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# Line 2  Line 2 
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
5  synopses of each function in the library have not been included. 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         5.10/5.11, including support for UTF-8 encoded strings and Unicode gen-
30         Unicode general category properties. However, UTF-8 and Unicode support         eral  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 5.2.0.
33    
34         In  addition to the Perl-compatible matching function, PCRE contains an         In  addition to the Perl-compatible matching function, PCRE contains an
35         alternative matching function that matches the same  compiled  patterns         alternative function that matches the same compiled patterns in a  dif-
36         in  a different way. In certain circumstances, the alternative function         ferent way. In certain circumstances, the alternative function has some
37         has some advantages. For a discussion of the two  matching  algorithms,         advantages.  For a discussion of the two matching algorithms,  see  the
38         see the pcrematching page.         pcrematching page.
39    
40         PCRE  is  written  in C and released as a C library. A number of people         PCRE  is  written  in C and released as a C library. A number of people
41         have written wrappers and interfaces of various kinds.  In  particular,         have written wrappers and interfaces of various kinds.  In  particular,
# Line 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 222  UTF-8 AND UNICODE PROPERTY SUPPORT Line 222  UTF-8 AND UNICODE PROPERTY SUPPORT
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
225         test characters of any code value, but the characters that PCRE  recog-         test characters of any code value, but, by default, the characters that
226         nizes  as  digits,  spaces,  or  word characters remain the same set as         PCRE  recognizes  as digits, spaces, or word characters remain the same
227         before, all with values less than 256. This remains true even when PCRE         set as before, all with values less than 256. This  remains  true  even
228         includes  Unicode  property support, because to do otherwise would slow         when  PCRE  is built to include Unicode property support, because to do
229         down PCRE in many common cases. If you really want to test for a  wider         otherwise would slow down PCRE in many common  cases.  Note  that  this
230         sense  of,  say,  "digit",  you must use Unicode property tests such as         also applies to \b, because it is defined in terms of \w and \W. If you
231         \p{Nd}. Note that this also applies to \b, because  it  is  defined  in         really want to test for a wider sense of, say,  "digit",  you  can  use
232         terms of \w and \W.         explicit  Unicode property tests such as \p{Nd}.  Alternatively, if you
233           set the PCRE_UCP option, the way that the  character  escapes  work  is
234           changed  so that Unicode properties are used to determine which charac-
235           ters match. There are more details in the section on generic  character
236           types in the pcrepattern documentation.
237    
238         7.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
239         are all low-valued characters.         are all low-valued characters, unless the PCRE_UCP option is set.
240    
241         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
242         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
243         acters.         acters, whether or not PCRE_UCP is set.
244    
245         9. Case-insensitive matching applies only to  characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
246         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
# Line 263  AUTHOR Line 267  AUTHOR
267    
268  REVISION  REVISION
269    
270         Last updated: 01 September 2009         Last updated: 12 May 2010
271         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
272  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
273    
274    
275  PCREBUILD(3)                                                      PCREBUILD(3)  PCREBUILD(3)                                                      PCREBUILD(3)
276    
277    
# Line 282  PCRE BUILD-TIME OPTIONS Line 286  PCRE BUILD-TIME OPTIONS
286         script,  where the optional features are selected or deselected by pro-         script,  where the optional features are selected or deselected by pro-
287         viding options to configure before running the make  command.  However,         viding options to configure before running the make  command.  However,
288         the  same  options  can be selected in both Unix-like and non-Unix-like         the  same  options  can be selected in both Unix-like and non-Unix-like
289         environments using the GUI facility of  CMakeSetup  if  you  are  using         environments using the GUI facility of cmake-gui if you are using CMake
290         CMake instead of configure to build PCRE.         instead of configure to build PCRE.
291    
292           There  is  a  lot more information about building PCRE in non-Unix-like
293           environments in the file called NON_UNIX_USE, which is part of the PCRE
294           distribution.  You  should consult this file as well as the README file
295           if you are building in a non-Unix-like environment.
296    
297         The complete list of options for configure (which includes the standard         The complete list of options for configure (which includes the standard
298         ones such as the  selection  of  the  installation  directory)  can  be         ones  such  as  the  selection  of  the  installation directory) can be
299         obtained by running         obtained by running
300    
301           ./configure --help           ./configure --help
302    
303         The  following  sections  include  descriptions  of options whose names         The following sections include  descriptions  of  options  whose  names
304         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
305         defaults  for  the configure command. Because of the way that configure         defaults for the configure command. Because of the way  that  configure
306         works, --enable and --disable always come in pairs, so  the  complemen-         works,  --enable  and --disable always come in pairs, so the complemen-
307         tary  option always exists as well, but as it specifies the default, it         tary option always exists as well, but as it specifies the default,  it
308         is not described.         is not described.
309    
310    
# Line 316  UTF-8 SUPPORT Line 325  UTF-8 SUPPORT
325    
326           --enable-utf8           --enable-utf8
327    
328         to the configure command. Of itself, this  does  not  make  PCRE  treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
329         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
330         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()
331         function.         or pcre_compile2() functions.
332    
333         If  you set --enable-utf8 when compiling in an EBCDIC environment, PCRE         If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
334         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
335         option).  It  is not possible to support both EBCDIC and UTF-8 codes in         option). It is not possible to support both EBCDIC and UTF-8  codes  in
336         the same  version  of  the  library.  Consequently,  --enable-utf8  and         the  same  version  of  the  library.  Consequently,  --enable-utf8 and
337         --enable-ebcdic are mutually exclusive.         --enable-ebcdic are mutually exclusive.
338    
339    
340  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
341    
342         UTF-8  support allows PCRE to process character values greater than 255         UTF-8 support allows PCRE to process character values greater than  255
343         in the strings that it handles. On its own, however, it does  not  pro-         in  the  strings that it handles. On its own, however, it does not pro-
344         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
345         you want to be able to use the pattern escapes \P, \p,  and  \X,  which         you  want  to  be able to use the pattern escapes \P, \p, and \X, which
346         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
347    
348           --enable-unicode-properties           --enable-unicode-properties
349    
350         to  the configure command. This implies UTF-8 support, even if you have         to the configure command. This implies UTF-8 support, even if you  have
351         not explicitly requested it.         not explicitly requested it.
352    
353         Including Unicode property support adds around 30K  of  tables  to  the         Including  Unicode  property  support  adds around 30K of tables to the
354         PCRE  library.  Only  the general category properties such as Lu and Nd         PCRE library. Only the general category properties such as  Lu  and  Nd
355         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
356    
357    
358  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
359    
360         By default, PCRE interprets the linefeed (LF) character  as  indicating         By  default,  PCRE interprets the linefeed (LF) character as indicating
361         the  end  of  a line. This is the normal newline character on Unix-like         the end of a line. This is the normal newline  character  on  Unix-like
362         systems. You can compile PCRE to use carriage return (CR)  instead,  by         systems.  You  can compile PCRE to use carriage return (CR) instead, by
363         adding         adding
364    
365           --enable-newline-is-cr           --enable-newline-is-cr
366    
367         to  the  configure  command.  There  is  also  a --enable-newline-is-lf         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
368         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
369    
370         Alternatively, you can specify that line endings are to be indicated by         Alternatively, you can specify that line endings are to be indicated by
# Line 367  CODE VALUE OF NEWLINE Line 376  CODE VALUE OF NEWLINE
376    
377           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
378    
379         which  causes  PCRE  to recognize any of the three sequences CR, LF, or         which causes PCRE to recognize any of the three sequences  CR,  LF,  or
380         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
381    
382           --enable-newline-is-any           --enable-newline-is-any
383    
384         causes PCRE to recognize any Unicode newline sequence.         causes PCRE to recognize any Unicode newline sequence.
385    
386         Whatever line ending convention is selected when PCRE is built  can  be         Whatever  line  ending convention is selected when PCRE is built can be
387         overridden  when  the library functions are called. At build time it is         overridden when the library functions are called. At build time  it  is
388         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
389    
390    
391  WHAT \R MATCHES  WHAT \R MATCHES
392    
393         By default, the sequence \R in a pattern matches  any  Unicode  newline         By  default,  the  sequence \R in a pattern matches any Unicode newline
394         sequence,  whatever  has  been selected as the line ending sequence. If         sequence, whatever has been selected as the line  ending  sequence.  If
395         you specify         you specify
396    
397           --enable-bsr-anycrlf           --enable-bsr-anycrlf
398    
399         the default is changed so that \R matches only CR, LF, or  CRLF.  What-         the  default  is changed so that \R matches only CR, LF, or CRLF. What-
400         ever  is selected when PCRE is built can be overridden when the library         ever is selected when PCRE is built can be overridden when the  library
401         functions are called.         functions are called.
402    
403    
404  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
405    
406         The PCRE building process uses libtool to build both shared and  static         The  PCRE building process uses libtool to build both shared and static
407         Unix  libraries by default. You can suppress one of these by adding one         Unix libraries by default. You can suppress one of these by adding  one
408         of         of
409    
410           --disable-shared           --disable-shared
# Line 407  BUILDING SHARED AND STATIC LIBRARIES Line 416  BUILDING SHARED AND STATIC LIBRARIES
416  POSIX MALLOC USAGE  POSIX MALLOC USAGE
417    
418         When PCRE is called through the POSIX interface (see the pcreposix doc-         When PCRE is called through the POSIX interface (see the pcreposix doc-
419         umentation),  additional  working  storage  is required for holding the         umentation), additional working storage is  required  for  holding  the
420         pointers to capturing substrings, because PCRE requires three  integers         pointers  to capturing substrings, because PCRE requires three integers
421         per  substring,  whereas  the POSIX interface provides only two. If the         per substring, whereas the POSIX interface provides only  two.  If  the
422         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
423         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
424         The default threshold above which the stack is no longer used is 10; it         The default threshold above which the stack is no longer used is 10; it
# Line 422  POSIX MALLOC USAGE Line 431  POSIX MALLOC USAGE
431    
432  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
433    
434         Within  a  compiled  pattern,  offset values are used to point from one         Within a compiled pattern, offset values are used  to  point  from  one
435         part to another (for example, from an opening parenthesis to an  alter-         part  to another (for example, from an opening parenthesis to an alter-
436         nation  metacharacter).  By default, two-byte values are used for these         nation metacharacter). By default, two-byte values are used  for  these
437         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets,  leading  to  a  maximum size for a compiled pattern of around
438         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
439         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless,  some  people do want to process truyl enormous patterns,
440         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-
441         adding a setting such as         sets by adding a setting such as
442    
443           --with-link-size=3           --with-link-size=3
444    
445         to the configure command. The value given must be 2,  3,  or  4.  Using         to  the  configure  command.  The value given must be 2, 3, or 4. Using
446         longer  offsets slows down the operation of PCRE because it has to load         longer offsets slows down the operation of PCRE because it has to  load
447         additional bytes when handling them.         additional bytes when handling them.
448    
449    
450  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
451    
452         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
453         ing  by  making recursive calls to an internal function called match().         ing by making recursive calls to an internal function  called  match().
454         In environments where the size of the stack is limited,  this  can  se-         In  environments  where  the size of the stack is limited, this can se-
455         verely  limit  PCRE's operation. (The Unix environment does not usually         verely limit PCRE's operation. (The Unix environment does  not  usually
456         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
457         the  maximum  stack size.  There is a discussion in the pcrestack docu-         the maximum stack size.  There is a discussion in the  pcrestack  docu-
458         mentation.) An alternative approach to recursion that uses memory  from         mentation.)  An alternative approach to recursion that uses memory from
459         the  heap  to remember data, instead of using recursive function calls,         the heap to remember data, instead of using recursive  function  calls,
460         has been implemented to work round the problem of limited  stack  size.         has  been  implemented to work round the problem of limited stack size.
461         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
462    
463           --disable-stack-for-recursion           --disable-stack-for-recursion
464    
465         to  the  configure  command. With this configuration, PCRE will use the         to the configure command. With this configuration, PCRE  will  use  the
466         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
467         ment  functions. By default these point to malloc() and free(), but you         ment functions. By default these point to malloc() and free(), but  you
468         can replace the pointers so that your own functions are used.         can replace the pointers so that your own functions are used instead.
469    
470         Separate functions are  provided  rather  than  using  pcre_malloc  and         Separate  functions  are  provided  rather  than  using pcre_malloc and
471         pcre_free  because  the  usage  is  very  predictable:  the block sizes         pcre_free because the  usage  is  very  predictable:  the  block  sizes
472         requested are always the same, and  the  blocks  are  always  freed  in         requested  are  always  the  same,  and  the blocks are always freed in
473         reverse  order.  A calling program might be able to implement optimized         reverse order. A calling program might be able to  implement  optimized
474         functions that perform better  than  malloc()  and  free().  PCRE  runs         functions  that  perform  better  than  malloc()  and free(). PCRE runs
475         noticeably more slowly when built in this way. This option affects only         noticeably more slowly when built in this way. This option affects only
476         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.  
477    
478    
479  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
# Line 554  PCRETEST OPTION FOR LIBREADLINE SUPPORT Line 562  PCRETEST OPTION FOR LIBREADLINE SUPPORT
562         to  the  configure  command,  pcretest  is  linked with the libreadline         to  the  configure  command,  pcretest  is  linked with the libreadline
563         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
564         readline() function. This provides line-editing and history facilities.         readline() function. This provides line-editing and history facilities.
565         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
566         pcretest linked in this way, there may be licensing issues.         pcretest linked in this way, there may be licensing issues.
567    
568         Setting  this  option  causes  the -lreadline option to be added to the         Setting  this  option  causes  the -lreadline option to be added to the
# Line 590  AUTHOR Line 598  AUTHOR
598    
599  REVISION  REVISION
600    
601         Last updated: 17 March 2009         Last updated: 29 September 2009
602         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
603  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
604    
605    
606  PCREMATCHING(3)                                                PCREMATCHING(3)  PCREMATCHING(3)                                                PCREMATCHING(3)
607    
608    
# Line 678  THE ALTERNATIVE MATCHING ALGORITHM Line 686  THE ALTERNATIVE MATCHING ALGORITHM
686         though  it is not implemented as a traditional finite state machine (it         though  it is not implemented as a traditional finite state machine (it
687         keeps multiple states active simultaneously).         keeps multiple states active simultaneously).
688    
689           Although the general principle of this matching algorithm  is  that  it
690           scans  the subject string only once, without backtracking, there is one
691           exception: when a lookaround assertion is encountered,  the  characters
692           following  or  preceding  the  current  point  have to be independently
693           inspected.
694    
695         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
696         there  are  no more unterminated paths. At this point, terminated paths         there  are  no more unterminated paths. At this point, terminated paths
697         represent the different matching possibilities (if there are none,  the         represent the different matching possibilities (if there are none,  the
698         match  has  failed).   Thus,  if there is more than one possible match,         match  has  failed).   Thus,  if there is more than one possible match,
699         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-
700         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
701         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
702    
703         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
704         subject. If the pattern         subject. If the pattern
# Line 757  ADVANTAGES OF THE ALTERNATIVE ALGORITHM Line 771  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
771         2.  Because  the  alternative  algorithm  scans the subject string just         2.  Because  the  alternative  algorithm  scans the subject string just
772         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
773         subject  strings  to  the matching function in several pieces, checking         subject  strings  to  the matching function in several pieces, checking
774         for partial matching each time.         for partial matching each time.  The  pcrepartial  documentation  gives
775           details of partial matching.
776    
777    
778  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
779    
780         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
781    
782         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
783         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
784         because it is less susceptible to optimization.         because it is less susceptible to optimization.
785    
786         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 783  AUTHOR Line 798  AUTHOR
798    
799  REVISION  REVISION
800    
801         Last updated: 25 August 2009         Last updated: 29 September 2009
802         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
803  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
804    
805    
806  PCREAPI(3)                                                          PCREAPI(3)  PCREAPI(3)                                                          PCREAPI(3)
807    
808    
# Line 891  PCRE API OVERVIEW Line 906  PCRE API OVERVIEW
906         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
907         for different releases of PCRE.         for different releases of PCRE.
