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# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few differences. (Certain features that appeared in Python and         just  a  few  differences. Certain features that appeared in Python and
22         PCRE before they appeared in Perl are also available using  the  Python         PCRE before they appeared in Perl are also available using  the  Python
23         syntax.)         syntax.  There is also some support for certain .NET and Oniguruma syn-
24           tax items, and there is an option for  requesting  some  minor  changes
25           that give better JavaScript compatibility.
26    
27         The  current  implementation of PCRE (release 7.x) corresponds approxi-         The  current  implementation of PCRE (release 7.x) corresponds approxi-
28         mately with Perl 5.10, including support for UTF-8 encoded strings  and         mately with Perl 5.10, including support for UTF-8 encoded strings  and
# Line 92  USER DOCUMENTATION Line 94  USER DOCUMENTATION
94           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
95           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
96    
97         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
98         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
99    
100    
101  LIMITATIONS  LIMITATIONS
102    
103         There are some size limitations in PCRE but it is hoped that they  will         There  are some size limitations in PCRE but it is hoped that they will
104         never in practice be relevant.         never in practice be relevant.
105    
106         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
107         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
108         process  regular  expressions  that are truly enormous, you can compile         process regular expressions that are truly enormous,  you  can  compile
109         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
110         the  source  distribution and the pcrebuild documentation for details).         the source distribution and the pcrebuild documentation  for  details).
111         In these cases the limit is substantially larger.  However,  the  speed         In  these  cases the limit is substantially larger.  However, the speed
112         of execution is slower.         of execution is slower.
113    
114         All values in repeating quantifiers must be less than 65536.         All values in repeating quantifiers must be less than 65536.
# Line 117  LIMITATIONS Line 119  LIMITATIONS
119         The maximum length of name for a named subpattern is 32 characters, and         The maximum length of name for a named subpattern is 32 characters, and
120         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
121    
122         The  maximum  length of a subject string is the largest positive number         The maximum length of a subject string is the largest  positive  number
123         that an integer variable can hold. However, when using the  traditional         that  an integer variable can hold. However, when using the traditional
124         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
125         inite repetition.  This means that the available stack space may  limit         inite  repetition.  This means that the available stack space may limit
126         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
127         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
128    
129    
130  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
131    
132         From release 3.3, PCRE has  had  some  support  for  character  strings         From  release  3.3,  PCRE  has  had  some support for character strings
133         encoded  in the UTF-8 format. For release 4.0 this was greatly extended         encoded in the UTF-8 format. For release 4.0 this was greatly  extended
134         to cover most common requirements, and in release 5.0  additional  sup-         to  cover  most common requirements, and in release 5.0 additional sup-
135         port for Unicode general category properties was added.         port for Unicode general category properties was added.
136    
137         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
138         support in the code, and, in addition,  you  must  call  pcre_compile()         support  in  the  code,  and, in addition, you must call pcre_compile()
139         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with the PCRE_UTF8 option flag. When you do this, both the pattern  and
140         any subject strings that are matched against it are  treated  as  UTF-8         any  subject  strings  that are matched against it are treated as UTF-8
141         strings instead of just strings of bytes.         strings instead of just strings of bytes.
142    
143         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,
144         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
145         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
146         very big.         very big.
147    
148         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
149         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
150         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
151         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
152         for a decimal number, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
153         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
154         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
155         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
156         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
157         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
158         does not support this.         does not support this.
159    
160         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
161    
162         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
163         subjects  are  checked for validity on entry to the relevant functions.         subjects are (by default) checked for validity on entry to the relevant
164         If an invalid UTF-8 string is passed, an error return is given. In some         functions.  From  release 7.3 of PCRE, the check is according the rules
165         situations,  you  may  already  know  that  your strings are valid, and         of RFC 3629, which are themselves derived from the  Unicode  specifica-
166         therefore want to skip these checks in order to improve performance. If         tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
167         you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,         allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
168         PCRE assumes that the pattern or subject  it  is  given  (respectively)         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
169         contains  only valid UTF-8 codes. In this case, it does not diagnose an         to U+DFFF.
170         invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when  
171         PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may         The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
172         crash.         which  the Unicode Standard says this: "The Low Surrogate Area does not
173           contain any  character  assignments,  consequently  no  character  code
174           charts or namelists are provided for this area. Surrogates are reserved
175           for use with UTF-16 and then must be used in pairs."  The  code  points
176           that  are  encoded  by  UTF-16  pairs are available as independent code
177           points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
178           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
179    
180           If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
181           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
182           that your strings are valid, and therefore want to skip these checks in
183           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
184           compile  time  or at run time, PCRE assumes that the pattern or subject
185           it is given (respectively) contains only valid  UTF-8  codes.  In  this
186           case, it does not diagnose an invalid UTF-8 string.
187    
188           If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
189           what happens depends on why the string is invalid. If the  string  con-
190           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
191           string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
192           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
193           strings according to the more liberal rules of RFC  2279.  However,  if
194           the  string does not even conform to RFC 2279, the result is undefined.
195           Your program may crash.
196    
197           If you want to process strings  of  values  in  the  full  range  0  to
198           0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
199           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
200           this situation, you will have to apply your own validity check.
201    
202         2. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a     General comments about UTF-8 mode
203    
204           1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
205         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
206    
207         3.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
208         characters for values greater than \177.         characters for values greater than \177.
209    
210         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
211         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
212    
213         5.  The dot metacharacter matches one UTF-8 character instead of a sin-         4. The dot metacharacter matches one UTF-8 character instead of a  sin-
214         gle byte.         gle byte.
215    
216         6. The escape sequence \C can be used to match a single byte  in  UTF-8         5.  The  escape sequence \C can be used to match a single byte in UTF-8
217         mode,  but  its  use can lead to some strange effects. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
218         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
219    
220         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
221         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but the characters that PCRE  recog-
222         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes  as  digits,  spaces,  or  word characters remain the same set as
223         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
224         includes Unicode property support, because to do otherwise  would  slow         includes  Unicode  property support, because to do otherwise would slow
225         down  PCRE in many common cases. If you really want to test for a wider         down PCRE in many common cases. If you really want to test for a  wider
226         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense  of,  say,  "digit",  you must use Unicode property tests such as
227         \p{Nd}.         \p{Nd}. Note that this also applies to \b, because  it  is  defined  in
228           terms of \w and \W.
229    
230         8.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
231         are all low-valued characters.         are all low-valued characters.
232    
233         9. However, the Perl 5.10 horizontal and vertical  whitespace  matching         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
234         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-
235         acters.         acters.
236    
237         10. Case-insensitive matching applies only to characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
238         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
239         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
240         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
# Line 226  AUTHOR Line 259  AUTHOR
259    
260  REVISION  REVISION
261    
262         Last updated: 06 August 2007         Last updated: 18 March 2009
263         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
264  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
265    
266    
# Line 241  NAME Line 274  NAME
274  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
275    
276         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
277         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
278         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
279         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
280         includes  the  standard  ones such as the selection of the installation         the  same  options  can be selected in both Unix-like and non-Unix-like
281         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
282           CMake instead of configure to build PCRE.
283    
284           The complete list of options for configure (which includes the standard
285           ones such as the  selection  of  the  installation  directory)  can  be
286           obtained by running
287    
288           ./configure --help           ./configure --help
289    
290         The following sections include  descriptions  of  options  whose  names         The  following  sections  include  descriptions  of options whose names
291         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
292         defaults for the configure command. Because of the way  that  configure         defaults  for  the configure command. Because of the way that configure
293         works,  --enable  and --disable always come in pairs, so the complemen-         works, --enable and --disable always come in pairs, so  the  complemen-
294         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
295         is not described.         is not described.
296    
297    
# Line 270  C++ SUPPORT Line 308  C++ SUPPORT
308    
309  UTF-8 SUPPORT  UTF-8 SUPPORT
310    
311         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
312    
313           --enable-utf8           --enable-utf8
314    
315         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
316         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
317         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()
318         function.         function.
319    
320           If  you set --enable-utf8 when compiling in an EBCDIC environment, PCRE
321           expects its input to be either ASCII or UTF-8 (depending on the runtime
322           option).  It  is not possible to support both EBCDIC and UTF-8 codes in
323           the same  version  of  the  library.  Consequently,  --enable-utf8  and
324           --enable-ebcdic are mutually exclusive.
325    
326    
327  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
328    
329         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
330         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-
331         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
332         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
333         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
334    
335           --enable-unicode-properties           --enable-unicode-properties
336    
337         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
338         not explicitly requested it.         not explicitly requested it.
