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diff --git a/ext/pcre/pcrelib/doc/pcre.txt b/ext/pcre/pcrelib/doc/pcre.txt index 2a2a82c7f1..9d69515c3b 100644 --- a/ext/pcre/pcrelib/doc/pcre.txt +++ b/ext/pcre/pcrelib/doc/pcre.txt @@ -8,13 +8,13 @@ pcretest commands. ----------------------------------------------------------------------------- -PCRE(3) PCRE(3) +PCRE(3) Library Functions Manual PCRE(3) + NAME PCRE - Perl-compatible regular expressions - INTRODUCTION The PCRE library is a set of functions that implement regular expres- @@ -33,110 +33,113 @@ INTRODUCTION possible was done by Zoltan Herczeg. Starting with release 8.32 it is possible to compile a third separate - PCRE library, which supports 32-bit character strings (including UTF-32 - strings). The build process allows any set of the 8-, 16- and 32-bit - libraries. The work to make this possible was done by Christian Persch. - - The three libraries contain identical sets of functions, except that - the names in the 16-bit library start with pcre16_ instead of pcre_, - and the names in the 32-bit library start with pcre32_ instead of - pcre_. To avoid over-complication and reduce the documentation mainte- + PCRE library that supports 32-bit character strings (including UTF-32 + strings). The build process allows any combination of the 8-, 16- and + 32-bit libraries. The work to make this possible was done by Christian + Persch. + + The three libraries contain identical sets of functions, except that + the names in the 16-bit library start with pcre16_ instead of pcre_, + and the names in the 32-bit library start with pcre32_ instead of + pcre_. To avoid over-complication and reduce the documentation mainte- nance load, most of the documentation describes the 8-bit library, with - the differences for the 16-bit and 32-bit libraries described sepa- - rately in the pcre16 and pcre32 pages. References to functions or - structures of the form pcre[16|32]_xxx should be read as meaning - "pcre_xxx when using the 8-bit library, pcre16_xxx when using the + the differences for the 16-bit and 32-bit libraries described sepa- + rately in the pcre16 and pcre32 pages. References to functions or + structures of the form pcre[16|32]_xxx should be read as meaning + "pcre_xxx when using the 8-bit library, pcre16_xxx when using the 16-bit library, or pcre32_xxx when using the 32-bit library". - The current implementation of PCRE corresponds approximately with Perl - 5.12, including support for UTF-8/16/32 encoded strings and Unicode - general category properties. However, UTF-8/16/32 and Unicode support + The current implementation of PCRE corresponds approximately with Perl + 5.12, including support for UTF-8/16/32 encoded strings and Unicode + general category properties. However, UTF-8/16/32 and Unicode support has to be explicitly enabled; it is not the default. The Unicode tables - correspond to Unicode release 6.2.0. + correspond to Unicode release 6.3.0. - In addition to the Perl-compatible matching function, PCRE contains an - alternative function that matches the same compiled patterns in a dif- + 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 + 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, + 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 + 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 + 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 + 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-AUTOTOOLS_BUILD 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_" or "_pcre32_", 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 + 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_" or "_pcre32_", 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. SECURITY CONSIDERATIONS - If you are using PCRE in a non-UTF application that permits users to - supply arbitrary patterns for compilation, you should be aware of a + If you are using PCRE in a non-UTF application that permits users to + supply arbitrary patterns for compilation, you should be aware of a feature that allows users to turn on UTF support from within a pattern, - provided that PCRE was built with UTF support. For example, an 8-bit - pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, - which interprets patterns and subjects as strings of UTF-8 characters - instead of individual 8-bit characters. This causes both the pattern + provided that PCRE was built with UTF support. For example, an 8-bit + pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, + which interprets patterns and subjects as strings of UTF-8 characters + instead of individual 8-bit characters. This causes both the pattern and any data against which it is matched to be checked for UTF-8 valid- - ity. If the data string is very long, such a check might use suffi- - ciently many resources as to cause your application to lose perfor- + ity. If the data string is very long, such a check might use suffi- + ciently many resources as to cause your application to lose perfor- mance. - The best way of guarding against this possibility is to use the - pcre_fullinfo() function to check the compiled pattern's options for - UTF. + One way of guarding against this possibility is to use the + pcre_fullinfo() function to check the compiled pattern's options for + UTF. Alternatively, from release 8.33, you can set the PCRE_NEVER_UTF + option at compile time. This causes an compile time error if a pattern + contains a UTF-setting sequence. - If your application is one that supports UTF, be aware that validity - checking can take time. If the same data string is to be matched many + If your application is one that supports UTF, be aware that validity + checking can take time. If the same data string is to be matched many times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to save redundant checks. - Another way that performance can be hit is by running a pattern that - has a very large search tree against a string that will never match. - Nested unlimited repeats in a pattern are a common example. PCRE pro- + Another way that performance can be hit is by running a pattern that + has a very large search tree against a string that will never match. + Nested unlimited repeats in a pattern are a common example. PCRE pro- vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea- ture in the pcreapi page. 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- + 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 + pcre-config show PCRE installation configuration information pcre16 details of the 16-bit library pcre32 details of the 32-bit library - pcre-config show PCRE installation configuration information pcreapi details of PCRE's native C API - pcrebuild options for building PCRE + pcrebuild building PCRE pcrecallout details of the callout feature pcrecompat discussion of Perl compatibility pcrecpp details of the C++ wrapper for the 8-bit library @@ -157,7 +160,7 @@ USER DOCUMENTATION pcretest description of the pcretest testing command pcreunicode discussion of Unicode and UTF-8/16/32 support - In addition, in the "man" and HTML formats, there is a short page for + In addition, in the "man" and HTML formats, there is a short page for each C library function, listing its arguments and results. @@ -167,19 +170,20 @@ AUTHOR 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, + 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: 11 November 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 13 May 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCRE(3) PCRE(3) +PCRE(3) Library Functions Manual PCRE(3) + NAME @@ -389,8 +393,10 @@ STRUCTURE TYPES SUBJECT STRING OFFSETS - The offsets within subject strings that are returned by the matching - functions are in 16-bit units rather than bytes. + The lengths and starting offsets of subject strings must be specified + in 16-bit data units, and the offsets within subject strings that are + returned by the matching functions are in also 16-bit units rather than + bytes. NAMED SUBPATTERNS @@ -503,12 +509,13 @@ AUTHOR REVISION - Last updated: 08 November 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 12 May 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCRE(3) PCRE(3) +PCRE(3) Library Functions Manual PCRE(3) + NAME @@ -525,7 +532,6 @@ PCRE 32-BIT API BASIC FUNCTIONS pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options, int *errorcodeptr, - const char **errptr, int *erroffset, const unsigned char *tableptr); pcre32_extra *pcre32_study(const pcre32 *code, int options, @@ -718,8 +724,10 @@ STRUCTURE TYPES SUBJECT STRING OFFSETS - The offsets within subject strings that are returned by the matching - functions are in 32-bit units rather than bytes. + The lengths and starting offsets of subject strings must be specified + in 32-bit data units, and the offsets within subject strings that are + returned by the matching functions are in also 32-bit units rather than + bytes. NAMED SUBPATTERNS @@ -829,33 +837,46 @@ AUTHOR REVISION - Last updated: 08 November 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 12 May 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREBUILD(3) PCREBUILD(3) +PCREBUILD(3) Library Functions Manual PCREBUILD(3) + NAME PCRE - Perl-compatible regular expressions +BUILDING PCRE + + PCRE is distributed with a configure script that can be used to build + the library in Unix-like environments using the applications known as + Autotools. Also in the distribution are files to support building + using CMake instead of configure. The text file README contains general + information about building with Autotools (some of which is repeated + below), and also has some comments about building on various operating + systems. There is a lot more information about building PCRE without + using Autotools (including information about using CMake and building + "by hand") in the text file called NON-AUTOTOOLS-BUILD. You should + consult this file as well as the README file if you are building in a + non-Unix-like environment. + 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. + The rest of 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 dese- + lected by providing options to configure before running the make com- + mand. 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 without using con- - figure (including information about using CMake or building "by hand") - in the file called NON-AUTOTOOLS-BUILD, which is part of the PCRE dis- - tribution. You should consult this file as well as the README file if - you are building in a non-Unix-like environment. + If you are not using Autotools or CMake, option selection can be done + by editing the config.h file, or by passing parameter settings to the + compiler, as described in NON-AUTOTOOLS-BUILD. The complete list of options for configure (which includes the standard ones such as the selection of the installation directory) can be @@ -882,10 +903,10 @@ BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES --enable-pcre16 - to the configure command. You can also build a separate library, called - libpcre32, in which strings are contained in vectors of 32-bit data - units and interpreted either as single-unit characters or UTF-32 - strings, by adding + to the configure command. You can also build yet another separate + library, called libpcre32, in which strings are contained in vectors of + 32-bit data units and interpreted either as single-unit characters or + UTF-32 strings, by adding --enable-pcre32 @@ -901,9 +922,9 @@ BUILDING 8-BIT, 16-BIT AND 32-BIT LIBRARIES 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 + The Autotools PCRE building process uses libtool to build both shared + and static libraries by default. You can suppress one of these by + adding one of --disable-shared --disable-static @@ -1319,18 +1340,18 @@ AUTHOR REVISION - Last updated: 30 October 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 12 May 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREMATCHING(3) PCREMATCHING(3) +PCREMATCHING(3) Library Functions Manual PCREMATCHING(3) + NAME PCRE - Perl-compatible regular expressions - PCRE MATCHING ALGORITHMS This document describes the two different algorithms that are available @@ -1436,72 +1457,81 @@ THE ALTERNATIVE MATCHING ALGORITHM at the fifth character of the subject. The algorithm does not automati- cally move on to find matches that start at later positions. + PCRE's "auto-possessification" optimization usually applies to charac- + ter repeats at the end of a pattern (as well as internally). For exam- + ple, the pattern "a\d+" is compiled as if it were "a\d++" because there + is no point even considering the possibility of backtracking into the + repeated digits. For DFA matching, this means that only one possible + match is found. If you really do want multiple matches in such cases, + either use an ungreedy repeat ("a\d+?") or set the PCRE_NO_AUTO_POSSESS + option when compiling. + 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 + 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, pos- - sessive quantifiers can make a difference when what follows could also + sessive 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 + 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 + 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 sub- strings are available. - 3. Because no substrings are captured, back references within the pat- + 3. Because no substrings are captured, back references within the pat- tern are not supported, and cause errors if encountered. - 4. For the same reason, conditional expressions that use a backrefer- - ence as the condition or test for a specific group recursion are not + 4. For the same reason, conditional expressions that use a backrefer- + ence 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 + 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 + 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 + 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, UTF-16 or UTF-32 modes, is - not supported in these modes, because the alternative algorithm moves + 7. The \C escape sequence, which (in the standard algorithm) always + matches a single data unit, even in UTF-8, UTF-16 or UTF-32 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 + 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 advan- + Using the alternative matching algorithm provides the following advan- tages: 1. All possible matches (at a single point in the subject) are automat- - ically found, and in particular, the longest match is found. To find + ically 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 + 2. Because the alternative algorithm scans the subject string just once, and never needs to backtrack (except for lookbehinds), it is pos- - sible to pass very long subject strings to the matching function in + sible 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 dis- + 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 dis- cusses multi-segment matching. @@ -1509,8 +1539,8 @@ 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 + 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. @@ -1528,12 +1558,13 @@ AUTHOR REVISION - Last updated: 08 January 2012 + Last updated: 12 November 2013 Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ -PCREAPI(3) PCREAPI(3) +PCREAPI(3) Library Functions Manual PCREAPI(3) + NAME @@ -1663,68 +1694,67 @@ PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES ues. References to bytes and UTF-8 in this document should be read as refer- - ences to 16-bit data quantities and UTF-16 when using the 16-bit - library, or 32-bit data quantities and UTF-32 when using the 32-bit - library, unless specified otherwise. More details of the specific dif- - ferences for the 16-bit and 32-bit libraries are given in the pcre16 - and pcre32 pages. + ences to 16-bit data units and UTF-16 when using the 16-bit library, or + 32-bit data units and UTF-32 when using the 32-bit library, unless + specified otherwise. More details of the specific differences for the + 16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages. 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 cor- - respond 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 + are also some wrapper functions (for the 8-bit library only) that cor- + respond 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 + 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 + 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_mal- + program against a non-dll pcre.a file, you must define PCRE_STATIC + before including pcre.h or pcrecpp.h, because otherwise the pcre_mal- loc() 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 sim- - plest way of using them is provided in the file called pcredemo.c in + 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 sim- + plest 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 + 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 + 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 + 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. - From release 8.32 there is also a direct interface for JIT execution, - which gives improved performance. The JIT-specific functions are dis- + From release 8.32 there is also a direct interface for JIT execution, + which gives improved performance. The JIT-specific functions are dis- cussed in the pcrejit documentation. A second matching function, pcre_dfa_exec(), which is not Perl-compati- - ble, is also provided. This uses a different algorithm for the match- - ing. 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 docu- + ble, is also provided. This uses a different algorithm for the match- + ing. 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 docu- mentation. - In addition to the main compiling and matching functions, there are + 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: @@ -1739,105 +1769,105 @@ PCRE API OVERVIEW 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 + 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 + 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 + 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, respec- + The global variables pcre_malloc and pcre_free initially contain the + entry points of the standard malloc() and free() functions, respec- tively. PCRE calls the memory management functions via these variables, - so a calling program can replace them if it wishes to intercept the + 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 + 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 environ- - ments 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 docu- + function. See the pcrebuild documentation for details of how to do + this. It is a non-standard way of building PCRE, for use in environ- + ments 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 docu- mentation. 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 + 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 (line- + PCRE supports five different conventions for indicating line breaks in + strings: a single CR (carriage return) character, a single LF (line- feed) character, the two-character sequence CRLF, any of the three pre- - ceding, or any Unicode newline sequence. The Unicode newline sequences - are the three just mentioned, plus the single characters VT (vertical + ceding, or any Unicode newline sequence. The Unicode newline sequences + are the three just mentioned, plus the single characters 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). - 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 stan- - dard. When PCRE is run, the default can be overridden, either when a + 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 stan- + dard. 