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diff --git a/ext/pcre/pcrelib/doc/pcre.txt b/ext/pcre/pcrelib/doc/pcre.txt index ac4254ec99..19f04f275a 100644 --- a/ext/pcre/pcrelib/doc/pcre.txt +++ b/ext/pcre/pcrelib/doc/pcre.txt @@ -25,11 +25,27 @@ INTRODUCTION items, and there is an option for requesting some minor changes that give better JavaScript compatibility. + Starting with release 8.30, it is possible to compile two separate PCRE + libraries: the original, which supports 8-bit character strings + (including UTF-8 strings), and a second library that supports 16-bit + character strings (including UTF-16 strings). The build process allows + either one or both to be built. The majority of the work to make this + possible was done by Zoltan Herczeg. + + The two libraries contain identical sets of functions, except that the + names in the 16-bit library start with pcre16_ instead of pcre_. To + avoid over-complication and reduce the documentation maintenance load, + most of the documentation describes the 8-bit library, with the differ- + ences for the 16-bit library described separately in the pcre16 page. + References to functions or structures of the form pcre[16]_xxx should + be read as meaning "pcre_xxx when using the 8-bit library and + pcre16_xxx when using the 16-bit library". + The current implementation of PCRE corresponds approximately with Perl - 5.12, including support for UTF-8 encoded strings and Unicode general - category properties. However, UTF-8 and Unicode support has to be - explicitly enabled; it is not the default. The Unicode tables corre- - spond to Unicode release 5.2.0. + 5.12, including support for UTF-8/16 encoded strings and Unicode gen- + eral category properties. However, UTF-8/16 and Unicode support has to + be explicitly enabled; it is not the default. The Unicode tables corre- + spond to Unicode release 6.0.0. In addition to the Perl-compatible matching function, PCRE contains an alternative function that matches the same compiled patterns in a dif- @@ -39,218 +55,401 @@ INTRODUCTION 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. This is now - included as part of the PCRE distribution. The pcrecpp page has details - of this interface. Other people's contributions can be found in the - Contrib directory at the primary FTP site, which is: + 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-UNIX-USE files in the source distribution. - The library 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_", 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. + The libraries contains a number of undocumented internal functions and + data tables that are used by more than one of the exported external + functions, but which are not intended for use by external callers. + Their names all begin with "_pcre_" or "_pcre16_", which hopefully will + not provoke any name clashes. In some environments, it is possible to + control which external symbols are exported when a shared library is + built, and in these cases the undocumented symbols are not exported. USER DOCUMENTATION - The user documentation for PCRE comprises a number of different sec- - tions. In the "man" format, each of these is a separate "man page". In - the HTML format, each is a separate page, linked from the index page. - In the plain text format, all the sections, except the pcredemo sec- + The user documentation for PCRE comprises a number of different sec- + tions. In the "man" format, each of these is a separate "man page". In + the HTML format, each is a separate page, linked from the index page. + In the plain text format, all the sections, except the pcredemo sec- tion, are concatenated, for ease of searching. The sections are as fol- lows: pcre this document + pcre16 details of the 16-bit library pcre-config show PCRE installation configuration information pcreapi details of PCRE's native C API pcrebuild options for building PCRE pcrecallout details of the callout feature pcrecompat discussion of Perl compatibility - pcrecpp details of the C++ wrapper + pcrecpp details of the C++ wrapper for the 8-bit library pcredemo a demonstration C program that uses PCRE - pcregrep description of the pcregrep command + pcregrep description of the pcregrep command (8-bit only) + pcrejit discussion of the just-in-time optimization support + pcrelimits details of size and other limits pcrematching discussion of the two matching algorithms pcrepartial details of the partial matching facility pcrepattern syntax and semantics of supported regular expressions pcreperform discussion of performance issues - pcreposix the POSIX-compatible C API + pcreposix the POSIX-compatible C API for the 8-bit library pcreprecompile details of saving and re-using precompiled patterns pcresample discussion of the pcredemo program pcrestack discussion of stack usage pcresyntax quick syntax reference pcretest description of the pcretest testing command + pcreunicode discussion of Unicode and UTF-8/16 support - In addition, in the "man" and HTML formats, there is a short page for - each C library function, listing its arguments and results. + In addition, in the "man" and HTML formats, there is a short page for + each 8-bit C library function, listing its arguments and results. -LIMITATIONS +AUTHOR - There are some size limitations in PCRE but it is hoped that they will - never in practice be relevant. + Philip Hazel + University Computing Service + Cambridge CB2 3QH, England. - The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE - is compiled with the default internal linkage size of 2. If you want to - process regular expressions that are truly enormous, you can compile - PCRE with an internal linkage size of 3 or 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. + 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. - 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. +REVISION - The maximum length of name for a named subpattern is 32 characters, and - the maximum number of named subpatterns is 10000. + Last updated: 10 January 2012 + Copyright (c) 1997-2012 University of Cambridge. +------------------------------------------------------------------------------ - 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 - the size of a subject string that can be processed by certain patterns. - For a discussion of stack issues, see the pcrestack documentation. +PCRE(3) PCRE(3) -UTF-8 AND UNICODE PROPERTY SUPPORT - From release 3.3, PCRE has had some support for character strings - encoded in the UTF-8 format. For release 4.0 this was greatly extended - to cover most common requirements, and in release 5.0 additional sup- - port for Unicode general category properties was added. +NAME + PCRE - Perl-compatible regular expressions - In order process UTF-8 strings, you must build PCRE to include UTF-8 - support in the code, and, in addition, you must call pcre_compile() - with the PCRE_UTF8 option flag, or the pattern must start with the - sequence (*UTF8). When either of these is the case, both the pattern - and any subject strings that are matched against it are treated as - UTF-8 strings instead of strings of 1-byte characters. + #include <pcre.h> - If you compile PCRE with UTF-8 support, but do not use it at run time, - the library will be a bit bigger, but the additional run time overhead - is limited to testing the PCRE_UTF8 flag occasionally, so should not be - very big. - If PCRE is built with Unicode character property support (which implies - UTF-8 support), the escape sequences \p{..}, \P{..}, and \X are sup- - ported. The available properties that can be tested are limited to the - general category properties such as Lu for an upper case letter or Nd - for a decimal number, the Unicode script names such as Arabic or Han, - and the derived properties Any and L&. A full list is given in the - pcrepattern documentation. Only the short names for properties are sup- - ported. For example, \p{L} matches a letter. Its Perl synonym, \p{Let- - ter}, is not supported. Furthermore, in Perl, many properties may - optionally be prefixed by "Is", for compatibility with Perl 5.6. PCRE - does not support this. +PCRE 16-BIT API BASIC FUNCTIONS - Validity of UTF-8 strings + pcre16 *pcre16_compile(PCRE_SPTR16 pattern, int options, + const char **errptr, int *erroffset, + const unsigned char *tableptr); - When you set the PCRE_UTF8 flag, the strings passed as patterns and - subjects are (by default) checked for validity on entry to the relevant - functions. From release 7.3 of PCRE, the check is according the rules - of RFC 3629, which are themselves derived from the Unicode specifica- - tion. Earlier releases of PCRE followed the rules of RFC 2279, which - allows the full range of 31-bit values (0 to 0x7FFFFFFF). The current - check allows only values in the range U+0 to U+10FFFF, excluding U+D800 - to U+DFFF. - - The excluded code points are the "Low Surrogate Area" of Unicode, of - which the Unicode Standard says this: "The Low Surrogate Area does not - contain any character assignments, consequently no character code - charts or namelists are provided for this area. Surrogates are reserved - for use with UTF-16 and then must be used in pairs." The code points - that are encoded by UTF-16 pairs are available as independent code - points in the UTF-8 encoding. (In other words, the whole surrogate - thing is a fudge for UTF-16 which unfortunately messes up UTF-8.) - - If an invalid UTF-8 string is passed to PCRE, an error return - (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know - that your strings are valid, and therefore want to skip these checks in - order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at - compile time or at run time, PCRE assumes that the pattern or subject - it is given (respectively) contains only valid UTF-8 codes. In this - case, it does not diagnose an invalid UTF-8 string. + pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options, + int *errorcodeptr, + const char **errptr, int *erroffset, + const unsigned char *tableptr); - If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, - what happens depends on why the string is invalid. If the string con- - forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a - string of characters in the range 0 to 0x7FFFFFFF. In other words, - apart from the initial validity test, PCRE (when in UTF-8 mode) handles - strings according to the more liberal rules of RFC 2279. However, if - the string does not even conform to RFC 2279, the result is undefined. - Your program may crash. + pcre16_extra *pcre16_study(const pcre16 *code, int options, + const char **errptr); - If you want to process strings of values in the full range 0 to - 0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you can - set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in - this situation, you will have to apply your own validity check. + void pcre16_free_study(pcre16_extra *extra); - General comments about UTF-8 mode + int pcre16_exec(const pcre16 *code, const pcre16_extra *extra, + PCRE_SPTR16 subject, int length, int startoffset, + int options, int *ovector, int ovecsize); - 1. An unbraced hexadecimal escape sequence (such as \xb3) matches a - two-byte UTF-8 character if the value is greater than 127. + int pcre16_dfa_exec(const pcre16 *code, const pcre16_extra *extra, + PCRE_SPTR16 subject, int length, int startoffset, + int options, int *ovector, int ovecsize, + int *workspace, int wscount); - 2. Octal numbers up to \777 are recognized, and match two-byte UTF-8 - characters for values greater than \177. - 3. Repeat quantifiers apply to complete UTF-8 characters, not to indi- - vidual bytes, for example: \x{100}{3}. +PCRE 16-BIT API STRING EXTRACTION FUNCTIONS - 4. The dot metacharacter matches one UTF-8 character instead of a sin- - gle byte. + int pcre16_copy_named_substring(const pcre16 *code, + PCRE_SPTR16 subject, int *ovector, + int stringcount, PCRE_SPTR16 stringname, + PCRE_UCHAR16 *buffer, int buffersize); - 5. The escape sequence \C can be used to match a single byte in UTF-8 - mode, but its use can lead to some strange effects. This facility is - not available in the alternative matching function, pcre_dfa_exec(). + int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector, + int stringcount, int stringnumber, PCRE_UCHAR16 *buffer, + int buffersize); - 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 before, all with values less than 256. This remains true even - when PCRE is built to include Unicode property support, because to do - otherwise would slow down PCRE in many common cases. Note in particular - that this applies to \b and \B, because they are defined in terms of \w - and \W. If you really want to test for a wider sense of, say, "digit", - you can use explicit Unicode property tests such as \p{Nd}. Alterna- - tively, if you set the PCRE_UCP option, the way that the character - escapes work is changed so that Unicode properties are used to deter- - mine which characters match. There are more details in the section on - generic character types in the pcrepattern documentation. + int pcre16_get_named_substring(const pcre16 *code, + PCRE_SPTR16 subject, int *ovector, + int stringcount, PCRE_SPTR16 stringname, + PCRE_SPTR16 *stringptr); - 7. Similarly, characters that match the POSIX named character classes - are all low-valued characters, unless the PCRE_UCP option is set. + int pcre16_get_stringnumber(const pcre16 *code, + PCRE_SPTR16 name); - 8. However, the horizontal and vertical whitespace matching escapes - (\h, \H, \v, and \V) do match all the appropriate Unicode characters, - whether or not PCRE_UCP is set. + int pcre16_get_stringtable_entries(const pcre16 *code, + PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last); - 9. Case-insensitive matching applies only to characters whose values - are less than 128, unless PCRE is built with Unicode property support. - Even when Unicode property support is available, PCRE still uses its - own character tables when checking the case of low-valued characters, - so as not to degrade performance. The Unicode property information is - used only for characters with higher values. Furthermore, PCRE supports - case-insensitive matching only when there is a one-to-one mapping - between a letter's cases. There are a small number of many-to-one map- - pings in Unicode; these are not supported by PCRE. + int pcre16_get_substring(PCRE_SPTR16 subject, int *ovector, + int stringcount, int stringnumber, + PCRE_SPTR16 *stringptr); + + int pcre16_get_substring_list(PCRE_SPTR16 subject, + int *ovector, int stringcount, PCRE_SPTR16 **listptr); + + void pcre16_free_substring(PCRE_SPTR16 stringptr); + + void pcre16_free_substring_list(PCRE_SPTR16 *stringptr); + + +PCRE 16-BIT API AUXILIARY FUNCTIONS + + pcre16_jit_stack *pcre16_jit_stack_alloc(int startsize, int maxsize); + + void pcre16_jit_stack_free(pcre16_jit_stack *stack); + + void pcre16_assign_jit_stack(pcre16_extra *extra, + pcre16_jit_callback callback, void *data); + + const unsigned char *pcre16_maketables(void); + + int pcre16_fullinfo(const pcre16 *code, const pcre16_extra *extra, + int what, void *where); + + int pcre16_refcount(pcre16 *code, int adjust); + + int pcre16_config(int what, void *where); + + const char *pcre16_version(void); + + int pcre16_pattern_to_host_byte_order(pcre16 *code, + pcre16_extra *extra, const unsigned char *tables); + + +PCRE 16-BIT API INDIRECTED FUNCTIONS + + void *(*pcre16_malloc)(size_t); + + void (*pcre16_free)(void *); + + void *(*pcre16_stack_malloc)(size_t); + + void (*pcre16_stack_free)(void *); + + int (*pcre16_callout)(pcre16_callout_block *); + + +PCRE 16-BIT API 16-BIT-ONLY FUNCTION + + int pcre16_utf16_to_host_byte_order(PCRE_UCHAR16 *output, + PCRE_SPTR16 input, int length, int *byte_order, + int keep_boms); + + +THE PCRE 16-BIT LIBRARY + + Starting with release 8.30, it is possible to compile a PCRE library + that supports 16-bit character strings, including UTF-16 strings, as + well as or instead of the original 8-bit library. The majority of the + work to make this possible was done by Zoltan Herczeg. The two + libraries contain identical sets of functions, used in exactly the same + way. Only the names of the functions and the data types of their argu- + ments and results are different. To avoid over-complication and reduce + the documentation maintenance load, most of the PCRE documentation + describes the 8-bit library, with only occasional references to the + 16-bit library. This page describes what is different when you use the + 16-bit library. + + WARNING: A single application can be linked with both libraries, but + you must take care when processing any particular pattern to use func- + tions from just one library. For example, if you want to study a pat- + tern that was compiled with pcre16_compile(), you must do so with + pcre16_study(), not pcre_study(), and you must free the study data with + pcre16_free_study(). + + +THE HEADER FILE + + There is only one header file, pcre.h. It contains prototypes for all + the functions in both libraries, as well as definitions of flags, + structures, error codes, etc. + + +THE LIBRARY NAME + + In Unix-like systems, the 16-bit library is called libpcre16, and can + normally be accesss by adding -lpcre16 to the command for linking an + application that uses PCRE. + + +STRING TYPES + + In the 8-bit library, strings are passed to PCRE library functions as + vectors of bytes with the C type "char *". In the 16-bit library, + strings are passed as vectors of unsigned 16-bit quantities. The macro + PCRE_UCHAR16 specifies an appropriate data type, and PCRE_SPTR16 is + defined as "const PCRE_UCHAR16 *". In very many environments, "short + int" is a 16-bit data type. When PCRE is built, it defines PCRE_UCHAR16 + as "short int", but checks that it really is a 16-bit data type. If it + is not, the build fails with an error message telling the maintainer to + modify the definition appropriately. + + +STRUCTURE TYPES + + The types of the opaque structures that are used for compiled 16-bit + patterns and JIT stacks are pcre16 and pcre16_jit_stack respectively. + The type of the user-accessible structure that is returned by + pcre16_study() is pcre16_extra, and the type of the structure that is + used for passing data to a callout function is pcre16_callout_block. + These structures contain the same fields, with the same names, as their + 8-bit counterparts. The only difference is that pointers to character + strings are 16-bit instead of 8-bit types. + + +16-BIT FUNCTIONS + + For every function in the 8-bit library there is a corresponding func- + tion in the 16-bit library with a name that starts with pcre16_ instead + of pcre_. The prototypes are listed above. In addition, there is one + extra function, pcre16_utf16_to_host_byte_order(). This is a utility + function that converts a UTF-16 character string to host byte order if + necessary. The other 16-bit functions expect the strings they are + passed to be in host byte order. + + The input and output arguments of pcre16_utf16_to_host_byte_order() may + point to the same address, that is, conversion in place is supported. + The output buffer must be at least as long as the input. + + The length argument specifies the number of 16-bit data units in the + input string; a negative value specifies a zero-terminated string. + + If byte_order is NULL, it is assumed that the string starts off in host + byte order. This may be changed by byte-order marks (BOMs) anywhere in + the string (commonly as the first character). + + If byte_order is not NULL, a non-zero value of the integer to which it + points means that the input starts off in host byte order, otherwise + the opposite order is assumed. Again, BOMs in the string can change + this. The final byte order is passed back at the end of processing. + + If keep_boms is not zero, byte-order mark characters (0xfeff) are + copied into the output string. Otherwise they are discarded. + + The result of the function is the number of 16-bit units placed into + the output buffer, including the zero terminator if the string was + zero-terminated. + + +SUBJECT STRING OFFSETS + + The offsets within subject strings that are returned by the matching + functions are in 16-bit units rather than bytes. + + +NAMED SUBPATTERNS + + The name-to-number translation table that is maintained for named sub- + patterns uses 16-bit characters. The pcre16_get_stringtable_entries() + function returns the length of each entry in the table as the number of + 16-bit data units. + + +OPTION NAMES + + There are two new general option names, PCRE_UTF16 and + PCRE_NO_UTF16_CHECK, which correspond to PCRE_UTF8 and + PCRE_NO_UTF8_CHECK in the 8-bit library. In fact, these new options + define the same bits in the options word. There is a discussion about + the validity of UTF-16 strings in the pcreunicode page. + + For the pcre16_config() function there is an option PCRE_CONFIG_UTF16 + that returns 1 if UTF-16 support is configured, otherwise 0. If this + option is given to pcre_config(), or if the PCRE_CONFIG_UTF8 option is + given to pcre16_config(), the result is the PCRE_ERROR_BADOPTION error. + + +CHARACTER CODES + + In 16-bit mode, when PCRE_UTF16 is not set, character values are + treated in the same way as in 8-bit, non UTF-8 mode, except, of course, + that they can range from 0 to 0xffff instead of 0 to 0xff. Character + types for characters less than 0xff can therefore be influenced by the + locale in the same way as before. Characters greater than 0xff have + only one case, and no "type" (such as letter or digit). + + In UTF-16 mode, the character code is Unicode, in the range 0 to + 0x10ffff, with the exception of values in the range 0xd800 to 0xdfff + because those are "surrogate" values that are used in pairs to encode + values greater than 0xffff. + + A UTF-16 string can indicate its endianness by special code knows as a + byte-order mark (BOM). The PCRE functions do not handle this, expecting + strings to be in host byte order. A utility function called + pcre16_utf16_to_host_byte_order() is provided to help with this (see + above). + + +ERROR NAMES + + The errors PCRE_ERROR_BADUTF16_OFFSET and PCRE_ERROR_SHORTUTF16 corre- + spond to their 8-bit counterparts. The error PCRE_ERROR_BADMODE is + given when a compiled pattern is passed to a function that processes + patterns in the other mode, for example, if a pattern compiled with + pcre_compile() is passed to pcre16_exec(). + + There are new error codes whose names begin with PCRE_UTF16_ERR for + invalid UTF-16 strings, corresponding to the PCRE_UTF8_ERR codes for + UTF-8 strings that are described in the section entitled "Reason codes + for invalid UTF-8 strings" in the main pcreapi page. The UTF-16 errors + are: + + PCRE_UTF16_ERR1 Missing low surrogate at end of string + PCRE_UTF16_ERR2 Invalid low surrogate follows high surrogate + PCRE_UTF16_ERR3 Isolated low surrogate + PCRE_UTF16_ERR4 Invalid character 0xfffe + + +ERROR TEXTS + + If there is an error while compiling a pattern, the error text that is + passed back by pcre16_compile() or pcre16_compile2() is still an 8-bit + character string, zero-terminated. + + +CALLOUTS + + The subject and mark fields in the callout block that is passed to a + callout function point to 16-bit vectors. + + +TESTING + + The pcretest program continues to operate with 8-bit input and output + files, but it can be used for testing the 16-bit library. If it is run + with the command line option -16, patterns and subject strings are con- + verted from 8-bit to 16-bit before being passed to PCRE, and the 16-bit + library functions are used instead of the 8-bit ones. Returned 16-bit + strings are converted to 8-bit for output. If the 8-bit library was not + compiled, pcretest defaults to 16-bit and the -16 option is ignored. + + When PCRE is being built, the RunTest script that is called by "make + check" uses the pcretest -C option to discover which of the 8-bit and + 16-bit libraries has been built, and runs the tests appropriately. + + +NOT SUPPORTED IN 16-BIT MODE + + Not all the features of the 8-bit library are available with the 16-bit + library. The C++ and POSIX wrapper functions support only the 8-bit + library, and the pcregrep program is at present 8-bit only. AUTHOR @@ -259,15 +458,11 @@ 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, - followed by the two digits 10, at the domain cam.ac.uk. - REVISION - Last updated: 13 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 14 April 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -307,46 +502,89 @@ PCRE BUILD-TIME OPTIONS is not described. +BUILDING 8-BIT and 16-BIT LIBRARIES + + By default, a library called libpcre is built, containing functions + that take string arguments contained in vectors of bytes, either as + single-byte characters, or interpreted as UTF-8 strings. You can also + build a separate library, called libpcre16, in which strings are con- + tained in vectors of 16-bit data units and interpreted either as sin- + gle-unit characters or UTF-16 strings, by adding + + --enable-pcre16 + + to the configure command. If you do not want the 8-bit library, add + + --disable-pcre8 + + as well. At least one of the two libraries must be built. Note that the + C++ and POSIX wrappers are for the 8-bit library only, and that pcre- + grep is an 8-bit program. None of these are built if you select only + the 16-bit library. + + +BUILDING SHARED AND STATIC LIBRARIES + + The PCRE building process uses libtool to build both shared and static + Unix libraries by default. You can suppress one of these by adding one + of + + --disable-shared + --disable-static + + to the configure command, as required. + + C++ SUPPORT - By default, the configure script will search for a C++ compiler and C++ - header files. If it finds them, it automatically builds the C++ wrapper - library for PCRE. You can disable this by adding + By default, if the 8-bit library is being built, the configure script + will search for a C++ compiler and C++ header files. If it finds them, + it automatically builds the C++ wrapper library (which supports only + 8-bit strings). You can disable this by adding --disable-cpp to the configure command. -UTF-8 SUPPORT +UTF-8 and UTF-16 SUPPORT + + To build PCRE with support for UTF Unicode character strings, add - To build PCRE with support for UTF-8 Unicode character strings, add + --enable-utf - --enable-utf8 + to the configure command. This setting applies to both libraries, + adding support for UTF-8 to the 8-bit library and support for UTF-16 to + the 16-bit library. There are no separate options for enabling UTF-8 + and UTF-16 independently because that would allow ridiculous settings + such as requesting UTF-16 support while building only the 8-bit + library. It is not possible to build one library with UTF support and + the other without in the same configuration. (For backwards compatibil- + ity, --enable-utf8 is a synonym of --enable-utf.) - to the configure command. Of itself, this does not make PCRE treat - strings as UTF-8. As well as compiling PCRE with this option, you also - have have to set the PCRE_UTF8 option when you call the pcre_compile() - or pcre_compile2() functions. + Of itself, this setting does not make PCRE treat strings as UTF-8 or + UTF-16. As well as compiling PCRE with this option, you also have have + to set the PCRE_UTF8 or PCRE_UTF16 option when you call one of the pat- + tern compiling functions. - If you set --enable-utf8 when compiling in an EBCDIC environment, PCRE - expects its input to be either ASCII or UTF-8 (depending on the runtime - option). It is not possible to support both EBCDIC and UTF-8 codes in - the same version of the library. Consequently, --enable-utf8 and + If you set --enable-utf when compiling in an EBCDIC environment, PCRE + expects its input to be either ASCII or UTF-8 (depending on the run- + time option). It is not possible to support both EBCDIC and UTF-8 codes + in the same version of the library. Consequently, --enable-utf and --enable-ebcdic are mutually exclusive. UNICODE CHARACTER PROPERTY SUPPORT - UTF-8 support allows PCRE to process character values greater than 255 - in the strings that it handles. On its own, however, it does not pro- - vide any facilities for accessing the properties of such characters. If - you want to be able to use the pattern escapes \P, \p, and \X, which - refer to Unicode character properties, you must add + UTF support allows the libraries to process character codepoints up to + 0x10ffff in the strings that they handle. On its own, however, it does + not provide any facilities for accessing the properties of such charac- + ters. If you want to be able to use the pattern escapes \P, \p, and \X, + which refer to Unicode character properties, you must add --enable-unicode-properties - to the configure command. This implies UTF-8 support, even if you have + to the configure command. This implies UTF support, even if you have not explicitly requested it. Including Unicode property support adds around 30K of tables to the @@ -354,6 +592,23 @@ UNICODE CHARACTER PROPERTY SUPPORT are supported. Details are given in the pcrepattern documentation. +JUST-IN-TIME COMPILER SUPPORT + + Just-in-time compiler support is included in the build by specifying + + --enable-jit + + This support is available only for certain hardware architectures. If + this option is set for an unsupported architecture, a compile time + error occurs. See the pcrejit documentation for a discussion of JIT + usage. When JIT support is enabled, pcregrep automatically makes use of + it, unless you add + + --disable-pcregrep-jit + + to the "configure" command. + + CODE VALUE OF NEWLINE By default, PCRE interprets the linefeed (LF) character as indicating @@ -400,28 +655,16 @@ WHAT \R MATCHES functions are called. -BUILDING SHARED AND STATIC LIBRARIES - - The PCRE building process uses libtool to build both shared and static - Unix libraries by default. You can suppress one of these by adding one - of - - --disable-shared - --disable-static - - to the configure command, as required. - - POSIX MALLOC USAGE - When PCRE is called through the POSIX interface (see the pcreposix doc- - umentation), additional working storage is required for holding the - pointers to capturing substrings, because PCRE requires three integers - per substring, whereas the POSIX interface provides only two. If the - number of expected substrings is small, the wrapper function uses space - on the stack, because this is faster than using malloc() for each call. - The default threshold above which the stack is no longer used is 10; it - can be changed by adding a setting such as + When the 8-bit library is called through the POSIX interface (see the + pcreposix documentation), additional working storage is required for + holding the pointers to capturing substrings, because PCRE requires + three integers per substring, whereas the POSIX interface provides only + two. If the number of expected substrings is small, the wrapper func- + tion uses space on the stack, because this is faster than using mal- + loc() for each call. The default threshold above which the stack is no + longer used is 10; it can be changed by adding a setting such as --with-posix-malloc-threshold=20 @@ -435,107 +678,108 @@ HANDLING VERY LARGE PATTERNS nation metacharacter). By default, two-byte values are used for these offsets, leading to a maximum size for a compiled pattern of around 64K. This is sufficient to handle all but the most gigantic patterns. - Nevertheless, some people do want to process truyl enormous patterns, + Nevertheless, some people do want to process truly enormous patterns, so it is possible to compile PCRE to use three-byte or four-byte off- sets by adding a setting such as --with-link-size=3 - to the configure command. The value given must be 2, 3, or 4. Using - longer offsets slows down the operation of PCRE because it has to load - additional bytes when handling them. + to the configure command. The value given must be 2, 3, or 4. For the + 16-bit library, a value of 3 is rounded up to 4. Using longer offsets + slows down the operation of PCRE because it has to load additional data + when handling them. AVOIDING EXCESSIVE STACK USAGE When matching with the pcre_exec() function, PCRE implements backtrack- - ing by making recursive calls to an internal function called match(). - In environments where the size of the stack is limited, this can se- - verely limit PCRE's operation. (The Unix environment does not usually + ing by making recursive calls to an internal function called match(). + In environments where the size of the stack is limited, this can se- + verely limit PCRE's operation. (The Unix environment does not usually suffer from this problem, but it may sometimes be necessary to increase - the maximum stack size. There is a discussion in the pcrestack docu- - mentation.) An alternative approach to recursion that uses memory from - the heap to remember data, instead of using recursive function calls, - has been implemented to work round the problem of limited stack size. + the maximum stack size. There is a discussion in the pcrestack docu- + mentation.) An alternative approach to recursion that uses memory from + the heap to remember data, instead of using recursive function calls, + has been implemented to work round the problem of limited stack size. If you want to build a version of PCRE that works this way, add --disable-stack-for-recursion - to the configure command. With this configuration, PCRE will use the - pcre_stack_malloc and pcre_stack_free variables to call memory manage- - ment functions. By default these point to malloc() and free(), but you + to the configure command. With this configuration, PCRE will use the + pcre_stack_malloc and pcre_stack_free variables to call memory manage- + ment functions. By default these point to malloc() and free(), but you can replace the pointers so that your own functions are used instead. - Separate functions are provided rather than using pcre_malloc and - pcre_free because the usage is very predictable: the block sizes - requested are always the same, and the blocks are always freed in - reverse order. A calling program might be able to implement optimized - functions that perform better than malloc() and free(). PCRE runs + Separate functions are provided rather than using pcre_malloc and + pcre_free because the usage is very predictable: the block sizes + requested are always the same, and the blocks are always freed in + reverse order. A calling program might be able to implement optimized + functions that perform better than malloc() and free(). PCRE runs noticeably more slowly when built in this way. This option affects only the pcre_exec() function; it is not relevant for pcre_dfa_exec(). LIMITING PCRE RESOURCE USAGE - Internally, PCRE has a function called match(), which it calls repeat- - edly (sometimes recursively) when matching a pattern with the - pcre_exec() function. By controlling the maximum number of times this - function may be called during a single matching operation, a limit can - be placed on the resources used by a single call to pcre_exec(). The - limit can be changed at run time, as described in the pcreapi documen- - tation. The default is 10 million, but this can be changed by adding a + Internally, PCRE has a function called match(), which it calls repeat- + edly (sometimes recursively) when matching a pattern with the + pcre_exec() function. By controlling the maximum number of times this + function may be called during a single matching operation, a limit can + be placed on the resources used by a single call to pcre_exec(). The + limit can be changed at run time, as described in the pcreapi documen- + tation. The default is 10 million, but this can be changed by adding a setting such as --with-match-limit=500000 - to the configure command. This setting has no effect on the + to the configure command. This setting has no effect on the pcre_dfa_exec() matching function. - In some environments it is desirable to limit the depth of recursive + In some environments it is desirable to limit the depth of recursive calls of match() more strictly than the total number of calls, in order - to restrict the maximum amount of stack (or heap, if --disable-stack- + to restrict the maximum amount of stack (or heap, if --disable-stack- for-recursion is specified) that is used. A second limit controls this; - it defaults to the value that is set for --with-match-limit, which - imposes no additional constraints. However, you can set a lower limit + it defaults to the value that is set for --with-match-limit, which + imposes no additional constraints. However, you can set a lower limit by adding, for example, --with-match-limit-recursion=10000 - to the configure command. This value can also be overridden at run + to the configure command. This value can also be overridden at run time. CREATING CHARACTER TABLES AT BUILD TIME - PCRE uses fixed tables for processing characters whose code values are - less than 256. By default, PCRE is built with a set of tables that are - distributed in the file pcre_chartables.c.dist. These tables are for + PCRE uses fixed tables for processing characters whose code values are + less than 256. By default, PCRE is built with a set of tables that are + distributed in the file pcre_chartables.c.dist. These tables are for ASCII codes only. If you add --enable-rebuild-chartables - to the configure command, the distributed tables are no longer used. - Instead, a program called dftables is compiled and run. This outputs + to the configure command, the distributed tables are no longer used. + Instead, a program called dftables is compiled and run. This outputs the source for new set of tables, created in the default locale of your - C runtime system. (This method of replacing the tables does not work if - you are cross compiling, because dftables is run on the local host. If - you need to create alternative tables when cross compiling, you will + C run-time system. (This method of replacing the tables does not work + if you are cross compiling, because dftables is run on the local host. + If you need to create alternative tables when cross compiling, you will have to do so "by hand".) USING EBCDIC CODE - PCRE assumes by default that it will run in an environment where the - character code is ASCII (or Unicode, which is a superset of ASCII). - This is the case for most computer operating systems. PCRE can, how- + PCRE assumes by default that it will run in an environment where the + character code is ASCII (or Unicode, which is a superset of ASCII). + This is the case for most computer operating systems. PCRE can, how- ever, be compiled to run in an EBCDIC environment by adding --enable-ebcdic to the configure command. This setting implies --enable-rebuild-charta- - bles. You should only use it if you know that you are in an EBCDIC - environment (for example, an IBM mainframe operating system). The - --enable-ebcdic option is incompatible with --enable-utf8. + bles. You should only use it if you know that you are in an EBCDIC + environment (for example, an IBM mainframe operating system). The + --enable-ebcdic option is incompatible with --enable-utf. PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT @@ -548,10 +792,26 @@ PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT --enable-pcregrep-libbz2 to the configure command. These options naturally require that the rel- - evant libraries are installed on your system. Configuration will fail + evant libraries are installed on your system. Configuration will fail if they are not. +PCREGREP BUFFER SIZE + + pcregrep uses an internal buffer to hold a "window" on the file it is + scanning, in order to be able to output "before" and "after" lines when + it finds a match. The size of the buffer is controlled by a parameter + whose default value is 20K. The buffer itself is three times this size, + but because of the way it is used for holding "before" lines, the long- + est line that is guaranteed to be processable is the parameter size. + You can change the default parameter value by adding, for example, + + --with-pcregrep-bufsize=50K + + to the configure command. The caller of pcregrep can, however, override + this value by specifying a run-time option. + + PCRETEST OPTION FOR LIBREADLINE SUPPORT If you add @@ -585,7 +845,7 @@ PCRETEST OPTION FOR LIBREADLINE SUPPORT SEE ALSO - pcreapi(3), pcre_config(3). + pcreapi(3), pcre16, pcre_config(3). AUTHOR @@ -597,8 +857,8 @@ AUTHOR REVISION - Last updated: 29 September 2009 - Copyright (c) 1997-2009 University of Cambridge. + Last updated: 07 January 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -614,13 +874,15 @@ PCRE MATCHING ALGORITHMS This document describes the two different algorithms that are available in PCRE for matching a compiled regular expression against a given sub- ject string. The "standard" algorithm is the one provided by the - pcre_exec() function. This works in the same was as Perl's matching - function, and provides a Perl-compatible matching operation. + pcre_exec() and pcre16_exec() functions. These work in the same was as + Perl's matching function, and provide a Perl-compatible matching opera- + tion. The just-in-time (JIT) optimization that is described in the + pcrejit documentation is compatible with these functions. - An alternative algorithm is provided by the pcre_dfa_exec() function; - this operates in a different way, and is not Perl-compatible. It has - advantages and disadvantages compared with the standard algorithm, and - these are described below. + An alternative algorithm is provided by the pcre_dfa_exec() and + pcre16_dfa_exec() functions; they operate in a different way, and are + not Perl-compatible. This alternative has advantages and disadvantages + compared with the standard algorithm, and these are described below. When there is only one possible way in which a given subject string can match a pattern, the two algorithms give the same answer. A difference @@ -748,42 +1010,43 @@ THE ALTERNATIVE MATCHING ALGORITHM 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) matches a - single byte, even in UTF-8 mode, is not supported because the alterna- - tive algorithm moves through the subject string one character at a - time, for all active paths through the tree. + 7. The \C escape sequence, which (in the standard algorithm) always + matches a single data unit, even in UTF-8 or UTF-16 modes, is not sup- + ported 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 - once, and never needs to backtrack, it is possible to pass very long - subject strings to the matching function in several pieces, checking - for partial matching each time. Although it is possible to do multi- - segment matching using the standard algorithm (pcre_exec()), by retain- - ing partially matched substrings, it is more complicated. The pcrepar- - tial documentation gives details of partial matching and discusses - multi-segment matching. + 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 + 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- + cusses multi-segment matching. DISADVANTAGES OF THE ALTERNATIVE ALGORITHM The alternative algorithm suffers from a number of disadvantages: - 1. It is substantially slower than the standard algorithm. This is - partly because it has to search for all possible matches, but is also + 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. @@ -801,8 +1064,8 @@ AUTHOR REVISION - Last updated: 17 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 08 January 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -812,10 +1075,10 @@ PCREAPI(3) PCREAPI(3) NAME PCRE - Perl-compatible regular expressions + #include <pcre.h> -PCRE NATIVE API - #include <pcre.h> +PCRE NATIVE API BASIC FUNCTIONS pcre *pcre_compile(const char *pattern, int options, const char **errptr, int *erroffset, @@ -829,6 +1092,8 @@ PCRE NATIVE API pcre_extra *pcre_study(const pcre *code, int options, const char **errptr); + void pcre_free_study(pcre_extra *extra); + int pcre_exec(const pcre *code, const pcre_extra *extra, const char *subject, int length, int startoffset, int options, int *ovector, int ovecsize); @@ -838,6 +1103,9 @@ PCRE NATIVE API int options, int *ovector, int ovecsize, int *workspace, int wscount); + +PCRE NATIVE API STRING EXTRACTION FUNCTIONS + int pcre_copy_named_substring(const pcre *code, const char *subject, int *ovector, int stringcount, const char *stringname, @@ -869,18 +1137,32 @@ PCRE NATIVE API void pcre_free_substring_list(const char **stringptr); + +PCRE NATIVE API AUXILIARY FUNCTIONS + + pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize); + + void pcre_jit_stack_free(pcre_jit_stack *stack); + + void pcre_assign_jit_stack(pcre_extra *extra, + pcre_jit_callback callback, void *data); + const unsigned char *pcre_maketables(void); int pcre_fullinfo(const pcre *code, const pcre_extra *extra, int what, void *where); - int pcre_info(const pcre *code, int *optptr, int *firstcharptr); - int pcre_refcount(pcre *code, int adjust); int pcre_config(int what, void *where); - char *pcre_version(void); + const char *pcre_version(void); + + int pcre_pattern_to_host_byte_order(pcre *code, + pcre_extra *extra, const unsigned char *tables); + + +PCRE NATIVE API INDIRECTED FUNCTIONS void *(*pcre_malloc)(size_t); @@ -893,46 +1175,80 @@ PCRE NATIVE API int (*pcre_callout)(pcre_callout_block *); +PCRE 8-BIT AND 16-BIT LIBRARIES + + From release 8.30, PCRE can be compiled as a library for handling + 16-bit character strings as well as, or instead of, the original + library that handles 8-bit character strings. To avoid too much compli- + cation, this document describes the 8-bit versions of the functions, + with only occasional references to the 16-bit library. + + The 16-bit functions operate in the same way as their 8-bit counter- + parts; they just use different data types for their arguments and + results, and their names start with pcre16_ instead of pcre_. For every + option that has UTF8 in its name (for example, PCRE_UTF8), there is a + corresponding 16-bit name with UTF8 replaced by UTF16. This facility is + in fact just cosmetic; the 16-bit option names define the same bit val- + 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, unless specified otherwise. More details of the specific dif- + ferences for the 16-bit library are given in the pcre16 page. + + PCRE API OVERVIEW PCRE has its own native API, which is described in this document. There - are also some wrapper functions that correspond to the POSIX regular - expression API. These are described in the pcreposix documentation. - Both of these APIs define a set of C function calls. A C++ wrapper is - 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 systems the 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 num- - bers for the library. Applications can use these to include support + 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 + macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release + numbers for the library. Applications can use these to include support for different releases of PCRE. In a Windows environment, if you want to statically link an application - program against a non-dll pcre.a file, you must define PCRE_STATIC - before including pcre.h or pcrecpp.h, because otherwise the pcre_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 + be built in appropriate hardware environments. It greatly speeds up the + matching performance of many patterns. Simple programs can easily + request that it be used if available, by setting an option that is + ignored when it is not relevant. More complicated programs might need + to make use of the functions pcre_jit_stack_alloc(), + pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control + the JIT code's memory usage. These functions are discussed in the + pcrejit documentation. + A second matching function, pcre_dfa_exec(), which is not Perl-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: @@ -947,103 +1263,106 @@ 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; pcre_info() is an obsolete version that returns only - some of the available information, but is retained for backwards com- - patibility. The function pcre_version() returns a pointer to a string - containing the version of PCRE and its date of release. + 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 - tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line + 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 + 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. However, compiling a regular expression - with one version of PCRE for use with a different version is not guar- - anteed to work and may cause crashes. + 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. CHECKING BUILD-TIME OPTIONS @@ -1057,72 +1376,99 @@ CHECKING BUILD-TIME OPTIONS 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 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. + able; otherwise it is set to zero. If this option is given to the + 16-bit version of this function, pcre16_config(), the result is + PCRE_ERROR_BADOPTION. + + PCRE_CONFIG_UTF16 + + The output is an integer that is set to one if UTF-16 support is avail- + 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 version of this function, the result is PCRE_ERROR_BADOP- + TION. PCRE_CONFIG_UNICODE_PROPERTIES The output is an integer that is set to one if support for Unicode character properties is available; otherwise it is set to zero. + PCRE_CONFIG_JIT + + The output is an integer that is set to one if support for just-in-time + compiling is available; otherwise it is set to zero. + + PCRE_CONFIG_JITTARGET + + The output is a pointer to a zero-terminated "const char *" string. If + JIT support is available, the string contains the name of the architec- + 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 four values that + The output is an integer whose value specifies the default character + sequence that is recognized as meaning "newline". The four values that are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, - and -1 for ANY. Though they are derived from ASCII, the same values + and -1 for ANY. Though they are derived from ASCII, the same values are returned in EBCDIC environments. 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 - internal linkage in compiled regular expressions. The value is 2, 3, or - 4. Larger values allow larger regular expressions to be compiled, at - the expense of slower matching. 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. + The output is an integer that contains the number of bytes used for + internal linkage in compiled regular expressions. For the 8-bit + library, the value can be 2, 3, or 4. For the 16-bit library, the value + is either 2 or 4 and is still a number of bytes. The default value of 2 + is sufficient for all but the most massive patterns, since it allows + the compiled pattern to be up to 64K in size. Larger values allow + larger regular expressions to be compiled, at the expense of slower + matching. PCRE_CONFIG_POSIX_MALLOC_THRESHOLD - The output is an integer that contains the threshold above which the - POSIX interface uses malloc() for output vectors. Further details are + The output is an integer that contains the threshold above which the + POSIX interface uses malloc() for output vectors. Further details are given in the pcreposix documentation. PCRE_CONFIG_MATCH_LIMIT - The output is a long integer that gives the default limit for the num- - ber of internal matching function calls in a pcre_exec() execution. + The output is a long integer that gives the default limit for the num- + ber of internal matching function calls in a pcre_exec() execution. Further details are given with pcre_exec() below. PCRE_CONFIG_MATCH_LIMIT_RECURSION The output is a long integer that gives the default limit for the depth - of recursion when calling the internal matching function in a - pcre_exec() execution. Further details are given with pcre_exec() + of recursion when calling the internal matching function in a + pcre_exec() execution. Further details are given with pcre_exec() below. PCRE_CONFIG_STACKRECURSE - The output is an integer that is set to one if internal recursion when + The output is an integer that is set to one if internal recursion when running pcre_exec() is implemented by recursive function calls that use - the stack to remember their state. This is the usual way that PCRE is + the stack to remember their state. This is the usual way that PCRE is compiled. The output is zero if PCRE was compiled to use blocks of data - on the heap instead of recursive function calls. In this case, - pcre_stack_malloc and pcre_stack_free are called to manage memory + on the heap instead of recursive function calls. In this case, + pcre_stack_malloc and pcre_stack_free are called to manage memory blocks on the heap, thus avoiding the use of the stack. @@ -1139,65 +1485,65 @@ COMPILING A PATTERN Either of the functions pcre_compile() or pcre_compile2() can be called to compile a pattern into an internal form. The only difference between - the two interfaces is that pcre_compile2() has an additional argument, - errorcodeptr, via which a numerical error code can be returned. To - avoid too much repetition, we refer just to pcre_compile() below, but + the two interfaces is that pcre_compile2() has an additional argument, + errorcodeptr, via which a numerical error code can be returned. To + avoid too much repetition, we refer just to pcre_compile() below, but the information applies equally to pcre_compile2(). The pattern is a C string terminated by a binary zero, and is passed in - the pattern argument. A pointer to a single block of memory that is - obtained via pcre_malloc is returned. This contains the compiled code + the pattern argument. A pointer to a single block of memory that is + obtained via pcre_malloc is returned. This contains the compiled code and related data. The pcre type is defined for the returned block; this is a typedef for a structure whose contents are not externally defined. It is up to the caller to free the memory (via pcre_free) when it is no longer required. - Although the compiled code of a PCRE regex is relocatable, that is, it + Although the compiled code of a PCRE regex is relocatable, that is, it does not depend on memory location, the complete pcre data block is not - fully relocatable, because it may contain a copy of the tableptr argu- + fully relocatable, because it may contain a copy of the tableptr argu- ment, which is an address (see below). The options argument contains various bit settings that affect the com- - pilation. It should be zero if no options are required. The available - options are described below. Some of them (in particular, those that - are compatible with Perl, but some others as well) can also be set and - unset from within the pattern (see the detailed description in the - pcrepattern documentation). For those options that can be different in - different parts of the pattern, the contents of the options argument + pilation. It should be zero if no options are required. The available + options are described below. Some of them (in particular, those that + are compatible with Perl, but some others as well) can also be set and + unset from within the pattern (see the detailed description in the + pcrepattern documentation). For those options that can be different in + different parts of the pattern, the contents of the options argument specifies their settings at the start of compilation and execution. The - PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and - PCRE_NO_START_OPT options can be set at the time of matching as well as - at compile time. + PCRE_ANCHORED, PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and + PCRE_NO_START_OPTIMIZE options can be set at the time of matching as + well as at compile time. If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise, - if compilation of a pattern fails, pcre_compile() returns NULL, and + if compilation of a pattern fails, pcre_compile() returns NULL, and 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. The offset from the start of the pattern to the byte - that was being processed when the error was discovered is placed in the - variable pointed to by erroffset, which must not be NULL. If it is, an - immediate error is given. Some errors are not detected until checks are - carried out when the whole pattern has been scanned; in this case the - offset is set to the end of the pattern. - + try to free it. Normally, the offset from the start of the pattern to + the byte that was being processed when the error was discovered is + placed in the variable pointed to by erroffset, which must not be NULL + (if it is, an immediate error is given). However, for an invalid UTF-8 + string, the offset is that of the first byte of the failing character. + + Some errors are not detected until the whole pattern has been scanned; + in these cases, the offset passed back is the length of the pattern. Note that the offset is in bytes, not characters, even in UTF-8 mode. - It may point into the middle of a UTF-8 character (for example, when - PCRE_ERROR_BADUTF8 is returned for an invalid UTF-8 string). + It may sometimes point into the middle of a UTF-8 character. - 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 - via this argument in the event of an error. This is in addition to the + 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 + via this argument in the event of an error. This is in addition to the textual error message. Error codes and messages are listed below. - If the final argument, tableptr, is NULL, PCRE uses a default set of - character tables that are built when PCRE is compiled, using the - default C locale. Otherwise, tableptr must be an address that is the - result of a call to pcre_maketables(). This value is stored with the - compiled pattern, and used again by pcre_exec(), unless another table + If the final argument, tableptr, is NULL, PCRE uses a default set of + character tables that are built when PCRE is compiled, using the + default C locale. Otherwise, tableptr must be an address that is the + result of a call to pcre_maketables(). This value is stored with the + compiled pattern, and used again by pcre_exec(), unless another table pointer is passed to it. For more discussion, see the section on locale support below. - This code fragment shows a typical straightforward call to pcre_com- + This code fragment shows a typical straightforward call to pcre_com- pile(): pcre *re; @@ -1210,147 +1556,161 @@ COMPILING A PATTERN &erroffset, /* for error offset */ NULL); /* use default character tables */ - The following names for option bits are defined in the pcre.h header + The following names for option bits are defined in the pcre.h header file: PCRE_ANCHORED If this bit is set, the pattern is forced to be "anchored", that is, it - is constrained to match only at the first matching point in the string - that is being searched (the "subject string"). This effect can also be - achieved by appropriate constructs in the pattern itself, which is the + is constrained to match only at the first matching point in the string + that is being searched (the "subject string"). This effect can also be + achieved by appropriate constructs in the pattern itself, which is the only way to do it in Perl. PCRE_AUTO_CALLOUT If this bit is set, pcre_compile() automatically inserts callout items, - all with number 255, before each pattern item. For discussion of the + all with number 255, before each pattern item. For discussion of the callout facility, see the pcrecallout documentation. PCRE_BSR_ANYCRLF PCRE_BSR_UNICODE These options (which are mutually exclusive) control what the \R escape - sequence matches. The choice is either to match only CR, LF, or CRLF, + sequence matches. The choice is either to match only CR, LF, or CRLF, or to match any Unicode newline sequence. The default is specified when PCRE is built. It can be overridden from within the pattern, or by set- ting an option when a compiled pattern is matched. PCRE_CASELESS - If this bit is set, letters in the pattern match both upper and lower - case letters. It is equivalent to Perl's /i option, and it can be - changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE - always understands the concept of case for characters whose values are - less than 128, so caseless matching is always possible. For characters - with higher values, the concept of case is supported if PCRE is com- - piled with Unicode property support, but not otherwise. If you want to - use caseless matching for characters 128 and above, you must ensure - that PCRE is compiled with Unicode property support as well as with + If this bit is set, letters in the pattern match both upper and lower + case letters. It is equivalent to Perl's /i option, and it can be + changed within a pattern by a (?i) option setting. In UTF-8 mode, PCRE + always understands the concept of case for characters whose values are + less than 128, so caseless matching is always possible. For characters + with higher values, the concept of case is supported if PCRE is com- + piled with Unicode property support, but not otherwise. If you want to + use caseless matching for characters 128 and above, you must ensure + that PCRE is compiled with Unicode property support as well as with UTF-8 support. PCRE_DOLLAR_ENDONLY - If this bit is set, a dollar metacharacter in the pattern matches only - at the end of the subject string. Without this option, a dollar also - matches immediately before a newline at the end of the string (but not - before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored - if PCRE_MULTILINE is set. There is no equivalent to this option in + If this bit is set, a dollar metacharacter in the pattern matches only + at the end of the subject string. Without this option, a dollar also + matches immediately before a newline at the end of the string (but not + before any other newlines). The PCRE_DOLLAR_ENDONLY option is ignored + if PCRE_MULTILINE is set. There is no equivalent to this option in Perl, and no way to set it within a pattern. PCRE_DOTALL - If this bit is set, a dot metacharacter in the pattern matches a char- + If this bit is set, a dot metacharacter in the pattern matches a char- acter of any value, including one that indicates a newline. However, it - only ever matches one character, even if newlines are coded as CRLF. - Without this option, a dot does not match when the current position is + only ever matches one character, even if newlines are coded as CRLF. + Without this option, a dot does not match when the current position is at a newline. This option is equivalent to Perl's /s option, and it can - be changed within a pattern by a (?s) option setting. A negative class + be changed within a pattern by a (?s) option setting. A negative class such as [^a] always matches newline characters, independent of the set- ting of this option. PCRE_DUPNAMES - If this bit is set, names used to identify capturing subpatterns need + If this bit is set, names used to identify capturing subpatterns need not be unique. This can be helpful for certain types of pattern when it - is known that only one instance of the named subpattern can ever be - matched. There are more details of named subpatterns below; see also + is known that only one instance of the named subpattern can ever be + matched. There are more details of named subpatterns below; see also the pcrepattern documentation. PCRE_EXTENDED - If this bit is set, whitespace data characters in the pattern are - totally ignored except when escaped or inside a character class. White- + 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- + 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. - Which characters are interpreted as newlines is controlled by the - options passed to pcre_compile() or by a special sequence at the start - of the pattern, as described in the section entitled "Newline conven- + Which characters are interpreted as newlines is controlled by the + options passed to pcre_compile() or by a special sequence at the start + of the pattern, as described in the section entitled "Newline conven- tions" in the pcrepattern documentation. Note that the end of this type - of comment is a literal newline sequence in the pattern; escape + of comment is a literal newline sequence in the pattern; escape sequences that happen to represent a newline do not count. - This option makes it possible to include comments inside complicated - patterns. Note, however, that this applies only to data characters. - Whitespace characters may never appear within special character + This option makes it possible to include comments inside complicated + patterns. Note, however, that this applies only to data characters. + White space characters may never appear within special character sequences in a pattern, for example within the sequence (?( that intro- duces a conditional subpattern. PCRE_EXTRA - This option was invented in order to turn on additional functionality - of PCRE that is incompatible with Perl, but it is currently of very - little use. When set, any backslash in a pattern that is followed by a - letter that has no special meaning causes an error, thus reserving - these combinations for future expansion. By default, as in Perl, a - backslash followed by a letter with no special meaning is treated as a + This option was invented in order to turn on additional functionality + of PCRE that is incompatible with Perl, but it is currently of very + little use. When set, any backslash in a pattern that is followed by a + letter that has no special meaning causes an error, thus reserving + these combinations for future expansion. By default, as in Perl, a + backslash followed by a letter with no special meaning is treated as a literal. (Perl can, however, be persuaded to give an error for this, by - running it with the -w option.) There are at present no other features - controlled by this option. It can also be set by a (?X) option setting + running it with the -w option.) There are at present no other features + controlled by this option. It can also be set by a (?X) option setting within a pattern. PCRE_FIRSTLINE - If this option is set, an unanchored pattern is required to match - before or at the first newline in the subject string, though the + If this option is set, an unanchored pattern is required to match + before or at the first newline in the subject string, though the matched text may continue over the newline. PCRE_JAVASCRIPT_COMPAT If this option is set, PCRE's behaviour is changed in some ways so that - it is compatible with JavaScript rather than Perl. The changes are as + it is compatible with JavaScript rather than Perl. The changes are as follows: - (1) A lone closing square bracket in a pattern causes a compile-time - error, because this is illegal in JavaScript (by default it is treated + (1) A lone closing square bracket in a pattern causes a compile-time + error, because this is illegal in JavaScript (by default it is treated as a data character). Thus, the pattern AB]CD becomes illegal when this option is set. - (2) At run time, a back reference to an unset subpattern group matches - an empty string (by default this causes the current matching alterna- - tive to fail). A pattern such as (\1)(a) succeeds when this option is - set (assuming it can find an "a" in the subject), whereas it fails by + (2) At run time, a back reference to an unset subpattern group matches + an empty string (by default this causes the current matching alterna- + tive to fail). A pattern such as (\1)(a) succeeds when this option is + set (assuming it can find an "a" in the subject), whereas it fails by default, for Perl compatibility. + (3) \U matches an upper case "U" character; by default \U causes a com- + pile time error (Perl uses \U to upper case subsequent characters). + + (4) \u matches a lower case "u" character unless it is followed by four + hexadecimal digits, in which case the hexadecimal number defines the + code point to match. By default, \u causes a compile time error (Perl + uses it to upper case the following character). + + (5) \x matches a lower case "x" character unless it is followed by two + hexadecimal digits, in which case the hexadecimal number defines the + code point to match. By default, as in Perl, a hexadecimal number is + always expected after \x, but it may have zero, one, or two digits (so, + for example, \xz matches a binary zero character followed by z). + PCRE_MULTILINE - By default, PCRE treats the subject string as consisting of a single - line of characters (even if it actually contains newlines). The "start - of line" metacharacter (^) matches only at the start of the string, - while the "end of line" metacharacter ($) matches only at the end of + By default, PCRE treats the subject string as consisting of a single + line of characters (even if it actually contains newlines). The "start + of line" metacharacter (^) matches only at the start of the string, + while the "end of line" metacharacter ($) 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 + 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_NEWLINE_CR @@ -1359,32 +1719,32 @@ COMPILING A PATTERN PCRE_NEWLINE_ANYCRLF PCRE_NEWLINE_ANY - These options override the default newline definition that was chosen - when PCRE was built. Setting the first or the second specifies that a - newline is indicated by a single character (CR or LF, respectively). - Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the - two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies + These options override the default newline definition that was chosen + when PCRE was built. Setting the first or the second specifies that a + newline is indicated by a single character (CR or LF, respectively). + Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the + two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three preceding sequences should be recognized. Setting - PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be + PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be recognized. The Unicode newline sequences are the three just mentioned, - plus the single characters VT (vertical tab, U+000B), FF (formfeed, - U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS - (paragraph separator, U+2029). The last two are recognized only in - UTF-8 mode. + 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). For the 8-bit library, the last two are + recognized only in UTF-8 mode. - The newline setting in the options word uses three bits that are + The newline setting in the options word uses three bits that are treated as a number, giving eight possibilities. Currently only six are - used (default plus the five values above). This means that if you set - more than one newline option, the combination may or may not be sensi- + used (default plus the five values above). This means that if you set + more than one newline option, the combination may or may not be sensi- ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to - PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and + PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and cause an error. - The only time that a line break in a pattern is specially recognized - when compiling is when PCRE_EXTENDED is set. CR and LF are whitespace - characters, and so are ignored in this mode. Also, an unescaped # out- - side a character class indicates a comment that lasts until after the - next line break sequence. In other circumstances, line break sequences + The only time that a line break in a pattern is specially recognized + when compiling is when PCRE_EXTENDED is set. CR and LF are white space + characters, and so are ignored in this mode. Also, an unescaped # out- + side a character class indicates a comment that lasts until after the + next line break sequence. In other circumstances, line break sequences in patterns are treated as literal data. The newline option that is set at compile time becomes the default that @@ -1393,66 +1753,67 @@ COMPILING A PATTERN PCRE_NO_AUTO_CAPTURE If this option is set, it disables the use of numbered capturing paren- - theses in the pattern. Any opening parenthesis that is not followed by - ? behaves as if it were followed by ?: but named parentheses can still - be used for capturing (and they acquire numbers in the usual way). + theses in the pattern. Any opening parenthesis that is not followed by + ? behaves as if it were followed by ?: but named parentheses can still + be used for capturing (and they acquire numbers in the usual way). There is no equivalent of this option in Perl. NO_START_OPTIMIZE - This is an option that acts at matching time; that is, it is really an - option for pcre_exec() or pcre_dfa_exec(). If it is set at compile - time, it is remembered with the compiled pattern and assumed at match- - ing time. For details see the discussion of 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. 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 - strings of UTF-8 characters instead of single-byte character strings. - However, it is available only when PCRE is built to include UTF-8 sup- - port. If not, the use of this option provokes an error. Details of how - this option changes the behaviour of PCRE are given in the section on - UTF-8 support in the main pcre page. + This option causes PCRE to regard both the pattern and the subject as + strings of UTF-8 characters instead of single-byte strings. However, it + is available only when PCRE is built to include UTF support. If not, + the use of this option provokes an error. Details of how this option + changes the behaviour of PCRE are given in the pcreunicode page. PCRE_NO_UTF8_CHECK When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is automatically checked. There is a discussion about the validity of - UTF-8 strings in the main pcre page. If an invalid UTF-8 sequence of - bytes is found, pcre_compile() returns an error. If you already know - that your pattern is valid, and you want to skip this check for perfor- - mance reasons, you can set the PCRE_NO_UTF8_CHECK option. When it is - set, the effect of passing an invalid UTF-8 string as a pattern is - undefined. It may cause your program to crash. Note that this option - can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the - UTF-8 validity checking of subject strings. + 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. 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. As PCRE has developed, some error codes have - fallen out of use. To avoid confusion, they have not been re-used. + both compiling functions. Note that error messages are always 8-bit + ASCII strings, even in 16-bit mode. As PCRE has developed, some error + codes have fallen out of use. To avoid confusion, they have not been + re-used. 0 no error 1 \ at end of pattern @@ -1486,26 +1847,26 @@ COMPILATION ERROR CODES 29 (?R or (?[+-]digits must be followed by ) 30 unknown POSIX class name 31 POSIX collating elements are not supported - 32 this version of PCRE is not compiled with PCRE_UTF8 support + 32 this version of PCRE is compiled without UTF support 33 [this code is not in use] 34 character value in \x{...} sequence is too large 35 invalid condition (?(0) 36 \C not allowed in lookbehind assertion - 37 PCRE does not support \L, \l, \N, \U, or \u + 37 PCRE does not support \L, \l, \N{name}, \U, or \u 38 number after (?C is > 255 39 closing ) for (?C expected 40 recursive call could loop indefinitely 41 unrecognized character after (?P 42 syntax error in subpattern name (missing terminator) 43 two named subpatterns have the same name - 44 invalid UTF-8 string + 44 invalid UTF-8 string (specifically UTF-8) 45 support for \P, \p, and \X has not been compiled 46 malformed \P or \p sequence 47 unknown property name after \P or \p 48 subpattern name is too long (maximum 32 characters) 49 too many named subpatterns (maximum 10000) 50 [this code is not in use] - 51 octal value is greater than \377 (not in UTF-8 mode) + 51 octal value is greater than \377 in 8-bit non-UTF-8 mode 52 internal error: overran compiling workspace 53 internal error: previously-checked referenced subpattern not found @@ -1524,7 +1885,17 @@ COMPILATION ERROR CODES 65 different names for subpatterns of the same number are not allowed 66 (*MARK) must have an argument - 67 this version of PCRE is not compiled with PCRE_UCP support + 67 this version of PCRE is not compiled with Unicode property + support + 68 \c must be followed by an ASCII character + 69 \k is not followed by a braced, angle-bracketed, or quoted name + 70 internal error: unknown opcode in find_fixedlength() + 71 \N is not supported in a class + 72 too many forward references + 73 disallowed Unicode code point (>= 0xd800 && <= 0xdfff) + 74 invalid UTF-16 string (specifically UTF-16) + 75 name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN) + 76 character value in \u.... sequence is too large 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. @@ -1553,8 +1924,26 @@ STUDYING A PATTERN wants to pass any of the other fields to pcre_exec() or pcre_dfa_exec(), it must set up its own pcre_extra block. - The second argument of pcre_study() contains option bits. At present, - no options are defined, and this argument should always be zero. + The second argument of pcre_study() contains option bits. There are + three options: + + 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 + other bits in the options argument must be zero. + + JIT compilation is a heavyweight optimization. It can take some time + for patterns to be analyzed, and for one-off matches and simple 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- + 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 @@ -1563,13 +1952,29 @@ STUDYING A PATTERN 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. - This is a typical call to pcre_study(): + 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 + to change to the new function when convenient. - pcre_extra *pe; - pe = pcre_study( + This is a typical way in which pcre_study() is used (except that in a + real application there should be tests for errors): + + int rc; + pcre *re; + pcre_extra *sd; + re = pcre_compile("pattern", 0, &error, &erroroffset, NULL); + sd = pcre_study( re, /* result of pcre_compile() */ - 0, /* no options exist */ + 0, /* no options */ &error); /* set to NULL or points to a message */ + rc = pcre_exec( /* see below for details of pcre_exec() options */ + re, sd, "subject", 7, 0, 0, ovector, 30); + ... + pcre_free_study(sd); + pcre_free(re); Studying a pattern does two things: first, a lower bound for the length of subject string that is needed to match the pattern is computed. This @@ -1582,70 +1987,73 @@ STUDYING A PATTERN Studying a pattern is also useful for non-anchored patterns that do not have a single fixed starting character. A bitmap of possible starting bytes is created. This speeds up finding a position in the subject at - which to start matching. + which to start matching. (In 16-bit mode, the bitmap is used for 16-bit + values less than 256.) - The two optimizations just described can be disabled by setting the - PCRE_NO_START_OPTIMIZE option when calling pcre_exec() or - pcre_dfa_exec(). You might want to do this if your pattern contains - callouts or (*MARK), and you want to make use of these facilities in - cases where matching fails. See the discussion of PCRE_NO_START_OPTI- - MIZE 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 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. 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 + 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 + 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- + 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 contains an internal set of tables that are used when the final - argument of pcre_compile() is NULL. These are sufficient for many + PCRE contains an internal set of tables that are used when the final + argument of pcre_compile() is NULL. These are sufficient for many applications. Normally, the internal tables recognize only ASCII char- acters. However, when PCRE is built, it is possible to cause the inter- nal tables to be rebuilt in the default "C" locale of the local system, which may cause them to be different. - The internal tables can always be overridden by tables supplied by the + The internal tables can always be overridden by tables supplied by the application that calls PCRE. These may be created in a different locale - from the default. As more and more applications change to using Uni- + from the default. As more and more applications change to using Uni- code, the need for this locale support is expected to die away. - External tables are built by calling the pcre_maketables() function, - which has no arguments, in the relevant locale. The result can then be - passed to pcre_compile() or pcre_exec() as often as necessary. For - example, to build and use tables that are appropriate for the French - locale (where accented characters with values greater than 128 are + External tables are built by calling the pcre_maketables() function, + which has no arguments, in the relevant locale. The result can then be + passed to pcre_compile() or pcre_exec() as often as necessary. For + example, to build and use tables that are appropriate for the French + locale (where accented characters with values greater than 128 are treated as letters), the following code could be used: setlocale(LC_CTYPE, "fr_FR"); tables = pcre_maketables(); re = pcre_compile(..., tables); - The locale name "fr_FR" is used on Linux and other Unix-like systems; + The locale name "fr_FR" is used on Linux and other Unix-like systems; if you are using Windows, the name for the French locale is "french". - When pcre_maketables() runs, the tables are built in memory that is - obtained via pcre_malloc. It is the caller's responsibility to ensure - that the memory containing the tables remains available for as long as + When pcre_maketables() runs, the tables are built in memory that is + obtained via pcre_malloc. It is the caller's responsibility to ensure + that the memory containing the tables remains available for as long as it is needed. The pointer that is passed to pcre_compile() is saved with the compiled - pattern, and the same tables are used via this pointer by pcre_study() + 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- tern, compilation, studying and matching all happen in the same locale, but different patterns can be compiled in different locales. - It is possible to pass a table pointer or NULL (indicating the use of - the internal tables) to pcre_exec(). Although not intended for this - purpose, this facility could be used to match a pattern in a different + 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. @@ -1655,32 +2063,35 @@ INFORMATION ABOUT A PATTERN int pcre_fullinfo(const pcre *code, const pcre_extra *extra, int what, void *where); - The pcre_fullinfo() function returns information about a compiled pat- - tern. It replaces the obsolete pcre_info() function, which is neverthe- - less retained for backwards compability (and is documented below). + The pcre_fullinfo() function returns information about a compiled pat- + tern. It replaces the pcre_info() function, which was removed from the + library at version 8.30, after more than 10 years of obsolescence. - The first argument for pcre_fullinfo() is a pointer to the compiled - pattern. The second argument is the result of pcre_study(), or NULL if - the pattern was not studied. The third argument specifies which piece - of information is required, and the fourth argument is a pointer to a - variable to receive the data. The yield of the function is zero for + The first argument for pcre_fullinfo() is a pointer to the compiled + pattern. The second argument is the result of pcre_study(), or NULL if + the pattern was not studied. The third argument specifies which piece + of information is required, and the fourth argument is a pointer to a + variable to receive the data. The yield of the function is zero for success, or one of the following negative numbers: - PCRE_ERROR_NULL the argument code was NULL - the argument where was NULL - PCRE_ERROR_BADMAGIC the "magic number" was not found - PCRE_ERROR_BADOPTION the value of what was invalid + PCRE_ERROR_NULL the argument code was NULL + the argument where was NULL + PCRE_ERROR_BADMAGIC the "magic number" was not found + PCRE_ERROR_BADENDIANNESS the pattern was compiled with different + endianness + PCRE_ERROR_BADOPTION the value of what was invalid - The "magic number" is placed at the start of each compiled pattern as - an simple check against passing an arbitrary memory pointer. Here is a - typical call of pcre_fullinfo(), to obtain the length of the compiled - pattern: + The "magic number" is placed at the start of each compiled pattern as + an simple check against passing an arbitrary memory pointer. The endi- + anness error can occur if a compiled pattern is saved and reloaded on a + different host. Here is a typical call of pcre_fullinfo(), to obtain + the length of the compiled pattern: int rc; size_t length; rc = pcre_fullinfo( re, /* result of pcre_compile() */ - pe, /* result of pcre_study(), or NULL */ + sd, /* result of pcre_study(), or NULL */ PCRE_INFO_SIZE, /* what is required */ &length); /* where to put the data */ @@ -1708,13 +2119,17 @@ INFORMATION ABOUT A PATTERN PCRE_INFO_FIRSTBYTE - Return information about the first byte of any matched string, for a - non-anchored pattern. The fourth argument should point to an int vari- - able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name - is still recognized for backwards compatibility.) + Return information about the first data unit of any matched string, for + a non-anchored pattern. (The name of this option refers to the 8-bit + library, where data units are bytes.) The fourth argument should point + to an int variable. - If there is a fixed first byte, for example, from a pattern such as - (cat|cow|coyote), its value is returned. Otherwise, if either + If there is a fixed first value, for example, the letter "c" from a + pattern such as (cat|cow|coyote), its value is returned. In the 8-bit + library, the value is always less than 256; in the 16-bit library the + value can be up to 0xffff. + + If there is no fixed first value, and if either (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch starts with "^", or @@ -1729,10 +2144,10 @@ INFORMATION ABOUT A PATTERN PCRE_INFO_FIRSTTABLE If the pattern was studied, and this resulted in the construction of a - 256-bit table indicating a fixed set of bytes for the first byte in any - matching string, a pointer to the table is returned. Otherwise NULL is - returned. The fourth argument should point to an unsigned char * vari- - able. + 256-bit table indicating a fixed set of values for the first data unit + in any matching string, a pointer to the table is returned. Otherwise + NULL is returned. The fourth argument should point to an unsigned char + * variable. PCRE_INFO_HASCRORLF @@ -1747,25 +2162,49 @@ INFORMATION ABOUT A PATTERN otherwise 0. The fourth argument should point to an int variable. (?J) and (?