13 2011-04-30 re> /^abc(\d+)/ data> abc123 0: abc123 1: 123 data> xyz No match Unset capturing substrings that are not followed by one that is set are not returned by pcre[16]_exec(), and are not shown by pcretest. In the following example, there are two capturing substrings, but when the first data line is matched, the second, unset substring is not shown. An "internal" unset substring is shown as "", as for the second data line. re> /(a)|(b)/ data> a 0: a 1: a data> b 0: b 1: 2: b If the strings contain any non-printing characters, they are output as \xhh escapes if the value is less than 256 and UTF mode is not set. Otherwise they are output as \x{hh...} escapes. See below for the defi- nition of non-printing characters. If the pattern has the /+ modifier, the output for substring 0 is followed by the the rest of the subject string, identified by "0+" like this: re> /cat/+ data> cataract 0: cat 0+ aract If the pattern has the /g or /G modifier, the results of successive matching attempts are output in sequence, like this: re> /\Bi(\w\w)/g data> Mississippi 0: iss 1: ss 0: iss 1: ss 0: ipp 1: pp "No match" is output only if the first match attempt fails. Here is an example of a failure message (the offset 4 that is specified by \>4 is past the end of the subject string): re> /xyz/ data> xyz\>4 Error -24 (bad offset value) If any of the sequences \C, \G, or \L are present in a data line that is successfully matched, the substrings extracted by the convenience functions are output with C, G, or L after the string number instead of a colon. This is in addition to the normal full list. The string length (that is, the return from the extraction function) is given in paren- theses after each string for \C and \G. Note that whereas patterns can be continued over several lines (a plain ">" prompt is used for continuations), data lines may not. However new- lines can be included in data by means of the \n escape (or \r, \r\n, etc., depending on the newline sequence setting). OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION When the alternative matching function, pcre[16]_dfa_exec(), is used (by means of the \D escape sequence or the -dfa command line option), the output consists of a list of all the matches that start at the first point in the subject where there is at least one match. For exam- ple: re> /(tang|tangerine|tan)/ data> yellow tangerine\D 0: tangerine 1: tang 2: tan (Using the normal matching function on this data finds only "tang".) The longest matching string is always given first (and numbered zero). After a PCRE_ERROR_PARTIAL return, the output is "Partial match:", fol- lowed by the partially matching substring. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind asser- tion, \K, \b, or \B was involved.) If /g is present on the pattern, the search for further matches resumes at the end of the longest match. For example: re> /(tang|tangerine|tan)/g data> yellow tangerine and tangy sultana\D 0: tangerine 1: tang 2: tan 0: tang 1: tan 0: tan Since the matching function does not support substring capture, the escape sequences that are concerned with captured substrings are not relevant. RESTARTING AFTER A PARTIAL MATCH When the alternative matching function has given the PCRE_ERROR_PARTIAL return, indicating that the subject partially matched the pattern, you can restart the match with additional subject data by means of the \R escape sequence. For example: re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ data> 23ja\P\D Partial match: 23ja data> n05\R\D 0: n05 For further information about partial matching, see the pcrepartial documentation. CALLOUTS If the pattern contains any callout requests, pcretest's callout func- tion is called during matching. This works with both matching func- tions. By default, the called function displays the callout number, the start and current positions in the text at the callout time, and the next pattern item to be tested. For example: --->pqrabcdef 0 ^ ^ \d This output indicates that callout number 0 occurred for a match attempt starting at the fourth character of the subject string, when the pointer was at the seventh character of the data, and when the next pattern item was \d. Just one circumflex is output if the start and current positions are the same. Callouts numbered 255 are assumed to be automatic callouts, inserted as a result of the /C pattern modifier. In this case, instead of showing the callout number, the offset in the pattern, preceded by a plus, is output. For example: re> /\d?[A-E]\*/C data> E* --->E* +0 ^ \d? +3 ^ [A-E] +8 ^^ \* +10 ^ ^ 0: E* If a pattern contains (*MARK) items, an additional line is output when- ever a change of latest mark is passed to the callout function. For example: re> /a(*MARK:X)bc/C data> abc --->abc +0 ^ a +1 ^^ (*MARK:X) +10 ^^ b Latest Mark: X +11 ^ ^ c +12 ^ ^ 0: abc The mark changes between matching "a" and "b", but stays the same for the rest of the match, so nothing more is output. If, as a result of backtracking, the mark reverts to being unset, the text "" is output. The callout function in pcretest returns zero (carry on matching) by default, but you can use a \C item in a data line (as described above) to change this and other parameters of the callout. Inserting callouts can be helpful when using pcretest to check compli- cated regular expressions. For further information about callouts, see the pcrecallout documentation. NON-PRINTING CHARACTERS When pcretest is outputting text in the compiled version of a pattern, bytes other than 32-126 are always treated as non-printing characters are are therefore shown as hex escapes. When pcretest is outputting text that is a matched part of a subject string, it behaves in the same way, unless a different locale has been set for the pattern (using the /L modifier). In this case, the isprint() function to distinguish printing and non-printing characters. SAVING AND RELOADING COMPILED PATTERNS The facilities described in this section are not available when the POSIX interface to PCRE is being used, that is, when the /P pattern modifier is specified. When the POSIX interface is not in use, you can cause pcretest to write a compiled pattern to a file, by following the modifiers with > and a file name. For example: /pattern/im >/some/file See the pcreprecompile documentation for a discussion about saving and re-using compiled patterns. Note that if the