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 + 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 char- - acter or pair of characters that indicate a line break". The choice of - newline convention affects the handling of the dot, circumflex, and + acter 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 advance- + CRLF is a recognized line ending sequence, the match position advance- ment 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, + 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 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 match- + The compiled form of a regular expression is not altered during match- ing, 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 sepa- - rate memory stack areas for each thread. See the pcrejit documentation + If the just-in-time optimization feature is being used, it needs sepa- + rate 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 regu- - lar expression with one version of PCRE for use with a different ver- + 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 regu- + lar expression with one version of PCRE for use with a different ver- sion is not guaranteed to work and may cause crashes. @@ -1845,45 +1875,45 @@ CHECKING BUILD-TIME OPTIONS int pcre_config(int what, void *where); - The function pcre_config() makes it possible for a PCRE client to dis- + The function pcre_config() makes it possible for a PCRE client to dis- cover which optional features have been compiled into the PCRE library. - The pcrebuild documentation has more details about these optional fea- + The pcrebuild documentation has more details about these optional fea- tures. - The first argument for pcre_config() is an integer, specifying which + 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 + 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 avail- - able; otherwise it is set to zero. This value should normally be given + The output is an integer that is set to one if UTF-8 support is avail- + able; otherwise it is set to zero. This value should normally be given to the 8-bit version of this function, pcre_config(). If it is given to - the 16-bit or 32-bit version of this function, the result is + the 16-bit or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION. PCRE_CONFIG_UTF16 The output is an integer that is set to one if UTF-16 support is avail- - able; otherwise it is set to zero. This value should normally be given + able; 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 or 32-bit version of this function, the result is + to the 8-bit or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION. PCRE_CONFIG_UTF32 The output is an integer that is set to one if UTF-32 support is avail- - able; otherwise it is set to zero. This value should normally be given + able; otherwise it is set to zero. This value should normally be given to the 32-bit version of this function, pcre32_config(). If it is given - to the 8-bit or 16-bit version of this function, the result is + to the 8-bit or 16-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 + 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 @@ -1893,49 +1923,56 @@ CHECKING BUILD-TIME OPTIONS PCRE_CONFIG_JITTARGET - The output is a pointer to a zero-terminated "const char *" string. If + The output is a pointer to a zero-terminated "const char *" string. If JIT support is available, the string contains the name of the architec- - ture for which the JIT compiler is configured, for example "x86 32bit - (little endian + unaligned)". If JIT support is not available, the + ture 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 values that are + The output is an integer whose value specifies the default character + sequence that is recognized as meaning "newline". The values that are supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 - for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, - ANYCRLF, and ANY yield the same values. However, the value for LF is - normally 21, though some EBCDIC environments use 37. The corresponding - values for CRLF are 3349 and 3365. The default should normally corre- + for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, + ANYCRLF, and ANY yield the same values. However, the value for LF is + normally 21, though some EBCDIC environments use 37. The corresponding + values for CRLF are 3349 and 3365. The default should normally corre- spond 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 + 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 pat- tern is compiled or matched. PCRE_CONFIG_LINK_SIZE - The output is an integer that contains the number of bytes used for + 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. For the 32-bit + is either 2 or 4 and is still a number of bytes. For the 32-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 + 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 + 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_PARENS_LIMIT + + The output is a long integer that gives the maximum depth of nesting of + parentheses (of any kind) in a pattern. This limit is imposed to cap + the amount of system stack used when a pattern is compiled. It is spec- + ified when PCRE is built; the default is 250. + PCRE_CONFIG_MATCH_LIMIT The output is a long integer that gives the default limit for the num- @@ -2008,15 +2045,17 @@ COMPILING A PATTERN sets the variable pointed to by errptr to point to a textual error mes- sage. 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 + the data unit 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. + or UTF-16 string, the offset is that of the first data unit 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. + 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 data units, not characters, even in a UTF + mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char- + acter. If pcre_compile2() is used instead of pcre_compile(), and the error- codeptr argument is not NULL, a non-zero error code number is returned @@ -2027,9 +2066,9 @@ COMPILING A PATTERN 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. + compiled pattern, and used again by pcre_exec() and pcre_dfa_exec() + when the pattern is matched. For more discussion, see the section on + locale support below. This code fragment shows a typical straightforward call to pcre_com- pile(): @@ -2113,13 +2152,23 @@ COMPILING A PATTERN PCRE_EXTENDED - If this bit is set, white space data characters in the pattern are - totally ignored except when escaped or inside a character class. White - space does not include the VT character (code 11). In addition, charac- - ters between an unescaped # outside a character class and the next new- - line, inclusive, are also ignored. This is equivalent to Perl's /x - option, and it can be changed within a pattern by a (?x) option set- - ting. + If this bit is set, most white space characters in the pattern are + totally ignored except when escaped or inside a character class. How- + ever, white space is not allowed within sequences such as (?> that + introduce various parenthesized subpatterns, nor within a numerical + quantifier such as {1,3}. However, ignorable white space is permitted + between an item and a following quantifier and between a quantifier and + a following + that indicates possessiveness. + + White space did not used to include the VT character (code 11), because + Perl did not treat this character as white space. However, Perl changed + at release 5.18, so PCRE followed at release 8.34, and VT is now + treated as white space. + + PCRE_EXTENDED also causes characters between an unescaped # outside a + character class and the next newline, inclusive, to be ignored. + PCRE_EXTENDED 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 @@ -2186,21 +2235,33 @@ COMPILING A PATTERN 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 ($) matches only at the end of - the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY - is set). This is the same as Perl. - - When PCRE_MULTILINE it is set, the "start of line" and "end of line" - constructs match immediately following or immediately before internal - newlines in the subject string, respectively, as well as at the very - start and end. This is equivalent to Perl's /m option, and it can be + By default, for the purposes of matching "start of line" and "end of + line", PCRE treats the subject string as consisting of a single line of + characters, even if it actually contains newlines. The "start of line" + metacharacter (^) matches only at the start of the string, and the "end + of line" metacharacter ($) matches only at the end of the string, or + before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set). + Note, however, that unless PCRE_DOTALL is set, the "any character" + metacharacter (.) does not match at a newline. This behaviour (for ^, + $, and dot) 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 new- - lines in a subject string, or no occurrences of ^ or $ in a pattern, + lines in a subject string, or no occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect. + PCRE_NEVER_UTF + + This option locks out interpretation of the pattern as UTF-8 (or UTF-16 + or UTF-32 in the 16-bit and 32-bit libraries). In particular, it pre- + vents the creator of the pattern from switching to UTF interpretation + by starting the pattern with (*UTF). This may be useful in applications + that process patterns from external sources. The combination of + PCRE_UTF8 and PCRE_NEVER_UTF also causes an error. + PCRE_NEWLINE_CR PCRE_NEWLINE_LF PCRE_NEWLINE_CRLF @@ -2255,63 +2316,74 @@ COMPILING A PATTERN be used for capturing (and they acquire numbers in the usual way). There is no equivalent of this option in Perl. - NO_START_OPTIMIZE + PCRE_NO_AUTO_POSSESS + + If this option is set, it disables "auto-possessification". This is an + optimization that, for example, turns a+b into a++b in order to avoid + backtracks into a+ that can never be successful. However, if callouts + are in use, auto-possessification means that some of them are never + taken. You can set this option if you want the matching functions to do + a full unoptimized search and run all the callouts, but it is mainly + provided for testing purposes. + + PCRE_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 match- - ing time. For details see the discussion of PCRE_NO_START_OPTIMIZE - below. + ing time. This is necessary if you want to use JIT execution, because + the JIT compiler needs to know whether or not this option is set. 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 prop- + 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 prop- erty 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 + 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 + 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 + 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 rea- - sons, you can set the PCRE_NO_UTF8_CHECK option. When it is set, the + 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 rea- + sons, 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 only. If the same string is being matched - many times, the option can be safely set for the second and subsequent + may cause your program to crash or loop. Note that this option can also + be passed to pcre_exec() and pcre_dfa_exec(), to suppress the validity + checking of subject strings only. If the same string is being matched + many times, the option can be safely set for the second and subsequent matchings to improve performance. 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 or 32-bit mode. As PCRE has developed, - some error codes have fallen out of use. To avoid confusion, they have + 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 or 32-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 @@ -2348,7 +2420,7 @@ COMPILATION ERROR CODES 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 + 34 character value in \x{} or \o{} 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 @@ -2376,7 +2448,7 @@ COMPILATION ERROR CODES 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 + 60 (*VERB) not recognized or malformed 61 number is too big 62 subpattern name expected 63 digit expected after (?+ @@ -2396,74 +2468,80 @@ COMPILATION ERROR CODES 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN) 76 character value in \u.... sequence is too large 77 invalid UTF-32 string (specifically UTF-32) - - The numbers 32 and 10000 in errors 48 and 49 are defaults; different + 78 setting UTF is disabled by the application + 79 non-hex character in \x{} (closing brace missing?) + 80 non-octal character in \o{} (closing brace missing?) + 81 missing opening brace after \o + 82 parentheses are too deeply nested + 83 invalid range in character class + + 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 + 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 + 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 pat- + matching. The function pcre_study() takes a pointer to a compiled pat- tern 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 + 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 con- - tains other fields that can be set by the caller before the block is + pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block also con- + tains 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 by default. In that circumstance, if the + If studying the pattern does not produce any useful information, + pcre_study() returns NULL by default. 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. However, if - pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it + pcre_dfa_exec(), it must set up its own pcre_extra block. However, if + pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it returns a pcre_extra block even if studying did not find any additional - information. It may still return NULL, however, if an error occurs in + information. It may still return NULL, however, if an error occurs in pcre_study(). - The second argument of pcre_study() contains option bits. There are + The second argument of pcre_study() contains option bits. There are three further options in addition to PCRE_STUDY_EXTRA_NEEDED: PCRE_STUDY_JIT_COMPILE PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE - If any of these are 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() interpretive matching function. If the - just-in-time compiler is not available, these options are ignored. All + If any of these are 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() interpretive matching function. If the + just-in-time compiler is not available, these options are ignored. All undefined 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 pat- - terns the benefit of faster execution might be offset by a much slower + JIT compilation is a heavyweight optimization. It can take some time + for patterns to be analyzed, and for one-off matches and simple pat- + terns 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 documenta- + those that cannot be handled, matching automatically falls back to the + pcre_exec() interpreter. For more details, see the pcrejit documenta- tion. - 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 + 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 + 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 + 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 JIT optimization is not used, but it is advisable + 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 JIT optimization 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 + 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; @@ -2483,41 +2561,50 @@ STUDYING A PATTERN 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 to + it does guarantee that no shorter strings match. The value is used 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 + 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 + 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. In 32-bit mode, the bitmap is used for 32-bit + values less than 256. In 32-bit mode, the bitmap is used for 32-bit values less than 256.) - These two optimizations apply to both pcre_exec() and pcre_dfa_exec(), - and the information is also used by the JIT compiler. The optimiza- - tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option when - calling pcre_exec() or pcre_dfa_exec(), but if this is done, JIT execu- - tion is also disabled. You might want to do this if your pattern con- - tains callouts or (*MARK) and you want to make use of these facilities - in cases where matching fails. See the discussion of - PCRE_NO_START_OPTIMIZE below. + These two optimizations apply to both pcre_exec() and pcre_dfa_exec(), + and the information is also used by the JIT compiler. The optimiza- + tions can be disabled by setting the PCRE_NO_START_OPTIMIZE option. + You might want to do this if your pattern contains callouts or (*MARK) + and you want to make use of these facilities in cases where matching + fails. + + PCRE_NO_START_OPTIMIZE can be specified at either compile time or exe- + cution time. However, if PCRE_NO_START_OPTIMIZE is passed to + pcre_exec(), (that is, after any JIT compilation has happened) JIT exe- + cution is disabled. For JIT execution to work with PCRE_NO_START_OPTI- + MIZE, the option must be set at compile time. + + There is a longer 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 charac- - ters with codes greater than 128, you should either use UTF-8 and Uni- - code, or use locales, but not try to mix the two. + PCRE handles caseless matching, and determines whether characters are + letters, digits, or whatever, by reference to a set of tables, indexed + by character code point. When running in UTF-8 mode, or in the 16- or + 32-bit libraries, this applies only to characters with code points less + than 256. By default, higher-valued code points never match escapes + such as \w or \d. However, if PCRE is built with Unicode property sup- + port, all characters can be tested with \p and \P, or, alternatively, + the PCRE_UCP option can be set when a pattern is compiled; this causes + \w and friends to use Unicode property support instead of the built-in + tables. + + The use of locales with Unicode is discouraged. If you are handling + characters with code points greater than 128, you should either use + Unicode support, 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 @@ -2533,10 +2620,10 @@ LOCALE SUPPORT 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: + passed to pcre_compile() 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 let- + ters), the following code could be used: setlocale(LC_CTYPE, "fr_FR"); tables = pcre_maketables(); @@ -2552,15 +2639,19 @@ LOCALE SUPPORT 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 pat- + and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pat- tern, compilation, studying and matching all happen in the same locale, - but different patterns can be compiled in different locales. + but different patterns can be processed 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. + the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus- + sion below in the section on matching a pattern). This facility is pro- + vided for use with pre-compiled patterns that have been saved and + reloaded. Character tables are not saved with patterns, so if a non- + standard table was used at compile time, it must be provided again when + the reloaded pattern is matched. Attempting to use this facility to + match a pattern in a different locale from the one in which it was com- + piled is likely to lead to anomalous (usually incorrect) results. INFORMATION ABOUT A PATTERN @@ -2585,6 +2676,7 @@ INFORMATION ABOUT A PATTERN PCRE_ERROR_BADENDIANNESS the pattern was compiled with different endianness PCRE_ERROR_BADOPTION the value of what was invalid + PCRE_ERROR_UNSET the requested field is not set The "magic number" is placed at the start of each compiled pattern as an simple check against passing an arbitrary memory pointer. The endi- @@ -2700,23 +2792,41 @@ INFORMATION ABOUT A PATTERN /^a\dz\d/ the returned value is -1. Since for the 32-bit library using the non-UTF-32 mode, this function - is unable to return the full 32-bit range of the character, this value - is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and + is unable to return the full 32-bit range of characters, this value is + deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and PCRE_INFO_REQUIREDCHAR values should be used. + PCRE_INFO_MATCH_EMPTY + + Return 1 if the pattern can match an empty string, otherwise 0. The + fourth argument should point to an int variable. + + PCRE_INFO_MATCHLIMIT + + If the pattern set a match limit by including an item of the form + (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth + argument should point to an unsigned 32-bit integer. If no such value + has been set, the call to pcre_fullinfo() returns the error + PCRE_ERROR_UNSET. + PCRE_INFO_MAXLOOKBEHIND - Return the number of characters (NB not bytes) in the longest lookbe- - hind assertion in the pattern. Note that the simple assertions \b and - \B require a one-character lookbehind. This information is useful when - doing multi-segment matching using the partial matching facilities. + Return the number of characters (NB not data units) in the longest + lookbehind assertion in the pattern. This information is useful when + doing multi-segment matching using the partial matching facilities. + Note that the simple assertions \b and \B require a one-character look- + behind. \A also registers a one-character lookbehind, though it does + not actually inspect the previous character. This is to ensure that at + least one character from the old segment is retained when a new segment + is processed. Otherwise, if there are no lookbehinds in the pattern, \A + might match incorrectly at the start of a new segment. 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 + value is -1. The value is a number of characters, which in UTF mode may + be different from the number of data units. 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 @@ -2744,30 +2854,31 @@ INFORMATION ABOUT A PATTERN the 8-bit library, where the first two bytes of each entry are the num- ber 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. In the 32-bit library, the + which contains the parenthesis number. In the 32-bit library, the pointer points to 32-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 pat- - tern. In the absence of (?