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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. Neither has  synopses of each function in the library have not been included. Neither has
6  the pcredemo program. There are separate text files for the pcregrep and  the pcredemo program. There are separate text files for the pcregrep and
7  pcretest commands.  pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
# Line 19  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.  There is also some support for certain .NET and Oniguruma syn-         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25         tax items, and there is an option for  requesting  some  minor  changes         items, and there is an option for requesting some  minor  changes  that
26         that give better JavaScript compatibility.         give better JavaScript compatibility.
27    
28         The  current implementation of PCRE (release 8.xx) corresponds approxi-         The  current implementation of PCRE corresponds approximately with Perl
29         mately with Perl 5.10, including support for UTF-8 encoded strings  and         5.10, including support for UTF-8 encoded strings and  Unicode  general
30         Unicode general category properties. However, UTF-8 and Unicode support         category  properties.  However,  UTF-8  and  Unicode  support has to be
31         has to be explicitly enabled; it is not the default. The Unicode tables         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32         correspond to Unicode release 5.1.         spond to Unicode release 5.1.
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 55  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 89  USER DOCUMENTATION Line 89  USER DOCUMENTATION
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 pcredemo 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 142  UTF-8 AND UNICODE PROPERTY SUPPORT Line 142  UTF-8 AND UNICODE PROPERTY SUPPORT
142         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         sequence (*UTF8). When either of these is the case,  both  the  pattern         sequence (*UTF8). When either of these is the case,  both  the  pattern
144         and  any  subject  strings  that  are matched against it are treated as         and  any  subject  strings  that  are matched against it are treated as
145         UTF-8 strings instead of just strings of bytes.         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
# Line 263  AUTHOR Line 263  AUTHOR
263    
264  REVISION  REVISION
265    
266         Last updated: 01 September 2009         Last updated: 28 September 2009
267         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
268  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
269    
270    
271  PCREBUILD(3)                                                      PCREBUILD(3)  PCREBUILD(3)                                                      PCREBUILD(3)
272    
273    
# Line 324  UTF-8 SUPPORT Line 324  UTF-8 SUPPORT
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         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         expects its input to be either ASCII or UTF-8 (depending on the runtime
# Line 432  HANDLING VERY LARGE PATTERNS Line 432  HANDLING VERY LARGE PATTERNS
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    
# Line 461  AVOIDING EXCESSIVE STACK USAGE Line 461  AVOIDING EXCESSIVE STACK USAGE
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
# Line 469  AVOIDING EXCESSIVE STACK USAGE Line 469  AVOIDING EXCESSIVE STACK USAGE
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
476    
477         Internally, PCRE has a function called match(), which it calls  repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
478         edly   (sometimes   recursively)  when  matching  a  pattern  with  the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
479         pcre_exec() function. By controlling the maximum number of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
480         function  may be called during a single matching operation, a limit can         function may be called during a single matching operation, a limit  can
481         be placed on the resources used by a single call  to  pcre_exec().  The         be  placed  on  the resources used by a single call to pcre_exec(). The
482         limit  can be changed at run time, as described in the pcreapi documen-         limit can be changed at run time, as described in the pcreapi  documen-
483         tation. The default is 10 million, but this can be changed by adding  a         tation.  The default is 10 million, but this can be changed by adding a
484         setting such as         setting such as
485    
486           --with-match-limit=500000           --with-match-limit=500000
487    
488         to   the   configure  command.  This  setting  has  no  effect  on  the         to  the  configure  command.  This  setting  has  no  effect   on   the
489         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
490    
491         In some environments it is desirable to limit the  depth  of  recursive         In  some  environments  it is desirable to limit the depth of recursive
492         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
493         to restrict the maximum amount of stack (or heap,  if  --disable-stack-         to  restrict  the maximum amount of stack (or heap, if --disable-stack-
494         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
495         it defaults to the value that  is  set  for  --with-match-limit,  which         it  defaults  to  the  value  that is set for --with-match-limit, which
496         imposes  no  additional constraints. However, you can set a lower limit         imposes no additional constraints. However, you can set a  lower  limit
497         by adding, for example,         by adding, for example,
498    
499           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
500    
501         to the configure command. This value can  also  be  overridden  at  run         to  the  configure  command.  This  value can also be overridden at run
502         time.         time.
503    
504    
505  CREATING CHARACTER TABLES AT BUILD TIME  CREATING CHARACTER TABLES AT BUILD TIME
506    
507         PCRE  uses fixed tables for processing characters whose code values are         PCRE uses fixed tables for processing characters whose code values  are
508         less than 256. By default, PCRE is built with a set of tables that  are         less  than 256. By default, PCRE is built with a set of tables that are
509         distributed  in  the  file pcre_chartables.c.dist. These tables are for         distributed in the file pcre_chartables.c.dist. These  tables  are  for
510         ASCII codes only. If you add         ASCII codes only. If you add
511    
512           --enable-rebuild-chartables           --enable-rebuild-chartables
513    
514         to the configure command, the distributed tables are  no  longer  used.         to  the  configure  command, the distributed tables are no longer used.
515         Instead,  a  program  called dftables is compiled and run. This outputs         Instead, a program called dftables is compiled and  run.  This  outputs
516         the source for new set of tables, created in the default locale of your         the source for new set of tables, created in the default locale of your
517         C runtime system. (This method of replacing the tables does not work if         C runtime system. (This method of replacing the tables does not work if
518         you are cross compiling, because dftables is run on the local host.  If         you  are cross compiling, because dftables is run on the local host. If
519         you  need  to  create alternative tables when cross compiling, you will         you need to create alternative tables when cross  compiling,  you  will
520         have to do so "by hand".)         have to do so "by hand".)
521    
522    
523  USING EBCDIC CODE  USING EBCDIC CODE
524    
525         PCRE assumes by default that it will run in an  environment  where  the         PCRE  assumes  by  default that it will run in an environment where the
526         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
527         This is the case for most computer operating systems.  PCRE  can,  how-         This  is  the  case for most computer operating systems. PCRE can, how-
528         ever, be compiled to run in an EBCDIC environment by adding         ever, be compiled to run in an EBCDIC environment by adding
529    
530           --enable-ebcdic           --enable-ebcdic
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). The         environment (for example,  an  IBM  mainframe  operating  system).  The
535         --enable-ebcdic option is incompatible with --enable-utf8.         --enable-ebcdic option is incompatible with --enable-utf8.
536    
537    
# Line 546  PCREGREP OPTIONS FOR COMPRESSED FILE SUP Line 545  PCREGREP OPTIONS FOR COMPRESSED FILE SUP
545           --enable-pcregrep-libbz2           --enable-pcregrep-libbz2
546    
547         to the configure command. These options naturally require that the rel-         to the configure command. These options naturally require that the rel-
548         evant  libraries  are installed on your system. Configuration will fail         evant libraries are installed on your system. Configuration  will  fail
549         if they are not.         if they are not.
550    
551    
# Line 556  PCRETEST OPTION FOR LIBREADLINE SUPPORT Line 555  PCRETEST OPTION FOR LIBREADLINE SUPPORT
555    
556           --enable-pcretest-libreadline           --enable-pcretest-libreadline
557    
558         to the configure command,  pcretest  is  linked  with  the  libreadline         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         library, and when its input is from a terminal, it reads it  using  the
560         readline() function. This provides line-editing and history facilities.         readline() function. This provides line-editing and history facilities.
561         Note that libreadline is GPL-licenced, so if you distribute a binary of         Note that libreadline is GPL-licensed, so if you distribute a binary of
562         pcretest linked in this way, there may be licensing issues.         pcretest linked in this way, there may be licensing issues.
563    
564         Setting this option causes the -lreadline option to  be  added  to  the         Setting  this  option  causes  the -lreadline option to be added to the
565         pcretest  build.  In many operating environments with a sytem-installed         pcretest build. In many operating environments with  a  sytem-installed
566         libreadline this is sufficient. However, in some environments (e.g.  if         libreadline this is sufficient. However, in some environments (e.g.  if
567         an  unmodified  distribution version of readline is in use), some extra         an unmodified distribution version of readline is in use),  some  extra
568         configuration may be necessary. The INSTALL file for  libreadline  says         configuration  may  be necessary. The INSTALL file for libreadline says
569         this:         this:
570    
571           "Readline uses the termcap functions, but does not link with the           "Readline uses the termcap functions, but does not link with the
572           termcap or curses library itself, allowing applications which link           termcap or curses library itself, allowing applications which link
573           with readline the to choose an appropriate library."           with readline the to choose an appropriate library."
574    
575         If  your environment has not been set up so that an appropriate library         If your environment has not been set up so that an appropriate  library
576         is automatically included, you may need to add something like         is automatically included, you may need to add something like
577    
578           LIBS="-ncurses"           LIBS="-ncurses"
# Line 595  AUTHOR Line 594  AUTHOR
594    
595  REVISION  REVISION
596    
597         Last updated: 06 September 2009         Last updated: 29 September 2009
598         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
599  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
600    
601    
602  PCREMATCHING(3)                                                PCREMATCHING(3)  PCREMATCHING(3)                                                PCREMATCHING(3)
603    
604    
# Line 683  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 701  THE ALTERNATIVE MATCHING ALGORITHM Line 706  THE ALTERNATIVE MATCHING ALGORITHM
706         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
707         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
708    
        Although the general principle of this matching algorithm  is  that  it  
        scans  the subject string only once, without backtracking, there is one  
        exception: when a lookbehind assertion is  encountered,  the  preceding  
        characters have to be re-inspected.  
   
709         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
710         supported by the alternative matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
711    
712         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
713         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
714         ungreedy quantifiers are treated in exactly the same way. However, pos-         ungreedy quantifiers are treated in exactly the same way. However, pos-
715         sessive  quantifiers can make a difference when what follows could also         sessive quantifiers can make a difference when what follows could  also
716         match what is quantified, for example in a pattern like this:         match what is quantified, for example in a pattern like this:
717    
718           ^a++\w!           ^a++\w!
719    
720         This pattern matches "aaab!" but not "aaa!", which would be matched  by         This  pattern matches "aaab!" but not "aaa!", which would be matched by
721         a  non-possessive quantifier. Similarly, if an atomic group is present,         a non-possessive quantifier. Similarly, if an atomic group is  present,
722         it is matched as if it were a standalone pattern at the current  point,         it  is matched as if it were a standalone pattern at the current point,
723         and  the  longest match is then "locked in" for the rest of the overall         and the longest match is then "locked in" for the rest of  the  overall
724         pattern.         pattern.
725    
726         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
727         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
728         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
729         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
730         strings are available.         strings are available.
731    
732         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
733         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
734    
735         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
736         ence as the condition or test for a specific group  recursion  are  not         ence  as  the  condition or test for a specific group recursion are not
737         supported.         supported.
738    
739         5.  Because  many  paths  through the tree may be active, the \K escape         5. Because many paths through the tree may be  active,  the  \K  escape
740         sequence, which resets the start of the match when encountered (but may         sequence, which resets the start of the match when encountered (but may
741         be  on  some  paths  and not on others), is not supported. It causes an         be on some paths and not on others), is not  supported.  It  causes  an
742         error if encountered.         error if encountered.
743    
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)         8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
753         are  not  supported.  (*FAIL)  is supported, and behaves like a failing         are not supported. (*FAIL) is supported, and  behaves  like  a  failing
754         negative assertion.         negative assertion.
755    
756    
757  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
758    
759         Using the alternative matching algorithm provides the following  advan-         Using  the alternative matching algorithm provides the following advan-
760         tages:         tages:
761    
762         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
763         ically found, and in particular, the longest match is  found.  To  find         ically  found,  and  in particular, the longest match is found. To find
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. Because the alternative algorithm  scans  the  subject  string  just         2.  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
# Line 793  AUTHOR Line 794  AUTHOR
794    
795  REVISION  REVISION
796    
797         Last updated: 05 September 2009         Last updated: 29 September 2009
798         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
799  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
800    
801    
802  PCREAPI(3)                                                          PCREAPI(3)  PCREAPI(3)                                                          PCREAPI(3)
803    
804    
# Line 1126  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 1144  COMPILING A PATTERN Line 1147  COMPILING A PATTERN
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, but also some others) can  also  be  set  and         are compatible with Perl, but some others as well) can also be set  and
1151         unset  from  within  the  pattern  (see the detailed description in the         unset  from  within  the  pattern  (see the detailed description in the
1152         pcrepattern documentation). For those options that can be different  in         pcrepattern documentation). For those options that can be different  in
1153         different  parts  of  the pattern, the contents of the options argument         different  parts  of  the pattern, the contents of the options argument
1154         specifies their initial settings at the start of compilation and execu-         specifies their settings at the start of compilation and execution. The
1155         tion.  The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at the         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1156         time of matching as well as at compile time.         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 byte offset from the start of the  pattern  to  the         try to free it. The byte offset from the start of the  pattern  to  the
1163         character  that  was  being  processes when the error was discovered is         character  that  was  being  processed when the error was discovered is
1164         placed in the variable pointed to by erroffset, which must not be NULL.         placed in the variable pointed to by erroffset, which must not be NULL.
1165         If  it  is,  an  immediate error is given. Some errors are not detected         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;         until checks are carried out when the whole pattern has  been  scanned;
# Line 1491  STUDYING A PATTERN Line 1494  STUDYING A PATTERN
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.
# Line 1518  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
1539    
1540         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1541         letters, digits, or whatever, by reference to a set of tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1542         by  character  value.  When running in UTF-8 mode, this applies only to         by character value. When running in UTF-8 mode, this  applies  only  to
1543         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1544         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1545         with Unicode character property support. The use of locales  with  Uni-         with  Unicode  character property support. The use of locales with Uni-
1546         code  is discouraged. If you are handling characters with codes greater         code is discouraged. If you are handling characters with codes  greater
1547         than 128, you should either use UTF-8 and Unicode, or use locales,  but         than  128, you should either use UTF-8 and Unicode, or use locales, but
1548         not try to mix the two.         not try to mix the two.
1549    
1550         PCRE  contains  an  internal set of tables that are used when the final         PCRE contains an internal set of tables that are used  when  the  final
1551         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1552         applications.  Normally, the internal tables recognize only ASCII char-         applications.  Normally, the internal tables recognize only ASCII char-
1553         acters. However, when PCRE is built, it is possible to cause the inter-         acters. However, when PCRE is built, it is possible to cause the inter-
1554         nal tables to be rebuilt in the default "C" locale of the local system,         nal tables to be rebuilt in the default "C" locale of the local system,
1555         which may cause them to be different.         which may cause them to be different.