pattern was successfully studied with JIT optimization, the JIT data cannot be saved. The data that is written is binary. The first eight bytes are the length of the compiled pattern data followed by the length of the optional study data, each written as four bytes in big-endian order (most significant byte first). If there is no study data (either the pattern was not studied, or studying did not return any data), the sec- ond length is zero. The lengths are followed by an exact copy of the compiled pattern. If there is additional study data, this (excluding any JIT data) follows immediately after the compiled pattern. After writing the file, pcretest expects to read a new pattern. A saved pattern can be reloaded into pcretest by specifying < and a file name instead of a pattern. The name of the file must not contain a < character, as otherwise pcretest will interpret the line as a pattern delimited by < characters. For example: re> . \K to reset the start of the matched string; for example, (foo)\Kbar matches bar preceded by foo, but only sets bar as the matched string. (?| introduces a group where the capturing parentheses in each alternative start from the same number; for example, (?|(abc)|(xyz)) sets capturing parentheses number 1 in both cases. \h, \H, \v, \V match horizontal and vertical whitespace, respectively. Release 7.1 24-Apr-07 --------------------- There is only one new feature in this release: a linebreak setting of PCRE_NEWLINE_ANYCRLF. It is a cut-down version of PCRE_NEWLINE_ANY, which recognizes only CRLF, CR, and LF as linebreaks. A few bugs are fixed (see ChangeLog for details), but the major change is a complete re-implementation of the build system. This now has full Autotools support and so is now "standard" in some sense. It should help with compiling PCRE in a wide variety of environments. NOTE: when building shared libraries for Windows, three dlls are now built, called libpcre, libpcreposix, and libpcrecpp. Previously, everything was included in a single dll. Another important change is that the dftables auxiliary program is no longer compiled and run at "make" time by default. Instead, a default set of character tables (assuming ASCII coding) is used. If you want to use dftables to generate the character tables as previously, add --enable-rebuild-chartables to the "configure" command. You must do this if you are compiling PCRE to run on a system that uses EBCDIC code. There is a discussion about character tables in the README file. The default is not to use dftables so that that there is no problem when cross-compiling. Release 7.0 19-Dec-06 --------------------- This release has a new major number because there have been some internal upheavals to facilitate the addition of new optimizations and other facilities, and to make subsequent maintenance and extension easier. Compilation is likely to be a bit slower, but there should be no major effect on runtime performance. Previously compiled patterns are NOT upwards compatible with this release. If you have saved compiled patterns from a previous release, you will have to re-compile them. Important changes that are visible to users are: 1. The Unicode property tables have been updated to Unicode 5.0.0, which adds some more scripts. 2. The option PCRE_NEWLINE_ANY causes PCRE to recognize any Unicode newline sequence as a newline. 3. The \R escape matches a single Unicode newline sequence as a single unit. 4. New features that will appear in Perl 5.10 are now in PCRE. These include alternative Perl syntax for named parentheses, and Perl syntax for recursion. 5. The C++ wrapper interface has been extended by the addition of a QuoteMeta function and the ability to allow copy construction and assignment. For a complete list of changes, see the ChangeLog file. Release 6.7 04-Jul-06 --------------------- The main additions to this release are the ability to use the same name for multiple sets of parentheses, and support for CRLF line endings in both the library and pcregrep (and in pcretest for testing). Thanks to Ian Taylor, the stack usage for many kinds of pattern has been significantly reduced for certain subject strings. Release 6.5 01-Feb-06 --------------------- Important changes in this release: 1. A number of new features have been added to pcregrep. 2. The Unicode property tables have been updated to Unicode 4.1.0, and the supported properties have been extended with script names such as "Arabic", and the derived properties "Any" and "L&". This has necessitated a change to the interal format of compiled patterns. Any saved compiled patterns that use \p or \P must be recompiled. 3. The specification of recursion in patterns has been changed so that all recursive subpatterns are automatically treated as atomic groups. Thus, for example, (?R) is treated as if it were (?>(?R)). This is necessary because otherwise there are situations where recursion does not work. See the ChangeLog for a complete list of changes, which include a number of bug fixes and tidies. Release 6.0 07-Jun-05 --------------------- The release number has been increased to 6.0 because of the addition of several major new pieces of functionality. A new function, pcre_dfa_exec(), which implements pattern matching using a DFA algorithm, has been added. This has a number of advantages for certain cases, though it does run more slowly, and lacks the ability to capture substrings. On the other hand, it does find all matches, not just the first, and it works better for partial matching. The pcrematching man page discusses the differences. The pcretest program has been enhanced so that it can make use of the new pcre_dfa_exec() matching function and the extra features it provides. The distribution now includes a C++ wrapper library. This is built automatically if a C++ compiler is found. The pcrecpp man page discusses this interface. The code itself has been re-organized into many more files, one for each function, so it no longer requires everything to be linked in when static linkage is used. As a consequence, some internal functions have had to have their names exposed. These functions all have names starting with _pcre_. They are undocumented, and are not intended for use by outside callers. The pcregrep program has been enhanced with new functionality such as multiline-matching and options for output more matching context. See the ChangeLog for a complete list of changes to the library and the utility programs. Release 5.0 13-Sep-04 --------------------- The licence under which PCRE is released has been changed to the more conventional "BSD" licence. In the code, some bugs have been fixed, and there are also some major changes in this release (which is why I've increased the number to 5.0). Some changes are internal rearrangements, and some provide a number of new facilities. The new features are: 1. There's an "automatic callout" feature that inserts callouts before every item in the regex, and there's a new callout field that gives the position in the pattern - useful for debugging and tracing. 