-J) set and unset the local PCRE_DUPNAMES option, respectively. + PCRE_INFO_JIT + + Return 1 if the pattern was studied with one of the JIT options, and + just-in-time compiling was successful. The fourth argument should point + to an int variable. A return value of 0 means that JIT support is not + available in this version of PCRE, or that the pattern was not studied + with a JIT option, or that the JIT compiler could not handle this par- + ticular pattern. See the pcrejit documentation for details of what can + and cannot be handled. + + PCRE_INFO_JITSIZE + + If the pattern was successfully studied with a JIT option, return the + size of the JIT compiled code, otherwise return zero. The fourth argu- + ment should point to a size_t variable. + PCRE_INFO_LASTLITERAL - Return the value of the rightmost literal byte that must exist in any - matched string, other than at its start, if such a byte has been + Return the value of the rightmost literal data unit that must exist in + any matched string, other than at its start, if such a value has been recorded. The fourth argument should point to an int variable. If there - is no such byte, -1 is returned. For anchored patterns, a last literal - byte is recorded only if it follows something of variable length. For + is no such value, -1 is returned. For anchored patterns, a last literal + value is recorded only if it follows something of variable length. For example, for the pattern /^a\d+z\d+/ the returned value is "z", but for /^a\dz\d/ the returned value is -1. + PCRE_INFO_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. + 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, not bytes (this may - be relevant in UTF-8 mode). The fourth argument should point to an int - variable. A non-negative value is a lower bound to the length of any - matching string. There may not be any strings of that length that do - actually match, but every string that does match is at least that long. + If the pattern was studied and a minimum length for matching subject + strings was computed, its value is returned. Otherwise the returned + value is -1. The value is a number of characters, which in UTF-8 mode + may be different from the number of bytes. The fourth argument should + point to an int variable. A non-negative value is a lower bound to the + length of any matching string. There may not be any strings of that + length that do actually match, but every string that does match is at + least that long. PCRE_INFO_NAMECOUNT PCRE_INFO_NAMEENTRYSIZE @@ -1785,10 +2224,12 @@ INFORMATION ABOUT A PATTERN gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each entry; both of these return an int value. The entry size depends on the length of the longest name. PCRE_INFO_NAMETABLE returns - a pointer to the first entry of the table (a pointer to char). The - first two bytes of each entry are the number of the capturing parenthe- - sis, most significant byte first. The rest of the entry is the corre- - sponding name, zero terminated. + a pointer to the first entry of the table. This is a pointer to char in + the 8-bit library, where the first two bytes of each entry are the 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. 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 @@ -1801,8 +2242,8 @@ INFORMATION ABOUT A PATTERN terns may have lower numbers. As a simple example of the name/number table, consider the following - pattern (assume PCRE_EXTENDED is set, so white space - including new- - lines - is ignored): + 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) ) @@ -1855,62 +2296,47 @@ INFORMATION ABOUT A PATTERN PCRE_INFO_SIZE - Return the size of the compiled pattern, that is, the value that was - passed as the argument to pcre_malloc() when PCRE was getting memory in - which to place the compiled data. The fourth argument should point to a - size_t variable. + 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. PCRE_INFO_STUDYSIZE - Return the size of the data block pointed to by the study_data field in - a pcre_extra block. That is, it is the value that was passed to - pcre_malloc() when PCRE was getting memory into which to place the data - created by pcre_study(). If pcre_extra is NULL, or there is no study - data, zero is returned. The fourth argument should point to a size_t - variable. - - -OBSOLETE INFO FUNCTION - - int pcre_info(const pcre *code, int *optptr, int *firstcharptr); - - The pcre_info() function is now obsolete because its interface is too - restrictive to return all the available data about a compiled pattern. - New programs should use pcre_fullinfo() instead. The yield of - pcre_info() is the number of capturing subpatterns, or one of the fol- - lowing negative numbers: - - PCRE_ERROR_NULL the argument code was NULL - PCRE_ERROR_BADMAGIC the "magic number" was not found - - If the optptr argument is not NULL, a copy of the options with which - the pattern was compiled is placed in the integer it points to (see - PCRE_INFO_OPTIONS above). - - If the pattern is not anchored and the firstcharptr argument is not - NULL, it is used to pass back information about the first character of - any matched string (see PCRE_INFO_FIRSTBYTE above). + 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). 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.) @@ -1920,18 +2346,22 @@ 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. 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 sec- - tion about the pcre_dfa_exec() function. + 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 + 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(): @@ -1950,35 +2380,40 @@ 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; void *study_data; + void *executable_jit; unsigned long int match_limit; unsigned long int match_limit_recursion; void *callout_data; const unsigned char *tables; unsigned char **mark; - The flags field is a bitmap that specifies which of the other fields - are set. The flag bits are: + In the 16-bit version of this structure, the mark field has type + "PCRE_UCHAR16 **". - PCRE_EXTRA_STUDY_DATA + The flags field is used to specify which of the other fields are set. + The flag bits are: + + PCRE_EXTRA_CALLOUT_DATA + PCRE_EXTRA_EXECUTABLE_JIT + PCRE_EXTRA_MARK PCRE_EXTRA_MATCH_LIMIT PCRE_EXTRA_MATCH_LIMIT_RECURSION - PCRE_EXTRA_CALLOUT_DATA + PCRE_EXTRA_STUDY_DATA PCRE_EXTRA_TABLES - PCRE_EXTRA_MARK - Other flag bits should be set to zero. The study_data field is set in - the pcre_extra block that is returned by pcre_study(), together with - the appropriate flag bit. You should not set this yourself, but you may - add to the block by setting the other fields and their corresponding - flag bits. + 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 @@ -1986,70 +2421,86 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION search trees. The classic example is a pattern that uses nested unlim- ited repeats. - Internally, PCRE uses a function called match() which it calls repeat- - edly (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. - - 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 + 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 + 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 exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT. - The match_limit_recursion field is similar to match_limit, but instead + The match_limit_recursion field is similar to match_limit, but instead of limiting the total number of times that match() is called, it limits - the depth of recursion. The recursion depth is a smaller number than - the total number of calls, because not all calls to match() are recur- + the depth of recursion. The recursion depth is a smaller number than + the total number of calls, because not all calls to match() are recur- sive. This limit is of use only if it is set smaller than match_limit. - Limiting the recursion depth limits the amount of stack that can be - used, or, when PCRE has been compiled to use memory on the heap instead - of the stack, the amount of heap memory that can be used. - - The default value for match_limit_recursion can be set when PCRE is - built; the default default is the same value as the default for - match_limit. You can override the default by suppling pcre_exec() with - a pcre_extra block in which match_limit_recursion is set, and - PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the + Limiting the recursion depth limits the amount of machine stack that + can be used, or, when PCRE has been compiled to use memory on the heap + instead of the stack, the amount of heap memory that can be used. This + limit is not relevant, and is ignored, when matching is done using JIT + compiled code. + + The default value for match_limit_recursion can be set when PCRE is + built; the default default is the same value as the default for + match_limit. You can override the default by suppling pcre_exec() with + a pcre_extra block in which match_limit_recursion is set, and + PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT. - The callout_data field is used in conjunction with the "callout" fea- + 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- + 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- + 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 char * 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 set to NULL. For details of the backtracking control verbs, see - the section entitled "Backtracking control" in the pcrepattern documen- - tation. + 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_SOFT, and - PCRE_PARTIAL_HARD. + 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 + (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 + interpretive code in pcre_exec() is run. PCRE_ANCHORED @@ -2172,7 +2623,9 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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. + 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. Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation. Consider the pattern @@ -2206,182 +2659,201 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8 string is automatically checked when pcre_exec() is subsequently - called. The value of startoffset is also checked to ensure that it - points to the start of a UTF-8 character. There is a discussion about - the validity of UTF-8 strings in the section on UTF-8 support in the - main pcre page. If an invalid UTF-8 sequence of bytes is found, - pcre_exec() returns the error PCRE_ERROR_BADUTF8 or, if PCRE_PAR- - TIAL_HARD is set and the problem is a truncated UTF-8 character at the - end of the subject, PCRE_ERROR_SHORTUTF8. If startoffset contains a - value that does not point to the start of a UTF-8 character (or to the - end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned. - - If you already know that your subject is valid, and you want to skip - these checks for performance reasons, you can set the - PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to - do this for the second and subsequent calls to pcre_exec() if you are - making repeated calls to find all the matches in a single subject - string. However, you should be sure that the value of startoffset - points to the start of a UTF-8 character (or the end of the subject). - When PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 - string as a subject or an invalid value of startoffset is undefined. - Your program may crash. + called. The entire string is checked before any other processing takes + place. The value of startoffset is also checked to ensure that it + points to the start of a UTF-8 character. There is a discussion about + the validity of UTF-8 strings in the pcreunicode page. If an invalid + sequence of bytes is found, pcre_exec() returns the error + PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a + truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In + both cases, information about the precise nature of the error may also + be returned (see the descriptions of these errors in the section enti- + tled Error return values from pcre_exec() below). If startoffset con- + tains a value that does not point to the start of a UTF-8 character (or + to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned. + + If you already know that your subject is valid, and you want to skip + these checks for performance reasons, you can set the + PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to + do this for the second and subsequent calls to pcre_exec() if you are + making repeated calls to find all the matches in a single subject + string. However, you should be sure that the value of startoffset + points to the start of a character (or the end of the subject). When + PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a + subject or an invalid value of startoffset is undefined. Your program + may crash. PCRE_PARTIAL_HARD PCRE_PARTIAL_SOFT - These options turn on the partial matching feature. For backwards com- - patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial - match occurs if the end of the subject string is reached successfully, - but there are not enough subject characters to complete the match. If + These options turn on the partial matching feature. For backwards com- + patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial + match occurs if the end of the subject string is reached successfully, + but there are not enough subject characters to complete the match. If this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, - matching continues by testing any remaining alternatives. Only if no - complete match can be found is PCRE_ERROR_PARTIAL returned instead of - PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the - caller is prepared to handle a partial match, but only if no complete + matching continues by testing any remaining alternatives. Only if no + complete match can be found is PCRE_ERROR_PARTIAL returned instead of + PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the + caller is prepared to handle a partial match, but only if no complete match can be found. - If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this - case, if a partial match is found, pcre_exec() immediately returns - PCRE_ERROR_PARTIAL, without considering any other alternatives. In - other words, when PCRE_PARTIAL_HARD is set, a partial match is consid- + If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this + case, if a partial match is found, pcre_exec() immediately returns + PCRE_ERROR_PARTIAL, without considering any other alternatives. In + other words, when PCRE_PARTIAL_HARD is set, a partial match is consid- ered to be more important that an alternative complete match. - In both cases, the portion of the string that was inspected when the + In both cases, the portion of the string that was inspected when the partial match was found is set as the first matching string. There is a - more detailed discussion of partial and multi-segment matching, with + more detailed discussion of partial and multi-segment matching, with examples, in the pcrepartial documentation. The string to be matched by pcre_exec() - The subject string is passed to pcre_exec() as a pointer in subject, a - length (in bytes) in length, and a starting byte offset in startoffset. - If this is negative or greater than the length of the subject, - pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is - zero, the search for a match starts at the beginning of the subject, + The subject string is passed to pcre_exec() as a pointer in subject, a + length in bytes in length, and a starting byte offset in startoffset. + If this is negative or greater than the length of the subject, + pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is + zero, the search for a match starts at the beginning of the subject, and this is by far the most common case. In UTF-8 mode, the byte offset - must point to the start of a UTF-8 character (or the end of the sub- - ject). Unlike the pattern string, the subject may contain binary zero + 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 + 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 + 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 + 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 the substring offsets are not of - interest, pcre_exec() may be called with ovector passed as NULL and - ovecsize as zero. However, if the pattern contains back references and - the ovector is not big enough to remember the related substrings, PCRE - has to get additional memory for use during matching. Thus it is usu- - ally 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 + match. For example, consider the pattern + + (a)(?:(b)c|bd) + + If a vector of 6 elements (allowing for only 1 captured substring) is + given with subject string "abd", pcre_exec() will try to set the second + captured string, thereby recording a vector overflow, before failing to + match "c" and backing up to try the second alternative. The zero + return, however, does correctly indicate that the maximum number of + slots (namely 2) have been filled. In similar cases where there is tem- + 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 of ovector that do not correspond to capturing parenthe- - ses in the pattern are never changed. That is, if a pattern contains n - capturing parentheses, no more than ovector[0] to ovector[2n+1] are set - by pcre_exec(). The other elements retain whatever values they previ- - ously had. + 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) @@ -2390,7 +2862,7 @@ 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) @@ -2399,76 +2871,82 @@ 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. However, if PCRE_PARTIAL_HARD is set and the problem is a - truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORT- - UTF8 is used instead. + 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), + 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 valid, 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) @@ -2478,7 +2956,7 @@ 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) @@ -2492,11 +2970,118 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION PCRE_ERROR_SHORTUTF8 (-25) - The subject string ended with an incomplete (truncated) UTF-8 charac- - ter, and the PCRE_PARTIAL_HARD option was set. Without this option, - PCRE_ERROR_BADUTF8 is returned in this situation. + 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 + position in the subject string. Some simple patterns that might do this + are detected and faulted at compile time, but more complicated cases, + in particular mutual recursions between two different subpatterns, 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 + pcrejit documentation for more details. + + PCRE_ERROR_BADMODE (-28) + + This error is given if a pattern that was compiled by the 8-bit library + is passed to a 16-bit library function, or vice versa. + + PCRE_ERROR_BADENDIANNESS (-29) + + This error is given if a pattern that was compiled and saved is + reloaded on a host with different endianness. The utility function + pcre_pattern_to_host_byte_order() can be used to convert such a pattern + so that it runs on the new host. + + Error numbers -16 to -20, -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 library is given in the pcre16 page. + + 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 + first output vector element (ovector[0]) and a reason code is placed in + the second element (ovector[1]). The reason codes are given names in + the pcre.h header file: + + PCRE_UTF8_ERR1 + PCRE_UTF8_ERR2 + PCRE_UTF8_ERR3 + PCRE_UTF8_ERR4 + PCRE_UTF8_ERR5 + + The string ends with a truncated UTF-8 character; the code specifies + how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 + characters to be no longer than 4 bytes, the encoding scheme (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 + PCRE_UTF8_ERR7 + PCRE_UTF8_ERR8 + PCRE_UTF8_ERR9 + PCRE_UTF8_ERR10 + + The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of + the character do not have the binary value 0b10 (that is, either the + most significant bit is 0, or the next bit is 1). - Error numbers -16 to -20 and -22 are not used by pcre_exec(). + PCRE_UTF8_ERR11 + PCRE_UTF8_ERR12 + + A character that is valid by the RFC 2279 rules is either 5 or 6 bytes + long; these code points are excluded by RFC 3629. + + PCRE_UTF8_ERR13 + + A 4-byte character has a value greater than 0x10fff; these code points + are excluded by RFC 3629. + + PCRE_UTF8_ERR14 + + A 3-byte character has a value in the range 0xd800 to 0xdfff; this + range of code points are reserved by RFC 3629 for use with UTF-16, and + so are excluded from UTF-8. + + PCRE_UTF8_ERR15 + PCRE_UTF8_ERR16 + PCRE_UTF8_ERR17 + PCRE_UTF8_ERR18 + PCRE_UTF8_ERR19 + + A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes + for a value that can be represented by fewer bytes, which is invalid. + For example, the two bytes 0xc0, 0xae give the value 0x2e, whose 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- + quent byte of a multi-byte character. + + PCRE_UTF8_ERR21 + + The first byte of a character has the value 0xfe or 0xff. These values + can never occur in a valid UTF-8 string. EXTRACTING CAPTURED SUBSTRINGS BY NUMBER @@ -2512,78 +3097,78 @@ EXTRACTING CAPTURED SUBSTRINGS BY NUMBER int pcre_get_substring_list(const char *subject, int *ovector, int stringcount, const char ***listptr); - Captured substrings can be accessed directly by using the offsets - returned by pcre_exec() in ovector. For convenience, the functions + Captured substrings can be accessed directly by using the offsets + returned by pcre_exec() in ovector. For convenience, the functions pcre_copy_substring(), pcre_get_substring(), and pcre_get_sub- - string_list() are provided for extracting captured substrings as new, - separate, zero-terminated strings. These functions identify substrings - by number. The next section describes functions for extracting named + string_list() are provided for extracting captured substrings as new, + separate, zero-terminated strings. These functions identify substrings + by number. The next section describes functions for extracting named substrings. - A substring that contains a binary zero is correctly extracted and has - a further zero added on the end, but the result is not, of course, a C - string. However, you can process such a string by referring to the - length that is returned by pcre_copy_substring() and pcre_get_sub- + A substring that contains a binary zero is correctly extracted and has + a further zero added on the end, but the result is not, of course, a C + string. However, you can process such a string by referring to the + length that is returned by pcre_copy_substring() and pcre_get_sub- string(). Unfortunately, the interface to pcre_get_substring_list() is - not adequate for handling strings containing binary zeros, because the + not adequate for handling strings containing binary zeros, because the end of the final string is not independently indicated. - The first three arguments are the same for all three of these func- - tions: subject is the subject string that has just been successfully + The first three arguments are the same for all three of these func- + tions: subject is the subject string that has just been successfully matched, ovector is a pointer to the vector of integer offsets that was passed to pcre_exec(), and stringcount is the number of substrings that - were captured by the match, including the substring that matched the + were captured by the match, including the substring that matched the entire regular expression. This is the value returned by pcre_exec() if - it is greater than zero. If pcre_exec() returned zero, indicating that - it ran out of space in ovector, the value passed as stringcount should + it is greater than zero. If pcre_exec() returned zero, indicating that + it ran out of space in ovector, the value passed as stringcount should be the number of elements in the vector divided by three. - The functions pcre_copy_substring() and pcre_get_substring() extract a - single substring, whose number is given as stringnumber. A value of - zero extracts the substring that matched the entire pattern, whereas - higher values extract the captured substrings. For pcre_copy_sub- - string(), the string is placed in buffer, whose length is given by - buffersize, while for pcre_get_substring() a new block of memory is - obtained via pcre_malloc, and its address is returned via stringptr. - The yield of the function is the length of the string, not including + The functions pcre_copy_substring() and pcre_get_substring() extract a + single substring, whose number is given as stringnumber. A value of + zero extracts the substring that matched the entire pattern, whereas + higher values extract the captured substrings. For pcre_copy_sub- + string(), the string is placed in buffer, whose length is given by + buffersize, while for pcre_get_substring() a new block of memory is + obtained via pcre_malloc, and its address is returned via stringptr. + The yield of the function is the length of the string, not including the terminating zero, or one of these error codes: PCRE_ERROR_NOMEMORY (-6) - The buffer was too small for pcre_copy_substring(), or the attempt to + The buffer was too small for pcre_copy_substring(), or the attempt to get memory failed for pcre_get_substring(). PCRE_ERROR_NOSUBSTRING (-7) There is no substring whose number is stringnumber. - The pcre_get_substring_list() function extracts all available sub- - strings and builds a list of pointers to them. All this is done in a + The pcre_get_substring_list() function extracts all available sub- + strings and builds a list of pointers to them. All this is done in a single block of memory that is obtained via pcre_malloc. The address of - the memory block is returned via listptr, which is also the start of - the list of string pointers. The end of the list is marked by a NULL - pointer. The yield of the function is zero if all went well, or the + the memory block is returned via listptr, which is also the start of + the list of string pointers. The end of the list is marked by a NULL + pointer. The yield of the function is zero if all went well, or the error code PCRE_ERROR_NOMEMORY (-6) if the attempt to get the memory block failed. - When any of these functions encounter a substring that is unset, which - can happen when capturing subpattern number n+1 matches some part of - the subject, but subpattern n has not been used at all, they return an + When any of these functions encounter a substring that is unset, which + can happen when capturing subpattern number n+1 matches some part of + the subject, but subpattern n has not been used at all, they return an empty string. This can be distinguished from a genuine zero-length sub- - string by inspecting the appropriate offset in ovector, which is nega- + string by inspecting the appropriate offset in ovector, which is nega- tive for unset substrings. - The two convenience functions pcre_free_substring() and pcre_free_sub- - string_list() can be used to free the memory returned by a previous + The two convenience functions pcre_free_substring() and pcre_free_sub- + string_list() can be used to free the memory returned by a previous call of pcre_get_substring() or pcre_get_substring_list(), respec- - tively. They do nothing more than call the function pointed to by - pcre_free, which of course could be called directly from a C program. - However, PCRE is used in some situations where it is linked via a spe- - cial interface to another programming language that cannot use - pcre_free directly; it is for these cases that the functions are pro- + tively. They do nothing more than call the function pointed to by + pcre_free, which of course could be called directly from a C program. + However, PCRE is used in some situations where it is linked via a spe- + cial interface to another programming language that cannot use + pcre_free directly; it is for these cases that the functions are pro- vided. @@ -2602,7 +3187,7 @@ EXTRACTING CAPTURED SUBSTRINGS BY NAME int stringcount, const char *stringname, const char **stringptr); - To extract a substring by name, you first have to find associated num- + To extract a substring by name, you first have to find associated num- ber. For example, for this pattern (a+)b(?<xxx>\d+)... @@ -2611,35 +3196,35 @@ EXTRACTING CAPTURED SUBSTRINGS BY NAME be unique (PCRE_DUPNAMES was not set), you can find the number from the name by calling pcre_get_stringnumber(). The first argument is the com- piled pattern, and the second is the name. The yield of the function is - the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no + the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of that name. Given the number, you can extract the substring directly, or use one of the functions described in the previous section. For convenience, there are also two functions that do the whole job. - Most of the arguments of pcre_copy_named_substring() and - pcre_get_named_substring() are the same as those for the similarly - named functions that extract by number. As these are described in the - previous section, they are not re-described here. There are just two + Most of the arguments of pcre_copy_named_substring() and + pcre_get_named_substring() are the same as those for the similarly + named functions that extract by number. As these are described in the + previous section, they are not re-described here. There are just two differences: - First, instead of a substring number, a substring name is given. Sec- + First, instead of a substring number, a substring name is given. Sec- ond, there is an extra argument, given at the start, which is a pointer - to the compiled pattern. This is needed in order to gain access to the + to the compiled pattern. This is needed in order to gain access to the name-to-number translation table. - These functions call pcre_get_stringnumber(), and if it succeeds, they - then call pcre_copy_substring() or pcre_get_substring(), as appropri- - ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the + These functions call pcre_get_stringnumber(), and if it succeeds, they + then call pcre_copy_substring() or pcre_get_substring(), as appropri- + ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the behaviour may not be what you want (see the next section). Warning: If the pattern uses the (?| feature to set up multiple subpat- - terns with the same number, as described in the section on duplicate - subpattern numbers in the pcrepattern page, you cannot use names to - distinguish the different subpatterns, because names are not included - in the compiled code. The matching process uses only numbers. For this - reason, the use of different names for subpatterns of the same number + terns with the same number, as described in the section on duplicate + subpattern numbers in the pcrepattern page, you cannot use names to + distinguish the different subpatterns, because names are not included + in the compiled code. The matching process uses only numbers. For this + reason, the use of different names for subpatterns of the same number causes an error at compile time. @@ -2648,54 +3233,79 @@ DUPLICATE SUBPATTERN NAMES int pcre_get_stringtable_entries(const pcre *code, const char *name, char **first, char **last); - When a pattern is compiled with the PCRE_DUPNAMES option, names for - subpatterns are not required to be unique. (Duplicate names are always - allowed for subpatterns with the same number, created by using the (?| - feature. Indeed, if such subpatterns are named, they are required to + When a pattern is compiled with the PCRE_DUPNAMES option, names for + subpatterns are not required to be unique. (Duplicate names are always + allowed for subpatterns with the same number, created by using the (?| + feature. Indeed, if such subpatterns are named, they are required to use the same names.) Normally, patterns with duplicate names are such that in any one match, - only one of the named subpatterns participates. An example is shown in + only one of the named subpatterns participates. An example is shown in the pcrepattern documentation. - When duplicates are present, pcre_copy_named_substring() and - pcre_get_named_substring() return the first substring corresponding to - the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING - (-7) is returned; no data is returned. The pcre_get_stringnumber() - function returns one of the numbers that are associated with the name, + When duplicates are present, pcre_copy_named_substring() and + pcre_get_named_substring() return the first substring corresponding to + the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING + (-7) is returned; no data is returned. The pcre_get_stringnumber() + function returns one of the numbers that are associated with the name, but it is not defined which it is. - If you want to get full details of all captured substrings for a given - name, you must use the pcre_get_stringtable_entries() function. The + If you want to get full details of all captured substrings for a given + name, you must use the pcre_get_stringtable_entries() function. The first argument is the compiled pattern, and the second is the name. The - third and fourth are pointers to variables which are updated by the + third and fourth are pointers to variables which are updated by the function. After it has run, they point to the first and last entries in - the name-to-number table for the given name. The function itself - returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if - there are none. The format of the table is described above in the sec- - tion entitled Information about a pattern. Given all the relevant - entries for the name, you can extract each of their numbers, and hence - the captured data, if any. + the name-to-number table for the given name. The function itself + returns the length of each entry, or PCRE_ERROR_NOSUBSTRING (-7) if + there are none. The format of the table is described above in the sec- + tion entitled Information about a pattern above. Given all the rele- + vant entries for the name, you can extract each of their numbers, and + hence the captured data, if any. FINDING ALL POSSIBLE MATCHES - The traditional matching function uses a similar algorithm to Perl, + The traditional matching function uses a similar algorithm to Perl, which stops when it finds the first match, starting at a given point in - the subject. If you want to find all possible matches, or the longest - possible match, consider using the alternative matching function (see - below) instead. If you cannot use the alternative function, but still - need to find all possible matches, you can kludge it up by making use + the subject. If you want to find all possible matches, or the longest + possible match, consider using the alternative matching function (see + below) instead. If you cannot use the alternative function, but still + need to find all possible matches, you can kludge it up by making use of the callout facility, which is described in the pcrecallout documen- tation. What you have to do is to insert a callout right at the end of the pat- - tern. When your callout function is called, extract and save the cur- - rent matched substring. Then return 1, which forces pcre_exec() to - backtrack and try other alternatives. Ultimately, when it runs out of + tern. When your callout function is called, extract and save the cur- + rent matched substring. Then return 1, which forces pcre_exec() to + backtrack and try other alternatives. Ultimately, when it runs out of matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. +OBTAINING AN ESTIMATE OF STACK USAGE + + Matching certain patterns using pcre_exec() can use a lot of process + stack, which in certain environments can be rather limited in size. + Some users find it helpful to have an estimate of the amount of stack + that is used by pcre_exec(), to help them set recursion limits, as + described in the pcrestack documentation. The estimate that is output + by pcretest when called with the -m and -C options is obtained by call- + ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its + first five arguments. + + Normally, if its first argument is NULL, pcre_exec() immediately + returns the negative error code PCRE_ERROR_NULL, but with this special + combination of arguments, it returns instead a negative number whose + absolute value is the approximate stack frame size in bytes. (A nega- + tive number is used so that it is clear that no match has happened.) + The value is approximate because in some cases, recursive calls to + pcre_exec() occur when there are one or two additional variables on the + stack. + + If PCRE has been compiled to use the heap instead of the stack for + recursion, the value returned is the size of each block that is + obtained from the heap. + + MATCHING A PATTERN: THE ALTERNATIVE FUNCTION int pcre_dfa_exec(const pcre *code, const pcre_extra *extra, @@ -2703,26 +3313,26 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION int options, int *ovector, int ovecsize, int *workspace, int wscount); - The function pcre_dfa_exec() is called to match a subject string - against a compiled pattern, using a matching algorithm that scans the - subject string just once, and does not backtrack. This has different - characteristics to the normal algorithm, and is not compatible with - Perl. Some of the features of PCRE patterns are not supported. Never- - theless, there are times when this kind of matching can be useful. For - a discussion of the two matching algorithms, and a list of features - that pcre_dfa_exec() does not support, see the pcrematching documenta- + The function pcre_dfa_exec() is called to match a subject string + against a compiled pattern, using a matching algorithm that scans the + subject string just once, and does not backtrack. This has different + characteristics to the normal algorithm, and is not compatible with + Perl. Some of the features of PCRE patterns are not supported. Never- + theless, there are times when this kind of matching can be useful. For + a discussion of the two matching algorithms, and a list of features + that pcre_dfa_exec() does not support, see the pcrematching documenta- tion. - The arguments for the pcre_dfa_exec() function are the same as for + The arguments for the pcre_dfa_exec() function are the same as for pcre_exec(), plus two extras. The ovector argument is used in a differ- - ent way, and this is described below. The other common arguments are - used in the same way as for pcre_exec(), so their description is not + ent way, and this is described below. The other common arguments are + used in the same way as for pcre_exec(), so their description is not repeated here. - The two additional arguments provide workspace for the function. The - workspace vector should contain at least 20 elements. It is used for + The two additional arguments provide workspace for the function. The + workspace vector should contain at least 20 elements. It is used for keeping track of multiple paths through the pattern tree. More - workspace will be needed for patterns and subjects where there are a + workspace will be needed for patterns and subjects where there are a lot of potential matches. Here is an example of a simple call to pcre_dfa_exec(): @@ -2744,55 +3354,55 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION Option bits for pcre_dfa_exec() - The unused bits of the options argument for pcre_dfa_exec() must be - zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW- + The unused bits of the options argument for pcre_dfa_exec() must be + zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEW- LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, - PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, - PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR- - TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last - four of these are exactly the same as for pcre_exec(), so their + PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, + PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR- + TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last + four of these are exactly the same as for pcre_exec(), so their description is not repeated here. PCRE_PARTIAL_HARD PCRE_PARTIAL_SOFT - These have the same general effect as they do for pcre_exec(), but the - details are slightly different. When PCRE_PARTIAL_HARD is set for - pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub- - ject is reached and there is still at least one matching possibility + These have the same general effect as they do for pcre_exec(), but the + details are slightly different. When PCRE_PARTIAL_HARD is set for + pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of the sub- + ject is reached and there is still at least one matching possibility that requires additional characters. This happens even if some complete matches have also been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end - of the subject is reached, there have been no complete matches, but - there is still at least one matching possibility. The portion of the - string that was inspected when the longest partial match was found is - set as the first matching string in both cases. There is a more - detailed discussion of partial and multi-segment matching, with exam- + of the subject is reached, there have been no complete matches, but + there is still at least one matching possibility. The portion of the + string that was inspected when the longest partial match was found is + set as the first matching string in both cases. There is a more + detailed discussion of partial and multi-segment matching, with exam- ples, in the pcrepartial documentation. PCRE_DFA_SHORTEST - Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to + Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as soon as it has found one match. Because of the way the alterna- - tive algorithm works, this is necessarily the shortest possible match + tive algorithm works, this is necessarily the shortest possible match at the first possible matching point in the subject string. PCRE_DFA_RESTART When pcre_dfa_exec() returns a partial match, it is possible to call it - again, with additional subject characters, and have it continue with - the same match. The PCRE_DFA_RESTART option requests this action; when - it is set, the workspace and wscount options must reference the same - vector as before because data about the match so far is left in them + again, with additional subject characters, and have it continue with + the same match. The PCRE_DFA_RESTART option requests this action; when + it is set, the workspace and wscount options must reference the same + vector as before because data about the match so far is left in them after a partial match. There is more discussion of this facility in the pcrepartial documentation. Successful returns from pcre_dfa_exec() - When pcre_dfa_exec() succeeds, it may have matched more than one sub- + When pcre_dfa_exec() succeeds, it may have matched more than one sub- string in the subject. Note, however, that all the matches from one run - of the function start at the same point in the subject. The shorter - matches are all initial substrings of the longer matches. For example, + of the function start at the same point in the subject. The shorter + matches are all initial substrings of the longer matches. For example, if the pattern <.