908    
909           In a Windows environment, if you want to statically link an application
910           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
911           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
912           loc()   and   pcre_free()   exported   functions   will   be   declared
913           __declspec(dllimport), with unwanted results.
914    
915         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
916         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
917         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
# Line 902  PCRE API OVERVIEW Line 923  PCRE API OVERVIEW
923         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
924         ble, is also provided. This uses a different algorithm for  the  match-         ble, is also provided. This uses a different algorithm for  the  match-
925         ing.  The  alternative algorithm finds all possible matches (at a given         ing.  The  alternative algorithm finds all possible matches (at a given
926         point in the subject), and scans the subject just once.  However,  this         point in the subject), and scans the subject just  once  (unless  there
927         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
928         matching algorithms and their advantages and disadvantages is given  in         captured substrings. A description of the two matching  algorithms  and
929         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
930           mentation.
931    
932         In  addition  to  the  main compiling and matching functions, there are         In addition to the main compiling and  matching  functions,  there  are
933         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
934         string that is matched by pcre_exec(). They are:         string that is matched by pcre_exec(). They are:
935    
# Line 922  PCRE API OVERVIEW Line 944  PCRE API OVERVIEW
944         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
945         to free the memory used for extracted strings.         to free the memory used for extracted strings.
946    
947         The function pcre_maketables() is used to  build  a  set  of  character         The  function  pcre_maketables()  is  used  to build a set of character
948         tables   in   the   current   locale  for  passing  to  pcre_compile(),         tables  in  the  current  locale   for   passing   to   pcre_compile(),
949         pcre_exec(), or pcre_dfa_exec(). This is an optional facility  that  is         pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
950         provided  for  specialist  use.  Most  commonly,  no special tables are         provided for specialist use.  Most  commonly,  no  special  tables  are
951         passed, in which case internal tables that are generated when  PCRE  is         passed,  in  which case internal tables that are generated when PCRE is
952         built are used.         built are used.
953    
954         The  function  pcre_fullinfo()  is used to find out information about a         The function pcre_fullinfo() is used to find out  information  about  a
955         compiled pattern; pcre_info() is an obsolete version that returns  only         compiled  pattern; pcre_info() is an obsolete version that returns only
956         some  of  the available information, but is retained for backwards com-         some of the available information, but is retained for  backwards  com-
957         patibility.  The function pcre_version() returns a pointer to a  string         patibility.   The function pcre_version() returns a pointer to a string
958         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
959    
960         The  function  pcre_refcount()  maintains  a  reference count in a data         The function pcre_refcount() maintains a  reference  count  in  a  data
961         block containing a compiled pattern. This is provided for  the  benefit         block  containing  a compiled pattern. This is provided for the benefit
962         of object-oriented applications.         of object-oriented applications.
963    
964         The  global  variables  pcre_malloc and pcre_free initially contain the         The global variables pcre_malloc and pcre_free  initially  contain  the
965         entry points of the standard malloc()  and  free()  functions,  respec-         entry  points  of  the  standard malloc() and free() functions, respec-
966         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
967         so a calling program can replace them if it  wishes  to  intercept  the         so  a  calling  program  can replace them if it wishes to intercept the
968         calls. This should be done before calling any PCRE functions.         calls. This should be done before calling any PCRE functions.
969    
970         The  global  variables  pcre_stack_malloc  and pcre_stack_free are also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
971         indirections to memory management functions.  These  special  functions         indirections  to  memory  management functions. These special functions
972         are  used  only  when  PCRE is compiled to use the heap for remembering         are used only when PCRE is compiled to use  the  heap  for  remembering
973         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
974         function.  See  the  pcrebuild  documentation  for details of how to do         function. See the pcrebuild documentation for  details  of  how  to  do
975         this. It is a non-standard way of building PCRE, for  use  in  environ-         this.  It  is  a non-standard way of building PCRE, for use in environ-
976         ments  that  have  limited stacks. Because of the greater use of memory         ments that have limited stacks. Because of the greater  use  of  memory
977         management, it runs more slowly. Separate  functions  are  provided  so         management,  it  runs  more  slowly. Separate functions are provided so
978         that  special-purpose  external  code  can  be used for this case. When         that special-purpose external code can be  used  for  this  case.  When
979         used, these functions are always called in a  stack-like  manner  (last         used,  these  functions  are always called in a stack-like manner (last
980         obtained,  first freed), and always for memory blocks of the same size.         obtained, first freed), and always for memory blocks of the same  size.
981         There is a discussion about PCRE's stack usage in the  pcrestack  docu-         There  is  a discussion about PCRE's stack usage in the pcrestack docu-
982         mentation.         mentation.
983    
984         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
985         by the caller to a "callout" function, which PCRE  will  then  call  at         by  the  caller  to  a "callout" function, which PCRE will then call at
986         specified  points during a matching operation. Details are given in the         specified points during a matching operation. Details are given in  the
987         pcrecallout documentation.         pcrecallout documentation.
988    
989    
990  NEWLINES  NEWLINES
991    
992         PCRE supports five different conventions for indicating line breaks  in         PCRE  supports five different conventions for indicating line breaks in
993         strings:  a  single  CR (carriage return) character, a single LF (line-         strings: a single CR (carriage return) character, a  single  LF  (line-
994         feed) character, the two-character sequence CRLF, any of the three pre-         feed) character, the two-character sequence CRLF, any of the three pre-
995         ceding,  or any Unicode newline sequence. The Unicode newline sequences         ceding, or any Unicode newline sequence. The Unicode newline  sequences
996         are the three just mentioned, plus the single characters  VT  (vertical         are  the  three just mentioned, plus the single characters VT (vertical
997         tab,  U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line         tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
998         separator, U+2028), and PS (paragraph separator, U+2029).         separator, U+2028), and PS (paragraph separator, U+2029).
999    
1000         Each of the first three conventions is used by at least  one  operating         Each  of  the first three conventions is used by at least one operating
1001         system  as its standard newline sequence. When PCRE is built, a default         system as its standard newline sequence. When PCRE is built, a  default
1002         can be specified.  The default default is LF, which is the  Unix  stan-         can  be  specified.  The default default is LF, which is the Unix stan-
1003         dard.  When  PCRE  is run, the default can be overridden, either when a         dard. When PCRE is run, the default can be overridden,  either  when  a
1004         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
1005    
1006         At compile time, the newline convention can be specified by the options         At compile time, the newline convention can be specified by the options
1007         argument  of  pcre_compile(), or it can be specified by special text at         argument of pcre_compile(), or it can be specified by special  text  at
1008         the start of the pattern itself; this overrides any other settings. See         the start of the pattern itself; this overrides any other settings. See
1009         the pcrepattern page for details of the special character sequences.         the pcrepattern page for details of the special character sequences.
1010    
1011         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
1012         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
1013         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
1014         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
1015         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
1016         ment for a non-anchored pattern. There is more detail about this in the         ment for a non-anchored pattern. There is more detail about this in the
1017         section on pcre_exec() options below.         section on pcre_exec() options below.
1018    
1019         The  choice of newline convention does not affect the interpretation of         The choice of newline convention does not affect the interpretation  of
1020         the \n or \r escape sequences, nor does  it  affect  what  \R  matches,         the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1021         which is controlled in a similar way, but by separate options.         which is controlled in a similar way, but by separate options.
1022    
1023    
1024  MULTITHREADING  MULTITHREADING
1025    
1026         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1027         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1028         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1029         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1030    
1031         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
1032         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
1033         at once.         at once.
1034    
# Line 1014  MULTITHREADING Line 1036  MULTITHREADING
1036  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
1037    
1038         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
1039         later  time,  possibly by a different program, and even on a host other         later time, possibly by a different program, and even on a  host  other
1040         than the one on which  it  was  compiled.  Details  are  given  in  the         than  the  one  on  which  it  was  compiled.  Details are given in the
1041         pcreprecompile  documentation.  However, compiling a regular expression         pcreprecompile documentation. However, compiling a  regular  expression
1042         with one version of PCRE for use with a different version is not  guar-         with  one version of PCRE for use with a different version is not guar-
1043         anteed to work and may cause crashes.         anteed to work and may cause crashes.
1044    
1045    
# Line 1025  CHECKING BUILD-TIME OPTIONS Line 1047  CHECKING BUILD-TIME OPTIONS
1047    
1048         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1049    
1050         The  function pcre_config() makes it possible for a PCRE client to dis-         The function pcre_config() makes it possible for a PCRE client to  dis-
1051         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1052         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
1053         tures.         tures.
1054    
1055         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
1056         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1057         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
1058         available:         available:
1059    
1060           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1061    
1062         The  output is an integer that is set to one if UTF-8 support is avail-         The output is an integer that is set to one if UTF-8 support is  avail-
1063         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1064    
1065           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1066    
1067         The output is an integer that is set to  one  if  support  for  Unicode         The  output  is  an  integer  that is set to one if support for Unicode
1068         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1069    
1070           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1071    
1072         The  output  is  an integer whose value specifies the default character         The output is an integer whose value specifies  the  default  character
1073         sequence that is recognized as meaning "newline". The four values  that         sequence  that is recognized as meaning "newline". The four values that
1074         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1075         and -1 for ANY.  Though they are derived from ASCII,  the  same  values         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1076         are returned in EBCDIC environments. The default should normally corre-         are returned in EBCDIC environments. The default should normally corre-
1077         spond to the standard sequence for your operating system.         spond to the standard sequence for your operating system.
1078    
1079           PCRE_CONFIG_BSR           PCRE_CONFIG_BSR
1080    
1081         The output is an integer whose value indicates what character sequences         The output is an integer whose value indicates what character sequences
1082         the  \R  escape sequence matches by default. A value of 0 means that \R         the \R escape sequence matches by default. A value of 0 means  that  \R
1083         matches any Unicode line ending sequence; a value of 1  means  that  \R         matches  any  Unicode  line ending sequence; a value of 1 means that \R
1084         matches only CR, LF, or CRLF. The default can be overridden when a pat-         matches only CR, LF, or CRLF. The default can be overridden when a pat-
1085         tern is compiled or matched.         tern is compiled or matched.
1086    
1087           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1088    
1089         The output is an integer that contains the number  of  bytes  used  for         The  output  is  an  integer that contains the number of bytes used for
1090         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1091         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1092         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1093         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1094         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1095    
1096           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1097    
1098         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1099         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1100         given in the pcreposix documentation.         given in the pcreposix documentation.
1101    
1102           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1103    
1104         The  output is a long integer that gives the default limit for the num-         The output is a long integer that gives the default limit for the  num-
1105         ber of internal matching function calls  in  a  pcre_exec()  execution.         ber  of  internal  matching  function calls in a pcre_exec() execution.
1106         Further details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1107    
1108           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1109    
1110         The output is a long integer that gives the default limit for the depth         The output is a long integer that gives the default limit for the depth
1111         of  recursion  when  calling  the  internal  matching  function  in   a         of   recursion  when  calling  the  internal  matching  function  in  a
1112         pcre_exec()  execution.  Further  details  are  given  with pcre_exec()         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1113         below.         below.
1114    
1115           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1116    
1117         The output is an integer that is set to one if internal recursion  when         The  output is an integer that is set to one if internal recursion when
1118         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1119         the stack to remember their state. This is the usual way that  PCRE  is         the  stack  to remember their state. This is the usual way that PCRE is
1120         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1121         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1122         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1123         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1124    
1125    
# Line 1114  COMPILING A PATTERN Line 1136  COMPILING A PATTERN
1136    
1137         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1138         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1139         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1140         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1141           avoid  too  much repetition, we refer just to pcre_compile() below, but
1142           the information applies equally to pcre_compile2().
1143    
1144         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
1145         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
1146         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1147         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1148         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1149         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1150         longer required.         longer required.
1151    
1152         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although the compiled code of a PCRE regex is relocatable, that is,  it
1153         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1154         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1155         ment, which is an address (see below).         ment, which is an address (see below).
1156    
1157         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1158         pilation.  It  should be zero if no options are required. The available         pilation. It should be zero if no options are required.  The  available
1159         options are described below. Some of them (in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1160         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
1161         unset from within the pattern (see  the  detailed  description  in  the         unset  from  within  the  pattern  (see the detailed description in the
1162         pcrepattern  documentation). For those options that can be different in         pcrepattern documentation). For those options that can be different  in
1163         different parts of the pattern, the contents of  the  options  argument         different  parts  of  the pattern, the contents of the options argument
1164         specifies their initial settings at the start of compilation and execu-         specifies their settings at the start of compilation and execution. The
1165         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
1166         time of matching as well as at compile time.         the time of matching as well as at compile time.
1167    
1168         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1169         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1170         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-
1171         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
1172         try to free it. The offset from the start of the pattern to the charac-         try to free it. The byte offset from the start of the  pattern  to  the
1173         ter where the error was discovered is placed in the variable pointed to         character  that  was  being  processed when the error was discovered is
1174         by  erroffset,  which must not be NULL. If it is, an immediate error is         placed in the variable pointed to by erroffset, which must not be NULL.
1175         given.         If  it  is,  an  immediate error is given. Some errors are not detected
1176           until checks are carried out when the whole pattern has  been  scanned;
1177         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         in this case the offset is set to the end of the pattern.
1178         codeptr  argument is not NULL, a non-zero error code number is returned  
1179         via this argument in the event of an error. This is in addition to  the         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1180           codeptr argument is not NULL, a non-zero error code number is  returned
1181           via  this argument in the event of an error. This is in addition to the
1182         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1183    
1184         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1185         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1186         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1187         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1188         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1189         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1190         support below.         support below.
1191    
1192         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1193         pile():         pile():
1194    
1195           pcre *re;           pcre *re;
# Line 1176  COMPILING A PATTERN Line 1202  COMPILING A PATTERN
1202             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1203             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1204    
1205         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1206         file:         file:
1207    
1208           PCRE_ANCHORED           PCRE_ANCHORED
1209    
1210         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1211         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1212         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1213         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1214         only way to do it in Perl.         only way to do it in Perl.
1215    
1216           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1217    
1218         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1219         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1220         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1221    
1222           PCRE_BSR_ANYCRLF           PCRE_BSR_ANYCRLF
1223           PCRE_BSR_UNICODE           PCRE_BSR_UNICODE
1224    
1225         These options (which are mutually exclusive) control what the \R escape         These options (which are mutually exclusive) control what the \R escape
1226         sequence matches. The choice is either to match only CR, LF,  or  CRLF,         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1227         or to match any Unicode newline sequence. The default is specified when         or to match any Unicode newline sequence. The default is specified when
1228         PCRE is built. It can be overridden from within the pattern, or by set-         PCRE is built. It can be overridden from within the pattern, or by set-
1229         ting an option when a compiled pattern is matched.         ting an option when a compiled pattern is matched.
1230    
1231           PCRE_CASELESS           PCRE_CASELESS
1232    
1233         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1234         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1235         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1236         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1237         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1238         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1239         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1240         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1241         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1242         UTF-8 support.         UTF-8 support.
1243    
1244           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1245    
1246         If this bit is set, a dollar metacharacter in the pattern matches  only         If  this bit is set, a dollar metacharacter in the pattern matches only
1247         at  the  end  of the subject string. Without this option, a dollar also         at the end of the subject string. Without this option,  a  dollar  also
1248         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1249         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1250         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1251         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1252    
1253           PCRE_DOTALL           PCRE_DOTALL
1254    
1255         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1256         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1257         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1258         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1259         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1260         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1261    
1262           PCRE_DUPNAMES           PCRE_DUPNAMES
1263    
1264         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1265         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1266         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1267         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1268         the pcrepattern documentation.         the pcrepattern documentation.
1269    
1270           PCRE_EXTENDED           PCRE_EXTENDED
1271    
1272         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1273         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1274         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1275         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1276         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1277         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1278         ting.         ting.
1279    
1280         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1281         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1282         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1283         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1284         introduces a conditional subpattern.         introduces a conditional subpattern.