| this is the order of increasing number; - when (?| is used this is not necessarily the case because later subpat- - terns may have lower numbers. - - As a simple example of the name/number table, consider the following + The names are in alphabetical order. If (?| is used to create multiple + groups with the same number, as described in the section on duplicate + subpattern numbers in the pcrepattern page, the groups may be given the + same name, but there is only one entry in the table. Different names + for groups of the same number are not permitted. Duplicate names for + subpatterns with different numbers are permitted, but only if PCRE_DUP- + NAMES is set. 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, + 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 ??: @@ -2776,31 +2887,31 @@ INFORMATION ABOUT A PATTERN 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 + 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 match- + 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 match- ing. 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 + 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, + 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 + 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 @@ -2812,42 +2923,50 @@ INFORMATION ABOUT A PATTERN For such patterns, the PCRE_ANCHORED bit is set in the options returned by pcre_fullinfo(). + PCRE_INFO_RECURSIONLIMIT + + If the pattern set a recursion limit by including an item of the form + (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth + argument should point to an unsigned 32-bit integer. If no such value + has been set, the call to pcre_fullinfo() returns the error + PCRE_ERROR_UNSET. + 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_mal- - loc() when pcre_compile() is getting memory in which to place the com- - piled 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. + Return the size of the compiled pattern in bytes (for all three + 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 pri- - vate, but its length is made available via this option so that it can - be saved and restored (see the pcreprecompile documentation for - details). + Return the size in bytes (for all three libraries) 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 argu- + ment 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). PCRE_INFO_FIRSTCHARACTERFLAGS Return information about the first data unit of any matched string, for - a non-anchored pattern. The fourth argument should point to an int + a non-anchored pattern. 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), 1 is returned, and the character + If there is a fixed first value, for example, the letter "c" from a + pattern such as (cat|cow|coyote), 1 is returned, and the character value can be retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no fixed first value, and if either - (a) the pattern was compiled with the PCRE_MULTILINE option, and every + (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 @@ -2859,45 +2978,33 @@ INFORMATION ABOUT A PATTERN PCRE_INFO_FIRSTCHARACTER - Return the fixed first character value, if PCRE_INFO_FIRSTCHARACTER- - FLAGS returned 1; otherwise returns 0. The fourth argument should point - to an uint_t variable. + Return the fixed first character value in the situation where + PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; otherwise return 0. The fourth + argument should point to an uint_t variable. - In the 8-bit library, the value is always less than 256. In the 16-bit - library the value can be up to 0xffff. In the 32-bit library in UTF-32 - mode the value can be up to 0x10ffff, and up to 0xffffffff when not + In the 8-bit library, the value is always less than 256. In the 16-bit + library the value can be up to 0xffff. In the 32-bit library in UTF-32 + mode the value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode. - 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_REQUIREDCHARFLAGS - Returns 1 if there is a rightmost literal data unit that must exist in + Returns 1 if there is a rightmost literal data unit that must exist in any matched string, other than at its start. The fourth argument should - point to an int variable. If there is no such value, 0 is returned. If + point to an int variable. If there is no such value, 0 is returned. If returning 1, the character value itself can be retrieved using PCRE_INFO_REQUIREDCHAR. For anchored patterns, a last literal value is recorded only if it fol- - lows something of variable length. For example, for the pattern - /^a\d+z\d+/ the returned value 1 (with "z" returned from + lows something of variable length. For example, for the pattern + /^a\d+z\d+/ the returned value 1 (with "z" returned from PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0. PCRE_INFO_REQUIREDCHAR - 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 uint32_t variable. If + 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 uint32_t variable. If there is no such value, 0 is returned. @@ -2905,21 +3012,21 @@ REFERENCE COUNTS int pcre_refcount(pcre *code, int adjust); - The pcre_refcount() function is used to maintain a reference count in + 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, + 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 + 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 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 + 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.) @@ -2929,22 +3036,22 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 argu- - ments as many times as you like, in order to match different subject + 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 argu- + ments 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 + 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 option- - ally studied) in the same process that calls pcre_exec(). However, it + In most applications, the pattern will have been compiled (and option- + ally 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 + 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(): @@ -2963,10 +3070,10 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 addi- - tional information in it. The pcre_extra block contains the following + 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 addi- + tional information in it. The pcre_extra block contains the following fields (not necessarily in this order): unsigned long int flags; @@ -2978,13 +3085,13 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION const unsigned char *tables; unsigned char **mark; - In the 16-bit version of this structure, the mark field has type + In the 16-bit version of this structure, the mark field has type "PCRE_UCHAR16 **". - In the 32-bit version of this structure, the mark field has type + In the 32-bit version of this structure, the mark field has type "PCRE_UCHAR32 **". - The flags field is used to specify which of the other fields are set. + The flags field is used to specify which of the other fields are set. The flag bits are: PCRE_EXTRA_CALLOUT_DATA @@ -2995,39 +3102,48 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION PCRE_EXTRA_STUDY_DATA PCRE_EXTRA_TABLES - Other flag bits should be set to zero. The study_data field and some- - times 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 + Other flag bits should be set to zero. The study_data field and some- + times 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 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 unlim- + 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 unlim- ited 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 + 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 a JIT option, the way that the matching is executed is entirely + with a JIT 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 match- ing 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 + 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. + A value for the match limit may also be supplied by an item at the + start of a pattern of the form + + (*LIMIT_MATCH=d) + + where d is a decimal number. However, such a setting is ignored unless + d is less than the limit set by the caller of pcre_exec() or, if no + such limit is set, less than the default. + 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 @@ -3047,60 +3163,73 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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" fea- + A value for the recursion limit may also be supplied by an item at the + start of a pattern of the form + + (*LIMIT_RECURSION=d) + + where d is a decimal number. However, such a setting is ignored unless + d is less than the limit set by the caller of pcre_exec() or, if no + such limit is set, less than the default. + + The callout_data field is used in conjunction with the "callout" fea- ture, 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 argu- - ment. 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 documenta- - tion 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 back- - tracking control verbs such as (*MARK:NAME), and the execution ends up - with a name to pass back, a pointer to the name string (zero termi- - nated) 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, + The tables field is provided for use with patterns that have been pre- + compiled using custom character tables, saved to disc or elsewhere, and + then reloaded, because the tables that were used to compile a pattern + are not saved with it. See the pcreprecompile documentation for a dis- + cussion of saving compiled patterns for later use. If NULL is passed + using this mechanism, it forces PCRE's internal tables to be used. + + Warning: The tables that pcre_exec() uses must be the same as those + that were used when the pattern was compiled. If this is not the case, + the behaviour of pcre_exec() is undefined. Therefore, when a pattern is + compiled and matched in the same process, this field should never be + set. In this (the most common) case, the correct table pointer is auto- + matically passed with the compiled pattern from pcre_compile() to + pcre_exec(). + + 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 back- + tracking control verbs such as (*MARK:NAME), and the execution ends up + with a name to pass back, a pointer to the name string (zero termi- + nated) 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 doc- umentation. 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_HARD, and + 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_HARD, and PCRE_PARTIAL_SOFT. - If the pattern was successfully studied with one of the just-in-time + If the pattern was successfully studied with one of the just-in-time (JIT) compile options, the only supported options for JIT execution are - PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, - PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an - unsupported option is used, JIT execution is disabled and the normal + PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, + PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. 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 + 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 + 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 @@ -3109,109 +3238,110 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 descrip- - tion of pcre_compile() above. During matching, the newline choice - affects the behaviour of the dot, circumflex, and dollar metacharac- - ters. It may also alter the way the match position is advanced after a + These options override the newline definition that was chosen or + defaulted when the pattern was compiled. For details, see the descrip- + tion of pcre_compile() above. During matching, the newline choice + affects the behaviour of the dot, circumflex, and dollar metacharac- + ters. 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 cur- - rent position is at a CRLF sequence, and the pattern contains no - explicit matches for CR or LF characters, the match position is + When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is + set, and a match attempt for an unanchored pattern fails when the cur- + rent 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 + 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 con- + 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 con- tains an explicit CR or LF reference, and so advances only by one char- acter 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 + 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 + 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 behav- + 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 behav- iour 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 with- + of a line, so the dollar metacharacter should not match it nor (except + in multiline mode) a newline immediately before it. Setting this with- out PCRE_MULTILINE (at compile time) causes dollar never to match. This - option affects only the behaviour of the dollar metacharacter. It does + 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 + 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 + 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 occur- rences 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 + 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 + 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 off- - set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that + set with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then if that fails, by advancing the starting offset (see below) and trying an ordi- - nary 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 + nary 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 + 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. + 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 pat- - tern 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 + tern is not considered until after a suitable starting point for the + match has been found. Also, when callouts or (*MARK) items are in use, + these "start-up" optimizations can cause them to be skipped if the pat- + tern 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. The use of - PCRE_NO_START_OPTIMIZE disables JIT execution; when it is set, matching - is always done using interpretively. + position in the subject string. If PCRE_NO_START_OPTIMIZE is set at + compile time, it cannot be unset at matching time. The use of + PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to + pcre_exec()) disables JIT execution; in this situation, matching is + always done using interpretively. Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation. Consider the pattern @@ -3267,7 +3397,7 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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. + may crash or loop. PCRE_PARTIAL_HARD PCRE_PARTIAL_SOFT @@ -3297,149 +3427,156 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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, + length in length, and a starting offset in startoffset. The units for + length and startoffset are bytes for the 8-bit library, 16-bit data + items for the 16-bit library, and 32-bit data items for the 32-bit + library. + + If startoffset 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 sub- - ject). 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 suc- - cess. Setting startoffset differs from just passing over a shortened - string and setting PCRE_NOTBOL in the case of a pattern that begins + and this is by far the most common case. In UTF-8 or UTF-16 mode, the + offset must point to the start of a character, or the end of the sub- + ject (in UTF-32 mode, one data unit equals one character, so all off- + sets are valid). Unlike the pattern string, the subject may contain + binary zeroes. + + A non-zero starting offset is useful when searching for another match + in the same subject by calling pcre_exec() again after a previous suc- + cess. 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, + 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 + 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 occur- - rence of "iss" because it is able to look behind the starting point to + rence 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 + 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 + 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 pcre- demo 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 + 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, + 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 + 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 sub- - string. PCRE supports several other kinds of parenthesized subpattern + 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 sub- + string. 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 vec- - tor is passed in ovecsize, which must be a non-negative number. Note: + whose address is passed in ovector. The number of elements in the vec- + tor 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 sub- - strings, each substring using a pair of integers. The remaining third - of the vector is used as workspace by pcre_exec() while matching cap- - turing subpatterns, and is not available for passing back information. - The number passed in ovecsize should always be a multiple of three. If + The first two-thirds of the vector is used to pass back captured sub- + strings, each substring using a pair of integers. The remaining third + of the vector is used as workspace by pcre_exec() while matching cap- + turing 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 + 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 offset of the first character in a + substring, and the second is set to the offset of the first character + after the end of a substring. These values are always data unit off- + sets, even in UTF mode. They are byte offsets in the 8-bit library, + 16-bit data item offsets in the 16-bit library, and 32-bit data item + offsets in the 32-bit library. Note: 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 + 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, + 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 - nor any captured substrings are of interest, pcre_exec() may be called - with ovector passed as NULL and ovecsize as zero. However, if the pat- - tern 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 + function returns a value of zero. If neither the actual string matched + nor any captured substrings are of interest, pcre_exec() may be called + with ovector passed as NULL and ovecsize as zero. However, if the pat- + tern 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 over- - flow) when in fact the vector is exactly the right size for the final + There are some cases where zero is returned (indicating vector over- + flow) 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 + 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 + 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 tem- - porary overflow, but the final number of used slots is actually less + porary 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 + 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 + 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 + 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 corre- + 2 is not. When this happens, both values in the offset pairs corre- sponding 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, + 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 corre- - spond to capturing parentheses in the pattern are never changed. That - is, if a pattern contains n capturing parentheses, no more than ovec- - tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in + Note: Elements in the first two-thirds of ovector that do not corre- + spond to capturing parentheses in the pattern are never changed. That + is, if a pattern contains n capturing parentheses, no more than ovec- + tor[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 + 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 + If pcre_exec() fails, it returns a negative number. The following are defined in the header file: PCRE_ERROR_NOMATCH (-1) @@ -3448,7 +3585,7 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION PCRE_ERROR_NULL (-2) - Either code or subject was passed as NULL, or ovector was NULL and + Either code or subject was passed as NULL, or ovector was NULL and ovecsize was not zero. PCRE_ERROR_BADOPTION (-3) @@ -3457,82 +3594,82 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION PCRE_ERROR_BADMAGIC (-4) - PCRE stores a 4-byte "magic number" at the start of the compiled code, + 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 + 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 + 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 + 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 + 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- + 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(), + 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 + 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. + 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 ele- - ment, and a reason code is placed in the second element. The reason + 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 ele- + ment, 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 char- - acter at the end of the subject (reason codes 1 to 5), + if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8 char- + acter 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 charac- + 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 charac- ter or the end of the subject. PCRE_ERROR_PARTIAL (-12) - The subject string did not match, but it did match partially. See the + 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 + 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 + 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) @@ -3542,7 +3679,7 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 + field in a pcre_extra structure (or defaulted) was reached. See the description above. PCRE_ERROR_BADNEWLINE (-23) @@ -3556,29 +3693,29 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 implementa- - tion of returned information; it is retained for backwards compatibil- + 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 implementa- + tion of returned information; it is retained for backwards compatibil- ity. 