339    
340         Including  Unicode  property  support  adds around 30K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
341         PCRE library. Only the general category properties such as  Lu  and  Nd         PCRE  library.  Only  the general category properties such as Lu and Nd
342         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
343    
344    
345  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
346    
347         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating         By default, PCRE interprets the linefeed (LF) character  as  indicating
348         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
349         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems. You can compile PCRE to use carriage return (CR)  instead,  by
350         instead, by adding         adding
351    
352           --enable-newline-is-cr           --enable-newline-is-cr
353    
354         to the  configure  command.  There  is  also  a  --enable-newline-is-lf         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
355         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
356    
357         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 319  CODE VALUE OF NEWLINE Line 363  CODE VALUE OF NEWLINE
363    
364           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
365    
366         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
367         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
368    
369           --enable-newline-is-any           --enable-newline-is-any
# Line 331  CODE VALUE OF NEWLINE Line 375  CODE VALUE OF NEWLINE
375         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
376    
377    
378    WHAT \R MATCHES
379    
380           By default, the sequence \R in a pattern matches  any  Unicode  newline
381           sequence,  whatever  has  been selected as the line ending sequence. If
382           you specify
383    
384             --enable-bsr-anycrlf
385    
386           the default is changed so that \R matches only CR, LF, or  CRLF.  What-
387           ever  is selected when PCRE is built can be overridden when the library
388           functions are called.
389    
390    
391  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
392    
393         The PCRE building process uses libtool to build both shared and  static         The PCRE building process uses libtool to build both shared and  static
# Line 466  USING EBCDIC CODE Line 523  USING EBCDIC CODE
523    
524         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
525         bles.  You  should  only  use  it if you know that you are in an EBCDIC         bles.  You  should  only  use  it if you know that you are in an EBCDIC
526         environment (for example, an IBM mainframe operating system).         environment (for example,  an  IBM  mainframe  operating  system).  The
527           --enable-ebcdic option is incompatible with --enable-utf8.
528    
529    
530    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
531    
532           By default, pcregrep reads all files as plain text. You can build it so
533           that it recognizes files whose names end in .gz or .bz2, and reads them
534           with libz or libbz2, respectively, by adding one or both of
535    
536             --enable-pcregrep-libz
537             --enable-pcregrep-libbz2
538    
539           to the configure command. These options naturally require that the rel-
540           evant libraries are installed on your system. Configuration  will  fail
541           if they are not.
542    
543    
544    PCRETEST OPTION FOR LIBREADLINE SUPPORT
545    
546           If you add
547    
548             --enable-pcretest-libreadline
549    
550           to  the  configure  command,  pcretest  is  linked with the libreadline
551           library, and when its input is from a terminal, it reads it  using  the
552           readline() function. This provides line-editing and history facilities.
553           Note that libreadline is GPL-licenced, so if you distribute a binary of
554           pcretest linked in this way, there may be licensing issues.
555    
556           Setting  this  option  causes  the -lreadline option to be added to the
557           pcretest build. In many operating environments with  a  sytem-installed
558           libreadline this is sufficient. However, in some environments (e.g.  if
559           an unmodified distribution version of readline is in use),  some  extra
560           configuration  may  be necessary. The INSTALL file for libreadline says
561           this:
562    
563             "Readline uses the termcap functions, but does not link with the
564             termcap or curses library itself, allowing applications which link
565             with readline the to choose an appropriate library."
566    
567           If your environment has not been set up so that an appropriate  library
568           is automatically included, you may need to add something like
569    
570             LIBS="-ncurses"
571    
572           immediately before the configure command.
573    
574    
575  SEE ALSO  SEE ALSO
# Line 483  AUTHOR Line 586  AUTHOR
586    
587  REVISION  REVISION
588    
589         Last updated: 30 July 2007         Last updated: 17 March 2009
590         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
591  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
592    
593    
# Line 627  THE ALTERNATIVE MATCHING ALGORITHM Line 730  THE ALTERNATIVE MATCHING ALGORITHM
730         6.  Callouts  are  supported, but the value of the capture_top field is         6.  Callouts  are  supported, but the value of the capture_top field is
731         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
732    
733         7.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
734         single  byte, even in UTF-8 mode, is not supported because the alterna-         single  byte, even in UTF-8 mode, is not supported because the alterna-
735         tive algorithm moves through the subject  string  one  character  at  a         tive algorithm moves through the subject  string  one  character  at  a
736         time, for all active paths through the tree.         time, for all active paths through the tree.
737    
738           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
739           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
740           negative assertion.
741    
742    
743  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
744    
# Line 678  AUTHOR Line 785  AUTHOR
785    
786  REVISION  REVISION
787    
788         Last updated: 29 May 2007         Last updated: 19 April 2008
789         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
790  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
791    
792    
# Line 791  PCRE API OVERVIEW Line 898  PCRE API OVERVIEW
898         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
899         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
900         the  source distribution. The pcresample documentation describes how to         the  source distribution. The pcresample documentation describes how to
901         run it.         compile and run it.
902    
903         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
904         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
# Line 875  NEWLINES Line 982  NEWLINES
982         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
983         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
984    
985           At compile time, the newline convention can be specified by the options
986           argument of pcre_compile(), or it can be specified by special  text  at
987           the start of the pattern itself; this overrides any other settings. See
988           the pcrepattern page for details of the special character sequences.
989    
990         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-
991         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
992         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
993         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
994         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
995         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
996         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
997    
998           The choice of newline convention does not affect the interpretation  of
999           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1000           which is controlled in a similar way, but by separate options.
1001    
1002    
1003  MULTITHREADING  MULTITHREADING
1004    
1005         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1006         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1007         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
1008         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
# Line 935  CHECKING BUILD-TIME OPTIONS Line 1051  CHECKING BUILD-TIME OPTIONS
1051         The output is an integer whose value specifies  the  default  character         The output is an integer whose value specifies  the  default  character
1052         sequence  that is recognized as meaning "newline". The four values that         sequence  that is recognized as meaning "newline". The four values that
1053         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,
1054         and  -1  for  ANY. The default should normally be the standard sequence         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1055         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1056           spond to the standard sequence for your operating system.
1057    
1058             PCRE_CONFIG_BSR
1059    
1060           The output is an integer whose value indicates what character sequences
1061           the \R escape sequence matches by default. A value of 0 means  that  \R
1062           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1063           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1064           tern is compiled or matched.
1065    
1066           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1067    
1068         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
1069         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1070         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1071         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1072         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1073         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1074    
1075           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1076    
1077         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1078         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1079         given in the pcreposix documentation.         given in the pcreposix documentation.
1080    
1081           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1082    
1083         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1084         internal matching function calls in a  pcre_exec()  execution.  Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1085         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1086    
1087           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1088    
1089         The  output is an integer that gives the default limit for the depth of         The output is a long integer that gives the default limit for the depth
1090         recursion when calling the internal matching function in a  pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1091         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1092           below.
1093    
1094           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1095    
# Line 1067  COMPILING A PATTERN Line 1193  COMPILING A PATTERN
1193         all with number 255, before each pattern item. For  discussion  of  the         all with number 255, before each pattern item. For  discussion  of  the
1194         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1195    
1196             PCRE_BSR_ANYCRLF
1197             PCRE_BSR_UNICODE
1198    
1199           These options (which are mutually exclusive) control what the \R escape
1200           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1201           or to match any Unicode newline sequence. The default is specified when
1202           PCRE is built. It can be overridden from within the pattern, or by set-
1203           ting an option when a compiled pattern is matched.
1204    
1205           PCRE_CASELESS           PCRE_CASELESS
1206    
1207         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
# Line 1140  COMPILING A PATTERN Line 1275  COMPILING A PATTERN
1275         before  or  at  the  first  newline  in  the subject string, though the         before  or  at  the  first  newline  in  the subject string, though the
1276         matched text may continue over the newline.         matched text may continue over the newline.
1277    
1278             PCRE_JAVASCRIPT_COMPAT
1279    
1280           If this option is set, PCRE's behaviour is changed in some ways so that
1281           it  is  compatible with JavaScript rather than Perl. The changes are as
1282           follows:
1283    
1284           (1) A lone closing square bracket in a pattern  causes  a  compile-time
1285           error,  because this is illegal in JavaScript (by default it is treated
1286           as a data character). Thus, the pattern AB]CD becomes illegal when this
1287           option is set.