*> @@ -2807,19 +3417,20 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION <something> <something else> <something> <something else> <something further> - On success, the yield of the function is a number greater than zero, - which is the number of matched substrings. The substrings themselves - are returned in ovector. Each string uses two elements; the first is - the offset to the start, and the second is the offset to the end. In - fact, all the strings have the same start offset. (Space could have - been saved by giving this only once, but it was decided to retain some - compatibility with the way pcre_exec() returns data, even though the + On success, the yield of the function is a number greater than zero, + which is the number of matched substrings. The substrings themselves + are returned in ovector. Each string uses two elements; the first is + the offset to the start, and the second is the offset to the end. In + fact, all the strings have the same start offset. (Space could have + been saved by giving this only once, but it was decided to retain some + compatibility with the way pcre_exec() returns data, even though the meaning of the strings is different.) The strings are returned in reverse order of length; that is, the long- - est matching string is given first. If there were too many matches to - fit into ovector, the yield of the function is zero, and the vector is - filled with the longest matches. + est matching string is given first. If there were too many matches to + fit into ovector, the yield of the function is zero, and the vector is + filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() + can use the entire ovector for returning matched strings. Error returns from pcre_dfa_exec() @@ -2843,26 +3454,35 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION 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 field. This is not supported - (it is meaningless). + 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 + checks fail, this error is given. + SEE ALSO - pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar- - tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3). + pcre16(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematch- + ing(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcresample(3), + pcrestack(3). AUTHOR @@ -2874,8 +3494,8 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 17 June 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -2890,24 +3510,27 @@ PCRE CALLOUTS int (*pcre_callout)(pcre_callout_block *); + int (*pcre16_callout)(pcre16_callout_block *); + PCRE provides a feature called "callout", which is a means of temporar- ily passing control to the caller of PCRE in the middle of pattern matching. The caller of PCRE provides an external function by putting - its entry point in the global variable pcre_callout. By default, this - variable contains NULL, which disables all calling out. - - Within a regular expression, (?C) indicates the points at which the - external function is to be called. Different callout points can be - identified by putting a number less than 256 after the letter C. The - default value is zero. For example, this pattern has two callout + its entry point in the global variable pcre_callout (pcre16_callout for + the 16-bit library). By default, this variable contains NULL, which + disables all calling out. + + Within a regular expression, (?C) indicates the points at which the + external function is to be called. Different callout points can be + identified by putting a number less than 256 after the letter C. The + default value is zero. For example, this pattern has two callout points: (?C1)abc(?C2)def - If the PCRE_AUTO_CALLOUT option bit is set when pcre_compile() or - pcre_compile2() is called, PCRE automatically inserts callouts, all - with number 255, before each item in the pattern. For example, if - PCRE_AUTO_CALLOUT is used with the pattern + If the PCRE_AUTO_CALLOUT option bit is set when a pattern is compiled, + PCRE automatically inserts callouts, all with number 255, before each + item in the pattern. For example, if PCRE_AUTO_CALLOUT is used with the + pattern A(\d{2}|--) @@ -2915,62 +3538,68 @@ PCRE CALLOUTS (?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 + Notice that there is a callout before and after each parenthesis and + alternation bar. Automatic callouts can be used for tracking the + progress of pattern matching. The pcretest command has an option that + sets automatic callouts; when it is used, the output indicates how the + pattern is matched. This is useful information when you are trying to optimize the performance of a particular pattern. + The use of callouts in a pattern makes it ineligible for optimization + by the just-in-time compiler. Studying such a pattern with the + PCRE_STUDY_JIT_COMPILE option always fails. + MISSING CALLOUTS - You should be aware that, because of optimizations in the way PCRE - matches patterns by default, callouts sometimes do not happen. For + You should be aware that, because of optimizations in the way PCRE + matches patterns by default, callouts sometimes do not happen. For example, if the pattern is ab(?C4)cd PCRE knows that any matching string must contain the letter "d". If the - subject string is "abyz", the lack of "d" means that matching doesn't - ever start, and the callout is never reached. However, with "abyd", + 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 pcre_compile(), pcre_exec(), or pcre_dfa_exec(), 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. + 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- - tion defined by pcre_callout is called (if it is set). This applies to - both the pcre_exec() and the pcre_dfa_exec() matching functions. The - only argument to the callout function is a pointer to a pcre_callout - block. This structure contains the following fields: - - int version; - int callout_number; - int *offset_vector; - const char *subject; - int subject_length; - int start_match; - int current_position; - int capture_top; - int capture_last; - void *callout_data; - int pattern_position; - int next_item_length; + tion defined by pcre_callout or pcre16_callout is called (if it is + set). This applies to both normal and DFA matching. The only argument + to the callout function is a pointer to a pcre_callout or pcre16_call- + out block. These structures contains the following fields: + + int version; + int callout_number; + int *offset_vector; + const char *subject; (8-bit version) + PCRE_SPTR16 subject; (16-bit version) + int subject_length; + int start_match; + int current_position; + int capture_top; + int capture_last; + void *callout_data; + int pattern_position; + int next_item_length; + const unsigned char *mark; (8-bit version) + const PCRE_UCHAR16 *mark; (16-bit version) The version field is an integer containing the version number of the - block format. The initial version was 0; the current version is 1. 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. @@ -2979,14 +3608,14 @@ THE CALLOUT INTERFACE 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 pcre_exec() or pcre_dfa_exec(). When - pcre_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 pcre_dfa_exec() - this field is not useful. + passed by the caller to the matching function. When pcre_exec() or + pcre16_exec() is used, the contents can be inspected, in order to + extract substrings that have been matched so far, in the same way as + for extracting substrings after a match has completed. For the DFA + matching functions, this field is not useful. The subject and subject_length fields contain copies of the values that - were passed to pcre_exec(). + 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 @@ -2998,38 +3627,46 @@ THE CALLOUT INTERFACE The current_position field contains the offset within the subject of the current match pointer. - When the pcre_exec() function is used, the capture_top field contains - one more than the number of the highest numbered captured substring so - far. If no substrings have been captured, the value of capture_top is - one. This is always the case when pcre_dfa_exec() is used, because it - does not support captured substrings. + When the pcre_exec() or pcre16_exec() is used, the capture_top field + contains one more than the number of the highest numbered captured sub- + string so far. If no substrings have been captured, the value of cap- + ture_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 when pcre_dfa_exec() is used. + This is always the case for the DFA matching functions. - The callout_data field contains a value that is passed to pcre_exec() - or pcre_dfa_exec() specifically so that it can be passed back in call- - outs. It is passed in the pcre_callout field of the pcre_extra data + The callout_data field contains a value that is passed to a matching + function specifically so that it can be passed back in callouts. It is + passed in the callout_data field of a pcre_extra or pcre16_extra data structure. If no such data was passed, the value of callout_data in a - pcre_callout block is NULL. There is a description of the pcre_extra - structure in the pcreapi documentation. + callout block is NULL. There is a description of the pcre_extra struc- + ture in the pcreapi documentation. - The pattern_position field is present from version 1 of the pcre_call- - out structure. It contains the offset to the next item to be matched in - the pattern string. + The pattern_position field is present from version 1 of the callout + structure. It contains the offset to the next item to be matched in the + pattern string. - The next_item_length field is present from version 1 of the pcre_call- - out structure. It contains the length of the next item to be matched in - the pattern string. When the callout immediately precedes an alterna- - tion bar, a closing parenthesis, or the end of the pattern, the length - is zero. When the callout precedes an opening parenthesis, the length - is that of the entire subpattern. + The next_item_length field is present from version 1 of the callout + structure. It contains the length of the next item to be matched in the + pattern string. When the callout immediately precedes an alternation + bar, a closing parenthesis, or the end of the pattern, the length is + zero. When the callout precedes an opening parenthesis, the length is + that of the entire subpattern. The pattern_position and next_item_length fields are intended to help in distinguishing between different automatic callouts, which all have the same callout number. However, they are set for all callouts. + The mark field is present from version 2 of the callout structure. In + callouts from pcre_exec() or pcre16_exec() it contains a pointer to the + zero-terminated name of the most recently passed (*MARK), (*PRUNE), or + (*THEN) item in the match, or NULL if no such items have been passed. + Instances of (*PRUNE) or (*THEN) without a name do not obliterate a + previous (*MARK). In callouts from the DFA matching functions this + field always contains NULL. + RETURN VALUES @@ -3037,8 +3674,8 @@ RETURN VALUES is zero, matching proceeds as normal. If the value is greater than zero, matching fails at the current point, but the testing of other matching possibilities goes ahead, just as if a lookahead assertion had - failed. If the value is less than zero, the match is abandoned, and - pcre_exec() or pcre_dfa_exec() returns the negative value. + failed. If the value is less than zero, the match is abandoned, the + matching function returns the negative value. Negative values should normally be chosen from the set of PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan- @@ -3056,8 +3693,8 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 08 Janurary 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -3074,43 +3711,53 @@ DIFFERENCES BETWEEN PCRE AND PERL handle regular expressions. The differences described here are with respect to Perl versions 5.10 and above. - 1. PCRE has only a subset of Perl's UTF-8 and Unicode support. Details - of what it does have are given in the section on UTF-8 support in the - main pcre page. + 1. PCRE has only a subset of Perl's Unicode support. Details of what it + does have are given in the pcreunicode page. - 2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl - permits them, but they do not mean what you might think. For example, - (?!a){3} does not assert that the next three characters are not "a". It - just asserts that the next character is not "a" three times. + 2. PCRE allows repeat quantifiers only on parenthesized assertions, but + they do not mean what you might think. For example, (?!a){3} does not + assert that the next three characters are not "a". It just asserts that + the next character is not "a" three times (in principle: PCRE optimizes + this to run the assertion just once). Perl allows repeat quantifiers on + other assertions such as \b, but these do not seem to have any use. - 3. Capturing subpatterns that occur inside negative lookahead 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 + 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 + ing), but only if the negative lookahead assertion contains just one branch. - 4. Though binary zero characters are supported in the subject string, + 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- mal C string, terminated by zero. The escape sequence \0 can be used in the pattern to represent a binary zero. - 5. The following Perl escape sequences are not supported: \l, \u, \L, - \U, and \N. In fact these are implemented by Perl's general string-han- - dling and are not part of its pattern matching engine. If any of these - are encountered by PCRE, an error is generated. - - 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE - is built with Unicode character property support. The properties that - can be tested with \p and \P are limited to the general category prop- - erties such as Lu and Nd, script names such as Greek or Han, and the - derived properties Any and L&. PCRE does support the Cs (surrogate) - property, which Perl does not; the Perl documentation says "Because + 5. The following Perl escape sequences are not supported: \l, \u, \L, + \U, and \N when followed by a character name or Unicode value. (\N on + its own, matching a non-newline character, is supported.) In fact these + are implemented by Perl's general string-handling and are not part of + its pattern matching engine. If any of these are encountered by PCRE, + an error is generated by default. However, if the PCRE_JAVASCRIPT_COM- + PAT option is set, \U and \u are interpreted as JavaScript interprets + them. + + 6. The Perl escape sequences \p, \P, and \X are supported only if PCRE + is built with Unicode character property support. The properties that + can be tested with \p and \P are limited to the general category prop- + erties such as Lu and Nd, script names such as Greek or Han, and the + derived properties Any and L&. PCRE does support the Cs (surrogate) + property, which Perl does not; the Perl documentation says "Because Perl hides the need for the user to understand the internal representa- - tion of Unicode characters, there is no need to implement the somewhat + tion of Unicode characters, there is no need to implement the somewhat messy concept of surrogates." - 7. PCRE does support the \Q...\E escape for quoting substrings. Charac- + 7. PCRE implements a simpler version of \X than Perl, which changed to + make \X match what Unicode calls an "extended grapheme cluster". This + is more complicated than an extended Unicode sequence, which is what + PCRE matches. + + 8. PCRE does support the \Q...\E escape for quoting substrings. Charac- ters in between are treated as literals. This is slightly different from Perl in that $ and @ are also handled as literals inside the quotes. In Perl, they cause variable interpolation (but of course PCRE @@ -3126,55 +3773,70 @@ DIFFERENCES BETWEEN PCRE AND PERL The \Q...\E sequence is recognized both inside and outside character classes. - 8. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) + 9. Fairly obviously, PCRE does not support the (?{code}) and (??{code}) constructions. However, there is support for recursive patterns. This is not available in Perl 5.8, but it is in Perl 5.10. Also, the PCRE "callout" feature allows an external function to be called during pat- tern matching. See the pcrecallout documentation for details. - 9. Subpatterns that are called recursively or as "subroutines" are - always treated as atomic groups in PCRE. This is like Python, but - unlike Perl. There is a discussion of an example that explains this in - more detail in the section on recursion differences from Perl in the - pcrepattern page. - - 10. 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 $2 + 10. Subpatterns that are called as subroutines (whether or not recur- + sively) are always treated as atomic groups in PCRE. This is like + Python, but unlike Perl. Captured values that are set outside a sub- + routine call can be reference from inside in PCRE, but not in Perl. + There is a discussion that explains these differences in more detail in + the section on recursion differences from Perl in the pcrepattern page. + + 11. If any of the backtracking control verbs are used in an assertion + or in a subpattern that is called as a subroutine (whether or not + recursively), their effect is confined to that subpattern; it does not + extend to the surrounding pattern. This is not always the case in Perl. + In particular, if (*THEN) is present in a group that is called as a + subroutine, its action is limited to that group, even if the group does + not contain any | characters. There is one exception to this: the name + from a *(MARK), (*PRUNE), or (*THEN) that is encountered in a success- + ful positive assertion is passed back when a match succeeds (compare + capturing parentheses in assertions). Note that such subpatterns are + processed as anchored at the point where they are tested. + + 12. There are some differences that are concerned with the settings of + captured strings when part of a pattern is repeated. For example, + matching "aba" against the pattern /^(a(b)?)+$/ in Perl leaves $2 unset, but in PCRE it is set to "b". - 11. PCRE's handling of duplicate subpattern numbers and duplicate sub- + 13. 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 - such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have - the same number but different names, is not supported, and causes an - error at compile time. If it were allowed, it would not be possible to - distinguish which parentheses matched, because both names map to cap- + ble to translate between numbers and names. In particular, a pattern + such as (?|(?<a>A)|(?<b)B), where the two capturing parentheses have + the same number but different names, is not supported, and causes an + error at compile time. If it were allowed, it would not be possible to + distinguish which parentheses matched, because both names map to cap- turing subpattern number 1. To avoid this confusing situation, an error is given at compile time. - 12. Perl recognizes comments in some places that PCRE doesn't, for - example, between the ( and ? at the start of a subpattern. + 14. Perl recognizes comments in some places that PCRE does not, for + example, between the ( and ? at the start of a subpattern. If the /x + modifier is set, Perl allows white space between ( and ? but PCRE never + does, even if the PCRE_EXTENDED option is set. - 13. 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 + 15. 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. @@ -3182,10 +3844,10 @@ 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. @@ -3193,12 +3855,14 @@ 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. + 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 function (pcre_dfa_exec()) matches in a - different way and is not Perl-compatible. + (k) The alternative matching functions (pcre_dfa_exec() and + pcre16_dfa_exec()) match in a different way and are not Perl-compati- + ble. - (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. @@ -3212,8 +3876,8 @@ AUTHOR REVISION - Last updated: 31 October 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 01 June 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -3242,42 +3906,45 @@ PCRE REGULAR EXPRESSION DETAILS intended as reference material. The original operation of PCRE was on strings of one-byte characters. - However, there is now also support for UTF-8 character strings. To use - this, PCRE must be built to include UTF-8 support, and you must call - pcre_compile() or pcre_compile2() with the PCRE_UTF8 option. There is - also a special sequence that can be given at the start of a pattern: + However, there is now also support for UTF-8 strings in the original + library, and a second library that supports 16-bit and UTF-16 character + strings. To use these features, PCRE must be built to include appropri- + ate support. When using UTF strings you must either call the compiling + function with the PCRE_UTF8 or PCRE_UTF16 option, or the pattern must + start with one of these special sequences: (*UTF8) + (*UTF16) - Starting a pattern with this sequence is equivalent to setting the - PCRE_UTF8 option. This feature is not Perl-compatible. How setting - UTF-8 mode affects pattern matching is mentioned in several places - below. There is also a summary of UTF-8 features in the section on - UTF-8 support in the main pcre page. + Starting a pattern with such a sequence is equivalent to setting the + relevant option. This feature is not Perl-compatible. How setting a UTF + mode affects pattern matching is mentioned in several places below. + There is also a summary of features in the pcreunicode page. - Another special sequence that may appear at the start of a pattern or - in combination with (*UTF8) is: + Another special sequence that may appear at the start of a pattern or + in combination with (*UTF8) or (*UTF16) is: (*UCP) - This has the same effect as setting the PCRE_UCP option: it causes - sequences such as \d and \w to use Unicode properties to determine + This has the same effect as setting the PCRE_UCP option: it causes + sequences such as \d and \w to use Unicode properties to determine character types, instead of recognizing only characters with codes less than 128 via a lookup table. - If a pattern starts with (*NO_START_OPT), it has the same effect as + 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. - The remainder of this document discusses the patterns that are sup- - ported by PCRE when its main matching function, pcre_exec(), is used. - From release 6.0, PCRE offers a second matching function, - pcre_dfa_exec(), which matches using a different algorithm that is not - Perl-compatible. Some of the features discussed below are not available - when pcre_dfa_exec() is used. The advantages and disadvantages of the - alternative function, and how it differs from the normal function, are - discussed in the pcrematching page. + 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 pcre16_exec() (16-bit), is used. PCRE also has alternative + matching functions, pcre_dfa_exec() and pcre16_dfa_exec(), which match + using a different algorithm that is not Perl-compatible. Some of the + features discussed below are not available when DFA matching is used. + The advantages and disadvantages of the alternative functions, and how + they differ from the normal functions, are discussed in the pcrematch- + ing page. NEWLINE CONVENTIONS @@ -3298,9 +3965,9 @@ NEWLINE CONVENTIONS (*ANYCRLF) any of the three above (*ANY) all Unicode newline sequences - These override the default and the options given to pcre_compile() or - pcre_compile2(). For example, on a Unix system where LF is the default - newline sequence, the pattern + These override the default and the options given to the compiling func- + tion. For example, on a Unix system where LF is the default newline + sequence, the pattern (*CR)a.b @@ -3330,13 +3997,13 @@ CHARACTERS AND METACHARACTERS matches a portion of a subject string that is identical to itself. When caseless matching is specified (the PCRE_CASELESS option), letters are - matched independently of case. In UTF-8 mode, PCRE always understands + matched independently of case. In a UTF mode, PCRE always understands the concept of case for characters whose values are less than 128, so caseless matching is always possible. For characters with higher val- ues, the concept of case is supported if PCRE is compiled with Unicode property support, but not otherwise. If you want to use caseless matching for characters 128 and above, you must ensure that PCRE is - compiled with Unicode property support as well as with UTF-8 support. + compiled with Unicode property support as well as with UTF support. The power of regular expressions comes from the ability to include alternatives and repetitions in the pattern. These are encoded in the @@ -3391,14 +4058,14 @@ BACKSLASH that it stands for itself. In particular, if you want to match a back- slash, you write \\. - In UTF-8 mode, only ASCII numbers and letters have any special meaning + In a UTF mode, only ASCII numbers and letters have any special meaning after a backslash. All other characters (in particular, those whose codepoints are greater than 127) are treated as literals. - If a pattern is compiled with the PCRE_EXTENDED option, whitespace in + 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 whitespace or # character as + ing 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- @@ -3415,7 +4082,11 @@ BACKSLASH \Qabc\E\$\Qxyz\E abc$xyz abc$xyz The \Q...\E sequence is recognized both inside and outside character - classes. An isolated \E that is not preceded by \Q is ignored. + classes. An isolated \E that is not preceded by \Q is ignored. If \Q + is not followed by \E later in the pattern, the literal interpretation + continues to the end of the pattern (that is, \E is assumed at the + end). If the isolated \Q is inside a character class, this causes an + error, because the character class is not terminated. Non-printing characters @@ -3429,61 +4100,77 @@ BACKSLASH \a alarm, that is, the BEL character (hex 07) \cx "control-x", where x is any ASCII character \e escape (hex 1B) - \f formfeed (hex 0C) + \f form feed (hex 0C) \n linefeed (hex 0A) \r carriage return (hex 0D) \t tab (hex 09) \ddd character with octal code ddd, or back reference \xhh character with hex code hh - \x{hhh..} character with hex code hhh.. + \x{hhh..} character with hex code hhh.. (non-JavaScript mode) + \uhhhh character with hex code hhhh (JavaScript mode only) The precise effect of \cx is as follows: if x is a lower case letter, it is converted to upper case. Then bit 6 of the character (hex 40) is inverted. Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({ is 7B), while \c; becomes hex 7B (; is 3B). If the byte following \c has a value greater than 127, a compile-time error occurs. This locks - out non-ASCII characters in both byte mode and UTF-8 mode. (When PCRE - is compiled in EBCDIC mode, all byte values are valid. A lower case - letter is converted to upper case, and then the 0xc0 bits are flipped.) - - After \x, from zero to two hexadecimal digits are read (letters can be - in upper or lower case). Any number of hexadecimal digits may appear - between \x{ and }, but the value of the character code must be less - than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is, - the maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger - than the largest Unicode code point, which is 10FFFF. - - If characters other than hexadecimal digits appear between \x{ and }, + out non-ASCII characters in all modes. (When PCRE is compiled in EBCDIC + mode, all byte values are valid. A lower case letter is converted to + upper case, and then the 0xc0 bits are flipped.) + + By default, after \x, from zero to two hexadecimal digits are read + (letters can be in upper or lower case). Any number of hexadecimal 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 + + Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- + called "surrogate" codepoints). + + If characters other than hexadecimal digits appear between \x{ and }, or if there is no terminating }, this form of escape is not recognized. - Instead, the initial \x will be interpreted as a basic hexadecimal - escape, with no following digits, giving a character whose value is + 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. There is no difference in the way they are han- - dled. For example, \xdc is exactly the same as \x{dc}. + 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 + 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 + (code value 7). Make sure you supply two digits after the initial zero if the pattern character that follows is itself an octal digit. The handling of a backslash followed by a digit other than 0 is 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 + 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 - description of how this works is given later, following the discussion + 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 + 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. In - non-UTF-8 mode, the value of a character specified in octal must be - less than \400. In UTF-8 mode, values up to \777 are permitted. For - example: + 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: \040 is another way of writing a space \40 is the same, provided there are fewer than 40 @@ -3496,7 +4183,7 @@ BACKSLASH \113 might be a back reference, otherwise the character with octal code 113 \377 might be a back reference, otherwise - the byte consisting entirely of 1 bits + the value 255 (decimal) \81 is either a back reference, or a binary zero followed by the two characters "8" and "1" @@ -3505,12 +4192,22 @@ BACKSLASH All the sequences that define a single character value can be used both inside and outside character classes. In addition, inside a character - class, the sequence \b is interpreted as the backspace character (hex - 08). The sequences \B, \N, \R, and \X are not special inside a charac- - ter class. Like any other unrecognized escape sequences, they are - treated as the literal characters "B", "N", "R", and "X" by default, - but cause an error if the PCRE_EXTRA option is set. Outside a character - class, these sequences have different meanings. + class, \b is interpreted as the backspace character (hex 08). + + \N is not allowed in a character class. \B, \R, and \X are not special + inside a character class. Like other unrecognized escape sequences, + they are treated as the literal characters "B", "R", and "X" by + default, but cause an error if the PCRE_EXTRA option is set. Outside a + character class, these sequences have different meanings. + + Unsupported escape sequences + + In Perl, the sequences \l, \L, \u, and \U are recognized by its string + handler and used to modify the case of following characters. By + default, PCRE does not support these escape sequences. However, if the + PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and + \u can be used to define a character by code point, as described in the + previous section. Absolute and relative back references @@ -3534,65 +4231,66 @@ BACKSLASH \d any decimal digit \D any character that is not a decimal digit - \h any horizontal whitespace character - \H any character that is not a horizontal whitespace character - \s any whitespace character - \S any character that is not a whitespace character - \v any vertical whitespace character - \V any character that is not a vertical whitespace character + \h any horizontal white space character + \H any character that is not a horizontal white space character + \s any white space character + \S any character that is not a white space character + \v any vertical white space character + \V any character that is not a vertical white space character \w any "word" character \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. - - 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 + 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 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 + 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 + 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 use of locales with Unicode is discouraged. - By default, in UTF-8 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-8 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 + 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: \d any character that \p{Nd} matches (decimal digit) \s any character that \p{Z} matches, plus HT, LF, FF, CR \w any character that \p{L} or \p{N} matches, plus underscore - The upper case escapes match the inverse sets of characters. Note that - \d matches only decimal digits, whereas \w matches any Unicode digit, - as well as any Unicode letter, and underscore. Note also that PCRE_UCP - affects \b, and \B because they are defined in terms of \w and \W. + The upper case escapes match the inverse sets of characters. Note that + \d matches only decimal digits, whereas \w matches any Unicode digit, + as well as any Unicode letter, and underscore. Note also that PCRE_UCP + affects \b, and \B because they are defined in terms of \w and \W. Matching these sequences is noticeably slower when PCRE_UCP is set. - The sequences \h, \H, \v, and \V are features that were added to Perl - at release 5.10. In contrast to the other sequences, which match only - ASCII characters by default, these always match certain high-valued - codepoints in UTF-8 mode, whether or not PCRE_UCP is set. The horizon- - tal space characters are: + 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- + acters are: U+0009 Horizontal tab U+0020 Space @@ -3618,28 +4316,31 @@ BACKSLASH U+000A Linefeed U+000B Vertical tab - U+000C Formfeed + U+000C Form feed U+000D Carriage return U+0085 Next line U+2028 Line separator U+2029 Paragraph separator + In 8-bit, non-UTF-8 mode, only the characters with codepoints less than + 256 are relevant. + Newline sequences Outside a character class, by default, the escape sequence \R matches - any Unicode newline sequence. In non-UTF-8 mode \R is equivalent to the - following: + any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent + to the following: (?>\r\n|\n|\x0b|\f|\r|\x85) This is an example of an "atomic group", details of which are given below. This particular group matches either the two-character sequence CR followed by LF, or one of the single characters LF (linefeed, - U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage - return, U+000D), or NEL (next line, U+0085). The two-character sequence - is treated as a single unit that cannot be split. + U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car- + riage return, U+000D), or NEL (next line, U+0085). The two-character + sequence is treated as a single unit that cannot be split. - In UTF-8 mode, two additional characters whose codepoints are greater + In other modes, two additional characters whose codepoints are greater than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa- rator, U+2029). Unicode character property support is not needed for these characters to be recognized. @@ -3656,28 +4357,28 @@ BACKSLASH (*BSR_ANYCRLF) CR, LF, or CRLF only (*BSR_UNICODE) any Unicode newline sequence - These override the default and the options given to pcre_compile() or - pcre_compile2(), but they can be overridden by options given to - pcre_exec() or pcre_dfa_exec(). Note that these special settings, which - are not Perl-compatible, are recognized only at the very start of a - pattern, and that they must be in upper case. If more than one of them - is present, the last one is used. They can be combined with a change of + These override the default and the options given to the compiling func- + tion, but they can themselves be overridden by options given to a + matching function. Note that these special settings, which are not + Perl-compatible, are recognized only at the very start of a pattern, + and that they must be in upper case. If more than one of them is + present, the last one is used. They can be combined with a change of newline convention; for example, a pattern can start with: (*ANY)(*BSR_ANYCRLF) - They can also be combined with the (*UTF8) or (*UCP) special sequences. - Inside a character class, \R is treated as an unrecognized escape - sequence, and so matches the letter "R" by default, but causes an error - if PCRE_EXTRA is set. + They can also be combined with the (*UTF8), (*UTF16), or (*UCP) special + sequences. Inside a character class, \R is treated as an unrecognized + escape sequence, and so matches the letter "R" by default, but causes + an error if PCRE_EXTRA is set. Unicode character properties When PCRE is built with Unicode character property support, three addi- tional escape sequences that match characters with specific properties - are available. When not in UTF-8 mode, these sequences are of course - limited to testing characters whose codepoints are less than 256, but - they do work in this mode. The extra escape sequences are: + are available. When in 8-bit non-UTF-8 mode, these sequences are of + course limited to testing characters whose codepoints are less than + 256, but they do work in this mode. The extra escape sequences are: \p{xx} a character with the xx property \P{xx} a character without the xx property @@ -3700,20 +4401,22 @@ BACKSLASH Those that are not part of an identified script are lumped together as "Common". The current list of scripts is: - Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille, - Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, - Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyp- - tian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek, - Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Impe- - rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian, - Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, - Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, - Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, - Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, - Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, - Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, - Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, - Ugaritic, Vai, Yi. + 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, + Yi. Each character has exactly one Unicode general category property, spec- ified by a two-letter abbreviation. For compatibility with Perl, nega- @@ -3780,45 +4483,50 @@ BACKSLASH classified as a modifier or "other". The Cs (Surrogate) property applies only to characters in the range - U+D800 to U+DFFF. Such characters are not valid in UTF-8 strings (see - RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check- - ing has been turned off (see the discussion of PCRE_NO_UTF8_CHECK in - the pcreapi page). Perl does not support the Cs property. - - The long synonyms for property names that Perl supports (such as - \p{Letter}) are not supported by PCRE, nor is it permitted to prefix + U+D800 to U+DFFF. Such characters are not valid in Unicode strings and + so cannot be tested by PCRE, unless UTF validity checking has been + turned off (see the discussion of PCRE_NO_UTF8_CHECK and + PCRE_NO_UTF16_CHECK in the pcreapi page). Perl does not support the Cs + property. + + The long synonyms for property names that Perl supports (such as + \p{Letter}) are not supported by PCRE, nor is it permitted to prefix any of these properties with "Is". No character that is in the Unicode table has the Cn (unassigned) prop- erty. Instead, this property is assumed for any code point that is not in the Unicode table. - Specifying caseless matching does not affect these escape sequences. + Specifying caseless matching does not affect these escape sequences. For example, \p{Lu} always matches only upper case letters. - The \X escape matches any number of Unicode characters that form an + The \X escape matches any number of Unicode characters that form an extended Unicode sequence. \X is equivalent to (?>\PM\pM*) - That is, it matches a character without the "mark" property, followed - by zero or more characters with the "mark" property, and treats the - sequence as an atomic group (see below). Characters with the "mark" - property are typically accents that affect the preceding character. - None of them have codepoints less than 256, so in non-UTF-8 mode \X - matches any one character. + That is, it matches a character without the "mark" property, followed + by zero or more characters with the "mark" property, and treats the + sequence as an atomic group (see below). Characters with the "mark" + property are typically accents that affect the preceding character. + None of them have codepoints less than 256, so in 8-bit non-UTF-8 mode + \X matches any one character. - Matching characters by Unicode property is not fast, because PCRE has - to search a structure that contains data for over fifteen thousand + Note that recent versions of Perl have changed \X to match what Unicode + calls an "extended grapheme cluster", which has a more complicated def- + inition. + + Matching characters by Unicode property is not fast, because PCRE has + to search a structure that contains data for over fifteen thousand characters. That is why the traditional escape sequences such as \d and - \w do not use Unicode properties in PCRE by default, though you can - make them do so by setting the PCRE_UCP option for pcre_compile() or by - starting the pattern with (*UCP). + \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 pat- + tern with (*UCP). PCRE's additional properties - As well as the standard Unicode properties described in the previous - section, PCRE supports four more that make it possible to convert tra- + As well as the standard Unicode properties described in the previous + section, PCRE supports four more that make it possible to convert tra- ditional escape sequences such as \w and \s and POSIX character classes to use Unicode properties. PCRE uses these non-standard, non-Perl prop- erties internally when PCRE_UCP is set. They are: @@ -3828,40 +4536,40 @@ BACKSLASH 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, - formfeed, or carriage return, and any other character that has the Z + 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. 