2. The extra_data structure can now be used to pass in a set of character tables at exec time. This is useful if compiled regex are saved and re-used at a later time when the tables may not be at the same address. If the default internal tables are used, the pointer saved with the compiled pattern is now set to NULL, which means that you don't need to do anything special unless you are using custom tables. 3. It is possible, with some restrictions on the content of the regex, to request "partial" matching. A special return code is given if all of the subject string matched part of the regex. This could be useful for testing an input field as it is being typed. 4. There is now some optional support for Unicode character properties, which means that the patterns items such as \p{Lu} and \X can now be used. Only the general category properties are supported. If PCRE is compiled with this support, an additional 90K data structure is include, which increases the size of the library dramatically. 5. There is support for saving compiled patterns and re-using them later. 6. There is support for running regular expressions that were compiled on a different host with the opposite endianness. 7. The pcretest program has been extended to accommodate the new features. The main internal rearrangement is that sequences of literal characters are no longer handled as strings. Instead, each character is handled on its own. This makes some UTF-8 handling easier, and makes the support of partial matching possible. Compiled patterns containing long literal strings will be larger as a result of this change; I hope that performance will not be much affected. Release 4.5 01-Dec-03 --------------------- Again mainly a bug-fix and tidying release, with only a couple of new features: 1. It's possible now to compile PCRE so that it does not use recursive function calls when matching. Instead it gets memory from the heap. This slows things down, but may be necessary on systems with limited stacks. 2. UTF-8 string checking has been tightened to reject overlong sequences and to check that a starting offset points to the start of a character. Failure of the latter returns a new error code: PCRE_ERROR_BADUTF8_OFFSET. 3. PCRE can now be compiled for systems that use EBCDIC code. Release 4.4 21-Aug-03 --------------------- This is mainly a bug-fix and tidying release. The only new feature is that PCRE checks UTF-8 strings for validity by default. There is an option to suppress this, just in case anybody wants that teeny extra bit of performance. Releases 4.1 - 4.3 ------------------ Sorry, I forgot about updating the NEWS file for these releases. Please take a look at ChangeLog. Release 4.0 17-Feb-03 --------------------- There have been a lot of changes for the 4.0 release, adding additional functionality and mending bugs. Below is a list of the highlights of the new functionality. For full details of these features, please consult the documentation. For a complete list of changes, see the ChangeLog file. 1. Support for Perl's \Q...\E escapes. 2. "Possessive quantifiers" ?+, *+, ++, and {,}+ which come from Sun's Java package. They provide some syntactic sugar for simple cases of "atomic grouping". 3. Support for the \G assertion. It is true when the current matching position is at the start point of the match. 4. A new feature that provides some of the functionality that Perl provides with (?{...}). The facility is termed a "callout". The way it is done in PCRE is for the caller to provide an optional function, by setting pcre_callout to its entry point. To get the function called, the regex must include (?C) at appropriate points. 5. Support for recursive calls to individual subpatterns. This makes it really easy to get totally confused. 6. Support for named subpatterns. The Python syntax (?P...) is used to name a group. 7. Several extensions to UTF-8 support; it is now fairly complete. There is an option for pcregrep to make it operate in UTF-8 mode. 8. The single man page has been split into a number of separate man pages. These also give rise to individual HTML pages which are put in a separate directory. There is an index.html page that lists them all. Some hyperlinking between the pages has been installed. Release 3.5 15-Aug-01 --------------------- 1. The configuring system has been upgraded to use later versions of autoconf and libtool. By default it builds both a shared and a static library if the OS supports it. You can use --disable-shared or --disable-static on the configure command if you want only one of them. 2. The pcretest utility is now installed along with pcregrep because it is useful for users (to test regexs) and by doing this, it automatically gets relinked by libtool. The documentation has been turned into a man page, so there are now .1, .txt, and .html versions in /doc. 3. Upgrades to pcregrep: (i) Added long-form option names like gnu grep. (ii) Added --help to list all options with an explanatory phrase. (iii) Added -r, --recursive to recurse into sub-directories. (iv) Added -f, --file to read patterns from a file. 4. Added --enable-newline-is-cr and --enable-newline-is-lf to the configure script, to force use of CR or LF instead of \n in the source. On non-Unix systems, the value can be set in config.h. 5. The limit of 200 on non-capturing parentheses is a _nesting_ limit, not an absolute limit. Changed the text of the error message to make this clear, and likewise updated the man page. 6. The limit of 99 on the number of capturing subpatterns has been removed. The new limit is 65535, which I hope will not be a "real" limit. Release 3.3 01-Aug-00 --------------------- There is some support for UTF-8 character strings. This is incomplete and experimental. The documentation describes what is and what is not implemented. Otherwise, this is just a bug-fixing release. Release 3.0 01-Feb-00 --------------------- 1. A "configure" script is now used to configure PCRE for Unix systems. It builds a Makefile, a config.h file, and the pcre-config script. 