1556    
1557         The internal tables can always be overridden by tables supplied by  the         The  internal tables can always be overridden by tables supplied by the
1558         application that calls PCRE. These may be created in a different locale         application that calls PCRE. These may be created in a different locale
1559         from the default. As more and more applications change  to  using  Uni-         from  the  default.  As more and more applications change to using Uni-
1560         code, the need for this locale support is expected to die away.         code, the need for this locale support is expected to die away.
1561    
1562         External  tables  are  built by calling the pcre_maketables() function,         External tables are built by calling  the  pcre_maketables()  function,
1563         which has no arguments, in the relevant locale. The result can then  be         which  has no arguments, in the relevant locale. The result can then be
1564         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1565         example, to build and use tables that are appropriate  for  the  French         example,  to  build  and use tables that are appropriate for the French
1566         locale  (where  accented  characters  with  values greater than 128 are         locale (where accented characters with  values  greater  than  128  are
1567         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1568    
1569           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1570           tables = pcre_maketables();           tables = pcre_maketables();
1571           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1572    
1573         The locale name "fr_FR" is used on Linux and other  Unix-like  systems;         The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1574         if you are using Windows, the name for the French locale is "french".         if you are using Windows, the name for the French locale is "french".
1575    
1576         When  pcre_maketables()  runs,  the  tables are built in memory that is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1577         obtained via pcre_malloc. It is the caller's responsibility  to  ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1578         that  the memory containing the tables remains available for as long as         that the memory containing the tables remains available for as long  as
1579         it is needed.         it is needed.
1580    
1581         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1582         pattern,  and the same tables are used via this pointer by pcre_study()         pattern, and the same tables are used via this pointer by  pcre_study()
1583         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1584         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1585         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1586    
1587         It is possible to pass a table pointer or NULL (indicating the  use  of         It  is  possible to pass a table pointer or NULL (indicating the use of
1588         the  internal  tables)  to  pcre_exec(). Although not intended for this         the internal tables) to pcre_exec(). Although  not  intended  for  this
1589         purpose, this facility could be used to match a pattern in a  different         purpose,  this facility could be used to match a pattern in a different
1590         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1591         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1592    
# Line 1584  INFORMATION ABOUT A PATTERN Line 1596  INFORMATION ABOUT A PATTERN
1596         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1597              int what, void *where);              int what, void *where);
1598    
1599         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1600         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1601         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1602    
1603         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1604         pattern.  The second argument is the result of pcre_study(), or NULL if         pattern. The second argument is the result of pcre_study(), or NULL  if
1605         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1606         of  information  is required, and the fourth argument is a pointer to a         of information is required, and the fourth argument is a pointer  to  a
1607         variable to receive the data. The yield of the  function  is  zero  for         variable  to  receive  the  data. The yield of the function is zero for
1608         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1609    
1610           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1600  INFORMATION ABOUT A PATTERN Line 1612  INFORMATION ABOUT A PATTERN
1612           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1613           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1614    
1615         The  "magic  number" is placed at the start of each compiled pattern as         The "magic number" is placed at the start of each compiled  pattern  as
1616         an simple check against passing an arbitrary memory pointer. Here is  a         an  simple check against passing an arbitrary memory pointer. Here is a
1617         typical  call  of pcre_fullinfo(), to obtain the length of the compiled         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1618         pattern:         pattern:
1619    
1620           int rc;           int rc;
# Line 1613  INFORMATION ABOUT A PATTERN Line 1625  INFORMATION ABOUT A PATTERN
1625             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1626             &length);         /* where to put the data */             &length);         /* where to put the data */
1627    
1628         The possible values for the third argument are defined in  pcre.h,  and         The  possible  values for the third argument are defined in pcre.h, and
1629         are as follows:         are as follows:
1630    
1631           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1632    
1633         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1634         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1635         there are no back references.         there are no back references.
1636    
1637           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1638    
1639         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1640         argument should point to an int variable.         argument should point to an int variable.
1641    
1642           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1643    
1644         Return a pointer to the internal default character tables within  PCRE.         Return  a pointer to the internal default character tables within PCRE.
1645         The  fourth  argument should point to an unsigned char * variable. This         The fourth argument should point to an unsigned char *  variable.  This
1646         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1647         tion.  External  callers  can  cause PCRE to use its internal tables by         tion. External callers can cause PCRE to use  its  internal  tables  by
1648         passing a NULL table pointer.         passing a NULL table pointer.
1649    
1650           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1651    
1652         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1653         non-anchored  pattern. The fourth argument should point to an int vari-         non-anchored pattern. The fourth argument should point to an int  vari-
1654         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1655         is still recognized for backwards compatibility.)         is still recognized for backwards compatibility.)
1656    
1657         If  there  is  a  fixed first byte, for example, from a pattern such as         If there is a fixed first byte, for example, from  a  pattern  such  as
1658         (cat|cow|coyote), its value is returned. Otherwise, if either         (cat|cow|coyote), its value is returned. Otherwise, if either
1659    
1660         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1661         branch starts with "^", or         branch starts with "^", or
1662    
1663         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1664         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1665    
1666         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1667         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1668         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1669    
1670           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1671    
1672         If the pattern was studied, and this resulted in the construction of  a         If  the pattern was studied, and this resulted in the construction of a
1673         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1674         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
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           PCRE_INFO_HASCRORLF
1679    
1680         Return 1 if the pattern contains any explicit  matches  for  CR  or  LF         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         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         variable.  An explicit match is either a literal CR or LF character, or
1683         \r or \n.         \r or \n.
1684    
1685           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1686    
1687         Return  1  if  the (?J) or (?-J) option setting is used in the pattern,         Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1688         otherwise 0. The fourth argument should point to an int variable.  (?J)         otherwise  0. The fourth argument should point to an int variable. (?J)
1689         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.         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 1726  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 with         Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1768         pcre_exec(), otherwise 0. The fourth argument should point  to  an  int         pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1769         variable.  From  release  8.00,  this  always  returns  1,  because the         variable. From  release  8.00,  this  always  returns  1,  because  the
1770         restrictions that previously applied  to  partial  matching  have  been         restrictions  that  previously  applied  to  partial matching have been
1771         lifted.  The  pcrepartial documentation gives details of partial match-         lifted. The pcrepartial documentation gives details of  partial  match-
1772         ing.         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 1764  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 1772  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 1830  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1863  MATCHING A PATTERN: THE TRADITIONAL FUNC
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-
# Line 1889  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1922  MATCHING A PATTERN: THE TRADITIONAL FUNC
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
# Line 2177  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2210  MATCHING A PATTERN: THE TRADITIONAL FUNC
2210         has to get additional memory for use during matching. Thus it  is  usu-         has to get additional memory for use during matching. Thus it  is  usu-
2211         ally 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 2438  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  sub-         Warning: If the pattern uses the (?| feature to set up multiple subpat-
2475         patterns  with  the  same  number,  you cannot use names to distinguish         terns  with  the  same number, as described in the section on duplicate
2476         them, because names are not included in the compiled code. The matching         subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2477         process uses only numbers.         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
# Line 2449  DUPLICATE SUBPATTERN NAMES Line 2485  DUPLICATE SUBPATTERN NAMES
2485         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
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
2500         the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING         the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2501         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()         (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2502         function  returns one of the numbers that are associated with the name,         function returns one of the numbers that are associated with the  name,
2503         but it is not defined which it is.         but it is not defined which it is.
2504    
2505         If you want to get full details of all captured substrings for a  given         If  you want to get full details of all captured substrings for a given
2506         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name, you must use  the  pcre_get_stringtable_entries()  function.  The
2507         first argument is the compiled pattern, and the second is the name. The         first argument is the compiled pattern, and the second is the name. The
2508         third  and  fourth  are  pointers to variables which are updated by the         third and fourth are pointers to variables which  are  updated  by  the
2509         function. After it has run, they point to the first and last entries in         function. After it has run, they point to the first and last entries in
2510         the  name-to-number  table  for  the  given  name.  The function itself         the name-to-number table  for  the  given  name.  The  function  itself
2511         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2512         there  are none. The format of the table is described above in the sec-         there are none. The format of the table is described above in the  sec-
2513         tion entitled Information about a  pattern.   Given  all  the  relevant         tion  entitled  Information  about  a  pattern.  Given all the relevant
2514         entries  for the name, you can extract each of their numbers, and hence         entries for the name, you can extract each of their numbers, and  hence
2515         the captured data, if any.         the captured data, if any.
2516    
2517    
2518  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2519    
2520         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2521         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2522         the subject. If you want to find all possible matches, or  the  longest         the  subject.  If you want to find all possible matches, or the longest
2523         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2524         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2525         need  to  find all possible matches, you can kludge it up by making use         need to find all possible matches, you can kludge it up by  making  use
2526         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2527         tation.         tation.
2528    
2529         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2530         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2531         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2532         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2533         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2534    
2535    
# Line 2500  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2540  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2540              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2541              int *workspace, int wscount);              int *workspace, int wscount);
2542    
2543         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2544         against a compiled pattern, using a matching algorithm that  scans  the         against  a  compiled pattern, using a matching algorithm that scans the
2545         subject  string  just  once, and does not backtrack. This has different         subject string just once, and does not backtrack.  This  has  different
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, and a list of features         a discussion of the two matching algorithms, and  a  list  of  features
2550         that pcre_dfa_exec() does not support, see the pcrematching  documenta-         that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2551         tion.         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 2541  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,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2587         PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-         PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2588         TIAL_SOFT,  PCRE_DFA_SHORTEST,  and  PCRE_DFA_RESTART. All but the last         TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last
2589         four of these are  exactly  the  same  as  for  pcre_exec(),  so  their         four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2590         description is not repeated here.         description is not repeated here.
2591    
2592           PCRE_PARTIAL_HARD           PCRE_PARTIAL_HARD
2593           PCRE_PARTIAL_SOFT           PCRE_PARTIAL_SOFT
2594    
2595         These  have the same general effect as they do for pcre_exec(), but the         These have the same general effect as they do for pcre_exec(), but  the
2596         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2597         pcre_dfa_exec(),  it  returns PCRE_ERROR_PARTIAL if the end of the sub-         pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub-
2598         ject is reached and there is still at least  one  matching  possibility         ject  is  reached  and there is still at least one matching possibility
2599         that requires additional characters. This happens even if some complete         that requires additional characters. This happens even if some complete
2600         matches have also been found. When PCRE_PARTIAL_SOFT is set, the return         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         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         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         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         string  that  was inspected when the longest partial match was found is
2605         set as the first matching string in both cases.         set as the first matching string in both cases.
2606    
2607           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2608    
2609         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2610         stop as soon as it has found one match. Because of the way the alterna-         stop as soon as it has found one match. Because of the way the alterna-
2611         tive  algorithm  works, this is necessarily the shortest possible match         tive algorithm works, this is necessarily the shortest  possible  match
2612         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2613    
2614           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2615    
2616         When pcre_dfa_exec() returns a partial match, it is possible to call it         When pcre_dfa_exec() returns a partial match, it is possible to call it
2617         again,  with  additional  subject characters, and have it continue with         again, with additional subject characters, and have  it  continue  with
2618         the same match. The PCRE_DFA_RESTART option requests this action;  when         the  same match. The PCRE_DFA_RESTART option requests this action; when
2619         it  is  set,  the workspace and wscount options must reference the same         it is set, the workspace and wscount options must  reference  the  same
2620         vector as before because data about the match so far is  left  in  them         vector  as  before  because data about the match so far is left in them
2621         after a partial match. There is more discussion of this facility in the         after a partial match. There is more discussion of this facility in the
2622         pcrepartial documentation.         pcrepartial 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 2601  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    
# Line 2668  AUTHOR Line 2708  AUTHOR
2708    
2709  REVISION  REVISION
2710    
2711         Last updated: 22 September 2009         Last updated: 03 October 2009
2712         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2713  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2714    
2715    
2716  PCRECALLOUT(3)                                                  PCRECALLOUT(3)  PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2717    
2718    
# Line 2698  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 2730  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         You can disable these optimizations by passing the  PCRE_NO_START_OPTI-         If the pattern is studied, PCRE knows the minimum length of a  matching
2774         MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the         string,  and will immediately give a "no match" return without actually
2775         matching process, but does ensure that callouts  such  as  the  example         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.         above are obeyed.
2782    
2783    
2784  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2785    
2786         During  matching, when PCRE reaches a callout point, the external func-         During matching, when PCRE reaches a callout point, the external  func-
2787         tion defined by pcre_callout is called (if it is set). This applies  to         tion  defined by pcre_callout is called (if it is set). This applies to
2788         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2789         only argument to the callout function is a pointer  to  a  pcre_callout         only  argument  to  the callout function is a pointer to a pcre_callout
2790         block. This structure contains the following fields:         block. This structure contains the following fields:
2791    
2792           int          version;           int          version;
# Line 2757  THE CALLOUT INTERFACE Line 2802  THE CALLOUT INTERFACE
2802           int          pattern_position;           int          pattern_position;
2803           int          next_item_length;           int          next_item_length;
2804    
2805         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2806         block format. The initial version was 0; the current version is 1.  The         block  format. The initial version was 0; the current version is 1. The
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 2844  AUTHOR Line 2889  AUTHOR
2889    
2890  REVISION  REVISION
2891    
2892         Last updated: 15 March 2009         Last updated: 29 September 2009
2893         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2894  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2895    
2896    
2897  PCRECOMPAT(3)                                                    PCRECOMPAT(3)  PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2898    
2899    
# Line 2859  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 in 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&. PCRE does  support  the  Cs  (surrogate)         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
2941         property,  which  Perl  does  not; the Perl documentation says "Because         property, which Perl does not; the  Perl  documentation  says  "Because
2942         Perl hides the need for the user to understand the internal representa-         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         tion of Unicode characters, there is no need to implement the  somewhat
2944         messy concept of surrogates."         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 2912  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 it is 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. There is a discussion of an example that explains this in         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         more  detail  in  the section on recursion differences from Perl in the
2972         pcrecompat page.         pcrepattern page.
2973    
2974         10.  There are some differences that are concerned with the settings of         10. There are some differences that are concerned with the settings  of
2975         captured strings when part of  a  pattern  is  repeated.  For  example,         captured  strings  when  part  of  a  pattern is repeated. For example,
2976         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching "aba" against the  pattern  /^(a(b)?)+$/  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  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2980         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in         (*FAIL), (*F), (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but  only  in
2981         the forms without an argument. PCRE does not support (*MARK).         the forms without an argument. PCRE does not support (*MARK).
2982    
2983         12. PCRE provides some extensions to the Perl regular expression facil-         12.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
2984         ities.   Perl  5.10  will  include new features that are not in earlier         pattern names is not as general as Perl's. This is a consequence of the
2985         versions, some of which (such as named parentheses) have been  in  PCRE         fact the PCRE works internally just with numbers, using an external ta-
2986         for some time. This list is with respect to Perl 5.10:         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         (a)  Although  lookbehind  assertions  must match fixed length strings,         the same number but different names, is not supported,  and  causes  an
2989         each alternative branch of a lookbehind assertion can match a different         error  at compile time. If it were allowed, it would not be possible to
2990         length of string. Perl requires them all to have the same length.         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    
# Line 2960  DIFFERENCES BETWEEN PCRE AND PERL Line 3016  DIFFERENCES BETWEEN PCRE AND PERL
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, PCRE_NOTEMPTY_ATSTART,         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3019         and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no  Perl  equiva-         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3020         lents.         lents.
3021    
3022         (g)  The  \R escape sequence can be restricted to match only CR, LF, or         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
3023         CRLF by the PCRE_BSR_ANYCRLF option.         CRLF by the PCRE_BSR_ANYCRLF option.
3024    
3025         (h) The callout facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
# Line 2973  DIFFERENCES BETWEEN PCRE AND PERL Line 3029  DIFFERENCES BETWEEN PCRE AND PERL
3029         (j) 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         (k)  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         (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         of a pattern that set overall options that cannot be changed within the
3037         pattern.         pattern.
3038    
# Line 2990  AUTHOR Line 3046  AUTHOR
3046    
3047  REVISION  REVISION
3048    
3049         Last updated: 18 September 2009         Last updated: 04 October 2009
3050         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
3051  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3052    
3053    
3054  PCREPATTERN(3)                                                  PCREPATTERN(3)  PCREPATTERN(3)                                                  PCREPATTERN(3)
3055    
3056    
# Line 3021  PCRE REGULAR EXPRESSION DETAILS Line 3077  PCRE REGULAR EXPRESSION DETAILS
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.  There  is also a special         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3082         sequence that can be given at the start of a pattern:         also a special sequence that can be given at the start of a pattern:
3083    
3084           (*UTF8)           (*UTF8)
3085    
# Line 3061  NEWLINE CONVENTIONS Line 3117  NEWLINE CONVENTIONS
3117           (*ANYCRLF)   any of the three above           (*ANYCRLF)   any of the three above
3118           (*ANY)       all Unicode newline sequences           (*ANY)       all Unicode newline sequences
3119    
3120         These override the default and the options given to pcre_compile(). For         These  override  the default and the options given to pcre_compile() or
3121         example, on a Unix system where LF is the default newline sequence, the         pcre_compile2(). For example, on a Unix system where LF is the  default
3122         pattern         newline sequence, the pattern
3123    
3124           (*CR)a.b           (*CR)a.b
3125    
# Line 3180  BACKSLASH Line 3236  BACKSLASH
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)
# Line 3392  BACKSLASH Line 3448  BACKSLASH
3448           (*BSR_ANYCRLF)   CR, LF, or CRLF only           (*BSR_ANYCRLF)   CR, LF, or CRLF only
3449           (*BSR_UNICODE)   any Unicode newline sequence           (*BSR_UNICODE)   any Unicode newline sequence
3450    
3451         These override the default and the options given to pcre_compile(), but         These override the default and the options given to  pcre_compile()  or
3452         they can be overridden by options given to pcre_exec(). Note that these         pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3453         special settings, which are not Perl-compatible, are recognized only at         pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3454         the  very  start  of a pattern, and that they must be in upper case. If         are  not  Perl-compatible,  are  recognized only at the very start of a
3455         more than one of them is present, the last one is  used.  They  can  be         pattern, and that they must be in upper case. If more than one of  them
3456         combined  with  a  change of newline convention, for example, a pattern         is present, the last one is used. They can be combined with a change of
3457         can start with:         newline convention, for example, a pattern can start with:
3458    
3459           (*ANY)(*BSR_ANYCRLF)           (*ANY)(*BSR_ANYCRLF)
3460    
# Line 3581  BACKSLASH Line 3637  BACKSLASH
3637         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
3638         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.
3639         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
3640         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively. Neither
3641           PCRE nor Perl has a separte "start of word" or "end  of  word"  metase-
3642           quence.  However,  whatever follows \b normally determines which it is.
3643           For example, the fragment \ba matches "a" at the start of a word.
3644    
3645         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
3646         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
3647         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
3648         set. Thus, they are independent of multiline mode. These  three  asser-         set.  Thus,  they are independent of multiline mode. These three asser-
3649         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
3650         affect only the behaviour of the circumflex and dollar  metacharacters.         affect  only the behaviour of the circumflex and dollar metacharacters.
3651         However,  if the startoffset argument of pcre_exec() is non-zero, indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3652         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
3653         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
3654         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
3655         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3656    
3657         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
3658         the start point of the match, as specified by the startoffset  argument         the  start point of the match, as specified by the startoffset argument
3659         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
3660         non-zero. By calling pcre_exec() multiple times with appropriate  argu-         non-zero.  By calling pcre_exec() multiple times with appropriate argu-
3661         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-
3662         mentation where \G can be useful.         mentation where \G can be useful.
3663    
3664         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
3665         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
3666         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
3667         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3668         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3669    
3670         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
3671         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3672         in the compiled regular expression.         in the compiled regular expression.
3673    
# Line 3616  BACKSLASH Line 3675  BACKSLASH
3675  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3676    
3677         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3678         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3679         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-
3680         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
3681         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3682         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3683    
3684         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
3685         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
3686         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
3687         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3688         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-
3689         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
3690         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3691    
3692         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
3693         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3694         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
3695         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
3696         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
3697         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3698    
3699         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
3700         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
3701         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3702    
3703         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3704         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
3705         matches immediately after internal newlines as well as at the start  of         matches  immediately after internal newlines as well as at the start of
3706         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
3707         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
3708         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
3709         as the two-character sequence CRLF, isolated CR and  LF  characters  do         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3710         not indicate newlines.         not indicate newlines.
3711    
3712         For  example, the pattern /^abc$/ matches the subject string "def\nabc"         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3713         (where \n represents a newline) in multiline mode, but  not  otherwise.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3714         Consequently,  patterns  that  are anchored in single line mode because         Consequently, patterns that are anchored in single  line  mode  because
3715         all branches start with ^ are not anchored in  multiline  mode,  and  a         all  branches  start  with  ^ are not anchored in multiline mode, and a
3716         match  for  circumflex  is  possible  when  the startoffset argument of         match for circumflex is  possible  when  the  startoffset  argument  of
3717         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
3718         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3719    
3720         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
3721         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
3722         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
3723         set.         set.
3724    
3725    
3726  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3727    
3728         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-
3729         ter  in  the subject string except (by default) a character that signi-         ter in the subject string except (by default) a character  that  signi-
3730         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
3731         more than one byte long.         more than one byte long.
3732    
3733         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
3734         that character; when the two-character sequence CRLF is used, dot  does         that  character; when the two-character sequence CRLF is used, dot does
3735         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
3736         matches all characters (including isolated CRs and LFs). When any  Uni-         matches  all characters (including isolated CRs and LFs). When any Uni-
3737         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
3738         any of the other line ending characters.         any of the other line ending characters.
3739    
3740         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
3741         PCRE_DOTALL  option  is  set,  a dot matches any one character, without         PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3742         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3743         string, it takes two dots to match it.         string, it takes two dots to match it.
3744    
3745         The  handling of dot is entirely independent of the handling of circum-         The handling of dot is entirely independent of the handling of  circum-
3746         flex and dollar, the only relationship being  that  they  both  involve         flex  and  dollar,  the  only relationship being that they both involve
3747         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3748    
3749    
3750  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3751    
3752         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3753         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
3754         line-ending  characters.  The  feature  is provided in Perl in order to         line-ending characters. The feature is provided in  Perl  in  order  to
3755         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-
3756         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-
3757         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
3758         avoided.         avoided.
3759    
3760         PCRE  does  not  allow \C to appear in lookbehind assertions (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3761         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-
3762         late the length of the lookbehind.         late the length of the lookbehind.
3763    
3764    
# Line 3707  SQUARE BRACKETS AND CHARACTER CLASSES Line 3766  SQUARE BRACKETS AND CHARACTER CLASSES
3766    
3767         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3768         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-
3769         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,
3770         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
3771         circumflex, if present) or escaped with a backslash.         square bracket is required as a member of the class, it should  be  the
3772           first  data  character  in  the  class (after an initial circumflex, if
3773           present) or escaped with a backslash.
3774    
3775         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
3776         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
3777         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
3778         character in the class definition is a circumflex, in  which  case  the         character  in  the  class definition is a circumflex, in which case the
3779         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
3780         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
3781         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3782    
3783         For  example, the character class [aeiou] matches any lower case vowel,         For example, the character class [aeiou] matches any lower case  vowel,
3784         while [^aeiou] matches any character that is not a  lower  case  vowel.         while  [^aeiou]  matches  any character that is not a lower case vowel.
3785         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3786         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
3787         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-
3788         sumes a character from the subject string, and therefore  it  fails  if         sumes  a  character  from the subject string, and therefore it fails if
3789         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3790    
3791         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
3792         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
3793         mechanism.         mechanism.
3794    
3795         When  caseless  matching  is set, any letters in a class represent both         When caseless matching is set, any letters in a  class  represent  both
3796         their upper case and lower case versions, so for  example,  a  caseless         their  upper  case  and lower case versions, so for example, a caseless
3797         [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
3798         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
3799         understands  the  concept  of case for characters whose values are less         understands the concept of case for characters whose  values  are  less
3800         than 128, so caseless matching is always possible. For characters  with         than  128, so caseless matching is always possible. For characters with
3801         higher  values,  the  concept  of case is supported if PCRE is compiled         higher values, the concept of case is supported  if  PCRE  is  compiled
3802         with Unicode property support, but not otherwise.  If you want  to  use         with  Unicode  property support, but not otherwise.  If you want to use
3803         caseless  matching  for  characters 128 and above, you must ensure that         caseless matching in UTF8-mode for characters 128 and above,  you  must
3804         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
3805         support.         with UTF-8 support.
3806    
3807         Characters  that  might  indicate  line breaks are never treated in any         Characters that might indicate line breaks are  never  treated  in  any
3808         special way  when  matching  character  classes,  whatever  line-ending         special  way  when  matching  character  classes,  whatever line-ending
3809         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3810         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
3811         of these characters.         of these characters.
3812    
3813         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-
3814         ters in a character  class.  For  example,  [d-m]  matches  any  letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
3815         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
3816         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
3817         where  it cannot be interpreted as indicating a range, typically as the         where it cannot be interpreted as indicating a range, typically as  the
3818         first or last character in the class.         first or last character in the class.
3819    
3820         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-
3821         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
3822         two characters ("W" and "-") followed by a literal string "46]", so  it         two  characters ("W" and "-") followed by a literal string "46]", so it
3823         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a
3824         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-
3825         preted  as a class containing a range followed by two other characters.         preted as a class containing a range followed by two other  characters.
3826         The octal or hexadecimal representation of "]" can also be used to  end         The  octal or hexadecimal representation of "]" can also be used to end
3827         a range.         a range.
3828    
3829         Ranges  operate in the collating sequence of character values. They can         Ranges operate in the collating sequence of character values. They  can
3830         also  be  used  for  characters  specified  numerically,  for   example         also   be  used  for  characters  specified  numerically,  for  example
3831         [\000-\037].  In UTF-8 mode, ranges can include characters whose values         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values
3832         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3833    
3834         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,
3835         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
3836         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3837         character  tables  for  a French locale are in use, [\xc8-\xcb] matches         character tables for a French locale are in  use,  [\xc8-\xcb]  matches
3838         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
3839         concept  of  case for characters with values greater than 128 only when         concept of case for characters with values greater than 128  only  when
3840         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3841    
3842         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
3843         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
3844         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3845         flex  can  conveniently  be used with the upper case character types to         flex can conveniently be used with the upper case  character  types  to
3846         specify a more restricted set of characters  than  the  matching  lower         specify  a  more  restricted  set of characters than the matching lower
3847         case  type.  For example, the class [^\W_] matches any letter or digit,         case type. For example, the class [^\W_] matches any letter  or  digit,
3848         but not underscore.         but not underscore.
3849    
3850         The only metacharacters that are recognized in  character  classes  are         The  only  metacharacters  that are recognized in character classes are
3851         backslash,  hyphen  (only  where  it can be interpreted as specifying a         backslash, hyphen (only where it can be  interpreted  as  specifying  a
3852         range), circumflex (only at the start), opening  square  bracket  (only         range),  circumflex  (only  at the start), opening square bracket (only
3853         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
3854         next section), and the terminating  closing  square  bracket.  However,         next  section),  and  the  terminating closing square bracket. However,
3855         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3856    
3857    
3858  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3859    
3860         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3861         enclosed by [: and :] within the enclosing square brackets.  PCRE  also         enclosed  by  [: and :] within the enclosing square brackets. PCRE also
3862         supports this notation. For example,         supports this notation. For example,
3863    
3864           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3820  POSIX CHARACTER CLASSES Line 3881  POSIX CHARACTER CLASSES
3881           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3882           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3883    
3884         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),
3885         and  space  (32). Notice that this list includes the VT character (code         and space (32). Notice that this list includes the VT  character  (code
3886         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
3887         Perl compatibility).         Perl compatibility).
3888    
3889         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
3890         from Perl 5.8. Another Perl extension is negation, which  is  indicated         from  Perl  5.8. Another Perl extension is negation, which is indicated
3891         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3892    
3893           [12[:^digit:]]           [12[:^digit:]]
3894    
3895         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
3896         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3897         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.
3898    
# Line 3841  POSIX CHARACTER CLASSES Line 3902  POSIX CHARACTER CLASSES
3902    
3903  VERTICAL BAR  VERTICAL BAR
3904    
3905         Vertical bar characters are used to separate alternative patterns.  For         Vertical  bar characters are used to separate alternative patterns. For
3906         example, the pattern         example, the pattern
3907    
3908           gilbert|sullivan           gilbert|sullivan
3909    
3910         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches either "gilbert" or "sullivan". Any number of alternatives  may
3911         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear,  and  an  empty  alternative  is  permitted (matching the empty
3912         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3913         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
3914         are  within a subpattern (defined below), "succeeds" means matching the         are within a subpattern (defined below), "succeeds" means matching  the
3915         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.
3916    
3917    
3918  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3919    
3920         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3921         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3922         within the pattern by  a  sequence  of  Perl  option  letters  enclosed         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3923         between "(?" and ")".  The option letters are         between "(?" and ")".  The option letters are
3924    
3925           i  for PCRE_CASELESS           i  for PCRE_CASELESS
# Line 3868  INTERNAL OPTION SETTING Line 3929  INTERNAL OPTION SETTING
3929    
3930         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3931         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
3932         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-
3933         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
3934         is  also  permitted.  If  a  letter  appears  both before and after the         is also permitted. If a  letter  appears  both  before  and  after  the
3935         hyphen, the option is unset.         hyphen, the option is unset.
3936    
3937         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3938         can  be changed in the same way as the Perl-compatible options by using         can be changed in the same way as the Perl-compatible options by  using
3939         the characters J, U and X respectively.         the characters J, U and X respectively.
3940    
3941         When one of these option changes occurs at  top  level  (that  is,  not         When  one  of  these  option  changes occurs at top level (that is, not
3942         inside  subpattern parentheses), the change applies to the remainder of         inside subpattern parentheses), the change applies to the remainder  of
3943         the pattern that follows. If the change is placed right at the start of         the pattern that follows. If the change is placed right at the start of
3944         a pattern, PCRE extracts it into the global options (and it will there-         a pattern, PCRE extracts it into the global options (and it will there-
3945         fore show up in data extracted by the pcre_fullinfo() function).         fore show up in data extracted by the pcre_fullinfo() function).
3946    
3947         An option change within a subpattern (see below for  a  description  of         An  option  change  within a subpattern (see below for a description of
3948         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
3949         it, so         it, so
3950    
3951           (a(?i)b)c           (a(?i)b)c
3952    
3953         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
3954         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3955         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3956         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3957         example,         example,
3958    
3959           (a(?i)b|c)           (a(?i)b|c)
3960    
3961         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3962         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3963         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3964         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3965    
3966         Note:  There  are  other  PCRE-specific  options that can be set by the         Note: There are other PCRE-specific options that  can  be  set  by  the
3967         application when the compile or match functions  are  called.  In  some         application  when  the  compile  or match functions are called. In some
3968         cases the pattern can contain special leading sequences such as (*CRLF)         cases the pattern can contain special leading sequences such as (*CRLF)
3969         to override what the application has set or what  has  been  defaulted.         to  override  what  the application has set or what has been defaulted.
3970         Details  are  given  in the section entitled "Newline sequences" above.         Details are given in the section entitled  "Newline  sequences"  above.
3971         There is also the (*UTF8) leading sequence that  can  be  used  to  set         There  is  also  the  (*UTF8)  leading sequence that can be used to set
3972         UTF-8 mode; this is equivalent to setting the PCRE_UTF8 option.         UTF-8 mode; this is equivalent to setting the PCRE_UTF8 option.
3973    
3974    
# Line 3920  SUBPATTERNS Line 3981  SUBPATTERNS
3981    
3982           cat(aract|erpillar|)           cat(aract|erpillar|)
3983    
3984         matches one of the words "cat", "cataract", or  "caterpillar".  Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3985         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3986         string.         string.
3987    
3988         2. It sets up the subpattern as  a  capturing  subpattern.  This  means         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
3989         that,  when  the  whole  pattern  matches,  that portion of the subject         that, when the whole pattern  matches,  that  portion  of  the  subject
3990         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
3991         ovector  argument  of pcre_exec(). Opening parentheses are counted from         ovector argument of pcre_exec(). Opening parentheses are  counted  from
3992         left to right (starting from 1) to obtain  numbers  for  the  capturing         left  to  right  (starting  from 1) to obtain numbers for the capturing
3993         subpatterns.         subpatterns.
3994    
3995         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-
3996         tern         tern
3997    
3998           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3939  SUBPATTERNS Line 4000  SUBPATTERNS
4000         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
4001         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
4002    
4003         The  fact  that  plain  parentheses  fulfil two functions is not always         The fact that plain parentheses fulfil  two  functions  is  not  always
4004         helpful.  There are often times when a grouping subpattern is  required         helpful.   There are often times when a grouping subpattern is required
4005         without  a capturing requirement. If an opening parenthesis is followed         without a capturing requirement. If an opening parenthesis is  followed
4006         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-
4007         ing,  and  is  not  counted when computing the number of any subsequent         ing, and is not counted when computing the  number  of  any  subsequent
4008         capturing subpatterns. For example, if the string "the white queen"  is         capturing  subpatterns. For example, if the string "the white queen" is
4009         matched against the pattern         matched against the pattern
4010    
4011           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3952  SUBPATTERNS Line 4013  SUBPATTERNS
4013         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
4014         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
4015    
4016         As a convenient shorthand, if any option settings are required  at  the         As  a  convenient shorthand, if any option settings are required at the
4017         start  of  a  non-capturing  subpattern,  the option letters may appear         start of a non-capturing subpattern,  the  option  letters  may  appear
4018         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
4019    
4020           (?i:saturday|sunday)           (?i:saturday|sunday)
4021           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
4022    
4023         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
4024         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
4025         the subpattern is reached, an option setting in one branch does  affect         the  subpattern is reached, an option setting in one branch does affect
4026         subsequent  branches,  so  the above patterns match "SUNDAY" as well as         subsequent branches, so the above patterns match "SUNDAY"  as  well  as
4027         "Saturday".         "Saturday".
4028    
4029    
4030  DUPLICATE SUBPATTERN NUMBERS  DUPLICATE SUBPATTERN NUMBERS
4031    
4032         Perl 5.10 introduced a feature whereby each alternative in a subpattern         Perl 5.10 introduced a feature whereby each alternative in a subpattern
4033         uses  the same numbers for its capturing parentheses. Such a subpattern         uses the same numbers for its capturing parentheses. Such a  subpattern
4034         starts with (?| and is itself a non-capturing subpattern. For  example,         starts  with (?| and is itself a non-capturing subpattern. For example,
4035         consider this pattern:         consider this pattern:
4036    
4037           (?|(Sat)ur|(Sun))day           (?|(Sat)ur|(Sun))day
4038    
4039         Because  the two alternatives are inside a (?| group, both sets of cap-         Because the two alternatives are inside a (?| group, both sets of  cap-
4040         turing parentheses are numbered one. Thus, when  the  pattern  matches,         turing  parentheses  are  numbered one. Thus, when the pattern matches,
4041         you  can  look  at captured substring number one, whichever alternative         you can look at captured substring number  one,  whichever  alternative
4042         matched. This construct is useful when you want to  capture  part,  but         matched.  This  construct  is useful when you want to capture part, but
4043         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-
4044         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
4045         each  branch. The numbers of any capturing buffers that follow the sub-         each branch. The numbers of any capturing buffers that follow the  sub-
4046         pattern start after the highest number used in any branch. The  follow-         pattern  start after the highest number used in any branch. The follow-
4047         ing  example  is taken from the Perl documentation.  The numbers under-         ing example is taken from the Perl documentation.  The  numbers  under-
4048         neath show in which buffer the captured content will be stored.         neath show in which buffer the captured content will be stored.
4049    
4050           # before  ---------------branch-reset----------- after           # before  ---------------branch-reset----------- after
4051           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4052           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4053    
4054         A backreference or a recursive call to  a  numbered  subpattern  always         A  backreference  to  a  numbered subpattern uses the most recent value
4055         refers to the first one in the pattern with the given number.         that is set for that number by any subpattern.  The  following  pattern
4056           matches "abcabc" or "defdef":
4057    
4058             /(?|(abc)|(def))\1/
4059    
4060           In  contrast, a recursive or "subroutine" call to a numbered subpattern
4061           always refers to the first one in the pattern with  the  given  number.
4062           The following pattern matches "abcabc" or "defabc":
4063    
4064             /(?|(abc)|(def))(?1)/
4065    
4066           If  a condition test for a subpattern's having matched refers to a non-
4067           unique number, the test is true if any of the subpatterns of that  num-
4068           ber have matched.
4069    
4070         An  alternative approach to using this "branch reset" feature is to use         An  alternative approach to using this "branch reset" feature is to use
4071         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
# Line 4006  NAMED SUBPATTERNS Line 4080  NAMED SUBPATTERNS
4080         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
4081         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
4082         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-
4083         tax.         tax.  Perl  allows  identically  numbered subpatterns to have different
4084           names, but PCRE does not.
4085    
4086         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>...)
4087         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
4088         to capturing parentheses from other parts of the pattern, such as back-         to capturing parentheses from other parts of the pattern, such as back-
4089         references, recursion, and conditions, can be made by name as  well  as         references,  recursion,  and conditions, can be made by name as well as
4090         by number.         by number.
4091    
4092         Names  consist  of  up  to  32 alphanumeric characters and underscores.         Names consist of up to  32  alphanumeric  characters  and  underscores.
4093         Named capturing parentheses are still  allocated  numbers  as  well  as         Named  capturing  parentheses  are  still  allocated numbers as well as
4094         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
4095         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
4096         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
4097         a captured substring by name.         a captured substring by name.
4098    
4099         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
4100         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4101         time. This can be useful for patterns where only one  instance  of  the         time.  (Duplicate  names are also always permitted for subpatterns with
4102         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-
4103         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
4104           named parentheses can match. Suppose you want to match the  name  of  a
4105           weekday,  either as a 3-letter abbreviation or as the full name, and in
4106         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
4107         the line breaks) does the job:         the line breaks) does the job:
4108    
# Line 4035  NAMED SUBPATTERNS Line 4112  NAMED SUBPATTERNS
4112           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
4113           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
4114    
4115         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
4116         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
4117         reset" subpattern, as described in the previous section.)         reset" subpattern, as described in the previous section.)
4118    
4119         The convenience function for extracting the data by  name  returns  the         The  convenience  function  for extracting the data by name returns the
4120         substring  for  the first (and in this example, the only) subpattern of         substring for the first (and in this example, the only)  subpattern  of
4121         that name that matched. This saves searching  to  find  which  numbered         that  name  that  matched.  This saves searching to find which numbered
4122         subpattern  it  was. If you make a reference to a non-unique named sub-         subpattern it was.
4123         pattern from elsewhere in the pattern, the one that corresponds to  the  
4124         lowest  number  is used. For further details of the interfaces for han-         If you make a backreference to a non-unique named subpattern from else-
4125         dling named subpatterns, see the pcreapi documentation.         where  in the pattern, the one that corresponds to the first occurrence
4126           of the name is used. In the absence of duplicate numbers (see the  pre-
4127           vious  section)  this  is  the one with the lowest number. If you use a
4128           named reference in a condition test (see the section  about  conditions
4129           below),  either  to check whether a subpattern has matched, or to check
4130           for recursion, all subpatterns with the same name are  tested.  If  the
4131           condition  is  true for any one of them, the overall condition is true.
4132           This is the same behaviour as testing by number. For further details of
4133           the interfaces for handling named subpatterns, see the pcreapi documen-
4134           tation.
4135    
4136         Warning: You cannot use different names to distinguish between two sub-         Warning: You cannot use different names to distinguish between two sub-
4137         patterns  with  the same number (see the previous section) because PCRE         patterns  with  the same number because PCRE uses only the numbers when
4138         uses only the numbers when matching.         matching. For this reason, an error is given at compile time if differ-
4139           ent  names  are given to subpatterns with the same number. However, you
4140           can give the same name to subpatterns with the same number,  even  when
4141           PCRE_DUPNAMES is not set.
4142    
4143    
4144  REPETITION  REPETITION
4145    
4146         Repetition is specified by quantifiers, which can  follow  any  of  the         Repetition  is  specified  by  quantifiers, which can follow any of the
4147         following items:         following items:
4148    
4149           a literal data character           a literal data character
# Line 4066  REPETITION Line 4155  REPETITION
4155           a character class           a character class
4156           a back reference (see next section)           a back reference (see next section)
4157           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4158             a recursive or "subroutine" call to a subpattern
4159    
4160         The  general repetition quantifier specifies a minimum and maximum num-         The general repetition quantifier specifies a minimum and maximum  num-
4161         ber of permitted matches, by giving the two numbers in  curly  brackets         ber  of  permitted matches, by giving the two numbers in curly brackets
4162         (braces),  separated  by  a comma. The numbers must be less than 65536,         (braces), separated by a comma. The numbers must be  less  than  65536,
4163         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:
4164    
4165           z{2,4}           z{2,4}
4166    
4167         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
4168         special  character.  If  the second number is omitted, but the comma is         special character. If the second number is omitted, but  the  comma  is
4169         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
4170         are  both omitted, the quantifier specifies an exact number of required         are both omitted, the quantifier specifies an exact number of  required
4171         matches. Thus         matches. Thus
4172    
4173           [aeiou]{3,}           [aeiou]{3,}
# Line 4086  REPETITION Line 4176  REPETITION
4176    
4177           \d{8}           \d{8}
4178    
4179         matches exactly 8 digits. An opening curly bracket that  appears  in  a         matches  exactly  8  digits. An opening curly bracket that appears in a
4180         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
4181         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-
4182         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.
4183    
4184         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
4185         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
4186         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
4187         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
4188         extended  sequences,  each of which may be several bytes long (and they         extended sequences, each of which may be several bytes long  (and  they
4189         may be of different lengths).         may be of different lengths).
4190    
4191         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4192         the previous item and the quantifier were not present. This may be use-         the previous item and the quantifier were not present. This may be use-
4193         ful for subpatterns that are referenced as subroutines  from  elsewhere         ful  for  subpatterns that are referenced as subroutines from elsewhere
4194         in the pattern. Items other than subpatterns that have a {0} quantifier         in the pattern. Items other than subpatterns that have a {0} quantifier
4195         are omitted from the compiled pattern.         are omitted from the compiled pattern.
4196    
4197         For convenience, the three most common quantifiers have  single-charac-         For  convenience, the three most common quantifiers have single-charac-
4198         ter abbreviations:         ter abbreviations:
4199    
4200           *    is equivalent to {0,}           *    is equivalent to {0,}
4201           +    is equivalent to {1,}           +    is equivalent to {1,}
4202           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4203    
4204         It  is  possible  to construct infinite loops by following a subpattern         It is possible to construct infinite loops by  following  a  subpattern
4205         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,
4206         for example:         for example:
4207    
4208           (a?)*           (a?)*
4209    
4210         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
4211         for such patterns. However, because there are cases where this  can  be         for  such  patterns. However, because there are cases where this can be
4212         useful,  such  patterns  are now accepted, but if any repetition of the         useful, such patterns are now accepted, but if any  repetition  of  the
4213         subpattern does in fact match no characters, the loop is forcibly  bro-         subpattern  does in fact match no characters, the loop is forcibly bro-
4214         ken.         ken.
4215    
4216         By  default,  the quantifiers are "greedy", that is, they match as much         By default, the quantifiers are "greedy", that is, they match  as  much
4217         as possible (up to the maximum  number  of  permitted  times),  without         as  possible  (up  to  the  maximum number of permitted times), without
4218         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
4219         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
4220         appear  between  /*  and  */ and within the comment, individual * and /         appear between /* and */ and within the comment,  individual  *  and  /
4221         characters may appear. An attempt to match C comments by  applying  the         characters  may  appear. An attempt to match C comments by applying the
4222         pattern         pattern
4223    
4224           /\*.*\*/           /\*.*\*/
# Line 4137  REPETITION Line 4227  REPETITION
4227    
4228           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4229    
4230         fails,  because it matches the entire string owing to the greediness of         fails, because it matches the entire string owing to the greediness  of
4231         the .*  item.         the .*  item.
4232    
4233         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
4234         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4235         the pattern         the pattern
4236    
4237           /\*.*?\*/           /\*.*?\*/
4238    
4239         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
4240         quantifiers  is  not  otherwise  changed,  just the preferred number of         quantifiers is not otherwise changed,  just  the  preferred  number  of
4241         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
4242         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
4243         appear doubled, as in         appear doubled, as in
4244    
4245           \d??\d           \d??\d
# Line 4157  REPETITION Line 4247  REPETITION
4247         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
4248         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4249    
4250         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
4251         Perl), the quantifiers are not greedy by default, but  individual  ones         Perl),  the  quantifiers are not greedy by default, but individual ones
4252         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
4253         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4254    
4255         When a parenthesized subpattern is quantified  with  a  minimum  repeat         When  a  parenthesized  subpattern  is quantified with a minimum repeat
4256         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
4257         required for the compiled pattern, in proportion to  the  size  of  the         required  for  the  compiled  pattern, in proportion to the size of the
4258         minimum or maximum.         minimum or maximum.
4259    
4260         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-
4261         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,
4262         the  pattern  is  implicitly anchored, because whatever follows will be         the pattern is implicitly anchored, because whatever  follows  will  be
4263         tried against every character position in the subject string, so  there         tried  against every character position in the subject string, so there
4264         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
4265         first. PCRE normally treats such a pattern as though it  were  preceded         first.  PCRE  normally treats such a pattern as though it were preceded
4266         by \A.         by \A.
4267    
4268         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-
4269         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-
4270         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4271    
4272         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
4273         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
4274         backreference  elsewhere  in the pattern, a match at the start may fail         backreference elsewhere in the pattern, a match at the start  may  fail
4275         where a later one succeeds. Consider, for example:         where a later one succeeds. Consider, for example:
4276    
4277           (.*)abc\1           (.*)abc\1
4278    
4279         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
4280         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4281    
4282         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 4195  REPETITION Line 4285  REPETITION
4285           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4286    
4287         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4288         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
4289         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
4290         tions. For example, after         tions. For example, after
4291    
4292           /(a|(b))+/           /(a|(b))+/
# Line 4206  REPETITION Line 4296  REPETITION
4296    
4297  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4298    
4299         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
4300         repetition, failure of what follows normally causes the  repeated  item         repetition,  failure  of what follows normally causes the repeated item
4301         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
4302         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,
4303         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
4304         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
4305         no point in carrying on.         no point in carrying on.
4306    
4307         Consider,  for  example, the pattern \d+foo when applied to the subject         Consider, for example, the pattern \d+foo when applied to  the  subject
4308         line         line
4309    
4310           123456bar           123456bar
4311    
4312         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
4313         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
4314         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.
4315         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides
4316         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
4317         to be re-evaluated in this way.         to be re-evaluated in this way.
4318    
4319         If  we  use atomic grouping for the previous example, the matcher gives         If we use atomic grouping for the previous example, the  matcher  gives
4320         up immediately on failing to match "foo" the first time.  The  notation         up  immediately  on failing to match "foo" the first time. The notation
4321         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4322    
4323           (?>\d+)foo           (?>\d+)foo
4324    
4325         This  kind  of  parenthesis "locks up" the  part of the pattern it con-         This kind of parenthesis "locks up" the  part of the  pattern  it  con-
4326         tains once it has matched, and a failure further into  the  pattern  is         tains  once  it  has matched, and a failure further into the pattern is
4327         prevented  from  backtracking into it. Backtracking past it to previous         prevented from backtracking into it. Backtracking past it  to  previous
4328         items, however, works as normal.         items, however, works as normal.
4329    
4330         An alternative description is that a subpattern of  this  type  matches         An  alternative  description  is that a subpattern of this type matches
4331         the  string  of  characters  that an identical standalone pattern would         the string of characters that an  identical  standalone  pattern  would
4332         match, if anchored at the current point in the subject string.         match, if anchored at the current point in the subject string.
4333    
4334         Atomic grouping subpatterns are not capturing subpatterns. Simple cases         Atomic grouping subpatterns are not capturing subpatterns. Simple cases
4335         such as the above example can be thought of as a maximizing repeat that         such as the above example can be thought of as a maximizing repeat that
4336         must swallow everything it can. So, while both \d+ and  \d+?  are  pre-         must  swallow  everything  it can. So, while both \d+ and \d+? are pre-
4337         pared  to  adjust  the number of digits they match in order to make the         pared to adjust the number of digits they match in order  to  make  the
4338         rest of the pattern match, (?>\d+) can only match an entire sequence of         rest of the pattern match, (?>\d+) can only match an entire sequence of
4339         digits.         digits.
4340    
4341         Atomic  groups in general can of course contain arbitrarily complicated         Atomic groups in general can of course contain arbitrarily  complicated
4342         subpatterns, and can be nested. However, when  the  subpattern  for  an         subpatterns,  and  can  be  nested. However, when the subpattern for an
4343         atomic group is just a single repeated item, as in the example above, a         atomic group is just a single repeated item, as in the example above, a
4344         simpler notation, called a "possessive quantifier" can  be  used.  This         simpler  notation,  called  a "possessive quantifier" can be used. This
4345         consists  of  an  additional  + character following a quantifier. Using         consists of an additional + character  following  a  quantifier.  Using
4346         this notation, the previous example can be rewritten as         this notation, the previous example can be rewritten as
4347    
4348           \d++foo           \d++foo
# Line 4262  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4352  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4352    
4353           (abc|xyz){2,3}+           (abc|xyz){2,3}+
4354    
4355         Possessive   quantifiers   are   always  greedy;  the  setting  of  the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
4356         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4357         simpler  forms  of atomic group. However, there is no difference in the         simpler forms of atomic group. However, there is no difference  in  the
4358         meaning of a possessive quantifier and  the  equivalent  atomic  group,         meaning  of  a  possessive  quantifier and the equivalent atomic group,
4359         though  there  may  be a performance difference; possessive quantifiers         though there may be a performance  difference;  possessive  quantifiers
4360         should be slightly faster.         should be slightly faster.
4361    
4362         The possessive quantifier syntax is an extension to the Perl  5.8  syn-         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
4363         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
4364         edition of his book. Mike McCloskey liked it, so implemented it when he         edition of his book. Mike McCloskey liked it, so implemented it when he
4365         built  Sun's Java package, and PCRE copied it from there. It ultimately         built Sun's Java package, and PCRE copied it from there. It  ultimately
4366         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4367    
4368         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4369         ple  pattern  constructs.  For  example, the sequence A+B is treated as         ple pattern constructs. For example, the sequence  A+B  is  treated  as
4370         A++B because there is no point in backtracking into a sequence  of  A's         A++B  because  there is no point in backtracking into a sequence of A's
4371         when B must follow.         when B must follow.
4372    
4373         When  a  pattern  contains an unlimited repeat inside a subpattern that         When a pattern contains an unlimited repeat inside  a  subpattern  that
4374         can itself be repeated an unlimited number of  times,  the  use  of  an         can  itself  be  repeated  an  unlimited number of times, the use of an
4375         atomic  group  is  the  only way to avoid some failing matches taking a         atomic group is the only way to avoid some  failing  matches  taking  a
4376         very long time indeed. The pattern         very long time indeed. The pattern
4377    
4378           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4379    
4380         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
4381         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
4382         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4383    
4384           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4385    
4386         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
4387         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
4388         * repeat in a large number of ways, and all  have  to  be  tried.  (The         *  repeat  in  a  large  number of ways, and all have to be tried. (The
4389         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
4390         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
4391         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
4392         ter that is required for a match, and fail early if it is  not  present         ter  that  is required for a match, and fail early if it is not present
4393         in  the  string.)  If  the pattern is changed so that it uses an atomic         in the string.) If the pattern is changed so that  it  uses  an  atomic
4394         group, like this:         group, like this:
4395    
4396           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
# Line 4312  BACK REFERENCES Line 4402  BACK REFERENCES
4402    
4403         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4404         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-
4405         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4406         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4407    
4408         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4409         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
4410         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4411         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4412         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
4413         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4414         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4415         tion.         tion.
4416    
4417         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
4418         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4419         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4420         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4421         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4422         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4423         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4424    
4425         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4426         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-
4427         ture introduced in Perl 5.10.  This  escape  must  be  followed  by  an         ture  introduced  in  Perl  5.10.  This  escape  must be followed by an
4428         unsigned  number  or  a negative number, optionally enclosed in braces.         unsigned number or a negative number, optionally  enclosed  in  braces.
4429         These examples are all identical:         These examples are all identical:
4430    
4431           (ring), \1           (ring), \1
4432           (ring), \g1           (ring), \g1
4433           (ring), \g{1}           (ring), \g{1}
4434    
4435         An unsigned number specifies an absolute reference without the  ambigu-         An  unsigned number specifies an absolute reference without the ambigu-
4436         ity that is present in the older syntax. It is also useful when literal         ity that is present in the older syntax. It is also useful when literal
4437         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4438         Consider this example:         Consider this example:
# Line 4350  BACK REFERENCES Line 4440  BACK REFERENCES
4440           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4441    
4442         The sequence \g{-1} is a reference to the most recently started captur-         The sequence \g{-1} is a reference to the most recently started captur-
4443         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4444         \g{-2} would be equivalent to \1. The use of relative references can be         \g{-2} would be equivalent to \1. The use of relative references can be
4445         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4446         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4447    
4448         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4449         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4450         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4451         of doing that). So the pattern         of doing that). So the pattern
4452    
4453           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4454    
4455         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4456         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4457         time of the back reference, the case of letters is relevant. For  exam-         time  of the back reference, the case of letters is relevant. For exam-
4458         ple,         ple,
4459    
4460           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4461    
4462         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the
4463         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4464    
4465         There are several different ways of writing back  references  to  named         There  are  several  different ways of writing back references to named
4466         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or
4467         \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4468         unified back reference syntax, in which \g can be used for both numeric         unified back reference syntax, in which \g can be used for both numeric
4469         and named references, is also supported. We  could  rewrite  the  above         and  named  references,  is  also supported. We could rewrite the above
4470         example in any of the following ways:         example in any of the following ways:
4471    
4472           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 4384  BACK REFERENCES Line 4474  BACK REFERENCES
4474           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4475           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4476    
4477         A  subpattern  that  is  referenced  by  name may appear in the pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4478         before or after the reference.         before or after the reference.
4479    
4480         There may be more than one back reference to the same subpattern. If  a         There  may be more than one back reference to the same subpattern. If a
4481         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
4482         references to it always fail. For example, the pattern         references to it always fail by default. For example, the pattern
4483    
4484           (a|(bc))\2           (a|(bc))\2
4485    
4486         always fails if it starts to match "a" rather than "bc". Because  there         always  fails  if  it starts to match "a" rather than "bc". However, if
4487         may  be  many  capturing parentheses in a pattern, all digits following         the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer-
4488         the backslash are taken as part of a potential back  reference  number.         ence to an unset value matches an empty string.
4489         If the pattern continues with a digit character, some delimiter must be  
4490         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         Because  there may be many capturing parentheses in a pattern, all dig-
4491         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         its following a backslash are taken as part of a potential back  refer-
4492         ments" below) can be used.         ence  number.   If  the  pattern continues with a digit character, some
4493           delimiter must  be  used  to  terminate  the  back  reference.  If  the
4494           PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{
4495           syntax or an empty comment (see "Comments" below) can be used.
4496    
4497         A back reference that occurs inside the parentheses to which it  refers         A back reference that occurs inside the parentheses to which it  refers
4498         fails  when  the subpattern is first used, so, for example, (a\1) never         fails  when  the subpattern is first used, so, for example, (a\1) never
# Line 4462  ASSERTIONS Line 4555  ASSERTIONS
4555         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
4556         most convenient way to do it is  with  (?!)  because  an  empty  string         most convenient way to do it is  with  (?!)  because  an  empty  string
4557         always  matches, so an assertion that requires there not to be an empty         always  matches, so an assertion that requires there not to be an empty
4558         string must always fail.         string must always fail.   The  Perl  5.10  backtracking  control  verb
4559           (*FAIL) or (*F) is essentially a synonym for (?!).
4560    
4561     Lookbehind assertions     Lookbehind assertions
4562    
4563         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4564         for negative assertions. For example,         for negative assertions. For example,
4565    
4566           (?<!foo)bar           (?<!foo)bar
4567    
4568         does  find  an  occurrence  of "bar" that is not preceded by "foo". The         does find an occurrence of "bar" that is not  preceded  by  "foo".  The
4569         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4570         strings it matches must have a fixed length. However, if there are sev-         strings it matches must have a fixed length. However, if there are sev-
4571         eral top-level alternatives, they do not all  have  to  have  the  same         eral  top-level  alternatives,  they  do  not all have to have the same
4572         fixed length. Thus         fixed length. Thus
4573    
4574           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4483  ASSERTIONS Line 4577  ASSERTIONS
4577    
4578           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4579    
4580         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4581         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4582         This  is an extension compared with Perl (5.8 and 5.10), which requires         This is an extension compared with Perl (5.8 and 5.10), which  requires
4583         all branches to match the same length of string. An assertion such as         all branches to match the same length of string. An assertion such as
4584    
4585           (?<=ab(c|de))           (?<=ab(c|de))
4586    
4587         is not permitted, because its single top-level  branch  can  match  two         is  not  permitted,  because  its single top-level branch can match two
4588         different lengths, but it is acceptable to PCRE if rewritten to use two         different lengths, but it is acceptable to PCRE if rewritten to use two
4589         top-level branches:         top-level branches:
4590    
4591           (?<=abc|abde)           (?<=abc|abde)
4592    
4593         In some cases, the Perl 5.10 escape sequence \K (see above) can be used         In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4594         instead  of  a  lookbehind  assertion  to  get  round  the fixed-length         instead of  a  lookbehind  assertion  to  get  round  the  fixed-length
4595         restriction.         restriction.
4596    
4597         The implementation of lookbehind assertions is, for  each  alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4598         to  temporarily  move the current position back by the fixed length and         to temporarily move the current position back by the fixed  length  and
4599         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4600         rent position, the assertion fails.         rent position, the assertion fails.
4601    
4602         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
4603         mode) to appear in lookbehind assertions, because it makes it  impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
4604         ble  to  calculate the length of the lookbehind. The \X and \R escapes,         ble to calculate the length of the lookbehind. The \X and  \R  escapes,
4605         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4606    
4607         "Subroutine" calls (see below) such as (?2) or (?&X) are  permitted  in         "Subroutine"  calls  (see below) such as (?2) or (?&X) are permitted in
4608         lookbehinds,  as  long as the subpattern matches a fixed-length string.         lookbehinds, as long as the subpattern matches a  fixed-length  string.
4609         Recursion, however, is not supported.         Recursion, however, is not supported.
4610    
4611         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4612         assertions  to  specify  efficient  matching  at the end of the subject         assertions to specify efficient matching of fixed-length strings at the
4613         string. Consider a simple pattern such as         end of subject strings. Consider a simple pattern such as
4614    
4615           abcd$           abcd$
4616    
4617         when applied to a long string that does  not  match.  Because  matching         when  applied  to  a  long string that does not match. Because matching
4618         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
4619         and then see if what follows matches the rest of the  pattern.  If  the         and  then  see  if what follows matches the rest of the pattern. If the
4620         pattern is specified as         pattern is specified as
4621    
4622           ^.*abcd$           ^.*abcd$
4623    
4624         the  initial .* matches the entire string at first, but when this fails         the initial .* matches the entire string at first, but when this  fails
4625         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
4626         last  character,  then all but the last two characters, and so on. Once         last character, then all but the last two characters, and so  on.  Once
4627         again the search for "a" covers the entire string, from right to  left,         again  the search for "a" covers the entire string, from right to left,
4628         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
4629    
4630           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4631    
4632         there  can  be  no backtracking for the .*+ item; it can match only the         there can be no backtracking for the .*+ item; it can  match  only  the
4633         entire string. The subsequent lookbehind assertion does a  single  test         entire  string.  The subsequent lookbehind assertion does a single test
4634         on  the last four characters. If it fails, the match fails immediately.         on the last four characters. If it fails, the match fails  immediately.
4635         For long strings, this approach makes a significant difference  to  the         For  long  strings, this approach makes a significant difference to the
4636         processing time.         processing time.
4637    
4638     Using multiple assertions     Using multiple assertions
# Line 4547  ASSERTIONS Line 4641  ASSERTIONS
4641    
4642           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4643    
4644         matches  "foo" preceded by three digits that are not "999". Notice that         matches "foo" preceded by three digits that are not "999". Notice  that
4645         each of the assertions is applied independently at the  same  point  in         each  of  the  assertions is applied independently at the same point in
4646         the  subject  string.  First  there  is a check that the previous three         the subject string. First there is a  check  that  the  previous  three
4647         characters are all digits, and then there is  a  check  that  the  same         characters  are  all  digits,  and  then there is a check that the same
4648         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4649         ceded by six characters, the first of which are  digits  and  the  last         ceded  by  six  characters,  the first of which are digits and the last
4650         three  of  which  are not "999". For example, it doesn't match "123abc-         three of which are not "999". For example, it  doesn't  match  "123abc-
4651         foo". A pattern to do that is         foo". A pattern to do that is
4652    
4653           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4654    
4655         This time the first assertion looks at the  preceding  six  characters,         This  time  the  first assertion looks at the preceding six characters,
4656         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4657         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4658    
# Line 4566  ASSERTIONS Line 4660  ASSERTIONS
4660    
4661           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4662    
4663         matches an occurrence of "baz" that is preceded by "bar" which in  turn         matches  an occurrence of "baz" that is preceded by "bar" which in turn
4664         is not preceded by "foo", while         is not preceded by "foo", while
4665    
4666           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4667    
4668         is  another pattern that matches "foo" preceded by three digits and any         is another pattern that matches "foo" preceded by three digits and  any
4669         three characters that are not "999".         three characters that are not "999".
4670    
4671    
4672  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4673    
4674         It is possible to cause the matching process to obey a subpattern  con-         It  is possible to cause the matching process to obey a subpattern con-
4675         ditionally  or to choose between two alternative subpatterns, depending         ditionally or to choose between two alternative subpatterns,  depending
4676         on the result of an assertion, or whether a previous capturing  subpat-         on  the result of an assertion, or whether a specific capturing subpat-
4677         tern  matched  or not. The two possible forms of conditional subpattern         tern has already been matched. The two possible  forms  of  conditional
4678         are         subpattern are:
4679    
4680           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4681           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4682    
4683         If the condition is satisfied, the yes-pattern is used;  otherwise  the         If  the  condition is satisfied, the yes-pattern is used; otherwise the
4684         no-pattern  (if  present)  is used. If there are more than two alterna-         no-pattern (if present) is used. If there are more  than  two  alterna-
4685         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4686    
4687         There are four kinds of condition: references  to  subpatterns,  refer-         There  are  four  kinds of condition: references to subpatterns, refer-
4688         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4689    
4690     Checking for a used subpattern by number     Checking for a used subpattern by number
4691    
4692         If  the  text between the parentheses consists of a sequence of digits,         If the text between the parentheses consists of a sequence  of  digits,
4693         the condition is true if the capturing subpattern of  that  number  has         the condition is true if a capturing subpattern of that number has pre-
4694         previously  matched.  An  alternative notation is to precede the digits         viously matched. If there is more than one  capturing  subpattern  with
4695         with a plus or minus sign. In this case, the subpattern number is rela-         the  same  number  (see  the earlier section about duplicate subpattern
4696         tive rather than absolute.  The most recently opened parentheses can be         numbers), the condition is true if any of them have been set. An alter-
4697         referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In         native  notation is to precede the digits with a plus or minus sign. In
4698         looping constructs it can also make sense to refer to subsequent groups         this case, the subpattern number is relative rather than absolute.  The
4699         with constructs such as (?(+2).         most  recently opened parentheses can be referenced by (?(-1), the next
4700           most recent by (?(-2), and so on. In looping  constructs  it  can  also
4701           make  sense  to  refer  to  subsequent  groups  with constructs such as
4702           (?(+2).
4703    
4704         Consider the following pattern, which  contains  non-significant  white         Consider the following pattern, which  contains  non-significant  white
4705         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
# Line 4645  CONDITIONAL SUBPATTERNS Line 4742  CONDITIONAL SUBPATTERNS
4742    
4743           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4744    
4745           If  the  name used in a condition of this kind is a duplicate, the test
4746           is applied to all subpatterns of the same name, and is true if any  one
4747           of them has matched.
4748    
4749     Checking for pattern recursion     Checking for pattern recursion
4750    
# Line 4655  CONDITIONAL SUBPATTERNS Line 4755  CONDITIONAL SUBPATTERNS
4755    
4756           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4757    
4758         the condition is true if the most recent recursion is into the  subpat-         the condition is true if the most recent recursion is into a subpattern
4759         tern  whose  number or name is given. This condition does not check the         whose number or name is given. This condition does not check the entire
4760         entire recursion stack.         recursion stack. If the name used in a condition  of  this  kind  is  a
4761           duplicate, the test is applied to all subpatterns of the same name, and
4762           is true if any one of them is the most recent recursion.
4763    
4764         At "top level", all these recursion test conditions are false.   Recur-         At "top level", all these recursion test  conditions  are  false.   The
4765         sive patterns are described below.         syntax for recursive patterns is described below.
4766    
4767     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4768    
# Line 4680  CONDITIONAL SUBPATTERNS Line 4782  CONDITIONAL SUBPATTERNS
4782         group  named "byte" is defined. This matches an individual component of         group  named "byte" is defined. This matches an individual component of
4783         an IPv4 address (a number less than 256). When  matching  takes  place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4784         this  part  of  the pattern is skipped because DEFINE acts like a false         this  part  of  the pattern is skipped because DEFINE acts like a false
4785         condition.         condition. The rest of the pattern uses references to the  named  group
4786           to  match the four dot-separated components of an IPv4 address, insist-
4787         The rest of the pattern uses references to the named group to match the         ing on a word boundary at each end.
        four  dot-separated  components of an IPv4 address, insisting on a word  
        boundary at each end.  
4788    
4789     Assertion conditions     Assertion conditions
4790    
# Line 4752  RECURSIVE PATTERNS Line 4852  RECURSIVE PATTERNS
4852         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This PCRE pattern solves the nested  parentheses  problem  (assume  the
4853         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4854    
4855           \( ( (?>[^()]+) | (?R) )* \)           \( ( [^()]++ | (?R) )* \)
4856    
4857         First  it matches an opening parenthesis. Then it matches any number of         First  it matches an opening parenthesis. Then it matches any number of
4858         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings which can either be a  sequence  of  non-parentheses,  or  a
4859         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
4860         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis. Note the use
4861           of a possessive quantifier to avoid backtracking into sequences of non-
4862           parentheses.
4863    
4864         If this were part of a larger pattern, you would not  want  to  recurse         If this were part of a larger pattern, you would not  want  to  recurse
4865         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4866    
4867           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( [^()]++ | (?1) )* \) )
4868    
4869         We  have  put the pattern into parentheses, and caused the recursion to         We  have  put the pattern into parentheses, and caused the recursion to
4870         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
4871    
4872         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be
4873         tricky.  This is made easier by the use of relative references. (A Perl         tricky.  This  is made easier by the use of relative references (a Perl
4874         5.10 feature.)  Instead of (?1) in the  pattern  above  you  can  write         5.10 feature).  Instead of (?1) in the  pattern  above  you  can  write
4875         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
4876         the recursion. In other  words,  a  negative  number  counts  capturing         the recursion. In other  words,  a  negative  number  counts  capturing
4877         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
# Line 4784  RECURSIVE PATTERNS Line 4886  RECURSIVE PATTERNS
4886         syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also         syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also
4887         supported. We could rewrite the above example as follows:         supported. We could rewrite the above example as follows:
4888    
4889           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( [^()]++ | (?&pn) )* \) )
4890    
4891         If  there  is more than one subpattern with the same name, the earliest         If  there  is more than one subpattern with the same name, the earliest
4892         one is used.         one is used.
4893    
4894         This particular example pattern that we have been looking  at  contains         This particular example pattern that we have been looking  at  contains
4895         nested  unlimited repeats, and so the use of atomic grouping for match-         nested unlimited repeats, and so the use of a possessive quantifier for
4896         ing strings of non-parentheses is important when applying  the  pattern         matching strings of non-parentheses is important when applying the pat-
4897         to strings that do not match. For example, when this pattern is applied         tern  to  strings  that do not match. For example, when this pattern is
4898         to         applied to
4899    
4900           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4901    
4902         it yields "no match" quickly. However, if atomic grouping is not  used,         it yields "no match" quickly. However, if a  possessive  quantifier  is
4903         the  match  runs  for a very long time indeed because there are so many         not  used, the match runs for a very long time indeed because there are
4904         different ways the + and * repeats can carve up the  subject,  and  all         so many different ways the + and * repeats can carve  up  the  subject,
4905         have to be tested before failure can be reported.         and all have to be tested before failure can be reported.
4906    
4907         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4908         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
# Line 4814  RECURSIVE PATTERNS Line 4916  RECURSIVE PATTERNS
4916         value taken on at the top level. If additional parentheses  are  added,         value taken on at the top level. If additional parentheses  are  added,
4917         giving         giving
4918    
4919           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( [^()]++ | (?R) )* ) \)
4920              ^                        ^              ^                        ^
4921              ^                        ^              ^                        ^
4922    
# Line 4894  RECURSIVE PATTERNS Line 4996  RECURSIVE PATTERNS
4996         If you want to match typical palindromic phrases, the  pattern  has  to         If you want to match typical palindromic phrases, the  pattern  has  to
4997         ignore all non-word characters, which can be done like this:         ignore all non-word characters, which can be done like this:
4998    
4999           ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+4|\W*+.\W*+))\W*+$           ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$
5000    
5001         If run with the PCRE_CASELESS option, this pattern matches phrases such         If run with the PCRE_CASELESS option, this pattern matches phrases such
5002         as "A man, a plan, a canal: Panama!" and it works well in both PCRE and         as "A man, a plan, a canal: Panama!" and it works well in both PCRE and
# Line 4903  RECURSIVE PATTERNS Line 5005  RECURSIVE PATTERNS
5005         great  deal  longer  (ten  times or more) to match typical phrases, and         great  deal  longer  (ten  times or more) to match typical phrases, and
5006         Perl takes so long that you think it has gone into a loop.         Perl takes so long that you think it has gone into a loop.
5007    
5008           WARNING: The palindrome-matching patterns above work only if  the  sub-
5009           ject  string  does not start with a palindrome that is shorter than the
5010           entire string.  For example, although "abcba" is correctly matched,  if
5011           the  subject  is "ababa", PCRE finds the palindrome "aba" at the start,
5012           then fails at top level because the end of the string does not  follow.
5013           Once  again, it cannot jump back into the recursion to try other alter-
5014           natives, so the entire match fails.
5015    
5016    
5017  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
5018    
# Line 5034  BACKTRACKING CONTROL Line 5144  BACKTRACKING CONTROL
5144    
5145         This verb causes the match to end successfully, skipping the  remainder         This verb causes the match to end successfully, skipping the  remainder
5146         of  the pattern. When inside a recursion, only the innermost pattern is         of  the pattern. When inside a recursion, only the innermost pattern is
5147         ended immediately. If the (*ACCEPT) is  inside  capturing  parentheses,         ended immediately. If (*ACCEPT) is inside  capturing  parentheses,  the
5148         the data so far is captured. (This feature was added to PCRE at release         data  so  far  is  captured. (This feature was added to PCRE at release
5149         8.00.) For example:         8.00.) For example:
5150    
5151           A((?:A|B(*ACCEPT)|C)D)           A((?:A|B(*ACCEPT)|C)D)
# Line 5068  BACKTRACKING CONTROL Line 5178  BACKTRACKING CONTROL
5178    
5179         This verb causes the whole match to fail outright if the  rest  of  the         This verb causes the whole match to fail outright if the  rest  of  the
5180         pattern  does  not match. Even if the pattern is unanchored, no further         pattern  does  not match. Even if the pattern is unanchored, no further
5181         attempts to find a match by advancing the start point take place.  Once         attempts to find a match by advancing the starting  point  take  place.
5182         (*COMMIT)  has been passed, pcre_exec() is committed to finding a match         Once  (*COMMIT)  has been passed, pcre_exec() is committed to finding a
5183         at the current starting point, or not at all. For example:         match at the current starting point, or not at all. For example:
5184    
5185           a+(*COMMIT)b           a+(*COMMIT)b
5186    
# Line 5102  BACKTRACKING CONTROL Line 5212  BACKTRACKING CONTROL
5212         If  the  subject  is  "aaaac...",  after  the first match attempt fails         If  the  subject  is  "aaaac...",  after  the first match attempt fails
5213         (starting at the first character in the  string),  the  starting  point         (starting at the first character in the  string),  the  starting  point
5214         skips on to start the next attempt at "c". Note that a possessive quan-         skips on to start the next attempt at "c". Note that a possessive quan-
5215         tifer does not have the same effect in this example; although it  would         tifer does not have the same effect as this example; although it  would
5216         suppress  backtracking  during  the  first  match  attempt,  the second         suppress  backtracking  during  the  first  match  attempt,  the second
5217         attempt would start at the second character instead of skipping  on  to         attempt would start at the second character instead of skipping  on  to
5218         "c".         "c".
# Line 5125  BACKTRACKING CONTROL Line 5235  BACKTRACKING CONTROL
5235    
5236  SEE ALSO  SEE ALSO
5237    
5238         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).         pcreapi(3), pcrecallout(3), pcrematching(3), pcresyntax(3), pcre(3).
5239    
5240    
5241  AUTHOR  AUTHOR
# Line 5137  AUTHOR Line 5247  AUTHOR
5247    
5248  REVISION  REVISION
5249    
5250         Last updated: 22 September 2009         Last updated: 04 October 2009
5251         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
5252  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
5253    
5254    
5255  PCRESYNTAX(3)                                                    PCRESYNTAX(3)  PCRESYNTAX(3)                                                    PCRESYNTAX(3)
5256    
5257    
# Line 5493  REVISION Line 5603  REVISION
5603         Last updated: 11 April 2009         Last updated: 11 April 2009
5604         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
5605  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
5606    
5607    
5608  PCREPARTIAL(3)                                                  PCREPARTIAL(3)  PCREPARTIAL(3)                                                  PCREPARTIAL(3)
5609    
5610    
# Line 5533  PARTIAL MATCHING IN PCRE Line 5643  PARTIAL MATCHING IN PCRE
5643         plete  match,  though the details differ between the two matching func-         plete  match,  though the details differ between the two matching func-
5644         tions. If both options are set, PCRE_PARTIAL_HARD takes precedence.         tions. If both options are set, PCRE_PARTIAL_HARD takes precedence.
5645    
5646         Setting a partial matching option disables one of PCRE's optimizations.         Setting a partial matching option disables two of PCRE's optimizations.
5647         PCRE  remembers the last literal byte in a pattern, and abandons match-         PCRE  remembers the last literal byte in a pattern, and abandons match-
5648         ing immediately if such a byte is not present in  the  subject  string.         ing immediately if such a byte is not present in  the  subject  string.
5649         This  optimization cannot be used for a subject string that might match         This  optimization cannot be used for a subject string that might match
5650         only partially.         only partially. If the pattern was  studied,  PCRE  knows  the  minimum
5651           length  of  a  matching string, and does not bother to run the matching
5652           function on shorter strings. This optimization  is  also  disabled  for
5653           partial matching.
5654    
5655    
5656  PARTIAL MATCHING USING pcre_exec()  PARTIAL MATCHING USING pcre_exec()
5657    
5658         A partial match occurs during a call to pcre_exec() whenever the end of         A partial match occurs during a call to pcre_exec() whenever the end of
5659         the  subject  string  is reached successfully, but matching cannot con-         the subject string is reached successfully, but  matching  cannot  con-
5660         tinue because more characters are needed. However, at least one charac-         tinue because more characters are needed. However, at least one charac-
5661         ter  must have been matched. (In other words, a partial match can never         ter must have been matched. (In other words, a partial match can  never
5662         be an empty string.)         be an empty string.)
5663    
5664         If PCRE_PARTIAL_SOFT is set,  the  partial  match  is  remembered,  but         If  PCRE_PARTIAL_SOFT  is  set,  the  partial  match is remembered, but
5665         matching continues as normal, and other alternatives in the pattern are         matching continues as normal, and other alternatives in the pattern are
5666         tried.  If  no  complete  match  can  be  found,  pcre_exec()   returns         tried.   If  no  complete  match  can  be  found,  pcre_exec()  returns
5667         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. If there are at least         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. If there are at least
5668         two slots in the offsets vector, the first of them is set to the offset         two slots in the offsets vector, the first of them is set to the offset
5669         of the earliest character that was inspected when the partial match was         of the earliest character that was inspected when the partial match was
5670         found. For convenience, the second offset points  to  the  end  of  the         found.  For  convenience,  the  second  offset points to the end of the
5671         string so that a substring can easily be extracted.         string so that a substring can easily be identified.
5672    
5673         For  the majority of patterns, the first offset identifies the start of         For the majority of patterns, the first offset identifies the start  of
5674         the partially matched string. However, for patterns that contain  look-         the  partially matched string. However, for patterns that contain look-
5675         behind  assertions,  or  \K, or begin with \b or \B, earlier characters         behind assertions, or \K, or begin with \b or  \B,  earlier  characters
5676         have been inspected while carrying out the match. For example:         have been inspected while carrying out the match. For example:
5677    
5678           /(?<=abc)123/           /(?<=abc)123/
5679    
5680         This pattern matches "123", but only if it is preceded by "abc". If the         This pattern matches "123", but only if it is preceded by "abc". If the
5681         subject string is "xyzabc12", the offsets after a partial match are for         subject string is "xyzabc12", the offsets after a partial match are for
5682         the substring "abc12", because  all  these  characters  are  needed  if         the  substring  "abc12",  because  all  these  characters are needed if
5683         another match is tried with extra characters added.         another match is tried with extra characters added.
5684    
5685         If  there  is more than one partial match, the first one that was found         If there is more than one partial match, the first one that  was  found
5686         provides the data that is returned. Consider this pattern:         provides the data that is returned. Consider this pattern:
5687    
5688           /123\w+X|dogY/           /123\w+X|dogY/
5689    
5690         If this is matched against the subject string "abc123dog", both  alter-         If  this is matched against the subject string "abc123dog", both alter-
5691         natives  fail  to  match,  but the end of the subject is reached during         natives fail to match, but the end of the  subject  is  reached  during
5692         matching,   so    PCRE_ERROR_PARTIAL    is    returned    instead    of         matching,    so    PCRE_ERROR_PARTIAL    is    returned    instead   of
5693         PCRE_ERROR_NOMATCH.  The  offsets  are  set  to  3  and  9, identifying         PCRE_ERROR_NOMATCH. The  offsets  are  set  to  3  and  9,  identifying
5694         "123dog" as the first partial match that was found. (In  this  example,         "123dog"  as  the first partial match that was found. (In this example,
5695         there  are  two  partial  matches,  because  "dog" on its own partially         there are two partial matches,  because  "dog"  on  its  own  partially
5696         matches the second alternative.)         matches the second alternative.)
5697    
5698         If PCRE_PARTIAL_HARD is set for pcre_exec(), it returns PCRE_ERROR_PAR-         If PCRE_PARTIAL_HARD is set for pcre_exec(), it returns PCRE_ERROR_PAR-
5699         TIAL  as soon as a partial match is found, without continuing to search         TIAL as soon as a partial match is found, without continuing to  search
5700         for possible complete matches. The difference between the  two  options         for  possible  complete matches. The difference between the two options
5701         can be illustrated by a pattern such as:         can be illustrated by a pattern such as:
5702    
5703           /dog(sbody)?/           /dog(sbody)?/
5704    
5705         This  matches either "dog" or "dogsbody", greedily (that is, it prefers         This matches either "dog" or "dogsbody", greedily (that is, it  prefers
5706         the longer string if possible). If it is  matched  against  the  string         the  longer  string  if  possible). If it is matched against the string
5707         "dog"  with  PCRE_PARTIAL_SOFT,  it  yields a complete match for "dog".         "dog" with PCRE_PARTIAL_SOFT, it yields a  complete  match  for  "dog".
5708         However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL.         However, if PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL.
5709         On  the  other hand, if the pattern is made ungreedy the result is dif-         On the other hand, if the pattern is made ungreedy the result  is  dif-
5710         ferent:         ferent:
5711    
5712           /dog(sbody)??/           /dog(sbody)??/
5713    
5714         In this case the result is always a complete match because  pcre_exec()         In  this case the result is always a complete match because pcre_exec()
5715         finds  that  first,  and  it  never continues after finding a match. It         finds that first, and it never continues  after  finding  a  match.  It
5716         might be easier to follow this explanation by thinking of the two  pat-         might  be easier to follow this explanation by thinking of the two pat-
5717         terns like this:         terns like this:
5718    
5719           /dog(sbody)?/    is the same as  /dogsbody|dog/           /dog(sbody)?/    is the same as  /dogsbody|dog/
5720           /dog(sbody)??/   is the same as  /dog|dogsbody/           /dog(sbody)??/   is the same as  /dog|dogsbody/
5721    
5722         The  second  pattern  will  never  match "dogsbody" when pcre_exec() is         The second pattern will never  match  "dogsbody"  when  pcre_exec()  is
5723         used, because it will always find the shorter match first.         used, because it will always find the shorter match first.
5724    
5725    
5726  PARTIAL MATCHING USING pcre_dfa_exec()  PARTIAL MATCHING USING pcre_dfa_exec()
5727    
5728         The pcre_dfa_exec() function moves along the subject  string  character         The  pcre_dfa_exec()  function moves along the subject string character
5729         by  character, without backtracking, searching for all possible matches         by character, without backtracking, searching for all possible  matches
5730         simultaneously. If the end of the subject is reached before the end  of         simultaneously.  If the end of the subject is reached before the end of
5731         the  pattern,  there  is the possibility of a partial match, again pro-         the pattern, there is the possibility of a partial  match,  again  pro-
5732         vided that at least one character has matched.         vided that at least one character has matched.
5733    
5734         When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned  only  if         When  PCRE_PARTIAL_SOFT  is set, PCRE_ERROR_PARTIAL is returned only if
5735         there  have  been  no complete matches. Otherwise, the complete matches         there have been no complete matches. Otherwise,  the  complete  matches
5736         are returned.  However, if PCRE_PARTIAL_HARD is set,  a  partial  match         are  returned.   However,  if PCRE_PARTIAL_HARD is set, a partial match
5737         takes  precedence  over any complete matches. The portion of the string         takes precedence over any complete matches. The portion of  the  string
5738         that was inspected when the longest partial match was found is  set  as         that  was  inspected when the longest partial match was found is set as
5739         the first matching string, provided there are at least two slots in the         the first matching string, provided there are at least two slots in the
5740         offsets vector.         offsets vector.
5741    
5742         Because pcre_dfa_exec() always searches for all possible  matches,  and         Because  pcre_dfa_exec()  always searches for all possible matches, and
5743         there  is no difference between greedy and ungreedy repetition, its be-         there is no difference between greedy and ungreedy repetition, its  be-
5744         haviour is different from pcre_exec when PCRE_PARTIAL_HARD is set. Con-         haviour is different from pcre_exec when PCRE_PARTIAL_HARD is set. Con-
5745         sider  the  string  "dog"  matched  against  the ungreedy pattern shown         sider the string "dog"  matched  against  the  ungreedy  pattern  shown
5746         above:         above:
5747    
5748           /dog(sbody)??/           /dog(sbody)??/
5749    
5750         Whereas pcre_exec() stops as soon as it finds the  complete  match  for         Whereas  pcre_exec()  stops  as soon as it finds the complete match for
5751         "dog", pcre_dfa_exec() also finds the partial match for "dogsbody", and         "dog", pcre_dfa_exec() also finds the partial match for "dogsbody", and
5752         so returns that when PCRE_PARTIAL_HARD is set.         so returns that when PCRE_PARTIAL_HARD is set.
5753    
5754    
5755  PARTIAL MATCHING AND WORD BOUNDARIES  PARTIAL MATCHING AND WORD BOUNDARIES
5756    
5757         If a pattern ends with one of sequences \w or \W, which test  for  word         If  a  pattern ends with one of sequences \w or \W, which test for word
5758         boundaries,  partial  matching with PCRE_PARTIAL_SOFT can give counter-         boundaries, partial matching with PCRE_PARTIAL_SOFT can  give  counter-
5759         intuitive results. Consider this pattern:         intuitive results. Consider this pattern:
5760    
5761           /\bcat\b/           /\bcat\b/
5762    
5763         This matches "cat", provided there is a word boundary at either end. If         This matches "cat", provided there is a word boundary at either end. If
5764         the subject string is "the cat", the comparison of the final "t" with a         the subject string is "the cat", the comparison of the final "t" with a
5765         following character cannot take place, so a  partial  match  is  found.         following  character  cannot  take  place, so a partial match is found.
5766         However,  pcre_exec() carries on with normal matching, which matches \b         However, pcre_exec() carries on with normal matching, which matches  \b
5767         at the end of the subject when the last character  is  a  letter,  thus         at  the  end  of  the subject when the last character is a letter, thus
5768         finding a complete match. The result, therefore, is not PCRE_ERROR_PAR-         finding a complete match. The result, therefore, is not PCRE_ERROR_PAR-
5769         TIAL. The same thing happens  with  pcre_dfa_exec(),  because  it  also         TIAL.  The  same  thing  happens  with pcre_dfa_exec(), because it also
5770         finds the complete match.         finds the complete match.
5771    
5772         Using  PCRE_PARTIAL_HARD  in  this  case does yield PCRE_ERROR_PARTIAL,         Using PCRE_PARTIAL_HARD in this  case  does  yield  PCRE_ERROR_PARTIAL,
5773         because then the partial match takes precedence.         because then the partial match takes precedence.
5774    
5775    
5776  FORMERLY RESTRICTED PATTERNS  FORMERLY RESTRICTED PATTERNS
5777    
5778         For releases of PCRE prior to 8.00, because of the way certain internal         For releases of PCRE prior to 8.00, because of the way certain internal
5779         optimizations   were  implemented  in  the  pcre_exec()  function,  the         optimizations  were  implemented  in  the  pcre_exec()  function,   the
5780         PCRE_PARTIAL option (predecessor of  PCRE_PARTIAL_SOFT)  could  not  be         PCRE_PARTIAL  option  (predecessor  of  PCRE_PARTIAL_SOFT) could not be
5781         used  with all patterns. From release 8.00 onwards, the restrictions no         used with all patterns. From release 8.00 onwards, the restrictions  no
5782         longer apply, and partial matching with pcre_exec()  can  be  requested         longer  apply,  and  partial matching with pcre_exec() can be requested
5783         for any pattern.         for any pattern.