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 @@ -3872,49 +4580,49 @@ 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 - UTF-8 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. @@ -3922,60 +4630,59 @@ BACKSLASH CIRCUMFLEX AND DOLLAR Outside a character class, in the default matching mode, the circumflex - character is an assertion that is true only if the current matching - point is at the start of the subject string. If the startoffset 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.) - A dollar character is an assertion that is true only if the current - matching point is at the end of the subject string, or immediately + A dollar character is an assertion that is true only if the current + matching point is at the end of the subject string, or immediately before a newline at the end of the string (by default). Dollar need not - be the last character of the pattern if a number of alternatives are - involved, but it should be the last item in any branch in which it + be the last character of the pattern if a number of alternatives are + involved, but it should be the last item in any branch in which it appears. Dollar has no special meaning in a character class. - The meaning of dollar can be changed so that it matches only at the - very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at + 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- - fies the end of a line. In UTF-8 mode, the matched character may be - more than one byte long. + 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 @@ -3995,23 +4702,47 @@ FULL STOP (PERIOD, DOT) AND \N 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. + 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 BYTE +MATCHING A SINGLE DATA UNIT - Outside a character class, the escape sequence \C matches any one byte, - both in and out of UTF-8 mode. Unlike a dot, it always matches any - line-ending characters. The feature is provided in Perl in order to - match individual bytes in UTF-8 mode. Because it breaks up UTF-8 char- - acters into individual bytes, the rest of the string may start with a - malformed UTF-8 character. For this reason, the \C escape sequence is - best avoided. + Outside a character class, the escape sequence \C matches any one data + unit, whether or not a UTF mode is set. In the 8-bit library, one data + unit is one byte; in the 16-bit library it is a 16-bit unit. Unlike a + dot, \C always matches line-ending characters. The feature is provided + in Perl in order to match individual bytes in UTF-8 mode, but it is + unclear how it can usefully be used. Because \C breaks up characters + into individual data units, matching one unit with \C in a UTF mode + means that the rest of the string may start with a malformed UTF char- + acter. 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 or + PCRE_NO_UTF16_CHECK option is used). PCRE does not allow \C to appear in lookbehind assertions (described - below), because in UTF-8 mode this would make it impossible to calcu- + 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 + line breaks): + + (?| (?=[\x00-\x7f])(\C) | + (?=[\x80-\x{7ff}])(\C)(\C) | + (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) | + (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C)) + + A group that starts with (?| resets the capturing parentheses numbers + in each alternative (see "Duplicate Subpattern Numbers" below). The + assertions at the start of each branch check the next UTF-8 character + for values whose encoding uses 1, 2, 3, or 4 bytes, respectively. The + character's individual bytes are then captured by the appropriate num- + ber of groups. + SQUARE BRACKETS AND CHARACTER CLASSES @@ -4019,109 +4750,109 @@ 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 UTF-8 - mode, the character may be more than one byte long. A matched character - must be in the set of characters defined by the class, unless the first - character in the class definition is a circumflex, in which case the - subject character must not be in the set defined by the class. If a - circumflex is actually required as a member of the class, ensure it is - not the first character, or escape it with a backslash. + A character class matches a single character in the subject. In a UTF + mode, the character may be more than one data unit long. A matched + character must be in the set of characters defined by the class, unless + the first character in the class definition is a circumflex, in which + case the subject character must not be in the set defined by the class. + If a circumflex is actually required as a member of the class, ensure + it is not the first character, or escape it with a backslash. - For example, the character class [aeiou] matches any lower case vowel, - while [^aeiou] matches any character that is not a lower case vowel. + 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 mode, characters with values greater than 255 can be included - in a class as a literal string of bytes, 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 UTF-8 mode, PCRE always - understands the concept of case for characters whose values are less - than 128, so caseless matching is always possible. For characters with - higher values, the concept of case is supported if PCRE is compiled - with Unicode property support, but not otherwise. If you want to use - caseless matching in UTF8-mode for characters 128 and above, you must - ensure that PCRE is compiled with Unicode property support as well as - with UTF-8 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 + In UTF-8 (UTF-16) mode, characters with values greater than 255 + (0xffff) can be included in a class as a literal string of data units, + or by using the \x{ escaping mechanism. + + When caseless matching is set, any letters in a class represent both + their upper case and lower case versions, so for example, a caseless + [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not + match "A", whereas a caseful version would. In a UTF mode, PCRE always + understands the concept of case for characters whose values are less + than 128, so caseless matching is always possible. For characters with + higher values, the concept of case is supported if PCRE is compiled + with Unicode property support, but not otherwise. If you want to use + caseless matching in a UTF mode for characters 128 and above, you must + ensure that PCRE is compiled with Unicode property support as well as + with UTF support. + + Characters that might indicate line breaks are never treated in any + special way when matching character classes, whatever line-ending + sequence is in use, and whatever setting of the PCRE_DOTALL and PCRE_MULTILINE options is used. A class such as [^a] always matches one of these characters. - The minus (hyphen) character can be used to specify a range of 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 + 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. 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. - Ranges operate in the collating sequence of character values. They can - also be used for characters specified numerically, for example - [\000-\037]. In UTF-8 mode, ranges can include characters whose values - are greater than 255, for example [\x{100}-\x{2ff}]. + Ranges operate in the collating sequence of character values. They can + also be used for characters specified numerically, for example + [\000-\037]. Ranges can include any characters that are valid for the + current mode. If a range that includes letters is used when caseless matching is set, it matches the letters in either case. For example, [W-c] is equivalent - to [][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if - character tables for a French locale are in use, [\xc8-\xcb] matches - accented E characters in both cases. In UTF-8 mode, PCRE supports the - concept of case for characters with values greater than 128 only when + to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if + character tables for a French locale are in use, [\xc8-\xcb] matches + accented E characters in both cases. In UTF modes, PCRE supports the + concept of case for characters with values greater than 128 only when it is compiled with Unicode property support. - The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, + The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, \w, and \W may appear in a character class, and add the characters that - they match to the class. For example, [\dABCDEF] matches any hexadeci- - mal digit. In UTF-8 mode, the PCRE_UCP option affects the meanings of - \d, \s, \w and their upper case partners, just as it does when they - appear outside a character class, as described in the section entitled + they match to the class. For example, [\dABCDEF] matches any hexadeci- + mal digit. In UTF modes, the PCRE_UCP option affects the meanings of + \d, \s, \w and their upper case partners, just as it does when they + appear outside a character class, as described in the section entitled "Generic character types" above. The escape sequence \b has a different - meaning inside a character class; it matches the backspace character. - The sequences \B, \N, \R, and \X are not special inside a character - class. Like any other unrecognized escape sequences, they are treated - as the literal characters "B", "N", "R", and "X" by default, but cause + meaning inside a character class; it matches the backspace character. + The sequences \B, \N, \R, and \X are not special inside a character + class. Like any other unrecognized escape sequences, they are treated + as the literal characters "B", "N", "R", and "X" by default, but cause an error if the PCRE_EXTRA option is set. - A circumflex can conveniently be used with the upper case character - types to specify a more restricted set of characters than the matching - lower case type. For example, the class [^\W_] matches any letter or + A circumflex can conveniently be used with the upper case character + types to specify a more restricted set of characters than the matching + lower case type. For example, the class [^\W_] matches any letter or digit, but not underscore, whereas [\w] includes underscore. A positive character class should be read as "something OR something OR ..." and a negative class as "NOT something AND NOT something AND NOT ...". - The only metacharacters that are recognized in character classes are - backslash, hyphen (only where it can be interpreted as specifying a - range), circumflex (only at the start), opening square bracket (only - when it can be interpreted as introducing a POSIX class name - see the - next section), and the terminating closing square bracket. However, + The only metacharacters that are recognized in character classes are + backslash, hyphen (only where it can be interpreted as specifying a + range), circumflex (only at the start), opening square bracket (only + when it can be interpreted as introducing a POSIX class name - see the + next section), and the terminating closing square bracket. However, escaping other non-alphanumeric characters does no harm. POSIX CHARACTER CLASSES Perl supports the POSIX notation for character classes. This uses names - enclosed by [: and :] within the enclosing square brackets. PCRE also + enclosed by [: and :] within the enclosing square brackets. PCRE also supports this notation. For example, [01[:alpha:]%] @@ -4144,24 +4875,24 @@ POSIX CHARACTER CLASSES 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 + The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), + and space (32). Notice that this list includes the VT character (code 11). This makes "space" different to \s, which does not include VT (for Perl compatibility). - The name "word" is a Perl extension, and "blank" is a GNU extension - from Perl 5.8. Another Perl extension is negation, which is indicated + The name "word" is a Perl extension, and "blank" is a GNU extension + from Perl 5.8. Another Perl extension is negation, which is indicated by a ^ character after the colon. For example, [12[:^digit:]] - matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the + matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not supported, and an error is given if they are encountered. - By default, in UTF-8 mode, 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 + 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: @@ -4174,31 +4905,31 @@ POSIX CHARACTER CLASSES [:upper:] becomes \p{Lu} [:word:] becomes \p{Xwd} - Negated versions, such as [:^alpha:] use \P instead of \p. The other + Negated versions, such as [:^alpha:] use \P instead of \p. The other POSIX classes are unchanged, and match only characters with code points less than 128. VERTICAL BAR - Vertical bar characters are used to separate alternative patterns. For + Vertical bar characters are used to separate alternative patterns. For example, the pattern gilbert|sullivan - matches either "gilbert" or "sullivan". Any number of alternatives may - appear, and an empty alternative is permitted (matching the empty + matches either "gilbert" or "sullivan". Any number of alternatives may + appear, and an empty alternative is permitted (matching the empty string). The matching process tries each alternative in turn, from left - to right, and the first one that succeeds is used. If the alternatives - are within a subpattern (defined below), "succeeds" means matching the + to right, and the first one that succeeds is used. If the alternatives + are within a subpattern (defined below), "succeeds" means matching the rest of the main pattern as well as the alternative in the subpattern. INTERNAL OPTION SETTING - The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and - PCRE_EXTENDED options (which are Perl-compatible) can be changed from - within the pattern by a sequence of Perl option letters enclosed + The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and + PCRE_EXTENDED options (which are Perl-compatible) can be changed from + within the pattern by a sequence of Perl option letters enclosed between "(?" and ")". The option letters are i for PCRE_CASELESS @@ -4208,48 +4939,49 @@ INTERNAL OPTION SETTING For example, (?im) sets caseless, multiline matching. It is also possi- ble to unset these options by preceding the letter with a hyphen, and a - combined setting and unsetting such as (?im-sx), which sets PCRE_CASE- - LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, - is also permitted. If a letter appears both before and after the + combined setting and unsetting such as (?im-sx), which sets PCRE_CASE- + LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, + is also permitted. If a letter appears both before and after the hyphen, the option is unset. - The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA - can be changed in the same way as the Perl-compatible options by using + The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA + can be changed in the same way as the Perl-compatible options by using the characters J, U and X respectively. - When one of these option changes occurs at top level (that is, not - inside subpattern parentheses), the change applies to the remainder of + When one of these option changes occurs at top level (that is, not + inside subpattern parentheses), the change applies to the remainder of the pattern that follows. If the change is placed right at the start of a pattern, PCRE extracts it into the global options (and it will there- fore show up in data extracted by the pcre_fullinfo() function). - An option change within a subpattern (see below for a description of - subpatterns) affects only that part of the subpattern that follows it, + An option change within a subpattern (see below for a description of + subpatterns) affects only that part of the subpattern that follows it, so (a(?i)b)c matches abc and aBc and no other strings (assuming PCRE_CASELESS is not - used). By this means, options can be made to have different settings - in different parts of the pattern. Any changes made in one alternative - do carry on into subsequent branches within the same subpattern. For + used). By this means, options can be made to have different settings + in different parts of the pattern. Any changes made in one alternative + do carry on into subsequent branches within the same subpattern. For example, (a(?i)b|c) - matches "ab", "aB", "c", and "C", even though when matching "C" the - first branch is abandoned before the option setting. This is because - the effects of option settings happen at compile time. There would be + matches "ab", "aB", "c", and "C", even though when matching "C" the + first branch is abandoned before the option setting. This is because + the effects of option settings happen at compile time. There would be some very weird behaviour otherwise. - Note: There are other PCRE-specific options that can be set by the - application when the compile or match functions are called. In some - cases the pattern can contain special leading sequences such as (*CRLF) - to override what the application has set or what has been defaulted. - Details are given in the section entitled "Newline sequences" above. - There are also the (*UTF8) and (*UCP) leading sequences that can be - used to set UTF-8 and Unicode property modes; they are equivalent to - setting the PCRE_UTF8 and the PCRE_UCP options, respectively. + Note: There are other PCRE-specific options that can be set by the + application when the compiling or matching functions are called. In + some cases the pattern can contain special leading sequences such as + (*CRLF) to override what the application has set or what has been + defaulted. Details are given in the section entitled "Newline + sequences" above. There are also the (*UTF8), (*UTF16), and (*UCP) + leading sequences that can be used to set UTF and Unicode property + modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, and + the PCRE_UCP options, respectively. SUBPATTERNS @@ -4267,22 +4999,25 @@ SUBPATTERNS 2. It sets up the subpattern as a capturing subpattern. This means that, when the whole pattern matches, that portion of the subject string that matched the subpattern is passed back to the caller via the - ovector argument of pcre_exec(). Opening parentheses are counted from - left to right (starting from 1) to obtain numbers for the capturing - subpatterns. For example, if the string "the red king" is matched - against the pattern + ovector argument of the matching function. (This applies only to the + traditional matching functions; the DFA matching functions do not sup- + port capturing.) + + Opening parentheses are counted from left to right (starting from 1) to + obtain numbers for the capturing subpatterns. For example, if the + string "the red king" is matched against the pattern the ((red|white) (king|queen)) the captured substrings are "red king", "red", and "king", and are num- bered 1, 2, and 3, respectively. - The fact that plain parentheses fulfil two functions is not always - helpful. There are often times when a grouping subpattern is required - without a capturing requirement. If an opening parenthesis is followed - by a question mark and a colon, the subpattern does not do any captur- - ing, and is not counted when computing the number of any subsequent - capturing subpatterns. For example, if the string "the white queen" is + The fact that plain parentheses fulfil two functions is not always + helpful. There are often times when a grouping subpattern is required + without a capturing requirement. If an opening parenthesis is followed + by a question mark and a colon, the subpattern does not do any captur- + ing, and is not counted when computing the number of any subsequent + capturing subpatterns. For example, if the string "the white queen" is matched against the pattern the ((?:red|white) (king|queen)) @@ -4290,37 +5025,37 @@ SUBPATTERNS the captured substrings are "white queen" and "queen", and are numbered 1 and 2. The maximum number of capturing subpatterns is 65535. - As a convenient shorthand, if any option settings are required at the - start of a non-capturing subpattern, the option letters may appear + As a convenient shorthand, if any option settings are required at the + start of a non-capturing subpattern, the option letters may appear between the "?" and the ":". Thus the two patterns (?i:saturday|sunday) (?:(?i)saturday|sunday) match exactly the same set of strings. Because alternative branches are - tried from left to right, and options are not reset until the end of - the subpattern is reached, an option setting in one branch does affect - subsequent branches, so the above patterns match "SUNDAY" as well as + tried from left to right, and options are not reset until the end of + the subpattern is reached, an option setting in one branch does affect + subsequent branches, so the above patterns match "SUNDAY" as well as "Saturday". DUPLICATE SUBPATTERN NUMBERS Perl 5.10 introduced a feature whereby each alternative in a subpattern - uses the same numbers for its capturing parentheses. Such a subpattern - starts with (?| and is itself a non-capturing subpattern. For example, + uses the same numbers for its capturing parentheses. Such a subpattern + starts with (?| and is itself a non-capturing subpattern. For example, consider this pattern: (?|(Sat)ur|(Sun))day - Because the two alternatives are inside a (?| group, both sets of cap- - turing parentheses are numbered one. Thus, when the pattern matches, - you can look at captured substring number one, whichever alternative - matched. This construct is useful when you want to capture part, but + Because the two alternatives are inside a (?| group, both sets of cap- + turing parentheses are numbered one. Thus, when the pattern matches, + you can look at captured substring number one, whichever alternative + matched. This construct is useful when you want to capture part, but not all, of one of a number of alternatives. Inside a (?| group, paren- - theses are numbered as usual, but the number is reset at the start of - each branch. The numbers of any capturing parentheses that follow the - subpattern start after the highest number used in any branch. The fol- + theses are numbered as usual, but the number is reset at the start of + each branch. The numbers of any capturing parentheses that follow the + subpattern start after the highest number used in any branch. The fol- lowing example is taken from the Perl documentation. The numbers under- neath show in which buffer the captured content will be stored. @@ -4328,58 +5063,58 @@ DUPLICATE SUBPATTERN NUMBERS / ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x # 1 2 2 3 2 3 4 - A back reference to a numbered subpattern uses the most recent value - that is set for that number by any subpattern. The following pattern + A back reference to a numbered subpattern uses the most recent value + that is set for that number by any subpattern. The following pattern matches "abcabc" or "defdef": /(?|(abc)|(def))\1/ - In contrast, a recursive or "subroutine" call to a numbered subpattern - always refers to the first one in the pattern with the given number. - The following pattern matches "abcabc" or "defabc": + In contrast, a subroutine call to a numbered subpattern always refers + to the first one in the pattern with the given number. The following + pattern matches "abcabc" or "defabc": /(?|(abc)|(def))(?1)/ - If a condition test for a subpattern's having matched refers to a non- - unique number, the test is true if any of the subpatterns of that num- + If a condition test for a subpattern's having matched refers to a non- + unique number, the test is true if any of the subpatterns of that num- ber have matched. - An alternative approach to using this "branch reset" feature is to use + An alternative approach to using this "branch reset" feature is to use duplicate named subpatterns, as described in the next section. NAMED SUBPATTERNS - Identifying capturing parentheses by number is simple, but it can be - very hard to keep track of the numbers in complicated regular expres- - sions. Furthermore, if an expression is modified, the numbers may - change. To help with this difficulty, PCRE supports the naming of sub- + Identifying capturing parentheses by number is simple, but it can be + very hard to keep track of the numbers in complicated regular expres- + sions. Furthermore, if an expression is modified, the numbers may + change. To help with this difficulty, PCRE supports the naming of sub- patterns. This feature was not added to Perl until release 5.10. Python - had the feature earlier, and PCRE introduced it at release 4.0, using - the Python syntax. PCRE now supports both the Perl and the Python syn- - tax. Perl allows identically numbered subpatterns to have different + had the feature earlier, and PCRE introduced it at release 4.0, using + the Python syntax. PCRE now supports both the Perl and the Python syn- + tax. Perl allows identically numbered subpatterns to have different names, but PCRE does not. - In PCRE, a subpattern can be named in one of three ways: (?<name>...) - or (?'name'...) as in Perl, or (?P<name>...) as in Python. References - to capturing parentheses from other parts of the pattern, such as back - references, recursion, and conditions, can be made by name as well as + In PCRE, a subpattern can be named in one of three ways: (?<name>...) + or (?'name'...) as in Perl, or (?P<name>...) as in Python. References + to capturing parentheses from other parts of the pattern, such as back + references, recursion, and conditions, can be made by name as well as by number. - Names consist of up to 32 alphanumeric characters and underscores. - Named capturing parentheses are still allocated numbers as well as - names, exactly as if the names were not present. The PCRE API provides + Names consist of up to 32 alphanumeric characters and underscores. + Named capturing parentheses are still allocated numbers as well as + names, exactly as if the names were not present. The PCRE API provides function calls for extracting the name-to-number translation table from a compiled pattern. There is also a convenience function for extracting a captured substring by name. - By default, a name must be unique within a pattern, but it is possible + By default, a name must be unique within a pattern, but it is possible to relax this constraint by setting the PCRE_DUPNAMES option at compile - time. (Duplicate names are also always permitted for subpatterns with - the same number, set up as described in the previous section.) Dupli- - cate names can be useful for patterns where only one instance of the - named parentheses can match. Suppose you want to match the name of a - weekday, either as a 3-letter abbreviation or as the full name, and in + time. (Duplicate names are also always permitted for subpatterns with + the same number, set up as described in the previous section.) Dupli- + cate names can be useful for patterns where only one instance of the + named parentheses can match. Suppose you want to match the name of a + weekday, either as a 3-letter abbreviation or as the full name, and in both cases you want to extract the abbreviation. This pattern (ignoring the line breaks) does the job: @@ -4389,62 +5124,62 @@ NAMED SUBPATTERNS (?<DN>Thu)(?:rsday)?| (?<DN>Sat)(?:urday)? - There are five capturing substrings, but only one is ever set after a + There are five capturing substrings, but only one is ever set after a match. (An alternative way of solving this problem is to use a "branch reset" subpattern, as described in the previous section.) - The convenience function for extracting the data by name returns the - substring for the first (and in this example, the only) subpattern of - that name that matched. This saves searching to find which numbered + The convenience function for extracting the data by name returns the + substring for the first (and in this example, the only) subpattern of + that name that matched. This saves searching to find which numbered subpattern it was. - If you make a back reference to a non-unique named subpattern from - elsewhere in the pattern, the one that corresponds to the first occur- + 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. + 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. 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 + 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. 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 the dot metacharacter the \C escape sequence - the \X escape sequence (in UTF-8 mode with Unicode properties) + the \X escape sequence the \R escape sequence an escape such as \d or \pL that matches a single character a character class a back reference (see next section) - a parenthesized subpattern (unless it is an assertion) - a recursive or "subroutine" call to a subpattern + 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,} @@ -4453,17 +5188,16 @@ 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-8 mode, quantifiers apply to UTF-8 characters rather than to - individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char- - acters, each of which is represented by a two-byte sequence. Similarly, - when Unicode property support is available, \X{3} matches three Unicode - extended sequences, each of which may be several bytes long (and they - may be of different lengths). + In UTF modes, quantifiers apply to characters rather than to individual + data units. Thus, for example, \x{100}{2} matches two characters, each + of which is represented by a two-byte sequence in a UTF-8 string. Simi- + larly, \X{3} matches three Unicode extended sequences, each of which + may be several data units long (and they may be of different lengths). The quantifier {0} is permitted, causing the expression to behave as if the previous item and the quantifier were not present. This may be use- @@ -4769,8 +5503,8 @@ BACK REFERENCES 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 whitespace. Otherwise, the \g{ - syntax or an empty comment (see "Comments" below) can be used. + 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 @@ -4807,13 +5541,29 @@ ASSERTIONS matched in the normal way, except that it does not cause the current matching position to be changed. - Assertion subpatterns are not capturing subpatterns, and may not be - repeated, because it makes no sense to assert the same thing several - times. If any kind of assertion contains capturing subpatterns within - it, these are counted for the purposes of numbering the capturing sub- - patterns in the whole pattern. 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, because it does not make sense for negative assertions. + + For compatibility with Perl, assertion subpatterns may be repeated; + though it makes no sense to assert the same thing several times, the + side effect of capturing parentheses may occasionally be useful. In + practice, there only three cases: + + (1) If the quantifier is {0}, the assertion is never obeyed during + matching. However, it may contain internal capturing parenthesized + groups that are called from elsewhere via the subroutine mechanism. + + (2) If quantifier is {0,n} where n is greater than zero, it is treated + as if it were {0,1}. At run time, the rest of the pattern match is + tried with and without the assertion, the order depending on the greed- + iness of the quantifier. + + (3) If the minimum repetition is greater than zero, the quantifier is + ignored. The assertion is obeyed just once when encountered during + matching. Lookahead assertions @@ -4883,40 +5633,41 @@ ASSERTIONS then try to match. If there are insufficient characters before the cur- rent position, the assertion fails. - PCRE does not allow the \C escape (which matches a single byte in UTF-8 - mode) to appear in lookbehind assertions, because it makes it impossi- - ble to calculate the length of the lookbehind. The \X and \R escapes, - which can match different numbers of bytes, are also not permitted. + In a UTF mode, PCRE does not allow the \C escape (which matches a sin- + gle data unit even in a UTF mode) to appear in lookbehind assertions, + because it makes it impossible to calculate the length of the lookbe- + hind. The \X and \R escapes, which can match different numbers of data + units, are also not permitted. - "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in - lookbehinds, as long as the subpattern matches a fixed-length string. + "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in + lookbehinds, as long as the subpattern matches a fixed-length string. Recursion, however, is not supported. - Possessive quantifiers can be used in conjunction with lookbehind + Possessive quantifiers can be used in conjunction with lookbehind assertions to specify efficient matching of fixed-length strings at the end of subject strings. Consider a simple pattern such as abcd$ - when applied to a long string that does not match. Because matching + when applied to a long string that does not match. Because matching proceeds from left to right, PCRE will look for each "a" in the subject - and then see if what follows matches the rest of the pattern. If the + and then see if what follows matches the rest of the pattern. If the pattern is specified as ^.*abcd$ - the initial .* matches the entire string at first, but when this fails + the initial .* matches the entire string at first, but when this fails (because there is no following "a"), it backtracks to match all but the - last character, then all but the last two characters, and so on. Once - again the search for "a" covers the entire string, from right to left, + last character, then all but the last two characters, and so on. Once + again the search for "a" covers the entire string, from right to left, so we are no better off. However, if the pattern is written as ^.*+(?<=abcd) - there can be no backtracking for the .*+ item; it can match only the - entire string. The subsequent lookbehind assertion does a single test - on the last four characters. If it fails, the match fails immediately. - For long strings, this approach makes a significant difference to the + there can be no backtracking for the .*+ item; it can match only the + entire string. The subsequent lookbehind assertion does a single test + on the last four characters. If it fails, the match fails immediately. + For long strings, this approach makes a significant difference to the processing time. Using multiple assertions @@ -4925,18 +5676,18 @@ ASSERTIONS (?<=\d{3})(?<!999)foo - matches "foo" preceded by three digits that are not "999". Notice that - each of the assertions is applied independently at the same point in - the subject string. First there is a check that the previous three - characters are all digits, and then there is a check that the same + matches "foo" preceded by three digits that are not "999". Notice that + each of the assertions is applied independently at the same point in + the subject string. First there is a check that the previous three + characters are all digits, and then there is a check that the same three characters are not "999". This pattern does not match "foo" pre- - ceded by six characters, the first of which are digits and the last - three of which are not "999". For example, it doesn't match "123abc- + ceded by six characters, the first of which are digits and the last + three of which are not "999". For example, it doesn't match "123abc- foo". A pattern to do that is (?<=\d{3}...)(?<!999)foo - This time the first assertion looks at the preceding six characters, + This time the first assertion looks at the preceding six characters, checking that the first three are digits, and then the second assertion checks that the preceding three characters are not "999". @@ -4944,29 +5695,29 @@ ASSERTIONS (?<=(?<!foo)bar)baz - matches an occurrence of "baz" that is preceded by "bar" which in turn + matches an occurrence of "baz" that is preceded by "bar" which in turn is not preceded by "foo", while (?<=\d{3}(?!999)...)foo - is another pattern that matches "foo" preceded by three digits and any + is another pattern that matches "foo" preceded by three digits and any three characters that are not "999". CONDITIONAL SUBPATTERNS - It is possible to cause the matching process to obey a subpattern con- - ditionally or to choose between two alternative subpatterns, depending - on the result of an assertion, or whether a specific capturing subpat- - tern has already been matched. The two possible forms of conditional + It is possible to cause the matching process to obey a subpattern con- + ditionally or to choose between two alternative subpatterns, depending + on the result of an assertion, or whether a specific capturing subpat- + tern has already been matched. The two possible forms of conditional subpattern are: (?(condition)yes-pattern) (?(condition)yes-pattern|no-pattern) - If the condition is satisfied, the yes-pattern is used; otherwise the - no-pattern (if present) is used. If there are more than two alterna- - tives in the subpattern, a compile-time error occurs. Each of the two + If the condition is satisfied, the yes-pattern is used; otherwise the + no-pattern (if present) is used. If there are more than two alterna- + tives in the subpattern, a compile-time error occurs. Each of the two alternatives may itself contain nested subpatterns of any form, includ- ing conditional subpatterns; the restriction to two alternatives applies only at the level of the condition. This pattern fragment is an @@ -4975,73 +5726,73 @@ CONDITIONAL SUBPATTERNS (?(1) (A|B|C) | (D | (?(2)E|F) | E) ) - There are four kinds of condition: references to subpatterns, refer- + There are four kinds of condition: references to subpatterns, refer- ences to recursion, a pseudo-condition called DEFINE, and assertions. Checking for a used subpattern by number - If the text between the parentheses consists of a sequence of digits, + If the text between the parentheses consists of a sequence of digits, the condition is true if a capturing subpattern of that number has pre- - viously matched. If there is more than one capturing subpattern with - the same number (see the earlier section about duplicate subpattern - numbers), the condition is true if any of them have matched. An alter- - native notation is to precede the digits with a plus or minus sign. In - this case, the subpattern number is relative rather than absolute. The - most recently opened parentheses can be referenced by (?(-1), the next - most recent by (?(-2), and so on. Inside loops it can also make sense + viously matched. If there is more than one capturing subpattern with + the same number (see the earlier section about duplicate subpattern + numbers), the condition is true if any of them have matched. An alter- + native notation is to precede the digits with a plus or minus sign. In + this case, the subpattern number is relative rather than absolute. The + most recently opened parentheses can be referenced by (?(-1), the next + most recent by (?(-2), and so on. Inside loops it can also make sense to refer to subsequent groups. The next parentheses to be opened can be - referenced as (?(+1), and so on. (The value zero in any of these forms + referenced as (?(+1), and so on. (The value zero in any of these forms is not used; it provokes a compile-time error.) - Consider the following pattern, which contains non-significant white + Consider the following pattern, which contains non-significant white space to make it more readable (assume the PCRE_EXTENDED option) and to divide it into three parts for ease of discussion: ( \( )? [^()]+ (?(1) \) ) - The first part matches an optional opening parenthesis, and if that + The first part matches an optional opening parenthesis, and if that character is present, sets it as the first captured substring. The sec- - ond part matches one or more characters that are not parentheses. The - third part is a conditional subpattern that tests whether or not the - first set of parentheses matched. If they did, that is, if subject - started with an opening parenthesis, the condition is true, and so the - yes-pattern is executed and a closing parenthesis is required. Other- - wise, since no-pattern is not present, the subpattern matches nothing. - In other words, this pattern matches a sequence of non-parentheses, + ond part matches one or more characters that are not parentheses. The + third part is a conditional subpattern that tests whether or not the + first set of parentheses matched. If they did, that is, if subject + started with an opening parenthesis, the condition is true, and so the + yes-pattern is executed and a closing parenthesis is required. Other- + wise, since no-pattern is not present, the subpattern matches nothing. + In other words, this pattern matches a sequence of non-parentheses, optionally enclosed in parentheses. - If you were embedding this pattern in a larger one, you could use a + If you were embedding this pattern in a larger one, you could use a relative reference: ...other stuff... ( \( )? [^()]+ (?(-1) \) ) ... - This makes the fragment independent of the parentheses in the larger + This makes the fragment independent of the parentheses in the larger pattern. Checking for a used subpattern by name - Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a - used subpattern by name. For compatibility with earlier versions of - PCRE, which had this facility before Perl, the syntax (?(name)...) is - also recognized. However, there is a possible ambiguity with this 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- + 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. 