1288    
1289           (2)  At run time, a back reference to an unset subpattern group matches
1290           an empty string (by default this causes the current  matching  alterna-
1291           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1292           set (assuming it can find an "a" in the subject), whereas it  fails  by
1293           default, for Perl compatibility.
1294    
1295           PCRE_MULTILINE           PCRE_MULTILINE
1296    
1297         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1298         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1299         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1300         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1301         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1302         is set). This is the same as Perl.         is set). This is the same as Perl.
1303    
1304         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1305         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1306         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1307         start and end. This is equivalent to Perl's /m option, and  it  can  be         start  and  end.  This is equivalent to Perl's /m option, and it can be
1308         changed within a pattern by a (?m) option setting. If there are no new-         changed within a pattern by a (?m) option setting. If there are no new-
1309         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1310         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1311    
1312           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1163  COMPILING A PATTERN Line 1315  COMPILING A PATTERN
1315           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1316           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1317    
1318         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1319         when PCRE was built. Setting the first or the second specifies  that  a         when  PCRE  was built. Setting the first or the second specifies that a
1320         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1321         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1322         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1323         that any of the three preceding sequences should be recognized. Setting         that any of the three preceding sequences should be recognized. Setting
1324         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1325         recognized. The Unicode newline sequences are the three just mentioned,         recognized. The Unicode newline sequences are the three just mentioned,
1326         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1327         U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1328         (paragraph  separator,  U+2029).  The  last  two are recognized only in         (paragraph separator, U+2029). The last  two  are  recognized  only  in
1329         UTF-8 mode.         UTF-8 mode.
1330    
1331         The newline setting in the  options  word  uses  three  bits  that  are         The  newline  setting  in  the  options  word  uses three bits that are
1332         treated as a number, giving eight possibilities. Currently only six are         treated as a number, giving eight possibilities. Currently only six are
1333         used (default plus the five values above). This means that if  you  set         used  (default  plus the five values above). This means that if you set
1334         more  than one newline option, the combination may or may not be sensi-         more than one newline option, the combination may or may not be  sensi-
1335         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1336         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1337         cause an error.         cause an error.
1338    
1339         The only time that a line break is specially recognized when  compiling         The  only time that a line break is specially recognized when compiling
1340         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1341         character class is encountered. This indicates  a  comment  that  lasts         character  class  is  encountered.  This indicates a comment that lasts
1342         until  after the next line break sequence. In other circumstances, line         until after the next line break sequence. In other circumstances,  line
1343         break  sequences  are  treated  as  literal  data,   except   that   in         break   sequences   are   treated  as  literal  data,  except  that  in
1344         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1345         and are therefore ignored.         and are therefore ignored.
1346    
1347         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1348         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1349    
1350           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1351    
# Line 1222  COMPILING A PATTERN Line 1374  COMPILING A PATTERN
1374           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1375    
1376         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1377         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically  checked.  There  is  a  discussion about the validity of
1378         pcre_compile() returns an error. If you already know that your  pattern         UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1379         is  valid, and you want to skip this check for performance reasons, you         bytes  is  found,  pcre_compile() returns an error. If you already know
1380         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1381         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1382         your program to crash.  Note that this option can  also  be  passed  to         set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1383         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined.  It  may  cause your program to crash. Note that this option
1384         ing of subject strings.         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1385           UTF-8 validity checking of subject strings.
1386    
1387    
1388  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1389    
1390         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1391         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1392         both compiling functions. As PCRE has developed, some error codes  have         both  compiling functions. As PCRE has developed, some error codes have
1393         fallen out of use. To avoid confusion, they have not been re-used.         fallen out of use. To avoid confusion, they have not been re-used.
1394    
1395            0  no error            0  no error
# Line 1251  COMPILATION ERROR CODES Line 1404  COMPILATION ERROR CODES
1404            9  nothing to repeat            9  nothing to repeat
1405           10  [this code is not in use]           10  [this code is not in use]
1406           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1407           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1408           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1409           14  missing )           14  missing )
1410           15  reference to non-existent subpattern           15  reference to non-existent subpattern
# Line 1259  COMPILATION ERROR CODES Line 1412  COMPILATION ERROR CODES
1412           17  unknown option bit(s) set           17  unknown option bit(s) set
1413           18  missing ) after comment           18  missing ) after comment
1414           19  [this code is not in use]           19  [this code is not in use]
1415           20  regular expression too large           20  regular expression is too large
1416           21  failed to get memory           21  failed to get memory
1417           22  unmatched parentheses           22  unmatched parentheses
1418           23  internal error: code overflow           23  internal error: code overflow
# Line 1288  COMPILATION ERROR CODES Line 1441  COMPILATION ERROR CODES
1441           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1442           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1443           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1444           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10000)
1445           50  [this code is not in use]           50  [this code is not in use]
1446           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1447           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1448           53   internal  error:  previously-checked  referenced  subpattern not           53  internal  error:  previously-checked  referenced  subpattern  not
1449         found         found
1450           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1451           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1452           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1453           57  \g is not followed by a braced name or an optionally braced           57  \g is not followed by a braced, angle-bracketed, or quoted
1454                 non-zero number                 name/number or by a plain number
1455           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number           58  a numbered reference must not be zero
1456             59  (*VERB) with an argument is not supported
1457             60  (*VERB) not recognized
1458             61  number is too big
1459             62  subpattern name expected
1460             63  digit expected after (?+
1461             64  ] is an invalid data character in JavaScript compatibility mode
1462    
1463           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1464           values may be used if the limits were changed when PCRE was built.
1465    
1466    
1467  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1488  INFORMATION ABOUT A PATTERN Line 1650  INFORMATION ABOUT A PATTERN
1650         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1651         able.         able.
1652    
1653             PCRE_INFO_HASCRORLF
1654    
1655           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1656           characters, otherwise 0. The fourth argument should  point  to  an  int
1657           variable.  An explicit match is either a literal CR or LF character, or
1658           \r or \n.
1659    
1660           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1661    
1662         Return  1  if the (?J) option setting is used in the pattern, otherwise         Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1663         0. The fourth argument should point to an int variable. The (?J) inter-         otherwise  0. The fourth argument should point to an int variable. (?J)
1664         nal option setting changes the local PCRE_DUPNAMES option.         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1665    
1666           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1667    
1668         Return  the  value of the rightmost literal byte that must exist in any         Return the value of the rightmost literal byte that must exist  in  any
1669         matched string, other than at its  start,  if  such  a  byte  has  been         matched  string,  other  than  at  its  start,  if such a byte has been
1670         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1671         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1672         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1673         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
1674         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1675    
# Line 1508  INFORMATION ABOUT A PATTERN Line 1677  INFORMATION ABOUT A PATTERN
1677           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1678           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1679    
1680         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1681         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1682         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1683         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1684         strings  by  name. It is also possible to extract the data directly, by         strings by name. It is also possible to extract the data  directly,  by
1685         first converting the name to a number in order to  access  the  correct         first  converting  the  name to a number in order to access the correct
1686         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1687         the conversion, you need  to  use  the  name-to-number  map,  which  is         the  conversion,  you  need  to  use  the  name-to-number map, which is
1688         described by these three values.         described by these three values.
1689    
1690         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1691         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1692         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1693         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1694         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
1695         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-
1696         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-
1697         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1698         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1699         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1700         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1701         ignored):         ignored):
1702    
1703           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1704           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1705    
1706         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1707         each  entry  in the table is eight bytes long. The table is as follows,         each entry in the table is eight bytes long. The table is  as  follows,
1708         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1709         as ??:         as ??:
1710    
# Line 1544  INFORMATION ABOUT A PATTERN Line 1713  INFORMATION ABOUT A PATTERN
1713           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1714           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1715    
1716         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1717         name-to-number map, remember that the length of the entries  is  likely         name-to-number  map,  remember that the length of the entries is likely
1718         to be different for each compiled pattern.         to be different for each compiled pattern.
1719    
1720           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1721    
1722         Return  1 if the pattern can be used for partial matching, otherwise 0.         Return 1 if the pattern can be used for partial matching, otherwise  0.
1723         The fourth argument should point to an int  variable.  The  pcrepartial         The  fourth  argument  should point to an int variable. The pcrepartial
1724         documentation  lists  the restrictions that apply to patterns when par-         documentation lists the restrictions that apply to patterns  when  par-
1725         tial matching is used.         tial matching is used.
