--- embedaddon/php/ext/pcre/pcrelib/doc/pcre.txt 2012/02/21 23:47:59 1.1 +++ embedaddon/php/ext/pcre/pcrelib/doc/pcre.txt 2013/07/22 01:31:58 1.1.1.2 @@ -25,24 +25,48 @@ INTRODUCTION items, and there is an option for requesting some minor changes that give better JavaScript compatibility. - 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. + 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. - In addition to the Perl-compatible matching function, PCRE contains an - alternative function that matches the same compiled patterns in a dif- + Starting with release 8.32 it is possible to compile a third separate + PCRE library, which supports 32-bit character strings (including UTF-32 + strings). The build process allows any set of the 8-, 16- and 32-bit + libraries. The work to make this possible was done by Christian Persch. + + The three libraries contain identical sets of functions, except that + the names in the 16-bit library start with pcre16_ instead of pcre_, + and the names in the 32-bit library start with pcre32_ instead of + pcre_. To avoid over-complication and reduce the documentation mainte- + nance load, most of the documentation describes the 8-bit library, with + the differences for the 16-bit and 32-bit libraries described sepa- + rately in the pcre16 and pcre32 pages. References to functions or + structures of the form pcre[16|32]_xxx should be read as meaning + "pcre_xxx when using the 8-bit library, pcre16_xxx when using the + 16-bit library, or pcre32_xxx when using the 32-bit library". + + The current implementation of PCRE corresponds approximately with Perl + 5.12, including support for UTF-8/16/32 encoded strings and Unicode + general category properties. However, UTF-8/16/32 and Unicode support + has to be explicitly enabled; it is not the default. The Unicode tables + correspond to Unicode release 6.2.0. + + In addition to the Perl-compatible matching function, PCRE contains an + alternative function that matches the same compiled patterns in a dif- ferent way. In certain circumstances, the alternative function has some - advantages. For a discussion of the two matching algorithms, see the + advantages. For a discussion of the two matching algorithms, see the pcrematching page. - PCRE is written in C and released as a C library. A number of people - have written wrappers and interfaces of various kinds. In particular, - Google Inc. have provided a comprehensive C++ wrapper. 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: + PCRE is written in C and released as a C library. A number of people + have written wrappers and interfaces of various kinds. In particular, + Google Inc. have provided a comprehensive C++ wrapper for the 8-bit + library. This is now included as part of the PCRE distribution. The + pcrecpp page has details of this interface. Other people's contribu- + tions can be found in the Contrib directory at the primary FTP site, + which is: ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre @@ -56,17 +80,48 @@ INTRODUCTION 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. + NON-AUTOTOOLS_BUILD files in the source distribution. - The library contains a number of undocumented internal functions and + 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_", 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. + Their names all begin with "_pcre_" or "_pcre16_" or "_pcre32_", which + hopefully will not provoke any name clashes. In some environments, it + is possible to control which external symbols are exported when a + shared library is built, and in these cases the undocumented symbols + are not exported. +SECURITY CONSIDERATIONS + + If you are using PCRE in a non-UTF application that permits users to + supply arbitrary patterns for compilation, you should be aware of a + feature that allows users to turn on UTF support from within a pattern, + provided that PCRE was built with UTF support. For example, an 8-bit + pattern that begins with "(*UTF8)" or "(*UTF)" turns on UTF-8 mode, + which interprets patterns and subjects as strings of UTF-8 characters + instead of individual 8-bit characters. This causes both the pattern + and any data against which it is matched to be checked for UTF-8 valid- + ity. If the data string is very long, such a check might use suffi- + ciently many resources as to cause your application to lose perfor- + mance. + + The best way of guarding against this possibility is to use the + pcre_fullinfo() function to check the compiled pattern's options for + UTF. + + If your application is one that supports UTF, be aware that validity + checking can take time. If the same data string is to be matched many + times, you can use the PCRE_NO_UTF[8|16|32]_CHECK option for the second + and subsequent matches to save redundant checks. + + Another way that performance can be hit is by running a pattern that + has a very large search tree against a string that will never match. + Nested unlimited repeats in a pattern are a common example. PCRE pro- + vides some protection against this: see the PCRE_EXTRA_MATCH_LIMIT fea- + ture in the pcreapi page. + + USER DOCUMENTATION The user documentation for PCRE comprises a number of different sec- @@ -77,197 +132,705 @@ USER DOCUMENTATION lows: pcre this document + pcre16 details of the 16-bit library + pcre32 details of the 32-bit library pcre-config show PCRE installation configuration information pcreapi details of PCRE's native C API pcrebuild options for building PCRE 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-8/16/32 support In addition, in the "man" and HTML formats, there is a short page for each 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: 11 November 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 - 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. + pcre16 *pcre16_compile2(PCRE_SPTR16 pattern, int options, + int *errorcodeptr, + const char **errptr, int *erroffset, + const unsigned char *tableptr); - 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.) + pcre16_extra *pcre16_study(const pcre16 *code, int options, + const char **errptr); - 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. + void pcre16_free_study(pcre16_extra *extra); - 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. + int pcre16_exec(const pcre16 *code, const pcre16_extra *extra, + PCRE_SPTR16 subject, int length, int startoffset, + int options, int *ovector, int ovecsize); - 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. + 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); - General comments about UTF-8 mode - 1. An unbraced hexadecimal escape sequence (such as \xb3) matches a - two-byte UTF-8 character if the value is greater than 127. +PCRE 16-BIT API STRING EXTRACTION FUNCTIONS - 2. Octal numbers up to \777 are recognized, and match two-byte UTF-8 - characters for values greater than \177. + int pcre16_copy_named_substring(const pcre16 *code, + PCRE_SPTR16 subject, int *ovector, + int stringcount, PCRE_SPTR16 stringname, + PCRE_UCHAR16 *buffer, int buffersize); - 3. Repeat quantifiers apply to complete UTF-8 characters, not to indi- - vidual bytes, for example: \x{100}{3}. + int pcre16_copy_substring(PCRE_SPTR16 subject, int *ovector, + int stringcount, int stringnumber, PCRE_UCHAR16 *buffer, + int buffersize); - 4. The dot metacharacter matches one UTF-8 character instead of a sin- - gle byte. + int pcre16_get_named_substring(const pcre16 *code, + PCRE_SPTR16 subject, int *ovector, + int stringcount, PCRE_SPTR16 stringname, + PCRE_SPTR16 *stringptr); - 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_get_stringnumber(const pcre16 *code, + PCRE_SPTR16 name); - 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_stringtable_entries(const pcre16 *code, + PCRE_SPTR16 name, PCRE_UCHAR16 **first, PCRE_UCHAR16 **last); - 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_substring(PCRE_SPTR16 subject, int *ovector, + int stringcount, int stringnumber, + PCRE_SPTR16 *stringptr); - 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_substring_list(PCRE_SPTR16 subject, + int *ovector, int stringcount, PCRE_SPTR16 **listptr); - 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. + 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 all libraries, as well as definitions of flags, struc- + tures, 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 "unsigned 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 pcre32_config(), or if the + PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF32 option is given to pcre16_con- + fig(), 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 Non-character + + +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 both the 8-bit and the + 32-bit libraries were 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, + 16-bit and 32-bit libraries has been built, and runs the tests appro- + priately. + + +NOT SUPPORTED IN 16-BIT MODE + + Not all the features of the 8-bit library are available with the 16-bit + library. The C++ and POSIX wrapper functions support only the 8-bit + library, and the pcregrep program is at present 8-bit only. + + AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. - 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: 08 November 2012 + Copyright (c) 1997-2012 University of Cambridge. +------------------------------------------------------------------------------ + + +PCRE(3) PCRE(3) + + +NAME + PCRE - Perl-compatible regular expressions + + #include + + +PCRE 32-BIT API BASIC FUNCTIONS + + pcre32 *pcre32_compile(PCRE_SPTR32 pattern, int options, + const char **errptr, int *erroffset, + const unsigned char *tableptr); + + pcre32 *pcre32_compile2(PCRE_SPTR32 pattern, int options, + int *errorcodeptr, + const char **errptr, int *erroffset, + const unsigned char *tableptr); + + pcre32_extra *pcre32_study(const pcre32 *code, int options, + const char **errptr); + + void pcre32_free_study(pcre32_extra *extra); + + int pcre32_exec(const pcre32 *code, const pcre32_extra *extra, + PCRE_SPTR32 subject, int length, int startoffset, + int options, int *ovector, int ovecsize); + + int pcre32_dfa_exec(const pcre32 *code, const pcre32_extra *extra, + PCRE_SPTR32 subject, int length, int startoffset, + int options, int *ovector, int ovecsize, + int *workspace, int wscount); + + +PCRE 32-BIT API STRING EXTRACTION FUNCTIONS + + int pcre32_copy_named_substring(const pcre32 *code, + PCRE_SPTR32 subject, int *ovector, + int stringcount, PCRE_SPTR32 stringname, + PCRE_UCHAR32 *buffer, int buffersize); + + int pcre32_copy_substring(PCRE_SPTR32 subject, int *ovector, + int stringcount, int stringnumber, PCRE_UCHAR32 *buffer, + int buffersize); + + int pcre32_get_named_substring(const pcre32 *code, + PCRE_SPTR32 subject, int *ovector, + int stringcount, PCRE_SPTR32 stringname, + PCRE_SPTR32 *stringptr); + + int pcre32_get_stringnumber(const pcre32 *code, + PCRE_SPTR32 name); + + int pcre32_get_stringtable_entries(const pcre32 *code, + PCRE_SPTR32 name, PCRE_UCHAR32 **first, PCRE_UCHAR32 **last); + + int pcre32_get_substring(PCRE_SPTR32 subject, int *ovector, + int stringcount, int stringnumber, + PCRE_SPTR32 *stringptr); + + int pcre32_get_substring_list(PCRE_SPTR32 subject, + int *ovector, int stringcount, PCRE_SPTR32 **listptr); + + void pcre32_free_substring(PCRE_SPTR32 stringptr); + + void pcre32_free_substring_list(PCRE_SPTR32 *stringptr); + + +PCRE 32-BIT API AUXILIARY FUNCTIONS + + pcre32_jit_stack *pcre32_jit_stack_alloc(int startsize, int maxsize); + + void pcre32_jit_stack_free(pcre32_jit_stack *stack); + + void pcre32_assign_jit_stack(pcre32_extra *extra, + pcre32_jit_callback callback, void *data); + + const unsigned char *pcre32_maketables(void); + + int pcre32_fullinfo(const pcre32 *code, const pcre32_extra *extra, + int what, void *where); + + int pcre32_refcount(pcre32 *code, int adjust); + + int pcre32_config(int what, void *where); + + const char *pcre32_version(void); + + int pcre32_pattern_to_host_byte_order(pcre32 *code, + pcre32_extra *extra, const unsigned char *tables); + + +PCRE 32-BIT API INDIRECTED FUNCTIONS + + void *(*pcre32_malloc)(size_t); + + void (*pcre32_free)(void *); + + void *(*pcre32_stack_malloc)(size_t); + + void (*pcre32_stack_free)(void *); + + int (*pcre32_callout)(pcre32_callout_block *); + + +PCRE 32-BIT API 32-BIT-ONLY FUNCTION + + int pcre32_utf32_to_host_byte_order(PCRE_UCHAR32 *output, + PCRE_SPTR32 input, int length, int *byte_order, + int keep_boms); + + +THE PCRE 32-BIT LIBRARY + + Starting with release 8.32, it is possible to compile a PCRE library + that supports 32-bit character strings, including UTF-32 strings, as + well as or instead of the original 8-bit library. This work was done by + Christian Persch, based on the work done by Zoltan Herczeg for the + 16-bit library. All three libraries contain identical sets of func- + tions, used in exactly the same way. Only the names of the functions + and the data types of their arguments and results are different. To + avoid over-complication and reduce the documentation maintenance load, + most of the PCRE documentation describes the 8-bit library, with only + occasional references to the 16-bit and 32-bit libraries. This page + describes what is different when you use the 32-bit library. + + WARNING: A single application can be linked with all or any of the + three libraries, but you must take care when processing any particular + pattern to use functions from just one library. For example, if you + want to study a pattern that was compiled with pcre32_compile(), you + must do so with pcre32_study(), not pcre_study(), and you must free the + study data with pcre32_free_study(). + + +THE HEADER FILE + + There is only one header file, pcre.h. It contains prototypes for all + the functions in all libraries, as well as definitions of flags, struc- + tures, error codes, etc. + + +THE LIBRARY NAME + + In Unix-like systems, the 32-bit library is called libpcre32, and can + normally be accesss by adding -lpcre32 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 32-bit library, + strings are passed as vectors of unsigned 32-bit quantities. The macro + PCRE_UCHAR32 specifies an appropriate data type, and PCRE_SPTR32 is + defined as "const PCRE_UCHAR32 *". In very many environments, "unsigned + int" is a 32-bit data type. When PCRE is built, it defines PCRE_UCHAR32 + as "unsigned int", but checks that it really is a 32-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 32-bit + patterns and JIT stacks are pcre32 and pcre32_jit_stack respectively. + The type of the user-accessible structure that is returned by + pcre32_study() is pcre32_extra, and the type of the structure that is + used for passing data to a callout function is pcre32_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 32-bit instead of 8-bit types. + + +32-BIT FUNCTIONS + + For every function in the 8-bit library there is a corresponding func- + tion in the 32-bit library with a name that starts with pcre32_ instead + of pcre_. The prototypes are listed above. In addition, there is one + extra function, pcre32_utf32_to_host_byte_order(). This is a utility + function that converts a UTF-32 character string to host byte order if + necessary. The other 32-bit functions expect the strings they are + passed to be in host byte order. + + The input and output arguments of pcre32_utf32_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 32-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 32-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 32-bit units rather than bytes. + + +NAMED SUBPATTERNS + + The name-to-number translation table that is maintained for named sub- + patterns uses 32-bit characters. The pcre32_get_stringtable_entries() + function returns the length of each entry in the table as the number of + 32-bit data units. + + +OPTION NAMES + + There are two new general option names, PCRE_UTF32 and + PCRE_NO_UTF32_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-32 strings in the pcreunicode page. + + For the pcre32_config() function there is an option PCRE_CONFIG_UTF32 + that returns 1 if UTF-32 support is configured, otherwise 0. If this + option is given to pcre_config() or pcre16_config(), or if the + PCRE_CONFIG_UTF8 or PCRE_CONFIG_UTF16 option is given to pcre32_con- + fig(), the result is the PCRE_ERROR_BADOPTION error. + + +CHARACTER CODES + + In 32-bit mode, when PCRE_UTF32 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 0x7fffffff instead of 0 to 0xff. Charac- + ter 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-32 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 ill-formed in UTF-32. + + A UTF-32 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 + pcre32_utf32_to_host_byte_order() is provided to help with this (see + above). + + +ERROR NAMES + + The error PCRE_ERROR_BADUTF32 corresponds to its 8-bit counterpart. + 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 pcre32_exec(). + + There are new error codes whose names begin with PCRE_UTF32_ERR for + invalid UTF-32 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-32 errors + are: + + PCRE_UTF32_ERR1 Surrogate character (range from 0xd800 to 0xdfff) + PCRE_UTF32_ERR2 Non-character + PCRE_UTF32_ERR3 Character > 0x10ffff + + +ERROR TEXTS + + If there is an error while compiling a pattern, the error text that is + passed back by pcre32_compile() or pcre32_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 32-bit vectors. + + +TESTING + + The pcretest program continues to operate with 8-bit input and output + files, but it can be used for testing the 32-bit library. If it is run + with the command line option -32, patterns and subject strings are con- + verted from 8-bit to 32-bit before being passed to PCRE, and the 32-bit + library functions are used instead of the 8-bit ones. Returned 32-bit + strings are converted to 8-bit for output. If both the 8-bit and the + 16-bit libraries were not compiled, pcretest defaults to 32-bit and the + -32 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, + 16-bit and 32-bit libraries has been built, and runs the tests appro- + priately. + + +NOT SUPPORTED IN 32-BIT MODE + + Not all the features of the 8-bit library are available with the 32-bit + library. The C++ and POSIX wrapper functions support only the 8-bit + library, and the pcregrep program is at present 8-bit only. + + +AUTHOR + + Philip Hazel + University Computing Service + Cambridge CB2 3QH, England. + + REVISION - Last updated: 13 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 08 November 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -288,82 +851,151 @@ PCRE BUILD-TIME OPTIONS environments using the GUI facility of cmake-gui if you are using CMake instead of configure to build PCRE. - There is a lot more information about building PCRE in non-Unix-like - environments in the file called NON_UNIX_USE, which is part of the PCRE - distribution. You should consult this file as well as the README file - if you are building in a non-Unix-like environment. + There is a lot more information about building PCRE without using con- + figure (including information about using CMake or building "by hand") + in the file called NON-AUTOTOOLS-BUILD, which is part of the PCRE dis- + tribution. You should consult this file as well as the README file if + you are building in a non-Unix-like environment. The complete list of options for configure (which includes the standard - ones such as the selection of the installation directory) can be + ones such as the selection of the installation directory) can be obtained by running ./configure --help - The following sections include descriptions of options whose names + The following sections include descriptions of options whose names begin with --enable or --disable. These settings specify changes to the - defaults for the configure command. Because of the way that configure - works, --enable and --disable always come in pairs, so the complemen- - tary option always exists as well, but as it specifies the default, it + defaults for the configure command. Because of the way that configure + works, --enable and --disable always come in pairs, so the complemen- + tary option always exists as well, but as it specifies the default, it is not described. +BUILDING 8-BIT, 16-BIT AND 32-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. You can also build a separate library, called + libpcre32, in which strings are contained in vectors of 32-bit data + units and interpreted either as single-unit characters or UTF-32 + strings, by adding + + --enable-pcre32 + + to the configure command. If you do not want the 8-bit library, add + + --disable-pcre8 + + as well. At least one of the three libraries must be built. Note that + the C++ and POSIX wrappers are for the 8-bit library only, and that + pcregrep is an 8-bit program. None of these are built if you select + only the 16-bit or 32-bit libraries. + + +BUILDING SHARED AND STATIC LIBRARIES + + The PCRE building process uses libtool to build both shared and static + Unix libraries by default. You can suppress one of these by adding one + of + + --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, UTF-16 AND UTF-32 SUPPORT - To build PCRE with support for UTF-8 Unicode character strings, add + To build PCRE with support for UTF Unicode character strings, add - --enable-utf8 + --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. + to the configure command. This setting applies to all three libraries, + adding support for UTF-8 to the 8-bit library, support for UTF-16 to + the 16-bit library, and support for UTF-32 to the to the 32-bit + library. There are no separate options for enabling UTF-8, UTF-16 and + UTF-32 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 another with- + out in the same configuration. (For backwards compatibility, --enable- + utf8 is a synonym of --enable-utf.) - 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 + Of itself, this setting does not make PCRE treat strings as UTF-8, + UTF-16 or UTF-32. As well as compiling PCRE with this option, you also + have have to set the PCRE_UTF8, PCRE_UTF16 or PCRE_UTF32 option (as + appropriate) when you call one of the pattern compiling functions. + + If you set --enable-utf when compiling in an EBCDIC environment, PCRE + expects its input to be either ASCII or UTF-8 (depending on the 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 - PCRE library. Only the general category properties such as Lu and Nd + Including Unicode property support adds around 30K of tables to the + PCRE library. Only the general category properties such as Lu and Nd are supported. Details are given in the pcrepattern documentation. +JUST-IN-TIME COMPILER SUPPORT + + Just-in-time compiler support is included in the build by specifying + + --enable-jit + + This support is available only for certain hardware architectures. If + this option is set for an unsupported architecture, a compile time + error occurs. See the pcrejit documentation for a discussion of JIT + usage. When JIT support is enabled, pcregrep automatically makes use of + it, unless you add + + --disable-pcregrep-jit + + to the "configure" command. + + CODE VALUE OF NEWLINE - By default, PCRE interprets the linefeed (LF) character as indicating - the end of a line. This is the normal newline character on Unix-like - systems. You can compile PCRE to use carriage return (CR) instead, by + By default, PCRE interprets the linefeed (LF) character as indicating + the end of a line. This is the normal newline character on Unix-like + systems. You can compile PCRE to use carriage return (CR) instead, by adding --enable-newline-is-cr - to the configure command. There is also a --enable-newline-is-lf + to the configure command. There is also a --enable-newline-is-lf option, which explicitly specifies linefeed as the newline character. Alternatively, you can specify that line endings are to be indicated by @@ -375,53 +1007,41 @@ CODE VALUE OF NEWLINE --enable-newline-is-anycrlf - which causes PCRE to recognize any of the three sequences CR, LF, or + which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as indicating a line ending. Finally, a fifth option, specified by --enable-newline-is-any causes PCRE to recognize any Unicode newline sequence. - Whatever line ending convention is selected when PCRE is built can be - overridden when the library functions are called. At build time it is + Whatever line ending convention is selected when PCRE is built can be + overridden when the library functions are called. At build time it is conventional to use the standard for your operating system. WHAT \R MATCHES - By default, the sequence \R in a pattern matches any Unicode newline - sequence, whatever has been selected as the line ending sequence. If + By default, the sequence \R in a pattern matches any Unicode newline + sequence, whatever has been selected as the line ending sequence. If you specify --enable-bsr-anycrlf - the default is changed so that \R matches only CR, LF, or CRLF. What- - ever is selected when PCRE is built can be overridden when the library + the default is changed so that \R matches only CR, LF, or CRLF. What- + ever is selected when PCRE is built can be overridden when the library functions are called. -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 @@ -430,20 +1050,23 @@ POSIX MALLOC USAGE HANDLING VERY LARGE PATTERNS - Within a compiled pattern, offset values are used to point from one - part to another (for example, from an opening parenthesis to an alter- - nation metacharacter). By default, two-byte values are used for these - offsets, leading to a maximum size for a compiled pattern of around - 64K. This is sufficient to handle all but the most gigantic patterns. - Nevertheless, some people do want to process truyl enormous patterns, - so it is possible to compile PCRE to use three-byte or four-byte off- - sets by adding a setting such as + Within a compiled pattern, offset values are used to point from one + part to another (for example, from an opening parenthesis to an alter- + nation metacharacter). By default, in the 8-bit and 16-bit libraries, + two-byte values are used for these offsets, leading to a maximum size + for a compiled pattern of around 64K. This is sufficient to handle all + but the most gigantic patterns. Nevertheless, some people do want to + process truly enormous patterns, so it is possible to compile PCRE to + use three-byte or four-byte offsets by adding a setting such as --with-link-size=3 - to the configure command. The value given must be 2, 3, or 4. 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. In these libraries, + using longer offsets slows down the operation of PCRE because it has to + load additional data when handling them. For the 32-bit library the + value is always 4 and cannot be overridden; the value of --with-link- + size is ignored. AVOIDING EXCESSIVE STACK USAGE @@ -517,9 +1140,9 @@ CREATING CHARACTER TABLES AT BUILD TIME 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".) @@ -535,9 +1158,24 @@ USING EBCDIC CODE 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. + --enable-ebcdic option is incompatible with --enable-utf. + The EBCDIC character that corresponds to an ASCII LF is assumed to have + the value 0x15 by default. However, in some EBCDIC environments, 0x25 + is used. In such an environment you should use + --enable-ebcdic-nl25 + + as well as, or instead of, --enable-ebcdic. The EBCDIC character for CR + has the same value as in ASCII, namely, 0x0d. Whichever of 0x15 and + 0x25 is not chosen as LF is made to correspond to the Unicode NEL char- + acter (which, in Unicode, is 0x85). + + The options that select newline behaviour, such as --enable-newline-is- + cr, and equivalent run-time options, refer to these character values in + an EBCDIC environment. + + PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT By default, pcregrep reads all files as plain text. You can build it so @@ -548,10 +1186,26 @@ 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 @@ -583,9 +1237,77 @@ PCRETEST OPTION FOR LIBREADLINE SUPPORT immediately before the configure command. +DEBUGGING WITH VALGRIND SUPPORT + + By adding the + + --enable-valgrind + + option to to the configure command, PCRE will use valgrind annotations + to mark certain memory regions as unaddressable. This allows it to + detect invalid memory accesses, and is mostly useful for debugging PCRE + itself. + + +CODE COVERAGE REPORTING + + If your C compiler is gcc, you can build a version of PCRE that can + generate a code coverage report for its test suite. To enable this, you + must install lcov version 1.6 or above. Then specify + + --enable-coverage + + to the configure command and build PCRE in the usual way. + + Note that using ccache (a caching C compiler) is incompatible with code + coverage reporting. If you have configured ccache to run automatically + on your system, you must set the environment variable + + CCACHE_DISABLE=1 + + before running make to build PCRE, so that ccache is not used. + + When --enable-coverage is used, the following addition targets are + added to the Makefile: + + make coverage + + This creates a fresh coverage report for the PCRE test suite. It is + equivalent to running "make coverage-reset", "make coverage-baseline", + "make check", and then "make coverage-report". + + make coverage-reset + + This zeroes the coverage counters, but does nothing else. + + make coverage-baseline + + This captures baseline coverage information. + + make coverage-report + + This creates the coverage report. + + make coverage-clean-report + + This removes the generated coverage report without cleaning the cover- + age data itself. + + make coverage-clean-data + + This removes the captured coverage data without removing the coverage + files created at compile time (*.gcno). + + make coverage-clean + + This cleans all coverage data including the generated coverage report. + For more information about code coverage, see the gcov and lcov docu- + mentation. + + SEE ALSO - pcreapi(3), pcre_config(3). + pcreapi(3), pcre16, pcre32, pcre_config(3). AUTHOR @@ -597,8 +1319,8 @@ AUTHOR REVISION - Last updated: 29 September 2009 - Copyright (c) 1997-2009 University of Cambridge. + Last updated: 30 October 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -614,13 +1336,17 @@ 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(), pcre16_exec() and pcre32_exec() functions. These work in + the same as as Perl's matching function, and provide a Perl-compatible + matching operation. The just-in-time (JIT) optimization that is + described in the pcrejit documentation is compatible with these func- + tions. - 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(), + pcre16_dfa_exec() and pcre32_dfa_exec() functions; they operate in a + different way, and are not Perl-compatible. This alternative has advan- + tages 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 +1474,43 @@ 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, UTF-16 or UTF-32 modes, is + not supported in these modes, because the alternative algorithm moves + through the subject string one character (not data unit) at a time, for + all active paths through the tree. - 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) - are not supported. (*FAIL) is supported, and behaves like a failing + 8. Except for (*FAIL), the backtracking control verbs such as (*PRUNE) + are not supported. (*FAIL) is supported, and behaves like a failing negative assertion. ADVANTAGES OF THE ALTERNATIVE ALGORITHM - Using the alternative matching algorithm provides the following advan- + Using the alternative matching algorithm provides the following advan- tages: 1. All possible matches (at a single point in the subject) are automat- - ically found, and in particular, the longest match is found. To find + ically found, and in particular, the longest match is found. To find more than one match using the standard algorithm, you have to do kludgy things with callouts. - 2. Because the alternative algorithm scans the subject string just - 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 +1528,8 @@ 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 +1539,10 @@ PCREAPI(3) NAME PCRE - Perl-compatible regular expressions + #include -PCRE NATIVE API - #include +PCRE NATIVE API BASIC FUNCTIONS pcre *pcre_compile(const char *pattern, int options, const char **errptr, int *erroffset, @@ -829,6 +1556,8 @@ 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 +1567,9 @@ 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, @@ -869,19 +1601,38 @@ PCRE NATIVE API void pcre_free_substring_list(const char **stringptr); + +PCRE NATIVE API AUXILIARY FUNCTIONS + + int pcre_jit_exec(const pcre *code, const pcre_extra *extra, + const char *subject, int length, int startoffset, + int options, int *ovector, int ovecsize, + pcre_jit_stack *jstack); + + 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); void (*pcre_free)(void *); @@ -893,36 +1644,77 @@ PCRE NATIVE API int (*pcre_callout)(pcre_callout_block *); +PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES + + As well as support for 8-bit character strings, PCRE also supports + 16-bit strings (from release 8.30) and 32-bit strings (from release + 8.32), by means of two additional libraries. They can be built as well + as, or instead of, the 8-bit library. To avoid too much complication, + this document describes the 8-bit versions of the functions, with only + occasional references to the 16-bit and 32-bit libraries. + + The 16-bit and 32-bit functions operate in the same way as their 8-bit + counterparts; they just use different data types for their arguments + and results, and their names start with pcre16_ or pcre32_ instead of + pcre_. For every option that has UTF8 in its name (for example, + PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 + replaced by UTF16 or UTF32, respectively. This facility is in fact just + cosmetic; the 16-bit and 32-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, or 32-bit data quantities and UTF-32 when using the 32-bit + library, unless specified otherwise. More details of the specific dif- + ferences for the 16-bit and 32-bit libraries are given in the pcre16 + and pcre32 pages. + + 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. + 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 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 + 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. + + From release 8.32 there is also a direct interface for JIT execution, + which gives improved performance. The JIT-specific functions are dis- + cussed in the pcrejit documentation. + A second matching function, pcre_dfa_exec(), which is not Perl-compati- ble, is also provided. This uses a different algorithm for the match- ing. The alternative algorithm finds all possible matches (at a given @@ -955,10 +1747,8 @@ PCRE API OVERVIEW 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. + 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 @@ -997,7 +1787,7 @@ NEWLINES 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 + 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 @@ -1035,66 +1825,110 @@ MULTITHREADING 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. + 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 int pcre_config(int what, void *where); - The function pcre_config() makes it possible for a PCRE client to dis- + The function pcre_config() makes it possible for a PCRE client to dis- cover which optional features have been compiled into the PCRE library. - The pcrebuild documentation has more details about these optional fea- + The pcrebuild documentation has more details about these optional fea- tures. - The first argument for pcre_config() is an integer, specifying which + The first argument for pcre_config() is an integer, specifying which information is required; the second argument is a pointer to a variable - into which the information is placed. The 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. + The output is an integer that is set to one if UTF-8 support is avail- + able; otherwise it is set to zero. This value should normally be given + to the 8-bit version of this function, pcre_config(). If it is given to + the 16-bit or 32-bit version of this function, the result is + 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 or 32-bit version of this function, the result is + PCRE_ERROR_BADOPTION. + + PCRE_CONFIG_UTF32 + + The output is an integer that is set to one if UTF-32 support is avail- + able; otherwise it is set to zero. This value should normally be given + to the 32-bit version of this function, pcre32_config(). If it is given + to the 8-bit or 16-bit version of this function, the result is + PCRE_ERROR_BADOPTION. + PCRE_CONFIG_UNICODE_PROPERTIES The output is an integer that is set to one if support for Unicode character properties is available; otherwise it is set to zero. + PCRE_CONFIG_JIT + + The output is an integer that is set to one if support for just-in-time + compiling is available; otherwise it is set to zero. + + PCRE_CONFIG_JITTARGET + + The output is a pointer to a zero-terminated "const char *" string. If + JIT support is available, the string contains the name of the 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 - are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, - and -1 for ANY. Though they are derived from ASCII, the same values - are returned in EBCDIC environments. The default should normally corre- + The output is an integer whose value specifies the default character + sequence that is recognized as meaning "newline". The values that are + supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 + for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, + ANYCRLF, and ANY yield the same values. However, the value for LF is + normally 21, though some EBCDIC environments use 37. The corresponding + values for CRLF are 3349 and 3365. The default should normally corre- 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. For the 32-bit + library, the value is either 2 or 4 and is still a number of bytes. The + default value of 2 is sufficient for all but the most massive patterns, + since it allows the compiled pattern to be up to 64K in size. Larger + values allow larger regular expressions to be compiled, at the expense + of slower matching. PCRE_CONFIG_POSIX_MALLOC_THRESHOLD @@ -1166,23 +2000,23 @@ COMPILING A PATTERN 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_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 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. - 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). + Some errors are not detected until the whole pattern has been scanned; + in these cases, the offset passed back is the length of the pattern. + Note that the offset is in bytes, not characters, even in UTF-8 mode. + It may sometimes point into the middle of a UTF-8 character. If pcre_compile2() is used instead of pcre_compile(), and the error- codeptr argument is not NULL, a non-zero error code number is returned @@ -1279,8 +2113,8 @@ COMPILING A PATTERN 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 @@ -1296,7 +2130,7 @@ COMPILING A PATTERN 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 + White space characters may never appear within special character sequences in a pattern, for example within the sequence (?( that intro- duces a conditional subpattern. @@ -1336,6 +2170,20 @@ COMPILING A PATTERN 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 @@ -1366,25 +2214,34 @@ COMPILING A PATTERN two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be - recognized. The Unicode newline sequences are the three just mentioned, - plus the single characters VT (vertical tab, U+000B), FF (formfeed, - U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS - (paragraph separator, U+2029). The last two are recognized only in - UTF-8 mode. + recognized. - The newline setting in the options word uses three bits that are + In an ASCII/Unicode environment, 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 sep- + arator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit + library, the last two are recognized only in UTF-8 mode. + + When PCRE is compiled to run in an EBCDIC (mainframe) environment, the + code for CR is 0x0d, the same as ASCII. However, the character code for + LF is normally 0x15, though in some EBCDIC environments 0x25 is used. + Whichever of these is not LF is made to correspond to Unicode's NEL + character. EBCDIC codes are all less than 256. For more details, see + the pcrebuild documentation. + + 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 +2250,69 @@ 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 only. If the same string is being matched + many times, the option can be safely set for the second and subsequent + matchings to improve performance. COMPILATION ERROR CODES The following table lists the error codes than may be returned by pcre_compile2(), along with the error messages that may be returned by - both compiling functions. 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 or 32-bit mode. As PCRE has developed, + some error codes have fallen out of use. To avoid confusion, they have + not been re-used. 0 no error 1 \ at end of pattern @@ -1486,26 +2346,26 @@ 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 +2384,18 @@ 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 + 77 invalid UTF-32 string (specifically UTF-32) 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. @@ -1549,13 +2420,35 @@ STUDYING A PATTERN passed; these are described below in the section on matching a pattern. If studying the pattern does not produce any useful information, - pcre_study() returns NULL. In that circumstance, if the calling program - wants to pass any of the other fields to pcre_exec() or - pcre_dfa_exec(), it must set up its own pcre_extra block. + pcre_study() returns NULL by default. In that circumstance, if the + calling program wants to pass any of the other fields to pcre_exec() or + pcre_dfa_exec(), it must set up its own pcre_extra block. However, if + pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it + returns a pcre_extra block even if studying did not find any additional + information. It may still return NULL, however, if an error occurs in + pcre_study(). - 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 further options in addition to PCRE_STUDY_EXTRA_NEEDED: + PCRE_STUDY_JIT_COMPILE + PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE + PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE + + If any of these are set, and the just-in-time compiler is available, + the pattern is further compiled into machine code that executes much + faster than the pcre_exec() interpretive matching function. If the + just-in-time compiler is not available, these options are ignored. All + undefined bits in the options argument must be zero. + + JIT compilation is a heavyweight optimization. It can take some time + for patterns to be analyzed, and for one-off matches and simple pat- + terns the benefit of faster execution might be offset by a much slower + 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 points to is set to NULL. Otherwise it is set to point to a textual @@ -1563,33 +2456,53 @@ 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 does not mean that there are any strings of that length that match, but - it does guarantee that no shorter strings match. The value is used by - pcre_exec() and pcre_dfa_exec() to avoid wasting time by trying to - match strings that are shorter than the lower bound. You can find out - the value in a calling program via the pcre_fullinfo() function. + it does guarantee that no shorter strings match. The value is used to + avoid wasting time by trying to match strings that are shorter than the + lower bound. You can find out the value in a calling program via the + pcre_fullinfo() function. Studying a pattern is also useful for non-anchored patterns that do not have a single fixed starting character. A bitmap of possible starting bytes is created. This speeds up finding a position in the subject at - which to start matching. + which to start matching. (In 16-bit mode, the bitmap is used for 16-bit + values less than 256. In 32-bit mode, the bitmap is used for 32-bit + values less than 256.) - 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 @@ -1656,8 +2569,8 @@ INFORMATION ABOUT A PATTERN 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). + 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 @@ -1666,56 +2579,64 @@ INFORMATION ABOUT A PATTERN 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: + 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 */ - The possible values for the third argument are defined in pcre.h, and + The possible values for the third argument are defined in pcre.h, and are as follows: PCRE_INFO_BACKREFMAX - Return the number of the highest back reference in the pattern. The - fourth argument should point to an int variable. Zero is returned if + Return the number of the highest back reference in the pattern. The + fourth argument should point to an int variable. Zero is returned if there are no back references. PCRE_INFO_CAPTURECOUNT - Return the number of capturing subpatterns in the pattern. The fourth + Return the number of capturing subpatterns in the pattern. The fourth argument should point to an int variable. PCRE_INFO_DEFAULT_TABLES - Return a pointer to the internal default character tables within PCRE. - The fourth argument should point to an unsigned char * variable. This + Return a pointer to the internal default character tables within PCRE. + The fourth argument should point to an unsigned char * variable. This information call is provided for internal use by the pcre_study() func- - tion. External callers can cause PCRE to use its internal tables by + tion. External callers can cause PCRE to use its internal tables by passing a NULL table pointer. 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. In the 32-bit library the value can be up to + 0x10ffff. + 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 @@ -1726,46 +2647,80 @@ INFORMATION ABOUT A PATTERN of a subject string or after any newline within the string. Otherwise -2 is returned. For anchored patterns, -2 is returned. + Since for the 32-bit library using the non-UTF-32 mode, this function + is unable to return the full 32-bit range of the character, this value + is deprecated; instead the PCRE_INFO_FIRSTCHARACTERFLAGS and + PCRE_INFO_FIRSTCHARACTER values should be used. + 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. + If the pattern was studied, and this resulted in the construction of a + 256-bit table indicating a fixed set of values for the first data unit + in any matching string, a pointer to the table is returned. Otherwise + NULL is returned. The fourth argument should point to an unsigned char + * variable. PCRE_INFO_HASCRORLF - Return 1 if the pattern contains any explicit matches for CR or LF - characters, otherwise 0. The fourth argument should point to an int - variable. An explicit match is either a literal CR or LF character, or + Return 1 if the pattern contains any explicit matches for CR or LF + characters, otherwise 0. The fourth argument should point to an int + variable. An explicit match is either a literal CR or LF character, or \r or \n. PCRE_INFO_JCHANGED - Return 1 if the (?J) or (?-J) option setting is used in the pattern, - otherwise 0. The fourth argument should point to an int variable. (?J) + Return 1 if the (?J) or (?-J) option setting is used in the pattern, + otherwise 0. The fourth argument should point to an int variable. (?J) and (?-J) set and unset the local PCRE_DUPNAMES option, respectively. + PCRE_INFO_JIT + + Return 1 if the pattern was studied with 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. + Since for the 32-bit library using the non-UTF-32 mode, this function + is unable to return the full 32-bit range of the character, this value + is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and + PCRE_INFO_REQUIREDCHAR values should be used. + + 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 +2740,14 @@ 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. In the 32-bit library, the + pointer points to 32-bit data units, the first of which contains the + parenthesis number. The rest of the entry is the corresponding name, + zero terminated. The names are in alphabetical order. Duplicate names may appear if (?| is used to create multiple groups with the same number, as described in @@ -1801,8 +2760,8 @@ 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): (? (?(\d\d)?\d\d) - (?\d\d) - (?\d\d) ) @@ -1855,43 +2814,93 @@ 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 + 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). + + PCRE_INFO_FIRSTCHARACTERFLAGS + + Return information about the first data unit of any matched string, for + a non-anchored pattern. The fourth argument should point to an int variable. + If there is a fixed first value, for example, the letter "c" from a + pattern such as (cat|cow|coyote), 1 is returned, and the character + value can be retrieved using PCRE_INFO_FIRSTCHARACTER. -OBSOLETE INFO FUNCTION + If there is no fixed first value, and if either - int pcre_info(const pcre *code, int *optptr, int *firstcharptr); + (a) the pattern was compiled with the PCRE_MULTILINE option, and every + branch starts with "^", or - 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: + (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not + set (if it were set, the pattern would be anchored), - PCRE_ERROR_NULL the argument code was NULL - PCRE_ERROR_BADMAGIC the "magic number" was not found + 2 is returned, indicating that the pattern matches only at the start of + a subject string or after any newline within the string. Otherwise 0 is + returned. For anchored patterns, 0 is returned. - 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). + PCRE_INFO_FIRSTCHARACTER - 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 fixed first character value, if PCRE_INFO_FIRSTCHARACTER- + FLAGS returned 1; otherwise returns 0. The fourth argument should point + to an uint_t variable. + In the 8-bit library, the value is always less than 256. In the 16-bit + library the value can be up to 0xffff. In the 32-bit library in UTF-32 + mode the value can be up to 0x10ffff, and up to 0xffffffff when not + using UTF-32 mode. + If there is no fixed first value, and if either + + (a) the pattern was compiled with the PCRE_MULTILINE option, and every + branch starts with "^", or + + (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not + set (if it were set, the pattern would be anchored), + + -1 is returned, indicating that the pattern matches only at the start + of a subject string or after any newline within the string. Otherwise + -2 is returned. For anchored patterns, -2 is returned. + + PCRE_INFO_REQUIREDCHARFLAGS + + Returns 1 if there is a rightmost literal data unit that must exist in + any matched string, other than at its start. The fourth argument should + point to an int variable. If there is no such value, 0 is returned. If + returning 1, the character value itself can be retrieved using + PCRE_INFO_REQUIREDCHAR. + + For anchored patterns, a last literal value is recorded only if it fol- + lows something of variable length. For example, for the pattern + /^a\d+z\d+/ the returned value 1 (with "z" returned from + PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0. + + PCRE_INFO_REQUIREDCHAR + + Return the value of the rightmost literal data unit that must exist in + any matched string, other than at its start, if such a value has been + recorded. The fourth argument should point to an uint32_t variable. If + there is no such value, 0 is returned. + + REFERENCE COUNTS int pcre_refcount(pcre *code, int adjust); @@ -1923,11 +2932,15 @@ MATCHING A PATTERN: THE TRADITIONAL 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. 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. + 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 is possible to save compiled patterns and study data, and then use them @@ -1958,27 +2971,35 @@ MATCHING A PATTERN: THE TRADITIONAL FUNCTION 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 + In the 32-bit version of this structure, the mark field has type + "PCRE_UCHAR32 **". + + The flags field is used to specify which of the other fields are set. + The 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 @@ -1986,71 +3007,87 @@ 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. + 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. - 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 + 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. + 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 + 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 The PCRE_ANCHORED option limits pcre_exec() to matching at the first @@ -2172,7 +3209,9 @@ 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 +3245,201 @@ 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. + 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 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. + 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 +3448,7 @@ 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 +3457,82 @@ 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 +3542,7 @@ 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) @@ -2492,13 +3556,141 @@ 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. - Error numbers -16 to -20 and -22 are not used by pcre_exec(). + 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 or 32-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. + + PCRE_ERROR_JIT_BADOPTION + + This error is returned when a pattern that was successfully studied + using a JIT compile option is being matched, but the matching mode + (partial or complete match) does not correspond to any JIT compilation + mode. When the JIT fast path function is used, this error may be also + given for invalid options. See the pcrejit documentation for more + details. + + PCRE_ERROR_BADLENGTH (-32) + + This error is given if pcre_exec() is called with a negative value for + the length argument. + + Error numbers -16 to -20, -22, and 30 are not used by pcre_exec(). + + Reason codes for invalid UTF-8 strings + + This section applies only to the 8-bit library. The corresponding + information for the 16-bit and 32-bit libraries is given in the pcre16 + and pcre32 pages. + + When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT- + UTF8, and the size of the output vector (ovecsize) is at least 2, the + offset of the start of the invalid UTF-8 character is placed in the + 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). + + 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. + + PCRE_UTF8_ERR2 + + Non-character. These are the last two characters in each plane (0xfffe, + 0xffff, 0x1fffe, 0x1ffff .. 0x10fffe, 0x10ffff), and the characters + 0xfdd0..0xfdef. + + EXTRACTING CAPTURED SUBSTRINGS BY NUMBER int pcre_copy_substring(const char *subject, int *ovector, @@ -2673,9 +3865,9 @@ DUPLICATE SUBPATTERN NAMES 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. + 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 @@ -2696,6 +3888,31 @@ FINDING ALL POSSIBLE MATCHES 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, @@ -2819,32 +4036,34 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION 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. + filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() + can use the entire ovector for returning matched strings. Error returns from pcre_dfa_exec() - The pcre_dfa_exec() function returns a negative number when it fails. - Many of the errors are the same as for pcre_exec(), and these are - described above. There are in addition the following errors that are + The pcre_dfa_exec() function returns a negative number when it fails. + Many of the errors are the same as for pcre_exec(), and these are + described above. There are in addition the following errors that are specific to pcre_dfa_exec(): PCRE_ERROR_DFA_UITEM (-16) - This return is given if pcre_dfa_exec() encounters an item in the pat- - tern that it does not support, for instance, the use of \C or a back + This return is given if pcre_dfa_exec() encounters an item in the pat- + tern that it does not support, for instance, the use of \C or a back reference. PCRE_ERROR_DFA_UCOND (-17) - This return is given if pcre_dfa_exec() encounters a condition item - that uses a back reference for the condition, or a test for recursion + This return is given if pcre_dfa_exec() encounters a condition item + that uses a back reference for the condition, or a test for recursion in a specific group. These are not supported. PCRE_ERROR_DFA_UMLIMIT (-18) - This return is given if pcre_dfa_exec() is called with an extra block - that contains a setting of the match_limit field. This is not supported - (it is meaningless). + This return is given if pcre_dfa_exec() is called with an extra block + that contains a setting of the match_limit or match_limit_recursion + fields. This is not supported (these fields are meaningless for DFA + matching). PCRE_ERROR_DFA_WSSIZE (-19) @@ -2858,11 +4077,19 @@ MATCHING A PATTERN: THE ALTERNATIVE FUNCTION 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), pcre32(3), pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), + pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre- + sample(3), pcrestack(3). AUTHOR @@ -2874,8 +4101,8 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 08 November 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -2886,28 +4113,38 @@ NAME PCRE - Perl-compatible regular expressions -PCRE CALLOUTS +SYNOPSIS + #include + int (*pcre_callout)(pcre_callout_block *); + int (*pcre16_callout)(pcre16_callout_block *); + + int (*pcre32_callout)(pcre32_callout_block *); + + +DESCRIPTION + 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. + its entry point in the global variable pcre_callout (pcre16_callout for + the 16-bit library, pcre32_callout for the 32-bit library). By default, + this variable contains NULL, which disables all calling out. - Within a regular expression, (?C) indicates the points at which the - external function is to be called. 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 + 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}|--) @@ -2915,135 +4152,152 @@ 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: + tion defined by pcre_callout or pcre[16|32]_callout is called (if it is + set). This applies to both normal and DFA matching. The only argument + to the callout function is a pointer to a pcre_callout or + pcre[16|32]_callout block. These structures contains the following + 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; + int version; + int callout_number; + int *offset_vector; + const char *subject; (8-bit version) + PCRE_SPTR16 subject; (16-bit version) + PCRE_SPTR32 subject; (32-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) + const PCRE_UCHAR32 *mark; (32-bit version) - The version field is an integer containing the version number of the - block format. The initial version was 0; the current version is 1. The - version number will change again in future if additional fields are + The version field is an integer containing the version number of the + block format. The initial version was 0; the current version is 2. The + version number will change again in future if additional fields are added, but the intention is never to remove any of the existing fields. - The callout_number field contains the number of the callout, as com- - piled into the pattern (that is, the number after ?C for manual call- + The callout_number field contains the number of the callout, as com- + piled into the pattern (that is, the number after ?C for manual call- outs, and 255 for automatically generated callouts). - The offset_vector field is a pointer to the vector of offsets that was - passed by the caller to 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. + The offset_vector field is a pointer to the vector of offsets that was + passed by the caller to the matching function. When pcre_exec() or + pcre[16|32]_exec() is used, the contents can be inspected, in order to + extract substrings that have been matched so far, in the same way as + for extracting substrings after a match has completed. For the DFA + matching functions, this field is not useful. The subject and subject_length fields contain copies of the values that - were passed to 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 - sequence \K has been encountered, this value is changed to reflect the - modified starting point. If the pattern is not anchored, the callout + The start_match field normally contains the offset within the subject + at which the current match attempt started. However, if the escape + sequence \K has been encountered, this value is changed to reflect the + modified starting point. If the pattern is not anchored, the callout function may be called several times from the same point in the pattern for different starting points in the subject. - The current_position field contains the offset within the subject of + The current_position field contains the offset within the subject of the current match pointer. - When the pcre_exec() 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 pcre[16|32]_exec() is used, the capture_top + field contains one more than the number of the highest numbered cap- + tured substring so far. If no substrings have been captured, the value + of capture_top is one. This is always the case when the DFA functions + are used, because they do not support captured substrings. - The capture_last field contains the number of the most recently cap- - tured substring. If no substrings have been captured, its value is -1. - This is always the case when pcre_dfa_exec() is used. + The capture_last field contains the number of the most recently cap- + tured substring. If no substrings have been captured, its value is -1. + This is always the case for the DFA matching functions. - The 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 - 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 + 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 pcre[16|32]_extra + data structure. If no such data was passed, the value of callout_data + in a callout block is NULL. There is a description of the pcre_extra structure in the pcreapi documentation. - The pattern_position field is present from version 1 of the 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 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 pcre[16|32]_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 func- + tions this field always contains NULL. + RETURN VALUES - The external callout function returns an integer to PCRE. If the value - is zero, matching proceeds as normal. If the value is greater than - zero, matching fails at the current point, but the testing of other + The external callout function returns an integer to PCRE. If the value + is zero, matching proceeds as normal. If the value is greater than + zero, matching fails at the current point, but the testing of other matching possibilities goes ahead, just as if a lookahead assertion had - failed. If the value is less than zero, the match is abandoned, 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 + Negative values should normally be chosen from the set of PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan- - dard "no match" failure. The error number PCRE_ERROR_CALLOUT is - reserved for use by callout functions; it will never be used by PCRE + dard "no match" failure. The error number PCRE_ERROR_CALLOUT is + reserved for use by callout functions; it will never be used by PCRE itself. @@ -3056,8 +4310,8 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 24 June 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -3074,46 +4328,51 @@ 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. + 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 + 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- - 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 + 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 does not have variables). Note the following examples: Pattern PCRE matches Perl matches @@ -3123,27 +4382,40 @@ DIFFERENCES BETWEEN PCRE AND PERL \Qabc\$xyz\E abc\$xyz abc\$xyz \Qabc\E\$\Qxyz\E abc$xyz abc$xyz - The \Q...\E sequence is recognized both inside and outside character + The \Q...\E sequence is recognized both inside and outside character classes. 8. 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- + 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. + 9. 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. - 10. There are some differences that are concerned with the settings of + 10. If any of the backtracking control verbs are used in an assertion + or in a subpattern that is called as a subroutine (whether or not + recursively), their effect is confined to that subpattern; it does not + extend to the surrounding pattern. This is not always the case in Perl. + In particular, if (*THEN) is present in a group that is called as a + subroutine, its action is limited to that group, even if the group does + not contain any | characters. There is one exception to this: the name + from a *(MARK), (*PRUNE), or (*THEN) that is encountered in a success- + ful positive assertion is passed back when a match succeeds (compare + capturing parentheses in assertions). Note that such subpatterns are + processed as anchored at the point where they are tested. + + 11. There are some differences that are concerned with the settings of 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- + 12. 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 @@ -3154,10 +4426,12 @@ DIFFERENCES BETWEEN PCRE AND PERL 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. + 13. 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- + 14. PCRE provides some extensions to the Perl regular expression facil- ities. Perl 5.10 includes new features that are not in earlier ver- sions of Perl, some of which (such as named parentheses) have been in PCRE for some time. This list is with respect to Perl 5.10: @@ -3193,10 +4467,12 @@ 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(), + pcre16_dfa_exec() and pcre32_dfa_exec(),) match in a different way and + are not Perl-compatible. (l) PCRE recognizes some special sequences such as (*CR) at the start of a pattern that set overall options that cannot be changed within the @@ -3212,8 +4488,8 @@ AUTHOR REVISION - Last updated: 31 October 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 25 August 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -3242,21 +4518,28 @@ 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, an extra library that supports 16-bit and UTF-16 character + strings, and a third library that supports 32-bit and UTF-32 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, PCRE_UTF16, or PCRE_UTF32 option, or the + pattern must start with one of these special sequences: (*UTF8) + (*UTF16) + (*UTF32) + (*UTF) - 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. + (*UTF) is a generic sequence that can be used with any of the + libraries. Starting a pattern with such a sequence is equivalent to + setting the relevant option. This feature is not Perl-compatible. How + setting a UTF mode affects pattern matching is mentioned in several + places below. There is also a summary of features in the pcreunicode + page. Another special sequence that may appear at the start of a pattern or - in combination with (*UTF8) is: + in combination with (*UTF8), (*UTF16), (*UTF32) or (*UTF) is: (*UCP) @@ -3271,25 +4554,35 @@ PCRE REGULAR EXPRESSION DETAILS 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. + ported by PCRE when one its main matching functions, pcre_exec() + (8-bit) or pcre[16|32]_exec() (16- or 32-bit), is used. PCRE also has + alternative matching functions, pcre_dfa_exec() and + pcre[16|32_dfa_exec(), which match using a different algorithm that is + not Perl-compatible. Some of the features discussed below are not + available when DFA matching is used. The advantages and disadvantages + of the alternative functions, and how they differ from the normal func- + tions, are discussed in the pcrematching page. +EBCDIC CHARACTER CODES + + PCRE can be compiled to run in an environment that uses EBCDIC as its + character code rather than ASCII or Unicode (typically a mainframe sys- + tem). In the sections below, character code values are ASCII or Uni- + code; in an EBCDIC environment these characters may have different code + values, and there are no code points greater than 255. + + NEWLINE CONVENTIONS - 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 pcreapi page has further - discussion about newlines, and shows how to set the newline convention + ceding, or any Unicode newline sequence. The pcreapi page has further + discussion about newlines, and shows how to set the newline convention in the options arguments for the compiling and matching functions. - It is also possible to specify a newline convention by starting a pat- + It is also possible to specify a newline convention by starting a pat- tern string with one of the following five sequences: (*CR) carriage return @@ -3298,25 +4591,26 @@ 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 changes the convention to CR. That pattern matches "a\nb" because LF is - no longer a newline. Note that these special settings, which are not - Perl-compatible, are recognized only at the very start of a pattern, - and that they must be in upper case. If more than one of them is + no longer a newline. Note that these special settings, which are not + Perl-compatible, are recognized only at the very start of a pattern, + and that they must be in upper case. If more than one of them is present, the last one is used. - The newline convention affects the interpretation of the dot metachar- - acter when PCRE_DOTALL is not set, and also the behaviour of \N. How- - ever, it does not affect what the \R escape sequence matches. By - default, this is any Unicode newline sequence, for Perl compatibility. - However, this can be changed; see the description of \R in the section - entitled "Newline sequences" below. A change of \R setting can be com- - bined with a change of newline convention. + The newline convention affects where the circumflex and dollar asser- + tions are true. It also affects the interpretation of the dot metachar- + acter when PCRE_DOTALL is not set, and the behaviour of \N. However, it + does not affect what the \R escape sequence matches. By default, this + is any Unicode newline sequence, for Perl compatibility. However, this + can be changed; see the description of \R in the section entitled "New- + line sequences" below. A change of \R setting can be combined with a + change of newline convention. CHARACTERS AND METACHARACTERS @@ -3330,13 +4624,13 @@ 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 +4685,14 @@ 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 +4709,11 @@ 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 @@ -3429,39 +4727,67 @@ 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.) + The precise effect of \cx on ASCII characters 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 \cA to \cZ become hex 01 to hex 1A + (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes + hex 7B (; is 3B). If the data item (byte or 16-bit value) following \c + has a value greater than 127, a compile-time error occurs. This locks + out non-ASCII characters in all modes. - 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. + The \c facility was designed for use with ASCII characters, but with + the extension to Unicode it is even less useful than it once was. It + is, however, recognized when PCRE is compiled in EBCDIC mode, where + data items are always bytes. In this mode, all values are valid after + \c. If the next character is a lower case letter, it is converted to + upper case. Then the 0xc0 bits of the byte are inverted. Thus \cA + becomes hex 01, as in ASCII (A is C1), but because the EBCDIC letters + are disjoint, \cZ becomes hex 29 (Z is E9), and other characters also + generate different values. + By default, after \x, from zero to two hexadecimal digits are read + (letters can be in upper or lower case). Any number of hexadecimal dig- + its may appear between \x{ and }, but the character code is constrained + as follows: + + 8-bit non-UTF mode less than 0x100 + 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint + 16-bit non-UTF mode less than 0x10000 + 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint + 32-bit non-UTF mode less than 0x80000000 + 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint + + Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so- + called "surrogate" codepoints), and 0xffef. + If characters other than hexadecimal digits appear between \x{ and }, or if there is no terminating }, this form of escape is not recognized. Instead, the initial \x will be interpreted as a basic hexadecimal escape, with no following digits, giving a character whose value is zero. + If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x + is as just described only when it is followed by two hexadecimal dig- + its. Otherwise, it matches a literal "x" character. In JavaScript + mode, support for code points greater than 256 is provided by \u, which + must be followed by four hexadecimal digits; otherwise it matches a + literal "u" character. Character codes specified by \u in JavaScript + mode are constrained in the same was as those specified by \x in non- + JavaScript mode. + Characters whose value is less than 256 can be defined by either of the - two syntaxes for \x. 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 @@ -3480,12 +4806,11 @@ BACKSLASH 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 + \040 is another way of writing an ASCII space \40 is the same, provided there are fewer than 40 previous capturing subpatterns \7 is always a back reference @@ -3496,36 +4821,46 @@ 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" - Note that octal values of 100 or greater must not be introduced by a + Note that octal values of 100 or greater must not be introduced by a leading zero, because no more than three octal digits are ever read. All the sequences that define a single character value can be used both - inside and outside character classes. In addition, inside a character - class, 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. + inside and outside character classes. In addition, inside a character + class, \b is interpreted as the backspace character (hex 08). + \N is not allowed in a character class. \B, \R, and \X are not special + inside a character class. Like other unrecognized escape sequences, + they are treated as the literal characters "B", "R", and "X" by + default, but cause an error if the PCRE_EXTRA option is set. Outside a + character class, these sequences have different meanings. + + Unsupported escape sequences + + In Perl, the sequences \l, \L, \u, and \U are recognized by its string + handler and used to modify the case of following characters. By + default, PCRE does not support these escape sequences. However, if the + PCRE_JAVASCRIPT_COMPAT option is set, \U matches a "U" character, and + \u can be used to define a character by code point, as described in the + previous section. + Absolute and relative back references - The sequence \g followed by an unsigned or a negative number, option- - ally enclosed in braces, is an absolute or relative back reference. A + The sequence \g followed by an unsigned or a negative number, option- + ally enclosed in braces, is an absolute or relative back reference. A named back reference can be coded as \g{name}. Back references are dis- cussed later, following the discussion of parenthesized subpatterns. Absolute and relative subroutine calls - For compatibility with Oniguruma, the non-Perl syntax \g followed by a + For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is - an alternative syntax for referencing a subpattern as a "subroutine". - Details are discussed later. Note that \g{...} (Perl syntax) and - \g<...> (Oniguruma syntax) are not synonymous. The former is a back + an alternative syntax for referencing a subpattern as a "subroutine". + Details are discussed later. Note that \g{...} (Perl syntax) and + \g<...> (Oniguruma syntax) are not synonymous. The former is a back reference; the latter is a subroutine call. Generic character types @@ -3534,18 +4869,19 @@ 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. + acter. This is the same as the "." metacharacter when PCRE_DOTALL is + not set. Perl also uses \N to match characters by name; PCRE does not + support this. Each pair of lower and upper case escape sequences partitions the com- plete set of characters into two disjoint sets. Any given character @@ -3570,9 +4906,9 @@ BACKSLASH 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 + 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-8 support was + 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 @@ -3591,10 +4927,10 @@ BACKSLASH The sequences \h, \H, \v, and \V are features that were added to Perl at release 5.10. In contrast to the other sequences, which match only ASCII characters by default, these always match certain high-valued - codepoints in UTF-8 mode, whether or not PCRE_UCP is set. The horizon- - tal space characters are: + codepoints, whether or not PCRE_UCP is set. The horizontal space char- + acters are: - U+0009 Horizontal tab + U+0009 Horizontal tab (HT) U+0020 Space U+00A0 Non-break space U+1680 Ogham space mark @@ -3616,114 +4952,119 @@ BACKSLASH The vertical space characters are: - U+000A Linefeed - U+000B Vertical tab - U+000C Formfeed - U+000D Carriage return - U+0085 Next line + U+000A Linefeed (LF) + U+000B Vertical tab (VT) + U+000C Form feed (FF) + U+000D Carriage return (CR) + U+0085 Next line (NEL) 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: + Outside a character class, by default, the escape sequence \R matches + any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent + to the following: (?>\r\n|\n|\x0b|\f|\r|\x85) - This is an example of an "atomic group", details of which are given + 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. + CR followed by LF, or one of the single characters LF (linefeed, + 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 + rator, U+2029). Unicode character property support is not needed for these characters to be recognized. It is possible to restrict \R to match only CR, LF, or CRLF (instead of - the complete set of Unicode line endings) by setting the option + the complete set of Unicode line endings) by setting the option PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched. (BSR is an abbrevation for "backslash R".) This can be made the default - when PCRE is built; if this is the case, the other behaviour can be - requested via the PCRE_BSR_UNICODE option. It is also possible to - specify these settings by starting a pattern string with one of the + when PCRE is built; if this is the case, the other behaviour can be + requested via the PCRE_BSR_UNICODE option. It is also possible to + specify these settings by starting a pattern string with one of the following sequences: (*BSR_ANYCRLF) CR, LF, or CRLF only (*BSR_UNICODE) any Unicode newline sequence - These override the default and the options given to 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), (*UTF32), (*UTF) + 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: + tional escape sequences that match characters with specific properties + are available. When in 8-bit non-UTF-8 mode, these sequences are of + course limited to testing characters whose codepoints are less than + 256, but they do work in this mode. The extra escape sequences are: \p{xx} a character with the xx property \P{xx} a character without the xx property - \X an extended Unicode sequence + \X a Unicode extended grapheme cluster - The property names represented by xx above are limited to the Unicode + The property names represented by xx above are limited to the Unicode script names, the general category properties, "Any", which matches any - character (including newline), and some special PCRE properties - (described in the next section). Other Perl properties such as "InMu- - sicalSymbols" are not currently supported by PCRE. Note that \P{Any} + character (including newline), and some special PCRE properties + (described in the next section). Other Perl properties such as "InMu- + sicalSymbols" are not currently supported by PCRE. Note that \P{Any} does not match any characters, so always causes a match failure. Sets of Unicode characters are defined as belonging to certain scripts. - A character from one of these sets can be matched using a script name. + A character from one of these sets can be matched using a script name. For example: \p{Greek} \P{Han} - Those that are not part of an identified script are lumped together as + 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- - tion can be specified by including a circumflex between the opening - brace and the property name. For example, \p{^Lu} is the same as + ified by a two-letter abbreviation. For compatibility with Perl, nega- + tion can be specified by including a circumflex between the opening + brace and the property name. For example, \p{^Lu} is the same as \P{Lu}. If only one letter is specified with \p or \P, it includes all the gen- - eral category properties that start with that letter. In this case, in - the absence of negation, the curly brackets in the escape sequence are + eral category properties that start with that letter. In this case, in + the absence of negation, the curly brackets in the escape sequence are optional; these two examples have the same effect: \p{L} @@ -3775,15 +5116,16 @@ BACKSLASH Zp Paragraph separator Zs Space separator - The special property L& is also supported: it matches a character that - has the Lu, Ll, or Lt property, in other words, a letter that is not + The special property L& is also supported: it matches a character that + has the Lu, Ll, or Lt property, in other words, a letter that is not classified as a modifier or "other". - The Cs (Surrogate) property applies only to characters in the range - U+D800 to U+DFFF. Such characters are not valid in 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 Cs (Surrogate) property applies only to characters in the range + U+D800 to U+DFFF. Such characters are not valid in Unicode strings and + so cannot be tested by PCRE, unless UTF validity checking has been + turned off (see the discussion of PCRE_NO_UTF8_CHECK, + PCRE_NO_UTF16_CHECK and PCRE_NO_UTF32_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 @@ -3796,72 +5138,103 @@ BACKSLASH Specifying caseless matching does not affect these escape sequences. For example, \p{Lu} always matches only upper case letters. - The \X escape matches any number of Unicode characters that form an - extended Unicode sequence. \X is equivalent to + Matching characters by Unicode property is not fast, because PCRE has + to do a multistage table lookup in order to find a character's prop- + erty. That is why the traditional escape sequences such as \d and \w do + not use Unicode properties in PCRE by default, though you can make them + do so by setting the PCRE_UCP option or by starting the pattern with + (*UCP). + Extended grapheme clusters + + The \X escape matches any number of Unicode characters that form an + "extended grapheme cluster", and treats the sequence as an atomic group + (see below). Up to and including release 8.31, PCRE matched an ear- + lier, simpler definition that was 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 matched a character without the "mark" property, followed + by zero or more characters with the "mark" property. Characters with + the "mark" property are typically non-spacing accents that affect the + preceding character. - 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). + This simple definition was extended in Unicode to include more compli- + cated kinds of composite character by giving each character a grapheme + breaking property, and creating rules that use these properties to + define the boundaries of extended grapheme clusters. In releases of + PCRE later than 8.31, \X matches one of these clusters. + \X always matches at least one character. Then it decides whether to + add additional characters according to the following rules for ending a + cluster: + + 1. End at the end of the subject string. + + 2. Do not end between CR and LF; otherwise end after any control char- + acter. + + 3. Do not break Hangul (a Korean script) syllable sequences. Hangul + characters are of five types: L, V, T, LV, and LVT. An L character may + be followed by an L, V, LV, or LVT character; an LV or V character may + be followed by a V or T character; an LVT or T character may be follwed + only by a T character. + + 4. Do not end before extending characters or spacing marks. Characters + with the "mark" property always have the "extend" grapheme breaking + property. + + 5. Do not end after prepend characters. + + 6. Otherwise, end the cluster. + 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- - 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: + As well as the standard Unicode properties described above, PCRE sup- + ports four more that make it possible to convert traditional escape + sequences such as \w and \s and POSIX character classes to use Unicode + properties. PCRE uses these non-standard, non-Perl properties inter- + nally when PCRE_UCP is set. They are: Xan Any alphanumeric character Xps Any POSIX space character Xsp Any Perl space character Xwd Any Perl "word" character - Xan matches characters that have either the L (letter) or the N (num- - ber) property. Xps matches the characters tab, linefeed, vertical tab, - 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 @@ -3872,76 +5245,81 @@ 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. CIRCUMFLEX AND DOLLAR + The circumflex and dollar metacharacters are zero-width assertions. + That is, they test for a particular condition being true without con- + suming any characters from the subject string. + Outside a character class, in the default matching mode, the circumflex - character is an assertion that is true only if the current matching - point is at the start of the subject string. If the startoffset argu- - ment of pcre_exec() is non-zero, circumflex can never match if the - PCRE_MULTILINE option is unset. Inside a character class, circumflex + character is an assertion that is true only if the current matching + point is at the start of the subject string. If the startoffset argu- + ment of pcre_exec() is non-zero, circumflex can never match if the + PCRE_MULTILINE option is unset. Inside a character class, circumflex has an entirely different meaning (see below). - Circumflex need not be the first character of the pattern if a number - of alternatives are involved, but it should be the first thing in each - alternative in which it appears if the pattern is ever to match that - branch. If all possible alternatives start with a circumflex, that is, - if the pattern is constrained to match only at the start of the sub- - ject, it is said to be an "anchored" pattern. (There are also other + Circumflex need not be the first character of the pattern if a number + of alternatives are involved, but it should be the first thing in each + alternative in which it appears if the pattern is ever to match that + branch. If all possible alternatives start with a circumflex, that is, + if the pattern is constrained to match only at the start of the sub- + ject, it is said to be an "anchored" pattern. (There are also other constructs that can cause a pattern to be anchored.) - A dollar character is an assertion that is true only if the current - matching point is at the end of the subject string, or immediately - before a newline at the end of the string (by default). Dollar need not - be the last character of the pattern if a number of alternatives are - involved, but it should be the last item in any branch in which it - appears. Dollar has no special meaning in a character class. + The dollar character is an assertion that is true only if the current + matching point is at the end of the subject string, or immediately + before a newline at the end of the string (by default). Note, however, + that it does not actually match the newline. Dollar need not be the + last character of the pattern if a number of alternatives are involved, + but it should be the last item in any branch in which it appears. Dol- + lar has no special meaning in a character class. The meaning of dollar can be changed so that it matches only at the very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at @@ -3974,154 +5352,178 @@ 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. + fies the end of a line. - When a line ending is defined as a single character, dot never matches - that character; when the two-character sequence CRLF is used, dot does - not match CR if it is immediately followed by LF, but otherwise it - matches all characters (including isolated CRs and LFs). When any Uni- - code line endings are being recognized, dot does not match CR or LF or + When a line ending is defined as a single character, dot never matches + that character; when the two-character sequence CRLF is used, dot does + not match CR if it is immediately followed by LF, but otherwise it + matches all characters (including isolated CRs and LFs). When any Uni- + code line endings are being recognized, dot does not match CR or LF or any of the other line ending characters. - The behaviour of dot with regard to newlines can be changed. If the - PCRE_DOTALL option is set, a dot matches any one character, without + The behaviour of dot with regard to newlines can be changed. If the + PCRE_DOTALL option is set, a dot matches any one character, without exception. If the two-character sequence CRLF is present in the subject string, it takes two dots to match it. - The handling of dot is entirely independent of the handling of circum- - flex and dollar, the only relationship being that they both involve + The handling of dot is entirely independent of the handling of circum- + flex and dollar, the only relationship being that they both involve newlines. Dot has no special meaning in a character class. - The escape sequence \N behaves like a dot, except that it is not - affected by the PCRE_DOTALL option. In other words, it matches any - character except one that signifies the end of a line. + The escape sequence \N behaves like a dot, except that it is not + affected by the PCRE_DOTALL option. In other words, it matches any + character except one that signifies the end of a line. Perl also uses + \N to match characters by name; PCRE does not support this. -MATCHING A SINGLE 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 + Outside a character class, the escape sequence \C matches any one data + unit, whether or not a UTF mode is set. In the 8-bit library, one data + unit is one byte; in the 16-bit library it is a 16-bit unit; in the + 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches line-ending characters. The feature is provided in Perl in order to - match individual bytes in UTF-8 mode. 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. + match individual bytes in UTF-8 mode, but it is unclear how it can use- + fully be used. Because \C breaks up characters into individual data + units, matching one unit with \C in a UTF mode means that the rest of + the string may start with a malformed UTF character. This has undefined + results, because PCRE assumes that it is dealing with valid UTF strings + (and by default it checks this at the start of processing unless the + PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or PCRE_NO_UTF32_CHECK option + 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 An opening square bracket introduces a character class, terminated by a 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. + In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255 + (0xffff) can be included in a class as a literal string of data units, + 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. + When caseless matching is set, any letters in a class represent both + their upper case and lower case versions, so for example, a caseless + [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not + match "A", whereas a caseful version would. In a UTF mode, PCRE always + understands the concept of case for characters whose values are less + than 128, so caseless matching is always possible. For characters with + higher values, the concept of case is supported if PCRE is compiled + with Unicode property support, but not otherwise. If you want to use + caseless matching in a UTF mode for characters 128 and above, you must + ensure that PCRE is compiled with Unicode property support as well as + with UTF support. - Characters that might indicate line breaks are never treated in any - special way when matching character classes, whatever line-ending - sequence is in use, and whatever setting of the PCRE_DOTALL and + Characters that might indicate line breaks are never treated in any + special way when matching character classes, whatever line-ending + sequence is in use, and whatever setting of the PCRE_DOTALL and PCRE_MULTILINE options is used. A class such as [^a] always matches one of these characters. - The minus (hyphen) character can be used to specify a range of charac- - ters in a character class. For example, [d-m] matches any letter - between d and m, inclusive. If a minus character is required in a - class, it must be escaped with a backslash or appear in a position - where it cannot be interpreted as indicating a range, typically as the + 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 +5546,24 @@ 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 +5576,31 @@ 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 +5610,50 @@ 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),(*UTF32), and + (*UCP) leading sequences that can be used to set UTF and Unicode prop- + erty modes; they are equivalent to setting the PCRE_UTF8, PCRE_UTF16, + PCRE_UTF32 and the PCRE_UCP options, respectively. The (*UTF) sequence + is a generic version that can be used with any of the libraries. SUBPATTERNS @@ -4261,17 +5665,20 @@ SUBPATTERNS cat(aract|erpillar|) - matches "cataract", "caterpillar", or "cat". Without the parentheses, + matches "cataract", "caterpillar", or "cat". Without the parentheses, it would match "cataract", "erpillar" or an empty string. - 2. It sets up the subpattern as a capturing subpattern. This means - that, when the whole pattern matches, that portion of the subject + 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- @@ -4334,9 +5741,9 @@ DUPLICATE SUBPATTERN NUMBERS /(?|(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)/ @@ -4426,13 +5833,13 @@ REPETITION 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 @@ -4458,12 +5865,12 @@ REPETITION 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 grapheme clusters, each of + which may be several data units long (and they may be of different + lengths). The quantifier {0} is permitted, causing the expression to behave as if the previous item and the quantifier were not present. This may be use- @@ -4547,7 +5954,7 @@ REPETITION lines, it is worth setting PCRE_DOTALL in order to obtain this opti- mization, or alternatively using ^ to indicate anchoring explicitly. - However, there is one situation where the optimization cannot be used. + However, there are some cases where the optimization cannot be used. When .* is inside capturing parentheses that are the subject of a back reference elsewhere in the pattern, a match at the start may fail where a later one succeeds. Consider, for example: @@ -4557,14 +5964,23 @@ REPETITION If the subject is "xyz123abc123" the match point is the fourth charac- ter. For this reason, such a pattern is not implicitly anchored. + Another case where implicit anchoring is not applied is when the lead- + ing .* is inside an atomic group. Once again, a match at the start may + fail where a later one succeeds. Consider this pattern: + + (?>.*?a)b + + It matches "ab" in the subject "aab". The use of the backtracking con- + trol verbs (*PRUNE) and (*SKIP) also disable this optimization. + When a capturing subpattern is repeated, the value captured is the sub- string that matched the final iteration. For example, after (tweedle[dume]{3}\s*)+ has matched "tweedledum tweedledee" the value of the captured substring - is "tweedledee". However, if there are nested capturing subpatterns, - the corresponding captured values may have been set in previous itera- + is "tweedledee". However, if there are nested capturing subpatterns, + the corresponding captured values may have been set in previous itera- tions. For example, after /(a|(b))+/ @@ -4574,53 +5990,53 @@ REPETITION ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS - With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") - repetition, failure of what follows normally causes the repeated item - to be re-evaluated to see if a different number of repeats allows the - rest of the pattern to match. Sometimes it is useful to prevent this, - either to change the nature of the match, or to cause it fail earlier - than it otherwise might, when the author of the pattern knows there is + With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy") + repetition, failure of what follows normally causes the repeated item + to be re-evaluated to see if a different number of repeats allows the + rest of the pattern to match. Sometimes it is useful to prevent this, + either to change the nature of the match, or to cause it fail earlier + than it otherwise might, when the author of the pattern knows there is no point in carrying on. - Consider, for example, the pattern \d+foo when applied to the subject + Consider, for example, the pattern \d+foo when applied to the subject line 123456bar After matching all 6 digits and then failing to match "foo", the normal - action of the matcher is to try again with only 5 digits matching the - \d+ item, and then with 4, and so on, before ultimately failing. - "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides - the means for specifying that once a subpattern has matched, it is not + action of the matcher is to try again with only 5 digits matching the + \d+ item, and then with 4, and so on, before ultimately failing. + "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides + the means for specifying that once a subpattern has matched, it is not to be re-evaluated in this way. - If we use atomic grouping for the previous example, the matcher gives - up immediately on failing to match "foo" the first time. The notation + If we use atomic grouping for the previous example, the matcher gives + up immediately on failing to match "foo" the first time. The notation is a kind of special parenthesis, starting with (?> as in this example: (?>\d+)foo - This kind of parenthesis "locks up" the part of the pattern it con- - tains once it has matched, and a failure further into the pattern is - prevented from backtracking into it. Backtracking past it to previous + This kind of parenthesis "locks up" the part of the pattern it con- + tains once it has matched, and a failure further into the pattern is + prevented from backtracking into it. Backtracking past it to previous items, however, works as normal. - An alternative description is that a subpattern of this type matches - the string of characters that an identical standalone pattern would + An alternative description is that a subpattern of this type matches + the string of characters that an identical standalone pattern would match, if anchored at the current point in the subject string. Atomic grouping subpatterns are not capturing subpatterns. Simple cases such as the above example can be thought of as a maximizing repeat that - must swallow everything it can. So, while both \d+ and \d+? are pre- - pared to adjust the number of digits they match in order to make the + must swallow everything it can. So, while both \d+ and \d+? are pre- + pared to adjust the number of digits they match in order to make the rest of the pattern match, (?>\d+) can only match an entire sequence of digits. - Atomic groups in general can of course contain arbitrarily complicated - subpatterns, and can be nested. However, when the subpattern for an + Atomic groups in general can of course contain arbitrarily complicated + subpatterns, and can be nested. However, when the subpattern for an atomic group is just a single repeated item, as in the example above, a - simpler notation, called a "possessive quantifier" can be used. This - consists of an additional + character following a quantifier. Using + simpler notation, called a "possessive quantifier" can be used. This + consists of an additional + character following a quantifier. Using this notation, the previous example can be rewritten as \d++foo @@ -4630,45 +6046,45 @@ ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS (abc|xyz){2,3}+ - Possessive quantifiers are always greedy; the setting of the + Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY option is ignored. They are a convenient notation for the - simpler forms of atomic group. However, there is no difference in the - meaning of a possessive quantifier and the equivalent atomic group, - though there may be a performance difference; possessive quantifiers + simpler forms of atomic group. However, there is no difference in the + meaning of a possessive quantifier and the equivalent atomic group, + though there may be a performance difference; possessive quantifiers should be slightly faster. - The possessive quantifier syntax is an extension to the Perl 5.8 syn- - tax. Jeffrey Friedl originated the idea (and the name) in the first + The possessive quantifier syntax is an extension to the Perl 5.8 syn- + tax. Jeffrey Friedl originated the idea (and the name) in the first edition of his book. Mike McCloskey liked it, so implemented it when he - built Sun's Java package, and PCRE copied it from there. It ultimately + built Sun's Java package, and PCRE copied it from there. It ultimately found its way into Perl at release 5.10. PCRE has an optimization that automatically "possessifies" certain sim- - ple pattern constructs. For example, the sequence A+B is treated as - A++B because there is no point in backtracking into a sequence of A's + ple pattern constructs. For example, the sequence A+B is treated as + A++B because there is no point in backtracking into a sequence of A's when B must follow. - When a pattern contains an unlimited repeat inside a subpattern that - can itself be repeated an unlimited number of times, the use of an - atomic group is the only way to avoid some failing matches taking a + When a pattern contains an unlimited repeat inside a subpattern that + can itself be repeated an unlimited number of times, the use of an + atomic group is the only way to avoid some failing matches taking a very long time indeed. The pattern (\D+|<\d+>)*[!?] - matches an unlimited number of substrings that either consist of non- - digits, or digits enclosed in <>, followed by either ! or ?. When it + matches an unlimited number of substrings that either consist of non- + digits, or digits enclosed in <>, followed by either ! or ?. When it matches, it runs quickly. However, if it is applied to aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa - it takes a long time before reporting failure. This is because the - string can be divided between the internal \D+ repeat and the external - * repeat in a large number of ways, and all have to be tried. (The - example uses [!?] rather than a single character at the end, because - both PCRE and Perl have an optimization that allows for fast failure - when a single character is used. They remember the last single charac- - ter that is required for a match, and fail early if it is not present - in the string.) If the pattern is changed so that it uses an atomic + it takes a long time before reporting failure. This is because the + string can be divided between the internal \D+ repeat and the external + * repeat in a large number of ways, and all have to be tried. (The + example uses [!?] rather than a single character at the end, because + both PCRE and Perl have an optimization that allows for fast failure + when a single character is used. They remember the last single charac- + ter that is required for a match, and fail early if it is not present + in the string.) If the pattern is changed so that it uses an atomic group, like this: ((?>\D+)|<\d+>)*[!?] @@ -4680,28 +6096,28 @@ BACK REFERENCES Outside a character class, a backslash followed by a digit greater than 0 (and possibly further digits) is a back reference to a capturing sub- - pattern earlier (that is, to its left) in the pattern, provided there + pattern earlier (that is, to its left) in the pattern, provided there have been that many previous capturing left parentheses. However, if the decimal number following the backslash is less than 10, - it is always taken as a back reference, and causes an error only if - there are not that many capturing left parentheses in the entire pat- - tern. In other words, the parentheses that are referenced need not be - to the left of the reference for numbers less than 10. A "forward back - reference" of this type can make sense when a repetition is involved - and the subpattern to the right has participated in an earlier itera- + it is always taken as a back reference, and causes an error only if + there are not that many capturing left parentheses in the entire pat- + tern. In other words, the parentheses that are referenced need not be + to the left of the reference for numbers less than 10. A "forward back + reference" of this type can make sense when a repetition is involved + and the subpattern to the right has participated in an earlier itera- tion. - It is not possible to have a numerical "forward back reference" to a - subpattern whose number is 10 or more using this syntax because a - sequence such as \50 is interpreted as a character defined in octal. + It is not possible to have a numerical "forward back reference" to a + subpattern whose number is 10 or more using this syntax because a + sequence such as \50 is interpreted as a character defined in octal. See the subsection entitled "Non-printing characters" above for further - details of the handling of digits following a backslash. There is no - such problem when named parentheses are used. A back reference to any + details of the handling of digits following a backslash. There is no + such problem when named parentheses are used. A back reference to any subpattern is possible using named parentheses (see below). - Another way of avoiding the ambiguity inherent in the use of digits - following a backslash is to use the \g escape sequence. This escape + Another way of avoiding the ambiguity inherent in the use of digits + following a backslash is to use the \g escape sequence. This escape must be followed by an unsigned number or a negative number, optionally enclosed in braces. These examples are all identical: @@ -4709,7 +6125,7 @@ BACK REFERENCES (ring), \g1 (ring), \g{1} - An unsigned number specifies an absolute reference without the ambigu- + An unsigned number specifies an absolute reference without the ambigu- ity that is present in the older syntax. It is also useful when literal digits follow the reference. A negative number is a relative reference. Consider this example: @@ -4718,33 +6134,33 @@ BACK REFERENCES The sequence \g{-1} is a reference to the most recently started captur- ing subpattern before \g, that is, is it equivalent to \2 in this exam- - ple. Similarly, \g{-2} would be equivalent to \1. The use of relative - references can be helpful in long patterns, and also in patterns that - are created by joining together fragments that contain references + ple. Similarly, \g{-2} would be equivalent to \1. The use of relative + references can be helpful in long patterns, and also in patterns that + are created by joining together fragments that contain references within themselves. - A back reference matches whatever actually matched the capturing sub- - pattern in the current subject string, rather than anything matching + A back reference matches whatever actually matched the capturing sub- + pattern in the current subject string, rather than anything matching the subpattern itself (see "Subpatterns as subroutines" below for a way of doing that). So the pattern (sens|respons)e and \1ibility - matches "sense and sensibility" and "response and responsibility", but - not "sense and responsibility". If caseful matching is in force at the - time of the back reference, the case of letters is relevant. For exam- + matches "sense and sensibility" and "response and responsibility", but + not "sense and responsibility". If caseful matching is in force at the + time of the back reference, the case of letters is relevant. For exam- ple, ((?i)rah)\s+\1 - matches "rah rah" and "RAH RAH", but not "RAH rah", even though the + matches "rah rah" and "RAH RAH", but not "RAH rah", even though the original capturing subpattern is matched caselessly. - There are several different ways of writing back references to named - subpatterns. The .NET syntax \k{name} and the Perl syntax \k or - \k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's + There are several different ways of writing back references to named + subpatterns. The .NET syntax \k{name} and the Perl syntax \k or + \k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's unified back reference syntax, in which \g can be used for both numeric - and named references, is also supported. We could rewrite the above + and named references, is also supported. We could rewrite the above example in any of the following ways: (?(?i)rah)\s+\k @@ -4752,69 +6168,85 @@ BACK REFERENCES (?P(?i)rah)\s+(?P=p1) (?(?i)rah)\s+\g{p1} - A subpattern that is referenced by name may appear in the pattern + A subpattern that is referenced by name may appear in the pattern before or after the reference. - There may be more than one back reference to the same subpattern. If a - subpattern has not actually been used in a particular match, any back + There may be more than one back reference to the same subpattern. If a + subpattern has not actually been used in a particular match, any back references to it always fail by default. For example, the pattern (a|(bc))\2 - always fails if it starts to match "a" rather than "bc". However, if + always fails if it starts to match "a" rather than "bc". However, if the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer- ence to an unset value matches an empty string. - Because there may be many capturing parentheses in a pattern, all dig- - its following a backslash are taken as part of a potential back refer- - ence number. If the pattern continues with a digit character, some - delimiter must be used to terminate the back reference. If the - PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{ - syntax or an empty comment (see "Comments" below) can be used. + Because there may be many capturing parentheses in a pattern, all dig- + its following a backslash are taken as part of a potential back refer- + ence number. If the pattern continues with a digit character, some + delimiter must be used to terminate the back reference. If the + PCRE_EXTENDED option is set, this can be white space. Otherwise, the + \g{ syntax or an empty comment (see "Comments" below) can be used. Recursive back references - A back reference that occurs inside the parentheses to which it refers - fails when the subpattern is first used, so, for example, (a\1) never - matches. However, such references can be useful inside repeated sub- + A back reference that occurs inside the parentheses to which it refers + fails when the subpattern is first used, so, for example, (a\1) never + matches. However, such references can be useful inside repeated sub- patterns. For example, the pattern (a|b\1)+ matches any number of "a"s and also "aba", "ababbaa" etc. At each iter- - ation of the subpattern, the back reference matches the character - string corresponding to the previous iteration. In order for this to - work, the pattern must be such that the first iteration does not need - to match the back reference. This can be done using alternation, as in + ation of the subpattern, the back reference matches the character + string corresponding to the previous iteration. In order for this to + work, the pattern must be such that the first iteration does not need + to match the back reference. This can be done using alternation, as in the example above, or by a quantifier with a minimum of zero. - Back references of this type cause the group that they reference to be - treated as an atomic group. Once the whole group has been matched, a - subsequent matching failure cannot cause backtracking into the middle + Back references of this type cause the group that they reference to be + treated as an atomic group. Once the whole group has been matched, a + subsequent matching failure cannot cause backtracking into the middle of the group. ASSERTIONS - An assertion is a test on the characters following or preceding the - current matching point that does not actually consume any characters. - The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are + An assertion is a test on the characters following or preceding the + current matching point that does not actually consume any characters. + The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described above. - More complicated assertions are coded as subpatterns. There are two - kinds: those that look ahead of the current position in the subject - string, and those that look behind it. An assertion subpattern is - matched in the normal way, except that it does not cause the current + More complicated assertions are coded as subpatterns. There are two + kinds: those that look ahead of the current position in the subject + string, and those that look behind it. An assertion subpattern is + matched in the normal way, except that it does not cause the current matching position to be changed. - Assertion subpatterns are not capturing subpatterns, 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 Lookahead assertions start with (?= for positive assertions and (?! for @@ -4822,38 +6254,38 @@ ASSERTIONS \w+(?=;) - matches a word followed by a semicolon, but does not include the semi- + matches a word followed by a semicolon, but does not include the semi- colon in the match, and foo(?!bar) - matches any occurrence of "foo" that is not followed by "bar". Note + matches any occurrence of "foo" that is not followed by "bar". Note that the apparently similar pattern (?!foo)bar - does not find an occurrence of "bar" that is preceded by something - other than "foo"; it finds any occurrence of "bar" whatsoever, because + does not find an occurrence of "bar" that is preceded by something + other than "foo"; it finds any occurrence of "bar" whatsoever, because the assertion (?!foo) is always true when the next three characters are "bar". A lookbehind assertion is needed to achieve the other effect. If you want to force a matching failure at some point in a pattern, the - most convenient way to do it is with (?!) because an empty string - always matches, so an assertion that requires there not to be an empty + most convenient way to do it is with (?!) because an empty string + always matches, so an assertion that requires there not to be an empty string must always fail. The backtracking control verb (*FAIL) or (*F) is a synonym for (?!). Lookbehind assertions - Lookbehind assertions start with (?<= for positive assertions and (? 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) ) \b (?&byte) (\.(?&byte)){3} \b - The first part of the pattern is a DEFINE group inside which a another - group named "byte" is defined. This matches an individual component of - an IPv4 address (a number less than 256). When matching takes place, - this part of the pattern is skipped because DEFINE acts like a false - condition. The rest of the pattern uses references to the named group - to match the four dot-separated components of an IPv4 address, insist- + The first part of the pattern is a DEFINE group inside which a another + group named "byte" is defined. This matches an individual component of + an IPv4 address (a number less than 256). When matching takes place, + this part of the pattern is skipped because DEFINE acts like a false + condition. The rest of the pattern uses references to the named group + to match the four dot-separated components of an IPv4 address, insist- ing on a word boundary at each end. Assertion conditions - If the condition is not in any of the above formats, it must be an - assertion. This may be a positive or negative lookahead or lookbehind - assertion. Consider this pattern, again containing non-significant + If the condition is not in any of the above formats, it must be an + assertion. This may be a positive or negative lookahead or lookbehind + assertion. Consider this pattern, again containing non-significant white space, and with the two alternatives on the second line: (?(?=[^a-z]*[a-z]) \d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} ) - The condition is a positive lookahead assertion that matches an - optional sequence of non-letters followed by a letter. In other words, - it tests for the presence of at least one letter in the subject. If a - letter is found, the subject is matched against the first alternative; - otherwise it is matched against the second. This pattern matches - strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are + The condition is a positive lookahead assertion that matches an + optional sequence of non-letters followed by a letter. In other words, + it tests for the presence of at least one letter in the subject. If a + letter is found, the subject is matched against the first alternative; + otherwise it is matched against the second. This pattern matches + strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits. @@ -5103,41 +6535,41 @@ COMMENTS There are two ways of including comments in patterns that are processed by PCRE. In both cases, the start of the comment must not be in a char- acter class, nor in the middle of any other sequence of related charac- - ters such as (?: or a subpattern name or number. The characters that + ters such as (?: or a subpattern name or number. The characters that make up a comment play no part in the pattern matching. - The sequence (?# marks the start of a comment that continues up to the - next closing parenthesis. Nested parentheses are not permitted. If the + The sequence (?# marks the start of a comment that continues up to the + next closing parenthesis. Nested parentheses are not permitted. If the PCRE_EXTENDED option is set, an unescaped # character also introduces a - comment, which in this case continues to immediately after the next - newline character or character sequence in the pattern. Which charac- + comment, which in this case continues to immediately after the next + newline character or character sequence in the pattern. Which charac- ters are interpreted as newlines is controlled by the options passed to - 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 - On encountering the # character, pcre_compile() skips along, looking - for a newline in the pattern. The sequence \n is still literal at this - stage, so it does not terminate the comment. Only an actual character + On encountering the # character, pcre_compile() skips along, looking + for a newline in the pattern. The sequence \n is still literal at this + stage, so it does not terminate the comment. Only an actual character with the code value 0x0a (the default newline) does so. RECURSIVE PATTERNS - Consider the problem of matching a string in parentheses, allowing for - unlimited nested parentheses. Without the use of recursion, the best - that can be done is to use a pattern that matches up to some fixed - depth of nesting. It is not possible to handle an arbitrary nesting + Consider the problem of matching a string in parentheses, allowing for + unlimited nested parentheses. Without the use of recursion, the best + that can be done is to use a pattern that matches up to some fixed + depth of nesting. It is not possible to handle an arbitrary nesting depth. For some time, Perl has provided a facility that allows regular expres- - sions to recurse (amongst other things). It does this by interpolating - Perl code in the expression at run time, and the code can refer to the + sions to recurse (amongst other things). It does this by interpolating + Perl code in the expression at run time, and the code can refer to the expression itself. A Perl pattern using code interpolation to solve the parentheses problem can be created like this: @@ -5147,84 +6579,85 @@ RECURSIVE PATTERNS refers recursively to the pattern in which it appears. Obviously, PCRE cannot support the interpolation of Perl code. Instead, - it supports special syntax for recursion of the entire pattern, and - also for individual subpattern recursion. After its introduction in - PCRE and Python, this kind of recursion was subsequently introduced + it supports special syntax for recursion of the entire pattern, and + also for individual subpattern recursion. After its introduction in + PCRE and Python, this kind of recursion was subsequently introduced into Perl at release 5.10. - A special item that consists of (? followed by a number greater than - zero and a closing parenthesis is a recursive 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. + A special item that consists of (? followed by a number greater than + zero and a closing parenthesis is a recursive subroutine call of the + subpattern of the given number, provided that it occurs inside that + subpattern. (If not, it is a non-recursive subroutine call, which is + described in the next section.) The special item (?R) or (?0) is a + recursive call of the entire regular expression. - This PCRE pattern solves the nested parentheses problem (assume the + This PCRE pattern solves the nested parentheses problem (assume the PCRE_EXTENDED option is set so that white space is ignored): \( ( [^()]++ | (?R) )* \) - First it matches an opening parenthesis. Then it matches any number of - substrings which can either be a sequence of non-parentheses, or a - recursive match of the pattern itself (that is, a correctly parenthe- + First it matches an opening parenthesis. Then it matches any number of + substrings which can either be a sequence of non-parentheses, or a + recursive match of the pattern itself (that is, a correctly parenthe- sized substring). Finally there is a closing parenthesis. Note the use of a possessive quantifier to avoid backtracking into sequences of non- parentheses. - If this were part of a larger pattern, you would not want to recurse + If this were part of a larger pattern, you would not want to recurse the entire pattern, so instead you could use this: ( \( ( [^()]++ | (?1) )* \) ) - We have put the pattern into parentheses, and caused the recursion to + We have put the pattern into parentheses, and caused the recursion to refer to them instead of the whole pattern. - In a larger pattern, keeping track of parenthesis numbers can be - tricky. This is made easier by the use of relative references. Instead + In a larger pattern, keeping track of parenthesis numbers can be + tricky. This is made easier by the use of relative references. Instead of (?1) in the pattern above you can write (?-2) to refer to the second - most recently opened parentheses preceding the recursion. In other - words, a negative number counts capturing parentheses leftwards from + most recently opened parentheses preceding the recursion. In other + words, a negative number counts capturing parentheses leftwards from the point at which it is encountered. - It is also possible to refer to subsequently opened parentheses, by - writing references such as (?+2). However, these cannot be recursive - because the reference is not inside the parentheses that are refer- - enced. They are always "subroutine" calls, as described in the next - section. + It is also possible to refer to subsequently opened parentheses, by + writing references such as (?+2). However, these cannot be recursive + because the reference is not inside the parentheses that are refer- + enced. They are always non-recursive subroutine calls, as described in + the next section. - An alternative approach is to use named parentheses instead. The Perl - syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also + An alternative approach is to use named parentheses instead. The Perl + syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also supported. We could rewrite the above example as follows: (? \( ( [^()]++ | (?