1285    
1286           PCRE_EXTRA           PCRE_EXTRA
1287    
1288         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1289         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1290         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1291         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1292         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1293         backslash  followed by a letter with no special meaning is treated as a         backslash followed by a letter with no special meaning is treated as  a
1294         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal. (Perl can, however, be persuaded to give an error for this, by
1295         There  are  at  present no other features controlled by this option. It         running it with the -w option.) There are at present no other  features
1296         can also be set by a (?X) option setting within a pattern.         controlled  by this option. It can also be set by a (?X) option setting
1297           within a pattern.
1298    
1299           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1300    
# Line 1355  COMPILING A PATTERN Line 1382  COMPILING A PATTERN
1382         be  used  for  capturing  (and  they acquire numbers in the usual way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1383         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1384    
1385             PCRE_UCP
1386    
1387           This option changes the way PCRE processes \b, \d, \s, \w, and some  of
1388           the POSIX character classes. By default, only ASCII characters are rec-
1389           ognized, but if PCRE_UCP is set, Unicode properties are used instead to
1390           classify  characters.  More details are given in the section on generic
1391           character types in the pcrepattern page. If you set PCRE_UCP,  matching
1392           one  of the items it affects takes much longer. The option is available
1393           only if PCRE has been compiled with Unicode property support.
1394    
1395           PCRE_UNGREEDY           PCRE_UNGREEDY
1396    
1397         This option inverts the "greediness" of the quantifiers  so  that  they         This option inverts the "greediness" of the quantifiers  so  that  they
# Line 1453  COMPILATION ERROR CODES Line 1490  COMPILATION ERROR CODES
1490           57  \g is not followed by a braced, angle-bracketed, or quoted           57  \g is not followed by a braced, angle-bracketed, or quoted
1491                 name/number or by a plain number                 name/number or by a plain number
1492           58  a numbered reference must not be zero           58  a numbered reference must not be zero
1493           59  (*VERB) with an argument is not supported           59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1494           60  (*VERB) not recognized           60  (*VERB) not recognized
1495           61  number is too big           61  number is too big
1496           62  subpattern name expected           62  subpattern name expected
1497           63  digit expected after (?+           63  digit expected after (?+
1498           64  ] is an invalid data character in JavaScript compatibility mode           64  ] is an invalid data character in JavaScript compatibility mode
1499             65   different  names  for  subpatterns  of  the  same number are not
1500           allowed
1501             66  (*MARK) must have an argument
1502             67  this version of PCRE is not compiled with PCRE_UCP support
1503    
1504         The  numbers  32  and 10000 in errors 48 and 49 are defaults; different         The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1505         values may be used if the limits were changed when PCRE was built.         values may be used if the limits were changed when PCRE was built.
1506    
1507    
# Line 1469  STUDYING A PATTERN Line 1510  STUDYING A PATTERN
1510         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1511              const char **errptr);              const char **errptr);
1512    
1513         If a compiled pattern is going to be used several times,  it  is  worth         If  a  compiled  pattern is going to be used several times, it is worth
1514         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1515         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1516         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1517         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1518         pointer  to a pcre_extra block, in which the study_data field points to         pointer to a pcre_extra block, in which the study_data field points  to
1519         the results of the study.         the results of the study.
1520    
1521         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1522         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con-
1523         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
1524         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1525    
1526         If  studying  the  pattern  does not produce any additional information         If studying the  pattern  does  not  produce  any  useful  information,
1527         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1528         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
1529         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1530    
1531         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1532         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1533    
1534         The  third argument for pcre_study() is a pointer for an error message.         The third argument for pcre_study() is a pointer for an error  message.
1535         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1536         points  to  is  set  to NULL. Otherwise it is set to point to a textual         points to is set to NULL. Otherwise it is set to  point  to  a  textual
1537         error message. This is a static string that is part of the library. You         error message. This is a static string that is part of the library. You
1538         must  not  try  to  free it. You should test the error pointer for NULL         must not try to free it. You should test the  error  pointer  for  NULL
1539         after calling pcre_study(), to be sure that it has run successfully.         after calling pcre_study(), to be sure that it has run successfully.
1540    
1541         This is a typical call to pcre_study():         This is a typical call to pcre_study():
# Line 1505  STUDYING A PATTERN Line 1546  STUDYING A PATTERN
1546             0,              /* no options exist */             0,              /* no options exist */
1547             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1548    
1549         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
1550         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
1551         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1552           it does guarantee that no shorter strings match. The value is  used  by
1553           pcre_exec()  and  pcre_dfa_exec()  to  avoid  wasting time by trying to
1554           match strings that are shorter than the lower bound. You can  find  out
1555           the value in a calling program via the pcre_fullinfo() function.
1556    
1557           Studying a pattern is also useful for non-anchored patterns that do not
1558           have a single fixed starting character. A bitmap of  possible  starting
1559           bytes  is  created. This speeds up finding a position in the subject at
1560           which to start matching.
1561    
1562    
1563  LOCALE SUPPORT  LOCALE SUPPORT
# Line 1515  LOCALE SUPPORT Line 1565  LOCALE SUPPORT
1565         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1566         letters,  digits, or whatever, by reference to a set of tables, indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1567         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
1568         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. By default, higher-valued codes
1569         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built         never match escapes such as \w or \d, but they can be tested with \p if
1570         with  Unicode  character property support. The use of locales with Uni-         PCRE  is  built with Unicode character property support. Alternatively,
1571         code is discouraged. If you are handling characters with codes  greater         the PCRE_UCP option can be set at compile  time;  this  causes  \w  and
1572         than  128, you should either use UTF-8 and Unicode, or use locales, but         friends to use Unicode property support instead of built-in tables. The
1573         not try to mix the two.         use of locales with Unicode is discouraged. If you are handling charac-
1574           ters  with codes greater than 128, you should either use UTF-8 and Uni-
1575           code, or use locales, but not try to mix the two.
1576    
1577         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
1578         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
# Line 1673  INFORMATION ABOUT A PATTERN Line 1725  INFORMATION ABOUT A PATTERN
1725         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
1726         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1727    
1728             PCRE_INFO_MINLENGTH
1729    
1730           If the pattern was studied and a minimum length  for  matching  subject
1731           strings  was  computed,  its  value is returned. Otherwise the returned
1732           value is -1. The value is a number of characters, not bytes  (this  may
1733           be  relevant in UTF-8 mode). The fourth argument should point to an int
1734           variable. A non-negative value is a lower bound to the  length  of  any
1735           matching  string.  There  may not be any strings of that length that do
1736           actually match, but every string that does match is at least that long.
1737    
1738           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1739           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1740           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
# Line 1694  INFORMATION ABOUT A PATTERN Line 1756  INFORMATION ABOUT A PATTERN
1756         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
1757         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-
1758         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-
1759         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
1760         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-  
1761         theses  numbers.  For  example,  consider the following pattern (assume         The  names are in alphabetical order. Duplicate names may appear if (?|
1762         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is         is used to create multiple groups with the same number, as described in
1763         ignored):         the  section  on  duplicate subpattern numbers in the pcrepattern page.
1764           Duplicate names for subpatterns with different  numbers  are  permitted
1765           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1766           appear in the table in the order in which they were found in  the  pat-
1767           tern.  In  the  absence  of (?| this is the order of increasing number;
1768           when (?| is used this is not necessarily the case because later subpat-
1769           terns may have lower numbers.
1770    
1771           As  a  simple  example of the name/number table, consider the following
1772           pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1773           lines - is ignored):
1774    
1775           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1776           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
# Line 1719  INFORMATION ABOUT A PATTERN Line 1791  INFORMATION ABOUT A PATTERN
1791    
1792           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1793    
1794         Return 1 if the pattern can be used for partial matching, otherwise  0.         Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1795         The fourth argument should point to an int variable. From release 8.00,         pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1796         this always returns 1, because the restrictions that previously applied         variable. From  release  8.00,  this  always  returns  1,  because  the
1797         to  partial  matching  have  been lifted. The pcrepartial documentation         restrictions  that  previously  applied  to  partial matching have been
1798         gives details of partial matching.         lifted. The pcrepartial documentation gives details of  partial  match-
1799           ing.
1800    
1801           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1802    
1803         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
1804         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1805         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1806         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
1807         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
1808         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
1809         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1810         and PCRE_EXTENDED.         and PCRE_EXTENDED.
1811    
1812         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
1813         alternatives begin with one of the following:         alternatives begin with one of the following:
1814    
1815           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1750  INFORMATION ABOUT A PATTERN Line 1823  INFORMATION ABOUT A PATTERN
1823    
1824           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1825    
1826         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
1827         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
1828         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
1829         size_t variable.         size_t variable.
# Line 1758  INFORMATION ABOUT A PATTERN Line 1831  INFORMATION ABOUT A PATTERN
1831           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1832    
1833         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
1834         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
1835         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
1836         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
1837           data,  zero  is  returned. The fourth argument should point to a size_t
1838         variable.         variable.
1839    
1840    
# Line 1816  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1890  MATCHING A PATTERN: THE TRADITIONAL FUNC
1890    
1891         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
1892         compiled pattern, which is passed in the code argument. If the  pattern         compiled pattern, which is passed in the code argument. If the  pattern
1893         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
1894         argument. This function is the main matching facility of  the  library,         argument. This function is the main matching facility of  the  library,
1895         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
1896         an alternative matching function, which is described below in the  sec-         an alternative matching function, which is described below in the  sec-
# Line 1856  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1930  MATCHING A PATTERN: THE TRADITIONAL FUNC
1930           unsigned long int match_limit_recursion;           unsigned long int match_limit_recursion;
1931           void *callout_data;           void *callout_data;
1932           const unsigned char *tables;           const unsigned char *tables;
1933             unsigned char **mark;
1934    
1935         The  flags  field  is a bitmap that specifies which of the other fields         The  flags  field  is a bitmap that specifies which of the other fields
1936         are set. The flag bits are:         are set. The flag bits are:
# Line 1865  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1940  MATCHING A PATTERN: THE TRADITIONAL FUNC
1940           PCRE_EXTRA_MATCH_LIMIT_RECURSION           PCRE_EXTRA_MATCH_LIMIT_RECURSION
1941           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1942           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1943             PCRE_EXTRA_MARK
1944    
1945         Other flag bits should be set to zero. The study_data field is  set  in         Other flag bits should be set to zero. The study_data field is  set  in
1946         the  pcre_extra  block  that is returned by pcre_study(), together with         the  pcre_extra  block  that is returned by pcre_study(), together with
# Line 1875  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1951  MATCHING A PATTERN: THE TRADITIONAL FUNC
1951         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
1952         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
1953         match, but which have a very large number  of  possibilities  in  their         match, but which have a very large number  of  possibilities  in  their
1954         search  trees.  The  classic  example  is  the  use of nested unlimited         search  trees. The classic example is a pattern that uses nested unlim-
1955         repeats.         ited repeats.
1956    
1957         Internally, PCRE uses a function called match() which it calls  repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1958         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly  (sometimes  recursively). The limit set by match_limit is imposed
# Line 1909  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1985  MATCHING A PATTERN: THE TRADITIONAL FUNC
1985         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1986         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1987    
1988         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  callout_data  field is used in conjunction with the "callout" fea-
1989         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
1990    
1991         The tables field  is  used  to  pass  a  character  tables  pointer  to         The tables field  is  used  to  pass  a  character  tables  pointer  to
1992         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec();  this overrides the value that is stored with the compiled
# Line 1923  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1999  MATCHING A PATTERN: THE TRADITIONAL FUNC
1999         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
2000         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
2001    
2002           If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
2003           set to point to a char * variable. If the pattern  contains  any  back-
2004           tracking  control verbs such as (*MARK:NAME), and the execution ends up
2005           with a name to pass back, a pointer to the  name  string  (zero  termi-
2006           nated)  is  placed  in  the  variable pointed to by the mark field. The
2007           names are within the compiled pattern; if you wish  to  retain  such  a
2008           name  you must copy it before freeing the memory of a compiled pattern.
2009           If there is no name to pass back, the variable pointed to by  the  mark
2010           field  set  to NULL. For details of the backtracking control verbs, see
2011           the section entitled "Backtracking control" in the pcrepattern documen-
2012           tation.
2013    
2014     Option bits for pcre_exec()     Option bits for pcre_exec()
2015    
2016         The  unused  bits of the options argument for pcre_exec() must be zero.         The  unused  bits of the options argument for pcre_exec() must be zero.
2017         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,         The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
2018         PCRE_NOTBOL,    PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_START_OPTIMIZE,         PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
2019         PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and PCRE_PARTIAL_HARD.         PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
2020           PCRE_PARTIAL_HARD.
2021    
2022           PCRE_ANCHORED           PCRE_ANCHORED
2023    
2024         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
2025         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
2026         turned out to be anchored by virtue of its contents, it cannot be  made         turned  out to be anchored by virtue of its contents, it cannot be made
2027         unachored at matching time.         unachored at matching time.
2028    
2029           PCRE_BSR_ANYCRLF           PCRE_BSR_ANYCRLF
2030           PCRE_BSR_UNICODE           PCRE_BSR_UNICODE
2031    
2032         These options (which are mutually exclusive) control what the \R escape         These options (which are mutually exclusive) control what the \R escape
2033         sequence matches. The choice is either to match only CR, LF,  or  CRLF,         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
2034         or  to  match  any Unicode newline sequence. These options override the         or to match any Unicode newline sequence. These  options  override  the
2035         choice that was made or defaulted when the pattern was compiled.         choice that was made or defaulted when the pattern was compiled.
2036    
2037           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1951  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2040  MATCHING A PATTERN: THE TRADITIONAL FUNC
2040           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
2041           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
2042    
2043         These options override  the  newline  definition  that  was  chosen  or         These  options  override  the  newline  definition  that  was chosen or
2044         defaulted  when the pattern was compiled. For details, see the descrip-         defaulted when the pattern was compiled. For details, see the  descrip-
2045         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
2046         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
2047         ters. It may also alter the way the match position is advanced after  a         ters.  It may also alter the way the match position is advanced after a
2048         match failure for an unanchored pattern.         match failure for an unanchored pattern.
2049    
2050         When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is         When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
2051         set, and a match attempt for an unanchored pattern fails when the  cur-         set,  and a match attempt for an unanchored pattern fails when the cur-
2052         rent  position  is  at  a  CRLF  sequence,  and the pattern contains no         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
2053         explicit matches for  CR  or  LF  characters,  the  match  position  is         explicit  matches  for  CR  or  LF  characters,  the  match position is
2054         advanced by two characters instead of one, in other words, to after the         advanced by two characters instead of one, in other words, to after the
2055         CRLF.         CRLF.
2056    
2057         The above rule is a compromise that makes the most common cases work as         The above rule is a compromise that makes the most common cases work as
2058         expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL         expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
2059         option is not set), it does not match the string "\r\nA" because, after         option is not set), it does not match the string "\r\nA" because, after
2060         failing  at the start, it skips both the CR and the LF before retrying.         failing at the start, it skips both the CR and the LF before  retrying.
2061         However, the pattern [\r\n]A does match that string,  because  it  con-         However,  the  pattern  [\r\n]A does match that string, because it con-
2062         tains an explicit CR or LF reference, and so advances only by one char-         tains an explicit CR or LF reference, and so advances only by one char-
2063         acter after the first failure.         acter after the first failure.
2064    
2065         An explicit match for CR of LF is either a literal appearance of one of         An explicit match for CR of LF is either a literal appearance of one of
2066         those  characters,  or  one  of the \r or \n escape sequences. Implicit         those characters, or one of the \r or  \n  escape  sequences.  Implicit
2067         matches such as [^X] do not count, nor does \s (which includes  CR  and         matches  such  as [^X] do not count, nor does \s (which includes CR and
2068         LF in the characters that it matches).         LF in the characters that it matches).
2069    
2070         Notwithstanding  the above, anomalous effects may still occur when CRLF         Notwithstanding the above, anomalous effects may still occur when  CRLF
2071         is a valid newline sequence and explicit \r or \n escapes appear in the         is a valid newline sequence and explicit \r or \n escapes appear in the
2072         pattern.         pattern.