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: @@ -5049,24 +5800,23 @@ 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 ref- - erenced from elsewhere. (The use of "subroutines" is described below.) - For example, a pattern to match an IPv4 address such as - "192.168.23.245" could be written like this (ignore whitespace and line - breaks): + 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 @@ -5112,12 +5862,12 @@ COMMENTS 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 - pcre_compile() or by a special sequence at the start of the pattern, as - described in the section entitled "Newline conventions" above. Note - that the end of this type of comment is a literal newline sequence in - the pattern; escape sequences that happen to represent a newline do not - count. For example, consider this pattern when PCRE_EXTENDED is set, - and the default newline convention is in force: + 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 + set, and the default newline convention is in force: abc #comment \n still comment @@ -5153,11 +5903,11 @@ RECURSIVE PATTERNS 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 call of the subpattern of - the given number, provided that it occurs inside that subpattern. (If - not, it is a "subroutine" call, which is described in the next sec- - tion.) The special item (?R) or (?0) is a recursive call of the entire - regular expression. + zero and a closing parenthesis is a recursive subroutine call of the + subpattern of the given number, provided that it occurs inside that + subpattern. (If not, it is a non-recursive subroutine call, which is + described in the next section.) The special item (?R) or (?0) is a + recursive call of the entire regular expression. This PCRE pattern solves the nested parentheses problem (assume the PCRE_EXTENDED option is set so that white space is ignored): @@ -5189,8 +5939,8 @@ RECURSIVE PATTERNS 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 "subroutine" calls, as described in the next - section. + 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 @@ -5223,28 +5973,30 @@ RECURSIVE PATTERNS 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 value is unset, even - if it is (temporarily) set at a deeper level. + 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. - Recursion difference from Perl + Differences in recursion processing between PCRE and Perl + Recursion processing in PCRE differs from Perl in two important ways. In PCRE (like Python, but unlike Perl), a recursive subpattern call is always treated as an atomic group. That is, once it has matched some of the subject string, it is never re-entered, even if it contains untried @@ -5317,14 +6069,30 @@ RECURSIVE PATTERNS 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 + pattern: + + ^(.)(\1|a(?2)) + + In PCRE, this pattern matches "bab". The first capturing parentheses + match "b", then in the second group, when the back reference \1 fails + to match "b", the second alternative matches "a" and then recurses. In + the recursion, \1 does now match "b" and so the whole match succeeds. + In Perl, the pattern fails to match because inside the recursive call + \1 cannot access the externally set value. + SUBPATTERNS AS SUBROUTINES - If the syntax for a recursive subpattern reference (either by number or - by name) is used outside the parentheses to which it refers, it oper- - ates like a subroutine in a programming language. The "called" subpat- - tern may be defined before or after the reference. A numbered reference - can be absolute or relative, as in these examples: + If the syntax for a recursive subpattern call (either by number or by + name) is used outside the parentheses to which it refers, it operates + like a subroutine in a programming language. The called subpattern may + be defined before or after the reference. A numbered reference can be + absolute or relative, as in these examples: (...(absolute)...)...(?2)... (...(relative)...)...(?-1)... @@ -5343,15 +6111,15 @@ SUBPATTERNS AS SUBROUTINES two strings. Another example is given in the discussion of DEFINE above. - Like recursive subpatterns, a subroutine 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. Any capturing parentheses that - are set during the subroutine call revert to their previous values - afterwards. + 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 + previous values afterwards. - When a subpattern is used as a subroutine, processing options such as - case-independence are fixed when the subpattern is defined. They 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)) @@ -5392,8 +6160,8 @@ CALLOUTS 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. By default, this variable contains NULL, which disables - all calling out. + pcre_callout (8-bit library) or pcre16_callout (16-bit library). By + default, this variable contains NULL, which disables all calling out. Within a regular expression, (?C) indicates the points at which the external function is to be called. If you want to identify different @@ -5403,17 +6171,17 @@ CALLOUTS (?C1)abc(?C2)def - If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts 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. - During matching, when PCRE reaches a callout point (and pcre_callout is - set), the external function is called. It is provided with the number - of the callout, the position in the pattern, and, optionally, one item - of data originally supplied by the caller of pcre_exec(). The callout - function may cause matching to proceed, to backtrack, or to fail alto- - gether. 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. A + complete description of the interface to the callout function is given + in the pcrecallout documentation. BACKTRACKING CONTROL @@ -5426,25 +6194,33 @@ BACKTRACKING CONTROL 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 - pcre_exec(), which uses a backtracking algorithm. With the exception of - (*FAIL), which behaves like a failing negative assertion, they cause an - error if encountered by pcre_dfa_exec(). - - If any of these verbs are used in an assertion or subroutine subpattern - (including recursive subpatterns), their effect is confined to that - subpattern; it does not extend to the surrounding pattern. Note that - such subpatterns are processed as anchored at the point where they are - tested. - - The new verbs make use of what was previously invalid syntax: an open- + 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. + + 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- 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. An name is - a sequence of letters, digits, and underscores. 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. + (*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 + 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 library. If the name is empty, that is, if the closing parenthe- + sis immediately follows the colon, the effect is as if the colon were + not there. Any number of these verbs may occur in a pattern. + + Optimizations that affect backtracking verbs 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 @@ -5454,60 +6230,64 @@ BACKTRACKING CONTROL course, be processed. You can suppress the start-of-match optimizations 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, + 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. When inside a recursion, only the innermost pattern is - ended immediately. If (*ACCEPT) is inside capturing parentheses, the - data so far is captured. (This feature was added to PCRE at release - 8.00.) 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) is inside capturing + parentheses, the data so far is captured. For example: A((?:A|B(*ACCEPT)|C)D) - This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is 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 the match to fail, 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) is - passed back to the caller via the pcre_extra data structure, as - described in the section on pcre_extra in the pcreapi documentation. No - data is returned for a partial match. 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) 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: - /X(*MARK:A)Y|X(*MARK:B)Z/K - XY + re> /X(*MARK:A)Y|X(*MARK:B)Z/K + data> XY 0: XY MK: A XZ @@ -5519,98 +6299,86 @@ BACKTRACKING CONTROL efficient way of obtaining this information than putting each alterna- tive in its own capturing parentheses. - A name may also be returned after a failed match if the final path - through the pattern involves (*MARK). However, unless (*MARK) used in - conjunction with (*COMMIT), this is unlikely to happen for an unan- - chored pattern because, as the starting point for matching is advanced, - the final check is often with an empty string, causing a failure before - (*MARK) is reached. For example: - - /X(*MARK:A)Y|X(*MARK:B)Z/K - XP - No match + 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. - There are three potential starting points for this match (starting with - X, starting with P, and with an empty string). If the pattern is - anchored, the result is different: + 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: - /^X(*MARK:A)Y|^X(*MARK:B)Z/K - XP + re> /X(*MARK:A)Y|X(*MARK:B)Z/K + data> XP No match, mark = B - PCRE's start-of-match optimizations can also interfere with this. For - example, if, as a result of a call to pcre_study(), it knows the mini- - mum subject length for a match, a shorter subject will not be scanned - at all. + 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. - Note that similar anomalies (though different in detail) exist in Perl, - no doubt for the same reasons. The use of (*MARK) data after a failed - match of an unanchored pattern is not recommended, unless (*COMMIT) is - involved. + 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 + 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.) - These verbs differ in exactly what kind of failure occurs when back- + These verbs differ in exactly what kind of failure occurs when back- tracking reaches them. (*COMMIT) - This verb, which may not be followed by a name, causes the whole match + 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 + pcre_exec() is committed to finding a match at the current starting point, or not at all. For example: a+(*COMMIT)b - This matches "xxaab" but not "aacaab". It can be thought of as a kind + 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. - 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 + 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: - /(*COMMIT)abc/ - xyzabc + re> /(*COMMIT)abc/ + data> xyzabc 0: abc xyzabc\Y No match - PCRE knows that any match must start with "a", so the optimization - skips along the subject to "a" before running the first match attempt, - which succeeds. When the optimization is disabled by the \Y escape in + PCRE knows that any match must start with "a", so the optimization + skips along the subject to "a" before running the first match attempt, + which succeeds. When the optimization is disabled by the \Y escape in the second subject, the match starts at "x" and so the (*COMMIT) causes it to fail without trying any other starting points. (*PRUNE) or (*PRUNE:NAME) - This verb causes the match to fail at the current starting position in - the subject if the rest of the pattern does not match. If the pattern - is unanchored, the normal "bumpalong" advance to the next starting - character then happens. Backtracking can occur as usual to the left of - (*PRUNE), before it is reached, or when matching to the right of - (*PRUNE), but if there is no match to the right, backtracking cannot - cross (*PRUNE). In simple cases, the use of (*PRUNE) is just an alter- - native to an atomic group or possessive quantifier, but there are some + 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) when the - match fails completely; the name is passed back if this is the final - attempt. (*PRUNE:NAME) does not pass back a name if the match suc- - ceeds. In an anchored pattern (*PRUNE) has the same effect as (*COM- - MIT). + iour of (*PRUNE:NAME) is the same as (*MARK:NAME)(*PRUNE). In an + anchored pattern (*PRUNE) has the same effect as (*COMMIT). (*SKIP) @@ -5637,49 +6405,85 @@ BACKTRACKING CONTROL 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, normal "bumpalong" of one - character happens (the (*SKIP) is ignored). + If no (*MARK) with a matching name is found, the (*SKIP) is ignored. (*THEN) or (*THEN:NAME) - This verb causes a skip to the next alternation in the innermost - enclosing group if the rest of the pattern does not match. That is, it - cancels pending backtracking, but only within the current alternation. - 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 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: ( 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 + 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 the overall match fails. If (*THEN) is not - directly inside an alternation, it acts like (*PRUNE). - - The above verbs provide four different "strengths" of control when sub- - sequent matching fails. (*THEN) is the weakest, carrying on the match - at the next alternation. (*PRUNE) comes next, failing the match at the - current starting position, but allowing an advance to the next charac- - ter (for an unanchored pattern). (*SKIP) is similar, except that the - advance may be more than one character. (*COMMIT) is the strongest, + (*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: + + A (B(*THEN)C) | D + + If A and B are matched, but there is a failure in C, matching does not + backtrack into A; instead it moves to the next alternative, that is, D. + However, if the subpattern containing (*THEN) is given an alternative, + it behaves differently: + + A (B(*THEN)C | (*FAIL)) | D + + The effect of (*THEN) is now confined to the inner subpattern. After a + failure in C, matching moves to (*FAIL), which causes the whole subpat- + 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 + alternatives, because only one is ever used. In other words, the | + character in a conditional subpattern has a different meaning. Ignoring + white space, consider: + + ^.*? (?(?=a) a | b(*THEN)c ) + + If the subject is "ba", this pattern does not match. Because .*? is + ungreedy, it initially matches zero characters. The condition (?=a) + then fails, the character "b" is matched, but "c" is not. At this + point, matching does not backtrack to .*? as might perhaps be expected + from the presence of the | character. The conditional subpattern is + part of the single alternative that comprises the whole pattern, and so + the match fails. (If there was a backtrack into .*?, allowing it to + match "b", the match would succeed.) + + The verbs just described provide four different "strengths" of control + when subsequent matching fails. (*THEN) is the weakest, carrying on the + match at the next alternative. (*PRUNE) comes next, failing the match + at the current starting position, but allowing an advance to the next + character (for an unanchored pattern). (*SKIP) is similar, except that + the advance may be more than one character. (*COMMIT) is the strongest, causing the entire match to fail. - If more than one is present in a pattern, the "stongest" one wins. For - example, consider this pattern, where A, B, etc. are complex pattern - fragments: + If more than one such verb is present in a pattern, the "strongest" one + wins. For example, consider this pattern, where A, B, etc. are complex + pattern fragments: (A(*COMMIT)B(*THEN)C|D) - Once A has matched, PCRE is committed to this match, at the current - starting position. If subsequently B matches, but C does not, the nor- - mal (*THEN) action of trying the next alternation (that is, D) does not + 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. SEE ALSO - pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3). + pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3), + pcre16(3). AUTHOR @@ -5691,8 +6495,8 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 17 June 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -5707,7 +6511,7 @@ PCRE REGULAR EXPRESSION SYNTAX SUMMARY The full syntax and semantics of the regular expressions that are sup- ported by PCRE are described in the pcrepattern documentation. This - document contains just a quick-reference summary of the syntax. + document contains a quick-reference summary of the syntax. QUOTING @@ -5721,7 +6525,7 @@ CHARACTERS \a alarm, that is, the BEL character (hex 07) \cx "control-x", where x is any ASCII character \e escape (hex 1B) - \f formfeed (hex 0C) + \f form feed (hex 0C) \n newline (hex 0A) \r carriage return (hex 0D) \t tab (hex 09) @@ -5734,25 +6538,25 @@ CHARACTER TYPES . any character except newline; in dotall mode, any character whatsoever - \C one byte, even in UTF-8 mode (best avoided) + \C one data unit, even in UTF mode (best avoided) \d a decimal digit \D a character that is not a decimal digit - \h a horizontal whitespace character - \H a character that is not a horizontal whitespace character + \h a horizontal white space character + \H a character that is not a horizontal white space character \N a character that is not a newline \p{xx} a character with the xx property \P{xx} a character without the xx property \R a newline sequence - \s a whitespace character - \S a character that is not a whitespace character - \v a vertical whitespace character - \V a character that is not a vertical whitespace character + \s a white space character + \S a character that is not a white space character + \v a vertical white space character + \V a character that is not a vertical white space character \w a "word" character \W a "non-word" character \X an extended Unicode sequence In PCRE, by default, \d, \D, \s, \S, \w, and \W recognize only ASCII - characters, even in UTF-8 mode. However, this can be changed by setting + characters, even in a UTF mode. However, this can be changed by setting the PCRE_UCP option. @@ -5814,20 +6618,22 @@ PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P SCRIPT NAMES FOR \p AND \P - Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille, - Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, - Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyp- - tian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek, - Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Impe- - rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian, - Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, - Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, - Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, - Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, - Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, - Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, - Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, - Ugaritic, Vai, Yi. + 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, + Yi. CHARACTER CLASSES @@ -5848,7 +6654,7 @@ CHARACTER CLASSES lower lower case letter print printing, including space punct printing, excluding alphanumeric - space whitespace + space white space upper upper case letter word same as \w xdigit hexadecimal digit @@ -5939,7 +6745,8 @@ OPTION SETTING one of the newline-setting options with similar syntax: (*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE) - (*UTF8) set UTF-8 mode (PCRE_UTF8) + (*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8) + (*UTF16) set UTF-16 mode: 16-bit library (PCRE_UTF16) (*UCP) set PCRE_UCP (use Unicode properties for \d etc) @@ -6008,6 +6815,7 @@ BACKTRACKING CONTROL (*ACCEPT) force successful match (*FAIL) force backtrack; synonym (*F) + (*MARK:NAME) set name to be passed back; synonym (*:NAME) The following act only when a subsequent match failure causes a back- track to reach them. They all force a match failure, but they differ in @@ -6016,14 +6824,18 @@ BACKTRACKING CONTROL (*COMMIT) overall failure, no advance of starting point (*PRUNE) advance to next starting character - (*SKIP) advance start to current matching position + (*PRUNE:NAME) equivalent to (*MARK:NAME)(*PRUNE) + (*SKIP) advance to current matching position + (*SKIP:NAME) advance to position corresponding to an earlier + (*MARK:NAME); if not found, the (*SKIP) is ignored (*THEN) local failure, backtrack to next alternation + (*THEN:NAME) equivalent to (*MARK:NAME)(*THEN) NEWLINE CONVENTIONS These are recognized only at the very start of the pattern or after a - (*BSR_...) or (*UTF8) or (*UCP) option. + (*BSR_...), (*UTF8), (*UTF16) or (*UCP) option. (*CR) carriage return only (*LF) linefeed only @@ -6035,7 +6847,7 @@ NEWLINE CONVENTIONS WHAT \R MATCHES These are recognized only at the very start of the pattern or after a - (*...) option that sets the newline convention or UTF-8 or UCP mode. + (*...) option that sets the newline convention or a UTF or UCP mode. (*BSR_ANYCRLF) CR, LF, or CRLF (*BSR_UNICODE) any Unicode newline sequence @@ -6061,8 +6873,594 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 10 January 2012 + Copyright (c) 1997-2012 University of Cambridge. +------------------------------------------------------------------------------ + + +PCREUNICODE(3) PCREUNICODE(3) + + +NAME + PCRE - Perl-compatible regular expressions + + +UTF-8, UTF-16, AND UNICODE PROPERTY SUPPORT + + From Release 8.30, in addition to its previous UTF-8 support, PCRE also + supports UTF-16 by means of a separate 16-bit library. This can be + built as well as, or instead of, the 8-bit library. + + +UTF-8 SUPPORT + + In order process UTF-8 strings, you must build PCRE's 8-bit library + with UTF support, and, in addition, you must call pcre_compile() with + the PCRE_UTF8 option flag, or the pattern must start with the sequence + (*UTF8). When either of these is the case, both the pattern and any + subject strings that are matched against it are treated as UTF-8 + strings instead of strings of 1-byte characters. + + +UTF-16 SUPPORT + + In order process UTF-16 strings, you must build PCRE's 16-bit library + with UTF support, and, in addition, you must call pcre16_compile() with + the PCRE_UTF16 option flag, or the pattern must start with the sequence + (*UTF16). When either of these is the case, both the pattern and any + subject strings that are matched against it are treated as UTF-16 + strings instead of strings of 16-bit characters. + + +UTF SUPPORT OVERHEAD + + If you compile PCRE with UTF support, but do not use it at run time, + the library will be a bit bigger, but the additional run time overhead + is limited to testing the PCRE_UTF8/16 flag occasionally, so should not + be very big. + + +UNICODE PROPERTY SUPPORT + + If PCRE is built with Unicode character property support (which implies + UTF support), the escape sequences \p{..}, \P{..}, and \X can be used. + The available properties that can be tested are limited to the general + category properties such as Lu for an upper case letter or Nd for a + decimal number, the Unicode script names such as Arabic or Han, and the + derived properties Any and L&. A full list is given in the pcrepattern + documentation. Only the short names for properties are supported. For + example, \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not + supported. Furthermore, in Perl, many properties may optionally be + prefixed by "Is", for compatibility with Perl 5.6. PCRE does not sup- + port this. + + Validity of UTF-8 strings + + When you set the PCRE_UTF8 flag, the byte strings passed as patterns + and subjects are (by default) checked for validity on entry to the rel- + evant functions. The entire string is checked before any other process- + ing takes place. From release 7.3 of PCRE, the check is according the + rules of RFC 3629, which are themselves derived from the Unicode speci- + 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 U+D800 to U+DFFF. + + The excluded code points are the "Surrogate Area" of Unicode. They are + reserved for use by UTF-16, where they are used in pairs to encode + codepoints with values greater than 0xFFFF. The code points that are + encoded by UTF-16 pairs are available independently in the UTF-8 encod- + ing. (In other words, the whole surrogate thing is a fudge for UTF-16 + which unfortunately messes up UTF-8.) + + If an invalid UTF-8 string is passed to PCRE, an error return is given. + At compile time, the only additional information is the offset to the + first byte of the failing character. The run-time functions pcre_exec() + and pcre_dfa_exec() also pass back this information, as well as a more + detailed reason code if the caller has provided memory in which to do + this. + + In some situations, you may already know that your strings are valid, + and therefore want to skip these checks in order to improve perfor- + mance, for example in the case of a long subject string that is being + scanned repeatedly with different patterns. If you set the + PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE assumes + that the pattern or subject it is given (respectively) contains only + valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 + string. + + If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, + what happens depends on why the string is invalid. If the string con- + forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a + string of characters in the range 0 to 0x7FFFFFFF by pcre_dfa_exec() + and the interpreted version of pcre_exec(). In other words, apart from + the initial validity test, these functions (when in UTF-8 mode) handle + strings according to the more liberal rules of RFC 2279. However, the + just-in-time (JIT) optimization for pcre_exec() supports only RFC 3629. + If you are using JIT optimization, or if the string does not even con- + form to RFC 2279, the result is undefined. Your program may crash. + + If you want to process strings of values in the full range 0 to + 0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you can + set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in + this situation, you will have to apply your own validity check, and + avoid the use of JIT optimization. + + Validity of UTF-16 strings + + When you set the PCRE_UTF16 flag, the strings of 16-bit data units that + are passed as patterns and subjects are (by default) checked for valid- + ity on entry to the relevant functions. Values other than those in the + surrogate range U+D800 to U+DFFF are independent code points. Values in + the surrogate range must be used in pairs in the correct manner. + + If an invalid UTF-16 string is passed to PCRE, an error return is + given. At compile time, the only additional information is the offset + to the first data unit of the failing character. The run-time functions + pcre16_exec() and pcre16_dfa_exec() also pass back this information, as + well as a more detailed reason code if the caller has provided memory + in which to do this. + + In some situations, you may already know that your strings are valid, + and therefore want to skip these checks in order to improve perfor- + mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at + run time, PCRE assumes that the pattern or subject it is given (respec- + tively) contains only valid UTF-16 sequences. In this case, it does not + diagnose an invalid UTF-16 string. + + General comments about UTF modes + + 1. Codepoints less than 256 can be specified by either braced or + unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). + Larger values have to use braced sequences. + + 2. Octal numbers up to \777 are recognized, and in UTF-8 mode, they + match two-byte characters for values greater than \177. + + 3. Repeat quantifiers apply to complete UTF characters, not to individ- + ual data units, for example: \x{100}{3}. + + 4. The dot metacharacter matches one UTF character instead of a single + data unit. + + 5. The escape sequence \C can be used to match a single byte in UTF-8 + mode, or a single 16-bit data unit in UTF-16 mode, but its use can lead + to some strange effects because it breaks up multi-unit characters (see + the description of \C in the pcrepattern documentation). The use of \C + is not supported in the alternative matching function + pcre[16]_dfa_exec(), nor is it supported in UTF mode by the JIT opti- + mization of pcre[16]_exec(). If JIT optimization is requested for a UTF + pattern that contains \C, it will not succeed, and so the matching will + be carried out by the normal interpretive function. + + 6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly + test characters of any code value, but, by default, the characters that + PCRE recognizes as digits, spaces, or word characters remain the same + set as in non-UTF mode, all with values less than 256. This remains + true even when PCRE is built to include Unicode property support, + because to do otherwise would slow down PCRE in many common cases. Note + in particular that this applies to \b and \B, because they are defined + in terms of \w and \W. If you really want to test for a wider sense of, + say, "digit", you can use explicit Unicode property tests such as + \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the + character escapes work is changed so that Unicode properties are used + to determine which characters match. There are more details in the sec- + tion on generic character types in the pcrepattern documentation. + + 7. Similarly, characters that match the POSIX named character classes + are all low-valued characters, unless the PCRE_UCP option is set. + + 8. However, the horizontal and vertical 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. + Even when Unicode property support is available, PCRE still uses its + own character tables when checking the case of low-valued characters, + so as not to degrade performance. The Unicode property information is + used only for characters with higher values. Furthermore, PCRE supports + case-insensitive matching only when there is a one-to-one mapping + between a letter's cases. There are a small number of many-to-one map- + pings in Unicode; these are not supported by PCRE. + + +AUTHOR + + Philip Hazel + University Computing Service + Cambridge CB2 3QH, England. + + +REVISION + + Last updated: 14 April 2012 + Copyright (c) 1997-2012 University of Cambridge. +------------------------------------------------------------------------------ + + +PCREJIT(3) 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 + speed up pattern matching. However, it comes at the cost of extra pro- + cessing before the match is performed. Therefore, it is of most benefit + when the same pattern is going to be matched many times. This does not + necessarily mean many calls of a matching function; if the pattern is + not anchored, matching attempts may take place many times at various + positions in the subject, even for a single call. Therefore, if the + subject string is very long, it may still pay to use JIT for one-off + matches. + + JIT support applies only to the traditional Perl-compatible matching + function. It does not apply when the DFA matching function is being + used. The code for this support was written by Zoltan Herczeg. + + +8-BIT and 16-BIT SUPPORT + + JIT support is available for both the 8-bit and 16-bit PCRE libraries. + To keep this documentation simple, only the 8-bit interface is + described in what follows. If you are using the 16-bit library, substi- + tute the 16-bit functions and 16-bit structures (for example, + pcre16_jit_stack instead of pcre_jit_stack). + + +AVAILABILITY OF JIT SUPPORT + + JIT support is an optional feature of PCRE. The "configure" option + --enable-jit (or equivalent CMake option) must be set when PCRE is + built if you want to use JIT. The support is limited to the following + hardware platforms: + + ARM v5, v7, and Thumb2 + Intel x86 32-bit and 64-bit + MIPS 32-bit + Power PC 32-bit and 64-bit + + If --enable-jit is set on an unsupported platform, compilation fails. + + A program that is linked with PCRE 8.20 or later can tell if JIT sup- + port is available by calling pcre_config() with the PCRE_CONFIG_JIT + option. The result is 1 when JIT is available, and 0 otherwise. How- + ever, a simple program does not need to check this in order to use JIT. + The API is implemented in a way that falls back to the interpretive + code if JIT is not available. + + If your program may sometimes be linked with versions of PCRE that are + older than 8.20, but you want to use JIT when it is available, you can + test the values of PCRE_MAJOR and PCRE_MINOR, or the existence of a JIT + macro such as PCRE_CONFIG_JIT, for compile-time control of your code. + + +SIMPLE USE OF JIT + + You have to do two things to make use of the JIT support in the sim- + plest way: + + (1) Call pcre_study() with the PCRE_STUDY_JIT_COMPILE option for + each compiled pattern, and pass the resulting pcre_extra block to + pcre_exec(). + + (2) Use pcre_free_study() to free the pcre_extra block when it is + no longer needed, instead of just freeing it yourself. This + ensures that any JIT data is also freed. + + For a program that may be linked with pre-8.20 versions of PCRE, you + can insert + + #ifndef PCRE_STUDY_JIT_COMPILE + #define PCRE_STUDY_JIT_COMPILE 0 + #endif + + so that no option is passed to pcre_study(), and then use something + like this to free the study data: + + #ifdef PCRE_CONFIG_JIT + pcre_free_study(study_ptr); + #else + pcre_free(study_ptr); + #endif + + PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for + complete matches. If you want to run partial matches using the + PCRE_PARTIAL_HARD or PCRE_PARTIAL_SOFT options of pcre_exec(), you + should set one or both of the following options in addition to, or + instead of, PCRE_STUDY_JIT_COMPILE when you call pcre_study(): + + PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE + PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE + + The JIT compiler generates different optimized code for each of the + three modes (normal, soft partial, hard partial). When pcre_exec() is + called, the appropriate code is run if it is available. Otherwise, the + pattern is matched using interpretive code. + + In some circumstances you may need to call additional functions. These + are described in the section entitled "Controlling the JIT stack" + below. + + If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are + ignored, and no JIT data is created. Otherwise, the compiled pattern is + passed to the JIT compiler, which turns it into machine code that exe- + cutes much faster than the normal interpretive code. When pcre_exec() + is passed a pcre_extra block containing a pointer to JIT code of the + appropriate mode (normal or hard/soft partial), it obeys that code + instead of running the interpreter. The result is identical, but the + compiled JIT code runs much faster. + + There are some pcre_exec() options that are not supported for JIT exe- + cution. There are also some pattern items that JIT cannot handle. + Details are given below. In both cases, execution automatically falls + back to the interpretive code. If you want to know whether JIT was + actually used for a particular match, you should arrange for a JIT + callback function to be set up as described in the section entitled + "Controlling the JIT stack" below, even if you do not need to supply a + non-default JIT stack. Such a callback function is called whenever JIT + code is about to be obeyed. If the execution options are not right for + JIT execution, the callback function is not obeyed. + + If the JIT compiler finds an unsupported item, no JIT data is gener- + ated. You can find out if JIT execution is available after studying a + pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A + result of 1 means that JIT compilation was successful. A result of 0 + means that JIT support is not available, or the pattern was not studied + with PCRE_STUDY_JIT_COMPILE etc., or the JIT compiler was not able to + handle the pattern. + + Once a pattern has been studied, with or without JIT, it can be used as + many times as you like for matching different subject strings. + + +UNSUPPORTED OPTIONS AND PATTERN ITEMS + + The only pcre_exec() options that are supported for JIT execution are + PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, + PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PAR- + TIAL_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. + + +RETURN VALUES FROM JIT EXECUTION + + When a pattern is matched using JIT execution, the return values are + the same as those given by the interpretive pcre_exec() code, with the + addition of one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means + that the memory used for the JIT stack was insufficient. See "Control- + ling the JIT stack" below for a discussion of JIT stack usage. For com- + patibility with the interpretive pcre_exec() code, no more than two- + thirds of the ovector argument is used for passing back captured sub- + strings. + + The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if + searching a very large pattern tree goes on for too long, as it is in + the same circumstance when JIT is not used, but the details of exactly + what is counted are not the same. The PCRE_ERROR_RECURSIONLIMIT error + code is never returned by JIT execution. + + +SAVING AND RESTORING COMPILED PATTERNS + + The code that is generated by the JIT compiler is architecture-spe- + cific, and is also position dependent. For those reasons it cannot be + saved (in a file or database) and restored later like the bytecode and + other data of a compiled pattern. Saving and restoring compiled pat- + terns is not something many people do. More detail about this facility + is given in the pcreprecompile documentation. It should be possible to + run pcre_study() on a saved and restored pattern, and thereby recreate + the JIT data, but because JIT compilation uses significant resources, + it is probably not worth doing this; you might as well recompile the + original pattern. + + +CONTROLLING THE JIT STACK + + When the compiled JIT code runs, it needs a block of memory to use as a + stack. By default, it uses 32K on the machine stack. However, some + large or complicated patterns need more than this. The error + PCRE_ERROR_JIT_STACKLIMIT is given when there is not enough stack. + Three functions are provided for managing blocks of memory for use as + JIT stacks. There is further discussion about the use of JIT stacks in + the section entitled "JIT stack FAQ" below. + + The pcre_jit_stack_alloc() function creates a JIT stack. Its arguments + are a starting size and a maximum size, and it returns a pointer to an + opaque structure of type pcre_jit_stack, or NULL if there is an error. + The pcre_jit_stack_free() function can be used to free a stack that is + no longer needed. (For the technically minded: the address space is + allocated by mmap or VirtualAlloc.) + + JIT uses far less memory for recursion than the interpretive code, and + a maximum stack size of 512K to 1M should be more than enough for any + pattern. + + The pcre_assign_jit_stack() function specifies which stack JIT code + should use. Its arguments are as follows: + + pcre_extra *extra + pcre_jit_callback callback + void *data + + The extra argument must be the result of studying a pattern with + PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the + other two options: + + (1) If callback is NULL and data is NULL, an internal 32K block + on the machine stack is used. + + (2) If callback is NULL and data is not NULL, data must be + a valid JIT stack, the result of calling pcre_jit_stack_alloc(). + + (3) If callback is not NULL, it must point to a function that is + called with data as an argument at the start of matching, in + order to set up a JIT stack. If the return from the callback + function is NULL, the internal 32K stack is used; otherwise the + return value must be a valid JIT stack, the result of calling + pcre_jit_stack_alloc(). + + A callback function is obeyed whenever JIT code is about to be run; it + is not obeyed when pcre_exec() is called with options that are incom- + patible for JIT execution. A callback function can therefore be used to + determine whether a match operation was executed by JIT or by the + interpreter. + + You may safely use the same JIT stack for more than one pattern (either + by assigning directly or by callback), as long as the patterns are all + matched sequentially in the same thread. In a multithread application, + if you do not specify a JIT stack, or if you assign or pass back NULL + from a callback, that is thread-safe, because each thread has its own + machine stack. However, if you assign or pass back a non-NULL JIT + stack, this must be a different stack for each thread so that the + application is thread-safe. + + Strictly speaking, even more is allowed. You can assign the same non- + NULL stack to any number of patterns as long as they are not used for + matching by multiple threads at the same time. For example, you can + assign the same stack to all compiled patterns, and use a global mutex + in the callback to wait until the stack is available for use. However, + this is an inefficient solution, and not recommended. + + This is a suggestion for how a multithreaded program that needs to set + up non-default JIT stacks might operate: + + During thread initalization + thread_local_var = pcre_jit_stack_alloc(...) + + During thread exit + pcre_jit_stack_free(thread_local_var) + + Use a one-line callback function + return thread_local_var + + All the functions described in this section do nothing if JIT is not + available, and pcre_assign_jit_stack() does nothing unless the extra + argument is non-NULL and points to a pcre_extra block that is the + result of a successful study with PCRE_STUDY_JIT_COMPILE etc. + + +JIT STACK FAQ + + (1) Why do we need JIT stacks? + + PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack + where the local data of the current node is pushed before checking its + child nodes. Allocating real machine stack on some platforms is diffi- + cult. For example, the stack chain needs to be updated every time if we + extend the stack on PowerPC. Although it is possible, its updating + time overhead decreases performance. So we do the recursion in memory. + + (2) Why don't we simply allocate blocks of memory with malloc()? + + Modern operating systems have a nice feature: they can reserve an + address space instead of allocating memory. We can safely allocate mem- + ory pages inside this address space, so the stack could grow without + moving memory data (this is important because of pointers). Thus we can + allocate 1M address space, and use only a single memory page (usually + 4K) if that is enough. However, we can still grow up to 1M anytime if + needed. + + (3) Who "owns" a JIT stack? + + The owner of the stack is the user program, not the JIT studied pattern + or anything else. The user program must ensure that if a stack is used + by pcre_exec(), (that is, it is assigned to the pattern currently run- + ning), that stack must not be used by any other threads (to avoid over- + writing the same memory area). The best practice for multithreaded pro- + grams is to allocate a stack for each thread, and return this stack + through the JIT callback function. + + (4) When should a JIT stack be freed? + + You can free a JIT stack at any time, as long as it will not be used by + pcre_exec() again. When you assign the stack to a pattern, only a + pointer is set. There is no reference counting or any other magic. You + can free the patterns and stacks in any order, anytime. Just do not + call pcre_exec() with a pattern pointing to an already freed stack, as + that will cause SEGFAULT. (Also, do not