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 + 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, + are detected and faulted at compile time, but more complicated cases, in particular mutual recursions between two different subpatterns, can- not be detected until run time. PCRE_ERROR_JIT_STACKLIMIT (-27) - This error is returned when a pattern that was successfully studied - using a JIT compile option is being matched, but the memory available - for the just-in-time processing stack is not large enough. See the + This error is returned when a pattern that was successfully studied + using a 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) @@ -3588,38 +3725,38 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 + 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. PCRE_ERROR_JIT_BADOPTION - This error is returned when a pattern that was successfully studied - using a JIT compile option is being matched, but the matching mode - (partial or complete match) does not correspond to any JIT compilation - mode. When the JIT fast path function is used, this error may be also - given for invalid options. See the pcrejit documentation for more + This error is returned when a pattern that was successfully studied + using a JIT compile option is being matched, but the matching mode + (partial or complete match) does not correspond to any JIT compilation + mode. When the JIT fast path function is used, this error may be also + given for invalid options. See the pcrejit documentation for more details. PCRE_ERROR_BADLENGTH (-32) - This error is given if pcre_exec() is called with a negative value for + This error is given if pcre_exec() is called with a negative value for the length argument. Error numbers -16 to -20, -22, and 30 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 and 32-bit libraries is given in the pcre16 + This section applies only to the 8-bit library. The corresponding + information for the 16-bit and 32-bit libraries is given in the pcre16 and pcre32 pages. When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT- - UTF8, 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 + UTF8, 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 second element (ovector[1]). The reason codes are given names in the pcre.h header file: PCRE_UTF8_ERR1 @@ -3628,10 +3765,10 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 (origi- - nally defined by RFC 2279) allows for up to 6 bytes, and this is + 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 (origi- + nally 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 @@ -3641,24 +3778,24 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 + 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 + 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 + 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 + 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 @@ -3667,28 +3804,29 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 cor- + 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 cor- rect 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 sec- - ond is 0). Such a byte can only validly occur as the second or subse- + binary value 0b10 (that is, the most significant bit is 1 and the sec- + ond is 0). Such a byte can only validly occur as the second or subse- quent byte of a multi-byte character. PCRE_UTF8_ERR21 - The first byte of a character has the value 0xfe or 0xff. These values + The first byte of a character has the value 0xfe or 0xff. These values can never occur in a valid UTF-8 string. - PCRE_UTF8_ERR2 + PCRE_UTF8_ERR22 - Non-character. These are the last two characters in each plane (0xfffe, - 0xffff, 0x1fffe, 0x1ffff .. 0x10fffe, 0x10ffff), and the characters - 0xfdd0..0xfdef. + This error code was formerly used when the presence of a so-called + "non-character" caused an error. Unicode corrigendum #9 makes it clear + that such characters should not cause a string to be rejected, and so + this code is no longer in use and is never returned. EXTRACTING CAPTURED SUBSTRINGS BY NUMBER @@ -4039,55 +4177,64 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() can use the entire ovector for returning matched strings. + NOTE: PCRE's "auto-possessification" optimization usually applies to + character repeats at the end of a pattern (as well as internally). For + example, the pattern "a\d+" is compiled as if it were "a\d++" because + there is no point even considering the possibility of backtracking into + the repeated digits. For DFA matching, this means that only one possi- + ble match is found. If you really do want multiple matches in such + cases, either use an ungreedy repeat ("a\d+?") or set the + PCRE_NO_AUTO_POSSESS option when compiling. + 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 + 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 pat- - tern that it does not support, for instance, the use of \C or a back + This return is given if pcre_dfa_exec() encounters an item in the pat- + tern 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 + 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 + 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 + 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 + 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. PCRE_ERROR_DFA_BADRESTART (-30) - When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some - plausibility checks are made on the contents of the workspace, which - should contain data about the previous partial match. If any of these + When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some + plausibility checks are made on the contents of the workspace, which + should contain data about the previous partial match. If any of these checks fail, this error is given. SEE ALSO - pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), + pcre16(3), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre- sample(3), pcrestack(3). @@ -4101,18 +4248,18 @@ AUTHOR REVISION - Last updated: 08 November 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 12 November 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCRECALLOUT(3) PCRECALLOUT(3) +PCRECALLOUT(3) Library Functions Manual PCRECALLOUT(3) + NAME PCRE - Perl-compatible regular expressions - SYNOPSIS #include <pcre.h> @@ -4153,48 +4300,88 @@ DESCRIPTION (?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. + alternation bar. If the pattern contains a conditional group whose con- + dition is an assertion, an automatic callout is inserted immediately + before the condition. Such a callout may also be inserted explicitly, + for example: + + (?(?C9)(?=a)ab|de) + + This applies only to assertion conditions (because they are themselves + independent groups). - 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. + Automatic callouts can be used for tracking the progress of pattern + matching. The pcretest program has a pattern qualifier (/C) that sets + automatic callouts; when it is used, the output indicates how the pat- + tern is being matched. This is useful information when you are trying + to optimize the performance of a particular pattern. 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 + You should be aware that, because of optimizations in the way PCRE com- + piles and matches patterns, callouts sometimes do not happen exactly as + you might expect. + + At compile time, PCRE "auto-possessifies" repeated items when it knows + that what follows cannot be part of the repeat. For example, a+[bc] is + compiled as if it were a++[bc]. The pcretest output when this pattern + is anchored and then applied with automatic callouts to the string + "aaaa" is: + + --->aaaa + +0 ^ ^ + +1 ^ a+ + +3 ^ ^ [bc] + No match + + This indicates that when matching [bc] fails, there is no backtracking + into a+ and therefore the callouts that would be taken for the back- + tracks do not occur. You can disable the auto-possessify feature by + passing PCRE_NO_AUTO_POSSESS to pcre_compile(), or starting the pattern + with (*NO_AUTO_POSSESS). If this is done in pcretest (using the /O + qualifier), the output changes to this: + + --->aaaa + +0 ^ ^ + +1 ^ a+ + +3 ^ ^ [bc] + +3 ^ ^ [bc] + +3 ^ ^ [bc] + +3 ^^ [bc] + No match + + This time, when matching [bc] fails, the matcher backtracks into a+ and + tries again, repeatedly, until a+ itself fails. + + Other optimizations that provide fast "no match" results also affect + callouts. 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", + 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 + 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_OPTI- - MIZE option to the matching function, or by starting the pattern with - (*NO_START_OPT). This slows down the matching process, but does ensure + You can disable these optimizations by passing the PCRE_NO_START_OPTI- + MIZE 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 func- + During matching, when PCRE reaches a callout point, the external func- tion defined by pcre_callout or pcre[16|32]_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 - pcre[16|32]_callout block. These structures contains the following + set). This applies to both normal and DFA matching. The only argument + to the callout function is a pointer to a pcre_callout or + pcre[16|32]_callout block. These structures contains the following fields: int version; @@ -4215,44 +4402,47 @@ THE CALLOUT INTERFACE const PCRE_UCHAR16 *mark; (16-bit version) const PCRE_UCHAR32 *mark; (32-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 + 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 com- - piled into the pattern (that is, the number after ?C for manual call- + The callout_number field contains the number of the callout, as com- + piled into the pattern (that is, the number after ?C for manual call- outs, 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 - pcre[16|32]_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 + 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 + pcre[16|32]_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 + 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_position field contains the offset within the subject of the current match pointer. - When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top - field contains one more than the number of the highest numbered cap- - tured 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 + When the pcre_exec() or pcre[16|32]_exec() is used, the capture_top + field contains one more than the number of the highest numbered cap- + tured 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 cap- - tured substring. If no substrings have been captured, its value is -1. - This is always the case for the DFA matching functions. + The capture_last field contains the number of the most recently cap- + tured substring. However, when a recursion exits, the value reverts to + what it was outside the recursion, as do the values of all captured + substrings. If no substrings have been captured, the value of cap- + ture_last is -1. This is always the case for the DFA matching func- + tions. 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 @@ -4310,18 +4500,18 @@ AUTHOR REVISION - Last updated: 24 June 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 12 November 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCRECOMPAT(3) PCRECOMPAT(3) +PCRECOMPAT(3) Library Functions Manual PCRECOMPAT(3) + NAME PCRE - Perl-compatible regular expressions - DIFFERENCES BETWEEN PCRE AND PERL This document describes the differences in the ways that PCRE and Perl @@ -4340,10 +4530,8 @@ DIFFERENCES BETWEEN PCRE AND PERL 3. Capturing subpatterns that occur inside negative lookahead asser- tions 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 succeed- - ing), but only if the negative lookahead assertion contains just one - branch. + set. Perl sometimes (but not always) sets its numerical variables from + inside negative assertions. 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 nor- @@ -4398,24 +4586,30 @@ DIFFERENCES BETWEEN PCRE AND PERL There is a discussion that explains these differences in more detail in the section on recursion differences from Perl in the pcrepattern page. - 10. If any of the backtracking control 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. This is not always the case in Perl. - In particular, 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. There is one exception to this: the name - from a *(MARK), (*PRUNE), or (*THEN) that is encountered in a success- - ful 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. - - 11. There are some differences that are concerned with the settings of + 10. If any of the backtracking control verbs are used 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 sur- + rounding pattern. This is not always the case in Perl. In particular, + 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. Note that such subpatterns are processed as anchored at + the point where they are tested. + + 11. If a pattern contains more than one backtracking control verb, the + first one that is backtracked onto acts. For example, in the pattern + A(*COMMIT)B(*PRUNE)C a failure in B triggers (*COMMIT), but a failure + in C triggers (*PRUNE). Perl's behaviour is more complex; in many cases + it is the same as PCRE, but there are examples where it differs. + + 12. Most backtracking verbs in assertions have their normal actions. + They are not confined to the assertion. + + 13. 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". - 12. PCRE's handling of duplicate subpattern numbers and duplicate sub- + 14. PCRE's handling of duplicate subpattern numbers and duplicate sub- pattern 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 ta- ble to translate between numbers and names. In particular, a pattern @@ -4426,29 +4620,42 @@ DIFFERENCES BETWEEN PCRE AND PERL turing subpattern number 1. To avoid this confusing situation, an error is given at compile time. - 13. Perl recognizes comments in some places that PCRE does not, for + 15. 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 white space between ( and ? but PCRE never - does, even if the PCRE_EXTENDED option is set. - - 14. PCRE provides some extensions to the Perl regular expression facil- - ities. Perl 5.10 includes new features that are not in earlier ver- - sions of Perl, some of which (such as named parentheses) have been in + modifier is set, Perl allows white space between ( and ? (though cur- + rent Perls warn that this is deprecated) but PCRE never does, even if + the PCRE_EXTENDED option is set. + + 16. Perl, when in warning mode, gives warnings for character classes + such as [A-\d] or [a-[:digit:]]. It then treats the hyphens as liter- + als. PCRE has no warning features, so it gives an error in these cases + because they are almost certainly user mistakes. + + 17. In PCRE, the upper/lower case character properties Lu and Ll are + not affected when case-independent matching is specified. For example, + \p{Lu} always matches an upper case letter. I think Perl has changed in + this respect; in the release at the time of writing (5.16), \p{Lu} and + \p{Ll} match all letters, regardless of case, when case independence is + specified. + + 18. PCRE provides some extensions to the Perl regular expression facil- + ities. Perl 5.10 includes new features that are not in earlier ver- + sions 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 + (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 $ + (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 spe- cial 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 quanti- + (d) If PCRE_UNGREEDY is set, the greediness of the repetition quanti- fiers is inverted, that is, by default they are not greedy, but if fol- lowed by a question mark they are. @@ -4456,10 +4663,10 @@ DIFFERENCES BETWEEN PCRE AND PERL 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 equiva- + and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no Perl equiva- lents. - (g) The \R escape sequence can be restricted to match only CR, LF, or + (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. @@ -4467,14 +4674,14 @@ DIFFERENCES BETWEEN PCRE AND PERL (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 + 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(), - pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and + pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and are not Perl-compatible. - (l) PCRE recognizes some special sequences such as (*CR) at the start + (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. @@ -4488,18 +4695,18 @@ AUTHOR REVISION - Last updated: 25 August 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 10 November 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREPATTERN(3) PCREPATTERN(3) +PCREPATTERN(3) Library Functions Manual PCREPATTERN(3) + NAME PCRE - Perl-compatible regular expressions - PCRE REGULAR EXPRESSION DETAILS The syntax and semantics of the regular expressions that are supported @@ -4517,6 +4724,29 @@ PCRE REGULAR EXPRESSION DETAILS great detail. This description of PCRE's regular expressions is intended as reference material. + This document discusses the patterns that are supported by PCRE when + one its main matching functions, pcre_exec() (8-bit) or + pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has alternative + matching functions, pcre_dfa_exec() and pcre[16|32_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. + + +SPECIAL START-OF-PATTERN ITEMS + + A number of options that can be passed to pcre_compile() can also be + set by special items at the start of a pattern. These are not Perl-com- + patible, but are provided to make these options accessible to pattern + writers who are not able to change the program that processes the pat- + tern. Any number of these items may appear, but they must all be + together right at the start of the pattern string, and the letters must + be in upper case. + + UTF support + 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, an extra library that supports 16-bit and UTF-16 character @@ -4533,47 +4763,39 @@ PCRE REGULAR EXPRESSION DETAILS (*UTF) is a generic sequence that can be used with any of the libraries. 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. + setting the relevant option. 