2073    
2074           PCRE_NOTBOL           PCRE_NOTBOL
2075    
2076         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
2077         the beginning of a line, so the  circumflex  metacharacter  should  not         the  beginning  of  a  line, so the circumflex metacharacter should not
2078         match  before it. Setting this without PCRE_MULTILINE (at compile time)         match before it. Setting this without PCRE_MULTILINE (at compile  time)
2079         causes circumflex never to match. This option affects only  the  behav-         causes  circumflex  never to match. This option affects only the behav-
2080         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
2081    
2082           PCRE_NOTEOL           PCRE_NOTEOL
2083    
2084         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
2085         of a line, so the dollar metacharacter should not match it nor  (except         of  a line, so the dollar metacharacter should not match it nor (except
2086         in  multiline mode) a newline immediately before it. Setting this with-         in multiline mode) a newline immediately before it. Setting this  with-
2087         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2088         option  affects only the behaviour of the dollar metacharacter. It does         option affects only the behaviour of the dollar metacharacter. It  does
2089         not affect \Z or \z.         not affect \Z or \z.
2090    
2091           PCRE_NOTEMPTY           PCRE_NOTEMPTY
2092    
2093         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
2094         set.  If  there are alternatives in the pattern, they are tried. If all         set. If there are alternatives in the pattern, they are tried.  If  all
2095         the alternatives match the empty string, the entire  match  fails.  For         the  alternatives  match  the empty string, the entire match fails. For
2096         example, if the pattern         example, if the pattern
2097    
2098           a?b?           a?b?
2099    
2100         is  applied  to  a string not beginning with "a" or "b", it matches the         is applied to a string not beginning with "a" or  "b",  it  matches  an
2101         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2102         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
2103         rences of "a" or "b".         rences of "a" or "b".
2104    
2105         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2106         cial  case  of  a  pattern match of the empty string within its split()  
2107         function, and when using the /g modifier. It  is  possible  to  emulate         This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2108         Perl's behaviour after matching a null string by first trying the match         not at the start of  the  subject  is  permitted.  If  the  pattern  is
2109         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         anchored, such a match can occur only if the pattern contains \K.
2110         if  that  fails by advancing the starting offset (see below) and trying  
2111         an ordinary match again. There is some code that demonstrates how to do         Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2112         this in the pcredemo sample program.         PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2113           match  of  the empty string within its split() function, and when using
2114           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2115           matching a null string by first trying the match again at the same off-
2116           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2117           fails, by advancing the starting offset (see below) and trying an ordi-
2118           nary match again. There is some code that demonstrates how to  do  this
2119           in the pcredemo sample program.
2120    
2121           PCRE_NO_START_OPTIMIZE           PCRE_NO_START_OPTIMIZE
2122    
# Line 2066  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2162  MATCHING A PATTERN: THE TRADITIONAL FUNC
2162         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2163         matching continues by testing any other alternatives. Only if they  all         matching continues by testing any other alternatives. Only if they  all
2164         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2165         The portion of the string that provided the partial match is set as the         The portion of the string that was inspected when the partial match was
2166         first  matching  string.  There  is  a  more detailed discussion in the         found  is  set  as  the first matching string. There is a more detailed
2167         pcrepartial documentation.         discussion in the pcrepartial documentation.
2168    
2169     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2170    
# Line 2155  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2251  MATCHING A PATTERN: THE TRADITIONAL FUNC
2251         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-
2252         ally advisable to supply an ovector.         ally advisable to supply an ovector.
2253    
2254         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
2255         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2256         ovector  that  will allow for n captured substrings, in addition to the         ovector  that  will allow for n captured substrings, in addition to the
2257         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 2218  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2314  MATCHING A PATTERN: THE TRADITIONAL FUNC
2314         purpose.  If the call via pcre_malloc() fails, this error is given. The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2315         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2316    
2317           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2318           This  can happen only when PCRE has been compiled with --disable-stack-
2319           for-recursion.
2320    
2321           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2322    
2323         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
# Line 2416  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2516  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2516         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
2517         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2518    
2519         Warning: If the pattern uses the "(?|" feature to set up multiple  sub-         Warning: If the pattern uses the (?| feature to set up multiple subpat-
2520         patterns  with  the  same  number,  you cannot use names to distinguish         terns  with  the  same number, as described in the section on duplicate
2521         them, because names are not included in the compiled code. The matching         subpattern numbers in the pcrepattern page, you  cannot  use  names  to
2522         process uses only numbers.         distinguish  the  different subpatterns, because names are not included
2523           in the compiled code. The matching process uses only numbers. For  this
2524           reason,  the  use of different names for subpatterns of the same number
2525           causes an error at compile time.
2526    
2527    
2528  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
# Line 2427  DUPLICATE SUBPATTERN NAMES Line 2530  DUPLICATE SUBPATTERN NAMES
2530         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2531              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2532    
2533         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2534         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns  are not required to be unique. (Duplicate names are always
2535         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  (?|
2536         subpatterns participates. An example is shown in the pcrepattern  docu-         feature.  Indeed,  if  such subpatterns are named, they are required to
2537         mentation.         use the same names.)
2538    
2539         When    duplicates   are   present,   pcre_copy_named_substring()   and         Normally, patterns with duplicate names are such that in any one match,
2540         pcre_get_named_substring() return the first substring corresponding  to         only  one of the named subpatterns participates. An example is shown in
2541         the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING         the pcrepattern documentation.
2542         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()  
2543         function  returns one of the numbers that are associated with the name,         When   duplicates   are   present,   pcre_copy_named_substring()    and
2544           pcre_get_named_substring()  return the first substring corresponding to
2545           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2546           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2547           function returns one of the numbers that are associated with the  name,
2548         but it is not defined which it is.         but it is not defined which it is.
2549    
2550         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
2551         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name, you must use  the  pcre_get_stringtable_entries()  function.  The
2552         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
2553         third  and  fourth  are  pointers to variables which are updated by the         third and fourth are pointers to variables which  are  updated  by  the
2554         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
2555         the  name-to-number  table  for  the  given  name.  The function itself         the name-to-number table  for  the  given  name.  The  function  itself
2556         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2557         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-
2558         tion entitled Information about a  pattern.   Given  all  the  relevant         tion  entitled  Information  about  a  pattern.  Given all the relevant
2559         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
2560         the captured data, if any.         the captured data, if any.
2561    
2562    
2563  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2564    
2565         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2566         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
2567         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
2568         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2569         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2570         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
2571         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2572         tation.         tation.
2573    
2574         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-
2575         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2576         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2577         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2578         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2579    
2580    
# Line 2478  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2585  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2585              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2586              int *workspace, int wscount);              int *workspace, int wscount);
2587    
2588         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2589         against a compiled pattern, using a matching algorithm that  scans  the         against  a  compiled pattern, using a matching algorithm that scans the
2590         subject  string  just  once, and does not backtrack. This has different         subject string just once, and does not backtrack.  This  has  different
2591         characteristics to the normal algorithm, and  is  not  compatible  with         characteristics  to  the  normal  algorithm, and is not compatible with
2592         Perl.  Some  of the features of PCRE patterns are not supported. Never-         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2593         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
2594         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, and  a  list  of  features
2595         mentation.         that  pcre_dfa_exec() does not support, see the pcrematching documenta-
2596           tion.
2597    
2598         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
2599         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-
# Line 2520  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2628  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2628    
2629         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
2630         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-
2631         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2632         PCRE_PARTIAL_HARD,     PCRE_PARTIAL_SOFT,     PCRE_DFA_SHORTEST,    and         PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2633         PCRE_DFA_RESTART. All but the last four of these are exactly  the  same         TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last
2634         as for pcre_exec(), so their description is not repeated here.         four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2635           description is not repeated here.
2636    
2637           PCRE_PARTIAL_HARD           PCRE_PARTIAL_HARD
2638           PCRE_PARTIAL_SOFT           PCRE_PARTIAL_SOFT
2639    
2640         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
2641         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2642         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-
2643         ject is reached and there is still at least  one  matching  possibility         ject  is  reached  and there is still at least one matching possibility
2644         that requires additional characters. This happens even if some complete         that requires additional characters. This happens even if some complete
2645         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
2646         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
2647         of the subject is reached, there have been  no  complete  matches,  but         of  the  subject  is  reached, there have been no complete matches, but
2648         there  is  still  at least one matching possibility. The portion of the         there is still at least one matching possibility. The  portion  of  the
2649         string that provided the longest partial match  is  set  as  the  first         string  that  was inspected when the longest partial match was found is
2650         matching string in both cases.         set as the first matching string in both cases.
2651    
2652           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2653    
2654         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2655         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-
2656         tive  algorithm  works, this is necessarily the shortest possible match         tive algorithm works, this is necessarily the shortest  possible  match
2657         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2658    
2659           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2660    
2661         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
2662         again,  with  additional  subject characters, and have it continue with         again, with additional subject characters, and have  it  continue  with
2663         the same match. The PCRE_DFA_RESTART option requests this action;  when         the  same match. The PCRE_DFA_RESTART option requests this action; when
2664         it  is  set,  the workspace and wscount options must reference the same         it is set, the workspace and wscount options must  reference  the  same
2665         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
2666         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
2667         pcrepartial documentation.         pcrepartial documentation.
2668    
2669     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2670    
2671         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-
2672         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
2673         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
2674         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2675         if the pattern         if the pattern
2676    
2677           <.*>           <.*>
# Line 2577  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2686  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2686           <something> <something else>           <something> <something else>
2687           <something> <something else> <something further>           <something> <something else> <something further>
2688    
2689         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,
2690         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2691         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2692         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
2693         fact, all the strings have the same start  offset.  (Space  could  have         fact,  all  the  strings  have the same start offset. (Space could have
2694         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
2695         compatibility with the way pcre_exec() returns data,  even  though  the         compatibility  with  the  way pcre_exec() returns data, even though the
2696         meaning of the strings is different.)         meaning of the strings is different.)
2697    
2698         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-
2699         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
2700         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
2701         filled with the longest matches.         filled with the longest matches.
2702    
2703     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2704    
2705         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2706         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
2707         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2708         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2709    
2710           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2711    
2712         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-
2713         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
2714         reference.         reference.
2715    
2716           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2717    
2718         This  return  is  given  if pcre_dfa_exec() encounters a condition item         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2719         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
2720         in a specific group. These are not supported.         in a specific group. These are not supported.
2721    
2722           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2723    
2724         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
2725         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
2726         (it is meaningless).         (it is meaningless).
2727    
2728           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2729    
2730         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
2731         workspace vector.         workspace vector.
2732    
2733           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2734    
2735         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2736         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2737         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
2738         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2739    
2740    
2741  SEE ALSO  SEE ALSO
2742    
2743         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2744         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2745    
2746    
# Line 2644  AUTHOR Line 2753  AUTHOR
2753    
2754  REVISION  REVISION
2755    
2756         Last updated: 01 September 2009         Last updated: 01 June 2010
2757         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
2758  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2759    
2760    
2761  PCRECALLOUT(3)                                                  PCRECALLOUT(3)  PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2762    
2763    
# Line 2674  PCRE CALLOUTS Line 2783  PCRE CALLOUTS
2783    
2784           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2785    
2786         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
2787         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2788         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
2789         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2790    
2791           A(\d{2}|--)           A(\d{2}|--)
2792    
# Line 2706  MISSING CALLOUTS Line 2815  MISSING CALLOUTS
2815         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2816         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2817    
2818         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
2819         MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the         string,  and will immediately give a "no match" return without actually
2820         matching process, but does ensure that callouts  such  as  the  example         running a match if the subject is not long enough, or,  for  unanchored
2821           patterns, if it has been scanned far enough.
2822    
2823           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2824           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2825           matching  process,  but  does  ensure that callouts such as the example
2826         above are obeyed.         above are obeyed.
2827    
2828    
2829  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2830    
2831         During  matching, when PCRE reaches a callout point, the external func-         During matching, when PCRE reaches a callout point, the external  func-
2832         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
2833         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2834         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
2835         block. This structure contains the following fields:         block. This structure contains the following fields:
2836    
2837           int          version;           int          version;
# Line 2733  THE CALLOUT INTERFACE Line 2847  THE CALLOUT INTERFACE
2847           int          pattern_position;           int          pattern_position;
2848           int          next_item_length;           int          next_item_length;
2849    
2850         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2851         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
2852         version  number  will  change  again in future if additional fields are         version number will change again in future  if  additional  fields  are
2853         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.
2854    
2855         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2856         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-
2857         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2858    
2859         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
2860         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2861         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
2862         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
2863         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2864         this field is not useful.         this field is not useful.
2865    
2866         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2867         were passed to pcre_exec().         were passed to pcre_exec().
2868    
2869         The start_match field normally contains the offset within  the  subject         The  start_match  field normally contains the offset within the subject
2870         at  which  the  current  match  attempt started. However, if the escape         at which the current match attempt  started.  However,  if  the  escape
2871         sequence \K has been encountered, this value is changed to reflect  the         sequence  \K has been encountered, this value is changed to reflect the
2872         modified  starting  point.  If the pattern is not anchored, the callout         modified starting point. If the pattern is not  anchored,  the  callout
2873         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
2874         for different starting points in the subject.         for different starting points in the subject.
2875    
2876         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2877         the current match pointer.         the current match pointer.
2878    
2879         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2880         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2881         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
2882         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
2883         does not support captured substrings.         does not support captured substrings.
2884    
2885         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2886         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2887         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2888    
2889         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()
2890         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-
2891         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
2892         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
2893         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
2894         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2895    
2896         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-
2897         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
2898         the pattern string.         the pattern string.
2899    
2900         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-
2901         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
2902         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2903         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
2904         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2905         is that of the entire subpattern.         is that of the entire subpattern.
2906    
2907         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2908         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2909         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2910    
2911    
2912  RETURN VALUES  RETURN VALUES
2913    
2914         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2915         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2916         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2917         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2918         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
2919         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2920    
2921         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2922         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2923         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2924         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
2925         itself.         itself.
2926    
2927    
# Line 2820  AUTHOR Line 2934  AUTHOR
2934    
2935  REVISION  REVISION
2936    
2937         Last updated: 15 March 2009         Last updated: 29 September 2009
2938         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2939  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2940    
2941    
2942  PCRECOMPAT(3)                                                    PCRECOMPAT(3)  PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2943    
2944    
# Line 2835  NAME Line 2949  NAME
2949  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2950    
2951         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2952         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences  described  here  are  with
2953         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         respect to Perl 5.10/5.11.
        some features that are in Perl 5.10.  
2954    
2955         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
2956         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
2957         main pcre page.         main pcre page.
2958    
2959         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2960         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,
2961         (?!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
2962         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
2963    
2964         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
2965         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
2966         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
2967         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
2968         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
2969         branch.         branch.
2970    
2971         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
2972         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-
2973         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
2974         the pattern to represent a binary zero.         the pattern to represent a binary zero.
2975    
2976         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
2977         \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-
2978         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
2979         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2980    
2981         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
2982         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
2983         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-
2984         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
2985         derived properties Any and L&.         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
2986           property, which Perl does not; the  Perl  documentation  says  "Because
2987           Perl hides the need for the user to understand the internal representa-
2988           tion of Unicode characters, there is no need to implement the  somewhat
2989           messy concept of surrogates."
2990    
2991         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2992         ters  in  between  are  treated as literals. This is slightly different         ters in between are treated as literals.  This  is  slightly  different
2993         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from  Perl  in  that  $  and  @ are also handled as literals inside the
2994         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
2995         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2996    
2997             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2884  DIFFERENCES BETWEEN PCRE AND PERL Line 3001  DIFFERENCES BETWEEN PCRE AND PERL
3001             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
3002             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
3003    
3004         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3005         classes.         classes.
3006    
3007         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3008         constructions. However, there is support for recursive  patterns.  This         constructions.  However,  there is support for recursive patterns. This
3009         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE         is not available in Perl 5.8, but it is in Perl 5.10.  Also,  the  PCRE
3010         "callout" feature allows an external function to be called during  pat-         "callout"  feature allows an external function to be called during pat-
3011         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
3012    
3013         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
3014         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always  treated  as  atomic  groups  in  PCRE. This is like Python, but
3015         unlike Perl.         unlike Perl. There is a discussion of an example that explains this  in
3016           more  detail  in  the section on recursion differences from Perl in the
3017         10.  There are some differences that are concerned with the settings of         pcrepattern page.