1726    
1727           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1728    
1729         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
1730         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1731         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1732         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
1733         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
1734         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
1735         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1736         and PCRE_EXTENDED.         and PCRE_EXTENDED.
1737    
1738         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
1739         alternatives begin with one of the following:         alternatives begin with one of the following:
1740    
1741           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1580  INFORMATION ABOUT A PATTERN Line 1749  INFORMATION ABOUT A PATTERN
1749    
1750           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1751    
1752         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
1753         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
1754         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
1755         size_t variable.         size_t variable.
# Line 1588  INFORMATION ABOUT A PATTERN Line 1757  INFORMATION ABOUT A PATTERN
1757           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1758    
1759         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
1760         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
1761         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
1762         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1763         variable.         variable.
1764    
1765    
# Line 1598  OBSOLETE INFO FUNCTION Line 1767  OBSOLETE INFO FUNCTION
1767    
1768         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1769    
1770         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1771         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1772         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1773         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1774         lowing negative numbers:         lowing negative numbers:
1775    
1776           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1777           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1778    
1779         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1780         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1781         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1782    
1783         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1784         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1785         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1786    
1787    
# Line 1620  REFERENCE COUNTS Line 1789  REFERENCE COUNTS
1789    
1790         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1791    
1792         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1793         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1794         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1795         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1796         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1797    
1798         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1799         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1800         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1801         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1802         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1803         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1804    
1805         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1806         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1807         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1808    
1809    
# Line 1728  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1897  MATCHING A PATTERN: THE TRADITIONAL FUNC
1897         the total number of calls, because not all calls to match() are  recur-         the total number of calls, because not all calls to match() are  recur-
1898         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1899    
1900         Limiting the recursion depth limits the amount of  stack  that  can  be         Limiting  the  recursion  depth  limits the amount of stack that can be
1901         used, or, when PCRE has been compiled to use memory on the heap instead         used, or, when PCRE has been compiled to use memory on the heap instead
1902         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1903    
1904         The default value for match_limit_recursion can be  set  when  PCRE  is         The  default  value  for  match_limit_recursion can be set when PCRE is
1905         built;  the  default  default  is  the  same  value  as the default for         built; the default default  is  the  same  value  as  the  default  for
1906         match_limit. You can override the default by suppling pcre_exec()  with         match_limit.  You can override the default by suppling pcre_exec() with
1907         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1908         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
1909         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1910    
1911         The  pcre_callout  field is used in conjunction with the "callout" fea-         The pcre_callout field is used in conjunction with the  "callout"  fea-
1912         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1913    
1914         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1915         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1916         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1917         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1918         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1919         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1920         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1921         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1922         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1923         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1924    
1925     Option bits for pcre_exec()     Option bits for pcre_exec()
1926    
1927         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.
1928         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,
1929         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,    PCRE_NO_START_OPTIMIZE,
1930         PCRE_PARTIAL.         PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
1931    
1932           PCRE_ANCHORED           PCRE_ANCHORED
1933    
1934         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1935         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1936         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
1937         unachored at matching time.         unachored at matching time.
1938    
1939             PCRE_BSR_ANYCRLF
1940             PCRE_BSR_UNICODE
1941    
1942           These options (which are mutually exclusive) control what the \R escape
1943           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1944           or to match any Unicode newline sequence. These  options  override  the
1945           choice that was made or defaulted when the pattern was compiled.
1946    
1947           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1948           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1949           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
# Line 1778  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1955  MATCHING A PATTERN: THE TRADITIONAL FUNC
1955         tion  of  pcre_compile()  above.  During  matching,  the newline choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1956         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1957         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
1958         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
1959         PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt  
1960         fails when the current position is at a CRLF sequence, the match  posi-         When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1961         tion  is  advanced by two characters instead of one, in other words, to         set,  and a match attempt for an unanchored pattern fails when the cur-
1962         after the CRLF.         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1963           explicit  matches  for  CR  or  LF  characters,  the  match position is
1964           advanced by two characters instead of one, in other words, to after the
1965           CRLF.
1966    
1967           The above rule is a compromise that makes the most common cases work as
1968           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1969           option is not set), it does not match the string "\r\nA" because, after
1970           failing at the start, it skips both the CR and the LF before  retrying.
1971           However,  the  pattern  [\r\n]A does match that string, because it con-
1972           tains an explicit CR or LF reference, and so advances only by one char-
1973           acter after the first failure.
1974    
1975           An explicit match for CR of LF is either a literal appearance of one of
1976           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1977           matches  such  as [^X] do not count, nor does \s (which includes CR and
1978           LF in the characters that it matches).
1979    
1980           Notwithstanding the above, anomalous effects may still occur when  CRLF
1981           is a valid newline sequence and explicit \r or \n escapes appear in the
1982           pattern.
1983    
1984           PCRE_NOTBOL           PCRE_NOTBOL
1985    
# Line 1824  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2021  MATCHING A PATTERN: THE TRADITIONAL FUNC
2021         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
2022         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
2023    
2024             PCRE_NO_START_OPTIMIZE
2025    
2026           There are a number of optimizations that pcre_exec() uses at the  start
2027           of  a  match,  in  order to speed up the process. For example, if it is
2028           known that a match must start with a specific  character,  it  searches
2029           the subject for that character, and fails immediately if it cannot find
2030           it, without actually running the main matching function. When  callouts
2031           are  in  use,  these  optimizations  can cause them to be skipped. This
2032           option disables the "start-up" optimizations,  causing  performance  to
2033           suffer, but ensuring that the callouts do occur.
2034    
2035           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2036    
2037         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
2038         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
2039         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
2040         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points to the start of a UTF-8 character. There is a  discussion  about
2041         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the  validity  of  UTF-8 strings in the section on UTF-8 support in the
2042         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
2043         returned.         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
2044           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2045    
2046         If you already know that your subject is valid, and you  want  to  skip         If you already know that your subject is valid, and you  want  to  skip
2047         these    checks    for   performance   reasons,   you   can   set   the         these    checks    for   performance   reasons,   you   can   set   the
# Line 1859  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2068  MATCHING A PATTERN: THE TRADITIONAL FUNC
2068     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2069    
2070         The subject string is passed to pcre_exec() as a pointer in subject,  a         The subject string is passed to pcre_exec() as a pointer in subject,  a
2071         length  in  length, and a starting byte offset in startoffset. In UTF-8         length (in bytes) in length, and a starting byte offset in startoffset.
2072         mode, the byte offset must point to the start  of  a  UTF-8  character.         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2073         Unlike  the  pattern string, the subject may contain binary zero bytes.         acter.  Unlike  the pattern string, the subject may contain binary zero
2074         When the starting offset is zero, the search for a match starts at  the         bytes. When the starting offset is zero, the search for a match  starts
2075         beginning of the subject, and this is by far the most common case.         at  the  beginning  of  the subject, and this is by far the most common
2076           case.
2077         A  non-zero  starting offset is useful when searching for another match  
2078         in the same subject by calling pcre_exec() again after a previous  suc-         A non-zero starting offset is useful when searching for  another  match
2079         cess.   Setting  startoffset differs from just passing over a shortened         in  the same subject by calling pcre_exec() again after a previous suc-
2080         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         cess.  Setting startoffset differs from just passing over  a  shortened
2081           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2082         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2083    
2084           \Biss\B           \Biss\B
2085    
2086         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
2087         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
2088         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
2089         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
2090         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
2091         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
2092         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2093         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
2094         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
2095         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2096    
2097         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
2098         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2099         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
2100         subject.         subject.
2101    
2102     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2103    
2104         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2105         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2106         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2107         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2108         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2109         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2110         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2111    
2112         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of integers
2113         offsets whose address is passed in ovector. The number of  elements  in         whose  address is passed in ovector. The number of elements in the vec-
2114         the  vector is passed in ovecsize, which must be a non-negative number.         tor is passed in ovecsize, which must be a non-negative  number.  Note:
2115         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2116    
2117         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2118         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2119         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2120         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2121         The length passed in ovecsize should always be a multiple of three.  If         The  number passed in ovecsize should always be a multiple of three. If
2122         it is not, it is rounded down.         it is not, it is rounded down.
2123    
2124         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2125         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2126         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
2127         element of a pair is set to the offset of the first character in a sub-         element  of  each pair is set to the byte offset of the first character
2128         string,  and  the  second  is  set to the offset of the first character         in a substring, and the second is set to the byte offset of  the  first
2129         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         character  after  the end of a substring. Note: these values are always
2130         tor[1],  identify  the  portion  of  the  subject string matched by the         byte offsets, even in UTF-8 mode. They are not character counts.