free a stack currently used by + pcre_exec() in another thread). You can also replace the stack for a + pattern at any time. You can even free the previous stack before + assigning a replacement. + + (5) Should I allocate/free a stack every time before/after calling + pcre_exec()? + + No, because this is too costly in terms of resources. However, you + could implement some clever idea which release the stack if it is not + used in let's say two minutes. The JIT callback can help to achive this + without keeping a list of the currently JIT studied patterns. + + (6) OK, the stack is for long term memory allocation. But what happens + if a pattern causes stack overflow with a stack of 1M? Is that 1M kept + until the stack is freed? + + Especially on embedded sytems, it might be a good idea to release mem- + ory sometimes without freeing the stack. There is no API for this at + the moment. Probably a function call which returns with the currently + allocated memory for any stack and another which allows releasing mem- + ory (shrinking the stack) would be a good idea if someone needs this. + + (7) This is too much of a headache. Isn't there any better solution for + JIT stack handling? + + No, thanks to Windows. If POSIX threads were used everywhere, we could + throw out this complicated API. + + +EXAMPLE CODE + + This is a single-threaded example that specifies a JIT stack without + using a callback. + + int rc; + int ovector[30]; + pcre *re; + pcre_extra *extra; + pcre_jit_stack *jit_stack; + + re = pcre_compile(pattern, 0, &error, &erroffset, NULL); + /* Check for errors */ + extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error); + jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024); + /* Check for error (NULL) */ + pcre_assign_jit_stack(extra, NULL, jit_stack); + rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30); + /* Check results */ + pcre_free(re); + pcre_free_study(extra); + pcre_jit_stack_free(jit_stack); + + +SEE ALSO + + pcreapi(3) + + +AUTHOR + + Philip Hazel (FAQ by Zoltan Herczeg) + University Computing Service + Cambridge CB2 3QH, England. + + +REVISION + + Last updated: 04 May 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -6075,11 +7473,11 @@ NAME PARTIAL MATCHING IN PCRE - In normal use of PCRE, if the subject string that is passed to - pcre_exec() or pcre_dfa_exec() matches as far as it goes, but is too - short to match the entire pattern, PCRE_ERROR_NOMATCH is returned. - There are circumstances where it might be helpful to distinguish this - case from other cases in which there is no match. + In normal use of PCRE, if the subject string that is passed to a match- + ing function matches as far as it goes, but is too short to match the + entire pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances + where it might be helpful to distinguish this case from other cases in + which there is no match. Consider, for example, an application where a human is required to type in data for a field with specific formatting requirements. An example @@ -6097,41 +7495,52 @@ PARTIAL MATCHING IN PCRE available at once. PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and - PCRE_PARTIAL_HARD options, which can be set when calling pcre_exec() or - pcre_dfa_exec(). For backwards compatibility, PCRE_PARTIAL is a synonym - for PCRE_PARTIAL_SOFT. The essential difference between the two options - is whether or not a partial match is preferred to an alternative com- - plete match, though the details differ between the two matching func- - tions. If both options are set, PCRE_PARTIAL_HARD takes precedence. - - Setting a partial matching option disables two of PCRE's optimizations. - PCRE remembers the last literal byte in a pattern, and abandons match- - ing immediately if such a byte is not present in the subject string. - This optimization cannot be used for a subject string that might match - only partially. If the pattern was studied, PCRE knows the minimum - length of a matching string, and does not bother to run the matching - function on shorter strings. This optimization is also disabled for - partial matching. - - -PARTIAL MATCHING USING pcre_exec() - - A partial match occurs during a call to pcre_exec() when the end of the - subject string is reached successfully, but matching cannot continue - because more characters are needed. However, at least one character in - the subject must have been inspected. This character need not form part - of the final matched string; lookbehind assertions and the \K escape - sequence provide ways of inspecting characters before the start of a - matched substring. The requirement for inspecting at least one charac- - ter exists because an empty string can always be matched; without such - a restriction there would always be a partial match of an empty string - at the end of the subject. - - If there are at least two slots in the offsets vector when pcre_exec() - returns with a partial match, the first slot is set to the offset of - the earliest character that was inspected when the partial match was - found. For convenience, the second offset points to the end of the sub- - ject so that a substring can easily be identified. + PCRE_PARTIAL_HARD options, which can be set when calling any of the + matching functions. For backwards compatibility, PCRE_PARTIAL is a syn- + onym for PCRE_PARTIAL_SOFT. The essential difference between the two + options is whether or not a partial match is preferred to an alterna- + tive complete match, though the details differ between the two types of + matching function. If both options are set, PCRE_PARTIAL_HARD takes + precedence. + + If you want to use partial matching with just-in-time optimized code, + you must call pcre_study() or pcre16_study() with one or both of these + options: + + PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE + PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE + + PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non- + partial matches on the same pattern. If the appropriate JIT study mode + has not been set for a match, the interpretive matching code is used. + + Setting a partial matching option disables two of PCRE's standard opti- + mizations. PCRE remembers the last literal data unit in a pattern, and + abandons matching immediately if it is not present in the subject + string. This optimization cannot be used for a subject string that + might match only partially. If the pattern was studied, PCRE knows the + minimum length of a matching string, and does not bother to run the + matching function on shorter strings. This optimization is also dis- + abled for partial matching. + + +PARTIAL MATCHING USING pcre_exec() OR pcre16_exec() + + A partial match occurs during a call to pcre_exec() or pcre16_exec() + when the end of the subject string is reached successfully, but match- + ing cannot continue because more characters are needed. However, at + least one character in the subject must have been inspected. This char- + acter need not form part of the final matched string; lookbehind asser- + tions and the \K escape sequence provide ways of inspecting characters + before the start of a matched substring. The requirement for inspecting + at least one character exists because an empty string can always be + matched; without such a restriction there would always be a partial + match of an empty string at the end of the subject. + + If there are at least two slots in the offsets vector when a partial + match is returned, the first slot is set to the offset of the earliest + character that was inspected. For convenience, the second offset points + to the end of the subject so that a substring can easily be identified. For the majority of patterns, the first offset identifies the start of the partially matched string. However, for patterns that contain look- @@ -6148,13 +7557,13 @@ PARTIAL MATCHING USING pcre_exec() What happens when a partial match is identified depends on which of the two partial matching options are set. - PCRE_PARTIAL_SOFT with pcre_exec() + PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre16_exec() - If PCRE_PARTIAL_SOFT is set when pcre_exec() identifies a partial - match, the partial match is remembered, but matching continues as nor- - mal, and other alternatives in the pattern are tried. If no complete - match can be found, pcre_exec() returns PCRE_ERROR_PARTIAL instead of - PCRE_ERROR_NOMATCH. + If PCRE_PARTIAL_SOFT is set when pcre_exec() or pcre16_exec() identi- + fies a partial match, the partial match is remembered, but matching + continues as normal, and other alternatives in the pattern are tried. + If no complete match can be found, PCRE_ERROR_PARTIAL is returned + instead of PCRE_ERROR_NOMATCH. This option is "soft" because it prefers a complete match over a par- tial match. All the various matching items in a pattern behave as if @@ -6174,22 +7583,24 @@ PARTIAL MATCHING USING pcre_exec() (In this example, there are two partial matches, because "dog" on its own partially matches the second alternative.) - PCRE_PARTIAL_HARD with pcre_exec() - - If PCRE_PARTIAL_HARD is set for pcre_exec(), it returns PCRE_ERROR_PAR- - TIAL as soon as a partial match is found, without continuing to search - for possible complete matches. This option is "hard" because it prefers - an earlier partial match over a later complete match. For this reason, - the assumption is made that the end of the supplied subject string may - not be the true end of the available data, and so, if \z, \Z, \b, \B, - or $ are encountered at the end of the subject, the result is - PCRE_ERROR_PARTIAL. - - Setting PCRE_PARTIAL_HARD also affects the way pcre_exec() checks UTF-8 - subject strings for validity. Normally, an invalid UTF-8 sequence - causes the error PCRE_ERROR_BADUTF8. However, in the special case of a - truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORT- - UTF8 is returned when PCRE_PARTIAL_HARD is set. + PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre16_exec() + + If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre16_exec(), + PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, + without continuing to search for possible complete matches. This option + is "hard" because it prefers an earlier partial match over a later com- + plete match. For this reason, the assumption is made that the end of + the supplied subject string may not be the true end of the available + data, and so, if \z, \Z, \b, \B, or $ are encountered at the end of the + subject, the result is PCRE_ERROR_PARTIAL, provided that at least one + character in the subject has been inspected. + + Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject + strings are checked for validity. Normally, an invalid sequence causes + the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the + special case of a truncated character at the end of the subject, + PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when + PCRE_PARTIAL_HARD is set. Comparing hard and soft partial matching @@ -6207,25 +7618,25 @@ PARTIAL MATCHING USING pcre_exec() /dog(sbody)??/ - In this case the result is always a complete match because pcre_exec() - finds that first, and it never continues after finding a match. It - might be easier to follow this explanation by thinking of the two pat- - terns like this: + In this case the result is always a complete match because that is + found first, and matching never continues after finding a complete + match. It might be easier to follow this explanation by thinking of the + two patterns like this: /dog(sbody)?/ is the same as /dogsbody|dog/ /dog(sbody)??/ is the same as /dog|dogsbody/ - The second pattern will never match "dogsbody" when pcre_exec() is - used, because it will always find the shorter match first. + The second pattern will never match "dogsbody", because it will always + find the shorter match first. -PARTIAL MATCHING USING pcre_dfa_exec() +PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec() - The pcre_dfa_exec() function moves along the subject string character - by character, without backtracking, searching for all possible matches - simultaneously. If the end of the subject is reached before the end of - the pattern, there is the possibility of a partial match, again pro- - vided that at least one character has been inspected. + The DFA functions move along the subject string character by character, + without backtracking, searching for all possible matches simultane- + ously. If the end of the subject is reached before the end of the pat- + tern, there is the possibility of a partial match, again provided that + at least one character has been inspected. When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if there have been no complete matches. Otherwise, the complete matches @@ -6235,17 +7646,17 @@ PARTIAL MATCHING USING pcre_dfa_exec() the first matching string, provided there are at least two slots in the offsets vector. - Because pcre_dfa_exec() always searches for all possible matches, and - there is no difference between greedy and ungreedy repetition, its be- - haviour is different from pcre_exec when PCRE_PARTIAL_HARD is set. Con- - sider the string "dog" matched against the ungreedy pattern shown - above: + Because the DFA functions always search for all possible matches, and + there is no difference between greedy and ungreedy repetition, their + behaviour is different from the standard functions when PCRE_PAR- + TIAL_HARD is set. Consider the string "dog" matched against the + ungreedy pattern shown above: /dog(sbody)??/ - Whereas pcre_exec() stops as soon as it finds the complete match for - "dog", pcre_dfa_exec() also finds the partial match for "dogsbody", and - so returns that when PCRE_PARTIAL_HARD is set. + Whereas the standard functions stop as soon as they find the complete + match for "dog", the DFA functions also find the partial match for + "dogsbody", and so return that when PCRE_PARTIAL_HARD is set. PARTIAL MATCHING AND WORD BOUNDARIES @@ -6259,37 +7670,34 @@ PARTIAL MATCHING AND WORD BOUNDARIES This matches "cat", provided there is a word boundary at either end. If the subject string is "the cat", the comparison of the final "t" with a following character cannot take place, so a partial match is found. - However, pcre_exec() carries on with normal matching, which matches \b - at the end of the subject when the last character is a letter, thus - finding a complete match. The result, therefore, is not PCRE_ERROR_PAR- - TIAL. The same thing happens with pcre_dfa_exec(), because it also - finds the complete match. - - Using PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, - because then the partial match takes precedence. + However, normal matching carries on, and \b matches at the end of the + subject when the last character is a letter, so a complete match is + found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using + PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because + then the partial match takes precedence. FORMERLY RESTRICTED PATTERNS For releases of PCRE prior to 8.00, because of the way certain internal - optimizations were implemented in the pcre_exec() function, the - PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be - used with all patterns. From release 8.00 onwards, the restrictions no - longer apply, and partial matching with pcre_exec() can be requested - for any pattern. + optimizations were implemented in the pcre_exec() function, the + PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be + used with all patterns. From release 8.00 onwards, the restrictions no + longer apply, and partial matching with can be requested for any pat- + tern. Items that were formerly restricted were repeated single characters and - repeated metasequences. If PCRE_PARTIAL was set for a pattern that did - not conform to the restrictions, pcre_exec() returned the error code - PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The - PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled + repeated metasequences. If PCRE_PARTIAL was set for a pattern that did + not conform to the restrictions, pcre_exec() returned the error code + PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The + PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if a compiled pattern can be used for partial matching now always returns 1. EXAMPLE OF PARTIAL MATCHING USING PCRETEST - If the escape sequence \P is present in a pcretest data line, the - PCRE_PARTIAL_SOFT option is used for the match. Here is a run of + If the escape sequence \P is present in a pcretest data line, the + PCRE_PARTIAL_SOFT option is used for the match. Here is a run of pcretest that uses the date example quoted above: re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ @@ -6305,25 +7713,25 @@ EXAMPLE OF PARTIAL MATCHING USING PCRETEST data> j\P No match - The first data string is matched completely, so pcretest shows the - matched substrings. The remaining four strings do not match the com- + The first data string is matched completely, so pcretest shows the + matched substrings. The remaining four strings do not match the com- plete pattern, but the first two are partial matches. Similar output is - obtained when pcre_dfa_exec() is used. + obtained if DFA matching is used. - If the escape sequence \P is present more than once in a pcretest data + If the escape sequence \P is present more than once in a pcretest data line, the PCRE_PARTIAL_HARD option is set for the match. -MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() +MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_dfa_exec() - When a partial match has been found using pcre_dfa_exec(), it is possi- - ble to continue the match by providing additional subject data and - calling pcre_dfa_exec() again with the same compiled regular expres- - sion, this time setting the PCRE_DFA_RESTART option. You must pass the + When a partial match has been found using a DFA matching function, it + is possible to continue the match by providing additional subject data + and calling the function again with the same compiled regular expres- + sion, this time setting the PCRE_DFA_RESTART option. You must pass the same working space as before, because this is where details of the pre- - vious partial match are stored. Here is an example using pcretest, - using the \R escape sequence to set the PCRE_DFA_RESTART option (\D - specifies the use of pcre_dfa_exec()): + vious partial match are stored. Here is an example using pcretest, + using the \R escape sequence to set the PCRE_DFA_RESTART option (\D + specifies the use of the DFA matching function): re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ data> 23ja\P\D @@ -6331,46 +7739,49 @@ MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() data> n05\R\D 0: n05 - The first call has "23ja" as the subject, and requests partial match- - ing; the second call has "n05" as the subject for the continued - (restarted) match. Notice that when the match is complete, only the - last part is shown; PCRE does not retain the previously partially- - matched string. It is up to the calling program to do that if it needs + The first call has "23ja" as the subject, and requests partial match- + ing; the second call has "n05" as the subject for the continued + (restarted) match. Notice that when the match is complete, only the + last part is shown; PCRE does not retain the previously partially- + matched string. It is up to the calling program to do that if it needs to. - You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with - PCRE_DFA_RESTART to continue partial matching over multiple segments. - This facility can be used to pass very long subject strings to - pcre_dfa_exec(). + You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with + PCRE_DFA_RESTART to continue partial matching over multiple segments. + This facility can be used to pass very long subject strings to the DFA + matching functions. -MULTI-SEGMENT MATCHING WITH pcre_exec() +MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec() - From release 8.00, pcre_exec() can also be used to do multi-segment - matching. Unlike pcre_dfa_exec(), it is not possible to restart the - previous match with a new segment of data. Instead, new data must be - added to the previous subject string, and the entire match re-run, - starting from the point where the partial match occurred. Earlier data - can be discarded. It is best to use PCRE_PARTIAL_HARD in this situa- - tion, because it does not treat the end of a segment as the end of the - subject when matching \z, \Z, \b, \B, and $. Consider an unanchored - pattern that matches dates: + From release 8.00, the standard matching functions can also be used to + do multi-segment matching. Unlike the DFA functions, it is not possible + to restart the previous match with a new segment of data. Instead, new + data must be added to the previous subject string, and the entire match + re-run, starting from the point where the partial match occurred. Ear- + lier data can be discarded. + + It is best to use PCRE_PARTIAL_HARD in this situation, because it does + not treat the end of a segment as the end of the subject when matching + \z, \Z, \b, \B, and $. Consider an unanchored pattern that matches + dates: re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/ data> The date is 23ja\P\P Partial match: 23ja - At this stage, an application could discard the text preceding "23ja", - add on text from the next segment, and call pcre_exec() again. Unlike - pcre_dfa_exec(), the entire matching string must always be available, - and the complete matching process occurs for each call, so more memory - and more processing time is needed. + At this stage, an application could discard the text preceding "23ja", + add on text from the next segment, and call the matching function + again. Unlike the DFA matching functions, the entire matching string + must always be available, and the complete matching process occurs for + each call, so more memory and more processing time is needed. - Note: If the pattern contains lookbehind assertions, or \K, or starts - with \b or \B, the string that is returned for a partial match will - include characters that precede the partially matched string itself, - because these must be retained when adding on more characters for a - subsequent matching attempt. + 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. ISSUES WITH MULTI-SEGMENT MATCHING @@ -6384,23 +7795,40 @@ ISSUES WITH MULTI-SEGMENT MATCHING option, but in practice when doing multi-segment matching you should be using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL. - 2. Lookbehind assertions at the start of a pattern are catered for in - the offsets that are returned for a partial match. However, in theory, - a lookbehind assertion later in the pattern could require even earlier - characters to be inspected, and it might not have been reached when a - partial match occurs. This is probably an extremely unlikely case; you - could guard against it to a certain extent by always including extra - characters at the start. - - 3. Matching a subject string that is split into multiple segments may - not always produce exactly the same result as matching over one single - long string, especially when PCRE_PARTIAL_SOFT is used. The section - "Partial Matching and Word Boundaries" above describes an issue that - arises if the pattern ends with \b or \B. Another kind of difference - may occur when there are multiple matching possibilities, because (for - PCRE_PARTIAL_SOFT) a partial match result is given only when there are + 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 + PCRE_INFO_MAXLOOKBEHIND option of the pcre_fullinfo() or + pcre16_fullinfo() functions to obtain the length of the largest lookbe- + hind 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.) + + 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: + + re> /c(?<=abc)x/ + data> ab\P + No match + + If the next segment begins "cx", a match should be found, but this will + only happen if characters from the previous segment are retained. For + this reason, a "no match" result should be interpreted as "partial + match of an empty string" when the pattern contains lookbehinds. + + 4. Matching a subject string that is split into multiple segments may + not always produce exactly the same result as matching over one single + long string, especially when PCRE_PARTIAL_SOFT is used. The section + "Partial Matching and Word Boundaries" above describes an issue that + arises if the pattern ends with \b or \B. Another kind of difference + may occur when there are multiple matching possibilities, because (for + PCRE_PARTIAL_SOFT) a partial match result is given only when there are no completed matches. This means that as soon as the shortest match has - been found, continuation to a new subject segment is no longer possi- + been found, continuation to a new subject segment is no longer possi- ble. Consider again this pcretest example: re> /dog(sbody)?/ @@ -6414,14 +7842,15 @@ ISSUES WITH MULTI-SEGMENT MATCHING 0: dogsbody 1: dog - The first data line passes the string "dogsb" to pcre_exec(), setting - the PCRE_PARTIAL_SOFT option. Although the string is a partial match - for "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the - shorter string "dog" is a complete match. Similarly, when the subject - is presented to pcre_dfa_exec() in several parts ("do" and "gsb" being - the first two) the match stops when "dog" has been found, and it is not - possible to continue. On the other hand, if "dogsbody" is presented as - a single string, pcre_dfa_exec() finds both matches. + The first data line passes the string "dogsb" to a standard matching + function, setting the PCRE_PARTIAL_SOFT option. Although the string is + a partial match for "dogsbody", the result is not PCRE_ERROR_PARTIAL, + because the shorter string "dog" is a complete match. Similarly, when + the subject is presented to a DFA matching function in several parts + ("do" and "gsb" being the first two) the match stops when "dog" has + been found, and it is not possible to continue. On the other hand, if + "dogsbody" is presented as a single string, a DFA matching function + finds both matches. Because of these problems, it is best to use PCRE_PARTIAL_HARD when matching multi-segment data. The example above then behaves differ- @@ -6435,28 +7864,27 @@ ISSUES WITH MULTI-SEGMENT MATCHING data> gsb\R\P\P\D Partial match: gsb - 4. Patterns that contain alternatives at the top level which do not all + 5. Patterns that contain alternatives at the top level which do not all start with the same pattern item may not work as expected when - PCRE_DFA_RESTART is used with pcre_dfa_exec(). For example, consider - this pattern: + PCRE_DFA_RESTART is used. For example, consider this pattern: 1234|3789 - If the first part of the subject is "ABC123", a partial match of the - first alternative is found at offset 3. There is no partial match for + If the first part of the subject is "ABC123", a partial match of the + first alternative is found at offset 3. There is no partial match for the second alternative, because such a match does not start at the same - point in the subject string. Attempting to continue with the string - "7890" does not yield a match because only those alternatives that - match at one point in the subject are remembered. The problem arises - because the start of the second alternative matches within the first - alternative. There is no problem with anchored patterns or patterns + point in the subject string. Attempting to continue with the string + "7890" does not yield a match because only those alternatives that + match at one point in the subject are remembered. The problem arises + because the start of the second alternative matches within the first + alternative. There is no problem with anchored patterns or patterns such as: 1234|ABCD - where no string can be a partial match for both alternatives. This is - not a problem if pcre_exec() is used, because the entire match has to - be rerun each time: + where no string can be a partial match for both alternatives. This is + not a problem if a standard matching function is used, because the + entire match has to be rerun each time: re> /1234|3789/ data> ABC123\P\P @@ -6465,11 +7893,11 @@ ISSUES WITH MULTI-SEGMENT MATCHING 0: 3789 Of course, instead of using PCRE_DFA_RESTART, the same technique of re- - running the entire match can also be used with pcre_dfa_exec(). Another - possibility is to work with two buffers. If a partial match at offset n - in the first buffer is followed by "no match" when PCRE_DFA_RESTART is - used on the second buffer, you can then try a new match starting at - offset n+1 in the first buffer. + running the entire match can also be used with the DFA matching func- + tions. Another possibility is to work with two buffers. If a partial + match at offset n in the first buffer is followed by "no match" when + PCRE_DFA_RESTART is used on the second buffer, you can then try a new + match starting at offset n+1 in the first buffer. AUTHOR @@ -6481,8 +7909,8 @@ AUTHOR REVISION - Last updated: 07 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 24 February 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -6500,26 +7928,32 @@ SAVING AND RE-USING PRECOMPILED PCRE PATTERNS form instead of having to compile them every time the application is run. If you are not using any private character tables (see the pcre_maketables() documentation), this is relatively straightforward. - If you are using private tables, it is a little bit more complicated. + If you are using private tables, it is a little bit more complicated. + However, if you are using the just-in-time optimization feature, it is + not possible to save and reload the JIT data. If you save compiled patterns to a file, you can copy them to a differ- - ent host and run them there. This works even if the new host has the - opposite endianness to the one on which the patterns were compiled. - There may be a small performance penalty, but it should be insignifi- - cant. However, compiling regular expressions with one version of PCRE - for use with a different version is not guaranteed to work and may - cause crashes. + ent host and run them there. If the two hosts have different endianness + (byte order), you should run the pcre[16]_pattern_to_host_byte_order() + function on the new host before trying to match the pattern. The match- + ing functions return PCRE_ERROR_BADENDIANNESS if they detect a pattern + with the wrong endianness. + + Compiling regular expressions with one version of PCRE for use with a + different version is not guaranteed to work and may cause crashes, and + saving and restoring a compiled pattern loses any JIT optimization + data. SAVING A COMPILED PATTERN - The value returned by pcre_compile() points to a single block of memory - that holds the compiled pattern and associated data. You can find the - length of this block in bytes by calling pcre_fullinfo() with an argu- - ment of PCRE_INFO_SIZE. You can then save the data in any appropriate - manner. Here is sample code that compiles a pattern and writes it to a - file. It assumes that the variable fd refers to a file that is open for - output: + The value returned by pcre[16]_compile() points to a single block of + memory that holds the compiled pattern and associated data. You can + find the length of this block in bytes by calling pcre[16]_fullinfo() + with an argument of PCRE_INFO_SIZE. You can then save the data in any + appropriate manner. Here is sample code for the 8-bit library that com- + piles a pattern and writes it to a file. It assumes that the variable + fd refers to a file that is open for output: int erroroffset, rc, size; char *error; @@ -6549,45 +7983,49 @@ SAVING A COMPILED PATTERN in the memory of some daemon process that passes them via sockets to the processes that want them. - If the pattern has been studied, it is also possible to save the study - data in a similar way to the compiled pattern itself. When studying - generates additional information, pcre_study() returns a pointer to a - pcre_extra data block. Its format is defined in the section on matching - a pattern in the pcreapi documentation. The study_data field points to - the binary study data, and this is what you must save (not the - pcre_extra block itself). The length of the study data can be obtained - by calling pcre_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. - Remember to check that pcre_study() did return a non-NULL value before - trying to save the study data. + If the pattern has been studied, it is also possible to save the normal + study data in a similar way to the compiled pattern itself. However, if + the PCRE_STUDY_JIT_COMPILE was used, the just-in-time data that is cre- + ated cannot be saved because it is too dependent on the current envi- + ronment. When studying generates additional information, + pcre[16]_study() returns a pointer to a pcre[16]_extra data block. Its + format is defined in the section on matching a pattern in the pcreapi + documentation. The study_data field points to the binary study data, + and this is what you must save (not the pcre[16]_extra block itself). + The length of the study data can be obtained by calling + pcre[16]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remember + to check that pcre[16]_study() did return a non-NULL value before try- + ing to save the study data. RE-USING A PRECOMPILED PATTERN - Re-using a precompiled pattern is straightforward. Having reloaded it - into main memory, you pass its pointer to pcre_exec() or - pcre_dfa_exec() in the usual way. This should work even on another - host, and even if that host has the opposite endianness to the one - where the pattern was compiled. + Re-using a precompiled pattern is straightforward. Having reloaded it + into main memory, called pcre[16]_pattern_to_host_byte_order() if nec- + essary, you pass its pointer to pcre[16]_exec() or pcre[16]_dfa_exec() + in the usual way. However, if you passed a pointer to custom character tables when the - pattern was compiled (the tableptr argument of pcre_compile()), you - must now pass a similar pointer to pcre_exec() or pcre_dfa_exec(), - because the value saved with the compiled pattern will obviously be - nonsense. A field in a pcre_extra() block is used to pass this data, as - described in the section on matching a pattern in the pcreapi documen- - tation. + pattern was compiled (the tableptr argument of pcre[16]_compile()), you + must now pass a similar pointer to pcre[16]_exec() or + pcre[16]_dfa_exec(), because the value saved with the compiled pattern + will obviously be nonsense. A field in a pcre[16]_extra() block is used + to pass this data, as described in the section on matching a pattern in + the pcreapi documentation. If you did not provide custom character tables when the pattern was - compiled, the pointer in the compiled pattern is NULL, which causes - pcre_exec() to use PCRE's internal tables. Thus, you do not need to - take any special action at run time in this case. + compiled, the pointer in the compiled pattern is NULL, which causes the + matching functions to use PCRE's internal tables. Thus, you do not need + to take any special action at run time in this case. If you saved study data with the compiled pattern, you need to create - your own pcre_extra data block and set the study_data field to point to - the reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA - bit in the flags field to indicate that study data is present. Then - pass the pcre_extra block to pcre_exec() or pcre_dfa_exec() in the - usual way. + your own pcre[16]_extra data block and set the study_data field to + point to the reloaded study data. You must also set the + PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study + data is present. Then pass the pcre[16]_extra block to the matching + function in the usual way. If the pattern was studied for just-in-time + optimization, that data cannot be saved, and so is lost by a + save/restore cycle. COMPATIBILITY WITH DIFFERENT PCRE RELEASES @@ -6606,8 +8044,8 @@ AUTHOR REVISION - Last updated: 17 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 10 January 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -6627,12 +8065,12 @@ PCRE PERFORMANCE COMPILED PATTERN MEMORY USAGE - Patterns are compiled by PCRE into a reasonably efficient byte code, so - that most simple patterns do not use much memory. However, there is one - case where the memory usage of a compiled pattern can be unexpectedly - large. If a parenthesized subpattern has a quantifier with a minimum - greater than 1 and/or a limited maximum, the whole subpattern is - repeated in the compiled code. For example, the pattern + Patterns are compiled by PCRE into a reasonably efficient interpretive + code, so that most simple patterns do not use much memory. However, + there is one case where the memory usage of a compiled pattern can be + unexpectedly large. If a parenthesized subpattern has a quantifier with + a minimum greater than 1 and/or a limited maximum, the whole subpattern + is repeated in the compiled code. For example, the pattern (abc|def){2,4} @@ -6650,64 +8088,66 @@ COMPILED PATTERN MEMORY USAGE ((ab){1,1000}c){1,3} - uses 51K bytes when compiled. When PCRE is compiled with its default - internal pointer size of two bytes, the size limit on a compiled pat- - tern is 64K, and this is reached with the above pattern if the outer - repetition is increased from 3 to 4. PCRE can be compiled to use larger - internal pointers and thus handle larger compiled patterns, but it is - better to try to rewrite your pattern to use less memory if you can. + uses 51K bytes when compiled using the 8-bit library. When PCRE is com- + piled with its default internal pointer size of two bytes, the size + limit on a compiled pattern is 64K data units, and this is reached with + the above pattern if the outer repetition is increased from 3 to 4. + PCRE can be compiled to use larger internal pointers and thus handle + larger compiled patterns, but it is better to try to rewrite your pat- + tern to use less memory if you can. - One way of reducing the memory usage for such patterns is to make use + One way of reducing the memory usage for such patterns is to make use of PCRE's "subroutine" facility. Re-writing the above pattern as ((ab)(?2){0,999}c)(?1){0,2} reduces the memory requirements to 18K, and indeed it remains under 20K - even with the outer repetition increased to 100. However, this pattern - is not exactly equivalent, because the "subroutine" calls are treated - as atomic groups into which there can be no backtracking if there is a - subsequent matching failure. Therefore, PCRE cannot do this kind of - rewriting automatically. Furthermore, there is a noticeable loss of - speed when executing the modified pattern. Nevertheless, if the atomic - grouping is not a problem and the loss of speed is acceptable, this - kind of rewriting will allow you to process patterns that PCRE cannot + even with the outer repetition increased to 100. However, this pattern + is not exactly equivalent, because the "subroutine" calls are treated + as atomic groups into which there can be no backtracking if there is a + subsequent matching failure. Therefore, PCRE cannot do this kind of + rewriting automatically. Furthermore, there is a noticeable loss of + speed when executing the modified pattern. Nevertheless, if the atomic + grouping is not a problem and the loss of speed is acceptable, this + kind of rewriting will allow you to process patterns that PCRE cannot otherwise handle. STACK USAGE AT RUN TIME - When pcre_exec() is used for matching, certain kinds of pattern can - cause it to use large amounts of the process stack. In some environ- - ments the default process stack is quite small, and if it runs out the - result is often SIGSEGV. This issue is probably the most frequently - raised problem with PCRE. Rewriting your pattern can often help. The - pcrestack documentation discusses this issue in detail. + When pcre_exec() or pcre16_exec() is used for matching, certain kinds + of pattern can cause it to use large amounts of the process stack. In + some environments the default process stack is quite small, and if it + runs out the result is often SIGSEGV. This issue is probably the most + frequently raised problem with PCRE. Rewriting your pattern can often + help. The pcrestack documentation discusses this issue in detail. PROCESSING TIME - Certain items in regular expression patterns are processed more effi- + Certain items in regular expression patterns are processed more effi- ciently than others. It is more efficient to use a character class like - [aeiou] than a set of single-character alternatives such as - (a|e|i|o|u). In general, the simplest construction that provides the + [aeiou] than a set of single-character alternatives such as + (a|e|i|o|u). In general, the simplest construction that provides the required behaviour is usually the most efficient. Jeffrey Friedl's book - contains a lot of useful general discussion about optimizing regular - expressions for efficient performance. This document contains a few + contains a lot of useful general discussion about optimizing regular + expressions for efficient performance. This document contains a few observations about PCRE. - Using Unicode character properties (the \p, \P, and \X escapes) is - slow, because PCRE has to scan a structure that contains data for over - fifteen thousand characters whenever it needs a character's property. - If you can find an alternative pattern that does not use character + Using Unicode character properties (the \p, \P, and \X escapes) is + slow, because PCRE has to scan a structure that contains data for over + fifteen thousand characters whenever it needs a character's property. + If you can find an alternative pattern that does not use character properties, it will probably be faster. - By default, the escape sequences \b, \d, \s, and \w, and the POSIX - character classes such as [:alpha:] do not use Unicode properties, + By default, the escape sequences \b, \d, \s, and \w, and the POSIX + character classes such as [:alpha:] do not use Unicode properties, partly for backwards compatibility, and partly for performance reasons. - However, you can set PCRE_UCP if you want Unicode character properties - to be used. This can double the matching time for items such as \d, - when matched with pcre_exec(); the performance loss is less with - pcre_dfa_exec(), and in both cases there is not much difference for \b. + However, you can set PCRE_UCP if you want Unicode character properties + to be used. This can double the matching time for items such as \d, + when matched with a traditional matching function; the performance loss + is less with a DFA matching function, and in both cases there is not + much difference for \b. When a pattern begins with .