3018         captured strings when part of  a  pattern  is  repeated.  For  example,  
3019         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         10. There are some differences that are concerned with the settings  of
3020           captured  strings  when  part  of  a  pattern is repeated. For example,
3021           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
3022         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
3023    
3024         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3025         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in         pattern names is not as general as Perl's. This is a consequence of the
3026         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If         fact the PCRE works internally just with numbers, using an external ta-
3027         (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-         ble to translate between numbers and names. In  particular,  a  pattern
3028         ture group; this is different to Perl.         such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3029           the same number but different names, is not supported,  and  causes  an
3030           error  at compile time. If it were allowed, it would not be possible to
3031           distinguish which parentheses matched, because both names map  to  cap-
3032           turing subpattern number 1. To avoid this confusing situation, an error
3033           is given at compile time.
3034    
3035         12. PCRE provides some extensions to the Perl regular expression facil-         12. PCRE provides some extensions to the Perl regular expression facil-
3036         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  includes new features that are not in earlier ver-
3037         versions, some of which (such as named parentheses) have been  in  PCRE         sions of Perl, some of which (such as named parentheses) have  been  in
3038         for some time. This list is with respect to Perl 5.10:         PCRE for some time. This list is with respect to Perl 5.10:
3039    
3040         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3041         each alternative branch of a lookbehind assertion can match a different         strings, each alternative branch of a lookbehind assertion can match  a
3042         length of string. Perl requires them all to have the same length.         different  length  of  string.  Perl requires them all to have the same
3043           length.
3044    
3045         (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  $
3046         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3047    
3048         (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-
3049         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3050         ignored.  (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
3051    
3052         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3053         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-
3054         lowed by a question mark they are.         lowed by a question mark they are.
3055    
3056         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
3057         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3058    
3059         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3060         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3061           lents.
3062    
3063         (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
3064         CRLF by the PCRE_BSR_ANYCRLF option.         CRLF by the PCRE_BSR_ANYCRLF option.
# Line 2961  AUTHOR Line 3087  AUTHOR
3087    
3088  REVISION  REVISION
3089    
3090         Last updated: 25 August 2009         Last updated: 12 May 2010
3091         Copyright (c) 1997-2009 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
3092  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3093    
3094    
3095  PCREPATTERN(3)                                                  PCREPATTERN(3)  PCREPATTERN(3)                                                  PCREPATTERN(3)
3096    
3097    
# Line 2992  PCRE REGULAR EXPRESSION DETAILS Line 3118  PCRE REGULAR EXPRESSION DETAILS
3118    
3119         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3120         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
3121         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
3122         pcre_compile()  with  the  PCRE_UTF8  option.  There  is also a special         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3123         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:
3124    
3125           (*UTF8)           (*UTF8)
3126    
# Line 3004  PCRE REGULAR EXPRESSION DETAILS Line 3130  PCRE REGULAR EXPRESSION DETAILS
3130         below.  There  is  also  a  summary of UTF-8 features in the section on         below.  There  is  also  a  summary of UTF-8 features in the section on
3131         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
3132    
3133           Another special sequence that may appear at the start of a  pattern  or
3134           in combination with (*UTF8) is:
3135    
3136             (*UCP)
3137    
3138           This  has  the  same  effect  as setting the PCRE_UCP option: it causes
3139           sequences such as \d and \w to  use  Unicode  properties  to  determine
3140           character types, instead of recognizing only characters with codes less
3141           than 128 via a lookup table.
3142    
3143         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3144         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
3145         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
# Line 3032  NEWLINE CONVENTIONS Line 3168  NEWLINE CONVENTIONS
3168           (*ANYCRLF)   any of the three above           (*ANYCRLF)   any of the three above
3169           (*ANY)       all Unicode newline sequences           (*ANY)       all Unicode newline sequences
3170    
3171         These override the default and the options given to pcre_compile(). For         These  override  the default and the options given to pcre_compile() or
3172         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
3173         pattern         newline sequence, the pattern
3174    
3175           (*CR)a.b           (*CR)a.b
3176    
# Line 3044  NEWLINE CONVENTIONS Line 3180  NEWLINE CONVENTIONS
3180         and that they must be in upper case.  If  more  than  one  of  them  is         and that they must be in upper case.  If  more  than  one  of  them  is
3181         present, the last one is used.         present, the last one is used.
3182    
3183         The  newline  convention  does  not  affect what the \R escape sequence         The  newline convention affects the interpretation of the dot metachar-
3184         matches. By default, this is any Unicode  newline  sequence,  for  Perl         acter when PCRE_DOTALL is not set, and also the behaviour of  \N.  How-
3185         compatibility.  However, this can be changed; see the description of \R         ever,  it  does  not  affect  what  the  \R escape sequence matches. By
3186         in the section entitled "Newline sequences" below. A change of \R  set-         default, this is any Unicode newline sequence, for Perl  compatibility.
3187         ting can be combined with a change of newline convention.         However,  this can be changed; see the description of \R in the section
3188           entitled "Newline sequences" below. A change of \R setting can be  com-
3189           bined with a change of newline convention.
3190    
3191    
3192  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
# Line 3151  BACKSLASH Line 3289  BACKSLASH
3289         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
3290         appearance of non-printing characters, apart from the binary zero  that         appearance of non-printing characters, apart from the binary zero  that
3291         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3292         editing, it is usually easier  to  use  one  of  the  following  escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3293         sequences than the binary character it represents:         sequences than the binary character it represents:
3294    
3295           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 3161  BACKSLASH Line 3299  BACKSLASH
3299           \n        linefeed (hex 0A)           \n        linefeed (hex 0A)
3300           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3301           \t        tab (hex 09)           \t        tab (hex 09)
3302           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3303           \xhh      character with hex code hh           \xhh      character with hex code hh
3304           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3305    
# Line 3230  BACKSLASH Line 3368  BACKSLASH
3368         All the sequences that define a single character value can be used both         All the sequences that define a single character value can be used both
3369         inside  and  outside character classes. In addition, inside a character         inside  and  outside character classes. In addition, inside a character
3370         class, the sequence \b is interpreted as the backspace  character  (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3371         08),  and the sequences \R and \X are interpreted as the characters "R"         08).  The sequences \B, \N, \R, and \X are not special inside a charac-
3372         and "X", respectively. Outside a character class, these sequences  have         ter class. Like any  other  unrecognized  escape  sequences,  they  are
3373         different meanings (see below).         treated  as  the  literal characters "B", "N", "R", and "X" by default,
3374           but cause an error if the PCRE_EXTRA option is set. Outside a character
3375           class, these sequences have different meanings.
3376    
3377     Absolute and relative back references     Absolute and relative back references
3378    
# Line 3252  BACKSLASH Line 3392  BACKSLASH
3392    
3393     Generic character types     Generic character types
3394    
3395         Another use of backslash is for specifying generic character types. The         Another use of backslash is for specifying generic character types:
        following are always recognized:  
3396    
3397           \d     any decimal digit           \d     any decimal digit
3398           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 3266  BACKSLASH Line 3405  BACKSLASH
3405           \w     any "word" character           \w     any "word" character
3406           \W     any "non-word" character           \W     any "non-word" character
3407    
3408         Each pair of escape sequences partitions the complete set of characters         There is also the single sequence \N, which matches a non-newline char-
3409         into  two disjoint sets. Any given character matches one, and only one,         acter.  This is the same as the "." metacharacter when  PCRE_DOTALL  is
3410         of each pair.         not set.
3411    
3412         These character type sequences can appear both inside and outside char-         Each  pair of lower and upper case escape sequences partitions the com-
3413         acter  classes.  They each match one character of the appropriate type.         plete set of characters into two disjoint  sets.  Any  given  character
3414         If the current matching point is at the end of the subject string,  all         matches  one, and only one, of each pair. The sequences can appear both
3415         of them fail, since there is no character to match.         inside and outside character classes. They each match one character  of
3416           the  appropriate  type.  If the current matching point is at the end of
3417           the subject string, all of them fail, because there is no character  to
3418           match.
3419    
3420         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3421         11).  This makes it different from the the POSIX "space" class. The  \s         11).  This makes it different from the the POSIX "space" class. The  \s
# Line 3281  BACKSLASH Line 3423  BACKSLASH
3423         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3424         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3425    
3426         In  UTF-8 mode, characters with values greater than 128 never match \d,         A  "word"  character is an underscore or any character that is a letter
3427         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         or digit.  By default, the definition of letters  and  digits  is  con-
3428         code  character  property  support is available. These sequences retain         trolled  by PCRE's low-valued character tables, and may vary if locale-
3429         their original meanings from before UTF-8 support was available, mainly         specific matching is taking place (see "Locale support" in the  pcreapi
3430         for  efficiency  reasons. Note that this also affects \b, because it is         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3431         defined in terms of \w and \W.         systems, or "french" in Windows, some character codes greater than  128
3432           are  used  for  accented letters, and these are then matched by \w. The
3433           use of locales with Unicode is discouraged.
3434    
3435           By default, in UTF-8 mode, characters  with  values  greater  than  128
3436           never  match  \d,  \s,  or  \w,  and always match \D, \S, and \W. These
3437           sequences retain their original meanings from before UTF-8 support  was
3438           available,  mainly for efficiency reasons. However, if PCRE is compiled
3439           with Unicode property support, and the PCRE_UCP option is set, the  be-
3440           haviour  is  changed  so  that Unicode properties are used to determine
3441           character types, as follows:
3442    
3443             \d  any character that \p{Nd} matches (decimal digit)
3444             \s  any character that \p{Z} matches, plus HT, LF, FF, CR
3445             \w  any character that \p{L} or \p{N} matches, plus underscore
3446    
3447           The upper case escapes match the inverse sets of characters. Note  that
3448           \d  matches  only decimal digits, whereas \w matches any Unicode digit,
3449           as well as any Unicode letter, and underscore. Note also that  PCRE_UCP
3450           affects  \b,  and  \B  because  they are defined in terms of \w and \W.
3451           Matching these sequences is noticeably slower when PCRE_UCP is set.
3452    
3453         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3454         the  other  sequences, these do match certain high-valued codepoints in         the  other  sequences,  which  match  only ASCII characters by default,
3455         UTF-8 mode.  The horizontal space characters are:         these always  match  certain  high-valued  codepoints  in  UTF-8  mode,
3456           whether or not PCRE_UCP is set. The horizontal space characters are:
3457    
3458           U+0009     Horizontal tab           U+0009     Horizontal tab
3459           U+0020     Space           U+0020     Space
# Line 3322  BACKSLASH Line 3485  BACKSLASH
3485           U+2028     Line separator           U+2028     Line separator
3486           U+2029     Paragraph separator           U+2029     Paragraph separator
3487    
        A "word" character is an underscore or any character less than 256 that  
        is  a  letter  or  digit.  The definition of letters and digits is con-  
        trolled by PCRE's low-valued character tables, and may vary if  locale-  
        specific  matching is taking place (see "Locale support" in the pcreapi  
        page). For example, in a French locale such  as  "fr_FR"  in  Unix-like  
        systems,  or "french" in Windows, some character codes greater than 128  
        are used for accented letters, and these are matched by \w. The use  of  
        locales with Unicode is discouraged.  
   
3488     Newline sequences     Newline sequences
3489    
3490         Outside  a  character class, by default, the escape sequence \R matches         Outside  a  character class, by default, the escape sequence \R matches
# Line 3363  BACKSLASH Line 3517  BACKSLASH
3517           (*BSR_ANYCRLF)   CR, LF, or CRLF only           (*BSR_ANYCRLF)   CR, LF, or CRLF only
3518           (*BSR_UNICODE)   any Unicode newline sequence           (*BSR_UNICODE)   any Unicode newline sequence
3519    
3520         These override the default and the options given to pcre_compile(), but         These override the default and the options given to  pcre_compile()  or
3521         they can be overridden by options given to pcre_exec(). Note that these         pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3522         special settings, which are not Perl-compatible, are recognized only at         pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3523         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
3524         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
3525         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
3526         can start with:         newline convention; for example, a pattern can start with:
3527    
3528           (*ANY)(*BSR_ANYCRLF)           (*ANY)(*BSR_ANYCRLF)
3529    
3530         Inside a character class, \R matches the letter "R".         They can also be combined with the (*UTF8) or (*UCP) special sequences.
3531           Inside  a  character  class,  \R  is  treated as an unrecognized escape
3532           sequence, and so matches the letter "R" by default, but causes an error
3533           if PCRE_EXTRA is set.
3534    
3535     Unicode character properties     Unicode character properties
3536    
3537         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3538         tional  escape sequences that match characters with specific properties         tional escape sequences that match characters with specific  properties
3539         are available.  When not in UTF-8 mode, these sequences are  of  course         are  available.   When not in UTF-8 mode, these sequences are of course
3540         limited  to  testing characters whose codepoints are less than 256, but         limited to testing characters whose codepoints are less than  256,  but
3541         they do work in this mode.  The extra escape sequences are:         they do work in this mode.  The extra escape sequences are:
3542    
3543           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3544           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3545           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3546    
3547         The property names represented by xx above are limited to  the  Unicode         The  property  names represented by xx above are limited to the Unicode
3548         script names, the general category properties, and "Any", which matches         script names, the general category properties, "Any", which matches any
3549         any character (including newline). Other properties such as "InMusical-         character   (including  newline),  and  some  special  PCRE  properties
3550         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does         (described in the next section).  Other Perl properties such as  "InMu-
3551         not match any characters, so always causes a match failure.         sicalSymbols"  are  not  currently supported by PCRE. Note that \P{Any}
3552           does not match any characters, so always causes a match failure.
3553    
3554         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3555         A  character from one of these sets can be matched using a script name.         A  character from one of these sets can be matched using a script name.
# Line 3403  BACKSLASH Line 3561  BACKSLASH
3561         Those that are not part of an identified script are lumped together  as         Those that are not part of an identified script are lumped together  as
3562         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3563    
3564         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3565         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,  Cherokee,  Common,
3566         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Coptic,   Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,  Egyp-
3567         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         tian_Hieroglyphs,  Ethiopic,  Georgian,  Glagolitic,   Gothic,   Greek,
3568         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         Gujarati,  Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana, Impe-
3569         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3570         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Javanese,  Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,
3571         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Latin,  Lepcha,  Limbu,  Linear_B,  Lisu,  Lycian,  Lydian,  Malayalam,
3572         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Meetei_Mayek,  Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,
3573           Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki,  Oriya,  Osmanya,
3574         Each  character has exactly one general category property, specified by         Phags_Pa,  Phoenician,  Rejang,  Runic, Samaritan, Saurashtra, Shavian,
3575         a two-letter abbreviation. For compatibility with Perl, negation can be         Sinhala, Sundanese, Syloti_Nagri, Syriac,  Tagalog,  Tagbanwa,  Tai_Le,
3576         specified  by  including a circumflex between the opening brace and the         Tai_Tham,  Tai_Viet,  Tamil,  Telugu,  Thaana, Thai, Tibetan, Tifinagh,
3577         property name. For example, \p{^Lu} is the same as \P{Lu}.         Ugaritic, Vai, Yi.
3578    
3579           Each character has exactly one Unicode general category property, spec-
3580           ified  by a two-letter abbreviation. For compatibility with Perl, nega-
3581           tion can be specified by including a  circumflex  between  the  opening
3582           brace  and  the  property  name.  For  example,  \p{^Lu} is the same as
3583           \P{Lu}.
3584    
3585         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3586         eral  category properties that start with that letter. In this case, in         eral  category properties that start with that letter. In this case, in
# Line 3480  BACKSLASH Line 3644  BACKSLASH
3644         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3645         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3646         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3647         the pcreapi page).         the pcreapi page). Perl does not support the Cs property.
3648    
3649         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  property  names  that  Perl supports (such as
3650         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3651         any of these properties with "Is".         any of these properties with "Is".