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), (*UTF16), (*UTF32) or (*UTF) is: + Some applications that allow their users to supply patterns may wish to + restrict them to non-UTF data for security reasons. If the + PCRE_NEVER_UTF option is set at compile time, (*UTF) etc. are not + allowed, and their appearance causes an error. - (*UCP) + Unicode property support - 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. + Another special sequence that may appear at the start of a pattern 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 deter- + mine 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 con- - cerned with the handling of newlines; they are described below. + Disabling auto-possessification - The remainder of this document discusses the patterns that are sup- - ported by PCRE when one its main matching functions, pcre_exec() - (8-bit) or pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has - alternative matching functions, pcre_dfa_exec() and - pcre[16|32_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 func- - tions, are discussed in the pcrematching page. + If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as + setting the PCRE_NO_AUTO_POSSESS option at compile time. This stops + PCRE from making quantifiers possessive when what follows cannot match + the repeated item. For example, by default a+b is treated as a++b. For + more details, see the pcreapi documentation. + Disabling start-up optimizations -EBCDIC CHARACTER CODES - - PCRE can be compiled to run in an environment that uses EBCDIC as its - character code rather than ASCII or Unicode (typically a mainframe sys- - tem). In the sections below, character code values are ASCII or Uni- - code; in an EBCDIC environment these characters may have different code - values, and there are no code points greater than 255. - + 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. This disables several optimizations for quickly reaching "no + match" results. For more details, see the pcreapi documentation. -NEWLINE CONVENTIONS + Newline conventions PCRE supports five different conventions for indicating line breaks in strings: a single CR (carriage return) character, a single LF (line- @@ -4598,10 +4820,8 @@ NEWLINE CONVENTIONS (*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. + no longer a newline. If more than one of these settings is present, the + last one is used. The newline convention affects where the circumflex and dollar asser- tions are true. It also affects the interpretation of the dot metachar- @@ -4612,6 +4832,36 @@ NEWLINE CONVENTIONS line sequences" below. A change of \R setting can be combined with a change of newline convention. + Setting match and recursion limits + + The caller of pcre_exec() can set a limit on the number of times the + internal match() function is called and on the maximum depth of recur- + sive calls. These facilities are provided to catch runaway matches that + are provoked by patterns with huge matching trees (a typical example is + a pattern with nested unlimited repeats) and to avoid running out of + system stack by too much recursion. When one of these limits is + reached, pcre_exec() gives an error return. The limits can also be set + by items at the start of the pattern of the form + + (*LIMIT_MATCH=d) + (*LIMIT_RECURSION=d) + + where d is any number of decimal digits. However, the value of the set- + ting must be less than the value set (or defaulted) by the caller of + pcre_exec() for it to have any effect. In other words, the pattern + writer can lower the limits set by the programmer, but not raise them. + If there is more than one setting of one of these limits, the lower + value is used. + + +EBCDIC CHARACTER CODES + + PCRE can be compiled to run in an environment that uses EBCDIC as its + character code rather than ASCII or Unicode (typically a mainframe sys- + tem). In the sections below, character code values are ASCII or Uni- + code; in an EBCDIC environment these characters may have different code + values, and there are no code points greater than 255. + CHARACTERS AND METACHARACTERS @@ -4689,11 +4939,11 @@ BACKSLASH 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, white space in - the pattern (other than in a character class) and characters between a - # outside a character class and the next newline are ignored. An escap- - ing backslash can be used to include a white space or # character as - part of the pattern. + If a pattern is compiled with the PCRE_EXTENDED option, most white + space in the pattern (other than in a character class), and characters + between a # outside a character class and the next newline, inclusive, + are ignored. An escaping backslash can be used to include a white space + or # character as part of the pattern. If you want to remove the special meaning from a sequence of charac- ters, you can do so by putting them between \Q and \E. This is differ- @@ -4731,7 +4981,9 @@ BACKSLASH \n linefeed (hex 0A) \r carriage return (hex 0D) \t tab (hex 09) + \0dd character with octal code 0dd \ddd character with octal code ddd, or back reference + \o{ddd..} character with octal code ddd.. \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) @@ -4754,61 +5006,38 @@ BACKSLASH are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also generate different values. - By default, after \x, from zero to two hexadecimal digits are read - (letters can be in upper or lower case). Any number of hexadecimal dig- - its 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 - 32-bit non-UTF mode less than 0x80000000 - 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint - - Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- - called "surrogate" codepoints), and 0xffef. - - 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 dig- - its. 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. Character codes specified by \u in JavaScript - mode are constrained in the same was as those specified by \x in non- - JavaScript mode. - - 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 differ- - ence 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 escape \o must be followed by a sequence of octal digits, enclosed + in braces. An error occurs if this is not the case. This escape is a + recent addition to Perl; it provides way of specifying character code + points as octal numbers greater than 0777, and it also allows octal + numbers and back references to be unambiguously specified. + + For greater clarity and unambiguity, it is best to avoid following \ by + a digit greater than zero. Instead, use \o{} or \x{} to specify charac- + ter numbers, and \g{} to specify back references. The following para- + graphs describe the old, ambiguous syntax. + The handling of a backslash followed by a digit other than 0 is compli- - cated. Outside a character class, PCRE reads it and any following dig- - its 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 + cated, and Perl has changed in recent releases, causing PCRE also to + change. Outside a character class, PCRE reads the digit and any follow- + ing digits as a decimal number. If the number is less than 8, 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 gen- - erate 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: + Inside a character class, or if the decimal number following \ is + greater than 7 and there have not been that many capturing subpatterns, + PCRE handles \8 and \9 as the literal characters "8" and "9", and oth- + erwise re-reads up to three octal digits following the backslash, using + them to generate a data character. Any subsequent digits stand for + themselves. For example: \040 is another way of writing an ASCII space \40 is the same, provided there are fewer than 40 @@ -4822,45 +5051,81 @@ BACKSLASH 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" + \81 is either a back reference, or the two + characters "8" and "1" + + Note that octal values of 100 or greater that are specified using this + syntax must not be introduced by a leading zero, because no more than + three octal digits are ever read. + + By default, after \x that is not followed by {, from zero to two hexa- + decimal digits are read (letters can be in upper or lower case). Any + number of hexadecimal digits may appear between \x{ and }. If a charac- + ter other than a hexadecimal digit appears between \x{ and }, or if + there is no terminating }, an error occurs. + + If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x + is as just described only when it is followed by two hexadecimal dig- + its. 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 differ- + ence in the way they are handled. For example, \xdc is exactly the same + as \x{dc} (or \u00dc in JavaScript mode). - 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. + Constraints on character values + + Characters that are specified using octal or hexadecimal numbers are + limited to certain values, 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 + 32-bit non-UTF mode less than 0x100000000 + 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint + + Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- + called "surrogate" codepoints), and 0xffef. + + Escape sequences in character classes All the sequences that define a single character value can be used both - inside and outside character classes. In addition, inside a character + 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 + \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 + 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, option- - ally enclosed in braces, is an absolute or relative back reference. A + The sequence \g followed by an unsigned or a negative number, option- + ally enclosed in braces, is an absolute or relative back reference. A named back reference can be coded as \g{name}. Back references are dis- cussed later, following the discussion of parenthesized subpatterns. Absolute and relative subroutine calls - For compatibility with Oniguruma, the non-Perl syntax \g followed by a + 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 + 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 @@ -4879,44 +5144,49 @@ BACKSLASH \W any "non-word" character There is also the single sequence \N, which matches a non-newline char- - acter. 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 + acter. 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 com- - plete 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 + Each pair of lower and upper case escape sequences partitions the com- + plete 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 charac- - ter. 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 con- - trolled 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 + For compatibility with Perl, \s did not used to match the VT character + (code 11), which made it different from the the POSIX "space" class. + However, Perl added VT at release 5.18, and PCRE followed suit at + release 8.34. The default \s characters are now HT (9), LF (10), VT + (11), FF (12), CR (13), and space (32), which are defined as white + space in the "C" locale. This list may vary if locale-specific matching + is taking place. For example, in some locales the "non-breaking space" + character (\xA0) is recognized as white space, and in others the VT + character is not. + + A "word" character is an underscore or any character that is a letter + or digit. By default, the definition of letters and digits is con- + trolled 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 127 + 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 be- - haviour is changed so that Unicode properties are used to determine - character types, as follows: + By default, characters whose code points are greater than 127 never + match \d, \s, or \w, and always match \D, \S, and \W, although this may + vary for characters in the range 128-255 when locale-specific matching + is happening. These escape sequences retain their original meanings + from before Unicode support was available, mainly for efficiency rea- + sons. If PCRE is compiled with Unicode property support, and the + PCRE_UCP option is set, the behaviour is changed so that Unicode prop- + erties 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 + \d any character that matches \p{Nd} (decimal digit) + \s any character that matches \p{Z} or \h or \v + \w any character that matches \p{L} or \p{N}, 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, @@ -4927,7 +5197,7 @@ BACKSLASH 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 char- + code points, whether or not PCRE_UCP is set. The horizontal space char- acters are: U+0009 Horizontal tab (HT) @@ -5136,52 +5406,53 @@ BACKSLASH in the Unicode table. Specifying caseless matching does not affect these escape sequences. - For example, \p{Lu} always matches only upper case letters. + For example, \p{Lu} always matches only upper case letters. This is + different from the behaviour of current versions of Perl. - Matching characters by Unicode property is not fast, because PCRE has - to do a multistage table lookup in order to find a character's prop- + Matching characters by Unicode property is not fast, because PCRE has + to do a multistage table lookup in order to find a character's prop- erty. 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 + do so by setting the PCRE_UCP option or by starting the pattern with (*UCP). Extended grapheme clusters - The \X escape matches any number of Unicode characters that form an + The \X escape matches any number of Unicode characters that form an "extended grapheme cluster", and treats the sequence as an atomic group - (see below). Up to and including release 8.31, PCRE matched an ear- + (see below). Up to and including release 8.31, PCRE matched an ear- lier, simpler definition that was equivalent to (?>\PM\pM*) - That is, it matched a character without the "mark" property, followed - by zero or more characters with the "mark" property. Characters with - the "mark" property are typically non-spacing accents that affect the + That is, it matched a character without the "mark" property, followed + by zero or more characters with the "mark" property. Characters with + the "mark" property are typically non-spacing accents that affect the preceding character. - This simple definition was extended in Unicode to include more compli- - cated kinds of composite character by giving each character a grapheme - breaking property, and creating rules that use these properties to - define the boundaries of extended grapheme clusters. In releases of + This simple definition was extended in Unicode to include more compli- + cated kinds of composite character by giving each character a grapheme + breaking property, and creating rules that use these properties to + define the boundaries of extended grapheme clusters. In releases of PCRE later than 8.31, \X matches one of these clusters. - \X always matches at least one character. Then it decides whether to + \X always matches at least one character. Then it decides whether to add additional characters according to the following rules for ending a cluster: 1. End at the end of the subject string. - 2. Do not end between CR and LF; otherwise end after any control char- + 2. Do not end between CR and LF; otherwise end after any control char- acter. - 3. Do not break Hangul (a Korean script) syllable sequences. Hangul - characters are of five types: L, V, T, LV, and LVT. An L character may - be followed by an L, V, LV, or LVT character; an LV or V character may + 3. Do not break Hangul (a Korean script) syllable sequences. Hangul + characters are of five types: L, V, T, LV, and LVT. An L character may + be followed by an L, V, LV, or LVT character; an LV or V character may be followed by a V or T character; an LVT or T character may be follwed only by a T character. - 4. Do not end before extending characters or spacing marks. Characters - with the "mark" property always have the "extend" grapheme breaking + 4. Do not end before extending characters or spacing marks. Characters + with the "mark" property always have the "extend" grapheme breaking property. 5. Do not end after prepend characters. @@ -5190,51 +5461,63 @@ BACKSLASH PCRE's additional properties - As well as the standard Unicode properties described above, PCRE sup- - ports 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 inter- - nally when PCRE_UCP is set. They are: + As well as the standard Unicode properties described above, PCRE sup- + ports four more that make it possible to convert traditional escape + sequences such as \w and \s to use Unicode properties. PCRE uses these + non-standard, non-Perl properties internally when PCRE_UCP is set. How- + ever, they may also be used explicitly. These properties 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 (num- - ber) property. Xps matches the characters tab, linefeed, vertical tab, - form feed, 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. + Xan matches characters that have either the L (letter) or the N (num- + ber) property. Xps matches the characters tab, linefeed, vertical tab, + form feed, or carriage return, and any other character that has the Z + (separator) property. Xsp is the same as Xps; it used to exclude ver- + tical tab, for Perl compatibility, but Perl changed, and so PCRE fol- + lowed at release 8.34. Xwd matches the same characters as Xan, plus + underscore. + + There is another non-standard property, Xuc, which matches any charac- + ter that can be represented by a Universal Character Name in C++ and + other programming languages. These are the characters $, @, ` (grave + accent), and all characters with Unicode code points greater than or + equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that + most base (ASCII) characters are excluded. (Universal Character Names + are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit. + Note that the Xuc property does not match these sequences but the char- + acters that they represent.) Resetting the match start - The escape sequence \K causes any previously matched characters not to + 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, + 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 + 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 asser- - tion 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 final use of backslash is for certain simple assertions. An asser- + tion 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 @@ -5245,161 +5528,161 @@ BACKSLASH \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 char- + 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 char- acter (for example, \B matches the letter B). However, if the - PCRE_EXTRA option is set, an "invalid escape sequence" error is gener- + PCRE_EXTRA option is set, an "invalid escape sequence" error is gener- ated 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" metase- - quence. However, whatever follows \b normally determines which it is. + 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" metase- + quence. 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 + 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 asser- + at the very start and end of the subject string, whatever options are + set. Thus, they are independent of multiline mode. These three asser- tions 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, indi- + affect only the behaviour of the circumflex and dollar metacharacters. + However, if the startoffset argument of pcre_exec() is non-zero, indi- cating 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 + 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 argu- + 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 argu- ments, you can mimic Perl's /g option, and it is in this kind of imple- mentation where \G can be useful. - Note, however, that PCRE's interpretation of \G, as the start of the + 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 + 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 + 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 - The circumflex and dollar metacharacters are zero-width assertions. - That is, they test for a particular condition being true without con- + The circumflex and dollar metacharacters are zero-width assertions. + That is, they test for a particular condition being true without con- suming any characters from the subject string. 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 argu- - ment of pcre_exec() is non-zero, circumflex can never match if the - PCRE_MULTILINE option is unset. Inside a character class, 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 argu- + ment 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 sub- - ject, it is said to be an "anchored" pattern. (There are also other + 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 sub- + ject, it is said to be an "anchored" pattern. (There are also other constructs that can cause a pattern to be anchored.) - The 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). Note, however, - that it does not actually match the newline. Dollar need not be the + The 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). Note, however, + that it does not actually match the newline. 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. Dol- + but it should be the last item in any branch in which it appears. Dol- lar 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 + 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 + 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 + 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 + 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 charac- - ter in the subject string except (by default) a character that signi- + ter in the subject string except (by default) a character that signi- fies 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 Uni- - code line endings are being recognized, dot does not match CR or LF or + 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 Uni- + code 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 + 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 circum- - flex and dollar, the only relationship being that they both involve + The handling of dot is entirely independent of the handling of circum- + flex 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 + 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; in the - 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches - line-ending characters. The feature is provided in Perl in order to + 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; in the + 32-bit library it is a 32-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 use- - fully 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 + fully 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, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option + (and by default it checks this at the start of processing unless the + PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_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 calcu- + PCRE does not allow \C to appear in lookbehind assertions (described + below) in a UTF mode, because this would make it impossible to calcu- late 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 pat- - tern, which could be used with a UTF-8 string (ignore white space and + 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 pat- + tern, which could be used with a UTF-8 string (ignore white space and line breaks): (?