2131         entire pattern. The next pair is used for the first  capturing  subpat-  
2132         tern, and so on. The value returned by pcre_exec() is one more than the         The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2133         highest numbered pair that has been set. For example, if two substrings         portion  of  the subject string matched by the entire pattern. The next
2134         have  been captured, the returned value is 3. If there are no capturing         pair is used for the first capturing subpattern, and so on.  The  value
2135         subpatterns, the return value from a successful match is 1,  indicating         returned by pcre_exec() is one more than the highest numbered pair that
2136         that just the first pair of offsets has been set.         has been set.  For example, if two substrings have been  captured,  the
2137           returned  value is 3. If there are no capturing subpatterns, the return
2138           value from a successful match is 1, indicating that just the first pair
2139           of offsets has been set.
2140    
2141         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2142         of the string that it matched that is returned.         of the string that it matched that is returned.
2143    
2144         If the vector is too small to hold all the captured substring  offsets,         If the vector is too small to hold all the captured substring  offsets,
2145         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2146         function returns a value of zero. In particular, if the substring  off-         function returns a value of zero. If the substring offsets are  not  of
2147         sets are not of interest, pcre_exec() may be called with ovector passed         interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2148         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         ovecsize as zero. However, if the pattern contains back references  and
2149         references  and  the  ovector is not big enough to remember the related         the  ovector is not big enough to remember the related substrings, PCRE
2150         substrings, PCRE has to get additional memory for use during  matching.         has to get additional memory for use during matching. Thus it  is  usu-
2151         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2152    
2153         The  pcre_info()  function  can  be used to find out how many capturing         The  pcre_info()  function  can  be used to find out how many capturing
2154         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
# Line 2047  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2260  MATCHING A PATTERN: THE TRADITIONAL FUNC
2260    
2261           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2262    
2263         This  error is given if the value of the ovecsize argument is negative.         This error is given if the value of the ovecsize argument is negative.
2264    
2265           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2266    
2267         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2268         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2269         description above.         description above.
2270    
2271           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
# Line 2075  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2288  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2288         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2289              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2290    
2291         Captured substrings can be  accessed  directly  by  using  the  offsets         Captured  substrings  can  be  accessed  directly  by using the offsets
2292         returned  by  pcre_exec()  in  ovector.  For convenience, the functions         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2293         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2294         string_list()  are  provided for extracting captured substrings as new,         string_list() are provided for extracting captured substrings  as  new,
2295         separate, zero-terminated strings. These functions identify  substrings         separate,  zero-terminated strings. These functions identify substrings
2296         by  number.  The  next section describes functions for extracting named         by number. The next section describes functions  for  extracting  named
2297         substrings.         substrings.
2298    
2299         A substring that contains a binary zero is correctly extracted and  has         A  substring that contains a binary zero is correctly extracted and has
2300         a  further zero added on the end, but the result is not, of course, a C         a further zero added on the end, but the result is not, of course, a  C
2301         string.  However, you can process such a string  by  referring  to  the         string.   However,  you  can  process such a string by referring to the
2302         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2303         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2304         not  adequate for handling strings containing binary zeros, because the         not adequate for handling strings containing binary zeros, because  the
2305         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2306    
2307         The first three arguments are the same for all  three  of  these  func-         The  first  three  arguments  are the same for all three of these func-
2308         tions:  subject  is  the subject string that has just been successfully         tions: subject is the subject string that has  just  been  successfully
2309         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2310         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2311         were captured by the match, including the substring  that  matched  the         were  captured  by  the match, including the substring that matched the
2312         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2313         it is greater than zero. If pcre_exec() returned zero, indicating  that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2314         it  ran out of space in ovector, the value passed as stringcount should         it ran out of space in ovector, the value passed as stringcount  should
2315         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2316    
2317         The functions pcre_copy_substring() and pcre_get_substring() extract  a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2318         single  substring,  whose  number  is given as stringnumber. A value of         single substring, whose number is given as  stringnumber.  A  value  of
2319         zero extracts the substring that matched the  entire  pattern,  whereas         zero  extracts  the  substring that matched the entire pattern, whereas
2320         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2321         string(), the string is placed in buffer,  whose  length  is  given  by         string(),  the  string  is  placed  in buffer, whose length is given by
2322         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2323         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2324         The  yield  of  the function is the length of the string, not including         The yield of the function is the length of the  string,  not  including
2325         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2326    
2327           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2328    
2329         The buffer was too small for pcre_copy_substring(), or the  attempt  to         The  buffer  was too small for pcre_copy_substring(), or the attempt to
2330         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2331    
2332           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2333    
2334         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2335    
2336         The  pcre_get_substring_list()  function  extracts  all  available sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2337         strings and builds a list of pointers to them. All this is  done  in  a         strings  and  builds  a list of pointers to them. All this is done in a
2338         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2339         the memory block is returned via listptr, which is also  the  start  of         the  memory  block  is returned via listptr, which is also the start of
2340         the  list  of  string pointers. The end of the list is marked by a NULL         the list of string pointers. The end of the list is marked  by  a  NULL
2341         pointer. The yield of the function is zero if all  went  well,  or  the         pointer.  The  yield  of  the function is zero if all went well, or the
2342         error code         error code
2343    
2344           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2345    
2346         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2347    
2348         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2349         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2350         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2351         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2352         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2353         tive for unset substrings.         tive for unset substrings.
2354    
2355         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2356         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2357         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2358         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2359         pcre_free, which of course could be called directly from a  C  program.         pcre_free,  which  of course could be called directly from a C program.
2360         However,  PCRE is used in some situations where it is linked via a spe-         However, PCRE is used in some situations where it is linked via a  spe-
2361         cial  interface  to  another  programming  language  that  cannot   use         cial   interface  to  another  programming  language  that  cannot  use
2362         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free directly; it is for these cases that the functions  are  pro-
2363         vided.         vided.
2364    
2365    
# Line 2165  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2378  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2378              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2379              const char **stringptr);              const char **stringptr);
2380    
2381         To extract a substring by name, you first have to find associated  num-         To  extract a substring by name, you first have to find associated num-
2382         ber.  For example, for this pattern         ber.  For example, for this pattern
2383    
2384           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2174  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2387  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2387         be unique (PCRE_DUPNAMES was not set), you can find the number from the         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2388         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2389         piled pattern, and the second is the name. The yield of the function is         piled pattern, and the second is the name. The yield of the function is
2390         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2391         subpattern of that name.         subpattern of that name.
2392    
2393         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2394         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2395         are also two functions that do the whole job.         are also two functions that do the whole job.
2396    
2397         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2398         pcre_get_named_substring()  are  the  same  as  those for the similarly         pcre_get_named_substring() are the same  as  those  for  the  similarly
2399         named functions that extract by number. As these are described  in  the         named  functions  that extract by number. As these are described in the
2400         previous  section,  they  are not re-described here. There are just two         previous section, they are not re-described here. There  are  just  two
2401         differences:         differences:
2402    
2403         First, instead of a substring number, a substring name is  given.  Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2404         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2405         to the compiled pattern. This is needed in order to gain access to  the         to  the compiled pattern. This is needed in order to gain access to the
2406         name-to-number translation table.         name-to-number translation table.
2407    
2408         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2409         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2410         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
2411         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2412    
2413           Warning:  If the pattern uses the "(?|" feature to set up multiple sub-
2414           patterns with the same number, you  cannot  use  names  to  distinguish
2415           them, because names are not included in the compiled code. The matching
2416           process uses only numbers.
2417    
2418    
2419  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2420    
# Line 2404  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2622  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2622  SEE ALSO  SEE ALSO
2623    
2624         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2625         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2626    
2627    
2628  AUTHOR  AUTHOR
# Line 2416  AUTHOR Line 2634  AUTHOR
2634    
2635  REVISION  REVISION
2636    
2637         Last updated: 30 July 2007         Last updated: 17 March 2009
2638         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2639  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2640    
2641    
# Line 2468  PCRE CALLOUTS Line 2686  PCRE CALLOUTS
2686  MISSING CALLOUTS  MISSING CALLOUTS
2687    
2688         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2689         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2690         pattern is         example, if the pattern is
2691    
2692           ab(?C4)cd           ab(?C4)cd
2693    
# Line 2478  MISSING CALLOUTS Line 2696  MISSING CALLOUTS
2696         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2697         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2698    
2699           You can disable these optimizations by passing the  PCRE_NO_START_OPTI-
2700           MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the
2701           matching process, but does ensure that callouts  such  as  the  example
2702           above are obeyed.