2. PCRE is built as a shared library by default. 3. There is support for POSIX classes such as [:alpha:]. 5. There is an experimental recursion feature. ---------------------------------------------------------------------------- IMPORTANT FOR THOSE UPGRADING FROM VERSIONS BEFORE 2.00 Please note that there has been a change in the API such that a larger ovector is required at matching time, to provide some additional workspace. The new man page has details. This change was necessary in order to support some of the new functionality in Perl 5.005. IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.00 Another (I hope this is the last!) change has been made to the API for the pcre_compile() function. An additional argument has been added to make it possible to pass over a pointer to character tables built in the current locale by pcre_maketables(). To use the default tables, this new arguement should be passed as NULL. IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.05 Yet another (and again I hope this really is the last) change has been made to the API for the pcre_exec() function. An additional argument has been added to make it possible to start the match other than at the start of the subject string. This is important if there are lookbehinds. The new man page has the details, but you just want to convert existing programs, all you need to do is to stick in a new fifth argument to pcre_exec(), with a value of zero. For example, change pcre_exec(pattern, extra, subject, length, options, ovec, ovecsize) to pcre_exec(pattern, extra, subject, length, 0, options, ovec, ovecsize) **** 07070100038366000081a40000000000000000000000014f79083e0006a8f9000000b500010002ffffffffffffffff0000002700000000root/usr/local/share/doc/pcre/pcre.txt----------------------------------------------------------------------------- This file contains a concatenation of the PCRE man pages, converted to plain text format for ease of searching with a text editor, or for use on systems that do not have a man page processor. The small individual files that give synopses of each function in the library have not been included. Neither has the pcredemo program. There are separate text files for the pcregrep and pcretest commands. ----------------------------------------------------------------------------- PCRE(3) PCRE(3) NAME PCRE - Perl-compatible regular expressions INTRODUCTION The PCRE library is a set of functions that implement regular expres- sion pattern matching using the same syntax and semantics as Perl, with just a few differences. Some features that appeared in Python and PCRE before they appeared in Perl are also available using the Python syn- tax, there is some support for one or two .NET and Oniguruma syntax items, and there is an option for requesting some minor changes that give better JavaScript compatibility. Starting with release 8.30, it is possible to compile two separate PCRE libraries: the original, which supports 8-bit character strings (including UTF-8 strings), and a second library that supports 16-bit character strings (including UTF-16 strings). The build process allows either one or both to be built. The majority of the work to make this possible was done by Zoltan Herczeg. The two libraries contain identical sets of functions, except that the names in the 16-bit library start with pcre16_ instead of pcre_. To avoid over-complication and reduce the documentation maintenance load, most of the documentation describes the 8-bit library, with the differ- ences for the 16-bit library described separately in the pcre16 page. References to functions or structures of the form pcre[16]_xxx should be read as meaning "pcre_xxx when using the 8-bit library and pcre16_xxx when using the 16-bit library". The current implementation of PCRE corresponds approximately with Perl 5.12, including support for UTF-8/16 encoded strings and Unicode gen- eral category properties. However, UTF-8/16 and Unicode support has to be explicitly enabled; it is not the default. The Unicode tables corre- spond to Unicode release 6.0.0. In addition to the Perl-compatible matching function, PCRE contains an alternative function that matches the same compiled patterns in a dif- ferent way. In certain circumstances, the alternative function has some advantages. For a discussion of the two matching algorithms, see the pcrematching page. PCRE is written in C and released as a C library. A number of people have written wrappers and interfaces of various kinds. In particular, Google Inc. have provided a comprehensive C++ wrapper for the 8-bit library. This is now included as part of the PCRE distribution. The pcrecpp page has details of this interface. Other people's contribu- tions can be found in the Contrib directory at the primary FTP site, which is: ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre Details of exactly which Perl regular expression features are and are not supported by PCRE are given in separate documents. See the pcrepat- tern and pcrecompat pages. There is a syntax summary in the pcresyntax page. Some features of PCRE can be included, excluded, or changed when the library is built. The pcre_config() function makes it possible for a client to discover which features are available. The features them- selves are described in the pcrebuild page. Documentation about build- ing PCRE for various operating systems can be found in the README and NON-UNIX-USE files in the source distribution. The libraries contains a number of undocumented internal functions and data tables that are used by more than one of the exported external functions, but which are not intended for use by external callers. Their names all begin with "_pcre_" or "_pcre16_", which hopefully will not provoke any name clashes. In some environments, it is possible to control which external symbols are exported when a shared library is built, and in these cases the undocumented symbols are not exported. USER DOCUMENTATION The user documentation for PCRE comprises a number of different sec- tions. In the "man" format, each of these is a separate "man page". In the HTML format, each