| (?=[\x00-\x7f])(\C) | @@ -5407,11 +5690,11 @@ MATCHING A SINGLE DATA UNIT (?=[\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 num- + 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 num- ber of groups. @@ -5421,64 +5704,71 @@ SQUARE BRACKETS AND CHARACTER CLASSES closing square bracket. A closing square bracket on its own is not spe- cial 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 + 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 + 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 + 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 + 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. + 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 con- - sumes a character from the subject string, and therefore it fails if + 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 con- + sumes 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, UTF-32) mode, characters with values greater than 255 - (0xffff) can be included in a class as a literal string of data units, + (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 + 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 + 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 charac- - ters 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. + The minus (hyphen) character can be used to specify a range of charac- + ters 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, or immediately after a range. For + example, [b-d-z] matches letters in the range b to d, a hyphen charac- + ter, or z. It is not possible to have the literal character "]" as the end charac- - ter 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 inter- - preted as a class containing a range followed by two other characters. - The octal or hexadecimal representation of "]" can also be used to end + ter 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 inter- + preted 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. + An error is generated if a POSIX character class (see below) or an + escape sequence other than one that defines a single character appears + at a point where a range ending character is expected. For example, + [z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not. + 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 @@ -5515,15 +5805,16 @@ SQUARE BRACKETS AND CHARACTER CLASSES 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. + when it can be interpreted as introducing a POSIX class name, or for a + special compatibility feature - see the next two sections), 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 + enclosed by [: and :] within the enclosing square brackets. PCRE also supports this notation. For example, [01[:alpha:]%] @@ -5541,15 +5832,18 @@ POSIX CHARACTER CLASSES 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) + space white space (the same as \s from PCRE 8.34) 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 default "space" characters are HT (9), LF (10), VT (11), FF (12), + CR (13), and space (32). If locale-specific matching is taking place, + the list of space characters may be different; there may be fewer or + more of them. "Space" used to be different to \s, which did not include + VT, for Perl compatibility. However, Perl changed at release 5.18, and + PCRE followed at release 8.34. "Space" and \s now match the same set + of characters. 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 @@ -5561,11 +5855,11 @@ POSIX CHARACTER CLASSES 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 replac- - ing the POSIX classes by other sequences, as follows: + By default, 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 certain + POSIX classes by other sequences, as follows: [:alnum:] becomes \p{Xan} [:alpha:] becomes \p{L} @@ -5576,9 +5870,48 @@ POSIX CHARACTER CLASSES [: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. + Negated versions, such as [:^alpha:] use \P instead of \p. Three other + POSIX classes are handled specially in UCP mode: + + [:graph:] This matches characters that have glyphs that mark the page + when printed. In Unicode property terms, it matches all char- + acters with the L, M, N, P, S, or Cf properties, except for: + + U+061C Arabic Letter Mark + U+180E Mongolian Vowel Separator + U+2066 - U+2069 Various "isolate"s + + + [:print:] This matches the same characters as [:graph:] plus space + characters that are not controls, that is, characters with + the Zs property. + + [:punct:] This matches all characters that have the Unicode P (punctua- + tion) property, plus those characters whose code points are + less than 128 that have the S (Symbol) property. + + The other POSIX classes are unchanged, and match only characters with + code points less than 128. + + +COMPATIBILITY FEATURE FOR WORD BOUNDARIES + + In the POSIX.2 compliant library that was included in 4.4BSD Unix, the + ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word" + and "end of word". PCRE treats these items as follows: + + [[:<:]] is converted to \b(?=\w) + [[:>:]] is converted to \b(?<=\w) + + Only these exact character sequences are recognized. A sequence such as + [a[:<:]b] provokes error for an unrecognized POSIX class name. This + support is not compatible with Perl. It is provided to help migrations + from other environments, and is best not used in any new patterns. Note + that \b matches at the start and the end of a word (see "Simple asser- + tions" above), and in a Perl-style pattern the preceding or following + character normally shows which is wanted, without the need for the + assertions that are used above in order to give exactly the POSIX be- + haviour. VERTICAL BAR @@ -5653,7 +5986,9 @@ INTERNAL OPTION SETTING (*UCP) leading sequences that can be used to set UTF and Unicode prop- erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence - is a generic version that can be used with any of the libraries. + is a generic version that can be used with any of the libraries. How- + ever, the application can set the PCRE_NEVER_UTF option, which locks + out the use of the (*UTF) sequences. SUBPATTERNS @@ -5773,12 +6108,12 @@ NAMED SUBPATTERNS 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. + Names consist of up to 32 alphanumeric characters and underscores, but + must start with a non-digit. 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 @@ -5806,28 +6141,38 @@ NAMED SUBPATTERNS 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 occur- - rence 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 documen- - tation. + elsewhere in the pattern, the subpatterns to which the name refers are + checked in the order in which they appear in the overall pattern. The + first one that is set is used for the reference. For example, this pat- + tern matches both "foofoo" and "barbar" but not "foobar" or "barfoo": + + (?:(?<n>foo)|(?<n>bar))\k<n> + + + If you make a subroutine call to a non-unique named subpattern, 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 sub- - patterns with the same number because PCRE uses only the numbers when + patterns with the same number because PCRE uses only the numbers when matching. For this reason, an error is given at compile time if differ- - ent 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. + ent names are given to subpatterns with the same number. However, you + can always 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 + Repetition is specified by quantifiers, which can follow any of the following items: a literal data character @@ -5841,17 +6186,17 @@ REPETITION a parenthesized subpattern (including assertions) a subroutine call to a subpattern (recursive or otherwise) - The general repetition quantifier specifies a minimum and maximum num- - ber of permitted matches, by giving the two numbers in curly brackets - (braces), separated by a comma. The numbers must be less than 65536, + The general repetition quantifier specifies a minimum and maximum num- + ber 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 "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,} @@ -5860,50 +6205,50 @@ REPETITION \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 exam- + 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 exam- ple, {,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 + 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. Simi- - larly, \X{3} matches three Unicode extended grapheme clusters, each of - which may be several data units long (and they may be of different + larly, \X{3} matches three Unicode extended grapheme clusters, 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 use- - ful for subpatterns that are referenced as subroutines from elsewhere + ful 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 + 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-charac- + For convenience, the three most common quantifiers have single-charac- ter 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 + 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 bro- + 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 bro- ken. - 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 + 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 + appear between /* and */ and within the comment, individual * and / + characters may appear. An attempt to match C comments by applying the pattern /\*.*\*/ @@ -5912,19 +6257,19 @@ REPETITION /* first comment */ not comment /* second comment */ - fails, because it matches the entire string owing to the greediness of + 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 + 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 + 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 @@ -5932,45 +6277,45 @@ REPETITION 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 + 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 + 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 (equiv- - alent 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 + alent 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 new- - lines, it is worth setting PCRE_DOTALL in order to obtain this opti- + In cases where it is known that the subject string contains no new- + lines, it is worth setting PCRE_DOTALL in order to obtain this opti- mization, or alternatively using ^ to indicate anchoring explicitly. - However, there are some cases where the optimization cannot be used. + However, there are some cases 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 charac- + If the subject is "xyz123abc123" the match point is the fourth charac- ter. For this reason, such a pattern is not implicitly anchored. - Another case where implicit anchoring is not applied is when the lead- - ing .* is inside an atomic group. Once again, a match at the start may + Another case where implicit anchoring is not applied is when the lead- + ing .* is inside an atomic group. Once again, a match at the start may fail where a later one succeeds. Consider this pattern: (?>.*?a)b - It matches "ab" in the subject "aab". The use of the backtracking con- + It matches "ab" in the subject "aab". The use of the backtracking con- trol verbs (*PRUNE) and (*SKIP) also disable this optimization. When a capturing subpattern is repeated, the value captured is the sub- @@ -5979,8 +6324,8 @@ REPETITION (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 itera- + is "tweedledee". However, if there are nested capturing subpatterns, + the corresponding captured values may have been set in previous itera- tions. For example, after /(a|(b))+/ @@ -5990,53 +6335,53 @@ REPETITION 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 + 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 + 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 + 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 + 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 con- - tains once it has matched, and a failure further into the pattern is - prevented from backtracking into it. Backtracking past it to previous + This kind of parenthesis "locks up" the part of the pattern it con- + tains 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 + 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 pre- - pared to adjust the number of digits they match in order to make the + must swallow everything it can. So, while both \d+ and \d+? are pre- + pared 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 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 + 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 @@ -6046,45 +6391,45 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS (abc|xyz){2,3}+ - Possessive quantifiers are always greedy; the setting of the + 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 + 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 syn- - tax. Jeffrey Friedl originated the idea (and the name) in the first + The possessive quantifier syntax is an extension to the Perl 5.8 syn- + tax. 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 + 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 sim- - ple 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 + ple 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 + 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 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 charac- - ter 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 + 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 charac- + ter 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+>)*[!?] @@ -6096,28 +6441,28 @@ 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 sub- - pattern earlier (that is, to its left) in the pattern, provided there + pattern 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 pat- - tern. 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 itera- + 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 pat- + tern. 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 itera- tion. - 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. + 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 + 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 + 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: @@ -6125,7 +6470,7 @@ BACK REFERENCES (ring), \g1 (ring), \g{1} - An unsigned number specifies an absolute reference without the ambigu- + An unsigned number specifies an absolute reference without the ambigu- ity 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: @@ -6134,33 +6479,33 @@ BACK REFERENCES The sequence \g{-1} is a reference to the most recently started captur- ing subpattern before \g, that is, is it equivalent to \2 in this exam- - ple. 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 + ple. 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 sub- - pattern in the current subject string, rather than anything matching + A back reference matches whatever actually matched the capturing sub- + pattern 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 exam- + 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 exam- ple, ((?i)rah)\s+\1 - matches "rah rah" and "RAH RAH", but not "RAH rah", even though the + 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 + 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 + and named references, is also supported. We could rewrite the above example in any of the following ways: (?<p1>(?i)rah)\s+\k<p1> @@ -6168,66 +6513,67 @@ BACK REFERENCES (?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 + 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 + 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 + 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 refer- ence to an unset value matches an empty string. - Because there may be many capturing parentheses in a pattern, all dig- - its following a backslash are taken as part of a potential back refer- - ence 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 white space. Otherwise, the + Because there may be many capturing parentheses in a pattern, all dig- + its following a backslash are taken as part of a potential back refer- + ence 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 white space. 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 sub- + 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 sub- patterns. For example, the pattern (a|b\1)+ matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- - ation 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 + ation 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 + 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 + 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 + 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 asser- - tion contains capturing subpatterns within it, these are counted for - the purposes of numbering the capturing subpatterns in the whole pat- - tern. However, substring capturing is carried out only for positive - assertions, because it does not make sense for negative assertions. + Assertion subpatterns are not capturing subpatterns. If such an asser- + tion contains capturing subpatterns within it, these are counted for + the purposes of numbering the capturing subpatterns in the whole pat- + tern. However, substring capturing is carried out only for positive + assertions. (Perl sometimes, but not always, does do capturing in nega- + tive assertions.) For compatibility with Perl, assertion subpatterns may be repeated; though it makes no sense to assert the same thing several times, the @@ -6456,25 +6802,20 @@ CONDITIONAL SUBPATTERNS 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 syn- - tax, 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 num- - ber, which must be greater than zero. Using subpattern names that con- - sist entirely of digits is not recommended. + also recognized. 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 + 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 + 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 amper- sand follow the letter R, for example: @@ -6482,51 +6823,51 @@ CONDITIONAL SUBPATTERNS 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 + 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 + 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 refer- - enced from elsewhere. (The use of subroutines is described below.) For - example, a pattern to match an IPv4 address such as "192.168.23.245" + 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 refer- + enced 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 white space 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, insist- + 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, insist- ing 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 + 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 + 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. @@ -6535,41 +6876,41 @@ 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 char- acter class, nor in the middle of any other sequence of related charac- - ters such as (?: or a subpattern name or number. The characters that + ters 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 + 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 charac- + comment, which in this case continues to immediately after the next + newline character or character sequence in the pattern. Which charac- ters are interpreted as newlines is controlled by the options passed to - a compiling function or by a special sequence at the start of the pat- + a compiling function or by a special sequence at the start of the pat- tern, 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 + 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 + 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 + 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 expres- - sions 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 + sions 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: @@ -6579,201 +6920,201 @@ RECURSIVE PATTERNS 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 + 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 + 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 + 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 parenthe- + 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 parenthe- sized 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 + 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 + 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 + 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 + 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 refer- - enced. They are always non-recursive subroutine calls, as described in + 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 refer- + enced. 