3652    
# Line 3508  BACKSLASH Line 3672  BACKSLASH
3672         Matching characters by Unicode property is not fast, because  PCRE  has         Matching characters by Unicode property is not fast, because  PCRE  has
3673         to  search  a  structure  that  contains data for over fifteen thousand         to  search  a  structure  that  contains data for over fifteen thousand
3674         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3675         \w do not use Unicode properties in PCRE.         \w  do  not  use  Unicode properties in PCRE by default, though you can
3676           make them do so by setting the PCRE_UCP option for pcre_compile() or by
3677           starting the pattern with (*UCP).
3678    
3679       PCRE's additional properties
3680    
3681           As  well  as  the standard Unicode properties described in the previous
3682           section, PCRE supports four more that make it possible to convert  tra-
3683           ditional escape sequences such as \w and \s and POSIX character classes
3684           to use Unicode properties. PCRE uses these non-standard, non-Perl prop-
3685           erties internally when PCRE_UCP is set. They are:
3686    
3687             Xan   Any alphanumeric character
3688             Xps   Any POSIX space character
3689             Xsp   Any Perl space character
3690             Xwd   Any Perl "word" character
3691    
3692           Xan  matches  characters that have either the L (letter) or the N (num-
3693           ber) property. Xps matches the characters tab, linefeed, vertical  tab,
3694           formfeed,  or  carriage  return, and any other character that has the Z
3695           (separator) property.  Xsp is the same as Xps, except that vertical tab
3696           is excluded. Xwd matches the same characters as Xan, plus underscore.
3697    
3698     Resetting the match start     Resetting the match start
3699    
# Line 3529  BACKSLASH Line 3714  BACKSLASH
3714    
3715         matches "foobar", the first substring is still set to "foo".         matches "foobar", the first substring is still set to "foo".
3716    
3717           Perl documents that the use  of  \K  within  assertions  is  "not  well
3718           defined".  In  PCRE,  \K  is  acted upon when it occurs inside positive
3719           assertions, but is ignored in negative assertions.
3720    
3721     Simple assertions     Simple assertions
3722    
3723         The final use of backslash is for certain simple assertions. An  asser-         The final use of backslash is for certain simple assertions. An  asser-
# Line 3545  BACKSLASH Line 3734  BACKSLASH
3734           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3735           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3736    
3737         These assertions may not appear in character classes (but note that  \b         Inside a character class, \b has a different meaning;  it  matches  the
3738         has a different meaning, namely the backspace character, inside a char-         backspace  character.  If  any  other  of these assertions appears in a
3739         acter class).         character class, by default it matches the corresponding literal  char-
3740           acter  (for  example,  \B  matches  the  letter  B).  However,  if  the
3741         A word boundary is a position in the subject string where  the  current         PCRE_EXTRA option is set, an "invalid escape sequence" error is  gener-
3742         character  and  the previous character do not both match \w or \W (i.e.         ated instead.
3743         one matches \w and the other matches \W), or the start or  end  of  the  
3744         string if the first or last character matches \w, respectively.         A  word  boundary is a position in the subject string where the current
3745           character and the previous character do not both match \w or  \W  (i.e.
3746           one  matches  \w  and the other matches \W), or the start or end of the
3747           string if the first or last  character  matches  \w,  respectively.  In
3748           UTF-8  mode,  the  meanings  of \w and \W can be changed by setting the
3749           PCRE_UCP option. When this is done, it also affects \b and \B.  Neither
3750           PCRE  nor  Perl has a separate "start of word" or "end of word" metase-
3751           quence. However, whatever follows \b normally determines which  it  is.
3752           For example, the fragment \ba matches "a" at the start of a word.
3753    
3754         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3755         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
# Line 3635  CIRCUMFLEX AND DOLLAR Line 3832  CIRCUMFLEX AND DOLLAR
3832         set.         set.
3833    
3834    
3835  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT) AND \N
3836    
3837         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-
3838         ter  in  the subject string except (by default) a character that signi-         ter  in  the subject string except (by default) a character that signi-
# Line 3658  FULL STOP (PERIOD, DOT) Line 3855  FULL STOP (PERIOD, DOT)
3855         flex and dollar, the only relationship being  that  they  both  involve         flex and dollar, the only relationship being  that  they  both  involve
3856         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3857    
3858           The escape sequence \N always behaves as a dot does when PCRE_DOTALL is
3859           not set. In other words, it matches any one character except  one  that
3860           signifies the end of a line.
3861    
3862    
3863  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3864    
# Line 3678  SQUARE BRACKETS AND CHARACTER CLASSES Line 3879  SQUARE BRACKETS AND CHARACTER CLASSES
3879    
3880         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3881         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-
3882         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,
3883         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
3884         circumflex, if present) or escaped with a backslash.         square  bracket  is required as a member of the class, it should be the
3885           first data character in the class  (after  an  initial  circumflex,  if
3886           present) or escaped with a backslash.
3887    
3888         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
3889         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
3890         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
3891         character in the class definition is a circumflex, in  which  case  the         character in the class definition is a circumflex, in  which  case  the
3892         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
# Line 3694  SQUARE BRACKETS AND CHARACTER CLASSES Line 3897  SQUARE BRACKETS AND CHARACTER CLASSES
3897         while [^aeiou] matches any character that is not a  lower  case  vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3898         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3899         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
3900         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-
3901         sumes a character from the subject string, and therefore  it  fails  if         sumes a character from the subject string, and therefore  it  fails  if
3902         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3903    
# Line 3710  SQUARE BRACKETS AND CHARACTER CLASSES Line 3913  SQUARE BRACKETS AND CHARACTER CLASSES
3913         than 128, so caseless matching is always possible. For characters  with         than 128, so caseless matching is always possible. For characters  with
3914         higher  values,  the  concept  of case is supported if PCRE is compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3915         with Unicode property support, but not otherwise.  If you want  to  use         with Unicode property support, but not otherwise.  If you want  to  use
3916         caseless  matching  for  characters 128 and above, you must ensure that         caseless  matching  in UTF8-mode for characters 128 and above, you must
3917         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
3918         support.         with UTF-8 support.
3919    
3920         Characters  that  might  indicate  line breaks are never treated in any         Characters  that  might  indicate  line breaks are never treated in any
3921         special way  when  matching  character  classes,  whatever  line-ending         special way  when  matching  character  classes,  whatever  line-ending
# Line 3749  SQUARE BRACKETS AND CHARACTER CLASSES Line 3952  SQUARE BRACKETS AND CHARACTER CLASSES
3952         concept  of  case for characters with values greater than 128 only when         concept  of  case for characters with values greater than 128 only when
3953         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3954    
3955         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear         The character types \d, \D, \h, \H, \p, \P, \s, \S, \v, \V, \w, and  \W
3956         in  a  character  class,  and add the characters that they match to the         may  also appear in a character class, and add the characters that they
3957         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         match to the class. For example,  [\dABCDEF]  matches  any  hexadecimal
3958         flex  can  conveniently  be used with the upper case character types to         digit.  A circumflex can conveniently be used with the upper case char-
3959         specify a more restricted set of characters  than  the  matching  lower         acter types to specify a more restricted set  of  characters  than  the
3960         case  type.  For example, the class [^\W_] matches any letter or digit,         matching  lower  case  type.  For example, the class [^\W_] matches any
3961         but not underscore.         letter or digit, but not underscore.
3962    
3963         The only metacharacters that are recognized in  character  classes  are         The only metacharacters that are recognized in  character  classes  are
3964         backslash,  hyphen  (only  where  it can be interpreted as specifying a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
# Line 3774  POSIX CHARACTER CLASSES Line 3977  POSIX CHARACTER CLASSES
3977           [01[:alpha:]%]           [01[:alpha:]%]
3978    
3979         matches "0", "1", any alphabetic character, or "%". The supported class         matches "0", "1", any alphabetic character, or "%". The supported class
3980         names are         names are:
3981    
3982           alnum    letters and digits           alnum    letters and digits
3983           alpha    letters           alpha    letters
# Line 3785  POSIX CHARACTER CLASSES Line 3988  POSIX CHARACTER CLASSES
3988           graph    printing characters, excluding space           graph    printing characters, excluding space
3989           lower    lower case letters           lower    lower case letters
3990           print    printing characters, including space           print    printing characters, including space
3991           punct    printing characters, excluding letters and digits           punct    printing characters, excluding letters and digits and space
3992           space    white space (not quite the same as \s)           space    white space (not quite the same as \s)
3993           upper    upper case letters           upper    upper case letters
3994           word     "word" characters (same as \w)           word     "word" characters (same as \w)
# Line 3806  POSIX CHARACTER CLASSES Line 4009  POSIX CHARACTER CLASSES
4009         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
4010         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.
4011    
4012         In UTF-8 mode, characters with values greater than 128 do not match any         By  default,  in UTF-8 mode, characters with values greater than 128 do
4013         of the POSIX character classes.         not match any of the POSIX character classes. However, if the  PCRE_UCP
4014           option  is passed to pcre_compile(), some of the classes are changed so
4015           that Unicode character properties are used. This is achieved by replac-
4016           ing the POSIX classes by other sequences, as follows:
4017    
4018             [:alnum:]  becomes  \p{Xan}
4019             [:alpha:]  becomes  \p{L}
4020             [:blank:]  becomes  \h
4021             [:digit:]  becomes  \p{Nd}
4022             [:lower:]  becomes  \p{Ll}
4023             [:space:]  becomes  \p{Xps}
4024             [:upper:]  becomes  \p{Lu}
4025             [:word:]   becomes  \p{Xwd}
4026    
4027           Negated  versions,  such  as [:^alpha:] use \P instead of \p. The other
4028           POSIX classes are unchanged, and match only characters with code points
4029           less than 128.
4030    
4031    
4032  VERTICAL BAR  VERTICAL BAR
4033    
4034         Vertical bar characters are used to separate alternative patterns.  For         Vertical  bar characters are used to separate alternative patterns. For
4035         example, the pattern         example, the pattern
4036    
4037           gilbert|sullivan           gilbert|sullivan
4038    
4039         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches either "gilbert" or "sullivan". Any number of alternatives  may
4040         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear,  and  an  empty  alternative  is  permitted (matching the empty
4041         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
4042         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
4043         are  within a subpattern (defined below), "succeeds" means matching the         are within a subpattern (defined below), "succeeds" means matching  the
4044         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.
4045    
4046    
4047  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
4048    
4049         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
4050         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
4051         within the pattern by  a  sequence  of  Perl  option  letters  enclosed         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
4052         between "(?" and ")".  The option letters are         between "(?" and ")".  The option letters are
4053    
4054           i  for PCRE_CASELESS           i  for PCRE_CASELESS
# Line 3839  INTERNAL OPTION SETTING Line 4058  INTERNAL OPTION SETTING
4058    
4059         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
4060         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
4061         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-
4062         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
4063         is  also  permitted.  If  a  letter  appears  both before and after the         is also permitted. If a  letter  appears  both  before  and  after  the
4064         hyphen, the option is unset.         hyphen, the option is unset.
4065    
4066         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
4067         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
4068         the characters J, U and X respectively.         the characters J, U and X respectively.
4069    
4070         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
4071         inside  subpattern parentheses), the change applies to the remainder of         inside subpattern parentheses), the change applies to the remainder  of
4072         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
4073         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-
4074         fore show up in data extracted by the pcre_fullinfo() function).         fore show up in data extracted by the pcre_fullinfo() function).
4075    
4076         An option change within a subpattern (see below for  a  description  of         An  option  change  within a subpattern (see below for a description of
4077         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
4078         it, so         it, so
4079    
4080           (a(?i)b)c           (a(?i)b)c
4081    
4082         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
4083         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
4084         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
4085         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
4086         example,         example,
4087    
4088           (a(?i)b|c)           (a(?i)b|c)
4089    
4090         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
4091         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
4092         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
4093         some very weird behaviour otherwise.         some very weird behaviour otherwise.
4094    
4095         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
4096         application when the compile or match functions  are  called.  In  some         application  when  the  compile  or match functions are called. In some
4097         cases the pattern can contain special leading sequences such as (*CRLF)         cases the pattern can contain special leading sequences such as (*CRLF)
4098         to override what the application has set or what  has  been  defaulted.         to  override  what  the application has set or what has been defaulted.
4099         Details  are  given  in the section entitled "Newline sequences" above.         Details are given in the section entitled  "Newline  sequences"  above.
4100         There is also the (*UTF8) leading sequence that  can  be  used  to  set         There  are  also  the  (*UTF8) and (*UCP) leading sequences that can be
4101         UTF-8 mode; this is equivalent to setting the PCRE_UTF8 option.         used to set UTF-8 and Unicode property modes; they  are  equivalent  to
4102           setting the PCRE_UTF8 and the PCRE_UCP options, respectively.
4103    
4104    
4105  SUBPATTERNS  SUBPATTERNS
# Line 3961  DUPLICATE SUBPATTERN NUMBERS Line 4181  DUPLICATE SUBPATTERN NUMBERS
4181           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4182           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4183    
4184         A backreference or a recursive call to  a  numbered  subpattern  always         A back reference to a numbered subpattern uses the  most  recent  value
4185         refers to the first one in the pattern with the given number.         that  is  set  for that number by any subpattern. The following pattern
4186           matches "abcabc" or "defdef":
4187    
4188             /(?|(abc)|(def))\1/
4189    
4190           In contrast, a recursive or "subroutine" call to a numbered  subpattern
4191           always  refers  to  the first one in the pattern with the given number.
4192           The following pattern matches "abcabc" or "defabc":
4193    
4194             /(?|(abc)|(def))(?1)/
4195    
4196           If a condition test for a subpattern's having matched refers to a  non-
4197           unique  number, the test is true if any of the subpatterns of that num-
4198           ber have matched.
4199    
4200         An  alternative approach to using this "branch reset" feature is to use         An alternative approach to using this "branch reset" feature is to  use
4201         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
4202    
4203    
4204  NAMED SUBPATTERNS  NAMED SUBPATTERNS
4205    
4206         Identifying capturing parentheses by number is simple, but  it  can  be         Identifying  capturing  parentheses  by number is simple, but it can be
4207         very  hard  to keep track of the numbers in complicated regular expres-         very hard to keep track of the numbers in complicated  regular  expres-
4208         sions. Furthermore, if an  expression  is  modified,  the  numbers  may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
4209         change.  To help with this difficulty, PCRE supports the naming of sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
4210         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
4211         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
4212         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-
4213         tax.         tax. Perl allows identically numbered  subpatterns  to  have  different
4214           names, but PCRE does not.
4215    
4216         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>...)
4217         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
4218         to capturing parentheses from other parts of the pattern, such as back-         to  capturing parentheses from other parts of the pattern, such as back
4219         references, recursion, and conditions, can be made by name as  well  as         references, recursion, and conditions, can be made by name as  well  as
4220         by number.         by number.
4221    
# Line 3994  NAMED SUBPATTERNS Line 4228  NAMED SUBPATTERNS
4228    
4229         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
4230         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4231         time. This can be useful for patterns where only one  instance  of  the         time. (Duplicate names are also always permitted for  subpatterns  with
4232           the  same  number, set up as described in the previous section.) Dupli-
4233           cate names can be useful for patterns where only one  instance  of  the
4234         named  parentheses  can  match. Suppose you want to match the name of a         named  parentheses  can  match. Suppose you want to match the name of a
4235         weekday, either as a 3-letter abbreviation or as the full name, and  in         weekday, either as a 3-letter abbreviation or as the full name, and  in
4236         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
# Line 4013  NAMED SUBPATTERNS Line 4249  NAMED SUBPATTERNS
4249         The convenience function for extracting the data by  name  returns  the         The convenience function for extracting the data by  name  returns  the
4250         substring  for  the first (and in this example, the only) subpattern of         substring  for  the first (and in this example, the only) subpattern of
4251         that name that matched. This saves searching  to  find  which  numbered         that name that matched. This saves searching  to  find  which  numbered
4252         subpattern  it  was. If you make a reference to a non-unique named sub-         subpattern it was.