is a separate page, linked from the index page. In the plain text format, all the sections, except the pcredemo sec- tion, are concatenated, for ease of searching. The sections are as fol- lows: pcre this document pcre16 details of the 16-bit library pcre-config show PCRE installation configuration information pcreapi details of PCRE's native C API pcrebuild options for building PCRE pcrecallout details of the callout feature pcrecompat discussion of Perl compatibility pcrecpp details of the C++ wrapper for the 8-bit library pcredemo a demonstration C program that uses PCRE pcregrep description of the pcregrep command (8-bit only) pcrejit discussion of the just-in-time optimization support pcrelimits details of size and other limits pcrematching discussion of the two matching algorithms pcrepartial details of the partial matching facility pcrepattern syntax and semantics of supported regular expressions pcreperform discussion of performance issues pcreposix the POSIX-compatible C API for the 8-bit library pcreprecompile details of saving and re-using precompiled patterns pcresample discussion of the pcredemo program pcrestack discussion of stack usage pcresyntax quick syntax reference pcretest description of the pcretest testing command pcreunicode discussion of Unicode and UTF-8/16 support In addition, in the "man" and HTML formats, there is a short page for each 8-bit C library function, listing its arguments and results. AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. Putting an actual email address here seems to have been a spam magnet, so I've taken it away. If you want to email me, use my two initials, followed by the two digits 10, at the domain cam.ac.uk. REVISION Last updated: 10 January 2012 Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ PCRE(3) PCRE(3) NAME PCRE - Perl-compatible regular expressions #include PCRE 16-BIT API BASIC FUNCTIONS pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options, const char **errptr, int *erroffset, const unsigned char *tableptr); pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options, int *errorcodeptr, const char **errptr, int *erroffset, const unsigned char *tableptr); pcre16_extra *pcre16_study(const pcre16 *code, int options, const char **errptr); void pcre16_free_study(pcre16_extra *extra); int pcre16_exec(const pcre16 *code, const pcre16_extra *extra, PCRE_SPTR16 subject, int length, int startoffset, int options, int *ovector, int ovecsize); int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra, PCRE_SPTR16 subject, int length, int startoffset, int options, int *ovector, int ovecsize, int *workspace, int wscount); PCRE 16-BIT API STRING EXTRACTION FUNCTIONS int pcre16_copy_named_substring(const pcre16 *code, PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 stringname, PCRE_UCHAR16 *buffer, int buffersize); int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector, int stringcount, int stringnumber, PCRE_UCHAR16 *buffer, int buffersize); int pcre16_get_named_substring(const pcre16 *code, PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 stringname, PCRE_SPTR16 *stringptr); int pcre16_get_stringnumber(const pcre16 *code, PCRE_SPTR16 name); int pcre16_get_stringtable_entries(const pcre16 *code, PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last); int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector, int stringcount, int stringnumber, PCRE_SPTR16 *stringptr); int pcre16_get_substring_list(PCRE_SPTR16 subject, int *ovector, int stringcount, PCRE_SPTR16 **listptr); void pcre16_free_substring(PCRE_SPTR16 stringptr); void pcre16_free_substring_list(PCRE_SPTR16 *stringptr); PCRE 16-BIT API AUXILIARY FUNCTIONS pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize); void pcre16_jit_stack_free(pcre16_jit_stack *stack); void pcre16_assign_jit_stack(pcre16_extra *extra, pcre16_jit_callback callback, void *data); const unsigned char *pcre16_maketables(void); int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra, int what, void *where); int pcre16_refcount(pcre16 *code, int adjust); int pcre16_config(int what, void *where); const char *pcre16_version(void); int pcre16_pattern_to_host_byte_order(pcre16 *code, pcre16_extra *extra, const unsigned char *tables); PCRE 16-BIT API INDIRECTED FUNCTIONS void *(*pcre16_malloc)(size_t); void (*pcre16_free)(void *); void *(*pcre16_stack_malloc)(size_t); void (*pcre16_stack_free)(void *); int (*pcre16_callout)(pcre16_callout_block *); PCRE 16-BIT API 16-BIT-ONLY FUNCTION int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output, PCRE_SPTR16 input, int length, int *byte_order, int keep_boms); THE PCRE 16-BIT LIBRARY Starting with release 8.30, it is possible to compile a PCRE library that supports 16-bit character strings, including UTF-16 strings, as well as or instead of the original 8-bit library. The majority of the work to make this possible was done by Zoltan Herczeg. The two libraries contain identical sets of functions, used in exactly the same way. Only the names of the functions and the data types of their argu- ments and results are different. To avoid over-complication and reduce the documentation maintenance load, most of the PCRE documentation describes the 8-bit library, with only occasional references to the 16-bit library. This page describes what is different when you use the 16-bit library. WARNING: A single application can be linked with both libraries, but you must take care when processing any particular pattern to use func- tions from just one library. For example, if you want to study a pat- tern that was compiled with pcre16_compile(), you must do so with pcre16_study(), not pcre_study(), and you must free the study data with pcre16_free_study(). THE HEADER FILE There is only one header file, pcre.h. It contains prototypes for all the functions in both libraries, as well as definitions of flags, structures, error codes, etc. THE LIBRARY NAME In Unix-like systems, the 16-bit library is called libpcre16, and can normally be accesss by adding -lpcre16 to the command for linking an application that uses PCRE. STRING TYPES In the 8-bit library, strings are passed to PCRE library functions as vectors of bytes with the C type "char *". In the 16-bit library, strings are passed as vectors of unsigned 16-bit quantities. The macro PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is defined as "const PCRE_UCHAR16 *". In very many environments, "short int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16 as "short int", but checks that it really is a 16-bit data type. If it is not, the build fails with an error message telling the maintainer to modify the definition appropriately. STRUCTURE TYPES The types of the opaque structures that are used for compiled 16-bit patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively. The type of the user-accessible structure that is returned by pcre16_study() is pcre16_extra, and the type of the structure that is used for passing data to a callout function is pcre16_callout_block. These structures contain the same fields, with the same names, as their 8-bit counterparts. The only difference is that pointers to character strings are 16-bit instead of 8-bit types. 