* not in parentheses, or in parentheses that are not the subject of a backreference, and the PCRE_DOTALL option @@ -6774,8 +8214,8 @@ AUTHOR REVISION - Last updated: 16 May 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 09 January 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -6804,51 +8244,52 @@ SYNOPSIS OF POSIX API DESCRIPTION - This set of functions provides a POSIX-style API to the PCRE regular - expression package. See the pcreapi documentation for a description of - PCRE's native API, which contains much additional functionality. + This set of functions provides a POSIX-style API for the PCRE regular + expression 8-bit library. See the pcreapi documentation for a descrip- + tion of PCRE's native API, which contains much additional functional- + ity. There is no POSIX-style wrapper for PCRE's 16-bit library. The functions described here are just wrapper functions that ultimately call the PCRE native API. Their prototypes are defined in the - pcreposix.h header file, and on Unix systems the library itself is - called pcreposix.a, so can be accessed by adding -lpcreposix to the - command for linking an application that uses them. Because the POSIX + pcreposix.h header file, and on Unix systems the library itself is + called pcreposix.a, so can be accessed by adding -lpcreposix to the + command for linking an application that uses them. Because the POSIX functions call the native ones, it is also necessary to add -lpcre. - I have implemented only those POSIX option bits that can be reasonably - mapped to PCRE native options. In addition, the option REG_EXTENDED is - defined with the value zero. This has no effect, but since programs - that are written to the POSIX interface often use it, this makes it - easier to slot in PCRE as a replacement library. Other POSIX options + I have implemented only those POSIX option bits that can be reasonably + mapped to PCRE native options. In addition, the option REG_EXTENDED is + defined with the value zero. This has no effect, but since programs + that are written to the POSIX interface often use it, this makes it + easier to slot in PCRE as a replacement library. Other POSIX options are not even defined. - There are also some other options that are not defined by POSIX. These + There are also some other options that are not defined by POSIX. These have been added at the request of users who want to make use of certain PCRE-specific features via the POSIX calling interface. - When PCRE is called via these functions, it is only the API that is - POSIX-like in style. The syntax and semantics of the regular expres- - sions themselves are still those of Perl, subject to the setting of - various PCRE options, as described below. "POSIX-like in style" means - that the API approximates to the POSIX definition; it is not fully - POSIX-compatible, and in multi-byte encoding domains it is probably + When PCRE is called via these functions, it is only the API that is + POSIX-like in style. The syntax and semantics of the regular expres- + sions themselves are still those of Perl, subject to the setting of + various PCRE options, as described below. "POSIX-like in style" means + that the API approximates to the POSIX definition; it is not fully + POSIX-compatible, and in multi-byte encoding domains it is probably even less compatible. - The header for these functions is supplied as pcreposix.h to avoid any - potential clash with other POSIX libraries. It can, of course, be + The header for these functions is supplied as pcreposix.h to avoid any + potential clash with other POSIX libraries. It can, of course, be renamed or aliased as regex.h, which is the "correct" name. It provides - two structure types, regex_t for compiled internal forms, and reg- - match_t for returning captured substrings. It also defines some con- - stants whose names start with "REG_"; these are used for setting + two structure types, regex_t for compiled internal forms, and reg- + match_t for returning captured substrings. It also defines some con- + stants whose names start with "REG_"; these are used for setting options and identifying error codes. COMPILING A PATTERN - The function regcomp() is called to compile a pattern into an internal - form. The pattern is a C string terminated by a binary zero, and is - passed in the argument pattern. The preg argument is a pointer to a - regex_t structure that is used as a base for storing information about + The function regcomp() is called to compile a pattern into an internal + form. The pattern is a C string terminated by a binary zero, and is + passed in the argument pattern. The preg argument is a pointer to a + regex_t structure that is used as a base for storing information about the compiled regular expression. The argument cflags is either zero, or contains one or more of the bits @@ -6862,58 +8303,58 @@ COMPILING A PATTERN REG_ICASE - The PCRE_CASELESS option is set when the regular expression is passed + The PCRE_CASELESS option is set when the regular expression is passed for compilation to the native function. REG_NEWLINE - The PCRE_MULTILINE option is set when the regular expression is passed - for compilation to the native function. Note that this does not mimic - the defined POSIX behaviour for REG_NEWLINE (see the following sec- + The PCRE_MULTILINE option is set when the regular expression is passed + for compilation to the native function. Note that this does not mimic + the defined POSIX behaviour for REG_NEWLINE (see the following sec- tion). REG_NOSUB - The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is + The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed for compilation to the native function. In addition, when a pat- - tern that is compiled with this flag is passed to regexec() for match- - ing, the nmatch and pmatch arguments are ignored, and no captured + tern that is compiled with this flag is passed to regexec() for match- + ing, the nmatch and pmatch arguments are ignored, and no captured strings are returned. REG_UCP - The PCRE_UCP option is set when the regular expression is passed for - compilation to the native function. This causes PCRE to use Unicode - properties when matchine \d, \w, etc., instead of just recognizing + The PCRE_UCP option is set when the regular expression is passed for + compilation to the native function. This causes PCRE to use Unicode + properties when matchine \d, \w, etc., instead of just recognizing ASCII values. Note that REG_UTF8 is not part of the POSIX standard. REG_UNGREEDY - The PCRE_UNGREEDY option is set when the regular expression is passed - for compilation to the native function. Note that REG_UNGREEDY is not + The PCRE_UNGREEDY option is set when the regular expression is passed + for compilation to the native function. Note that REG_UNGREEDY is not part of the POSIX standard. REG_UTF8 - The PCRE_UTF8 option is set when the regular expression is passed for - compilation to the native function. This causes the pattern itself and - all data strings used for matching it to be treated as UTF-8 strings. + The PCRE_UTF8 option is set when the regular expression is passed for + compilation to the native function. This causes the pattern itself and + all data strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8 is not part of the POSIX standard. - In the absence of these flags, no options are passed to the native - function. This means the the regex is compiled with PCRE default - semantics. In particular, the way it handles newline characters in the - subject string is the Perl way, not the POSIX way. Note that setting - PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. - It does not affect the way newlines are matched by . (they are not) or + In the absence of these flags, no options are passed to the native + function. This means the the regex is compiled with PCRE default + semantics. In particular, the way it handles newline characters in the + subject string is the Perl way, not the POSIX way. Note that setting + PCRE_MULTILINE has only some of the effects specified for REG_NEWLINE. + It does not affect the way newlines are matched by . (they are not) or by a negative class such as [^a] (they are). - The yield of regcomp() is zero on success, and non-zero otherwise. The + The yield of regcomp() is zero on success, and non-zero otherwise. The preg structure is filled in on success, and one member of the structure - is public: re_nsub contains the number of capturing subpatterns in the + is public: re_nsub contains the number of capturing subpatterns in the regular expression. Various error codes are defined in the header file. - NOTE: If the yield of regcomp() is non-zero, you must not attempt to + NOTE: If the yield of regcomp() is non-zero, you must not attempt to use the contents of the preg structure. If, for example, you pass it to regexec(), the result is undefined and your program is likely to crash. @@ -6921,9 +8362,9 @@ COMPILING A PATTERN MATCHING NEWLINE CHARACTERS This area is not simple, because POSIX and Perl take different views of - things. It is not possible to get PCRE to obey POSIX semantics, but - then PCRE was never intended to be a POSIX engine. The following table - lists the different possibilities for matching newline characters in + things. It is not possible to get PCRE to obey POSIX semantics, but + then PCRE was never intended to be a POSIX engine. The following table + lists the different possibilities for matching newline characters in PCRE: Default Change with @@ -6945,19 +8386,19 @@ MATCHING NEWLINE CHARACTERS ^ matches \n in middle no REG_NEWLINE PCRE's behaviour is the same as Perl's, except that there is no equiva- - lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is + lent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop newline from matching [^a]. - The default POSIX newline handling can be obtained by setting - PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE + The default POSIX newline handling can be obtained by setting + PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the REG_NEWLINE action. MATCHING A PATTERN - The function regexec() is called to match a compiled pattern preg - against a given string, which is by default terminated by a zero byte - (but see REG_STARTEND below), subject to the options in eflags. These + The function regexec() is called to match a compiled pattern preg + against a given string, which is by default terminated by a zero byte + (but see REG_STARTEND below), subject to the options in eflags. These can be: REG_NOTBOL @@ -6979,17 +8420,17 @@ MATCHING A PATTERN REG_STARTEND - The string is considered to start at string + pmatch[0].rm_so and to - have a terminating NUL located at string + pmatch[0].rm_eo (there need - not actually be a NUL at that location), regardless of the value of - nmatch. This is a BSD extension, compatible with but not specified by - IEEE Standard 1003.2 (POSIX.2), and should be used with caution in + The string is considered to start at string + pmatch[0].rm_so and to + have a terminating NUL located at string + pmatch[0].rm_eo (there need + not actually be a NUL at that location), regardless of the value of + nmatch. This is a BSD extension, compatible with but not specified by + IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software intended to be portable to other systems. Note that a non-zero rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not how it is matched. - If the pattern was compiled with the REG_NOSUB flag, no data about any - matched strings is returned. The nmatch and pmatch arguments of + If the pattern was compiled with the REG_NOSUB flag, no data about any + matched strings is returned. The nmatch and pmatch arguments of regexec() are ignored. If the value of nmatch is zero, or if the value pmatch is NULL, no data @@ -6997,34 +8438,34 @@ MATCHING A PATTERN Otherwise,the portion of the string that was matched, and also any cap- tured substrings, are returned via the pmatch argument, which points to - an array of nmatch structures of type regmatch_t, containing the mem- - bers rm_so and rm_eo. These contain the offset to the first character - of each substring and the offset to the first character after the end - of each substring, respectively. The 0th element of the vector relates - to the entire portion of string that was matched; subsequent elements - relate to the capturing subpatterns of the regular expression. Unused + an array of nmatch structures of type regmatch_t, containing the mem- + bers rm_so and rm_eo. These contain the offset to the first character + of each substring and the offset to the first character after the end + of each substring, respectively. The 0th element of the vector relates + to the entire portion of string that was matched; subsequent elements + relate to the capturing subpatterns of the regular expression. Unused entries in the array have both structure members set to -1. - A successful match yields a zero return; various error codes are - defined in the header file, of which REG_NOMATCH is the "expected" + A successful match yields a zero return; various error codes are + defined in the header file, of which REG_NOMATCH is the "expected" failure code. ERROR MESSAGES The regerror() function maps a non-zero errorcode from either regcomp() - or regexec() to a printable message. If preg is not NULL, the error + or regexec() to a printable message. If preg is not NULL, the error should have arisen from the use of that structure. A message terminated - by a binary zero is placed in errbuf. The length of the message, - including the zero, is limited to errbuf_size. The yield of the func- + by a binary zero is placed in errbuf. The length of the message, + including the zero, is limited to errbuf_size. The yield of the func- tion is the size of buffer needed to hold the whole message. MEMORY USAGE - Compiling a regular expression causes memory to be allocated and asso- - ciated with the preg structure. The function regfree() frees all such - memory, after which preg may no longer be used as a compiled expres- + Compiling a regular expression causes memory to be allocated and asso- + ciated with the preg structure. The function regfree() frees all such + memory, after which preg may no longer be used as a compiled expres- sion. @@ -7037,8 +8478,8 @@ AUTHOR REVISION - Last updated: 16 May 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 09 January 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -7059,13 +8500,14 @@ DESCRIPTION The C++ wrapper for PCRE was provided by Google Inc. Some additional functionality was added by Giuseppe Maxia. This brief man page was con- structed from the notes in the pcrecpp.h file, which should be con- - sulted for further details. + sulted for further details. Note that the C++ wrapper supports only the + original 8-bit PCRE library. There is no 16-bit support at present. MATCHING INTERFACE - The "FullMatch" operation checks that supplied text matches a supplied - pattern exactly. If pointer arguments are supplied, it copies matched + The "FullMatch" operation checks that supplied text matches a supplied + pattern exactly. If pointer arguments are supplied, it copies matched sub-strings that match sub-patterns into them. Example: successful match @@ -7079,10 +8521,10 @@ MATCHING INTERFACE Example: creating a temporary RE object: pcrecpp::RE("h.*o").FullMatch("hello"); - You can pass in a "const char*" or a "string" for "text". The examples - below tend to use a const char*. You can, as in the different examples - above, store the RE object explicitly in a variable or use a temporary - RE object. The examples below use one mode or the other arbitrarily. + You can pass in a "const char*" or a "string" for "text". The examples + below tend to use a const char*. You can, as in the different examples + above, store the RE object explicitly in a variable or use a temporary + RE object. The examples below use one mode or the other arbitrarily. Either could correctly be used for any of these examples. You must supply extra pointer arguments to extract matched subpieces. @@ -7108,7 +8550,7 @@ MATCHING INTERFACE Example: fails because string cannot be stored in integer !pcrecpp::RE("(.*)").FullMatch("ruby", &i); - The provided pointer arguments can be pointers to any scalar numeric + The provided pointer arguments can be pointers to any scalar numeric type, or one of: string (matched piece is copied to string) @@ -7116,7 +8558,7 @@ MATCHING INTERFACE T (where "bool T::ParseFrom(const char*, int)" exists) NULL (the corresponding matched sub-pattern is not copied) - The function returns true iff all of the following conditions are sat- + The function returns true iff all of the following conditions are sat- isfied: a. "text" matches "pattern" exactly; @@ -7131,41 +8573,41 @@ MATCHING INTERFACE number of sub-patterns, "i"th captured sub-pattern is ignored. - CAVEAT: An optional sub-pattern that does not exist in the matched - string is assigned the empty string. Therefore, the following will + CAVEAT: An optional sub-pattern that does not exist in the matched + string is assigned the empty string. Therefore, the following will return false (because the empty string is not a valid number): int number; pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number); - The matching interface supports at most 16 arguments per call. If you - need more, consider using the more general interface + The matching interface supports at most 16 arguments per call. If you + need more, consider using the more general interface pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for DoMatch. - NOTE: Do not use no_arg, which is used internally to mark the end of a - list of optional arguments, as a placeholder for missing arguments, as + NOTE: Do not use no_arg, which is used internally to mark the end of a + list of optional arguments, as a placeholder for missing arguments, as this can lead to segfaults. QUOTING METACHARACTERS - You can use the "QuoteMeta" operation to insert backslashes before all - potentially meaningful characters in a string. The returned string, + You can use the "QuoteMeta" operation to insert backslashes before all + potentially meaningful characters in a string. The returned string, used as a regular expression, will exactly match the original string. Example: string quoted = RE::QuoteMeta(unquoted); - Note that it's legal to escape a character even if it has no special - meaning in a regular expression -- so this function does that. (This - also makes it identical to the perl function of the same name; see - "perldoc -f quotemeta".) For example, "1.5-2.0?" becomes + Note that it's legal to escape a character even if it has no special + meaning in a regular expression -- so this function does that. (This + also makes it identical to the perl function of the same name; see + "perldoc -f quotemeta".) For example, "1.5-2.0?" becomes "1\.5\-2\.0\?". PARTIAL MATCHES - You can use the "PartialMatch" operation when you want the pattern to + You can use the "PartialMatch" operation when you want the pattern to match any substring of the text. Example: simple search for a string: @@ -7180,13 +8622,13 @@ PARTIAL MATCHES UTF-8 AND THE MATCHING INTERFACE - By default, pattern and text are plain text, one byte per character. - The UTF8 flag, passed to the constructor, causes both pattern and + By default, pattern and text are plain text, one byte per character. + The UTF8 flag, passed to the constructor, causes both pattern and string to be treated as UTF-8 text, still a byte stream but potentially - multiple bytes per character. In practice, the text is likelier to be - UTF-8 than the pattern, but the match returned may depend on the UTF8 - flag, so always use it when matching UTF8 text. For example, "." will - match one byte normally but with UTF8 set may match up to three bytes + multiple bytes per character. In practice, the text is likelier to be + UTF-8 than the pattern, but the match returned may depend on the UTF8 + flag, so always use it when matching UTF8 text. For example, "." will + match one byte normally but with UTF8 set may match up to three bytes of a multi-byte character. Example: @@ -7205,9 +8647,9 @@ UTF-8 AND THE MATCHING INTERFACE PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE - PCRE defines some modifiers to change the behavior of the regular - expression engine. The C++ wrapper defines an auxiliary class, - RE_Options, as a vehicle to pass such modifiers to a RE class. Cur- + PCRE defines some modifiers to change the behavior of the regular + expression engine. The C++ wrapper defines an auxiliary class, + RE_Options, as a vehicle to pass such modifiers to a RE class. Cur- rently, the following modifiers are supported: modifier description Perl corresponding @@ -7217,20 +8659,20 @@ PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE PCRE_DOTALL dot matches newlines /s PCRE_DOLLAR_ENDONLY $ matches only at end N/A PCRE_EXTRA strict escape parsing N/A - PCRE_EXTENDED ignore whitespaces /x + PCRE_EXTENDED ignore white spaces /x PCRE_UTF8 handles UTF8 chars built-in PCRE_UNGREEDY reverses * and *? N/A PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*) - (*) Both Perl and PCRE allow non capturing parentheses by means of the - "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not cap- + (*) Both Perl and PCRE allow non capturing parentheses by means of the + "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not cap- ture, while (ab|cd) does. - For a full account on how each modifier works, please check the PCRE + For a full account on how each modifier works, please check the PCRE API reference page. - For each modifier, there are two member functions whose name is made - out of the modifier in lowercase, without the "PCRE_" prefix. For + For each modifier, there are two member functions whose name is made + out of the modifier in lowercase, without the "PCRE_" prefix. For instance, PCRE_CASELESS is handled by bool caseless() @@ -7240,28 +8682,28 @@ PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE RE_Options & set_caseless(bool) which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can - be accessed through the set_match_limit() and match_limit() member - functions. Setting match_limit to a non-zero value will limit the exe- - cution of pcre to keep it from doing bad things like blowing the stack - or taking an eternity to return a result. A value of 5000 is good - enough to stop stack blowup in a 2MB thread stack. Setting match_limit - to zero disables match limiting. Alternatively, you can call - match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to - limit how much PCRE recurses. match_limit() limits the number of + be accessed through the set_match_limit() and match_limit() member + functions. Setting match_limit to a non-zero value will limit the exe- + cution of pcre to keep it from doing bad things like blowing the stack + or taking an eternity to return a result. A value of 5000 is good + enough to stop stack blowup in a 2MB thread stack. Setting match_limit + to zero disables match limiting. Alternatively, you can call + match_limit_recursion() which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to + limit how much PCRE recurses. match_limit() limits the number of matches PCRE does; match_limit_recursion() limits the depth of internal recursion, and therefore the amount of stack that is used. - Normally, to pass one or more modifiers to a RE class, you declare a + Normally, to pass one or more modifiers to a RE class, you declare a RE_Options object, set the appropriate options, and pass this object to a RE constructor. Example: - RE_options opt; + RE_Options opt; opt.set_caseless(true); if (RE("HELLO", opt).PartialMatch("hello world")) ... RE_options has two constructors. The default constructor takes no argu- - ments and creates a set of flags that are off by default. The optional - parameter option_flags is to facilitate transfer of legacy code from C + ments and creates a set of flags that are off by default. The optional + parameter option_flags is to facilitate transfer of legacy code from C programs. This lets you do RE(pattern, @@ -7275,15 +8717,15 @@ PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE If you are going to pass one of the most used modifiers, there are some convenience functions that return a RE_Options class with the appropri- - ate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(), + ate modifier already set: CASELESS(), UTF8(), MULTILINE(), DOTALL(), and EXTENDED(). - If you need to set several options at once, and you don't want to go - through the pains of declaring a RE_Options object and setting several - options, there is a parallel method that give you such ability on the - fly. You can concatenate several set_xxxxx() member functions, since - each of them returns a reference to its class object. For example, to - pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one + If you need to set several options at once, and you don't want to go + through the pains of declaring a RE_Options object and setting several + options, there is a parallel method that give you such ability on the + fly. You can concatenate several set_xxxxx() member functions, since + each of them returns a reference to its class object. For example, to + pass PCRE_CASELESS, PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one statement, you may write: RE(" ^ xyz \\s+ .* blah$", @@ -7295,10 +8737,10 @@ PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE SCANNING TEXT INCREMENTALLY - The "Consume" operation may be useful if you want to repeatedly match + The "Consume" operation may be useful if you want to repeatedly match regular expressions at the front of a string and skip over them as they - match. This requires use of the "StringPiece" type, which represents a - sub-range of a real string. Like RE, StringPiece is defined in the + match. This requires use of the "StringPiece" type, which represents a + sub-range of a real string. Like RE, StringPiece is defined in the pcrecpp namespace. Example: read lines of the form "var = value" from a string. @@ -7312,11 +8754,11 @@ SCANNING TEXT INCREMENTALLY ...; } - Each successful call to "Consume" will set "var/value", and also + Each successful call to "Consume" will set "var/value", and also advance "input" so it points past the matched text. - The "FindAndConsume" operation is similar to "Consume" but does not - anchor your match at the beginning of the string. For example, you + The "FindAndConsume" operation is similar to "Consume" but does not + anchor your match at the beginning of the string. For example, you could extract all words from a string by repeatedly calling pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word) @@ -7325,10 +8767,10 @@ SCANNING TEXT INCREMENTALLY PARSING HEX/OCTAL/C-RADIX NUMBERS By default, if you pass a pointer to a numeric value, the corresponding - text is interpreted as a base-10 number. You can instead wrap the + text is interpreted as a base-10 number. You can instead wrap the pointer with a call to one of the operators Hex(), Octal(), or CRadix() - to interpret the text in another base. The CRadix operator interprets - C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to + to interpret the text in another base. The CRadix operator interprets + C-style "0" (base-8) and "0x" (base-16) prefixes, but defaults to base-10. Example: @@ -7343,30 +8785,30 @@ PARSING HEX/OCTAL/C-RADIX NUMBERS REPLACING PARTS OF STRINGS - You can replace the first match of "pattern" in "str" with "rewrite". - Within "rewrite", backslash-escaped digits (\1 to \9) can be used to - insert text matching corresponding parenthesized group from the pat- + You can replace the first match of "pattern" in "str" with "rewrite". + Within "rewrite", backslash-escaped digits (\1 to \9) can be used to + insert text matching corresponding parenthesized group from the pat- tern. \0 in "rewrite" refers to the entire matching text. For example: string s = "yabba dabba doo"; pcrecpp::RE("b+").Replace("d", &s); - will leave "s" containing "yada dabba doo". The result is true if the + will leave "s" containing "yada dabba doo". The result is true if the pattern matches and a replacement occurs, false otherwise. - GlobalReplace is like Replace except that it replaces all occurrences - of the pattern in the string with the rewrite. Replacements are not + GlobalReplace is like Replace except that it replaces all occurrences + of the pattern in the string with the rewrite. Replacements are not subject to re-matching. For example: string s = "yabba dabba doo"; pcrecpp::RE("b+").GlobalReplace("d", &s); - will leave "s" containing "yada dada doo". It returns the number of + will leave "s" containing "yada dada doo". It returns the number of replacements made. - Extract is like Replace, except that if the pattern matches, "rewrite" - is copied into "out" (an additional argument) with substitutions. The - non-matching portions of "text" are ignored. Returns true iff a match + Extract is like Replace, except that if the pattern matches, "rewrite" + is copied into "out" (an additional argument) with substitutions. The + non-matching portions of "text" are ignored. Returns true iff a match occurred and the extraction happened successfully; if no match occurs, the string is left unaffected. @@ -7379,7 +8821,7 @@ AUTHOR REVISION - Last updated: 17 March 2009 + Last updated: 08 January 2012 ------------------------------------------------------------------------------ @@ -7398,57 +8840,58 @@ PCRE SAMPLE PROGRAM do not have a copy of the PCRE distribution, you can save this listing to re-create pcredemo.c. - The program compiles the regular expression that is its first argument, - and matches it against the subject string in its second argument. No - PCRE options are set, and default character tables are used. If match- - ing succeeds, the program outputs the portion of the subject that - matched, together with the contents of any captured substrings. + The demonstration program, which uses the original PCRE 8-bit library, + compiles the regular expression that is its first argument, and matches + it against the subject string in its second argument. No PCRE options + are set, and default character tables are used. If matching succeeds, + the program outputs the portion of the subject that matched, together + with the contents of any captured substrings. If the -g option is given on the command line, the program then goes on to check for further matches of the same regular expression in the same - subject string. The logic is a little bit tricky because of the possi- - bility of matching an empty string. Comments in the code explain what + subject string. The logic is a little bit tricky because of the possi- + bility of matching an empty string. Comments in the code explain what is going on. - If PCRE is installed in the standard include and library directories + If PCRE is installed in the standard include and library directories for your operating system, you should be able to compile the demonstra- tion program using this command: gcc -o pcredemo pcredemo.c -lpcre - If PCRE is installed elsewhere, you may need to add additional options - to the command line. For example, on a Unix-like system that has PCRE - installed in /usr/local, you can compile the demonstration program + If PCRE is installed elsewhere, you may need to add additional options + to the command line. For example, on a Unix-like system that has PCRE + installed in /usr/local, you can compile the demonstration program using a command like this: gcc -o pcredemo -I/usr/local/include pcredemo.c \ -L/usr/local/lib -lpcre - In a Windows environment, if you want to statically link the program + In a Windows environment, if you want to statically link the program against a non-dll pcre.a file, you must uncomment the line that defines - PCRE_STATIC before including pcre.h, because otherwise the pcre_mal- + PCRE_STATIC before including pcre.h, because otherwise the pcre_mal- loc() and pcre_free() exported functions will be declared __declspec(dllimport), with unwanted results. - Once you have compiled and linked the demonstration program, you can + Once you have compiled and linked the demonstration program, you can run simple tests like this: ./pcredemo 'cat|dog' 'the cat sat on the mat' ./pcredemo -g 'cat|dog' 'the dog sat on the cat' - Note that there is a much more comprehensive test program, called - pcretest, which supports many more facilities for testing regular - expressions and the PCRE library. The pcredemo program is provided as a - simple coding example. + Note that there is a much more comprehensive test program, called + pcretest, which supports many more facilities for testing regular + expressions and both PCRE libraries. The pcredemo program is provided + as a simple coding example. - If you try to run pcredemo when PCRE is not installed in the standard - library directory, you may get an error like this on some operating + If you try to run pcredemo when PCRE is not installed in the standard + library directory, you may get an error like this on some operating systems (e.g. Solaris): - ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or + ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or directory - This is caused by the way shared library support works on those sys- + This is caused by the way shared library support works on those sys- tems. You need to add -R/usr/local/lib @@ -7465,9 +8908,71 @@ AUTHOR REVISION - Last updated: 17 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 10 January 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ +PCRELIMITS(3) 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, 16-bit units for the 16-bit + library) if PCRE is compiled with the default internal linkage size of + 2 bytes. If you want to process regular expressions that are truly + enormous, you can compile PCRE with an internal linkage size of 3 or 4 + (when building the 16-bit library, 3 is rounded up to 4). See the + README file in the source distribution and the pcrebuild documentation + for details. In these cases the limit is substantially larger. How- + ever, the speed of execution is slower. + + All values in repeating quantifiers must be less than 65536. + + There is no limit to the number of parenthesized subpatterns, but there + can be no more than 65535 capturing subpatterns. + + There is a limit to the number of forward references to subsequent 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 + 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 + library. + + 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 + the size of a subject string that can be processed by certain patterns. + For a discussion of stack issues, see the pcrestack documentation. + + +AUTHOR + + Philip Hazel + University Computing Service + Cambridge CB2 3QH, England. + + +REVISION + + Last updated: 04 May 2012 + Copyright (c) 1997-2012 University of Cambridge. +------------------------------------------------------------------------------ + + PCRESTACK(3) PCRESTACK(3) @@ -7477,12 +8982,14 @@ NAME PCRE DISCUSSION OF STACK USAGE - When you call pcre_exec(), it makes use of an internal function called - match(). This calls itself recursively at branch points in the pattern, - in order to remember the state of the match so that it can back up and - try a different alternative if the first one fails. As matching pro- - ceeds deeper and deeper into the tree of possibilities, the recursion - depth increases. + When you call pcre[16]_exec(), it makes use of an internal function + called match(). This calls itself recursively at branch points in the + pattern, in order to remember the state of the match so that it can + back up and try a different alternative if the first one fails. As + matching proceeds deeper and deeper into the tree of possibilities, the + recursion depth increases. The match() function is also called in other + circumstances, for example, whenever a parenthesized sub-pattern is + entered, and in certain cases of repetition. Not all calls of match() increase the recursion depth; for an item such as a* it may be called several times at the same level, after matching @@ -7491,20 +8998,28 @@ PCRE DISCUSSION OF STACK USAGE result of the current call (a "tail recursion"), the function is just restarted instead. - The pcre_dfa_exec() function operates in an entirely different way, and - uses recursion only when there is a regular expression recursion or + The above comments apply when pcre[16]_exec() is run in its normal + interpretive manner. If the pattern was studied with the + PCRE_STUDY_JIT_COMPILE option, and just-in-time compiling was success- + ful, and the options passed to pcre[16]_exec() were not incompatible, + the matching process uses the JIT-compiled code instead of the match() + function. In this case, the memory requirements are handled entirely + differently. See the pcrejit documentation for details. + + The pcre[16]_dfa_exec() function operates in an entirely different way, + and uses recursion only when there is a regular expression recursion or subroutine call in the pattern. This includes the processing of asser- tion and "once-only" subpatterns, which are handled like subroutine calls. Normally, these are never very deep, and the limit on the com- - plexity of pcre_dfa_exec() is controlled by the amount of workspace it - is given. However, it is possible to write patterns with runaway infi- - nite recursions; such patterns will cause pcre_dfa_exec() to run out of - stack. At present, there is no protection against this. + plexity of pcre[16]_dfa_exec() is controlled by the amount of workspace + it is given. However, it is possible to write patterns with runaway + infinite recursions; such patterns will cause pcre[16]_dfa_exec() to + run out of stack. At present, there is no protection against this. - The comments that follow do NOT apply to pcre_dfa_exec(); they are rel- - evant only for pcre_exec(). + The comments that follow do NOT apply to pcre[16]_dfa_exec(); they are + relevant only for pcre[16]_exec() without the JIT optimization. - Reducing pcre_exec()'s stack usage + Reducing pcre[16]_exec()'s stack usage Each time that match() is actually called recursively, it uses memory from the process stack. For certain kinds of pattern and data, very @@ -7537,31 +9052,31 @@ PCRE DISCUSSION OF STACK USAGE ing long subject strings is to write repeated parenthesized subpatterns to match more than one character whenever possible. - Compiling PCRE to use heap instead of stack for pcre_exec() + Compiling PCRE to use heap instead of stack for pcre[16]_exec() In environments where stack memory is constrained, you might want to compile PCRE to use heap memory instead of stack for remembering back- - up points when pcre_exec() is running. This makes it run a lot more + up points when pcre[16]_exec() is running. This makes it run a lot more slowly, however. Details of how to do this are given in the pcrebuild documentation. When built in this way, instead of using the stack, PCRE obtains and frees memory by calling the functions that are pointed to - by the pcre_stack_malloc and pcre_stack_free variables. By default, - these point to malloc() and free(), but you can replace the pointers to - cause PCRE to use your own functions. Since the block sizes are always - the same, and are always freed in reverse order, it may be possible to - implement customized memory handlers that are more efficient than the - standard functions. + by the pcre[16]_stack_malloc and pcre[16]_stack_free variables. By + default, these point to malloc() and free(), but you can replace the + pointers to cause PCRE to use your own functions. Since the block sizes + are always the same, and are always freed in reverse order, it may be + possible to implement customized memory handlers that are more effi- + cient than the standard functions. - Limiting pcre_exec()'s stack usage + Limiting pcre[16]_exec()'s stack usage You can set limits on the number of times that match() is called, both - in total and recursively. If a limit is exceeded, pcre_exec() returns - an error code. Setting suitable limits should prevent it from running - out of stack. The default values of the limits are very large, and - unlikely ever to operate. They can be changed when PCRE is built, and - they can also be set when pcre_exec() is called. For details of these - interfaces, see the pcrebuild documentation and the section on extra - data for pcre_exec() in the pcreapi documentation. + in total and recursively. If a limit is exceeded, pcre[16]_exec() + returns an error code. Setting suitable limits should prevent it from + running out of stack. The default values of the limits are very large, + and unlikely ever to operate. They can be changed when PCRE is built, + and they can also be set when pcre[16]_exec() is called. For details of + these interfaces, see the pcrebuild documentation and the section on + extra data for pcre[16]_exec() in the pcreapi documentation. As a very rough rule of thumb, you should reckon on about 500 bytes per recursion. Thus, if you want to limit your stack usage to 8Mb, you @@ -7572,9 +9087,33 @@ PCRE DISCUSSION OF STACK USAGE option (-S) that can be used to increase the size of its stack. As long as the stack is large enough, another option (-M) can be used to find the smallest limits that allow a particular pattern to match a given - subject string. This is done by calling pcre_exec() repeatedly with + subject string. This is done by calling pcre[16]_exec() repeatedly with different limits. + Obtaining an estimate of stack usage + + The actual amount of stack used per recursion can vary quite a lot, + depending on the compiler that was used to build PCRE and the optimiza- + tion or debugging options that were set for it. The rule of thumb value + of 500 bytes mentioned above may be larger or smaller than what is + actually needed. A better approximation can be obtained by running this + command: + + pcretest -m -C + + The -C option causes pcretest to output information about the options + with which PCRE was compiled. When -m is also given (before -C), infor- + mation about stack use is given in a line like this: + + Match recursion uses stack: approximate frame size = 640 bytes + + The value is approximate because some recursions need a bit more (up to + perhaps 16 more bytes). + + If the above command is given when PCRE is compiled to use the heap + instead of the stack for recursion, the value that is output is the + size of each block that is obtained from the heap. + Changing stack size in Unix-like systems In Unix-like environments, there is not often a problem with the stack @@ -7595,7 +9134,7 @@ PCRE DISCUSSION OF STACK USAGE This reads the current limits (soft and hard) using getrlimit(), then attempts to increase the soft limit to 100Mb using setrlimit(). You - must do this before calling pcre_exec(). + must do this before calling pcre[16]_exec(). Changing stack size in Mac OS X @@ -7614,8 +9153,8 @@ AUTHOR REVISION - Last updated: 03 January 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 21 January 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ |