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# Line 2  Line 2 
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
5  synopses of each function in the library have not been included. There are  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
10    
# Line 18  INTRODUCTION Line 19  INTRODUCTION
19    
20         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
21         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
22         just  a  few differences. (Certain features that appeared in Python and         just  a few differences. Some features that appeared in Python and PCRE
23         PCRE before they appeared in Perl are also available using  the  Python         before they appeared in Perl are also available using the  Python  syn-
24         syntax.)         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25           items, and there is an option for requesting some  minor  changes  that
26         The  current  implementation of PCRE (release 7.x) corresponds approxi-         give better JavaScript compatibility.
27         mately with Perl 5.10, including support for UTF-8 encoded strings  and  
28         Unicode general category properties. However, UTF-8 and Unicode support         The  current implementation of PCRE corresponds approximately with Perl
29         has to be explicitly enabled; it is not the default. The Unicode tables         5.10, including support for UTF-8 encoded strings and  Unicode  general
30         correspond to Unicode release 5.0.0.         category  properties.  However,  UTF-8  and  Unicode  support has to be
31           explicitly enabled; it is not the default. The  Unicode  tables  corre-
32           spond to Unicode release 5.2.0.
33    
34         In  addition to the Perl-compatible matching function, PCRE contains an         In  addition to the Perl-compatible matching function, PCRE contains an
35         alternative matching function that matches the same  compiled  patterns         alternative function that matches the same compiled patterns in a  dif-
36         in  a different way. In certain circumstances, the alternative function         ferent way. In certain circumstances, the alternative function has some
37         has some advantages. For a discussion of the two  matching  algorithms,         advantages.  For a discussion of the two matching algorithms,  see  the
38         see the pcrematching page.         pcrematching page.
39    
40         PCRE  is  written  in C and released as a C library. A number of people         PCRE  is  written  in C and released as a C library. A number of people
41         have written wrappers and interfaces of various kinds.  In  particular,         have written wrappers and interfaces of various kinds.  In  particular,
# Line 52  INTRODUCTION Line 55  INTRODUCTION
55         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
56         client  to  discover  which  features are available. The features them-         client  to  discover  which  features are available. The features them-
57         selves are described in the pcrebuild page. Documentation about  build-         selves are described in the pcrebuild page. Documentation about  build-
58         ing  PCRE for various operating systems can be found in the README file         ing  PCRE  for various operating systems can be found in the README and
59         in the source distribution.         NON-UNIX-USE files in the source distribution.
60    
61         The library contains a number of undocumented  internal  functions  and         The library contains a number of undocumented  internal  functions  and
62         data  tables  that  are  used by more than one of the exported external         data  tables  that  are  used by more than one of the exported external
# Line 69  USER DOCUMENTATION Line 72  USER DOCUMENTATION
72         The user documentation for PCRE comprises a number  of  different  sec-         The user documentation for PCRE comprises a number  of  different  sec-
73         tions.  In the "man" format, each of these is a separate "man page". In         tions.  In the "man" format, each of these is a separate "man page". In
74         the HTML format, each is a separate page, linked from the  index  page.         the HTML format, each is a separate page, linked from the  index  page.
75         In  the  plain text format, all the sections are concatenated, for ease         In  the  plain  text format, all the sections, except the pcredemo sec-
76         of searching. The sections are as follows:         tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79           pcre              this document           pcre              this document
80           pcre-config       show PCRE installation configuration information           pcre-config       show PCRE installation configuration information
# Line 79  USER DOCUMENTATION Line 83  USER DOCUMENTATION
83           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
84           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
85           pcrecpp           details of the C++ wrapper           pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
88           pcrematching      discussion of the two matching algorithms           pcrematching      discussion of the two matching algorithms
89           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
90           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
91                               regular expressions                               regular expressions
          pcresyntax        quick syntax reference  
92           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
93           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
94           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
95           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
96           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
99    
100         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
# Line 134  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
142         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         any subject strings that are matched against it are  treated  as  UTF-8         sequence (*UTF8). When either of these is the case,  both  the  pattern
144         strings instead of just strings of bytes.         and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of strings of 1-byte characters.
146    
147         If  you compile PCRE with UTF-8 support, but do not use it at run time,         If you compile PCRE with UTF-8 support, but do not use it at run  time,
148         the library will be a bit bigger, but the additional run time  overhead         the  library will be a bit bigger, but the additional run time overhead
149         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150         very big.         very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
156         for a decimal number, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
158         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
159         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         does not support this.         does not support this.
163    
164         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
165    
166           When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
167           subjects are (by default) checked for validity on entry to the relevant
168           functions.  From  release 7.3 of PCRE, the check is according the rules
169           of RFC 3629, which are themselves derived from the  Unicode  specifica-
170           tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171           allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173           to U+DFFF.
174    
175           The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176           which  the Unicode Standard says this: "The Low Surrogate Area does not
177           contain any  character  assignments,  consequently  no  character  code
178           charts or namelists are provided for this area. Surrogates are reserved
179           for use with UTF-16 and then must be used in pairs."  The  code  points
180           that  are  encoded  by  UTF-16  pairs are available as independent code
181           points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184           If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186           that your strings are valid, and therefore want to skip these checks in
187           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188           compile  time  or at run time, PCRE assumes that the pattern or subject
189           it is given (respectively) contains only valid  UTF-8  codes.  In  this
190           case, it does not diagnose an invalid UTF-8 string.
191    
192           If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193           what happens depends on why the string is invalid. If the  string  con-
194           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195           string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197           strings according to the more liberal rules of RFC  2279.  However,  if
198           the  string does not even conform to RFC 2279, the result is undefined.
199           Your program may crash.
200    
201           If you want to process strings  of  values  in  the  full  range  0  to
202           0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204           this situation, you will have to apply your own validity check.
205    
206         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and     General comments about UTF-8 mode
        subjects  are  checked for validity on entry to the relevant functions.  
        If an invalid UTF-8 string is passed, an error return 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. If you pass an invalid UTF-8 string to PCRE  when  
        PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may  
        crash.  
207    
208         2. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a         1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
210    
211         3.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
212         characters for values greater than \177.         characters for values greater than \177.
213    
214         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
216    
217         5.  The dot metacharacter matches one UTF-8 character instead of a sin-         4. The dot metacharacter matches one UTF-8 character instead of a  sin-
218         gle byte.         gle byte.
219    
220         6. The escape sequence \C can be used to match a single byte  in  UTF-8         5.  The  escape sequence \C can be used to match a single byte in UTF-8
221         mode,  but  its  use can lead to some strange effects. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
225         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but the characters that PCRE  recog-
226         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes  as  digits,  spaces,  or  word characters remain the same set as
227         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
228         includes Unicode property support, because to do otherwise  would  slow         includes  Unicode  property support, because to do otherwise would slow
229         down  PCRE in many common cases. If you really want to test for a wider         down PCRE in many common cases. If you really want to test for a  wider
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense  of,  say,  "digit",  you must use Unicode property tests such as
231         \p{Nd}.         \p{Nd}. Note that this also applies to \b, because  it  is  defined  in
232           terms of \w and \W.
233    
234         8.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
235         are all low-valued characters.         are all low-valued characters.
236    
237         9. However, the Perl 5.10 horizontal and vertical  whitespace  matching         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
238         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
239         acters.         acters.
240    
241         10. Case-insensitive matching applies only to characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
242         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
243         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
244         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
# Line 226  AUTHOR Line 263  AUTHOR
263    
264  REVISION  REVISION
265    
266         Last updated: 06 August 2007         Last updated: 01 March 2010
267         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
268  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
269    
270    
# Line 241  NAME Line 278  NAME
278  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
279    
280         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
281         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
282         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
283         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
284         includes  the  standard  ones such as the selection of the installation         the  same  options  can be selected in both Unix-like and non-Unix-like
285         directory) can be obtained by running         environments using the GUI facility of cmake-gui if you are using CMake
286           instead of configure to build PCRE.
287    
288           There  is  a  lot more information about building PCRE in non-Unix-like
289           environments in the file called NON_UNIX_USE, which is part of the PCRE
290           distribution.  You  should consult this file as well as the README file
291           if you are building in a non-Unix-like environment.
292    
293           The complete list of options for configure (which includes the standard
294           ones  such  as  the  selection  of  the  installation directory) can be
295           obtained by running
296    
297           ./configure --help           ./configure --help
298    
# Line 270  C++ SUPPORT Line 317  C++ SUPPORT
317    
318  UTF-8 SUPPORT  UTF-8 SUPPORT
319    
320         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
321    
322           --enable-utf8           --enable-utf8
323    
324         to  the  configure  command.  Of  itself, this does not make PCRE treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
325         strings as UTF-8. As well as compiling PCRE with this option, you  also         strings as UTF-8. As well as compiling PCRE with this option, you  also
326         have  have to set the PCRE_UTF8 option when you call the pcre_compile()         have  have to set the PCRE_UTF8 option when you call the pcre_compile()
327         function.         or pcre_compile2() functions.
328    
329           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
330           expects its input to be either ASCII or UTF-8 (depending on the runtime
331           option). It is not possible to support both EBCDIC and UTF-8  codes  in
332           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
333           --enable-ebcdic are mutually exclusive.
334    
335    
336  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
# Line 300  UNICODE CHARACTER PROPERTY SUPPORT Line 353  UNICODE CHARACTER PROPERTY SUPPORT
353    
354  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
355    
356         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating         By  default,  PCRE interprets the linefeed (LF) character as indicating
357         the end of a line. This is the normal newline  character  on  Unix-like         the end of a line. This is the normal newline  character  on  Unix-like
358         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems.  You  can compile PCRE to use carriage return (CR) instead, by
359         instead, by adding         adding
360    
361           --enable-newline-is-cr           --enable-newline-is-cr
362    
# Line 326  CODE VALUE OF NEWLINE Line 379  CODE VALUE OF NEWLINE
379    
380         causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
381    
382         Whatever line ending convention is selected when PCRE is built  can  be         Whatever  line  ending convention is selected when PCRE is built can be
383         overridden  when  the library functions are called. At build time it is         overridden when the library functions are called. At build time  it  is
384         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
385    
386    
387    WHAT \R MATCHES
388    
389           By  default,  the  sequence \R in a pattern matches any Unicode newline
390           sequence, whatever has been selected as the line  ending  sequence.  If
391           you specify
392    
393             --enable-bsr-anycrlf
394    
395           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
396           ever is selected when PCRE is built can be overridden when the  library
397           functions are called.
398    
399    
400  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
401    
402         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
403         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
404         of         of
405    
406           --disable-shared           --disable-shared
# Line 346  BUILDING SHARED AND STATIC LIBRARIES Line 412  BUILDING SHARED AND STATIC LIBRARIES
412  POSIX MALLOC USAGE  POSIX MALLOC USAGE
413    
414         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
415         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
416         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
417         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
418         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
419         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
420         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 361  POSIX MALLOC USAGE Line 427  POSIX MALLOC USAGE
427    
428  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
429    
430         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
431         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
432         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
433         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
434         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
435         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process truyl enormous patterns,
436         is  possible  to compile PCRE to use three-byte or four-byte offsets by         so it is possible to compile PCRE to use three-byte or  four-byte  off-
437         adding a setting such as         sets by adding a setting such as
438    
439           --with-link-size=3           --with-link-size=3
440    
441         to the configure command. The value given must be 2,  3,  or  4.  Using         to  the  configure  command.  The value given must be 2, 3, or 4. Using
442         longer  offsets slows down the operation of PCRE because it has to load         longer offsets slows down the operation of PCRE because it has to  load
443         additional bytes when handling them.         additional bytes when handling them.
444    
445    
446  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
447    
448         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
449         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
450         In environments where the size of the stack is limited,  this  can  se-         In  environments  where  the size of the stack is limited, this can se-
451         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
452         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
453         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
454         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
455         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
456         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
457         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
458    
459           --disable-stack-for-recursion           --disable-stack-for-recursion
460    
461         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
462         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
463         ment  functions. By default these point to malloc() and free(), but you         ment functions. By default these point to malloc() and free(), but  you
464         can replace the pointers so that your own functions are used.         can replace the pointers so that your own functions are used instead.
465    
466         Separate functions are  provided  rather  than  using  pcre_malloc  and         Separate  functions  are  provided  rather  than  using pcre_malloc and
467         pcre_free  because  the  usage  is  very  predictable:  the block sizes         pcre_free because the  usage  is  very  predictable:  the  block  sizes
468         requested are always the same, and  the  blocks  are  always  freed  in         requested  are  always  the  same,  and  the blocks are always freed in
469         reverse  order.  A calling program might be able to implement optimized         reverse order. A calling program might be able to  implement  optimized
470         functions that perform better  than  malloc()  and  free().  PCRE  runs         functions  that  perform  better  than  malloc()  and free(). PCRE runs
471         noticeably more slowly when built in this way. This option affects only         noticeably more slowly when built in this way. This option affects only
472         the  pcre_exec()  function;  it   is   not   relevant   for   the   the         the pcre_exec() function; it is not relevant for pcre_dfa_exec().
        pcre_dfa_exec() function.  
473    
474    
475  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
# Line 466  USING EBCDIC CODE Line 531  USING EBCDIC CODE
531    
532         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
533         bles.  You  should  only  use  it if you know that you are in an EBCDIC         bles.  You  should  only  use  it if you know that you are in an EBCDIC
534         environment (for example, an IBM mainframe operating system).         environment (for example,  an  IBM  mainframe  operating  system).  The
535           --enable-ebcdic option is incompatible with --enable-utf8.
536    
537    
538    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
539    
540           By default, pcregrep reads all files as plain text. You can build it so
541           that it recognizes files whose names end in .gz or .bz2, and reads them
542           with libz or libbz2, respectively, by adding one or both of
543    
544             --enable-pcregrep-libz
545             --enable-pcregrep-libbz2
546    
547           to the configure command. These options naturally require that the rel-
548           evant libraries are installed on your system. Configuration  will  fail
549           if they are not.
550    
551    
552    PCRETEST OPTION FOR LIBREADLINE SUPPORT
553    
554           If you add
555    
556             --enable-pcretest-libreadline
557    
558           to  the  configure  command,  pcretest  is  linked with the libreadline
559           library, and when its input is from a terminal, it reads it  using  the
560           readline() function. This provides line-editing and history facilities.
561           Note that libreadline is GPL-licensed, so if you distribute a binary of
562           pcretest linked in this way, there may be licensing issues.
563    
564           Setting  this  option  causes  the -lreadline option to be added to the
565           pcretest build. In many operating environments with  a  sytem-installed
566           libreadline this is sufficient. However, in some environments (e.g.  if
567           an unmodified distribution version of readline is in use),  some  extra
568           configuration  may  be necessary. The INSTALL file for libreadline says
569           this:
570    
571             "Readline uses the termcap functions, but does not link with the
572             termcap or curses library itself, allowing applications which link
573             with readline the to choose an appropriate library."
574    
575           If your environment has not been set up so that an appropriate  library
576           is automatically included, you may need to add something like
577    
578             LIBS="-ncurses"
579    
580           immediately before the configure command.
581    
582    
583  SEE ALSO  SEE ALSO
# Line 483  AUTHOR Line 594  AUTHOR
594    
595  REVISION  REVISION
596    
597         Last updated: 30 July 2007         Last updated: 29 September 2009
598         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
599  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
600    
601    
# Line 571  THE ALTERNATIVE MATCHING ALGORITHM Line 682  THE ALTERNATIVE MATCHING ALGORITHM
682         though  it is not implemented as a traditional finite state machine (it         though  it is not implemented as a traditional finite state machine (it
683         keeps multiple states active simultaneously).         keeps multiple states active simultaneously).
684    
685           Although the general principle of this matching algorithm  is  that  it
686           scans  the subject string only once, without backtracking, there is one
687           exception: when a lookaround assertion is encountered,  the  characters
688           following  or  preceding  the  current  point  have to be independently
689           inspected.
690    
691         The scan continues until either the end of the subject is  reached,  or         The scan continues until either the end of the subject is  reached,  or
692         there  are  no more unterminated paths. At this point, terminated paths         there  are  no more unterminated paths. At this point, terminated paths
693         represent the different matching possibilities (if there are none,  the         represent the different matching possibilities (if there are none,  the
694         match  has  failed).   Thus,  if there is more than one possible match,         match  has  failed).   Thus,  if there is more than one possible match,
695         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
696         est.  In PCRE, there is an option to stop the algorithm after the first         est.  There  is  an  option to stop the algorithm after the first match
697         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
698    
699         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
700         subject. If the pattern         subject. If the pattern
# Line 627  THE ALTERNATIVE MATCHING ALGORITHM Line 744  THE ALTERNATIVE MATCHING ALGORITHM
744         6.  Callouts  are  supported, but the value of the capture_top field is         6.  Callouts  are  supported, but the value of the capture_top field is
745         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
746    
747         7.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
748         single  byte, even in UTF-8 mode, is not supported because the alterna-         single  byte, even in UTF-8 mode, is not supported because the alterna-
749         tive algorithm moves through the subject  string  one  character  at  a         tive algorithm moves through the subject  string  one  character  at  a
750         time, for all active paths through the tree.         time, for all active paths through the tree.
751    
752           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
753           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
754           negative assertion.
755    
756    
757  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
758    
# Line 643  ADVANTAGES OF THE ALTERNATIVE ALGORITHM Line 764  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
764         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
765         things with callouts.         things with callouts.
766    
767         2.  There is much better support for partial matching. The restrictions         2.  Because  the  alternative  algorithm  scans the subject string just
        on the content of the pattern that apply when using the standard  algo-  
        rithm  for  partial matching do not apply to the alternative algorithm.  
        For non-anchored patterns, the starting position of a partial match  is  
        available.  
   
        3.  Because  the  alternative  algorithm  scans the subject string just  
768         once, and never needs to backtrack, it is possible to  pass  very  long         once, and never needs to backtrack, it is possible to  pass  very  long
769         subject  strings  to  the matching function in several pieces, checking         subject  strings  to  the matching function in several pieces, checking
770         for partial matching each time.         for partial matching each time.  The  pcrepartial  documentation  gives
771           details of partial matching.
772    
773    
774  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
775    
776         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
777    
778         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
779         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
780         because it is less susceptible to optimization.         because it is less susceptible to optimization.
781    
782         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 678  AUTHOR Line 794  AUTHOR
794    
795  REVISION  REVISION
796    
797         Last updated: 29 May 2007         Last updated: 29 September 2009
798         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
799  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
800    
801    
# Line 790  PCRE API OVERVIEW Line 906  PCRE API OVERVIEW
906         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
907         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
908         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
909         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
910         run it.         pcredemo documentation, and the pcresample documentation describes  how
911           to compile and run it.
912    
913         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
914         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
915         ing. The alternative algorithm finds all possible matches (at  a  given         ing.  The  alternative algorithm finds all possible matches (at a given
916         point  in  the subject), and scans the subject just once. However, this         point in the subject), and scans the subject just  once  (unless  there
917         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
918         matching  algorithms and their advantages and disadvantages is given in         captured substrings. A description of the two matching  algorithms  and
919         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
920           mentation.
921    
922         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
923         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 875  NEWLINES Line 993  NEWLINES
993         dard. When PCRE is run, the default can be overridden,  either  when  a         dard. When PCRE is run, the default can be overridden,  either  when  a
994         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
995    
996           At compile time, the newline convention can be specified by the options
997           argument of pcre_compile(), or it can be specified by special  text  at
998           the start of the pattern itself; this overrides any other settings. See
999           the pcrepattern page for details of the special character sequences.
1000    
1001         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
1002         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
1003         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
1004         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
1005         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
1006         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
1007         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
1008    
1009           The choice of newline convention does not affect the interpretation  of
1010           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1011           which is controlled in a similar way, but by separate options.
1012    
1013    
1014  MULTITHREADING  MULTITHREADING
1015    
1016         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1017         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1018         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1019         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
# Line 935  CHECKING BUILD-TIME OPTIONS Line 1062  CHECKING BUILD-TIME OPTIONS
1062         The output is an integer whose value specifies  the  default  character         The output is an integer whose value specifies  the  default  character
1063         sequence  that is recognized as meaning "newline". The four values that         sequence  that is recognized as meaning "newline". The four values that
1064         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1065         and  -1  for  ANY. The default should normally be the standard sequence         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1066         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1067           spond to the standard sequence for your operating system.
1068    
1069             PCRE_CONFIG_BSR
1070    
1071           The output is an integer whose value indicates what character sequences
1072           the \R escape sequence matches by default. A value of 0 means  that  \R
1073           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1074           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1075           tern is compiled or matched.
1076    
1077           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1078    
1079         The output is an integer that contains the number  of  bytes  used  for         The  output  is  an  integer that contains the number of bytes used for
1080         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1081         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1082         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1083         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1084         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1085    
1086           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1087    
1088         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1089         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1090         given in the pcreposix documentation.         given in the pcreposix documentation.
1091    
1092           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1093    
1094         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1095         internal matching function calls in a  pcre_exec()  execution.  Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1096         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1097    
1098           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1099    
1100         The  output is an integer that gives the default limit for the depth of         The output is a long integer that gives the default limit for the depth
1101         recursion when calling the internal matching function in a  pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1102         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1103           below.
1104    
1105           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1106    
# Line 990  COMPILING A PATTERN Line 1127  COMPILING A PATTERN
1127         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1128         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1129         the  two interfaces is that pcre_compile2() has an additional argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1130         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1131           avoid  too  much repetition, we refer just to pcre_compile() below, but
1132           the information applies equally to pcre_compile2().
1133    
1134         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1135         the  pattern  argument.  A  pointer to a single block of memory that is         the  pattern  argument.  A  pointer to a single block of memory that is
# Line 1007  COMPILING A PATTERN Line 1146  COMPILING A PATTERN
1146    
1147         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1148         pilation. It should be zero if no options are required.  The  available         pilation. It should be zero if no options are required.  The  available
1149         options  are  described  below. Some of them, in particular, those that         options  are  described  below. Some of them (in particular, those that
1150         are compatible with Perl, can also be set and  unset  from  within  the         are compatible with Perl, but some others as well) can also be set  and
1151         pattern  (see  the  detailed  description in the pcrepattern documenta-         unset  from  within  the  pattern  (see the detailed description in the
1152         tion). For these options, the contents of the options  argument  speci-         pcrepattern documentation). For those options that can be different  in
1153         fies  their initial settings at the start of compilation and execution.         different  parts  of  the pattern, the contents of the options argument
1154         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         specifies their settings at the start of compilation and execution. The
1155         of matching as well as at compile time.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1156           the time of matching as well as at compile time.
1157    
1158         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1159         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1160         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1161         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1162         try to free it. The offset from the start of the pattern to the charac-         try to free it. The byte offset from the start of the  pattern  to  the
1163         ter where the error was discovered is placed in the variable pointed to         character  that  was  being  processed when the error was discovered is
1164         by  erroffset,  which must not be NULL. If it is, an immediate error is         placed in the variable pointed to by erroffset, which must not be NULL.
1165         given.         If  it  is,  an  immediate error is given. Some errors are not detected
1166           until checks are carried out when the whole pattern has  been  scanned;
1167         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         in this case the offset is set to the end of the pattern.
1168         codeptr  argument is not NULL, a non-zero error code number is returned  
1169         via this argument in the event of an error. This is in addition to  the         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1170           codeptr argument is not NULL, a non-zero error code number is  returned
1171           via  this argument in the event of an error. This is in addition to the
1172         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1173    
1174         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1175         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1176         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1177         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1178         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1179         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1180         support below.         support below.
1181    
1182         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1183         pile():         pile():
1184    
1185           pcre *re;           pcre *re;
# Line 1050  COMPILING A PATTERN Line 1192  COMPILING A PATTERN
1192             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1193             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1194    
1195         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1196         file:         file:
1197    
1198           PCRE_ANCHORED           PCRE_ANCHORED
1199    
1200         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1201         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1202         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1203         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1204         only way to do it in Perl.         only way to do it in Perl.
1205    
1206           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1207    
1208         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1209         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1210         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1211    
1212             PCRE_BSR_ANYCRLF
1213             PCRE_BSR_UNICODE
1214    
1215           These options (which are mutually exclusive) control what the \R escape
1216           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1217           or to match any Unicode newline sequence. The default is specified when
1218           PCRE is built. It can be overridden from within the pattern, or by set-
1219           ting an option when a compiled pattern is matched.
1220    
1221           PCRE_CASELESS           PCRE_CASELESS
1222    
1223         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1224         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1225         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1226         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1227         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1228         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1229         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1230         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1231         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1232         UTF-8 support.         UTF-8 support.
1233    
1234           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1235    
1236         If this bit is set, a dollar metacharacter in the pattern matches  only         If  this bit is set, a dollar metacharacter in the pattern matches only
1237         at  the  end  of the subject string. Without this option, a dollar also         at the end of the subject string. Without this option,  a  dollar  also
1238         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1239         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1240         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1241         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1242    
1243           PCRE_DOTALL           PCRE_DOTALL
1244    
1245         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1246         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1247         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1248         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1249         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1250         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1251    
1252           PCRE_DUPNAMES           PCRE_DUPNAMES
1253    
1254         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1255         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1256         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1257         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1258         the pcrepattern documentation.         the pcrepattern documentation.
1259    
1260           PCRE_EXTENDED           PCRE_EXTENDED
1261    
1262         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1263         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1264         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1265         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1266         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1267         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1268         ting.         ting.
1269    
1270         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1271         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1272         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1273         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1274         introduces a conditional subpattern.         introduces a conditional subpattern.
1275    
1276           PCRE_EXTRA           PCRE_EXTRA
1277    
1278         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1279         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1280         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1281         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1282         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1283         backslash  followed by a letter with no special meaning is treated as a         backslash followed by a letter with no special meaning is treated as  a
1284         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1285         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1286         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1287    
1288           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1289    
1290         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1291         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1292         matched text may continue over the newline.         matched text may continue over the newline.
1293    
1294             PCRE_JAVASCRIPT_COMPAT
1295    
1296           If this option is set, PCRE's behaviour is changed in some ways so that
1297           it is compatible with JavaScript rather than Perl. The changes  are  as
1298           follows:
1299    
1300           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1301           error, because this is illegal in JavaScript (by default it is  treated
1302           as a data character). Thus, the pattern AB]CD becomes illegal when this
1303           option is set.
1304    
1305           (2) At run time, a back reference to an unset subpattern group  matches
1306           an  empty  string (by default this causes the current matching alterna-
1307           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1308           set  (assuming  it can find an "a" in the subject), whereas it fails by
1309           default, for Perl compatibility.
1310    
1311           PCRE_MULTILINE           PCRE_MULTILINE
1312    
1313         By default, PCRE treats the subject string as consisting  of  a  single         By default, PCRE treats the subject string as consisting  of  a  single
# Line 1193  COMPILING A PATTERN Line 1361  COMPILING A PATTERN
1361         and are therefore ignored.         and are therefore ignored.
1362    
1363         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1364         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1365    
1366           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1367    
1368         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1369         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1370         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1371         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1372         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1373    
1374           PCRE_UNGREEDY           PCRE_UNGREEDY
1375    
1376         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1377         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1378         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1379         within the pattern.         within the pattern.
1380    
1381           PCRE_UTF8           PCRE_UTF8
1382    
1383         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1384         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1385         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1386         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1387         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1388         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1389    
1390           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1391    
1392         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1393         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1394         pcre_compile() returns an error. If you already know that your  pattern         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1395         is  valid, and you want to skip this check for performance reasons, you         bytes is found, pcre_compile() returns an error. If  you  already  know
1396         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1397         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1398         your program to crash.  Note that this option can  also  be  passed  to         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1399         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined. It may cause your program to crash. Note  that  this  option
1400         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1401           UTF-8 validity checking of subject strings.
1402    
1403    
1404  COMPILATION ERROR CODES  COMPILATION ERROR CODES
# Line 1251  COMPILATION ERROR CODES Line 1420  COMPILATION ERROR CODES
1420            9  nothing to repeat            9  nothing to repeat
1421           10  [this code is not in use]           10  [this code is not in use]
1422           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1423           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1424           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1425           14  missing )           14  missing )
1426           15  reference to non-existent subpattern           15  reference to non-existent subpattern
# Line 1259  COMPILATION ERROR CODES Line 1428  COMPILATION ERROR CODES
1428           17  unknown option bit(s) set           17  unknown option bit(s) set
1429           18  missing ) after comment           18  missing ) after comment
1430           19  [this code is not in use]           19  [this code is not in use]
1431           20  regular expression too large           20  regular expression is too large
1432           21  failed to get memory           21  failed to get memory
1433           22  unmatched parentheses           22  unmatched parentheses
1434           23  internal error: code overflow           23  internal error: code overflow
# Line 1288  COMPILATION ERROR CODES Line 1457  COMPILATION ERROR CODES
1457           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1458           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1459           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1460           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10000)
1461           50  [this code is not in use]           50  [this code is not in use]
1462           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1463           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
# Line 1296  COMPILATION ERROR CODES Line 1465  COMPILATION ERROR CODES
1465         found         found
1466           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1467           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1468           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1469           57  \g is not followed by a braced name or an optionally braced           57  \g is not followed by a braced, angle-bracketed, or quoted
1470                 non-zero number                 name/number or by a plain number
1471           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number           58  a numbered reference must not be zero
1472             59  (*VERB) with an argument is not supported
1473             60  (*VERB) not recognized
1474             61  number is too big
1475             62  subpattern name expected
1476             63  digit expected after (?+
1477             64  ] is an invalid data character in JavaScript compatibility mode
1478    
1479           The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1480           values may be used if the limits were changed when PCRE was built.
1481    
1482    
1483  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1307  STUDYING A PATTERN Line 1485  STUDYING A PATTERN
1485         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1486              const char **errptr);              const char **errptr);
1487    
1488         If a compiled pattern is going to be used several times,  it  is  worth         If  a  compiled  pattern is going to be used several times, it is worth
1489         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1490         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1491         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1492         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1493         pointer  to a pcre_extra block, in which the study_data field points to         pointer to a pcre_extra block, in which the study_data field points  to
1494         the results of the study.         the results of the study.
1495    
1496         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1497         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1498         that can be set by the caller before the block  is  passed;  these  are         tains  other  fields  that can be set by the caller before the block is
1499         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1500    
1501         If  studying  the  pattern  does not produce any additional information         If studying the  pattern  does  not  produce  any  useful  information,
1502         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1503         wants  to  pass  any of the other fields to pcre_exec(), it must set up         wants  to  pass  any  of   the   other   fields   to   pcre_exec()   or
1504         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1505    
1506         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1507         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1508    
1509         The  third argument for pcre_study() is a pointer for an error message.         The third argument for pcre_study() is a pointer for an error  message.
1510         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1511         points  to  is  set  to NULL. Otherwise it is set to point to a textual         points to is set to NULL. Otherwise it is set to  point  to  a  textual
1512         error message. This is a static string that is part of the library. You         error message. This is a static string that is part of the library. You
1513         must  not  try  to  free it. You should test the error pointer for NULL         must not try to free it. You should test the  error  pointer  for  NULL
1514         after calling pcre_study(), to be sure that it has run successfully.         after calling pcre_study(), to be sure that it has run successfully.
1515    
1516         This is a typical call to pcre_study():         This is a typical call to pcre_study():
# Line 1343  STUDYING A PATTERN Line 1521  STUDYING A PATTERN
1521             0,              /* no options exist */             0,              /* no options exist */
1522             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1523    
1524         At present, studying a pattern is useful only for non-anchored patterns         Studying a pattern does two things: first, a lower bound for the length
1525         that  do not have a single fixed starting character. A bitmap of possi-         of subject string that is needed to match the pattern is computed. This
1526         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1527           it does guarantee that no shorter strings match. The value is  used  by
1528           pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1529           match strings that are shorter than the lower bound. You can  find  out
1530           the value in a calling program via the pcre_fullinfo() function.
1531    
1532           Studying a pattern is also useful for non-anchored patterns that do not
1533           have a single fixed starting character. A bitmap of  possible  starting
1534           bytes  is  created. This speeds up finding a position in the subject at
1535           which to start matching.
1536    
1537    
1538  LOCALE SUPPORT  LOCALE SUPPORT
# Line 1488  INFORMATION ABOUT A PATTERN Line 1675  INFORMATION ABOUT A PATTERN
1675         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1676         able.         able.
1677    
1678             PCRE_INFO_HASCRORLF
1679    
1680           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1681           characters, otherwise 0. The fourth argument should  point  to  an  int
1682           variable.  An explicit match is either a literal CR or LF character, or
1683           \r or \n.
1684    
1685           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1686    
1687         Return  1  if the (?J) option setting is used in the pattern, otherwise         Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1688         0. The fourth argument should point to an int variable. The (?J) inter-         otherwise  0. The fourth argument should point to an int variable. (?J)
1689         nal option setting changes the local PCRE_DUPNAMES option.         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1690    
1691           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1692    
1693         Return  the  value of the rightmost literal byte that must exist in any         Return the value of the rightmost literal byte that must exist  in  any
1694         matched string, other than at its  start,  if  such  a  byte  has  been         matched  string,  other  than  at  its  start,  if such a byte has been
1695         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1696         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1697         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1698         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1699         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1700    
1701             PCRE_INFO_MINLENGTH
1702    
1703           If the pattern was studied and a minimum length  for  matching  subject
1704           strings  was  computed,  its  value is returned. Otherwise the returned
1705           value is -1. The value is a number of characters, not bytes  (this  may
1706           be  relevant in UTF-8 mode). The fourth argument should point to an int
1707           variable. A non-negative value is a lower bound to the  length  of  any
1708           matching  string.  There  may not be any strings of that length that do
1709           actually match, but every string that does match is at least that long.
1710    
1711           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1712           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1713           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1714    
1715         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1716         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1717         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1718         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1719         strings  by  name. It is also possible to extract the data directly, by         strings by name. It is also possible to extract the data  directly,  by
1720         first converting the name to a number in order to  access  the  correct         first  converting  the  name to a number in order to access the correct
1721         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1722         the conversion, you need  to  use  the  name-to-number  map,  which  is         the  conversion,  you  need  to  use  the  name-to-number map, which is
1723         described by these three values.         described by these three values.
1724    
1725         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1726         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1727         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1728         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1729         a  pointer  to  the  first  entry of the table (a pointer to char). The         a pointer to the first entry of the table  (a  pointer  to  char).  The
1730         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1731         sis,  most  significant byte first. The rest of the entry is the corre-         sis, most significant byte first. The rest of the entry is  the  corre-
1732         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated.
1733         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-  
1734         theses numbers. For example, consider  the  following  pattern  (assume         The  names are in alphabetical order. Duplicate names may appear if (?|
1735         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         is used to create multiple groups with the same number, as described in
1736         ignored):         the  section  on  duplicate subpattern numbers in the pcrepattern page.
1737           Duplicate names for subpatterns with different  numbers  are  permitted
1738           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1739           appear in the table in the order in which they were found in  the  pat-
1740           tern.  In  the  absence  of (?| this is the order of increasing number;
1741           when (?| is used this is not necessarily the case because later subpat-
1742           terns may have lower numbers.
1743    
1744           As  a  simple  example of the name/number table, consider the following
1745           pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1746           lines - is ignored):
1747    
1748           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1749           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1750    
1751         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1752         each  entry  in the table is eight bytes long. The table is as follows,         each entry in the table is eight bytes long. The table is  as  follows,
1753         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1754         as ??:         as ??:
1755    
# Line 1544  INFORMATION ABOUT A PATTERN Line 1758  INFORMATION ABOUT A PATTERN
1758           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1759           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1760    
1761         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1762         name-to-number map, remember that the length of the entries  is  likely         name-to-number  map,  remember that the length of the entries is likely
1763         to be different for each compiled pattern.         to be different for each compiled pattern.
1764    
1765           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1766    
1767         Return  1 if the pattern can be used for partial matching, otherwise 0.         Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1768         The fourth argument should point to an int  variable.  The  pcrepartial         pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1769         documentation  lists  the restrictions that apply to patterns when par-         variable. From  release  8.00,  this  always  returns  1,  because  the
1770         tial matching is used.         restrictions  that  previously  applied  to  partial matching have been
1771           lifted. The pcrepartial documentation gives details of  partial  match-
1772           ing.
1773    
1774           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1775    
1776         Return a copy of the options with which the pattern was  compiled.  The         Return  a  copy of the options with which the pattern was compiled. The
1777         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1778         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1779         by any top-level option settings at the start of the pattern itself. In         by any top-level option settings at the start of the pattern itself. In
1780         other words, they are the options that will be in force  when  matching         other  words,  they are the options that will be in force when matching
1781         starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with         starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1782         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1783         and PCRE_EXTENDED.         and PCRE_EXTENDED.
1784    
1785         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1786         alternatives begin with one of the following:         alternatives begin with one of the following:
1787    
1788           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1580  INFORMATION ABOUT A PATTERN Line 1796  INFORMATION ABOUT A PATTERN
1796    
1797           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1798    
1799         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1800         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1801         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1802         size_t variable.         size_t variable.
# Line 1588  INFORMATION ABOUT A PATTERN Line 1804  INFORMATION ABOUT A PATTERN
1804           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1805    
1806         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1807         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1808         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1809         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). If pcre_extra is NULL, or there  is  no  study
1810           data,  zero  is  returned. The fourth argument should point to a size_t
1811         variable.         variable.
1812    
1813    
# Line 1644  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1861  MATCHING A PATTERN: THE TRADITIONAL FUNC
1861              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1862              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1863    
1864         The function pcre_exec() is called to match a subject string against  a         The  function pcre_exec() is called to match a subject string against a
1865         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1866         has been studied, the result of the study should be passed in the extra         was  studied,  the  result  of  the study should be passed in the extra
1867         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1868         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1869         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1870         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1871    
1872         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1873         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1874         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1875         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1876         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1877    
1878         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1674  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1891  MATCHING A PATTERN: THE TRADITIONAL FUNC
1891    
1892     Extra data for pcre_exec()     Extra data for pcre_exec()
1893    
1894         If the extra argument is not NULL, it must point to a  pcre_extra  data         If  the  extra argument is not NULL, it must point to a pcre_extra data
1895         block.  The pcre_study() function returns such a block (when it doesn't         block. The pcre_study() function returns such a block (when it  doesn't
1896         return NULL), but you can also create one for yourself, and pass  addi-         return  NULL), but you can also create one for yourself, and pass addi-
1897         tional  information  in it. The pcre_extra block contains the following         tional information in it. The pcre_extra block contains  the  following
1898         fields (not necessarily in this order):         fields (not necessarily in this order):
1899    
1900           unsigned long int flags;           unsigned long int flags;
# Line 1687  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1904  MATCHING A PATTERN: THE TRADITIONAL FUNC
1904           void *callout_data;           void *callout_data;
1905           const unsigned char *tables;           const unsigned char *tables;
1906    
1907         The flags field is a bitmap that specifies which of  the  other  fields         The  flags  field  is a bitmap that specifies which of the other fields
1908         are set. The flag bits are:         are set. The flag bits are:
1909    
1910           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1696  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1913  MATCHING A PATTERN: THE TRADITIONAL FUNC
1913           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1914           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1915    
1916         Other  flag  bits should be set to zero. The study_data field is set in         Other flag bits should be set to zero. The study_data field is  set  in
1917         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1918         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1919         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1920         flag bits.         flag bits.
1921    
1922         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1923         a vast amount of resources when running patterns that are not going  to         a  vast amount of resources when running patterns that are not going to
1924         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1925         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees. The classic example is a pattern that uses nested unlim-
1926         repeats.         ited repeats.
1927    
1928         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1929         edly (sometimes recursively). The limit set by match_limit  is  imposed         edly  (sometimes  recursively). The limit set by match_limit is imposed
1930         on  the  number  of times this function is called during a match, which         on the number of times this function is called during  a  match,  which
1931         has the effect of limiting the amount of  backtracking  that  can  take         has  the  effect  of  limiting the amount of backtracking that can take
1932         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1933         for each position in the subject string.         for each position in the subject string.
1934    
1935         The default value for the limit can be set  when  PCRE  is  built;  the         The  default  value  for  the  limit can be set when PCRE is built; the
1936         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1937         cases. You can override the default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1938         pcre_extra     block    in    which    match_limit    is    set,    and         pcre_extra    block    in    which    match_limit    is    set,     and
1939         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1940         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1941    
1942         The  match_limit_recursion field is similar to match_limit, but instead         The match_limit_recursion field is similar to match_limit, but  instead
1943         of limiting the total number of times that match() is called, it limits         of limiting the total number of times that match() is called, it limits
1944         the  depth  of  recursion. The recursion depth is a smaller number than         the depth of recursion. The recursion depth is a  smaller  number  than
1945         the total number of calls, because not all calls to match() are  recur-         the  total number of calls, because not all calls to match() are recur-
1946         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1947    
1948         Limiting the recursion depth limits the amount of  stack  that  can  be         Limiting the recursion depth limits the amount of  stack  that  can  be
# Line 1739  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1956  MATCHING A PATTERN: THE TRADITIONAL FUNC
1956         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1957         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1958    
1959         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  callout_data  field is used in conjunction with the "callout" fea-
1960         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
1961    
1962         The tables field  is  used  to  pass  a  character  tables  pointer  to         The tables field  is  used  to  pass  a  character  tables  pointer  to
1963         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec();  this overrides the value that is stored with the compiled
# Line 1757  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1974  MATCHING A PATTERN: THE TRADITIONAL FUNC
1974    
1975         The  unused  bits of the options argument for pcre_exec() must be zero.         The  unused  bits of the options argument for pcre_exec() must be zero.
1976         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1977         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
1978         PCRE_PARTIAL.         PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
1979           PCRE_PARTIAL_HARD.
1980    
1981           PCRE_ANCHORED           PCRE_ANCHORED
1982    
1983         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1984         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1985         turned out to be anchored by virtue of its contents, it cannot be  made         turned  out to be anchored by virtue of its contents, it cannot be made
1986         unachored at matching time.         unachored at matching time.
1987    
1988             PCRE_BSR_ANYCRLF
1989             PCRE_BSR_UNICODE
1990    
1991           These options (which are mutually exclusive) control what the \R escape
1992           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1993           or to match any Unicode newline sequence. These  options  override  the
1994           choice that was made or defaulted when the pattern was compiled.
1995    
1996           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1997           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1998           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
# Line 1778  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2004  MATCHING A PATTERN: THE TRADITIONAL FUNC
2004         tion  of  pcre_compile()  above.  During  matching,  the newline choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
2005         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
2006         ters.  It may also alter the way the match position is advanced after a         ters.  It may also alter the way the match position is advanced after a
2007         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
2008         PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt  
2009         fails when the current position is at a CRLF sequence, the match  posi-         When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
2010         tion  is  advanced by two characters instead of one, in other words, to         set,  and a match attempt for an unanchored pattern fails when the cur-
2011         after the CRLF.         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
2012           explicit  matches  for  CR  or  LF  characters,  the  match position is
2013           advanced by two characters instead of one, in other words, to after the
2014           CRLF.
2015    
2016           The above rule is a compromise that makes the most common cases work as
2017           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
2018           option is not set), it does not match the string "\r\nA" because, after
2019           failing at the start, it skips both the CR and the LF before  retrying.
2020           However,  the  pattern  [\r\n]A does match that string, because it con-
2021           tains an explicit CR or LF reference, and so advances only by one char-
2022           acter after the first failure.
2023    
2024           An explicit match for CR of LF is either a literal appearance of one of
2025           those characters, or one of the \r or  \n  escape  sequences.  Implicit
2026           matches  such  as [^X] do not count, nor does \s (which includes CR and
2027           LF in the characters that it matches).
2028    
2029           Notwithstanding the above, anomalous effects may still occur when  CRLF
2030           is a valid newline sequence and explicit \r or \n escapes appear in the
2031           pattern.
2032    
2033           PCRE_NOTBOL           PCRE_NOTBOL
2034    
# Line 1810  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2056  MATCHING A PATTERN: THE TRADITIONAL FUNC
2056    
2057           a?b?           a?b?
2058    
2059         is applied to a string not beginning with "a" or "b",  it  matches  the         is applied to a string not beginning with "a" or  "b",  it  matches  an
2060         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2061         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
2062         rences of "a" or "b".         rences of "a" or "b".
2063    
2064         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2065         cial case of a pattern match of the empty  string  within  its  split()  
2066         function,  and  when  using  the /g modifier. It is possible to emulate         This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2067         Perl's behaviour after matching a null string by first trying the match         not at the start of  the  subject  is  permitted.  If  the  pattern  is
2068         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         anchored, such a match can occur only if the pattern contains \K.
2069         if that fails by advancing the starting offset (see below)  and  trying  
2070         an ordinary match again. There is some code that demonstrates how to do         Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2071         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2072           match  of  the empty string within its split() function, and when using
2073           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2074           matching a null string by first trying the match again at the same off-
2075           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2076           fails, by advancing the starting offset (see below) and trying an ordi-
2077           nary match again. There is some code that demonstrates how to  do  this
2078           in the pcredemo sample program.
2079    
2080             PCRE_NO_START_OPTIMIZE
2081    
2082           There  are a number of optimizations that pcre_exec() uses at the start
2083           of a match, in order to speed up the process. For  example,  if  it  is
2084           known  that  a  match must start with a specific character, it searches
2085           the subject for that character, and fails immediately if it cannot find
2086           it,  without actually running the main matching function. When callouts
2087           are in use, these optimizations can cause  them  to  be  skipped.  This
2088           option  disables  the  "start-up" optimizations, causing performance to
2089           suffer, but ensuring that the callouts do occur.
2090    
2091           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2092    
2093         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
2094         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
2095         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
2096         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points  to  the start of a UTF-8 character. There is a discussion about
2097         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the validity of UTF-8 strings in the section on UTF-8  support  in  the
2098         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2099         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2100           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2101         If you already know that your subject is valid, and you  want  to  skip  
2102         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
2103         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
2104         do  this  for the second and subsequent calls to pcre_exec() if you are         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2105         making repeated calls to find all  the  matches  in  a  single  subject         do this for the second and subsequent calls to pcre_exec() if  you  are
2106         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
2107         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         string. However, you should be  sure  that  the  value  of  startoffset
2108         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2109         value of startoffset that does not point to the start of a UTF-8  char-         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2110           value  of startoffset that does not point to the start of a UTF-8 char-
2111         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2112    
2113           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2114             PCRE_PARTIAL_SOFT
2115    
2116         This  option  turns  on  the  partial  matching feature. If the subject         These options turn on the partial matching feature. For backwards  com-
2117         string fails to match the pattern, but at some point during the  match-         patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2118         ing  process  the  end of the subject was reached (that is, the subject         match occurs if the end of the subject string is reached  successfully,
2119         partially matches the pattern and the failure to  match  occurred  only         but  there  are not enough subject characters to complete the match. If
2120         because  there were not enough subject characters), pcre_exec() returns         this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2121         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2122         used,  there  are restrictions on what may appear in the pattern. These         matching continues by testing any other alternatives. Only if they  all
2123         are discussed in the pcrepartial documentation.         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2124           The portion of the string that was inspected when the partial match was
2125           found  is  set  as  the first matching string. There is a more detailed
2126           discussion in the pcrepartial documentation.
2127    
2128     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2129    
2130         The subject string is passed to pcre_exec() as a pointer in subject,  a         The subject string is passed to pcre_exec() as a pointer in subject,  a
2131         length  in  length, and a starting byte offset in startoffset. In UTF-8         length (in bytes) in length, and a starting byte offset in startoffset.
2132         mode, the byte offset must point to the start  of  a  UTF-8  character.         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2133         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter.  Unlike  the pattern string, the subject may contain binary zero
2134         When the starting offset is zero, the search for a match starts at  the         bytes. When the starting offset is zero, the search for a match  starts
2135         beginning of the subject, and this is by far the most common case.         at  the  beginning  of  the subject, and this is by far the most common
2136           case.
2137         A  non-zero  starting offset is useful when searching for another match  
2138         in the same subject by calling pcre_exec() again after a previous  suc-         A non-zero starting offset is useful when searching for  another  match
2139         cess.   Setting  startoffset differs from just passing over a shortened         in  the same subject by calling pcre_exec() again after a previous suc-
2140         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         cess.  Setting startoffset differs from just passing over  a  shortened
2141           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2142         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2143    
2144           \Biss\B           \Biss\B
2145    
2146         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2147         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
2148         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2149         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2150         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2151         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
2152         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
2153         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
2154         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
2155         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2156    
2157         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,
2158         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2159         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
2160         subject.         subject.
2161    
2162     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2163    
2164         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2165         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2166         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2167         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2168         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2169         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2170         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2171    
2172         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2173         offsets whose address is passed in ovector. The number of  elements  in         whose  address is passed in ovector. The number of elements in the vec-
2174         the  vector is passed in ovecsize, which must be a non-negative number.         tor is passed in ovecsize, which must be a non-negative  number.  Note:
2175         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2176    
2177         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2178         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2179         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2180         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2181         The length passed in ovecsize should always be a multiple of three.  If         The  number passed in ovecsize should always be a multiple of three. If
2182         it is not, it is rounded down.         it is not, it is rounded down.
2183    
2184         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2185         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2186         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
2187         element of a pair is set to the offset of the first character in a sub-         element  of  each pair is set to the byte offset of the first character
2188         string,  and  the  second  is  set to the offset of the first character         in a substring, and the second is set to the byte offset of  the  first
2189         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         character  after  the end of a substring. Note: these values are always
2190         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2191         entire pattern. The next pair is used for the first  capturing  subpat-  
2192         tern, and so on. The value returned by pcre_exec() is one more than the         The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2193         highest numbered pair that has been set. For example, if two substrings         portion  of  the subject string matched by the entire pattern. The next
2194         have  been captured, the returned value is 3. If there are no capturing         pair is used for the first capturing subpattern, and so on.  The  value
2195         subpatterns, the return value from a successful match is 1,  indicating         returned by pcre_exec() is one more than the highest numbered pair that
2196         that just the first pair of offsets has been set.         has been set.  For example, if two substrings have been  captured,  the
2197           returned  value is 3. If there are no capturing subpatterns, the return
2198           value from a successful match is 1, indicating that just the first pair
2199           of offsets has been set.
2200    
2201         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2202         of the string that it matched that is returned.         of the string that it matched that is returned.
2203    
2204         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,
2205         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2206         function returns a value of zero. In particular, if the substring  off-         function returns a value of zero. If the substring offsets are  not  of
2207         sets are not of interest, pcre_exec() may be called with ovector passed         interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2208         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         ovecsize as zero. However, if the pattern contains back references  and
2209         references  and  the  ovector is not big enough to remember the related         the  ovector is not big enough to remember the related substrings, PCRE
2210         substrings, PCRE has to get additional memory for use during  matching.         has to get additional memory for use during matching. Thus it  is  usu-
2211         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2212    
2213         The  pcre_info()  function  can  be used to find out how many capturing         The pcre_fullinfo() function can be used to find out how many capturing
2214         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2215         ovector  that  will allow for n captured substrings, in addition to the         ovector  that  will allow for n captured substrings, in addition to the
2216         offsets of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
# Line 2036  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2309  MATCHING A PATTERN: THE TRADITIONAL FUNC
2309    
2310           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2311    
2312         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2313         items  that are not supported for partial matching. See the pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2314         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2315           onwards, there are no restrictions on partial matching.
2316    
2317           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2318    
2319         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2320         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2321    
2322           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2323    
2324         This  error is given if the value of the ovecsize argument is negative.         This error is given if the value of the ovecsize argument is negative.
2325    
2326           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2327    
# Line 2197  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2471  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2471         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2472         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2473    
2474           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2475           terns  with  the  same number, as described in the section on duplicate
2476           subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2477           distinguish  the  different subpatterns, because names are not included
2478           in the compiled code. The matching process uses only numbers. For  this
2479           reason,  the  use of different names for subpatterns of the same number
2480           causes an error at compile time.
2481    
2482    
2483  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2484    
# Line 2204  DUPLICATE SUBPATTERN NAMES Line 2486  DUPLICATE SUBPATTERN NAMES
2486              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2487    
2488         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2489         subpatterns  are  not  required  to  be unique. Normally, patterns with         subpatterns  are not required to be unique. (Duplicate names are always
2490         duplicate names are such that in any one match, only one of  the  named         allowed for subpatterns with the same number, created by using the  (?|
2491         subpatterns  participates. An example is shown in the pcrepattern docu-         feature.  Indeed,  if  such subpatterns are named, they are required to
2492         mentation.         use the same names.)
2493    
2494           Normally, patterns with duplicate names are such that in any one match,
2495           only  one of the named subpatterns participates. An example is shown in
2496           the pcrepattern documentation.
2497    
2498         When   duplicates   are   present,   pcre_copy_named_substring()    and         When   duplicates   are   present,   pcre_copy_named_substring()    and
2499         pcre_get_named_substring()  return the first substring corresponding to         pcre_get_named_substring()  return the first substring corresponding to
# Line 2260  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2546  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2546         characteristics  to  the  normal  algorithm, and is not compatible with         characteristics  to  the  normal  algorithm, and is not compatible with
2547         Perl. Some of the features of PCRE patterns are not  supported.  Never-         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2548         theless,  there are times when this kind of matching can be useful. For         theless,  there are times when this kind of matching can be useful. For
2549         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, and  a  list  of  features
2550         mentation.         that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2551           tion.
2552    
2553         The  arguments  for  the  pcre_dfa_exec()  function are the same as for         The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2554         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
2555         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2556         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2557         repeated here.         repeated here.
2558    
2559         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2560         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2561         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2562         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2563         lot of potential matches.         lot of potential matches.
2564    
2565         Here is an example of a simple call to pcre_dfa_exec():         Here is an example of a simple call to pcre_dfa_exec():
# Line 2294  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2581  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2581    
2582     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2583    
2584         The  unused  bits  of  the options argument for pcre_dfa_exec() must be         The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2585         zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2586         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2587         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2588         three of these are the same as for pcre_exec(), so their description is         TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last
2589         not repeated here.         four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2590           description is not repeated here.
2591           PCRE_PARTIAL  
2592             PCRE_PARTIAL_HARD
2593         This has the same general effect as it does for  pcre_exec(),  but  the           PCRE_PARTIAL_SOFT
2594         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for  
2595         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         These have the same general effect as they do for pcre_exec(), but  the
2596         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2597         been no complete matches, but there is still at least one matching pos-         pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub-
2598         sibility.  The portion of the string that provided the partial match is         ject  is  reached  and there is still at least one matching possibility
2599         set as the first matching string.         that requires additional characters. This happens even if some complete
2600           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2601           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2602           of  the  subject  is  reached, there have been no complete matches, but
2603           there is still at least one matching possibility. The  portion  of  the
2604           string  that  was inspected when the longest partial match was found is
2605           set as the first matching string in both cases.
2606    
2607           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2608    
# Line 2320  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2613  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2613    
2614           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2615    
2616         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec() returns a partial match, it is possible to call it
2617         returns a partial match, it is possible to call it  again,  with  addi-         again, with additional subject characters, and have  it  continue  with
2618         tional  subject  characters,  and have it continue with the same match.         the  same match. The PCRE_DFA_RESTART option requests this action; when
2619         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         it is set, the workspace and wscount options must  reference  the  same
2620         workspace  and wscount options must reference the same vector as before         vector  as  before  because data about the match so far is left in them
2621         because data about the match so far is left in  them  after  a  partial         after a partial match. There is more discussion of this facility in the
2622         match.  There  is  more  discussion of this facility in the pcrepartial         pcrepartial documentation.
        documentation.  
2623    
2624     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2625    
2626         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2627         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2628         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2629         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2630         if the pattern         if the pattern
2631    
2632           <.*>           <.*>
# Line 2349  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2641  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2641           <something> <something else>           <something> <something else>
2642           <something> <something else> <something further>           <something> <something else> <something further>
2643    
2644         On success, the yield of the function is a number  greater  than  zero,         On  success,  the  yield of the function is a number greater than zero,
2645         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2646         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2647         the  offset  to  the start, and the second is the offset to the end. In         the offset to the start, and the second is the offset to  the  end.  In
2648         fact, all the strings have the same start  offset.  (Space  could  have         fact,  all  the  strings  have the same start offset. (Space could have
2649         been  saved by giving this only once, but it was decided to retain some         been saved by giving this only once, but it was decided to retain  some
2650         compatibility with the way pcre_exec() returns data,  even  though  the         compatibility  with  the  way pcre_exec() returns data, even though the
2651         meaning of the strings is different.)         meaning of the strings is different.)
2652    
2653         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2654         est matching string is given first. If there were too many  matches  to         est  matching  string is given first. If there were too many matches to
2655         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2656         filled with the longest matches.         filled with the longest matches.
2657    
2658     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2659    
2660         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2661         Many  of  the  errors  are  the  same as for pcre_exec(), and these are         Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2662         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2663         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2664    
2665           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2666    
2667         This  return is given if pcre_dfa_exec() encounters an item in the pat-         This return is given if pcre_dfa_exec() encounters an item in the  pat-
2668         tern that it does not support, for instance, the use of \C  or  a  back         tern  that  it  does not support, for instance, the use of \C or a back
2669         reference.         reference.
2670    
2671           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2672    
2673         This  return  is  given  if pcre_dfa_exec() encounters a condition item         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2674         that uses a back reference for the condition, or a test  for  recursion         that  uses  a back reference for the condition, or a test for recursion
2675         in a specific group. These are not supported.         in a specific group. These are not supported.
2676    
2677           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2678    
2679         This  return  is given if pcre_dfa_exec() is called with an extra block         This return is given if pcre_dfa_exec() is called with an  extra  block
2680         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2681         (it is meaningless).         (it is meaningless).
2682    
2683           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2684    
2685         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2686         workspace vector.         workspace vector.
2687    
2688           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2689    
2690         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2691         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2692         This error is given if the output vector  is  not  large  enough.  This         This  error  is  given  if  the output vector is not large enough. This
2693         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2694    
2695    
2696  SEE ALSO  SEE ALSO
2697    
2698         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2699         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2700    
2701    
2702  AUTHOR  AUTHOR
# Line 2416  AUTHOR Line 2708  AUTHOR
2708    
2709  REVISION  REVISION
2710    
2711         Last updated: 30 July 2007         Last updated: 03 October 2009
2712         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2713  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2714    
2715    
# Line 2446  PCRE CALLOUTS Line 2738  PCRE CALLOUTS
2738    
2739           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2740    
2741         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
2742         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2743         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is         with  number  255,  before  each  item  in the pattern. For example, if
2744         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2745    
2746           A(\d{2}|--)           A(\d{2}|--)
2747    
# Line 2468  PCRE CALLOUTS Line 2760  PCRE CALLOUTS
2760  MISSING CALLOUTS  MISSING CALLOUTS
2761    
2762         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2763         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2764         pattern is         example, if the pattern is
2765    
2766           ab(?C4)cd           ab(?C4)cd
2767    
# Line 2478  MISSING CALLOUTS Line 2770  MISSING CALLOUTS
2770         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2771         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2772    
2773           If the pattern is studied, PCRE knows the minimum length of a  matching
2774           string,  and will immediately give a "no match" return without actually
2775           running a match if the subject is not long enough, or,  for  unanchored
2776           patterns, if it has been scanned far enough.
2777    
2778           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2779           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2780           matching  process,  but  does  ensure that callouts such as the example
2781           above are obeyed.
2782    
2783    
2784  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2785    
# Line 2505  THE CALLOUT INTERFACE Line 2807  THE CALLOUT INTERFACE
2807         version number will change again in future  if  additional  fields  are         version number will change again in future  if  additional  fields  are
2808         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2809    
2810         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2811         piled  into  the pattern (that is, the number after ?C for manual call-         piled into the pattern (that is, the number after ?C for  manual  call-
2812         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2813    
2814         The offset_vector field is a pointer to the vector of offsets that  was         The  offset_vector field is a pointer to the vector of offsets that was
2815         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2816         pcre_exec() is used, the contents can be inspected in order to  extract         pcre_exec()  is used, the contents can be inspected in order to extract
2817         substrings  that  have  been  matched  so  far,  in the same way as for         substrings that have been matched so  far,  in  the  same  way  as  for
2818         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2819         this field is not useful.         this field is not useful.
2820    
2821         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2822         were passed to pcre_exec().         were passed to pcre_exec().
2823    
2824         The start_match field normally contains the offset within  the  subject         The  start_match  field normally contains the offset within the subject
2825         at  which  the  current  match  attempt started. However, if the escape         at which the current match attempt  started.  However,  if  the  escape
2826         sequence \K has been encountered, this value is changed to reflect  the         sequence  \K has been encountered, this value is changed to reflect the
2827         modified  starting  point.  If the pattern is not anchored, the callout         modified starting point. If the pattern is not  anchored,  the  callout
2828         function may be called several times from the same point in the pattern         function may be called several times from the same point in the pattern
2829         for different starting points in the subject.         for different starting points in the subject.
2830    
2831         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2832         the current match pointer.         the current match pointer.
2833    
2834         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2835         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2836         far. If no substrings have been captured, the value of  capture_top  is         far.  If  no substrings have been captured, the value of capture_top is
2837         one.  This  is always the case when pcre_dfa_exec() is used, because it         one. This is always the case when pcre_dfa_exec() is used,  because  it
2838         does not support captured substrings.         does not support captured substrings.
2839    
2840         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2841         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2842         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2843    
2844         The callout_data field contains a value that is passed  to  pcre_exec()         The  callout_data  field contains a value that is passed to pcre_exec()
2845         or  pcre_dfa_exec() specifically so that it can be passed back in call-         or pcre_dfa_exec() specifically so that it can be passed back in  call-
2846         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data         outs.  It  is  passed  in the pcre_callout field of the pcre_extra data
2847         structure.  If  no such data was passed, the value of callout_data in a         structure. If no such data was passed, the value of callout_data  in  a
2848         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout  block  is  NULL. There is a description of the pcre_extra
2849         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2850    
2851         The  pattern_position field is present from version 1 of the pcre_call-         The pattern_position field is present from version 1 of the  pcre_call-
2852         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2853         the pattern string.         the pattern string.
2854    
2855         The  next_item_length field is present from version 1 of the pcre_call-         The next_item_length field is present from version 1 of the  pcre_call-
2856         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2857         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2858         tion bar, a closing parenthesis, or the end of the pattern, the  length         tion  bar, a closing parenthesis, or the end of the pattern, the length
2859         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2860         is that of the entire subpattern.         is that of the entire subpattern.
2861    
2862         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2863         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2864         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2865    
2866    
2867  RETURN VALUES  RETURN VALUES
2868    
2869         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2870         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2871         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2872         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2873         failed. If the value is less than zero, the  match  is  abandoned,  and         failed.  If  the  value  is less than zero, the match is abandoned, and
2874         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2875    
2876         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2877         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2878         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2879         reserved for use by callout functions; it will never be  used  by  PCRE         reserved  for  use  by callout functions; it will never be used by PCRE
2880         itself.         itself.
2881    
2882    
# Line 2587  AUTHOR Line 2889  AUTHOR
2889    
2890  REVISION  REVISION
2891    
2892         Last updated: 29 May 2007         Last updated: 29 September 2009
2893         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2894  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2895    
2896    
# Line 2602  NAME Line 2904  NAME
2904  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2905    
2906         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2907         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences  described  here  are  with
2908         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         respect to Perl 5.10.
        some features that are expected to be in the forthcoming Perl 5.10.  
2909    
2910         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
2911         of  what  it does have are given in the section on UTF-8 support in the         of what it does have are given in the section on UTF-8 support  in  the
2912         main pcre page.         main pcre page.
2913    
2914         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2915         permits  them,  but they do not mean what you might think. For example,         permits them, but they do not mean what you might think.  For  example,
2916         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
2917         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
2918    
2919         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
2920         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
2921         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
2922         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
2923         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
2924         branch.         branch.
2925    
2926         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
2927         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2928         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
2929         the pattern to represent a binary zero.         the pattern to represent a binary zero.
2930    
2931         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
2932         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
2933         dling  and are not part of its pattern matching engine. If any of these         dling and are not part of its pattern matching engine. If any of  these
2934         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2935    
2936         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE
2937         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
2938         can be tested with \p and \P are limited to the general category  prop-         can  be tested with \p and \P are limited to the general category prop-
2939         erties  such  as  Lu and Nd, script names such as Greek or Han, and the         erties such as Lu and Nd, script names such as Greek or  Han,  and  the
2940         derived properties Any and L&.         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
2941           property, which Perl does not; the  Perl  documentation  says  "Because
2942           Perl hides the need for the user to understand the internal representa-
2943           tion of Unicode characters, there is no need to implement the  somewhat
2944           messy concept of surrogates."
2945    
2946         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2947         ters  in  between  are  treated as literals. This is slightly different         ters in between are treated as literals.  This  is  slightly  different
2948         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from  Perl  in  that  $  and  @ are also handled as literals inside the
2949         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
2950         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2951    
2952             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2651  DIFFERENCES BETWEEN PCRE AND PERL Line 2956  DIFFERENCES BETWEEN PCRE AND PERL
2956             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2957             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2958    
2959         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
2960         classes.         classes.
2961    
2962         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2963         constructions. However, there is support for recursive  patterns.  This         constructions.  However,  there is support for recursive patterns. This
2964         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE         is not available in Perl 5.8, but it is in Perl 5.10.  Also,  the  PCRE
2965         "callout" feature allows an external function to be called during  pat-         "callout"  feature allows an external function to be called during pat-
2966         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2967    
2968         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
2969         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always  treated  as  atomic  groups  in  PCRE. This is like Python, but
2970         unlike Perl.         unlike Perl. There is a discussion of an example that explains this  in
2971           more  detail  in  the section on recursion differences from Perl in the
2972         10.  There are some differences that are concerned with the settings of         pcrepattern page.
2973         captured strings when part of  a  pattern  is  repeated.  For  example,  
2974         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         10. There are some differences that are concerned with the settings  of
2975           captured  strings  when  part  of  a  pattern is repeated. For example,
2976           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
2977         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2978    
2979         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2980         ities.   Perl  5.10  will  include new features that are not in earlier         (*FAIL), (*F), (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but  only  in
2981         versions, some of which (such as named parentheses) have been  in  PCRE         the forms without an argument. PCRE does not support (*MARK).
2982         for some time. This list is with respect to Perl 5.10:  
2983           12.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
2984         (a)  Although  lookbehind  assertions  must match fixed length strings,         pattern names is not as general as Perl's. This is a consequence of the
2985         each alternative branch of a lookbehind assertion can match a different         fact the PCRE works internally just with numbers, using an external ta-
2986         length of string. Perl requires them all to have the same length.         ble to translate between numbers and names. In  particular,  a  pattern
2987           such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
2988           the same number but different names, is not supported,  and  causes  an
2989           error  at compile time. If it were allowed, it would not be possible to
2990           distinguish which parentheses matched, because both names map  to  cap-
2991           turing subpattern number 1. To avoid this confusing situation, an error
2992           is given at compile time.
2993    
2994           13. PCRE provides some extensions to the Perl regular expression facil-
2995           ities.   Perl  5.10  includes new features that are not in earlier ver-
2996           sions of Perl, some of which (such as named parentheses) have  been  in
2997           PCRE for some time. This list is with respect to Perl 5.10:
2998    
2999           (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3000           strings, each alternative branch of a lookbehind assertion can match  a
3001           different  length  of  string.  Perl requires them all to have the same
3002           length.
3003    
3004         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
3005         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3006    
3007         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
3008         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3009         ignored.  (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
3010    
3011         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3012         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
3013         lowed by a question mark they are.         lowed by a question mark they are.
3014    
3015         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
3016         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3017    
3018         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3019         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3020           lents.
3021    
3022           (g) The \R escape sequence can be restricted to match only CR,  LF,  or
3023           CRLF by the PCRE_BSR_ANYCRLF option.
3024    
3025         (g) The callout facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
3026    
3027         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
3028    
3029         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
3030         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
3031    
3032         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
3033         different way and is not Perl-compatible.         different way and is not Perl-compatible.
3034    
3035           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
3036           of a pattern that set overall options that cannot be changed within the
3037           pattern.
3038    
3039    
3040  AUTHOR  AUTHOR
3041    
# Line 2715  AUTHOR Line 3046  AUTHOR
3046    
3047  REVISION  REVISION
3048    
3049         Last updated: 13 June 2007         Last updated: 04 October 2009
3050         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
3051  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3052    
3053    
# Line 2731  PCRE REGULAR EXPRESSION DETAILS Line 3062  PCRE REGULAR EXPRESSION DETAILS
3062    
3063         The  syntax and semantics of the regular expressions that are supported         The  syntax and semantics of the regular expressions that are supported
3064         by PCRE are described in detail below. There is a quick-reference  syn-         by PCRE are described in detail below. There is a quick-reference  syn-
3065         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
3066         described in its own documentation, and regular expressions in  general         semantics as closely as it can. PCRE  also  supports  some  alternative
3067         are  covered in a number of books, some of which have copious examples.         regular  expression  syntax (which does not conflict with the Perl syn-
3068         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by         tax) in order to provide some compatibility with regular expressions in
3069         O'Reilly,  covers regular expressions in great detail. This description         Python, .NET, and Oniguruma.
3070         of PCRE's regular expressions is intended as reference material.  
3071           Perl's  regular expressions are described in its own documentation, and
3072           regular expressions in general are covered in a number of  books,  some
3073           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
3074           Expressions", published by  O'Reilly,  covers  regular  expressions  in
3075           great  detail.  This  description  of  PCRE's  regular  expressions  is
3076           intended as reference material.
3077    
3078         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3079         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
3080         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, PCRE must be built to include UTF-8 support, and  you  must  call
3081         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3082         matching is mentioned in several places below. There is also a  summary         also a special sequence that can be given at the start of a pattern:
3083         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3084         page.           (*UTF8)
3085    
3086           Starting a pattern with this sequence  is  equivalent  to  setting  the
3087           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3088           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3089           below.  There  is  also  a  summary of UTF-8 features in the section on
3090           UTF-8 support in the main pcre page.
3091    
3092         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3093         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
# Line 2756  PCRE REGULAR EXPRESSION DETAILS Line 3099  PCRE REGULAR EXPRESSION DETAILS
3099         discussed in the pcrematching page.         discussed in the pcrematching page.
3100    
3101    
3102    NEWLINE CONVENTIONS
3103    
3104           PCRE  supports five different conventions for indicating line breaks in
3105           strings: a single CR (carriage return) character, a  single  LF  (line-
3106           feed) character, the two-character sequence CRLF, any of the three pre-
3107           ceding, or any Unicode newline sequence. The pcreapi page  has  further
3108           discussion  about newlines, and shows how to set the newline convention
3109           in the options arguments for the compiling and matching functions.
3110    
3111           It is also possible to specify a newline convention by starting a  pat-
3112           tern string with one of the following five sequences:
3113    
3114             (*CR)        carriage return
3115             (*LF)        linefeed
3116             (*CRLF)      carriage return, followed by linefeed
3117             (*ANYCRLF)   any of the three above
3118             (*ANY)       all Unicode newline sequences
3119    
3120           These  override  the default and the options given to pcre_compile() or
3121           pcre_compile2(). For example, on a Unix system where LF is the  default
3122           newline sequence, the pattern
3123    
3124             (*CR)a.b
3125    
3126           changes the convention to CR. That pattern matches "a\nb" because LF is
3127           no longer a newline. Note that these special settings,  which  are  not
3128           Perl-compatible,  are  recognized  only at the very start of a pattern,
3129           and that they must be in upper case.  If  more  than  one  of  them  is
3130           present, the last one is used.
3131    
3132           The  newline  convention  does  not  affect what the \R escape sequence
3133           matches. By default, this is any Unicode  newline  sequence,  for  Perl
3134           compatibility.  However, this can be changed; see the description of \R
3135           in the section entitled "Newline sequences" below. A change of \R  set-
3136           ting can be combined with a change of newline convention.
3137    
3138    
3139  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
3140    
3141         A  regular  expression  is  a pattern that is matched against a subject         A  regular  expression  is  a pattern that is matched against a subject
# Line 2811  CHARACTERS AND METACHARACTERS Line 3191  CHARACTERS AND METACHARACTERS
3191                    syntax)                    syntax)
3192           ]      terminates the character class           ]      terminates the character class
3193    
3194         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the metacharacters.
3195    
3196    
3197  BACKSLASH  BACKSLASH
3198    
3199         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3200         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
3201         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
3202         applies both inside and outside character classes.         applies both inside and outside character classes.
3203    
3204         For  example,  if  you want to match a * character, you write \* in the         For example, if you want to match a * character, you write  \*  in  the
3205         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
3206         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
3207         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
3208         that  it stands for itself. In particular, if you want to match a back-         that it stands for itself. In particular, if you want to match a  back-
3209         slash, you write \\.         slash, you write \\.
3210    
3211         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3212         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
3213         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3214         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
3215         part of the pattern.         part of the pattern.
3216    
3217         If you want to remove the special meaning from a  sequence  of  charac-         If  you  want  to remove the special meaning from a sequence of charac-
3218         ters,  you can do so by putting them between \Q and \E. This is differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
3219         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
3220         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
3221         tion. Note the following examples:         tion. Note the following examples:
3222    
3223           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2847  BACKSLASH Line 3227  BACKSLASH
3227           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3228           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3229    
3230         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3231         classes.         classes.
3232    
3233     Non-printing characters     Non-printing characters
3234    
3235         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3236         acters in patterns in a visible manner. There is no restriction on  the         acters  in patterns in a visible manner. There is no restriction on the
3237         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3238         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3239         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3240         sequences than the binary character it represents:         sequences than the binary character it represents:
3241    
3242           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3243           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3244           \e        escape (hex 1B)           \e        escape (hex 1B)
3245           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3246           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3247           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3248           \t        tab (hex 09)           \t        tab (hex 09)
3249           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3250           \xhh      character with hex code hh           \xhh      character with hex code hh
3251           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3252    
3253         The precise effect of \cx is as follows: if x is a lower  case  letter,         The  precise  effect of \cx is as follows: if x is a lower case letter,
3254         it  is converted to upper case. Then bit 6 of the character (hex 40) is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
3255         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
3256         becomes hex 7B.         becomes hex 7B.
3257    
3258         After  \x, from zero to two hexadecimal digits are read (letters can be         After \x, from zero to two hexadecimal digits are read (letters can  be
3259         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3260         between  \x{  and  },  but the value of the character code must be less         between \x{ and }, but the value of the character  code  must  be  less
3261         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3262         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3263         hexadecimal digits appear between \x{ and }, or if there is  no  termi-         than the largest Unicode code point, which is 10FFFF.
3264         nating  }, this form of escape is not recognized.  Instead, the initial  
3265         \x will be interpreted as a basic hexadecimal escape, with no following         If  characters  other than hexadecimal digits appear between \x{ and },
3266         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3267           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3268           escape, with no following digits, giving a  character  whose  value  is
3269           zero.
3270    
3271         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
3272         two syntaxes for \x. There is no difference in the way  they  are  han-         two syntaxes for \x. There is no difference in the way  they  are  han-
# Line 2943  BACKSLASH Line 3326  BACKSLASH
3326         named back reference can be coded as \g{name}. Back references are dis-         named back reference can be coded as \g{name}. Back references are dis-
3327         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3328    
3329       Absolute and relative subroutine calls
3330    
3331           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3332           name or a number enclosed either in angle brackets or single quotes, is
3333           an alternative syntax for referencing a subpattern as  a  "subroutine".
3334           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3335           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3336           reference; the latter is a subroutine call.
3337    
3338     Generic character types     Generic character types
3339    
3340         Another use of backslash is for specifying generic character types. The         Another use of backslash is for specifying generic character types. The
# Line 2960  BACKSLASH Line 3352  BACKSLASH
3352           \W     any "non-word" character           \W     any "non-word" character
3353    
3354         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3355         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3356         of each pair.         of each pair.
3357    
3358         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3359         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3360         If  the current matching point is at the end of the subject string, all         If the current matching point is at the end of the subject string,  all
3361         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3362    
3363         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3364         11).   This makes it different from the the POSIX "space" class. The \s         11).  This makes it different from the the POSIX "space" class. The  \s
3365         characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3366         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3367         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3368    
3369         In UTF-8 mode, characters with values greater than 128 never match  \d,         In  UTF-8 mode, characters with values greater than 128 never match \d,
3370         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3371         code character property support is available.  These  sequences  retain         code  character  property  support is available. These sequences retain
3372         their original meanings from before UTF-8 support was available, mainly         their original meanings from before UTF-8 support was available, mainly
3373         for efficiency reasons.         for  efficiency  reasons. Note that this also affects \b, because it is
3374           defined in terms of \w and \W.
3375    
3376         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3377         the  other  sequences, these do match certain high-valued codepoints in         the  other  sequences, these do match certain high-valued codepoints in
# Line 3025  BACKSLASH Line 3418  BACKSLASH
3418    
3419     Newline sequences     Newline sequences
3420    
3421         Outside  a  character class, the escape sequence \R matches any Unicode         Outside  a  character class, by default, the escape sequence \R matches
3422         newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R  is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3423         equivalent to the following:         mode \R is equivalent to the following:
3424    
3425           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3426    
# Line 3043  BACKSLASH Line 3436  BACKSLASH
3436         rator, U+2029).  Unicode character property support is not  needed  for         rator, U+2029).  Unicode character property support is not  needed  for
3437         these characters to be recognized.         these characters to be recognized.
3438    
3439           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3440           the complete set  of  Unicode  line  endings)  by  setting  the  option
3441           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3442           (BSR is an abbrevation for "backslash R".) This can be made the default
3443           when  PCRE  is  built;  if this is the case, the other behaviour can be
3444           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3445           specify  these  settings  by  starting a pattern string with one of the
3446           following sequences:
3447    
3448             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3449             (*BSR_UNICODE)   any Unicode newline sequence
3450    
3451           These override the default and the options given to  pcre_compile()  or
3452           pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3453           pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3454           are  not  Perl-compatible,  are  recognized only at the very start of a
3455           pattern, and that they must be in upper case. If more than one of  them
3456           is present, the last one is used. They can be combined with a change of
3457           newline convention, for example, a pattern can start with:
3458    
3459             (*ANY)(*BSR_ANYCRLF)
3460    
3461         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3462    
3463     Unicode character properties     Unicode character properties
3464    
3465         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3466         tional escape sequences that match characters with specific  properties         tional  escape sequences that match characters with specific properties
3467         are  available.   When not in UTF-8 mode, these sequences are of course         are available.  When not in UTF-8 mode, these sequences are  of  course
3468         limited to testing characters whose codepoints are less than  256,  but         limited  to  testing characters whose codepoints are less than 256, but
3469         they do work in this mode.  The extra escape sequences are:         they do work in this mode.  The extra escape sequences are:
3470    
3471           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3472           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3473           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3474    
3475         The  property  names represented by xx above are limited to the Unicode         The property names represented by xx above are limited to  the  Unicode
3476         script names, the general category properties, and "Any", which matches         script names, the general category properties, and "Any", which matches
3477         any character (including newline). Other properties such as "InMusical-         any character (including newline). Other properties such as "InMusical-
3478         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
3479         not match any characters, so always causes a match failure.         not match any characters, so always causes a match failure.
3480    
3481         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3482         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.
3483         For example:         For example:
3484    
3485           \p{Greek}           \p{Greek}
3486           \P{Han}           \P{Han}
3487    
3488         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
3489         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3490    
3491         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3492         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,         Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,  Cherokee,  Common,
3493         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Coptic,   Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,  Egyp-
3494         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-         tian_Hieroglyphs,  Ethiopic,  Georgian,  Glagolitic,   Gothic,   Greek,
3495         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,         Gujarati,  Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana, Impe-
3496         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3497         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,         Javanese,  Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,
3498         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Latin,  Lepcha,  Limbu,  Linear_B,  Lisu,  Lycian,  Lydian,  Malayalam,
3499         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Meetei_Mayek,  Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,
3500           Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki,  Oriya,  Osmanya,
3501           Phags_Pa,  Phoenician,  Rejang,  Runic, Samaritan, Saurashtra, Shavian,
3502           Sinhala, Sundanese, Syloti_Nagri, Syriac,  Tagalog,  Tagbanwa,  Tai_Le,
3503           Tai_Tham,  Tai_Viet,  Tamil,  Telugu,  Thaana, Thai, Tibetan, Tifinagh,
3504           Ugaritic, Vai, Yi.
3505    
3506         Each character has exactly one general category property, specified  by         Each character has exactly one general category property, specified  by
3507         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
# Line 3146  BACKSLASH Line 3566  BACKSLASH
3566         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3567         classified as a modifier or "other".         classified as a modifier or "other".
3568    
3569         The long synonyms for these properties  that  Perl  supports  (such  as         The Cs (Surrogate) property applies only to  characters  in  the  range
3570           U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3571           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3572           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3573           the pcreapi page). Perl does not support the Cs property.
3574    
3575           The long synonyms for  property  names  that  Perl  supports  (such  as
3576         \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix         \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3577         any of these properties with "Is".         any of these properties with "Is".
3578    
# Line 3193  BACKSLASH Line 3619  BACKSLASH
3619    
3620         matches "foobar", the first substring is still set to "foo".         matches "foobar", the first substring is still set to "foo".
3621    
3622           Perl  documents  that  the  use  of  \K  within assertions is "not well
3623           defined". In PCRE, \K is acted upon  when  it  occurs  inside  positive
3624           assertions, but is ignored in negative assertions.
3625    
3626     Simple assertions     Simple assertions
3627    
3628         The  final use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
# Line 3216  BACKSLASH Line 3646  BACKSLASH
3646         A  word  boundary is a position in the subject string where the current         A  word  boundary is a position in the subject string where the current
3647         character and the previous character do not both match \w or  \W  (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3648         one  matches  \w  and the other matches \W), or the start or end of the         one  matches  \w  and the other matches \W), or the start or end of the
3649         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively. Neither
3650           PCRE  nor  Perl  has a separte "start of word" or "end of word" metase-
3651           quence. However, whatever follows \b normally determines which  it  is.
3652           For example, the fragment \ba matches "a" at the start of a word.
3653    
3654         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3655         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3656         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3657         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3658         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3659         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3660         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3661         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3662         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
3663         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3664         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3665    
3666         The \G assertion is true only when the current matching position is  at         The  \G assertion is true only when the current matching position is at
3667         the  start point of the match, as specified by the startoffset argument         the start point of the match, as specified by the startoffset  argument
3668         of pcre_exec(). It differs from \A when the  value  of  startoffset  is         of  pcre_exec().  It  differs  from \A when the value of startoffset is
3669         non-zero.  By calling pcre_exec() multiple times with appropriate argu-         non-zero. By calling pcre_exec() multiple times with appropriate  argu-
3670         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3671         mentation where \G can be useful.         mentation where \G can be useful.
3672    
3673         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
3674         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3675         end  of  the  previous  match. In Perl, these can be different when the         end of the previous match. In Perl, these can  be  different  when  the
3676         previously matched string was empty. Because PCRE does just  one  match         previously  matched  string was empty. Because PCRE does just one match
3677         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3678    
3679         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
3680         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3681         in the compiled regular expression.         in the compiled regular expression.
3682    
# Line 3251  BACKSLASH Line 3684  BACKSLASH
3684  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3685    
3686         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3687         character is an assertion that is true only  if  the  current  matching         character  is  an  assertion  that is true only if the current matching
3688         point  is  at the start of the subject string. If the startoffset argu-         point is at the start of the subject string. If the  startoffset  argu-
3689         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
3690         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
3691         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3692    
3693         Circumflex need not be the first character of the pattern if  a  number         Circumflex  need  not be the first character of the pattern if a number
3694         of  alternatives are involved, but it should be the first thing in each         of alternatives are involved, but it should be the first thing in  each
3695         alternative in which it appears if the pattern is ever  to  match  that         alternative  in  which  it appears if the pattern is ever to match that
3696         branch.  If all possible alternatives start with a circumflex, that is,         branch. If all possible alternatives start with a circumflex, that  is,
3697         if the pattern is constrained to match only at the start  of  the  sub-         if  the  pattern  is constrained to match only at the start of the sub-
3698         ject,  it  is  said  to be an "anchored" pattern. (There are also other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
3699         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3700    
3701         A dollar character is an assertion that is true  only  if  the  current         A  dollar  character  is  an assertion that is true only if the current
3702         matching  point  is  at  the  end of the subject string, or immediately         matching point is at the end of  the  subject  string,  or  immediately
3703         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3704         be  the  last  character of the pattern if a number of alternatives are         be the last character of the pattern if a number  of  alternatives  are
3705         involved, but it should be the last item in  any  branch  in  which  it         involved,  but  it  should  be  the last item in any branch in which it
3706         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3707    
3708         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3709         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3710         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3711    
3712         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3713         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3714         matches  immediately after internal newlines as well as at the start of         matches immediately after internal newlines as well as at the start  of
3715         the subject string. It does not match after a  newline  that  ends  the         the  subject  string.  It  does not match after a newline that ends the
3716         string.  A dollar matches before any newlines in the string, as well as         string. A dollar matches before any newlines in the string, as well  as
3717         at the very end, when PCRE_MULTILINE is set. When newline is  specified         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3718         as  the  two-character  sequence CRLF, isolated CR and LF characters do         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3719         not indicate newlines.         not indicate newlines.
3720    
3721         For example, the pattern /^abc$/ matches the subject string  "def\nabc"         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3722         (where  \n  represents a newline) in multiline mode, but not otherwise.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3723         Consequently, patterns that are anchored in single  line  mode  because         Consequently,  patterns  that  are anchored in single line mode because
3724         all  branches  start  with  ^ are not anchored in multiline mode, and a         all branches start with ^ are not anchored in  multiline  mode,  and  a
3725         match for circumflex is  possible  when  the  startoffset  argument  of         match  for  circumflex  is  possible  when  the startoffset argument of
3726         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3727         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3728    
3729         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3730         and  end of the subject in both modes, and if all branches of a pattern         and end of the subject in both modes, and if all branches of a  pattern
3731         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3732         set.         set.
3733    
3734    
3735  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3736    
3737         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3738         ter in the subject string except (by default) a character  that  signi-         ter  in  the subject string except (by default) a character that signi-
3739         fies  the  end  of  a line. In UTF-8 mode, the matched character may be         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3740         more than one byte long.         more than one byte long.
3741    
3742         When a line ending is defined as a single character, dot never  matches         When  a line ending is defined as a single character, dot never matches
3743         that  character; when the two-character sequence CRLF is used, dot does         that character; when the two-character sequence CRLF is used, dot  does
3744         not match CR if it is immediately followed  by  LF,  but  otherwise  it         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3745         matches  all characters (including isolated CRs and LFs). When any Uni-         matches all characters (including isolated CRs and LFs). When any  Uni-
3746         code line endings are being recognized, dot does not match CR or LF  or         code  line endings are being recognized, dot does not match CR or LF or
3747         any of the other line ending characters.         any of the other line ending characters.
3748    
3749         The  behaviour  of  dot  with regard to newlines can be changed. If the         The behaviour of dot with regard to newlines can  be  changed.  If  the
3750         PCRE_DOTALL option is set, a dot matches  any  one  character,  without         PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3751         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3752         string, it takes two dots to match it.         string, it takes two dots to match it.
3753    
3754         The handling of dot is entirely independent of the handling of  circum-         The  handling of dot is entirely independent of the handling of circum-
3755         flex  and  dollar,  the  only relationship being that they both involve         flex and dollar, the only relationship being  that  they  both  involve
3756         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3757    
3758    
3759  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3760    
3761         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3762         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3763         line-ending characters. The feature is provided in  Perl  in  order  to         line-ending  characters.  The  feature  is provided in Perl in order to
3764         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3765         acters into individual bytes, what remains in the string may be a  mal-         acters  into individual bytes, what remains in the string may be a mal-
3766         formed  UTF-8  string.  For this reason, the \C escape sequence is best         formed UTF-8 string. For this reason, the \C escape  sequence  is  best
3767         avoided.         avoided.
3768    
3769         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3770         below),  because  in UTF-8 mode this would make it impossible to calcu-         below), because in UTF-8 mode this would make it impossible  to  calcu-
3771         late the length of the lookbehind.         late the length of the lookbehind.
3772    
3773    
# Line 3342  SQUARE BRACKETS AND CHARACTER CLASSES Line 3775  SQUARE BRACKETS AND CHARACTER CLASSES
3775    
3776         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3777         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3778         cial. If a closing square bracket is required as a member of the class,         cial by default.  However, if the PCRE_JAVASCRIPT_COMPAT option is set,
3779         it  should  be  the first data character in the class (after an initial         a lone closing square bracket causes a compile-time error. If a closing
3780         circumflex, if present) or escaped with a backslash.         square  bracket  is required as a member of the class, it should be the
3781           first data character in the class  (after  an  initial  circumflex,  if
3782           present) or escaped with a backslash.
3783    
3784         A character class matches a single character in the subject.  In  UTF-8         A  character  class matches a single character in the subject. In UTF-8
3785         mode,  the character may occupy more than one byte. A matched character         mode, the character may be more than one byte long. A matched character
3786         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3787         character  in  the  class definition is a circumflex, in which case the         character in the class definition is a circumflex, in  which  case  the
3788         subject character must not be in the set defined by  the  class.  If  a         subject  character  must  not  be in the set defined by the class. If a
3789         circumflex  is actually required as a member of the class, ensure it is         circumflex is actually required as a member of the class, ensure it  is
3790         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3791    
3792         For example, the character class [aeiou] matches any lower case  vowel,         For  example, the character class [aeiou] matches any lower case vowel,
3793         while  [^aeiou]  matches  any character that is not a lower case vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3794         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3795         characters  that  are in the class by enumerating those that are not. A         characters that are in the class by enumerating those that are  not.  A
3796         class that starts with a circumflex is not an assertion: it still  con-         class  that starts with a circumflex is not an assertion; it still con-
3797         sumes  a  character  from the subject string, and therefore it fails if         sumes a character from the subject string, and therefore  it  fails  if
3798         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3799    
3800         In UTF-8 mode, characters with values greater than 255 can be  included         In  UTF-8 mode, characters with values greater than 255 can be included
3801         in  a  class as a literal string of bytes, or by using the \x{ escaping         in a class as a literal string of bytes, or by using the  \x{  escaping
3802         mechanism.         mechanism.
3803    
3804         When caseless matching is set, any letters in a  class  represent  both         When  caseless  matching  is set, any letters in a class represent both
3805         their  upper  case  and lower case versions, so for example, a caseless         their upper case and lower case versions, so for  example,  a  caseless
3806         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
3807         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always
3808         understands the concept of case for characters whose  values  are  less         understands  the  concept  of case for characters whose values are less
3809         than  128, so caseless matching is always possible. For characters with         than 128, so caseless matching is always possible. For characters  with
3810         higher values, the concept of case is supported  if  PCRE  is  compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3811         with  Unicode  property support, but not otherwise.  If you want to use         with Unicode property support, but not otherwise.  If you want  to  use
3812         caseless matching for characters 128 and above, you  must  ensure  that         caseless  matching  in UTF8-mode for characters 128 and above, you must
3813         PCRE  is  compiled  with Unicode property support as well as with UTF-8         ensure that PCRE is compiled with Unicode property support as  well  as
3814         support.         with UTF-8 support.
3815    
3816         Characters that might indicate line breaks are  never  treated  in  any         Characters  that  might  indicate  line breaks are never treated in any
3817         special  way  when  matching  character  classes,  whatever line-ending         special way  when  matching  character  classes,  whatever  line-ending
3818         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and
3819         PCRE_MULTILINE options is used. A class such as [^a] always matches one         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3820         of these characters.         of these characters.
3821    
3822         The minus (hyphen) character can be used to specify a range of  charac-         The  minus (hyphen) character can be used to specify a range of charac-
3823         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters in a character  class.  For  example,  [d-m]  matches  any  letter
3824         between d and m, inclusive. If a  minus  character  is  required  in  a         between  d  and  m,  inclusive.  If  a minus character is required in a
3825         class,  it  must  be  escaped  with a backslash or appear in a position         class, it must be escaped with a backslash  or  appear  in  a  position
3826         where it cannot be interpreted as indicating a range, typically as  the         where  it cannot be interpreted as indicating a range, typically as the
3827         first or last character in the class.         first or last character in the class.
3828    
3829         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3830         ter of a range. A pattern such as [W-]46] is interpreted as a class  of         ter  of a range. A pattern such as [W-]46] is interpreted as a class of
3831         two  characters ("W" and "-") followed by a literal string "46]", so it         two characters ("W" and "-") followed by a literal string "46]", so  it
3832         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a
3833         backslash  it is interpreted as the end of range, so [W-\]46] is inter-         backslash it is interpreted as the end of range, so [W-\]46] is  inter-
3834         preted as a class containing a range followed by two other  characters.         preted  as a class containing a range followed by two other characters.
3835         The  octal or hexadecimal representation of "]" can also be used to end         The octal or hexadecimal representation of "]" can also be used to  end
3836         a range.         a range.
3837    
3838         Ranges operate in the collating sequence of character values. They  can         Ranges  operate in the collating sequence of character values. They can
3839         also   be  used  for  characters  specified  numerically,  for  example         also  be  used  for  characters  specified  numerically,  for   example
3840         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values         [\000-\037].  In UTF-8 mode, ranges can include characters whose values
3841         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3842    
3843         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3844         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3845         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if
3846         character tables for a French locale are in  use,  [\xc8-\xcb]  matches         character  tables  for  a French locale are in use, [\xc8-\xcb] matches
3847         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented E characters in both cases. In UTF-8 mode, PCRE  supports  the
3848         concept of case for characters with values greater than 128  only  when         concept  of  case for characters with values greater than 128 only when
3849         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3850    
3851         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear
3852         in a character class, and add the characters that  they  match  to  the         in  a  character  class,  and add the characters that they match to the
3853         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3854         flex can conveniently be used with the upper case  character  types  to         flex  can  conveniently  be used with the upper case character types to
3855         specify  a  more  restricted  set of characters than the matching lower         specify a more restricted set of characters  than  the  matching  lower
3856         case type. For example, the class [^\W_] matches any letter  or  digit,         case  type.  For example, the class [^\W_] matches any letter or digit,
3857         but not underscore.         but not underscore.
3858    
3859         The  only  metacharacters  that are recognized in character classes are         The only metacharacters that are recognized in  character  classes  are
3860         backslash, hyphen (only where it can be  interpreted  as  specifying  a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
3861         range),  circumflex  (only  at the start), opening square bracket (only         range), circumflex (only at the start), opening  square  bracket  (only
3862         when it can be interpreted as introducing a POSIX class name - see  the         when  it can be interpreted as introducing a POSIX class name - see the
3863         next  section),  and  the  terminating closing square bracket. However,         next section), and the terminating  closing  square  bracket.  However,
3864         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3865    
3866    
3867  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3868    
3869         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3870         enclosed  by  [: and :] within the enclosing square brackets. PCRE also         enclosed by [: and :] within the enclosing square brackets.  PCRE  also
3871         supports this notation. For example,         supports this notation. For example,
3872    
3873           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3455  POSIX CHARACTER CLASSES Line 3890  POSIX CHARACTER CLASSES
3890           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3891           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3892    
3893         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),
3894         and space (32). Notice that this list includes the VT  character  (code         and  space  (32). Notice that this list includes the VT character (code
3895         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
3896         Perl compatibility).         Perl compatibility).
3897    
3898         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension
3899         from  Perl  5.8. Another Perl extension is negation, which is indicated         from Perl 5.8. Another Perl extension is negation, which  is  indicated
3900         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3901    
3902           [12[:^digit:]]           [12[:^digit:]]
3903    
3904         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
3905         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3906         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
3907    
# Line 3486  VERTICAL BAR Line 3921  VERTICAL BAR
3921         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3922         to right, and the first one that succeeds is used. If the  alternatives         to right, and the first one that succeeds is used. If the  alternatives
3923         are  within a subpattern (defined below), "succeeds" means matching the         are  within a subpattern (defined below), "succeeds" means matching the
3924         rest of the main pattern as well as the alternative in the  subpattern.         rest of the main pattern as well as the alternative in the subpattern.
3925    
3926    
3927  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3928    
3929         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and
3930         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from
3931         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within the pattern by  a  sequence  of  Perl  option  letters  enclosed
3932         option letters are         between "(?" and ")".  The option letters are
3933    
3934           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3935           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3503  INTERNAL OPTION SETTING Line 3938  INTERNAL OPTION SETTING
3938    
3939         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3940         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
3941         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-
3942         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,
3943         is also permitted. If a  letter  appears  both  before  and  after  the         is  also  permitted.  If  a  letter  appears  both before and after the
3944         hyphen, the option is unset.         hyphen, the option is unset.
3945    
3946         When  an option change occurs at top level (that is, not inside subpat-         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3947         tern parentheses), the change applies to the remainder of  the  pattern         can  be changed in the same way as the Perl-compatible options by using
3948         that follows.  If the change is placed right at the start of a pattern,         the characters J, U and X respectively.
3949         PCRE extracts it into the global options (and it will therefore show up  
3950         in data extracted by the pcre_fullinfo() function).         When one of these option changes occurs at  top  level  (that  is,  not
3951           inside  subpattern parentheses), the change applies to the remainder of
3952           the pattern that follows. If the change is placed right at the start of
3953           a pattern, PCRE extracts it into the global options (and it will there-
3954           fore show up in data extracted by the pcre_fullinfo() function).
3955    
3956         An  option  change  within a subpattern (see below for a description of         An option change within a subpattern (see below for  a  description  of
3957         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
3958         it, so         it, so
3959    
3960           (a(?i)b)c           (a(?i)b)c
3961    
3962         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3963         used).  By this means, options can be made to have  different  settings         used).   By  this means, options can be made to have different settings
3964         in  different parts of the pattern. Any changes made in one alternative         in different parts of the pattern. Any changes made in one  alternative
3965         do carry on into subsequent branches within the  same  subpattern.  For         do  carry  on  into subsequent branches within the same subpattern. For
3966         example,         example,
3967    
3968           (a(?i)b|c)           (a(?i)b|c)
3969    
3970         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the
3971         first branch is abandoned before the option setting.  This  is  because         first  branch  is  abandoned before the option setting. This is because
3972         the  effects  of option settings happen at compile time. There would be         the effects of option settings happen at compile time. There  would  be
3973         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3974    
3975         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note:  There  are  other  PCRE-specific  options that can be set by the
3976         can  be changed in the same way as the Perl-compatible options by using         application when the compile or match functions  are  called.  In  some
3977         the characters J, U and X respectively.         cases the pattern can contain special leading sequences such as (*CRLF)
3978           to override what the application has set or what  has  been  defaulted.
3979           Details  are  given  in the section entitled "Newline sequences" above.
3980           There is also the (*UTF8) leading sequence that  can  be  used  to  set
3981           UTF-8 mode; this is equivalent to setting the PCRE_UTF8 option.
3982    
3983    
3984  SUBPATTERNS  SUBPATTERNS
# Line 3547  SUBPATTERNS Line 3990  SUBPATTERNS
3990    
3991           cat(aract|erpillar|)           cat(aract|erpillar|)
3992    
3993         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches one of the words "cat", "cataract", or  "caterpillar".  Without
3994         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty
3995         string.         string.
3996    
3997         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2. It sets up the subpattern as  a  capturing  subpattern.  This  means
3998         that, when the whole pattern  matches,  that  portion  of  the  subject         that,  when  the  whole  pattern  matches,  that portion of the subject
3999         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
4000         ovector argument of pcre_exec(). Opening parentheses are  counted  from         ovector  argument  of pcre_exec(). Opening parentheses are counted from
4001         left  to  right  (starting  from 1) to obtain numbers for the capturing         left to right (starting from 1) to obtain  numbers  for  the  capturing
4002         subpatterns.         subpatterns.
4003    
4004         For example, if the string "the red king" is matched against  the  pat-         For  example,  if the string "the red king" is matched against the pat-
4005         tern         tern
4006    
4007           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3566  SUBPATTERNS Line 4009  SUBPATTERNS
4009         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
4010         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
4011    
4012         The fact that plain parentheses fulfil  two  functions  is  not  always         The  fact  that  plain  parentheses  fulfil two functions is not always
4013         helpful.   There are often times when a grouping subpattern is required         helpful.  There are often times when a grouping subpattern is  required
4014         without a capturing requirement. If an opening parenthesis is  followed         without  a capturing requirement. If an opening parenthesis is followed
4015         by  a question mark and a colon, the subpattern does not do any captur-         by a question mark and a colon, the subpattern does not do any  captur-
4016         ing, and is not counted when computing the  number  of  any  subsequent         ing,  and  is  not  counted when computing the number of any subsequent
4017         capturing  subpatterns. For example, if the string "the white queen" is         capturing subpatterns. For example, if the string "the white queen"  is
4018         matched against the pattern         matched against the pattern
4019    
4020           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3579  SUBPATTERNS Line 4022  SUBPATTERNS
4022         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
4023         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
4024    
4025         As  a  convenient shorthand, if any option settings are required at the         As a convenient shorthand, if any option settings are required  at  the
4026         start of a non-capturing subpattern,  the  option  letters  may  appear         start  of  a  non-capturing  subpattern,  the option letters may appear
4027         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
4028    
4029           (?i:saturday|sunday)           (?i:saturday|sunday)
4030           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
4031    
4032         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
4033         tried from left to right, and options are not reset until  the  end  of         tried  from  left  to right, and options are not reset until the end of
4034         the  subpattern is reached, an option setting in one branch does affect         the subpattern is reached, an option setting in one branch does  affect
4035         subsequent branches, so the above patterns match "SUNDAY"  as  well  as         subsequent  branches,  so  the above patterns match "SUNDAY" as well as
4036         "Saturday".         "Saturday".
4037    
4038    
4039  DUPLICATE SUBPATTERN NUMBERS  DUPLICATE SUBPATTERN NUMBERS
4040    
4041         Perl 5.10 introduced a feature whereby each alternative in a subpattern         Perl 5.10 introduced a feature whereby each alternative in a subpattern
4042         uses the same numbers for its capturing parentheses. Such a  subpattern         uses  the same numbers for its capturing parentheses. Such a subpattern
4043         starts  with (?| and is itself a non-capturing subpattern. For example,         starts with (?| and is itself a non-capturing subpattern. For  example,
4044         consider this pattern:         consider this pattern:
4045    
4046           (?|(Sat)ur|(Sun))day           (?|(Sat)ur|(Sun))day
4047    
4048         Because the two alternatives are inside a (?| group, both sets of  cap-         Because  the two alternatives are inside a (?| group, both sets of cap-
4049         turing  parentheses  are  numbered one. Thus, when the pattern matches,         turing parentheses are numbered one. Thus, when  the  pattern  matches,
4050         you can look at captured substring number  one,  whichever  alternative         you  can  look  at captured substring number one, whichever alternative
4051         matched.  This  construct  is useful when you want to capture part, but         matched. This construct is useful when you want to  capture  part,  but
4052         not all, of one of a number of alternatives. Inside a (?| group, paren-         not all, of one of a number of alternatives. Inside a (?| group, paren-
4053         theses  are  numbered as usual, but the number is reset at the start of         theses are numbered as usual, but the number is reset at the  start  of
4054         each branch. The numbers of any capturing buffers that follow the  sub-         each  branch. The numbers of any capturing buffers that follow the sub-
4055         pattern  start after the highest number used in any branch. The follow-         pattern start after the highest number used in any branch. The  follow-
4056         ing example is taken from the Perl documentation.  The  numbers  under-         ing  example  is taken from the Perl documentation.  The numbers under-
4057         neath show in which buffer the captured content will be stored.         neath show in which buffer the captured content will be stored.