&pn) )* \) ) - If there is more than one subpattern with the same name, the earliest + If there is more than one subpattern with the same name, the earliest one is used. - This particular example pattern that we have been looking at contains + This particular example pattern that we have been looking at contains nested unlimited repeats, and so the use of a possessive quantifier for matching strings of non-parentheses is important when applying the pat- - tern to strings that do not match. For example, when this pattern is + tern to strings that do not match. For example, when this pattern is applied to (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa() - it yields "no match" quickly. However, if a possessive quantifier is - not used, the match runs for a very long time indeed because there are - so many different ways the + and * repeats can carve up the subject, + it yields "no match" quickly. However, if a possessive quantifier is + not used, the match runs for a very long time indeed because there are + so many different ways the + and * repeats can carve up the subject, and all have to be tested before failure can be reported. - At the end of a match, the values of capturing parentheses are those - from the outermost level. If you want to obtain intermediate values, a - callout function can be used (see below and the pcrecallout documenta- + At the end of a match, the values of capturing parentheses are those + from the outermost level. If you want to obtain intermediate values, a + callout function can be used (see below and the pcrecallout documenta- tion). If the pattern above is matched against (ab(cd)ef) - the value for the inner capturing parentheses (numbered 2) is "ef", - which is the last value taken on at the top level. If a capturing sub- - pattern is not matched at the top level, its final value is unset, even - if it is (temporarily) set at a deeper level. + the value for the inner capturing parentheses (numbered 2) is "ef", + which is the last value taken on at the top level. If a capturing sub- + pattern is not matched at the top level, its final captured value is + unset, even if it was (temporarily) set at a deeper level during the + matching process. If there are more than 15 capturing parentheses in a pattern, PCRE has to obtain extra memory to store data during a recursion, which it does @@ -5243,88 +6676,105 @@ RECURSIVE PATTERNS 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 - In PCRE (like Python, but unlike Perl), a recursive subpattern call is + Recursion processing in PCRE differs from Perl in two important ways. + In PCRE (like Python, but unlike Perl), a recursive subpattern call is always treated as an atomic group. That is, once it has matched some of the subject string, it is never re-entered, even if it contains untried - alternatives and there is a subsequent matching failure. This can be - illustrated by the following pattern, which purports to match a palin- - dromic string that contains an odd number of characters (for example, + alternatives and there is a subsequent matching failure. This can be + illustrated by the following pattern, which purports to match a palin- + dromic string that contains an odd number of characters (for example, "a", "aba", "abcba", "abcdcba"): ^(.|(.)(?1)\2)$ The idea is that it either matches a single character, or two identical - characters surrounding a sub-palindrome. In Perl, this pattern works; - in PCRE it does not if the pattern is longer than three characters. + characters surrounding a sub-palindrome. In Perl, this pattern works; + in PCRE it does not if the pattern is longer than three characters. Consider the subject string "abcba": - At the top level, the first character is matched, but as it is not at + At the top level, the first character is matched, but as it is not at the end of the string, the first alternative fails; the second alterna- tive is taken and the recursion kicks in. The recursive call to subpat- - tern 1 successfully matches the next character ("b"). (Note that the + tern 1 successfully matches the next character ("b"). (Note that the beginning and end of line tests are not part of the recursion). - Back at the top level, the next character ("c") is compared with what - subpattern 2 matched, which was "a". This fails. Because the recursion - is treated as an atomic group, there are now no backtracking points, - and so the entire match fails. (Perl is able, at this point, to re- - enter the recursion and try the second alternative.) However, if the + Back at the top level, the next character ("c") is compared with what + subpattern 2 matched, which was "a". This fails. Because the recursion + is treated as an atomic group, there are now no backtracking points, + and so the entire match fails. (Perl is able, at this point, to re- + enter the recursion and try the second alternative.) However, if the pattern is written with the alternatives in the other order, things are different: ^((.)(?1)\2|.)$ - This time, the recursing alternative is tried first, and continues to - recurse until it runs out of characters, at which point the recursion - fails. But this time we do have another alternative to try at the - higher level. That is the big difference: in the previous case the + This time, the recursing alternative is tried first, and continues to + recurse until it runs out of characters, at which point the recursion + fails. But this time we do have another alternative to try at the + higher level. That is the big difference: in the previous case the remaining alternative is at a deeper recursion level, which PCRE cannot use. - To change the pattern so that it matches all palindromic strings, not - just those with an odd number of characters, it is tempting to change + To change the pattern so that it matches all palindromic strings, not + just those with an odd number of characters, it is tempting to change the pattern to this: ^((.)(?1)\2|.?)$ - Again, this works in Perl, but not in PCRE, and for the same reason. - When a deeper recursion has matched a single character, it cannot be - entered again in order to match an empty string. The solution is to - separate the two cases, and write out the odd and even cases as alter- + Again, this works in Perl, but not in PCRE, and for the same reason. + When a deeper recursion has matched a single character, it cannot be + entered again in order to match an empty string. The solution is to + separate the two cases, and write out the odd and even cases as alter- natives at the higher level: ^(?:((.)(?1)\2|)|((.)(?3)\4|.)) - If you want to match typical palindromic phrases, the pattern has to + If you want to match typical palindromic phrases, the pattern has to ignore all non-word characters, which can be done like this: ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$ If run with the PCRE_CASELESS option, this pattern matches phrases such as "A man, a plan, a canal: Panama!" and it works well in both PCRE and - Perl. Note the use of the possessive quantifier *+ to avoid backtrack- - ing into sequences of non-word characters. Without this, PCRE takes a - great deal longer (ten times or more) to match typical phrases, and + Perl. Note the use of the possessive quantifier *+ to avoid backtrack- + ing into sequences of non-word characters. Without this, PCRE takes a + great deal longer (ten times or more) to match typical phrases, and Perl takes so long that you think it has gone into a loop. - WARNING: The palindrome-matching patterns above work only if the sub- - ject string does not start with a palindrome that is shorter than the - entire string. For example, although "abcba" is correctly matched, if - the subject is "ababa", PCRE finds the palindrome "aba" at the start, - then fails at top level because the end of the string does not follow. - Once again, it cannot jump back into the recursion to try other alter- + WARNING: The palindrome-matching patterns above work only if the sub- + ject string does not start with a palindrome that is shorter than the + entire string. For example, although "abcba" is correctly matched, if + the subject is "ababa", PCRE finds the palindrome "aba" at the start, + then fails at top level because the end of the string does not follow. + Once again, it cannot jump back into the recursion to try other alter- natives, so the entire match fails. + The second way in which PCRE and Perl differ in their recursion pro- + cessing is in the handling of captured values. In Perl, when a subpat- + tern is called recursively or as a subpattern (see the next section), + it has no access to any values that were captured outside the recur- + sion, whereas in PCRE these values can be referenced. Consider this + 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)... @@ -5334,66 +6784,67 @@ SUBPATTERNS AS SUBROUTINES (sens|respons)e and \1ibility - matches "sense and sensibility" and "response and responsibility", but + matches "sense and sensibility" and "response and responsibility", but not "sense and responsibility". If instead the pattern (sens|respons)e and (?1)ibility - is used, it does match "sense and responsibility" as well as the other - two strings. Another example is given in the discussion of DEFINE + is used, it does match "sense and responsibility" as well as the other + two strings. Another example is given in the discussion of DEFINE above. - 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)) - It matches "abcabc". It does not match "abcABC" because the change of + It matches "abcabc". It does not match "abcABC" because the change of processing option does not affect the called subpattern. ONIGURUMA SUBROUTINE SYNTAX - For compatibility with Oniguruma, the non-Perl syntax \g followed by a + For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or a number enclosed either in angle brackets or single quotes, is - an alternative syntax for referencing a subpattern as a subroutine, - possibly recursively. Here are two of the examples used above, rewrit- + an alternative syntax for referencing a subpattern as a subroutine, + possibly recursively. Here are two of the examples used above, rewrit- ten using this syntax: (? \( ( (?>[^()]+) | \g )* \) ) (sens|respons)e and \g'1'ibility - PCRE supports an extension to Oniguruma: if a number is preceded by a + PCRE supports an extension to Oniguruma: if a number is preceded by a plus or a minus sign it is taken as a relative reference. For example: (abc)(?i:\g<-1>) - Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not - synonymous. The former is a back reference; the latter is a subroutine + Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not + synonymous. The former is a back reference; the latter is a subroutine call. CALLOUTS Perl has a feature whereby using the sequence (?{...}) causes arbitrary - Perl code to be obeyed in the middle of matching a regular expression. + Perl code to be obeyed in the middle of matching a regular expression. This makes it possible, amongst other things, to extract different sub- strings that match the same pair of parentheses when there is a repeti- tion. PCRE provides a similar feature, but of course it cannot obey arbitrary Perl code. The feature is called "callout". The caller of PCRE provides - an external function by putting its entry point in the global variable - pcre_callout. By default, this variable contains NULL, which disables - all calling out. + an external function by putting its entry point in the global variable + pcre_callout (8-bit library) or pcre[16|32]_callout (16-bit or 32-bit + library). By default, this variable contains NULL, which disables all + calling out. Within a regular expression, (?C) indicates the points at which the external function is to be called. If you want to identify different @@ -5403,17 +6854,17 @@ 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 @@ -5426,26 +6877,34 @@ 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(). + 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 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. + If any of these verbs are used in an assertion or in a subpattern that + is called as a subroutine (whether or not recursively), their effect is + confined to that subpattern; it does not extend to the surrounding pat- + tern, with one exception: the name from a *(MARK), (*PRUNE), or (*THEN) + that is encountered in a successful positive assertion is passed back + when a match succeeds (compare capturing parentheses in assertions). + Note that such subpatterns are processed as anchored at the point where + they are tested. Note also that Perl's treatment of subroutines and + assertions is different in some cases. - The new verbs make use of what was previously invalid syntax: an open- + The new verbs make use of what was previously invalid syntax: an open- ing parenthesis followed by an asterisk. They are generally of the form - (*VERB) or (*VERB:NAME). Some may take either form, with differing be- - haviour, depending on whether or not an argument is present. 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 and 32-bit library. If the name is empty, that is, if the clos- + ing parenthesis immediately follows the colon, the effect is as if the + colon were not there. Any number of these verbs may occur in a pattern. + 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 may know the minimum length of matching subject, or that a particular @@ -5454,60 +6913,64 @@ 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 +6982,86 @@ 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: + 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. - /X(*MARK:A)Y|X(*MARK:B)Z/K - XP - No match + 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: - 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: - - /^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 +7088,85 @@ 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). + (*MARK:NAME)(*THEN). If (*THEN) is not 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, + 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), pcre32(3). AUTHOR @@ -5691,8 +7178,8 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 11 November 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -5707,7 +7194,7 @@ 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 +7208,7 @@ 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 +7221,25 @@ 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 + \X a Unicode extended grapheme cluster 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 +7301,22 @@ 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 +7337,7 @@ 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 +7428,10 @@ 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) + (*UTF32) set UTF-32 mode: 32-bit library (PCRE_UTF32) + (*UTF) set appropriate UTF mode for the library in use (*UCP) set PCRE_UCP (use Unicode properties for \d etc) @@ -6008,6 +7500,7 @@ 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 +7509,18 @@ 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), (*UTF32) or (*UCP) option. (*CR) carriage return only (*LF) linefeed only @@ -6035,7 +7532,7 @@ 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 @@ -6061,11 +7558,656 @@ AUTHOR REVISION - Last updated: 21 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 11 November 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ +PCREUNICODE(3) PCREUNICODE(3) + + +NAME + PCRE - Perl-compatible regular expressions + + +UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT + + As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) + and UTF-32 (from release 8.32), by means of two additional libraries. + They 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) or (*UTF). 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 individual 1-byte characters. + + +UTF-16 AND UTF-32 SUPPORT + + In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit + or 32-bit library with UTF support, and, in addition, you must call + pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32 + option flag, as appropriate. Alternatively, the pattern must start with + the sequence (*UTF16), (*UTF32), as appropriate, or (*UTF), which can + be used with either library. When UTF mode is set, both the pattern and + any subject strings that are matched against it are treated as UTF-16 + or UTF-32 strings instead of strings of individual 16-bit or 32-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_UTF[8|16|32] 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&. Full lists is given in the pcrepattern + and pcresyntax documentation. Only the short names for properties are + supported. For example, \p{L} matches a letter. Its Perl synonym, + \p{Letter}, is not supported. Furthermore, in Perl, many properties + may optionally be prefixed by "Is", for compatibility with Perl 5.6. + PCRE does not support this. + + Validity of UTF-8 strings + + When you set the PCRE_UTF8 flag, the byte strings passed as patterns + and subjects are (by default) checked for validity on entry to the 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 the surrogate area and the non-characters. + + Characters in the "Surrogate Area" of Unicode are reserved for use by + UTF-16, where they are used in pairs to encode codepoints with values + greater than 0xFFFF. The code points that are encoded by UTF-16 pairs + are available independently in the UTF-8 and UTF-32 encodings. (In + other words, the whole surrogate thing is a fudge for UTF-16 which + unfortunately messes up UTF-8 and UTF-32.) + + Also excluded are the "Non-Character" code points, which are U+FDD0 to + U+FDEF and the last two code points in each plane, U+??FFFE and + U+??FFFF. + + If an invalid UTF-8 string is passed to PCRE, an error return is given. + At compile time, the only additional information is the offset to the + first byte of the failing character. The run-time functions pcre_exec() + 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. 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. + + Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() just disables + the check for the pattern; it does not also apply to subject strings. + If you want to disable the check for a subject string you must pass + this option to pcre_exec() or pcre_dfa_exec(). + + If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the + result is undefined and your program may crash. + + 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. + + Excluded are the "Non-Character" code points, which are U+FDD0 to + U+FDEF and the last two code points in each plane, U+??FFFE and + U+??FFFF. + + If an invalid UTF-16 string is passed to PCRE, an error return is + given. At compile time, the only additional information is the offset + to the first data unit of the failing character. The run-time functions + 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. However, if an invalid string is + passed, the result is undefined. + + Validity of UTF-32 strings + + When you set the PCRE_UTF32 flag, the strings of 32-bit data units that + are passed as patterns and subjects are (by default) checked for valid- + ity on entry to the relevant functions. This check allows only values + in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to + U+DFFF, and the "Non-Character" code points, which are U+FDD0 to U+FDEF + and the last two characters in each plane, U+??FFFE and U+??FFFF. + + If an invalid UTF-32 string is passed to PCRE, an error return is + given. At compile time, the only additional information is the offset + to the first data unit of the failing character. The run-time functions + pcre32_exec() and pcre32_dfa_exec() also pass back this information, as + well as a more detailed reason code if the caller has provided memory + in which to do this. + + In some situations, you may already know that your strings are valid, + and therefore want to skip these checks in order to improve perfor- + mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at + run time, PCRE assumes that the pattern or subject it is given (respec- + tively) contains only valid UTF-32 sequences. In this case, it does not + diagnose an invalid UTF-32 string. However, if an invalid string is + passed, the result is undefined. + + General comments about UTF modes + + 1. Codepoints less than 256 can be specified in patterns by either + braced or unbraced hexadecimal escape sequences (for example, \x{b3} or + \xb3). Larger values have to use braced sequences. + + 2. Octal numbers up to \777 are recognized, and in UTF-8 mode they + 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, or a single 32-bit + data unit in UTF-32 mode, but its use can lead to some strange effects + because it breaks up multi-unit characters (see the description of \C + in the pcrepattern documentation). The use of \C is not supported in + the alternative matching function pcre[16|32]_dfa_exec(), nor is it + supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If + JIT optimization is requested for a UTF pattern that contains \C, it + 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. + A few Unicode characters such as Greek sigma have more than two code- + points that are case-equivalent. Up to and including PCRE release 8.31, + only one-to-one case mappings were supported, but later releases (with + Unicode