2703    
2704    
2705  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2706    
2707         During matching, when PCRE reaches a callout point, the external  func-         During  matching, when PCRE reaches a callout point, the external func-
2708         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
2709         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
2710         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
2711         block. This structure contains the following fields:         block. This structure contains the following fields:
2712    
2713           int          version;           int          version;
# Line 2500  THE CALLOUT INTERFACE Line 2723  THE CALLOUT INTERFACE
2723           int          pattern_position;           int          pattern_position;
2724           int          next_item_length;           int          next_item_length;
2725    
2726         The version field is an integer containing the version  number  of  the         The  version  field  is an integer containing the version number of the
2727         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
2728         version number will change again in future  if  additional  fields  are         version  number  will  change  again in future if additional fields are
2729         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.
2730    
2731         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
# Line 2587  AUTHOR Line 2810  AUTHOR
2810    
2811  REVISION  REVISION
2812    
2813         Last updated: 29 May 2007         Last updated: 15 March 2009
2814         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2815  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2816    
2817    
# Line 2669  DIFFERENCES BETWEEN PCRE AND PERL Line 2892  DIFFERENCES BETWEEN PCRE AND PERL
2892         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2893         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2894    
2895         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2896           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2897           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2898           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2899           ture group; this is different to Perl.
2900    
2901           12. PCRE provides some extensions to the Perl regular expression facil-
2902         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  will  include new features that are not in earlier
2903         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2904         for some time. This list is with respect to Perl 5.10:         for some time. This list is with respect to Perl 5.10:
# Line 2695  DIFFERENCES BETWEEN PCRE AND PERL Line 2924  DIFFERENCES BETWEEN PCRE AND PERL
2924         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2925         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2926    
2927         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2928           CRLF by the PCRE_BSR_ANYCRLF option.
2929    
2930           (h) The callout facility is PCRE-specific.
2931    
2932         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
2933    
2934         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2935         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2936    
2937         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2938         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2939    
2940           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2941           of a pattern that set overall options that cannot be changed within the
2942           pattern.
2943    
2944    
2945  AUTHOR  AUTHOR
2946    
# Line 2715  AUTHOR Line 2951  AUTHOR
2951    
2952  REVISION  REVISION
2953    
2954         Last updated: 13 June 2007         Last updated: 11 September 2007
2955         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2956  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2957    
# Line 2731  PCRE REGULAR EXPRESSION DETAILS Line 2967  PCRE REGULAR EXPRESSION DETAILS
2967    
2968         The  syntax and semantics of the regular expressions that are supported         The  syntax and semantics of the regular expressions that are supported
2969         by PCRE are described in detail below. There is a quick-reference  syn-         by PCRE are described in detail below. There is a quick-reference  syn-
2970         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
2971         described in its own documentation, and regular expressions in  general         semantics as closely as it can. PCRE  also  supports  some  alternative
2972         are  covered in a number of books, some of which have copious examples.         regular  expression  syntax (which does not conflict with the Perl syn-
2973         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by         tax) in order to provide some compatibility with regular expressions in
2974         O'Reilly,  covers regular expressions in great detail. This description         Python, .NET, and Oniguruma.
2975         of PCRE's regular expressions is intended as reference material.  
2976           Perl's  regular expressions are described in its own documentation, and
2977           regular expressions in general are covered in a number of  books,  some
2978           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
2979           Expressions", published by  O'Reilly,  covers  regular  expressions  in
2980           great  detail.  This  description  of  PCRE's  regular  expressions  is
2981           intended as reference material.
2982    
2983         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2984         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
# Line 2756  PCRE REGULAR EXPRESSION DETAILS Line 2998  PCRE REGULAR EXPRESSION DETAILS
2998         discussed in the pcrematching page.         discussed in the pcrematching page.
2999    
3000    
3001    NEWLINE CONVENTIONS
3002    
3003           PCRE  supports five different conventions for indicating line breaks in
3004           strings: a single CR (carriage return) character, a  single  LF  (line-
3005           feed) character, the two-character sequence CRLF, any of the three pre-
3006           ceding, or any Unicode newline sequence. The pcreapi page  has  further
3007           discussion  about newlines, and shows how to set the newline convention
3008           in the options arguments for the compiling and matching functions.
3009    
3010           It is also possible to specify a newline convention by starting a  pat-
3011           tern string with one of the following five sequences:
3012    
3013             (*CR)        carriage return
3014             (*LF)        linefeed
3015             (*CRLF)      carriage return, followed by linefeed
3016             (*ANYCRLF)   any of the three above
3017             (*ANY)       all Unicode newline sequences
3018    
3019           These override the default and the options given to pcre_compile(). For
3020           example, on a Unix system where LF is the default newline sequence, the
3021           pattern
3022    
3023             (*CR)a.b
3024    
3025           changes the convention to CR. That pattern matches "a\nb" because LF is
3026           no longer a newline. Note that these special settings,  which  are  not
3027           Perl-compatible,  are  recognized  only at the very start of a pattern,
3028           and that they must be in upper case.  If  more  than  one  of  them  is
3029           present, the last one is used.
3030    
3031           The  newline  convention  does  not  affect what the \R escape sequence
3032           matches. By default, this is any Unicode  newline  sequence,  for  Perl
3033           compatibility.  However, this can be changed; see the description of \R
3034           in the section entitled "Newline sequences" below. A change of \R  set-
3035           ting can be combined with a change of newline convention.
3036    
3037    
3038  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
3039    
3040         A  regular  expression  is  a pattern that is matched against a subject         A  regular  expression  is  a pattern that is matched against a subject
# Line 2811  CHARACTERS AND METACHARACTERS Line 3090  CHARACTERS AND METACHARACTERS
3090                    syntax)                    syntax)
3091           ]      terminates the character class           ]      terminates the character class
3092    
3093         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the metacharacters.
3094    
3095    
3096  BACKSLASH  BACKSLASH
3097    
3098         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3099         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
3100         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
3101         applies both inside and outside character classes.         applies both inside and outside character classes.
3102    
3103         For  example,  if  you want to match a * character, you write \* in the         For example, if you want to match a * character, you write  \*  in  the
3104         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
3105         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
3106         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
3107         that  it stands for itself. In particular, if you want to match a back-         that it stands for itself. In particular, if you want to match a  back-
3108         slash, you write \\.         slash, you write \\.
3109    
3110         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3111         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
3112         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3113         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
3114         part of the pattern.         part of the pattern.
3115    
3116         If you want to remove the special meaning from a  sequence  of  charac-         If  you  want  to remove the special meaning from a sequence of charac-
3117         ters,  you can do so by putting them between \Q and \E. This is differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
3118         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
3119         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
3120         tion. Note the following examples:         tion. Note the following examples:
3121    
3122           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2847  BACKSLASH Line 3126  BACKSLASH
3126           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3127           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3128    
3129         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3130         classes.         classes.
3131    
3132     Non-printing characters     Non-printing characters
3133    
3134         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3135         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
3136         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3137         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3138         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is usually easier  to  use  one  of  the  following  escape
3139         sequences than the binary character it represents:         sequences than the binary character it represents:
3140    
3141           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3142           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3143           \e        escape (hex 1B)           \e        escape (hex 1B)
3144           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3145           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3146           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3147           \t        tab (hex 09)           \t        tab (hex 09)
3148           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3149           \xhh      character with hex code hh           \xhh      character with hex code hh
3150           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3151    
3152         The precise effect of \cx is as follows: if x is a lower  case  letter,         The  precise  effect of \cx is as follows: if x is a lower case letter,
3153         it  is converted to upper case. Then bit 6 of the character (hex 40) is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
3154         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
3155         becomes hex 7B.         becomes hex 7B.
3156    
3157         After  \x, from zero to two hexadecimal digits are read (letters can be         After \x, from zero to two hexadecimal digits are read (letters can  be
3158         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3159         between  \x{  and  },  but the value of the character code must be less         between \x{ and }, but the value of the character  code  must  be  less
3160         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3161         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3162         hexadecimal digits appear between \x{ and }, or if there is  no  termi-         than the largest Unicode code point, which is 10FFFF.
3163         nating  }, this form of escape is not recognized.  Instead, the initial  
3164         \x will be interpreted as a basic hexadecimal escape, with no following         If  characters  other than hexadecimal digits appear between \x{ and },
3165         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3166           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3167           escape, with no following digits, giving a  character  whose  value  is
3168           zero.