4058    
4059           # before  ---------------branch-reset----------- after           # before  ---------------branch-reset----------- after
4060           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4061           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4062    
4063         A  backreference  or  a  recursive call to a numbered subpattern always         A back reference to a numbered subpattern uses the  most  recent  value
4064         refers to the first one in the pattern with the given number.         that  is  set  for that number by any subpattern. The following pattern
4065           matches "abcabc" or "defdef":
4066    
4067             /(?|(abc)|(def))\1/
4068    
4069           In contrast, a recursive or "subroutine" call to a numbered  subpattern
4070           always  refers  to  the first one in the pattern with the given number.
4071           The following pattern matches "abcabc" or "defabc":
4072    
4073             /(?|(abc)|(def))(?1)/
4074    
4075           If a condition test for a subpattern's having matched refers to a  non-
4076           unique  number, the test is true if any of the subpatterns of that num-
4077           ber have matched.
4078    
4079         An alternative approach to using this "branch reset" feature is to  use         An alternative approach to using this "branch reset" feature is to  use
4080         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
# Line 3633  NAMED SUBPATTERNS Line 4089  NAMED SUBPATTERNS
4089         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
4090         had the feature earlier, and PCRE introduced it at release  4.0,  using         had the feature earlier, and PCRE introduced it at release  4.0,  using
4091         the  Python syntax. PCRE now supports both the Perl and the Python syn-         the  Python syntax. PCRE now supports both the Perl and the Python syn-
4092         tax.         tax. Perl allows identically numbered  subpatterns  to  have  different
4093           names, but PCRE does not.
4094    
4095         In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
4096         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
4097         to capturing parentheses from other parts of the pattern, such as back-         to  capturing parentheses from other parts of the pattern, such as back
4098         references,  recursion,  and conditions, can be made by name as well as         references, recursion, and conditions, can be made by name as  well  as
4099         by number.         by number.
4100    
4101         Names consist of up to  32  alphanumeric  characters  and  underscores.         Names  consist  of  up  to  32 alphanumeric characters and underscores.
4102         Named  capturing  parentheses  are  still  allocated numbers as well as         Named capturing parentheses are still  allocated  numbers  as  well  as
4103         names, exactly as if the names were not present. The PCRE API  provides         names,  exactly as if the names were not present. The PCRE API provides
4104         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
4105         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
4106         a captured substring by name.         a captured substring by name.
4107    
4108         By  default, a name must be unique within a pattern, but it is possible         By default, a name must be unique within a pattern, but it is  possible
4109         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4110         time.  This  can  be useful for patterns where only one instance of the         time. (Duplicate names are also always permitted for  subpatterns  with
4111         named parentheses can match. Suppose you want to match the  name  of  a         the  same  number, set up as described in the previous section.) Dupli-
4112         weekday,  either as a 3-letter abbreviation or as the full name, and in         cate names can be useful for patterns where only one  instance  of  the
4113           named  parentheses  can  match. Suppose you want to match the name of a
4114           weekday, either as a 3-letter abbreviation or as the full name, and  in
4115         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
4116         the line breaks) does the job:         the line breaks) does the job:
4117    
# Line 3662  NAMED SUBPATTERNS Line 4121  NAMED SUBPATTERNS
4121           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
4122           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
4123    
4124         There  are  five capturing substrings, but only one is ever set after a         There are five capturing substrings, but only one is ever set  after  a
4125         match.  (An alternative way of solving this problem is to use a "branch         match.  (An alternative way of solving this problem is to use a "branch
4126         reset" subpattern, as described in the previous section.)         reset" subpattern, as described in the previous section.)
4127    
4128         The  convenience  function  for extracting the data by name returns the         The convenience function for extracting the data by  name  returns  the
4129         substring for the first (and in this example, the only)  subpattern  of         substring  for  the first (and in this example, the only) subpattern of
4130         that  name  that  matched.  This saves searching to find which numbered         that name that matched. This saves searching  to  find  which  numbered
4131         subpattern it was. If you make a reference to a non-unique  named  sub-         subpattern it was.
4132         pattern  from elsewhere in the pattern, the one that corresponds to the  
4133         lowest number is used. For further details of the interfaces  for  han-         If  you  make  a  back  reference to a non-unique named subpattern from
4134         dling named subpatterns, see the pcreapi documentation.         elsewhere in the pattern, the one that corresponds to the first  occur-
4135           rence of the name is used. In the absence of duplicate numbers (see the
4136           previous section) this is the one with the lowest number. If you use  a
4137           named  reference  in a condition test (see the section about conditions
4138           below), either to check whether a subpattern has matched, or  to  check
4139           for  recursion,  all  subpatterns with the same name are tested. If the
4140           condition is true for any one of them, the overall condition  is  true.
4141           This is the same behaviour as testing by number. For further details of
4142           the interfaces for handling named subpatterns, see the pcreapi documen-
4143           tation.
4144    
4145           Warning: You cannot use different names to distinguish between two sub-
4146           patterns with the same number because PCRE uses only the  numbers  when
4147           matching. For this reason, an error is given at compile time if differ-
4148           ent names are given to subpatterns with the same number.  However,  you
4149           can  give  the same name to subpatterns with the same number, even when
4150           PCRE_DUPNAMES is not set.
4151    
4152    
4153  REPETITION  REPETITION
4154    
4155         Repetition  is  specified  by  quantifiers, which can follow any of the         Repetition is specified by quantifiers, which can  follow  any  of  the
4156         following items:         following items:
4157    
4158           a literal data character           a literal data character
# Line 3689  REPETITION Line 4164  REPETITION
4164           a character class           a character class
4165           a back reference (see next section)           a back reference (see next section)
4166           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4167             a recursive or "subroutine" call to a subpattern
4168    
4169         The general repetition quantifier specifies a minimum and maximum  num-         The  general repetition quantifier specifies a minimum and maximum num-
4170         ber  of  permitted matches, by giving the two numbers in curly brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
4171         (braces), separated by a comma. The numbers must be  less  than  65536,         (braces),  separated  by  a comma. The numbers must be less than 65536,
4172         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
4173    
4174           z{2,4}           z{2,4}
4175    
4176         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a
4177         special character. If the second number is omitted, but  the  comma  is         special  character.  If  the second number is omitted, but the comma is
4178         present,  there  is  no upper limit; if the second number and the comma         present, there is no upper limit; if the second number  and  the  comma
4179         are both omitted, the quantifier specifies an exact number of  required         are  both omitted, the quantifier specifies an exact number of required
4180         matches. Thus         matches. Thus
4181    
4182           [aeiou]{3,}           [aeiou]{3,}
# Line 3709  REPETITION Line 4185  REPETITION
4185    
4186           \d{8}           \d{8}
4187    
4188         matches  exactly  8  digits. An opening curly bracket that appears in a         matches exactly 8 digits. An opening curly bracket that  appears  in  a
4189         position where a quantifier is not allowed, or one that does not  match         position  where a quantifier is not allowed, or one that does not match
4190         the  syntax of a quantifier, is taken as a literal character. For exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
4191         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
4192    
4193         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
# Line 3722  REPETITION Line 4198  REPETITION
4198         may be of different lengths).         may be of different lengths).
4199    
4200         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4201         the previous item and the quantifier were not present.         the previous item and the quantifier were not present. This may be use-
4202           ful for subpatterns that are referenced as subroutines  from  elsewhere
4203           in the pattern. Items other than subpatterns that have a {0} quantifier
4204           are omitted from the compiled pattern.
4205    
4206         For  convenience, the three most common quantifiers have single-charac-         For convenience, the three most common quantifiers have  single-charac-
4207         ter abbreviations:         ter abbreviations:
4208    
4209           *    is equivalent to {0,}           *    is equivalent to {0,}
4210           +    is equivalent to {1,}           +    is equivalent to {1,}
4211           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4212    
4213         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
4214         that can match no characters with a quantifier that has no upper limit,         that can match no characters with a quantifier that has no upper limit,
4215         for example:         for example:
4216    
4217           (a?)*           (a?)*
4218    
4219         Earlier versions of Perl and PCRE used to give an error at compile time         Earlier versions of Perl and PCRE used to give an error at compile time
4220         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
4221         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
4222         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
4223         ken.         ken.
4224    
4225         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
4226         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
4227         causing the rest of the pattern to fail. The classic example  of  where         causing  the  rest of the pattern to fail. The classic example of where
4228         this gives problems is in trying to match comments in C programs. These         this gives problems is in trying to match comments in C programs. These
4229         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
4230         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
4231         pattern         pattern
4232    
4233           /\*.*\*/           /\*.*\*/
# Line 3757  REPETITION Line 4236  REPETITION
4236    
4237           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4238    
4239         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
4240         the .*  item.         the .*  item.
4241    
4242         However,  if  a quantifier is followed by a question mark, it ceases to         However, if a quantifier is followed by a question mark, it  ceases  to
4243         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4244         the pattern         the pattern
4245    
4246           /\*.*?\*/           /\*.*?\*/
4247    
4248         does  the  right  thing with the C comments. The meaning of the various         does the right thing with the C comments. The meaning  of  the  various
4249         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
4250         matches.   Do  not  confuse this use of question mark with its use as a         matches.  Do not confuse this use of question mark with its  use  as  a
4251         quantifier in its own right. Because it has two uses, it can  sometimes         quantifier  in its own right. Because it has two uses, it can sometimes
4252         appear doubled, as in         appear doubled, as in
4253    
4254           \d??\d           \d??\d
# Line 3777  REPETITION Line 4256  REPETITION
4256         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
4257         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4258    
4259         If the PCRE_UNGREEDY option is set (an option that is not available  in         If  the PCRE_UNGREEDY option is set (an option that is not available in
4260         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
4261         can be made greedy by following them with a  question  mark.  In  other         can  be  made  greedy  by following them with a question mark. In other
4262         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4263    
4264         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
4265         count that is greater than 1 or with a limited maximum, more memory  is         count  that is greater than 1 or with a limited maximum, more memory is
4266         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
4267         minimum or maximum.         minimum or maximum.
4268    
4269         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
4270         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,         alent to Perl's /s) is set, thus allowing the dot  to  match  newlines,
4271         the pattern is implicitly anchored, because whatever  follows  will  be         the  pattern  is  implicitly anchored, because whatever follows will be
4272         tried  against every character position in the subject string, so there         tried against every character position in the subject string, so  there
4273         is no point in retrying the overall match at  any  position  after  the         is  no  point  in  retrying the overall match at any position after the
4274         first.  PCRE  normally treats such a pattern as though it were preceded         first. PCRE normally treats such a pattern as though it  were  preceded
4275         by \A.         by \A.
4276    
4277         In cases where it is known that the subject  string  contains  no  new-         In  cases  where  it  is known that the subject string contains no new-
4278         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-
4279         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4280    
4281         However, there is one situation where the optimization cannot be  used.         However,  there is one situation where the optimization cannot be used.
4282         When  .*   is  inside  capturing  parentheses that are the subject of a         When .*  is inside capturing parentheses that are the subject of a back
4283         backreference elsewhere in the pattern, a match at the start  may  fail         reference elsewhere in the pattern, a match at the start may fail where
4284         where a later one succeeds. Consider, for example:         a later one succeeds. Consider, for example:
4285    
4286           (.*)abc\1           (.*)abc\1
4287    
4288         If  the subject is "xyz123abc123" the match point is the fourth charac-         If the subject is "xyz123abc123" the match point is the fourth  charac-
4289         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4290    
4291         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3815  REPETITION Line 4294  REPETITION
4294           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4295    
4296         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4297         is "tweedledee". However, if there are  nested  capturing  subpatterns,         is  "tweedledee".  However,  if there are nested capturing subpatterns,
4298         the  corresponding captured values may have been set in previous itera-         the corresponding captured values may have been set in previous  itera-
4299         tions. For example, after         tions. For example, after
4300    
4301           /(a|(b))+/           /(a|(b))+/
# Line 3826  REPETITION Line 4305  REPETITION
4305    
4306  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4307    
4308         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
4309         repetition,  failure  of what follows normally causes the repeated item         repetition, failure of what follows normally causes the  repeated  item
4310         to be re-evaluated to see if a different number of repeats  allows  the         to  be  re-evaluated to see if a different number of repeats allows the
4311         rest  of  the pattern to match. Sometimes it is useful to prevent this,         rest of the pattern to match. Sometimes it is useful to  prevent  this,
4312         either to change the nature of the match, or to cause it  fail  earlier         either  to  change the nature of the match, or to cause it fail earlier
4313         than  it otherwise might, when the author of the pattern knows there is         than it otherwise might, when the author of the pattern knows there  is
4314         no point in carrying on.         no point in carrying on.
4315    
4316         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider,  for  example, the pattern \d+foo when applied to the subject
4317         line         line
4318    
4319           123456bar           123456bar
4320    
4321         After matching all 6 digits and then failing to match "foo", the normal         After matching all 6 digits and then failing to match "foo", the normal
4322         action of the matcher is to try again with only 5 digits  matching  the         action  of  the matcher is to try again with only 5 digits matching the
4323         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.
4324         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides
4325         the  means for specifying that once a subpattern has matched, it is not         the means for specifying that once a subpattern has matched, it is  not
4326         to be re-evaluated in this way.         to be re-evaluated in this way.
4327    
4328         If we use atomic grouping for the previous example, the  matcher  gives         If  we  use atomic grouping for the previous example, the matcher gives
4329         up  immediately  on failing to match "foo" the first time. The notation         up immediately on failing to match "foo" the first time.  The  notation
4330         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4331    
4332           (?>\d+)foo           (?>\d+)foo
# Line 3925  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4404  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4404    
4405           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4406    
4407         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences of non-digits cannot be broken, and failure happens quickly.
4408    
4409    
4410  BACK REFERENCES  BACK REFERENCES
4411    
4412         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4413         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
4414         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
4415         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4416    
4417         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4418         it  is  always  taken  as a back reference, and causes an error only if         it is always taken as a back reference, and causes  an  error  only  if
4419         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
4420         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
4421         to the left of the reference for numbers less than 10. A "forward  back         to  the left of the reference for numbers less than 10. A "forward back
4422         reference"  of  this  type can make sense when a repetition is involved         reference" of this type can make sense when a  repetition  is  involved
4423         and the subpattern to the right has participated in an  earlier  itera-         and  the  subpattern to the right has participated in an earlier itera-
4424         tion.         tion.
4425    
4426         It  is  not  possible to have a numerical "forward back reference" to a         It is not possible to have a numerical "forward back  reference"  to  a
4427         subpattern whose number is 10 or  more  using  this  syntax  because  a         subpattern  whose  number  is  10  or  more using this syntax because a
4428         sequence  such  as  \50 is interpreted as a character defined in octal.         sequence such as \50 is interpreted as a character  defined  in  octal.
4429         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4430         details  of  the  handling of digits following a backslash. There is no         details of the handling of digits following a backslash.  There  is  no
4431         such problem when named parentheses are used. A back reference  to  any         such  problem  when named parentheses are used. A back reference to any
4432         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4433    
4434         Another  way  of  avoiding  the ambiguity inherent in the use of digits         Another way of avoiding the ambiguity inherent in  the  use  of  digits
4435         following a backslash is to use the \g escape sequence, which is a fea-         following a backslash is to use the \g escape sequence, which is a fea-