property support) do treat as case-equivalent all versions of + characters such as Greek sigma. + + +AUTHOR + + Philip Hazel + University Computing Service + Cambridge CB2 3QH, England. + + +REVISION + + Last updated: 11 November 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, 16-BIT AND 32-BIT SUPPORT + + JIT support is available for all of the 8-bit, 16-bit and 32-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, sub- + stitute the 16-bit functions and 16-bit structures (for example, + pcre16_jit_stack instead of pcre_jit_stack). If you are using the + 32-bit library, substitute the 32-bit functions and 32-bit structures + (for example, pcre32_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 + SPARC 32-bit (experimental) + + 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 normal API is implemented in a way that falls back to the interpre- + tive code if JIT is not available. For programs that need the best pos- + sible performance, there is also a "fast path" API that is JIT-spe- + cific. + + 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_NO_UTF32_CHECK, PCRE_NOT- + BOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PAR- + TIAL_HARD, and PCRE_PARTIAL_SOFT. + + The unsupported pattern items are: + + \C match a single byte; not supported in UTF-8 mode + (?Cn) callouts + (*PRUNE) ) + (*SKIP) ) backtracking control verbs + (*THEN) ) + + Support for some of these may be added in future. + + +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 achieve + 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); + + +JIT FAST PATH API + + Because the API described above falls back to interpreted execution + when JIT is not available, it is convenient for programs that are writ- + ten for general use in many environments. However, calling JIT via + pcre_exec() does have a performance impact. Programs that are written + for use where JIT is known to be available, and which need the best + possible performance, can instead use a "fast path" API to call JIT + execution directly instead of calling pcre_exec() (obviously only for + patterns that have been successfully studied by JIT). + + The fast path function is called pcre_jit_exec(), and it takes exactly + the same arguments as pcre_exec(), plus one additional argument that + must point to a JIT stack. The JIT stack arrangements described above + do not apply. The return values are the same as for pcre_exec(). + + When you call pcre_exec(), as well as testing for invalid options, a + number of other sanity checks are performed on the arguments. For exam- + ple, if the subject pointer is NULL, or its length is negative, an + immediate error is given. Also, unless PCRE_NO_UTF[8|16|32] is set, a + UTF subject string is tested for validity. In the interests of speed, + these checks do not happen on the JIT fast path, and if invalid data is + passed, the result is undefined. + + Bypassing the sanity checks and the pcre_exec() wrapping can give + speedups of more than 10%. + + +SEE ALSO + + pcreapi(3) + + +AUTHOR + + Philip Hazel (FAQ by Zoltan Herczeg) + University Computing Service + Cambridge CB2 3QH, England. + + +REVISION + + Last updated: 31 October 2012 + Copyright (c) 1997-2012 University of Cambridge. +------------------------------------------------------------------------------ + + PCREPARTIAL(3) PCREPARTIAL(3) @@ -6075,11 +8217,11 @@ 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 @@ -6097,186 +8239,197 @@ 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. + 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. - 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. + If you want to use partial matching with just-in-time optimized code, + you must call pcre_study(), pcre16_study() or pcre32_study() with one + or both of these options: + PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE + PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE -PARTIAL MATCHING USING pcre_exec() + 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. - 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. + 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. - 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. - For the majority of patterns, the first offset identifies the start of - the partially matched string. However, for patterns that contain look- - behind assertions, or \K, or begin with \b or \B, earlier characters +PARTIAL MATCHING USING pcre_exec() OR pcre[16|32]_exec() + + A partial match occurs during a call to pcre_exec() or + pcre[16|32]_exec() when the end of the subject string is reached suc- + cessfully, but matching cannot continue because more characters are + needed. However, at least one character in the subject must have been + inspected. This character need not form part of the final matched + string; lookbehind assertions and the \K escape sequence provide ways + of inspecting characters before the start of a matched substring. The + requirement for inspecting at least one character exists because an + empty string can always be matched; without such a restriction there + would always be a partial match of an empty string at the end of the + subject. + + If there are at least two slots in the offsets vector when a partial + match is returned, the first slot is set to the offset of the earliest + character that was inspected. For convenience, the second offset points + to the end of the subject so that a substring can easily be identified. + + For the majority of patterns, the first offset identifies the start of + the partially matched string. However, for patterns that contain look- + behind assertions, or \K, or begin with \b or \B, earlier characters have been inspected while carrying out the match. For example: /(?<=abc)123/ This pattern matches "123", but only if it is preceded by "abc". If the subject string is "xyzabc12", the offsets after a partial match are for - the substring "abc12", because all these characters are needed if + the substring "abc12", because all these characters are needed if another match is tried with extra characters added to the subject. What happens when a partial match is identified depends on which of the two partial matching options are set. - PCRE_PARTIAL_SOFT with pcre_exec() + PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre[16|32]_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 pcre[16|32]_exec() + identifies a partial match, the partial match is remembered, but match- + ing 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 - the subject string is potentially complete. For example, \z, \Z, and $ - match at the end of the subject, as normal, and for \b and \B the end + 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 + the subject string is potentially complete. For example, \z, \Z, and $ + match at the end of the subject, as normal, and for \b and \B the end of the subject is treated as a non-alphanumeric. - If there is more than one partial match, the first one that was found + If there is more than one partial match, the first one that was found provides the data that is returned. Consider this pattern: /123\w+X|dogY/ - If this is matched against the subject string "abc123dog", both alter- - natives fail to match, but the end of the subject is reached during - matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 - and 9, identifying "123dog" as the first partial match that was found. - (In this example, there are two partial matches, because "dog" on its + If this is matched against the subject string "abc123dog", both alter- + natives fail to match, but the end of the subject is reached during + matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 + and 9, identifying "123dog" as the first partial match that was found. + (In this example, there are two partial matches, because "dog" on its own partially matches the second alternative.) - PCRE_PARTIAL_HARD with pcre_exec() + PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre[16|32]_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. + If PCRE_PARTIAL_HARD is set for pcre_exec() or pcre[16|32]_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 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. + Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16 subject + strings are checked for validity. Normally, an invalid sequence causes + the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the + special case of a truncated character at the end of the subject, + PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when + PCRE_PARTIAL_HARD is set. Comparing hard and soft partial matching - The difference between the two partial matching options can be illus- + The difference between the two partial matching options can be illus- trated by a pattern such as: /dog(sbody)?/ - This matches either "dog" or "dogsbody", greedily (that is, it prefers - the longer string if possible). If it is matched against the string - "dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog". + This matches either "dog" or "dogsbody", greedily (that is, it prefers + the longer string if possible). If it is matched against the string + "dog" with PCRE_PARTIAL_SOFT, it yields a complete match for "dog". However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL. - On the other hand, if the pattern is made ungreedy the result is dif- + On the other hand, if the pattern is made ungreedy the result is dif- ferent: /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 pcre[16|32]_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 - are returned. However, if PCRE_PARTIAL_HARD is set, a partial match - takes precedence over any complete matches. The portion of the string - that was inspected when the longest partial match was found is set as + When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if + there have been no complete matches. Otherwise, the complete matches + are returned. However, if PCRE_PARTIAL_HARD is set, a partial match + takes precedence over any complete matches. The portion of the string + that was inspected when the longest partial match was found is set as the first matching string, provided there are at least two slots in the offsets vector. - Because 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 - If a pattern ends with one of sequences \b or \B, which test for word - boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter- + If a pattern ends with one of sequences \b or \B, which test for word + boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter- intuitive results. Consider this pattern: /\bcat\b/ This matches "cat", provided there is a word boundary at either end. If the subject string is "the cat", the comparison of the final "t" with a - following character cannot take place, so a partial match is found. - However, 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. + following character cannot take place, so a partial match is found. + However, normal matching carries on, and \b matches at the end of the + subject when the last character is a letter, so a complete match is + found. The result, therefore, is not PCRE_ERROR_PARTIAL. Using + PCRE_PARTIAL_HARD in this case does yield PCRE_ERROR_PARTIAL, because + then the partial match takes precedence. - 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. + 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 @@ -6308,22 +8461,22 @@ EXAMPLE OF PARTIAL MATCHING USING PCRETEST 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 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 pcre[16|32]_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- + 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()): + 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 @@ -6340,37 +8493,40 @@ MULTI-SEGMENT MATCHING WITH 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 - pcre_dfa_exec(). + 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 pcre[16|32]_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. + 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. + 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 @@ -6379,20 +8535,37 @@ ISSUES WITH MULTI-SEGMENT MATCHING whichever matching function is used. 1. If the pattern contains a test for the beginning of a line, you need - to pass the PCRE_NOTBOL option when the subject string for any call - does start at the beginning of a line. There is also a PCRE_NOTEOL + to pass the PCRE_NOTBOL option when the subject string for any call + does start at the beginning of a line. There is also a PCRE_NOTEOL option, but in practice when doing multi-segment matching you should be using PCRE_PARTIAL_HARD, which includes the effect of PCRE_NOTEOL. - 2. Lookbehind assertions 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. + 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 + pcre[16|32]_fullinfo() functions to obtain the length of the largest + lookbehind in the pattern. This length is given in characters, not + bytes. If you always retain at least that many characters before the + partially matched string, all should be well. (Of course, near the + start of the subject, fewer characters may be present; in that case all + characters should be retained.) - 3. Matching a subject string that is split into multiple segments may + 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 @@ -6414,17 +8587,18 @@ 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- + Because of these problems, it is best to use PCRE_PARTIAL_HARD when + matching multi-segment data. The example above then behaves differ- ently: re> /dog(sbody)?/ @@ -6435,10 +8609,9 @@ 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 - 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: + 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. For example, consider this pattern: 1234|3789 @@ -6455,8 +8628,8 @@ ISSUES WITH MULTI-SEGMENT MATCHING 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: + 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 +8638,11 @@ 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 +8654,8 @@ AUTHOR REVISION - Last updated: 07 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 24 June 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -6500,26 +8673,32 @@ 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|32]_pat- + tern_to_host_byte_order() function on the new host before trying to + match the pattern. The matching functions return PCRE_ERROR_BADENDIAN- + NESS 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|32]_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|32]_fullinfo() with an argument of PCRE_INFO_SIZE. You can then + save the data in any appropriate manner. Here is sample code for the + 8-bit library that compiles a pattern and writes it to a file. It + assumes that the variable fd refers to a file that is open for output: int erroroffset, rc, size; char *error; @@ -6549,45 +8728,49 @@ 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|32]_study() returns a pointer to a pcre[16|32]_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|32]_extra + block itself). The length of the study data can be obtained by calling + pcre[16|32]_fullinfo() with an argument of PCRE_INFO_STUDYSIZE. Remem- + ber to check that pcre[16|32]_study() did return a non-NULL value + before trying to save the study data. RE-USING A PRECOMPILED PATTERN - Re-using a precompiled pattern is straightforward. Having reloaded it - into main memory, 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|32]_pattern_to_host_byte_order() if + necessary, you pass its pointer to pcre[16|32]_exec() or + pcre[16|32]_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|32]_compile()), + you must now pass a similar pointer to pcre[16|32]_exec() or + pcre[16|32]_dfa_exec(), because the value saved with the compiled pat- + tern will obviously be nonsense. A field in a pcre[16|32]_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|32]_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|32]_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 +8789,8 @@ AUTHOR REVISION - Last updated: 17 November 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 24 June 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -6627,12 +8810,12 @@ 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} @@ -6650,38 +8833,40 @@ 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 pcre[16|32]_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 @@ -6696,18 +8881,18 @@ PROCESSING TIME observations about PCRE. Using Unicode character properties (the \p, \P, and \X escapes) is - slow, because PCRE has to scan a structure that contains data for over - fifteen thousand characters whenever it needs a character's property. - If you can find an alternative pattern that does not use character - properties, it will probably be faster. + slow, because PCRE has to use a multi-stage table lookup 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 +8959,8 @@ AUTHOR REVISION - Last updated: 16 May 2010 - Copyright (c) 1997-2010 University of Cambridge. + Last updated: 25 August 2012 + Copyright (c) 1997-2012 University of Cambridge. ------------------------------------------------------------------------------ @@ -6804,9 +8989,11 @@ 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 and 32-bit + library. The functions described here are just wrapper functions that ultimately call the PCRE native API. Their prototypes are defined in the @@ -7037,8 +9224,8 @@ 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. ------------------------------------------------------------------------------ @@ -7059,7 +9246,9 @@ 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 or 32-bit support at + present. MATCHING INTERFACE @@ -7217,7 +9406,7 @@ 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 (*) @@ -7255,7 +9444,7 @@ PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE 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")) ... @@ -7379,7 +9568,7 @@ AUTHOR REVISION - Last updated: 17 March 2009 + Last updated: 08 January 2012 ------------------------------------------------------------------------------ @@ -7398,57 +9587,58 @@ 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 +9655,72 @@ 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, 32-bit units for the 32-bit + library, and 32-bit units for the 32-bit library) if PCRE is compiled + with the default internal linkage size of 2 bytes. If you want to + process regular expressions that are truly enormous, you can compile + PCRE with an internal linkage size of 3 or 4 (when building the 16-bit + or 32-bit library, 3 is rounded up to 4). See the README file in the + source distribution and the pcrebuild documentation for details. In + these cases the limit is substantially larger. However, the speed of + 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 and + 32-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 +9730,14 @@ 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|32]_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 @@ -7491,101 +9746,134 @@ 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 - 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. + The above comments apply when pcre[16|32]_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|32]_exec() were not incompati- + ble, 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 comments that follow do NOT apply to pcre_dfa_exec(); they are rel- - evant only for pcre_exec(). + The pcre[16|32]_dfa_exec() function operates in an entirely different + way, and uses recursion only when there is a regular expression recur- + sion or subroutine call in the pattern. This includes the processing of + assertion and "once-only" subpatterns, which are handled like subrou- + tine calls. Normally, these are never very deep, and the limit on the + complexity of pcre[16|32]_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|32]_dfa_exec() to run out of stack. At present, there is no + protection against this. - Reducing pcre_exec()'s stack usage + The comments that follow do NOT apply to pcre[16|32]_dfa_exec(); they + are relevant only for pcre[16|32]_exec() without the JIT optimization. - Each time that match() is actually called recursively, it uses memory - from the process stack. For certain kinds of pattern and data, very - large amounts of stack may be needed, despite the recognition of "tail - recursion". You can often reduce the amount of recursion, and there- - fore the amount of stack used, by modifying the pattern that is being + Reducing pcre[16|32]_exec()'s stack usage + + Each time that match() is actually called recursively, it uses memory + from the process stack. For certain kinds of pattern and data, very + large amounts of stack may be needed, despite the recognition of "tail + recursion". You can often reduce the amount of recursion, and there- + fore the amount of stack used, by modifying the pattern that is being matched. Consider, for example, this pattern: ([^<]|<(?!inet))+ - It matches from wherever it starts until it encounters "