16-BIT FUNCTIONS For every function in the 8-bit library there is a corresponding func- tion in the 16-bit library with a name that starts with pcre16_ instead of pcre_. The prototypes are listed above. In addition, there is one extra function, pcre16_utf16_to_host_byte_order(). This is a utility function that converts a UTF-16 character string to host byte order if necessary. The other 16-bit functions expect the strings they are passed to be in host byte order. The input and output arguments of pcre16_utf16_to_host_byte_order() may point to the same address, that is, conversion in place is supported. The output buffer must be at least as long as the input. The length argument specifies the number of 16-bit data units in the input string; a negative value specifies a zero-terminated string. If byte_order is NULL, it is assumed that the string starts off in host byte order. This may be changed by byte-order marks (BOMs) anywhere in the string (commonly as the first character). If byte_order is not NULL, a non-zero value of the integer to which it points means that the input starts off in host byte order, otherwise the opposite order is assumed. Again, BOMs in the string can change this. The final byte order is passed back at the end of processing. If keep_boms is not zero, byte-order mark characters (0xfeff) are copied into the output string. Otherwise they are discarded. The result of the function is the number of 16-bit units placed into the output buffer, including the zero terminator if the string was zero-terminated. SUBJECT STRING OFFSETS The offsets within subject strings that are returned by the matching functions are in 16-bit units rather than bytes. NAMED SUBPATTERNS The name-to-number translation table that is maintained for named sub- patterns uses 16-bit characters. The pcre16_get_stringtable_entries() function returns the length of each entry in the table as the number of 16-bit data units. OPTION NAMES There are two new general option names, PCRE_UTF16 and PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options define the same bits in the options word. For the pcre16_config() function there is an option PCRE_CONFIG_UTF16 that returns 1 if UTF-16 support is configured, otherwise 0. If this option is given to pcre_config(), or if the PCRE_CONFIG_UTF8 option is given to pcre16_config(), the result is the PCRE_ERROR_BADOPTION error. CHARACTER CODES In 16-bit mode, when PCRE_UTF16 is not set, character values are treated in the same way as in 8-bit, non UTF-8 mode, except, of course, that they can range from 0 to 0xffff instead of 0 to 0xff. Character types for characters less than 0xff can therefore be influenced by the locale in the same way as before. Characters greater than 0xff have only one case, and no "type" (such as letter or digit). In UTF-16 mode, the character code is Unicode, in the range 0 to 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff because those are "surrogate" values that are used in pairs to encode values greater than 0xffff. A UTF-16 string can indicate its endianness by special code knows as a byte-order mark (BOM). The PCRE functions do not handle this, expecting strings to be in host byte order. A utility function called pcre16_utf16_to_host_byte_order() is provided to help with this (see above). ERROR NAMES The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre- spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is given when a compiled pattern is passed to a function that processes patterns in the other mode, for example, if a pattern compiled with pcre_compile() is passed to pcre16_exec(). There are new error codes whose names begin with PCRE_UTF16_ERR for invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for UTF-8 strings that are described in the section entitled "Reason codes for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors are: PCRE_UTF16_ERR1 Missing low surrogate at end of string PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate PCRE_UTF16_ERR3 Isolated low surrogate PCRE_UTF16_ERR4 Invalid character 0xfffe ERROR TEXTS If there is an error while compiling a pattern, the error text that is passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit character string, zero-terminated. CALLOUTS The subject and mark fields in the callout block that is passed to a callout function point to 16-bit vectors. TESTING The pcretest program continues to operate with 8-bit input and output files, but it can be used for testing the 16-bit library. If it is run with the command line option -16, patterns and subject strings are con- verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit library functions are used instead of the 8-bit ones. Returned 16-bit strings are converted to 8-bit for output. If the 8-bit library was not compiled, pcretest defaults to 16-bit and the -16 option is ignored. When PCRE is being built, the RunTest script that is called by "make check" uses the pcretest -C option to discover which of the 8-bit and 16-bit libraries has been built, and runs the tests appropriately. NOT SUPPORTED IN 16-BIT MODE Not all the features of the 8-bit library are available with the 16-bit library. The C++ and POSIX wrapper functions support only the 8-bit library, and the pcregrep program is at present 8-bit only. AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 08 January 2012 Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ PCREBUILD(3) PCREBUILD(3) NAME PCRE - Perl-compatible regular expressions PCRE BUILD-TIME OPTIONS This document describes the optional features of PCRE that can be selected when the library is compiled. It assumes