4253         pattern from elsewhere in the pattern, the one that corresponds to  the  
4254         lowest  number  is used. For further details of the interfaces for han-         If  you  make  a  back  reference to a non-unique named subpattern from
4255         dling named subpatterns, see the pcreapi documentation.         elsewhere in the pattern, the one that corresponds to the first  occur-
4256           rence of the name is used. In the absence of duplicate numbers (see the
4257           previous section) this is the one with the lowest number. If you use  a
4258           named  reference  in a condition test (see the section about conditions
4259           below), either to check whether a subpattern has matched, or  to  check
4260           for  recursion,  all  subpatterns with the same name are tested. If the
4261           condition is true for any one of them, the overall condition  is  true.
4262           This is the same behaviour as testing by number. For further details of
4263           the interfaces for handling named subpatterns, see the pcreapi documen-
4264           tation.
4265    
4266         Warning: You cannot use different names to distinguish between two sub-         Warning: You cannot use different names to distinguish between two sub-
4267         patterns  with  the same number (see the previous section) because PCRE         patterns with the same number because PCRE uses only the  numbers  when
4268         uses only the numbers when matching.         matching. For this reason, an error is given at compile time if differ-
4269           ent names are given to subpatterns with the same number.  However,  you
4270           can  give  the same name to subpatterns with the same number, even when
4271           PCRE_DUPNAMES is not set.
4272    
4273    
4274  REPETITION  REPETITION
# Line 4037  REPETITION Line 4285  REPETITION
4285           a character class           a character class
4286           a back reference (see next section)           a back reference (see next section)
4287           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4288             a recursive or "subroutine" call to a subpattern
4289    
4290         The  general repetition quantifier specifies a minimum and maximum num-         The  general repetition quantifier specifies a minimum and maximum num-
4291         ber of permitted matches, by giving the two numbers in  curly  brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
# Line 4151  REPETITION Line 4400  REPETITION
4400         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4401    
4402         However,  there is one situation where the optimization cannot be used.         However,  there is one situation where the optimization cannot be used.
4403         When .*  is inside capturing parentheses that  are  the  subject  of  a         When .*  is inside capturing parentheses that are the subject of a back
4404         backreference  elsewhere  in the pattern, a match at the start may fail         reference elsewhere in the pattern, a match at the start may fail where
4405         where a later one succeeds. Consider, for example:         a later one succeeds. Consider, for example:
4406    
4407           (.*)abc\1           (.*)abc\1
4408    
# Line 4360  BACK REFERENCES Line 4609  BACK REFERENCES
4609    
4610         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
4611         subpattern  has  not actually been used in a particular match, any back         subpattern  has  not actually been used in a particular match, any back
4612         references to it always fail. For example, the pattern         references to it always fail by default. For example, the pattern
4613    
4614           (a|(bc))\2           (a|(bc))\2
4615    
4616         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
4617         may  be  many  capturing parentheses in a pattern, all digits following         the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer-
4618         the backslash are taken as part of a potential back  reference  number.         ence to an unset value matches an empty string.
4619         If the pattern continues with a digit character, some delimiter must be  
4620         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         Because there may be many capturing parentheses in a pattern, all  dig-
4621         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         its  following a backslash are taken as part of a potential back refer-
4622         ments" below) can be used.         ence number.  If the pattern continues with  a  digit  character,  some
4623           delimiter  must  be  used  to  terminate  the  back  reference.  If the
4624         A back reference that occurs inside the parentheses to which it  refers         PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{
4625         fails  when  the subpattern is first used, so, for example, (a\1) never         syntax or an empty comment (see "Comments" below) can be used.
4626         matches.  However, such references can be useful inside  repeated  sub-  
4627       Recursive back references
4628    
4629           A  back reference that occurs inside the parentheses to which it refers
4630           fails when the subpattern is first used, so, for example,  (a\1)  never
4631           matches.   However,  such references can be useful inside repeated sub-
4632         patterns. For example, the pattern         patterns. For example, the pattern
4633    
4634           (a|b\1)+           (a|b\1)+
4635    
4636         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
4637         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4638         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4639         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
4640         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
4641         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4642    
4643           Back  references of this type cause the group that they reference to be
4644           treated as an atomic group.  Once the whole group has been  matched,  a
4645           subsequent  matching  failure cannot cause backtracking into the middle
4646           of the group.
4647    
4648    
4649  ASSERTIONS  ASSERTIONS
4650    
# Line 4433  ASSERTIONS Line 4692  ASSERTIONS
4692         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
4693         most convenient way to do it is  with  (?!)  because  an  empty  string         most convenient way to do it is  with  (?!)  because  an  empty  string
4694         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
4695         string must always fail.         string must always fail.   The  Perl  5.10  backtracking  control  verb
4696           (*FAIL) or (*F) is essentially a synonym for (?!).
4697    
4698     Lookbehind assertions     Lookbehind assertions
4699    
4700         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4701         for negative assertions. For example,         for negative assertions. For example,
4702    
4703           (?<!foo)bar           (?<!foo)bar
4704    
4705         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
4706         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4707         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-
4708         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
4709         fixed length. Thus         fixed length. Thus
4710    
4711           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4454  ASSERTIONS Line 4714  ASSERTIONS
4714    
4715           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4716    
4717         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4718         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4719         This  is  an  extension  compared  with  Perl (at least for 5.8), which         This is an extension compared with Perl (5.8 and 5.10), which  requires
4720         requires all branches to match the same length of string. An  assertion         all branches to match the same length of string. An assertion such as
        such as  
4721    
4722           (?<=ab(c|de))           (?<=ab(c|de))
4723    
4724         is  not  permitted,  because  its single top-level branch can match two         is  not  permitted,  because  its single top-level branch can match two
4725         different lengths, but it is acceptable if rewritten to  use  two  top-         different lengths, but it is acceptable to PCRE if rewritten to use two
4726         level branches:         top-level branches:
4727    
4728           (?<=abc|abde)           (?<=abc|abde)
4729    
4730         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
4731         instead of a lookbehind assertion; this is not restricted to  a  fixed-         instead of  a  lookbehind  assertion  to  get  round  the  fixed-length
4732         length.         restriction.
4733    
4734         The  implementation  of lookbehind assertions is, for each alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4735         to temporarily move the current position back by the fixed  length  and         to temporarily move the current position back by the fixed  length  and
# Line 4482  ASSERTIONS Line 4741  ASSERTIONS
4741         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,
4742         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4743    
4744           "Subroutine"  calls  (see below) such as (?2) or (?&X) are permitted in
4745           lookbehinds, as long as the subpattern matches a  fixed-length  string.
4746           Recursion, however, is not supported.
4747    
4748         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4749         assertions to specify efficient matching at  the  end  of  the  subject         assertions to specify efficient matching of fixed-length strings at the
4750         string. Consider a simple pattern such as         end of subject strings. Consider a simple pattern such as
4751    
4752           abcd$           abcd$
4753    
# Line 4547  CONDITIONAL SUBPATTERNS Line 4810  CONDITIONAL SUBPATTERNS
4810    
4811         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-
4812         ditionally or to choose between two alternative subpatterns,  depending         ditionally or to choose between two alternative subpatterns,  depending
4813         on  the result of an assertion, or whether a previous capturing subpat-         on  the result of an assertion, or whether a specific capturing subpat-
4814         tern matched or not. The two possible forms of  conditional  subpattern         tern has already been matched. The two possible  forms  of  conditional
4815         are         subpattern are:
4816    
4817           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4818           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
# Line 4564  CONDITIONAL SUBPATTERNS Line 4827  CONDITIONAL SUBPATTERNS
4827     Checking for a used subpattern by number     Checking for a used subpattern by number
4828    
4829         If the text between the parentheses consists of a sequence  of  digits,         If the text between the parentheses consists of a sequence  of  digits,
4830         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-
4831         previously matched. An alternative notation is to  precede  the  digits         viously matched. If there is more than one  capturing  subpattern  with
4832         with a plus or minus sign. In this case, the subpattern number is rela-         the  same  number  (see  the earlier section about duplicate subpattern
4833         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-
4834         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
4835         looping constructs it can also make sense to refer to subsequent groups         this case, the subpattern number is relative rather than absolute.  The
4836         with constructs such as (?(+2).         most  recently opened parentheses can be referenced by (?(-1), the next
4837           most recent by (?(-2), and so on. In looping  constructs  it  can  also
4838           make  sense  to  refer  to  subsequent  groups  with constructs such as
4839           (?(+2).
4840    
4841         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4842         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
4843         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4844    
4845           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4846    
4847         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4848         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4849         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4850         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4851         of parentheses matched or not. If they did, that is, if subject started         of parentheses matched or not. If they did, that is, if subject started
4852         with an opening parenthesis, the condition is true, and so the yes-pat-         with an opening parenthesis, the condition is true, and so the yes-pat-
4853         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4854         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4855         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4856         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4857    
4858         If you were embedding this pattern in a larger one,  you  could  use  a         If  you  were  embedding  this pattern in a larger one, you could use a
4859         relative reference:         relative reference:
4860    
4861           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4862    
4863         This  makes  the  fragment independent of the parentheses in the larger         This makes the fragment independent of the parentheses  in  the  larger
4864         pattern.         pattern.
4865    
4866     Checking for a used subpattern by name     Checking for a used subpattern by name
4867    
4868         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4869         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4870         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4871         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4872         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4873         looks  first for a named subpattern; if it cannot find one and the name         looks first for a named subpattern; if it cannot find one and the  name
4874         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4875         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4876         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4877    
4878         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
4879    
4880           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4881    
4882           If  the  name used in a condition of this kind is a duplicate, the test
4883           is applied to all subpatterns of the same name, and is true if any  one
4884           of them has matched.
4885    
4886     Checking for pattern recursion     Checking for pattern recursion
4887    
4888         If the condition is the string (R), and there is no subpattern with the         If the condition is the string (R), and there is no subpattern with the
4889         name  R, the condition is true if a recursive call to the whole pattern         name R, the condition is true if a recursive call to the whole  pattern
4890         or any subpattern has been made. If digits or a name preceded by amper-         or any subpattern has been made. If digits or a name preceded by amper-
4891         sand follow the letter R, for example:         sand follow the letter R, for example:
4892    
4893           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4894    
4895         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
4896         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
4897         entire recursion stack.         recursion stack. If the name used in a condition  of  this  kind  is  a
4898           duplicate, the test is applied to all subpatterns of the same name, and
4899           is true if any one of them is the most recent recursion.
4900    
4901         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test  conditions  are  false.   The
4902         sive patterns are described below.         syntax for recursive patterns is described below.
4903    
4904     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4905    
4906         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4907         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4908         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4909         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4910         DEFINE is that it can be used to define "subroutines" that can be  ref-         DEFINE  is that it can be used to define "subroutines" that can be ref-
4911         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4912         For example, a pattern to match an IPv4 address could be  written  like         For  example,  a pattern to match an IPv4 address could be written like
4913         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4914    
4915           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4916           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4917    
4918         The  first part of the pattern is a DEFINE group inside which a another         The first part of the pattern is a DEFINE group inside which a  another
4919         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4920         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4921         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
4922         condition.         condition. The rest of the pattern uses references to the  named  group
4923           to  match the four dot-separated components of an IPv4 address, insist-
4924         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.  
4925    
4926     Assertion conditions     Assertion conditions
4927    
4928         If  the  condition  is  not  in any of the above formats, it must be an         If the condition is not in any of the above  formats,  it  must  be  an
4929         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4930         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4931         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4932    
4933           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4934           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
4935    
4936         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4937         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4938         it tests for the presence of at least one letter in the subject.  If  a         it  tests  for the presence of at least one letter in the subject. If a
4939         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4940         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4941         strings  in  one  of the two forms dd-aaa-dd or dd-dd-dd, where aaa are         strings in one of the two forms dd-aaa-dd or dd-dd-dd,  where  aaa  are
4942         letters and dd are digits.         letters and dd are digits.
4943    
4944    
4945  COMMENTS  COMMENTS
4946    
4947         The sequence (?# marks the start of a comment that continues up to  the         The  sequence (?# marks the start of a comment that continues up to the
4948         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4949         characters that make up a comment play no part in the pattern  matching         characters  that make up a comment play no part in the pattern matching
4950         at all.         at all.
4951    
4952         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4953         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4954         after the next newline in the pattern.         after the next newline in the pattern.
4955    
4956    
4957  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4958    
4959         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4960         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4961         that  can  be  done  is  to use a pattern that matches up to some fixed         that can be done is to use a pattern that  matches  up  to  some  fixed
4962         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4963         depth.         depth.
4964    
4965         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4966         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4967         Perl  code in the expression at run time, and the code can refer to the         Perl code in the expression at run time, and the code can refer to  the
4968         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4969         parentheses problem can be created like this:         parentheses problem can be created like this:
4970    
# Line 4705  RECURSIVE PATTERNS Line 4974  RECURSIVE PATTERNS
4974         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4975    
4976         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4977         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4978         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4979         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of  recursion  was  subsequently  introduced
4980         release 5.10.         into Perl at release 5.10.
4981    
4982         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4983         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
4984         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4985         not,  it  is  a  "subroutine" call, which is described in the next sec-         not, it is a "subroutine" call, which is described  in  the  next  sec-
4986         tion.) The special item (?R) or (?0) is a recursive call of the  entire         tion.)  The special item (?R) or (?0) is a recursive call of the entire
4987         regular expression.         regular expression.
4988    
        In  PCRE (like Python, but unlike Perl), a recursive subpattern call is  
        always treated as an atomic group. That is, once it has matched some of  
        the subject string, it is never re-entered, even if it contains untried  
        alternatives and there is a subsequent matching failure.  
   
4989         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This PCRE pattern solves the nested  parentheses  problem  (assume  the
4990         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4991    
4992           \( ( (?>[^()]+) | (?R) )* \)           \( ( [^()]++ | (?R) )* \)
4993    
4994         First  it matches an opening parenthesis. Then it matches any number of         First  it matches an opening parenthesis. Then it matches any number of
4995         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings which can either be a  sequence  of  non-parentheses,  or  a
4996         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
4997         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis. Note the use
4998           of a possessive quantifier to avoid backtracking into sequences of non-
4999           parentheses.
5000    
5001         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
5002         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
5003    
5004           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( [^()]++ | (?1) )* \) )
5005    
5006         We  have  put the pattern into parentheses, and caused the recursion to         We  have  put the pattern into parentheses, and caused the recursion to
5007         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
5008    
5009         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be
5010         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
5011         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
5012         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
5013         the recursion. In other  words,  a  negative  number  counts  capturing         the recursion. In other  words,  a  negative  number  counts  capturing
5014         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
# Line 4757  RECURSIVE PATTERNS Line 5023  RECURSIVE PATTERNS
5023         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
5024         supported. We could rewrite the above example as follows:         supported. We could rewrite the above example as follows:
5025    
5026           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( [^()]++ | (?&pn) )* \) )
5027    
5028         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
5029         one is used.         one is used.
5030    
5031         This particular example pattern that we have been looking  at  contains         This particular example pattern that we have been looking  at  contains
5032         nested  unlimited repeats, and so the use of atomic grouping for match-         nested unlimited repeats, and so the use of a possessive quantifier for
5033         ing strings of non-parentheses is important when applying  the  pattern         matching strings of non-parentheses is important when applying the pat-
5034         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
5035         to         applied to
5036    
5037           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
5038    
5039         it yields "no match" quickly. However, if atomic grouping is not  used,         it yields "no match" quickly. However, if a  possessive  quantifier  is
5040         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
5041         different ways the + and * repeats can carve up the  subject,  and  all         so many different ways the + and * repeats can carve  up  the  subject,
5042         have to be tested before failure can be reported.         and all have to be tested before failure can be reported.
5043    
5044         At the end of a match, the values set for any capturing subpatterns are         At  the  end  of a match, the values of capturing parentheses are those
5045         those from the outermost level of the recursion at which the subpattern         from the outermost level. If you want to obtain intermediate values,  a
5046         value  is  set.   If  you want to obtain intermediate values, a callout         callout  function can be used (see below and the pcrecallout documenta-
5047         function can be used (see below and the pcrecallout documentation).  If         tion). If the pattern above is matched against
        the pattern above is matched against  
5048    
5049           (ab(cd)ef)           (ab(cd)ef)
5050    
5051         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the inner capturing parentheses  (numbered  2)  is  "ef",
5052         value taken on at the top level. If additional parentheses  are  added,         which  is the last value taken on at the top level. If a capturing sub-
5053         giving         pattern is not matched at the top level, its final value is unset, even
5054           if it is (temporarily) set at a deeper level.