5784    
5785         Items that were formerly restricted were repeated single characters and         Items that were formerly restricted were repeated single characters and
5786         repeated metasequences. If PCRE_PARTIAL was set for a pattern that  did         repeated  metasequences. If PCRE_PARTIAL was set for a pattern that did
5787         not  conform  to  the restrictions, pcre_exec() returned the error code         not conform to the restrictions, pcre_exec() returned  the  error  code
5788         PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in  use.  The         PCRE_ERROR_BADPARTIAL  (-13).  This error code is no longer in use. The
5789         PCRE_INFO_OKPARTIAL  call  to pcre_fullinfo() to find out if a compiled         PCRE_INFO_OKPARTIAL call to pcre_fullinfo() to find out if  a  compiled
5790         pattern can be used for partial matching now always returns 1.         pattern can be used for partial matching now always returns 1.
5791    
5792    
5793  EXAMPLE OF PARTIAL MATCHING USING PCRETEST  EXAMPLE OF PARTIAL MATCHING USING PCRETEST
5794    
5795         If the escape sequence \P is present  in  a  pcretest  data  line,  the         If  the  escape  sequence  \P  is  present in a pcretest data line, the
5796         PCRE_PARTIAL_SOFT  option  is  used  for  the  match.  Here is a run of         PCRE_PARTIAL_SOFT option is used for  the  match.  Here  is  a  run  of
5797         pcretest that uses the date example quoted above:         pcretest that uses the date example quoted above:
5798    
5799             re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/             re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
# Line 5696  EXAMPLE OF PARTIAL MATCHING USING PCRETE Line 5809  EXAMPLE OF PARTIAL MATCHING USING PCRETE
5809           data> j\P           data> j\P
5810           No match           No match
5811    
5812         The first data string is matched  completely,  so  pcretest  shows  the         The  first  data  string  is  matched completely, so pcretest shows the
5813         matched  substrings.  The  remaining four strings do not match the com-         matched substrings. The remaining four strings do not  match  the  com-
5814         plete pattern, but the first two are partial matches. Similar output is         plete pattern, but the first two are partial matches. Similar output is
5815         obtained when pcre_dfa_exec() is used.         obtained when pcre_dfa_exec() is used.
5816    
5817         If  the escape sequence \P is present more than once in a pcretest data         If the escape sequence \P is present more than once in a pcretest  data
5818         line, the PCRE_PARTIAL_HARD option is set for the match.         line, the PCRE_PARTIAL_HARD option is set for the match.
5819    
5820    
5821  MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()  MULTI-SEGMENT MATCHING WITH pcre_dfa_exec()
5822    
5823         When a partial match has been found using pcre_dfa_exec(), it is possi-         When a partial match has been found using pcre_dfa_exec(), it is possi-
5824         ble  to  continue  the  match  by providing additional subject data and         ble to continue the match by  providing  additional  subject  data  and
5825         calling pcre_dfa_exec() again with the same  compiled  regular  expres-         calling  pcre_dfa_exec()  again  with the same compiled regular expres-
5826         sion,  this time setting the PCRE_DFA_RESTART option. You must pass the         sion, this time setting the PCRE_DFA_RESTART option. You must pass  the
5827         same working space as before, because this is where details of the pre-         same working space as before, because this is where details of the pre-
5828         vious  partial  match  are  stored.  Here is an example using pcretest,         vious partial match are stored. Here  is  an  example  using  pcretest,
5829         using the \R escape sequence to set  the  PCRE_DFA_RESTART  option  (\D         using  the  \R  escape  sequence to set the PCRE_DFA_RESTART option (\D
5830         specifies the use of pcre_dfa_exec()):         specifies the use of pcre_dfa_exec()):
5831    
5832             re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/             re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
# Line 5722  MULTI-SEGMENT MATCHING WITH pcre_dfa_exe Line 5835  MULTI-SEGMENT MATCHING WITH pcre_dfa_exe
5835           data> n05\R\D           data> n05\R\D
5836            0: n05            0: n05
5837    
5838         The  first  call has "23ja" as the subject, and requests partial match-         The first call has "23ja" as the subject, and requests  partial  match-
5839         ing; the second call  has  "n05"  as  the  subject  for  the  continued         ing;  the  second  call  has  "n05"  as  the  subject for the continued
5840         (restarted)  match.   Notice  that when the match is complete, only the         (restarted) match.  Notice that when the match is  complete,  only  the
5841         last part is shown; PCRE does  not  retain  the  previously  partially-         last  part  is  shown;  PCRE  does not retain the previously partially-
5842         matched  string. It is up to the calling program to do that if it needs         matched string. It is up to the calling program to do that if it  needs
5843         to.         to.
5844    
5845         You can set the PCRE_PARTIAL_SOFT  or  PCRE_PARTIAL_HARD  options  with         You  can  set  the  PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with
5846         PCRE_DFA_RESTART  to  continue partial matching over multiple segments.         PCRE_DFA_RESTART to continue partial matching over  multiple  segments.
5847         This facility can  be  used  to  pass  very  long  subject  strings  to         This  facility  can  be  used  to  pass  very  long  subject strings to
5848         pcre_dfa_exec().         pcre_dfa_exec().
5849    
5850    
5851  MULTI-SEGMENT MATCHING WITH pcre_exec()  MULTI-SEGMENT MATCHING WITH pcre_exec()
5852    
5853         From  release  8.00,  pcre_exec()  can also be used to do multi-segment         From release 8.00, pcre_exec() can also be  used  to  do  multi-segment
5854         matching. Unlike pcre_dfa_exec(), it is not  possible  to  restart  the         matching.  Unlike  pcre_dfa_exec(),  it  is not possible to restart the
5855         previous  match  with  a new segment of data. Instead, new data must be         previous match with a new segment of data. Instead, new  data  must  be
5856         added to the previous subject string,  and  the  entire  match  re-run,         added  to  the  previous  subject  string, and the entire match re-run,
5857         starting  from the point where the partial match occurred. Earlier data         starting from the point where the partial match occurred. Earlier  data
5858         can be discarded.  Consider an unanchored pattern that matches dates:         can be discarded.  Consider an unanchored pattern that matches dates:
5859    
5860             re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/             re> /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/
# Line 5749  MULTI-SEGMENT MATCHING WITH pcre_exec() Line 5862  MULTI-SEGMENT MATCHING WITH pcre_exec()
5862           Partial match: 23ja           Partial match: 23ja
5863    
5864         The this stage, an application could discard the text preceding "23ja",         The this stage, an application could discard the text preceding "23ja",
5865         add  on  text from the next segment, and call pcre_exec() again. Unlike         add on text from the next segment, and call pcre_exec()  again.  Unlike
5866         pcre_dfa_exec(), the entire matching string must always  be  available,         pcre_dfa_exec(),  the  entire matching string must always be available,
5867         and  the complete matching process occurs for each call, so more memory         and the complete matching process occurs for each call, so more  memory
5868         and more processing time is needed.         and more processing time is needed.
5869    
5870         Note: If the pattern contains lookbehind assertions, or \K,  or  starts         Note:  If  the pattern contains lookbehind assertions, or \K, or starts
5871         with  \b  or  \B,  the string that is returned for a partial match will         with \b or \B, the string that is returned for  a  partial  match  will
5872         include characters that precede the partially  matched  string  itself,         include  characters  that  precede the partially matched string itself,
5873         because  these  must  be  retained when adding on more characters for a         because these must be retained when adding on  more  characters  for  a
5874         subsequent matching attempt.         subsequent matching attempt.
5875    
5876    
# Line 5766  ISSUES WITH MULTI-SEGMENT MATCHING Line 5879  ISSUES WITH MULTI-SEGMENT MATCHING
5879         Certain types of pattern may give problems with multi-segment matching,         Certain types of pattern may give problems with multi-segment matching,
5880         whichever matching function is used.         whichever matching function is used.
5881    
5882         1.  If  the  pattern contains tests for the beginning or end of a line,         1. If the pattern contains tests for the beginning or end  of  a  line,
5883         you need to pass the PCRE_NOTBOL or PCRE_NOTEOL options,  as  appropri-         you  need  to pass the PCRE_NOTBOL or PCRE_NOTEOL options, as appropri-
5884         ate,  when  the subject string for any call does not contain the begin-         ate, when the subject string for any call does not contain  the  begin-
5885         ning or end of a line.         ning or end of a line.
5886    
5887         2. Lookbehind assertions at the start of a pattern are catered  for  in         2.  Lookbehind  assertions at the start of a pattern are catered for in
5888         the  offsets that are returned for a partial match. However, in theory,         the offsets that are returned for a partial match. However, in  theory,
5889         a lookbehind assertion later in the pattern could require even  earlier         a  lookbehind assertion later in the pattern could require even earlier
5890         characters  to  be inspected, and it might not have been reached when a         characters to be inspected, and it might not have been reached  when  a
5891         partial match occurs. This is probably an extremely unlikely case;  you         partial  match occurs. This is probably an extremely unlikely case; you
5892         could  guard  against  it to a certain extent by always including extra         could guard against it to a certain extent by  always  including  extra
5893         characters at the start.         characters at the start.
5894    
5895         3. Matching a subject string that is split into multiple  segments  may         3.  Matching  a subject string that is split into multiple segments may
5896         not  always produce exactly the same result as matching over one single         not always produce exactly the same result as matching over one  single
5897         long string, especially when PCRE_PARTIAL_SOFT  is  used.  The  section         long  string,  especially  when  PCRE_PARTIAL_SOFT is used. The section
5898         "Partial  Matching  and  Word Boundaries" above describes an issue that         "Partial Matching and Word Boundaries" above describes  an  issue  that
5899         arises if the pattern ends with \b or \B. Another  kind  of  difference         arises  if  the  pattern ends with \b or \B. Another kind of difference
5900         may  occur  when  there  are multiple matching possibilities, because a         may occur when there are multiple  matching  possibilities,  because  a
5901         partial match result is given only when there are no completed matches.         partial match result is given only when there are no completed matches.
5902         This means that as soon as the shortest match has been found, continua-         This means that as soon as the shortest match has been found, continua-
5903         tion to a new subject segment is no longer  possible.   Consider  again         tion  to  a  new subject segment is no longer possible.  Consider again
5904         this pcretest example:         this pcretest example:
5905    
5906             re> /dog(sbody)?/             re> /dog(sbody)?/
# Line 5801  ISSUES WITH MULTI-SEGMENT MATCHING Line 5914  ISSUES WITH MULTI-SEGMENT MATCHING
5914            0: dogsbody            0: dogsbody
5915            1: dog            1: dog
5916    
5917         The  first  data line passes the string "dogsb" to pcre_exec(), setting         The first data line passes the string "dogsb" to  pcre_exec(),  setting
5918         the PCRE_PARTIAL_SOFT option. Although the string is  a  partial  match         the  PCRE_PARTIAL_SOFT  option.  Although the string is a partial match
5919         for  "dogsbody",  the  result  is  not  PCRE_ERROR_PARTIAL, because the         for "dogsbody", the  result  is  not  PCRE_ERROR_PARTIAL,  because  the
5920         shorter string "dog" is a complete match. Similarly, when  the  subject         shorter  string  "dog" is a complete match. Similarly, when the subject
5921         is  presented to pcre_dfa_exec() in several parts ("do" and "gsb" being         is presented to pcre_dfa_exec() in several parts ("do" and "gsb"  being
5922         the first two) the match stops when "dog" has been found, and it is not         the first two) the match stops when "dog" has been found, and it is not
5923         possible  to continue. On the other hand, if "dogsbody" is presented as         possible to continue. On the other hand, if "dogsbody" is presented  as
5924         a single string, pcre_dfa_exec() finds both matches.         a single string, pcre_dfa_exec() finds both matches.
5925    
5926         Because of these problems, it is probably best to use PCRE_PARTIAL_HARD         Because of these problems, it is probably best to use PCRE_PARTIAL_HARD
5927         when  matching  multi-segment data. The example above then behaves dif-         when matching multi-segment data. The example above then  behaves  dif-
5928         ferently:         ferently:
5929    
5930             re> /dog(sbody)?/             re> /dog(sbody)?/
# Line 5824  ISSUES WITH MULTI-SEGMENT MATCHING Line 5937  ISSUES WITH MULTI-SEGMENT MATCHING
5937    
5938    
5939         4. Patterns that contain alternatives at the top level which do not all         4. Patterns that contain alternatives at the top level which do not all
5940         start  with  the  same  pattern  item  may  not  work  as expected when         start with the  same  pattern  item  may  not  work  as  expected  when
5941         pcre_dfa_exec() is used. For example, consider this pattern:         pcre_dfa_exec() is used. For example, consider this pattern:
5942    
5943           1234|3789           1234|3789
5944    
5945         If the first part of the subject is "ABC123", a partial  match  of  the         If  the  first  part of the subject is "ABC123", a partial match of the
5946         first  alternative  is found at offset 3. There is no partial match for         first alternative is found at offset 3. There is no partial  match  for
5947         the second alternative, because such a match does not start at the same         the second alternative, because such a match does not start at the same
5948         point  in  the  subject  string. Attempting to continue with the string         point in the subject string. Attempting to  continue  with  the  string
5949         "7890" does not yield a match  because  only  those  alternatives  that         "7890"  does  not  yield  a  match because only those alternatives that
5950         match  at  one  point in the subject are remembered. The problem arises         match at one point in the subject are remembered.  The  problem  arises
5951         because the start of the second alternative matches  within  the  first         because  the  start  of the second alternative matches within the first
5952         alternative.  There  is  no  problem with anchored patterns or patterns         alternative. There is no problem with  anchored  patterns  or  patterns
5953         such as:         such as:
5954    
5955           1234|ABCD           1234|ABCD
5956    
5957         where no string can be a partial match for both alternatives.  This  is         where  no  string can be a partial match for both alternatives. This is
5958         not  a  problem if pcre_exec() is used, because the entire match has to         not a problem if pcre_exec() is used, because the entire match  has  to
5959         be rerun each time:         be rerun each time:
5960    
5961             re> /1234|3789/             re> /1234|3789/
# Line 5861  AUTHOR Line 5974  AUTHOR
5974    
5975  REVISION  REVISION
5976    
5977         Last updated: 05 September 2009         Last updated: 29 September 2009
5978         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
5979  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
5980    
5981    
5982  PCREPRECOMPILE(3)                                            PCREPRECOMPILE(3)  PCREPRECOMPILE(3)                                            PCREPRECOMPILE(3)
5983    
5984    
# Line 5988  REVISION Line 6101  REVISION
6101         Last updated: 13 June 2007         Last updated: 13 June 2007
6102         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
6103  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
6104    
6105    
6106  PCREPERFORM(3)                                                  PCREPERFORM(3)  PCREPERFORM(3)                                                  PCREPERFORM(3)