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 + 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 + 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 + 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 pat- - tern to strings that do not match. For example, when this pattern is + tern 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, + 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 documenta- + 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 documenta- tion). 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 sub- - pattern 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 + 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 sub- + pattern 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 + 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 brack- - ets, allowing for arbitrary nesting. Only digits are allowed in nested - brackets (that is, when recursing), whereas any characters are permit- + Do not confuse the (?R) item with the condition (R), which tests for + recursion. Consider this pattern, which matches text in angle brack- + ets, allowing for arbitrary nesting. Only digits are allowed in nested + brackets (that is, when recursing), whereas any characters are permit- ted 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. + 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 + 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 palin- - dromic string that contains an odd number of characters (for example, + alternatives and there is a subsequent matching failure. This can be + illustrated by the following pattern, which purports to match a palin- + dromic 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. + 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 + 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 alterna- tive is taken and the recursion kicks in. The recursive call to subpat- - tern 1 successfully matches the next character ("b"). (Note that the + tern 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 + 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 + 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 + 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 alter- + 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 alter- natives at the higher level: ^(?:((.)(?1)\2|)|((.)(?3)\4|.)) - If you want to match typical palindromic phrases, the pattern has to + 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 backtrack- - ing into sequences of non-word characters. Without this, PCRE takes a - great deal longer (ten times or more) to match typical phrases, and + Perl. Note the use of the possessive quantifier *+ to avoid backtrack- + ing 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 sub- - ject 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 alter- + WARNING: The palindrome-matching patterns above work only if the sub- + ject 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 alter- natives, so the entire match fails. - The second way in which PCRE and Perl differ in their recursion pro- - cessing is in the handling of captured values. In Perl, when a subpat- - tern is called recursively or as a subpattern (see the next section), - it has no access to any values that were captured outside the recur- - sion, whereas in PCRE these values can be referenced. Consider this + The second way in which PCRE and Perl differ in their recursion pro- + cessing is in the handling of captured values. In Perl, when a subpat- + tern is called recursively or as a subpattern (see the next section), + it has no access to any values that were captured outside the recur- + sion, 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 + 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 + 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)... @@ -6784,190 +7125,203 @@ SUBPATTERNS AS SUBROUTINES (sens|respons)e and \1ibility - matches "sense and sensibility" and "response and responsibility", but + 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 + 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 sub- + All subroutine calls, whether recursive or not, are always treated as + atomic groups. That is, once a subroutine has matched some of the sub- ject string, it is never re-entered, even if it contains untried alter- - natives and there is a subsequent matching failure. Any capturing - parentheses that are set during the subroutine call revert to their + natives 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 subpat- - tern is defined, so if it is used as a subroutine, such options cannot + Processing options such as case-independence are fixed when a subpat- + tern 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 + 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 + 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, rewrit- + an alternative syntax for referencing a subpattern as a subroutine, + possibly recursively. Here are two of the examples used above, rewrit- ten 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 + 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 + 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. + Perl code to be obeyed in the middle of matching a regular expression. This makes it possible, amongst other things, to extract different sub- strings that match the same pair of parentheses when there is a repeti- tion. 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 pcre[16|32]_callout (16-bit or 32-bit - library). By default, this variable contains NULL, which disables all + an external function by putting its entry point in the global variable + pcre_callout (8-bit library) or pcre[16|32]_callout (16-bit or 32-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 + 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, call- - outs are automatically installed before each item in the pattern. They - are all numbered 255. + If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, call- + outs are automatically installed before each item in the pattern. They + are all numbered 255. If there is a conditional group in the pattern + whose condition is an assertion, an additional callout is inserted just + before the condition. An explicit callout may also be set at this posi- + tion, as in this example: + + (?(?C9)(?=a)abc|def) + + Note that this applies only to assertion conditions, not to other types + of condition. - During matching, when PCRE reaches a callout point, the external func- - tion 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. + During matching, when PCRE reaches a callout point, the external func- + tion 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. + + By default, PCRE implements a number of optimizations at compile time + and matching time, and one side-effect is that sometimes callouts are + skipped. If you need all possible callouts to happen, you need to set + options that disable the relevant optimizations. More details, and a + complete description of the interface to the callout function, are + 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 sub- - ject 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 func- - tion. + which are still 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. - 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 pat- - tern, 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 and - assertions is different in some cases. - - The new verbs make use of what was previously invalid syntax: an open- + The new verbs make use of what was previously invalid syntax: an open- ing parenthesis followed by an asterisk. They are generally of the form - (*VERB) or (*VERB:NAME). Some may take either form, with differing be- - haviour, depending on whether or not an argument is present. A name is + (*VERB) or (*VERB:NAME). Some may take either form, possibly behaving + differently depending on whether or not a name is present. A name is any sequence of characters that does not include a closing parenthesis. The maximum length of name is 255 in the 8-bit library and 65535 in the - 16-bit and 32-bit library. If the name is empty, that is, if the clos- - ing 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. + 16-bit and 32-bit libraries. 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. + + 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, because these use a backtracking + algorithm. With the exception of (*FAIL), which behaves like a failing + negative assertion, the backtracking control verbs cause an error if + encountered by a DFA matching function. + + The behaviour of these verbs in repeated groups, assertions, and in + subpatterns called as subroutines (whether or not recursively) is docu- + mented below. Optimizations that affect backtracking verbs - PCRE contains some optimizations that are used to speed up matching by + 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 + may know the minimum length of matching subject, or that a particular + character must be present. When one of these optimizations bypasses 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_com- + by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_com- pile() or pcre_exec(), or by starting the pattern with (*NO_START_OPT). There is more discussion of this option in the section entitled "Option bits for pcre_exec()" in the pcreapi documentation. - Experiments with Perl suggest that it too has similar optimizations, + 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 + 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: + 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) in triggered in a posi- + tive assertion, the assertion succeeds; in a negative assertion, the + assertion fails. + + If (*ACCEPT) is inside capturing parentheses, the data so far is cap- + tured. For example: A((?:A|B(*ACCEPT)|C)D) - This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- + This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap- tured 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 pat- + 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 pat- tern: a+(?C)(*FAIL) - A match with the string "aaaa" always fails, but the callout is taken + 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 + 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 + 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: + When a match succeeds, the name of the last-encountered (*MARK:NAME), + (*PRUNE:NAME), or (*THEN:NAME) 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 out- + putting of (*MARK) data: re> /X(*MARK:A)Y|X(*MARK:B)Z/K data> XY @@ -6982,57 +7336,67 @@ BACKTRACKING CONTROL efficient way of obtaining this information than putting each alterna- tive 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. + If a verb with a name is encountered in a positive assertion that is + true, the name is recorded and passed back if it is the last-encoun- + tered. This does not happen for negative assertions or failing positive + assertions. - After a partial match or a failed match, the name of the last encoun- - tered (*MARK) in the entire match process is returned. For example: + After a partial match or a failed match, the last encountered name 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 + Note that in this unanchored example the mark is retained from the match attempt that started at the letter "X" in the subject. 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. - If you are interested in (*MARK) values after failed matches, you - should probably set the PCRE_NO_START_OPTIMIZE option (see above) to + If you are interested in (*MARK) values after failed matches, you + should probably set the PCRE_NO_START_OPTIMIZE option (see above) to ensure that the match is always attempted. Verbs that act after backtracking The following verbs do nothing when they are encountered. Matching con- - tinues 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 backtrack- - ing 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.) + tinues 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 or an assertion that is true, its effect + is confined to that group, because once the group has been matched, + there is never any backtracking into it. In this situation, backtrack- + ing can "jump back" to the left of the entire atomic group or asser- + tion. (Remember also, as stated above, that this localization also + applies in subroutine calls.) These verbs differ in exactly what kind of failure occurs when back- - tracking reaches them. + tracking reaches them. The behaviour described below is what happens + when the verb is not in a subroutine or an assertion. Subsequent sec- + tions cover these special cases. (*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: + to fail outright if there is a later matching failure that causes back- + tracking to reach it. Even if the pattern is unanchored, no further + attempts to find a match by advancing the starting point take place. If + (*COMMIT) is the only backtracking verb that is encountered, once it + has been passed pcre_exec() is committed to finding a match at the cur- + rent 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 + 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) + most recently passed (*MARK) in the path is passed back when (*COMMIT) forces a match failure. + If there is more than one backtracking verb in a pattern, a different + one that follows (*COMMIT) may be triggered first, so merely passing + (*COMMIT) during a match does not always guarantee that a match must be + at this starting point. + 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: @@ -7052,66 +7416,80 @@ BACKTRACKING CONTROL (*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 alter- - native to an atomic group or possessive quantifier, but there are some - uses of (*PRUNE) that cannot be expressed in any other way. The behav- - iour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an - anchored pattern (*PRUNE) has the same effect as (*COMMIT). + the subject if there is a later matching failure that causes backtrack- + ing to reach it. 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 quan- + tifier, but there are some uses of (*PRUNE) that cannot be expressed in + any other way. In an anchored pattern (*PRUNE) has the same effect as + (*COMMIT). + + The behaviour of (*PRUNE:NAME) is the not the same as + (*MARK:NAME)(*PRUNE). It is like (*MARK:NAME) in that the name is + remembered for passing back to the caller. However, (*SKIP:NAME) + searches only for names set with (*MARK). (*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 + 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 encoun- - tered. (*SKIP) signifies that whatever text was matched leading up to + tered. (*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 + 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 quan- - tifer 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 + tifer 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 cor- - responds to that (*MARK) instead of to where (*SKIP) was encountered. - If no (*MARK) with a matching name is found, the (*SKIP) is ignored. + When (*SKIP) has an associated name, its behaviour is modified. When it + is triggered, 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. + + Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It + ignores names that are set by (*PRUNE:NAME) or (*THEN:NAME). (*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 backtrack- - ing, 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: + This verb causes a skip to the next innermost alternative when back- + tracking reaches it. That is, it cancels any further backtracking + 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 sub- - pattern to the enclosing alternative. Consider this pattern, where A, - B, etc. are complex pattern fragments that do not contain any | charac- - ters at this level: + into COND1. If that succeeds and BAR fails, COND3 is tried. If subse- + quently BAZ fails, there are no more alternatives, so there is a back- + track to whatever came before the entire group. If (*THEN) is not + inside an alternation, it acts like (*PRUNE). + + The behaviour of (*THEN:NAME) is the not the same as + (*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is + remembered for passing back to the caller. However, (*SKIP:NAME) + searches only for names set with (*MARK). + + 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 @@ -7127,7 +7505,7 @@ BACKTRACKING CONTROL tern 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 + Note 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: @@ -7151,16 +7529,78 @@ BACKTRACKING CONTROL 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: + More than one backtracking verb + + If more than one backtracking verb is present in a pattern, the one + that is backtracked onto first acts. For example, consider this pat- + tern, where A, B, etc. are complex pattern fragments: + + (A(*COMMIT)B(*THEN)C|ABD) + + If A matches but B fails, the backtrack to (*COMMIT) causes the entire + match to fail. However, if A and B match, but C fails, the backtrack to + (*THEN) causes the next alternative (ABD) to be tried. This behaviour + is consistent, but is not always the same as Perl's. It means that if + two or more backtracking verbs appear in succession, all the the last + of them has no effect. Consider this example: + + ...(*COMMIT)(*PRUNE)... + + If there is a matching failure to the right, backtracking onto (*PRUNE) + causes it to be triggered, and its action is taken. There can never be + a backtrack onto (*COMMIT). + + Backtracking verbs in repeated groups + + PCRE differs from Perl in its handling of backtracking verbs in + repeated groups. For example, consider: + + /(a(*COMMIT)b)+ac/ + + If the subject is "abac", Perl matches, but PCRE fails because the + (*COMMIT) in the second repeat of the group acts. + + Backtracking verbs in assertions + + (*FAIL) in an assertion has its normal effect: it forces an immediate + backtrack. + + (*ACCEPT) in a positive assertion causes the assertion to succeed with- + out any further processing. In a negative assertion, (*ACCEPT) causes + the assertion to fail without any further processing. - (A(*COMMIT)B(*THEN)C|D) + The other backtracking verbs are not treated specially if they appear + in a positive assertion. In particular, (*THEN) skips to the next + alternative in the innermost enclosing group that has alternations, + whether or not this is within the assertion. - Once A has matched, PCRE is committed to this match, at the current - starting position. If subsequently B matches, but C does not, the nor- - mal (*THEN) action of trying the next alternative (that is, D) does not - happen because (*COMMIT) overrides. + Negative assertions are, however, different, in order to ensure that + changing a positive assertion into a negative assertion changes its + result. Backtracking into (*COMMIT), (*SKIP), or (*PRUNE) causes a neg- + ative assertion to be true, without considering any further alternative + branches in the assertion. Backtracking into (*THEN) causes it to skip + to the next enclosing alternative within the assertion (the normal be- + haviour), but if the assertion does not have such an alternative, + (*THEN) behaves like (*PRUNE). + + Backtracking verbs in subroutines + + These behaviours occur whether or not the subpattern is called recur- + sively. Perl's treatment of subroutines is different in some cases. + + (*FAIL) in a subpattern called as a subroutine has its normal effect: + it forces an immediate backtrack. + + (*ACCEPT) in a subpattern called as a subroutine causes the subroutine + match to succeed without any further processing. Matching then contin- + ues after the subroutine call. + + (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine + cause the subroutine match to fail. + + (*THEN) skips to the next alternative in the innermost enclosing group + within the subpattern that has alternatives. If there is no such group + within the subpattern, (*THEN) causes the subroutine match to fail. SEE ALSO @@ -7178,18 +7618,18 @@ AUTHOR REVISION - Last updated: 11 November 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 03 December 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCRESYNTAX(3) PCRESYNTAX(3) +PCRESYNTAX(3) Library Functions Manual PCRESYNTAX(3) + NAME PCRE - Perl-compatible regular expressions - PCRE REGULAR EXPRESSION SYNTAX SUMMARY The full syntax and semantics of the regular expressions that are sup- @@ -7212,10 +7652,15 @@ CHARACTERS \n newline (hex 0A) \r carriage return (hex 0D) \t tab (hex 09) + \0dd character with octal code 0dd \ddd character with octal code ddd, or backreference + \o{ddd..