use of the configure script, where the optional features are selected or deselected by pro- viding options to configure before running the make command. However, the same options can be selected in both Unix-like and non-Unix-like environments using the GUI facility of cmake-gui if you are using CMake instead of configure to build PCRE. There is a lot more information about building PCRE in non-Unix-like environments in the file called NON_UNIX_USE, which is part of the PCRE distribution. You should consult this file as well as the README file if you are building in a non-Unix-like environment. The complete list of options for configure (which includes the standard ones such as the selection of the installation directory) can be obtained by running ./configure --help The following sections include descriptions of options whose names begin with --enable or --disable. These settings specify changes to the defaults for the configure command. Because of the way that configure works, --enable and --disable always come in pairs, so the complemen- tary option always exists as well, but as it specifies the default, it is not described. BUILDING 8-BIT and 16-BIT LIBRARIES By default, a library called libpcre is built, containing functions that take string arguments contained in vectors of bytes, either as single-byte characters, or interpreted as UTF-8 strings. You can also build a separate library, called libpcre16, in which strings are con- tained in vectors of 16-bit data units and interpreted either as sin- gle-unit characters or UTF-16 strings, by adding --enable-pcre16 to the configure command. If you do not want the 8-bit library, add --disable-pcre8 as well. At least one of the two libraries must be built. Note that the C++ and POSIX wrappers are for the 8-bit library only, and that pcre- grep is an 8-bit program. None of these are built if you select only the 16-bit library. BUILDING SHARED AND STATIC LIBRARIES The PCRE building process uses libtool to build both shared and static Unix libraries by default. You can suppress one of these by adding one of --disable-shared --disable-static to the configure command, as required. C++ SUPPORT By default, if the 8-bit library is being built, the configure script will search for a C++ compiler and C++ header files. If it finds them, it automatically builds the C++ wrapper library (which supports only 8-bit strings). You can disable this by adding --disable-cpp to the configure command. UTF-8 and UTF-16 SUPPORT To build PCRE with support for UTF Unicode character strings, add --enable-utf to the configure command. This setting applies to both libraries, adding support for UTF-8 to the 8-bit library and support for UTF-16 to the 16-bit library. There are no separate options for enabling UTF-8 and UTF-16 independently because that would allow ridiculous settings such as requesting UTF-16 support while building only the 8-bit library. It is not possible to build one library with UTF support and the other without in the same configuration. (For backwards compatibil- ity, --enable-utf8 is a synonym of --enable-utf.) Of itself, this setting does not make PCRE treat strings as UTF-8 or UTF-16. As well as compiling PCRE with this option, you also have have to set the PCRE_UTF8 or PCRE_UTF16 option when you call one of the pat- tern compiling functions. If you set --enable-utf when compiling in an EBCDIC environment, PCRE expects its input to be either ASCII or UTF-8 (depending on the runtime option). It is not possible to support both EBCDIC and UTF-8 codes in the same version of the library. Consequently, --enable-utf and --enable-ebcdic are mutually exclusive. UNICODE CHARACTER PROPERTY SUPPORT UTF support allows the libraries to process character codepoints up to 0x10ffff in the strings that they handle. On its own, however, it does not provide any facilities for accessing the properties of such charac- ters. If you want to be able to use the pattern escapes \P, \p, and \X, which refer to Unicode character properties, you must add --enable-unicode-properties to the configure command. This implies UTF support, even if you have not explicitly requested it. Including Unicode property support adds around 30K of tables to the PCRE library. Only the general category properties such as Lu and Nd are supported. Details are given in the pcrepattern documentation. JUST-IN-TIME COMPILER SUPPORT Just-in-time compiler support is included in the build by specifying --enable-jit This support is available only for certain hardware architectures. If this option is set for an unsupported architecture, a compile time error occurs. See the pcrejit documentation for a discussion of JIT usage. When JIT support is enabled, pcregrep automatically makes use of it, unless you add --disable-pcregrep-jit to the "configure" command. CODE VALUE OF NEWLINE By default, PCRE interprets the linefeed (LF) character as indicating the end of a line. This is the normal newline character on Unix-like systems. You can compile PCRE to use carriage return (CR) instead, by adding --enable-newline-is-cr to the configure command. There is also a --enable-newline-is-lf option, which explicitly specifies linefeed as the newline character. Alternatively, you can specify that line endings are to be indicated by the two character sequence CRLF. If you want this, add --enable-newline-is-crlf to the configure command. There is a fourth option, specified by --enable-newline-is-anycrlf which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as indicating a line ending. Finally, a fifth option, specified by --enable-newline-is-any causes PCRE to recognize any Unicode newline sequence. Whatever line ending convention is selected when PCRE is built can be overridden when the library functions are called. At build time it is conventional to use the standard for your operating system. WHAT \R MATCHES By default, the sequence \R in a pattern matches any Unicode newline sequence, whatever has been selected as the line ending sequence. If you specify --enable-bsr-anycrlf the default is changed so that \R matches only CR, LF, or CRLF. What- ever is selected when PCRE is built can be overridden when the library functions are called. POSIX MALLOC USAGE When the 8-bit library is called through the POSIX interface (see the pcreposix documentation), additional working storage is required for holding the pointers to capturing