3169    
3170         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
3171         two syntaxes for \x. There is no difference in the way  they  are  han-         two syntaxes for \x. There is no difference in the way  they  are  han-
# Line 2943  BACKSLASH Line 3225  BACKSLASH
3225         named back reference can be coded as \g{name}. Back references are dis-         named back reference can be coded as \g{name}. Back references are dis-
3226         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3227    
3228       Absolute and relative subroutine calls
3229    
3230           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3231           name or a number enclosed either in angle brackets or single quotes, is
3232           an alternative syntax for referencing a subpattern as  a  "subroutine".
3233           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3234           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3235           reference; the latter is a subroutine call.
3236    
3237     Generic character types     Generic character types
3238    
3239         Another use of backslash is for specifying generic character types. The         Another use of backslash is for specifying generic character types. The
# Line 2960  BACKSLASH Line 3251  BACKSLASH
3251           \W     any "non-word" character           \W     any "non-word" character
3252    
3253         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3254         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3255         of each pair.         of each pair.
3256    
3257         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3258         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3259         If  the current matching point is at the end of the subject string, all         If the current matching point is at the end of the subject string,  all
3260         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3261    
3262         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3263         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
3264         characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3265         "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-
3266         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3267    
3268         In UTF-8 mode, characters with values greater than 128 never match  \d,         In  UTF-8 mode, characters with values greater than 128 never match \d,
3269         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3270         code character property support is available.  These  sequences  retain         code  character  property  support is available. These sequences retain
3271         their original meanings from before UTF-8 support was available, mainly         their original meanings from before UTF-8 support was available, mainly
3272         for efficiency reasons.         for  efficiency  reasons. Note that this also affects \b, because it is
3273           defined in terms of \w and \W.
3274    
3275         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
3276         the  other  sequences, these do match certain high-valued codepoints in         the  other  sequences, these do match certain high-valued codepoints in
# Line 3025  BACKSLASH Line 3317  BACKSLASH
3317    
3318     Newline sequences     Newline sequences
3319    
3320         Outside  a  character class, the escape sequence \R matches any Unicode         Outside  a  character class, by default, the escape sequence \R matches
3321         newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R  is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3322         equivalent to the following:         mode \R is equivalent to the following:
3323    
3324           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3325    
# Line 3043  BACKSLASH Line 3335  BACKSLASH
3335         rator, U+2029).  Unicode character property support is not  needed  for         rator, U+2029).  Unicode character property support is not  needed  for
3336         these characters to be recognized.         these characters to be recognized.
3337    
3338           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3339           the complete set  of  Unicode  line  endings)  by  setting  the  option
3340           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3341           (BSR is an abbrevation for "backslash R".) This can be made the default
3342           when  PCRE  is  built;  if this is the case, the other behaviour can be
3343           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3344           specify  these  settings  by  starting a pattern string with one of the
3345           following sequences:
3346    
3347             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3348             (*BSR_UNICODE)   any Unicode newline sequence
3349    
3350           These override the default and the options given to pcre_compile(), but
3351           they can be overridden by options given to pcre_exec(). Note that these
3352           special settings, which are not Perl-compatible, are recognized only at
3353           the  very  start  of a pattern, and that they must be in upper case. If
3354           more than one of them is present, the last one is  used.  They  can  be
3355           combined  with  a  change of newline convention, for example, a pattern
3356           can start with:
3357    
3358             (*ANY)(*BSR_ANYCRLF)
3359    
3360         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3361    
3362     Unicode character properties     Unicode character properties
3363    
3364         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3365         tional escape sequences that match characters with specific  properties         tional  escape sequences that match characters with specific properties
3366         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
3367         limited to testing characters whose codepoints are less than  256,  but         limited  to  testing characters whose codepoints are less than 256, but
3368         they do work in this mode.  The extra escape sequences are:         they do work in this mode.  The extra escape sequences are:
3369    
3370           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3371           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
3372           \X       an extended Unicode sequence           \X       an extended Unicode sequence
3373    
3374         The  property  names represented by xx above are limited to the Unicode         The property names represented by xx above are limited to  the  Unicode
3375         script names, the general category properties, and "Any", which matches         script names, the general category properties, and "Any", which matches
3376         any character (including newline). Other properties such as "InMusical-         any character (including newline). Other properties such as "InMusical-
3377         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
3378         not match any characters, so always causes a match failure.         not match any characters, so always causes a match failure.
3379    
3380         Sets of Unicode characters are defined as belonging to certain scripts.         Sets of Unicode characters are defined as belonging to certain scripts.
3381         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.
3382         For example:         For example:
3383    
3384           \p{Greek}           \p{Greek}
3385           \P{Han}           \P{Han}
3386    
3387         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
3388         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3389    
3390         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3391         Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3392         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3393         Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3394         gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3395         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3396         Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3397         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3398         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3399    
3400         Each character has exactly one general category property, specified  by         Each  character has exactly one general category property, specified by
3401         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
3402         specified by including a circumflex between the opening brace  and  the         specified  by  including a circumflex between the opening brace and the
3403         property name. For example, \p{^Lu} is the same as \P{Lu}.         property name. For example, \p{^Lu} is the same as \P{Lu}.
3404    
3405         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-
3406         eral category properties that start with that letter. In this case,  in         eral  category properties that start with that letter. In this case, in
3407         the  absence of negation, the curly brackets in the escape sequence are         the absence of negation, the curly brackets in the escape sequence  are
3408         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3409    
3410           \p{L}           \p{L}
# Line 3142  BACKSLASH Line 3456  BACKSLASH
3456           Zp    Paragraph separator           Zp    Paragraph separator
3457           Zs    Space separator           Zs    Space separator
3458    
3459         The special property L& is also supported: it matches a character  that         The  special property L& is also supported: it matches a character that
3460         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3461         classified as a modifier or "other".         classified as a modifier or "other".
3462    
3463         The long synonyms for these properties  that  Perl  supports  (such  as         The  Cs  (Surrogate)  property  applies only to characters in the range
3464         \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3465           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3466           ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3467           the pcreapi page).
3468    
3469           The  long  synonyms  for  these  properties that Perl supports (such as
3470           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3471         any of these properties with "Is".         any of these properties with "Is".
3472    
3473         No character that is in the Unicode table has the Cn (unassigned) prop-         No character that is in the Unicode table has the Cn (unassigned) prop-
3474         erty.  Instead, this property is assumed for any code point that is not         erty.  Instead, this property is assumed for any code point that is not
3475         in the Unicode table.         in the Unicode table.
3476    
3477         Specifying caseless matching does not affect  these  escape  sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3478         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3479    
3480         The  \X  escape  matches  any number of Unicode characters that form an         The \X escape matches any number of Unicode  characters  that  form  an
3481         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3482    
3483           (?>\PM\pM*)           (?>\PM\pM*)
3484    
3485         That is, it matches a character without the "mark"  property,  followed         That  is,  it matches a character without the "mark" property, followed
3486         by  zero  or  more  characters with the "mark" property, and treats the         by zero or more characters with the "mark"  property,  and  treats  the
3487         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3488         property  are  typically  accents  that affect the preceding character.         property are typically accents that  affect  the  preceding  character.
3489         None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X         None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X
3490         matches any one character.         matches any one character.
3491    
3492         Matching  characters  by Unicode property is not fast, because PCRE has         Matching characters by Unicode property is not fast, because  PCRE  has
3493         to search a structure that contains  data  for  over  fifteen  thousand         to  search  a  structure  that  contains data for over fifteen thousand
3494         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3495         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3496    
3497     Resetting the match start     Resetting the match start
3498    
3499         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3500         ously  matched  characters  not  to  be  included  in the final matched         ously matched characters not  to  be  included  in  the  final  matched
3501         sequence. For example, the pattern:         sequence. For example, the pattern:
3502    
3503           foo\Kbar           foo\Kbar
3504    
3505         matches "foobar", but reports that it has matched "bar".  This  feature         matches  "foobar",  but reports that it has matched "bar". This feature
3506         is  similar  to  a lookbehind assertion (described below).  However, in         is similar to a lookbehind assertion (described  below).   However,  in
3507         this case, the part of the subject before the real match does not  have         this  case, the part of the subject before the real match does not have
3508         to  be of fixed length, as lookbehind assertions do. The use of \K does         to be of fixed length, as lookbehind assertions do. The use of \K  does
3509         not interfere with the setting of captured  substrings.   For  example,         not  interfere  with  the setting of captured substrings.  For example,
3510         when the pattern         when the pattern
3511    
3512           (foo)\Kbar           (foo)\Kbar
# Line 3195  BACKSLASH Line 3515  BACKSLASH
3515    
3516     Simple assertions     Simple assertions
3517    
3518         The  final use of backslash is for certain simple assertions. An asser-         The final use of backslash is for certain simple assertions. An  asser-
3519         tion specifies a condition that has to be met at a particular point  in         tion  specifies a condition that has to be met at a particular point in
3520         a  match, without consuming any characters from the subject string. The         a match, without consuming any characters from the subject string.  The
3521         use of subpatterns for more complicated assertions is described  below.         use  of subpatterns for more complicated assertions is described below.