} character with octal code ddd.. \xhh character with hex code hh \x{hhh..} character with hex code hhh.. + Note that \0dd is always an octal code, and that \8 and \9 are the lit- + eral characters "8" and "9". + CHARACTER TYPES @@ -7238,9 +7683,12 @@ CHARACTER TYPES \W a "non-word" character \X a Unicode extended grapheme cluster - 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. + By default, \d, \s, and \w match only ASCII characters, even in UTF-8 + mode or in the 16- bit and 32-bit libraries. However, if locale-spe- + cific matching is happening, \s and \w may also match characters with + code points in the range 128-255. If the PCRE_UCP option is set, the + behaviour of these escape sequences is changed to use Unicode proper- + ties and they match many more characters. GENERAL CATEGORY PROPERTIES FOR \p and \P @@ -7295,27 +7743,32 @@ 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 + Xsp Perl space: property Z or tab, NL, VT, FF, CR + Xuc Univerally-named character: one that can be + represented by a Universal Character Name Xwd Perl word: property Xan or underscore + Perl and POSIX space are now the same. Perl added VT to its space char- + acter set at release 5.18 and PCRE changed at release 8.34. + SCRIPT NAMES FOR \p AND \P - Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, - Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, - Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, - Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, - Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- - gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- - tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, - Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, + Arabic, Armenian, Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo, + Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Chakma, + Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, + Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, + Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira- + gana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscrip- + tional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, + Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, Mandaic, Meetei_Mayek, Meroitic_Cursive, - Meroitic_Hieroglyphs, Miao, 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, Samari- - tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, - Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, - Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, + Meroitic_Hieroglyphs, Miao, 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, Samari- + tan, Saurashtra, Sharada, Shavian, Sinhala, Sora_Sompeng, Sundanese, + Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, + Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, Yi. @@ -7342,8 +7795,8 @@ CHARACTER CLASSES 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. + 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. @@ -7424,9 +7877,11 @@ OPTION SETTING (?x) extended (ignore white space) (?-...) unset option(s) - The following are recognized only at the start of a pattern or after + The following are recognized only at the start of a pattern or after one of the newline-setting options with similar syntax: + (*LIMIT_MATCH=d) set the match limit to d (decimal number) + (*LIMIT_RECURSION=d) set the recursion limit to d (decimal number) (*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) @@ -7434,6 +7889,9 @@ OPTION SETTING (*UTF) set appropriate UTF mode for the library in use (*UCP) set PCRE_UCP (use Unicode properties for \d etc) + Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce the value of + the limits set by the caller of pcre_exec(), not increase them. + LOOKAHEAD AND LOOKBEHIND ASSERTIONS @@ -7558,18 +8016,18 @@ AUTHOR REVISION - Last updated: 11 November 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 12 November 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREUNICODE(3) PCREUNICODE(3) +PCREUNICODE(3) Library Functions Manual PCREUNICODE(3) + NAME PCRE - Perl-compatible regular expressions - UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) @@ -7632,7 +8090,9 @@ UNICODE PROPERTY SUPPORT fication. 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, exclud- - ing the surrogate area and the non-characters. + ing the surrogate area. (From release 8.33 the so-called "non-charac- + ter" code points are no longer excluded because Unicode corrigendum #9 + makes it clear that they should not be.) Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16, where they are used in pairs to encode codepoints with values @@ -7641,10 +8101,6 @@ UNICODE PROPERTY SUPPORT other words, the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and UTF-32.) - Also excluded are the "Non-Character" code points, which are U+FDD0 to - U+FDEF and the last two code points in each plane, U+??FFFE and - U+??FFFF. - 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 run-time functions pcre_exec() @@ -7676,10 +8132,6 @@ UNICODE PROPERTY SUPPORT 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. - Excluded are the "Non-Character" code points, which are U+FDD0 to - U+FDEF and the last two code points in each plane, U+??FFFE and - U+??FFFF. - 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 run-time functions @@ -7701,77 +8153,76 @@ UNICODE PROPERTY SUPPORT are passed as patterns and subjects are (by default) checked for valid- ity on entry to the relevant functions. This check allows only values in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to - U+DFFF, and the "Non-Character" code points, which are U+FDD0 to U+FDEF - and the last two characters in each plane, U+??FFFE and U+??FFFF. + U+DFFF. - If an invalid UTF-32 string is passed to PCRE, an error return is - given. At compile time, the only additional information is the offset + If an invalid UTF-32 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 run-time functions pcre32_exec() and pcre32_dfa_exec() also pass back this information, as - well as a more detailed reason code if the caller has provided memory + 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 perfor- - mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at + In some situations, you may already know that your strings are valid, + and therefore want to skip these checks in order to improve perfor- + mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at run time, PCRE assumes that the pattern or subject it is given (respec- tively) contains only valid UTF-32 sequences. In this case, it does not - diagnose an invalid UTF-32 string. However, if an invalid string is + diagnose an invalid UTF-32 string. However, if an invalid string is passed, the result is undefined. General comments about UTF modes - 1. Codepoints less than 256 can be specified in patterns by either + 1. Codepoints less than 256 can be specified in patterns 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 + 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 individ- ual data units, for example: \x{100}{3}. - 4. The dot metacharacter matches one UTF character instead of a single + 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, or a single 32-bit - data unit in UTF-32 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|32]_dfa_exec(), nor is it + 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, or a single 32-bit + data unit in UTF-32 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|32]_dfa_exec(), nor is it supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If - JIT optimization is requested for a UTF pattern that contains \C, it + 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 + 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, + 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 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 + 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 + character escapes work is changed so that Unicode properties are used to determine which characters match. There are more details in the sec- tion on generic character types in the pcrepattern documentation. - 7. Similarly, characters that match the POSIX named character classes + 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 white space matching escapes - (\h, \H, \v, and \V) do match all the appropriate Unicode characters, + 8. However, the horizontal and vertical white space 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. - A few Unicode characters such as Greek sigma have more than two code- + 9. Case-insensitive matching applies only to characters whose values + are less than 128, unless PCRE is built with Unicode property support. + A few Unicode characters such as Greek sigma have more than two code- points that are case-equivalent. Up to and including PCRE release 8.31, - only one-to-one case mappings were supported, but later releases (with - Unicode property support) do treat as case-equivalent all versions of + only one-to-one case mappings were supported, but later releases (with + Unicode property support) do treat as case-equivalent all versions of characters such as Greek sigma. @@ -7784,18 +8235,18 @@ AUTHOR REVISION - Last updated: 11 November 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 27 February 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREJIT(3) PCREJIT(3) +PCREJIT(3) Library Functions Manual PCREJIT(3) + NAME PCRE - Perl-compatible regular expressions - PCRE JUST-IN-TIME COMPILER SUPPORT Just-in-time compiling is a heavyweight optimization that can greatly @@ -7941,15 +8392,9 @@ UNSUPPORTED OPTIONS AND PATTERN ITEMS BOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PAR- TIAL_HARD, and PCRE_PARTIAL_SOFT. - The unsupported pattern items are: - - \C match a single byte; not supported in UTF-8 mode - (?Cn) callouts - (*PRUNE) ) - (*SKIP) ) backtracking control verbs - (*THEN) ) - - Support for some of these may be added in future. + The only unsupported pattern items are \C (match a single data unit) + when running in a UTF mode, and a callout immediately before an asser- + tion condition in a conditional group. RETURN VALUES FROM JIT EXECUTION @@ -8203,18 +8648,18 @@ AUTHOR REVISION - Last updated: 31 October 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 17 March 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREPARTIAL(3) PCREPARTIAL(3) +PCREPARTIAL(3) Library Functions Manual PCREPARTIAL(3) + NAME PCRE - Perl-compatible regular expressions - PARTIAL MATCHING IN PCRE In normal use of PCRE, if the subject string that is passed to a match- @@ -8273,7 +8718,7 @@ PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec() A partial match occurs during a call to pcre_exec() or pcre[16|32]_exec() when the end of the subject string is reached suc- cessfully, but matching cannot continue because more characters are - needed. However, at least one character in the subject must have been + 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 @@ -8286,18 +8731,22 @@ PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec() 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. + If there are at least three slots in the offsets vector, the third slot + is set to the offset of the character where matching started. - For the majority of patterns, the first offset identifies the start of - the partially matched string. However, for patterns that contain look- - behind assertions, or \K, or begin with \b or \B, earlier characters - have been inspected while carrying out the match. For example: + For the majority of patterns, the contents of the first and third slots + will be the same. However, for patterns that contain lookbehind asser- + tions, or begin with \b or \B, characters before the one where matching + started may have been inspected while carrying out the match. For exam- + ple, consider this pattern: /(?<=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. + subject string is "xyzabc12", the first two offsets after a partial + match are for the substring "abc12", because all these characters were + inspected. However, the third offset is set to 6, because that is the + offset where matching began. What happens when a partial match is identified depends on which of the two partial matching options are set. @@ -8491,6 +8940,16 @@ MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre[16|32]_dfa_exec() matched string. It is up to the calling program to do that if it needs to. + That means that, for an unanchored pattern, if a continued match fails, + it is not possible to try again at a new starting point. All this + facility is capable of doing is continuing with the previous match + attempt. In the previous example, if the second set of data is "ug23" + the result is no match, even though there would be a match for "aug23" + if the entire string were given at once. Depending on the application, + this may or may not be what you want. The only way to allow for start- + ing again at the next character is to retain the matched part of the + subject and try a new complete match. + 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 @@ -8523,10 +8982,9 @@ MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre[16|32]_exec() 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. However, in some cases you may need to retain even - earlier characters, as discussed in the next section. + characters that precede the start of what would be returned for a com- + plete match, because it contains all the characters that were inspected + during the partial match. ISSUES WITH MULTI-SEGMENT MATCHING @@ -8535,23 +8993,44 @@ ISSUES 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 + 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 that have already been obeyed are catered for + 2. Lookbehind assertions that have already been obeyed are catered for in the offsets that are returned for a partial match. However a lookbe- - hind assertion later in the pattern could require even earlier charac- - ters to be inspected. You can handle this case by using the + hind assertion later in the pattern could require even earlier charac- + ters to be inspected. You can handle this case by using the PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or - pcre[16|32]_fullinfo() functions to obtain the length of the largest - lookbehind in the pattern. This length is given in characters, not - bytes. If you always retain at least that many characters before the - partially matched string, all should be well. (Of course, near the + pcre[16|32]_fullinfo() functions to obtain the length of the longest + lookbehind in the pattern. This length is given in characters, not + bytes. If you always retain at least that many characters before the + partially matched string, all should be well. (Of course, near the start of the subject, fewer characters may be present; in that case all characters should be retained.) + From release 8.33, there is a more accurate way of deciding which char- + acters to retain. Instead of subtracting the length of the longest + lookbehind from the earliest inspected character (offsets[0]), the + match start position (offsets[2]) should be used, and the next match + attempt started at the offsets[2] character by setting the startoffset + argument of pcre_exec() or pcre_dfa_exec(). + + For example, if the pattern "(?<=123)abc" is partially matched against + the string "xx123a", the three offset values returned are 2, 6, and 5. + This indicates that the matching process that gave a partial match + started at offset 5, but the characters "123a" were all inspected. The + maximum lookbehind for that pattern is 3, so taking that away from 5 + shows that we need only keep "123a", and the next match attempt can be + started at offset 3 (that is, at "a") when further characters have been + added. When the match start is not the earliest inspected character, + pcretest shows it explicitly: + + re> "(?<=123)abc" + data> xx123a\P\P + Partial match at offset 5: 123a + 3. Because a partial match must always contain at least one character, what might be considered a partial match of an empty string actually gives a "no match" result. For example: @@ -8654,18 +9133,18 @@ AUTHOR REVISION - Last updated: 24 June 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 02 July 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREPRECOMPILE(3) PCREPRECOMPILE(3) +PCREPRECOMPILE(3) Library Functions Manual PCREPRECOMPILE(3) + NAME PCRE - Perl-compatible regular expressions - SAVING AND RE-USING PRECOMPILED PCRE PATTERNS If you are running an application that uses a large number of regular @@ -8758,6 +9237,10 @@ RE-USING A PRECOMPILED PATTERN is used to pass this data, as described in the section on matching a pattern in the pcreapi documentation. + Warning: The tables that pcre_exec() and pcre_dfa_exec() use must be + the same as those that were used when the pattern was compiled. If this + is not the case, the behaviour is undefined. + 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 @@ -8789,18 +9272,18 @@ AUTHOR REVISION - Last updated: 24 June 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 12 November 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCREPERFORM(3) PCREPERFORM(3) +PCREPERFORM(3) Library Functions Manual PCREPERFORM(3) + NAME PCRE - Perl-compatible regular expressions - PCRE PERFORMANCE Two aspects of performance are discussed below: memory usage and pro- @@ -8964,14 +9447,14 @@ REVISION ------------------------------------------------------------------------------ -PCREPOSIX(3) PCREPOSIX(3) +PCREPOSIX(3) Library Functions Manual PCREPOSIX(3) + NAME PCRE - Perl-compatible regular expressions. - -SYNOPSIS OF POSIX API +SYNOPSIS #include <pcreposix.h> @@ -8980,8 +9463,7 @@ SYNOPSIS OF POSIX API 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, + size_t regerror(int errcode, const regex_t *preg, char *errbuf, size_t errbuf_size); void regfree(regex_t *preg); @@ -9229,13 +9711,13 @@ REVISION ------------------------------------------------------------------------------ -PCRECPP(3) PCRECPP(3) +PCRECPP(3) Library Functions Manual PCRECPP(3) + NAME PCRE - Perl-compatible regular expressions. - SYNOPSIS OF C++ WRAPPER #include <pcrecpp.h> @@ -9572,13 +10054,13 @@ REVISION ------------------------------------------------------------------------------ -PCRESAMPLE(3) PCRESAMPLE(3) +PCRESAMPLE(3) Library Functions Manual PCRESAMPLE(3) + NAME PCRE - Perl-compatible regular expressions - PCRE SAMPLE PROGRAM A simple, complete demonstration program, to get you started with using @@ -9658,51 +10140,56 @@ REVISION Last updated: 10 January 2012 Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ -PCRELIMITS(3) PCRELIMITS(3) +PCRELIMITS(3) Library Functions Manual PCRELIMITS(3) + NAME PCRE - Perl-compatible regular expressions - 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, 32-bit units for the 32-bit + units (bytes for the 8-bit library, 16-bit units for the 16-bit library, and 32-bit units for the 32-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 - or 32-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 + with the default internal linkage size, which is 2 bytes for the 8-bit + and 16-bit libraries, and 4 bytes for the 32-bit library. 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 + or 32-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. + can be no more than 65535 capturing subpatterns. There is, however, a + limit to the depth of nesting of parenthesized subpatterns of all + kinds. This is imposed in order to limit the amount of system stack + used at compile time. The limit can be specified when PCRE is built; + the default is 250. There is a limit to the number of forward references to subsequent sub- - patterns 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 + patterns 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 name in a (*MARK), (*PRUNE), (*SKIP), or - (*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit and - 32-bit library. + The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or + (*THEN) verb is 255 for the 8-bit library and 65535 for the 16-bit and + 32-bit libraries. - The maximum length of a subject string is the largest positive number - that an integer variable can hold. However, when using the traditional + 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 indef- - inite repetition. This means that the available stack space may limit + inite 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. @@ -9716,18 +10203,18 @@ AUTHOR REVISION - Last updated: 04 May 2012 - Copyright (c) 1997-2012 University of Cambridge. + Last updated: 05 November 2013 + Copyright (c) 1997-2013 University of Cambridge. ------------------------------------------------------------------------------ -PCRESTACK(3) PCRESTACK(3) +PCRESTACK(3) Library Functions Manual PCRESTACK(3) + NAME PCRE - Perl-compatible regular expressions - PCRE DISCUSSION OF STACK USAGE When you call pcre[16|32]_exec(), it makes use of an internal function |