substrings, because PCRE requires three integers per substring, whereas the POSIX interface provides only two. If the number of expected substrings is small, the wrapper func- tion uses space on the stack, because this is faster than using mal- loc() for each call. The default threshold above which the stack is no longer used is 10; it can be changed by adding a setting such as --with-posix-malloc-threshold=20 to the configure command. HANDLING VERY LARGE PATTERNS Within a compiled pattern, offset values are used to point from one part to another (for example, from an opening parenthesis to an alter- nation metacharacter). By default, two-byte values are used for these offsets, leading to a maximum size for a compiled pattern of around 64K. This is sufficient to handle all but the most gigantic patterns. Nevertheless, some people do want to process truly enormous patterns, so it is possible to compile PCRE to use three-byte or four-byte off- sets by adding a setting such as --with-link-size=3 to the configure command. The value given must be 2, 3, or 4. For the 16-bit library, a value of 3 is rounded up to 4. Using longer offsets slows down the operation of PCRE because it has to load additional data when handling them. AVOIDING EXCESSIVE STACK USAGE When matching with the pcre_exec() function, PCRE implements backtrack- ing by making recursive calls to an internal function called match(). In environments where the size of the stack is limited, this can se- verely limit PCRE's operation. (The Unix environment does not usually suffer from this problem, but it may sometimes be necessary to increase the maximum stack size. There is a discussion in the pcrestack docu- mentation.) An alternative approach to recursion that uses memory from the heap to remember data, instead of using recursive function calls, has been implemented to work round the problem of limited stack size. If you want to build a version of PCRE that works this way, add --disable-stack-for-recursion to the configure command. With this configuration, PCRE will use the pcre_stack_malloc and pcre_stack_free variables to call memory manage- ment functions. By default these point to malloc() and free(), but you can replace the pointers so that your own functions are used instead. Separate functions are provided rather than using pcre_malloc and pcre_free because the usage is very predictable: the block sizes requested are always the same, and the blocks are always freed in reverse order. A calling program might be able to implement optimized functions that perform better than malloc() and free(). PCRE runs noticeably more slowly when built in this way. This option affects only the pcre_exec() function; it is not relevant for pcre_dfa_exec(). LIMITING PCRE RESOURCE USAGE Internally, PCRE has a function called match(), which it calls repeat- edly (sometimes recursively) when matching a pattern with the pcre_exec() function. By controlling the maximum number of times this function may be called during a single matching operation, a limit can be placed on the resources used by a single call to pcre_exec(). The limit can be changed at run time, as described in the pcreapi documen- tation. The default is 10 million, but this can be changed by adding a setting such as --with-match-limit=500000 to the configure command. This setting has no effect on the pcre_dfa_exec() matching function. In some environments it is desirable to limit the depth of recursive calls of match() more strictly than the total number of calls, in order to restrict the maximum amount of stack (or heap, if --disable-stack- for-recursion is specified) that is used. A second limit controls this; it defaults to the value that is set for --with-match-limit, which imposes no additional constraints. However, you can set a lower limit by adding, for example, --with-match-limit-recursion=10000 to the configure command. This value can also be overridden at run time. CREATING CHARACTER TABLES AT BUILD TIME PCRE uses fixed tables for processing characters whose code values are less than 256. By default, PCRE is built with a set of tables that are distributed in the file pcre_chartables.c.dist. These tables are for ASCII codes only. If you add --enable-rebuild-chartables to the configure command, the distributed tables are no longer used. Instead, a program called dftables is compiled and run. This outputs the source for new set of tables, created in the default locale of your C runtime system. (This method of replacing the tables does not work if you are cross compiling, because dftables is run on the local host. If you need to create alternative tables when cross compiling, you will have to do so "by hand".) USING EBCDIC CODE PCRE assumes by default that it will run in an environment where the character code is ASCII (or Unicode, which is a superset of ASCII). This is the case for most computer operating systems. PCRE can, how- ever, be compiled to run in an EBCDIC environment by adding --enable-ebcdic to the configure command. This setting implies --enable-rebuild-charta- bles. You should only use it if you know that you are in an EBCDIC environment (for example, an IBM mainframe operating system). The --enable-ebcdic option is incompatible with --enable-utf. PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT By default, pcregrep reads all files as plain text. You can build it so that it recognizes files whose names end in .gz or .bz2, and reads them with libz or libbz2, respectively, by adding one or both of --enable-pcregrep-libz --enable-pcregrep-libbz2 to the configure command. These options naturally require that the rel- evant libraries are installed on your system. Configuration will fail if they are not. PCREGREP BUFFER SIZE pcregrep uses an internal buffer to hold a "window" on the file it is scanning, in order to be able to output "before" and "after" lines when it finds a match. The size of the buffer is controlled by a parameter whose default value is 20K. The buffer itself is three times this size, but because of the way it is used for holding "before" lines, the long- est line that is guaranteed to be processable is the parameter size. You can change the default parameter value by adding, for example, --with-pcregrep-bufsize=50K to the configure command. The caller of pcregrep can, however, override this value by specifying a run-time option. PCRETEST OPTION FOR LIBREADLINE