5055           \( ( ( (?>[^()]+) | (?R) )* ) \)  
5056              ^                        ^         If  there are more than 15 capturing parentheses in a pattern, PCRE has
5057              ^                        ^         to obtain extra memory to store data during a recursion, which it  does
5058           by using pcre_malloc, freeing it via pcre_free afterwards. If no memory
5059         the  string  they  capture is "ab(cd)ef", the contents of the top level         can be obtained, the match fails with the PCRE_ERROR_NOMEMORY error.
        parentheses. If there are more than 15 capturing parentheses in a  pat-  
        tern, PCRE has to obtain extra memory to store data during a recursion,  
        which it does by using pcre_malloc, freeing  it  via  pcre_free  after-  
        wards.  If  no  memory  can  be  obtained,  the  match  fails  with the  
        PCRE_ERROR_NOMEMORY error.  
5060    
5061         Do not confuse the (?R) item with the condition (R),  which  tests  for         Do not confuse the (?R) item with the condition (R),  which  tests  for
5062         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.   Consider  this pattern, which matches text in angle brack-
# Line 4810  RECURSIVE PATTERNS Line 5070  RECURSIVE PATTERNS
5070         two  different  alternatives for the recursive and non-recursive cases.         two  different  alternatives for the recursive and non-recursive cases.
5071         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
5072    
5073       Recursion difference from Perl
5074    
5075           In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
5076           always treated as an atomic group. That is, once it has matched some of
5077           the subject string, it is never re-entered, even if it contains untried
5078           alternatives  and  there  is a subsequent matching failure. This can be
5079           illustrated by the following pattern, which purports to match a  palin-
5080           dromic  string  that contains an odd number of characters (for example,
5081           "a", "aba", "abcba", "abcdcba"):
5082    
5083             ^(.|(.)(?1)\2)$
5084    
5085           The idea is that it either matches a single character, or two identical
5086           characters  surrounding  a sub-palindrome. In Perl, this pattern works;
5087           in PCRE it does not if the pattern is  longer  than  three  characters.
5088           Consider the subject string "abcba":
5089    
5090           At  the  top level, the first character is matched, but as it is not at
5091           the end of the string, the first alternative fails; the second alterna-
5092           tive is taken and the recursion kicks in. The recursive call to subpat-
5093           tern 1 successfully matches the next character ("b").  (Note  that  the
5094           beginning and end of line tests are not part of the recursion).
5095    
5096           Back  at  the top level, the next character ("c") is compared with what
5097           subpattern 2 matched, which was "a". This fails. Because the  recursion
5098           is  treated  as  an atomic group, there are now no backtracking points,
5099           and so the entire match fails. (Perl is able, at  this  point,  to  re-
5100           enter  the  recursion  and try the second alternative.) However, if the
5101           pattern is written with the alternatives in the other order, things are
5102           different:
5103    
5104             ^((.)(?1)\2|.)$
5105    
5106           This  time,  the recursing alternative is tried first, and continues to
5107           recurse until it runs out of characters, at which point  the  recursion
5108           fails.  But  this  time  we  do  have another alternative to try at the
5109           higher level. That is the big difference:  in  the  previous  case  the
5110           remaining alternative is at a deeper recursion level, which PCRE cannot
5111           use.
5112    
5113           To change the pattern so that matches all palindromic strings, not just
5114           those  with  an  odd number of characters, it is tempting to change the
5115           pattern to this:
5116    
5117             ^((.)(?1)\2|.?)$
5118    
5119           Again, this works in Perl, but not in PCRE, and for  the  same  reason.
5120           When  a  deeper  recursion has matched a single character, it cannot be
5121           entered again in order to match an empty string.  The  solution  is  to
5122           separate  the two cases, and write out the odd and even cases as alter-
5123           natives at the higher level:
5124    
5125             ^(?:((.)(?1)\2|)|((.)(?3)\4|.))
5126    
5127           If you want to match typical palindromic phrases, the  pattern  has  to
5128           ignore all non-word characters, which can be done like this:
5129    
5130             ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$
5131    
5132           If run with the PCRE_CASELESS option, this pattern matches phrases such
5133           as "A man, a plan, a canal: Panama!" and it works well in both PCRE and
5134           Perl.  Note the use of the possessive quantifier *+ to avoid backtrack-
5135           ing into sequences of non-word characters. Without this, PCRE  takes  a
5136           great  deal  longer  (ten  times or more) to match typical phrases, and
5137           Perl takes so long that you think it has gone into a loop.
5138    
5139           WARNING: The palindrome-matching patterns above work only if  the  sub-
5140           ject  string  does not start with a palindrome that is shorter than the
5141           entire string.  For example, although "abcba" is correctly matched,  if
5142           the  subject  is "ababa", PCRE finds the palindrome "aba" at the start,
5143           then fails at top level because the end of the string does not  follow.
5144           Once  again, it cannot jump back into the recursion to try other alter-
5145           natives, so the entire match fails.
5146    
5147    
5148  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
5149    
# Line 4836  SUBPATTERNS AS SUBROUTINES Line 5170  SUBPATTERNS AS SUBROUTINES
5170         two strings. Another example is  given  in  the  discussion  of  DEFINE         two strings. Another example is  given  in  the  discussion  of  DEFINE
5171         above.         above.
5172    
5173         Like recursive subpatterns, a "subroutine" call is always treated as an         Like  recursive  subpatterns, a subroutine call is always treated as an
5174         atomic group. That is, once it has matched some of the subject  string,         atomic group. That is, once it has matched some of the subject  string,
5175         it  is  never  re-entered, even if it contains untried alternatives and         it  is  never  re-entered, even if it contains untried alternatives and
5176         there is a subsequent matching failure.         there is a subsequent matching failure. Any capturing parentheses  that
5177           are  set  during  the  subroutine  call revert to their previous values
5178           afterwards.
5179    
5180         When a subpattern is used as a subroutine, processing options  such  as         When a subpattern is used as a subroutine, processing options  such  as
5181         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
# Line 4922  BACKTRACKING CONTROL Line 5258  BACKTRACKING CONTROL
5258         (*FAIL), which behaves like a failing negative assertion, they cause an         (*FAIL), which behaves like a failing negative assertion, they cause an
5259         error if encountered by pcre_dfa_exec().         error if encountered by pcre_dfa_exec().
5260    
5261           If any of these verbs are used in an assertion or subroutine subpattern
5262           (including recursive subpatterns), their effect  is  confined  to  that
5263           subpattern;  it  does  not extend to the surrounding pattern. Note that
5264           such subpatterns are processed as anchored at the point where they  are
5265           tested.
5266    
5267         The  new verbs make use of what was previously invalid syntax: an open-         The  new verbs make use of what was previously invalid syntax: an open-
5268         ing parenthesis followed by an asterisk. In Perl, they are generally of         ing parenthesis followed by an asterisk. They are generally of the form
5269         the form (*VERB:ARG) but PCRE does not support the use of arguments, so         (*VERB)  or (*VERB:NAME). Some may take either form, with differing be-
5270         its general form is just (*VERB). Any number of these verbs  may  occur         haviour, depending on whether or not an argument is present. An name is
5271         in a pattern. There are two kinds:         a  sequence  of letters, digits, and underscores. If the name is empty,
5272           that is, if the closing parenthesis immediately follows the colon,  the
5273           effect is as if the colon were not there. Any number of these verbs may
5274           occur in a pattern.
5275    
5276           PCRE contains some optimizations that are used to speed up matching  by
5277           running some checks at the start of each match attempt. For example, it
5278           may know the minimum length of matching subject, or that  a  particular
5279           character  must  be present. When one of these optimizations suppresses
5280           the running of a match, any included backtracking verbs  will  not,  of
5281           course, be processed. You can suppress the start-of-match optimizations
5282           by setting the PCRE_NO_START_OPTIMIZE option when calling pcre_exec().
5283    
5284     Verbs that act immediately     Verbs that act immediately
5285    
5286         The following verbs act as soon as they are encountered:         The following verbs act as soon as they are encountered. They  may  not
5287           be followed by a name.
5288    
5289            (*ACCEPT)            (*ACCEPT)
5290    
5291         This  verb causes the match to end successfully, skipping the remainder         This  verb causes the match to end successfully, skipping the remainder
5292         of the pattern. When inside a recursion, only the innermost pattern  is         of the pattern. When inside a recursion, only the innermost pattern  is
5293         ended  immediately.  PCRE  differs  from  Perl  in  what happens if the         ended  immediately.  If  (*ACCEPT) is inside capturing parentheses, the
5294         (*ACCEPT) is inside capturing parentheses. In Perl, the data so far  is         data so far is captured. (This feature was added  to  PCRE  at  release
5295         captured: in PCRE no data is captured. For example:         8.00.) For example:
5296    
5297           A(A|B(*ACCEPT)|C)D           A((?:A|B(*ACCEPT)|C)D)
5298    
5299         This  matches  "AB", "AAD", or "ACD", but when it matches "AB", no data         This  matches  "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-
5300         is captured.         tured by the outer parentheses.
5301    
5302           (*FAIL) or (*F)           (*FAIL) or (*F)
5303    
# Line 4959  BACKTRACKING CONTROL Line 5313  BACKTRACKING CONTROL
5313         A  match  with the string "aaaa" always fails, but the callout is taken         A  match  with the string "aaaa" always fails, but the callout is taken
5314         before each backtrack happens (in this example, 10 times).         before each backtrack happens (in this example, 10 times).
5315    
5316       Recording which path was taken
5317    
5318           There is one verb whose main purpose  is  to  track  how  a  match  was
5319           arrived  at,  though  it  also  has a secondary use in conjunction with
5320           advancing the match starting point (see (*SKIP) below).
5321    
5322             (*MARK:NAME) or (*:NAME)
5323    
5324           A name is always  required  with  this  verb.  There  may  be  as  many
5325           instances  of  (*MARK) as you like in a pattern, and their names do not
5326           have to be unique.
5327    
5328           When a match succeeds, the name  of  the  last-encountered  (*MARK)  is
5329           passed  back  to  the  caller  via  the  pcre_extra  data structure, as
5330           described in the section on pcre_extra in the pcreapi documentation. No
5331           data  is  returned  for a partial match. Here is an example of pcretest
5332           output, where the /K modifier requests the retrieval and outputting  of
5333           (*MARK) data:
5334    
5335             /X(*MARK:A)Y|X(*MARK:B)Z/K
5336             XY
5337              0: XY
5338             MK: A
5339             XZ
5340              0: XZ
5341             MK: B
5342    
5343           The (*MARK) name is tagged with "MK:" in this output, and in this exam-
5344           ple it indicates which of the two alternatives matched. This is a  more
5345           efficient  way of obtaining this information than putting each alterna-
5346           tive in its own capturing parentheses.
5347    
5348           A name may also be returned after a failed  match  if  the  final  path
5349           through  the  pattern involves (*MARK). However, unless (*MARK) used in
5350           conjunction with (*COMMIT), this is unlikely to  happen  for  an  unan-
5351           chored pattern because, as the starting point for matching is advanced,
5352           the final check is often with an empty string, causing a failure before
5353           (*MARK) is reached. For example:
5354    
5355             /X(*MARK:A)Y|X(*MARK:B)Z/K
5356             XP
5357             No match
5358    
5359           There are three potential starting points for this match (starting with
5360           X, starting with P, and with  an  empty  string).  If  the  pattern  is
5361           anchored, the result is different:
5362    
5363             /^X(*MARK:A)Y|^X(*MARK:B)Z/K
5364             XP
5365             No match, mark = B
5366    
5367           PCRE's  start-of-match  optimizations can also interfere with this. For
5368           example, if, as a result of a call to pcre_study(), it knows the  mini-
5369           mum  subject  length for a match, a shorter subject will not be scanned
5370           at all.
5371    
5372           Note that similar anomalies (though different in detail) exist in Perl,
5373           no  doubt  for the same reasons. The use of (*MARK) data after a failed
5374           match of an unanchored pattern is not recommended, unless (*COMMIT)  is
5375           involved.
5376    
5377     Verbs that act after backtracking     Verbs that act after backtracking
5378    
5379         The following verbs do nothing when they are encountered. Matching con-         The following verbs do nothing when they are encountered. Matching con-
5380         tinues  with what follows, but if there is no subsequent match, a fail-         tinues with what follows, but if there is no subsequent match,  causing
5381         ure is forced.  The verbs  differ  in  exactly  what  kind  of  failure         a  backtrack  to  the  verb, a failure is forced. That is, backtracking
5382         occurs.         cannot pass to the left of the verb. However, when one of  these  verbs
5383           appears  inside  an atomic group, its effect is confined to that group,
5384           because once the group has been matched, there is never any  backtrack-
5385           ing  into  it.  In  this situation, backtracking can "jump back" to the
5386           left of the entire atomic group. (Remember also, as stated above,  that
5387           this localization also applies in subroutine calls and assertions.)
5388    
5389           These  verbs  differ  in exactly what kind of failure occurs when back-
5390           tracking reaches them.
5391    
5392           (*COMMIT)           (*COMMIT)
5393    
5394         This  verb  causes  the whole match to fail outright if the rest of the         This verb, which may not be followed by a name, causes the whole  match
5395         pattern does not match. Even if the pattern is unanchored,  no  further         to fail outright if the rest of the pattern does not match. Even if the
5396         attempts  to find a match by advancing the start point take place. Once         pattern is unanchored, no further attempts to find a match by advancing
5397         (*COMMIT) has been passed, pcre_exec() is committed to finding a  match         the  starting  point  take  place.  Once  (*COMMIT)  has  been  passed,
5398         at the current starting point, or not at all. For example:         pcre_exec() is committed to finding a match  at  the  current  starting
5399           point, or not at all. For example:
5400    
5401           a+(*COMMIT)b           a+(*COMMIT)b
5402    
5403         This  matches  "xxaab" but not "aacaab". It can be thought of as a kind         This  matches  "xxaab" but not "aacaab". It can be thought of as a kind
5404         of dynamic anchor, or "I've started, so I must finish."         of dynamic anchor, or "I've started, so I must finish." The name of the
5405           most  recently passed (*MARK) in the path is passed back when (*COMMIT)
5406           (*PRUNE)         forces a match failure.
5407    
5408           Note that (*COMMIT) at the start of a pattern is not  the  same  as  an
5409           anchor,  unless  PCRE's start-of-match optimizations are turned off, as
5410           shown in this pcretest example:
5411    
5412             /(*COMMIT)abc/
5413             xyzabc
5414              0: abc
5415             xyzabc\Y
5416             No match
5417    
5418         This verb causes the match to fail at the current position if the  rest         PCRE knows that any match must start  with  "a",  so  the  optimization
5419         of the pattern does not match. If the pattern is unanchored, the normal         skips  along the subject to "a" before running the first match attempt,
5420         "bumpalong" advance to the next starting character then happens.  Back-         which succeeds. When the optimization is disabled by the \Y  escape  in
5421         tracking  can  occur as usual to the left of (*PRUNE), or when matching         the second subject, the match starts at "x" and so the (*COMMIT) causes
5422         to the right of (*PRUNE), but if there is no match to the right,  back-         it to fail without trying any other starting points.
5423         tracking  cannot  cross (*PRUNE).  In simple cases, the use of (*PRUNE)  
5424         is just an alternative to an atomic group or possessive quantifier, but           (*PRUNE) or (*PRUNE:NAME)
5425         there  are  some uses of (*PRUNE) that cannot be expressed in any other  
5426         way.         This verb causes the match to fail at the current starting position  in
5427           the  subject  if the rest of the pattern does not match. If the pattern
5428           is unanchored, the normal "bumpalong"  advance  to  the  next  starting
5429           character  then happens. Backtracking can occur as usual to the left of
5430           (*PRUNE), before it is reached,  or  when  matching  to  the  right  of
5431           (*PRUNE),  but  if  there is no match to the right, backtracking cannot