3522         The backslashed assertions are:         The backslashed assertions are:
3523    
3524           \b     matches at a word boundary           \b     matches at a word boundary
# Line 3209  BACKSLASH Line 3529  BACKSLASH
3529           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3530           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3531    
3532         These  assertions may not appear in character classes (but note that \b         These assertions may not appear in character classes (but note that  \b
3533         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3534         acter class).         acter class).
3535    
3536         A  word  boundary is a position in the subject string where the current         A word boundary is a position in the subject string where  the  current
3537         character and the previous character do not both match \w or  \W  (i.e.         character  and  the previous character do not both match \w or \W (i.e.
3538         one  matches  \w  and the other matches \W), or the start or end of the         one matches \w and the other matches \W), or the start or  end  of  the
3539         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3540    
3541         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3542         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
3543         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3544         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3545         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3546         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3547         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3548         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3549         the subject, \A can never match. The difference between \Z  and  \z  is         the  subject,  \A  can never match. The difference between \Z and \z is
3550         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3551         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3552    
3553         The \G assertion is true only when the current matching position is  at         The  \G assertion is true only when the current matching position is at
3554         the  start point of the match, as specified by the startoffset argument         the start point of the match, as specified by the startoffset  argument
3555         of pcre_exec(). It differs from \A when the  value  of  startoffset  is         of  pcre_exec().  It  differs  from \A when the value of startoffset is
3556         non-zero.  By calling pcre_exec() multiple times with appropriate argu-         non-zero. By calling pcre_exec() multiple times with appropriate  argu-
3557         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3558         mentation where \G can be useful.         mentation where \G can be useful.
3559    
3560         Note,  however,  that  PCRE's interpretation of \G, as the start of the         Note, however, that PCRE's interpretation of \G, as the  start  of  the
3561         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3562         end  of  the  previous  match. In Perl, these can be different when the         end of the previous match. In Perl, these can  be  different  when  the
3563         previously matched string was empty. Because PCRE does just  one  match         previously  matched  string was empty. Because PCRE does just one match
3564         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3565    
3566         If  all  the alternatives of a pattern begin with \G, the expression is         If all the alternatives of a pattern begin with \G, the  expression  is
3567         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3568         in the compiled regular expression.         in the compiled regular expression.
3569    
# Line 3251  BACKSLASH Line 3571  BACKSLASH
3571  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3572    
3573         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3574         character is an assertion that is true only  if  the  current  matching         character  is  an  assertion  that is true only if the current matching
3575         point  is  at the start of the subject string. If the startoffset argu-         point is at the start of the subject string. If the  startoffset  argu-
3576         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
3577         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
3578         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3579    
3580         Circumflex need not be the first character of the pattern if  a  number         Circumflex  need  not be the first character of the pattern if a number
3581         of  alternatives are involved, but it should be the first thing in each         of alternatives are involved, but it should be the first thing in  each
3582         alternative in which it appears if the pattern is ever  to  match  that         alternative  in  which  it appears if the pattern is ever to match that
3583         branch.  If all possible alternatives start with a circumflex, that is,         branch. If all possible alternatives start with a circumflex, that  is,
3584         if the pattern is constrained to match only at the start  of  the  sub-         if  the  pattern  is constrained to match only at the start of the sub-
3585         ject,  it  is  said  to be an "anchored" pattern. (There are also other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
3586         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3587    
3588         A dollar character is an assertion that is true  only  if  the  current         A  dollar  character  is  an assertion that is true only if the current
3589         matching  point  is  at  the  end of the subject string, or immediately         matching point is at the end of  the  subject  string,  or  immediately
3590         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3591         be  the  last  character of the pattern if a number of alternatives are         be the last character of the pattern if a number  of  alternatives  are
3592         involved, but it should be the last item in  any  branch  in  which  it         involved,  but  it  should  be  the last item in any branch in which it
3593         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3594    
3595         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3596         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3597         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3598    
3599         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3600         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3601         matches  immediately after internal newlines as well as at the start of         matches immediately after internal newlines as well as at the start  of
3602         the subject string. It does not match after a  newline  that  ends  the         the  subject  string.  It  does not match after a newline that ends the
3603         string.  A dollar matches before any newlines in the string, as well as         string. A dollar matches before any newlines in the string, as well  as
3604         at the very end, when PCRE_MULTILINE is set. When newline is  specified         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3605         as  the  two-character  sequence CRLF, isolated CR and LF characters do         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3606         not indicate newlines.         not indicate newlines.
3607    
3608         For example, the pattern /^abc$/ matches the subject string  "def\nabc"         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3609         (where  \n  represents a newline) in multiline mode, but not otherwise.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3610         Consequently, patterns that are anchored in single  line  mode  because         Consequently,  patterns  that  are anchored in single line mode because
3611         all  branches  start  with  ^ are not anchored in multiline mode, and a         all branches start with ^ are not anchored in  multiline  mode,  and  a
3612         match for circumflex is  possible  when  the  startoffset  argument  of         match  for  circumflex  is  possible  when  the startoffset argument of
3613         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3614         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3615    
3616         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3617         and  end of the subject in both modes, and if all branches of a pattern         and end of the subject in both modes, and if all branches of a  pattern
3618         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3619         set.         set.
3620    
3621    
3622  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3623    
3624         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-
3625         ter in the subject string except (by default) a character  that  signi-         ter  in  the subject string except (by default) a character that signi-
3626         fies  the  end  of  a line. In UTF-8 mode, the matched character may be         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3627         more than one byte long.         more than one byte long.
3628    
3629         When a line ending is defined as a single character, dot never  matches         When  a line ending is defined as a single character, dot never matches
3630         that  character; when the two-character sequence CRLF is used, dot does         that character; when the two-character sequence CRLF is used, dot  does
3631         not match CR if it is immediately followed  by  LF,  but  otherwise  it         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3632         matches  all characters (including isolated CRs and LFs). When any Uni-         matches all characters (including isolated CRs and LFs). When any  Uni-
3633         code line endings are being recognized, dot does not match CR or LF  or         code  line endings are being recognized, dot does not match CR or LF or
3634         any of the other line ending characters.         any of the other line ending characters.
3635    
3636         The  behaviour  of  dot  with regard to newlines can be changed. If the         The behaviour of dot with regard to newlines can  be  changed.  If  the
3637         PCRE_DOTALL option is set, a dot matches  any  one  character,  without         PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3638         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3639         string, it takes two dots to match it.         string, it takes two dots to match it.
3640    
3641         The handling of dot is entirely independent of the handling of  circum-         The  handling of dot is entirely independent of the handling of circum-
3642         flex  and  dollar,  the  only relationship being that they both involve         flex and dollar, the only relationship being  that  they  both  involve
3643         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3644    
3645    
3646  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3647    
3648         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3649         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3650         line-ending characters. The feature is provided in  Perl  in  order  to         line-ending  characters.  The  feature  is provided in Perl in order to
3651         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3652         acters into individual bytes, what remains in the string may be a  mal-         acters  into individual bytes, what remains in the string may be a mal-
3653         formed  UTF-8  string.  For this reason, the \C escape sequence is best         formed UTF-8 string. For this reason, the \C escape  sequence  is  best
3654         avoided.         avoided.
3655    
3656         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3657         below),  because  in UTF-8 mode this would make it impossible to calcu-         below), because in UTF-8 mode this would make it impossible  to  calcu-
3658         late the length of the lookbehind.         late the length of the lookbehind.
3659    
3660    
# Line 3343  SQUARE BRACKETS AND CHARACTER CLASSES Line 3663  SQUARE BRACKETS AND CHARACTER CLASSES
3663         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3664         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-
3665         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3666         it  should  be  the first data character in the class (after an initial         it should be the first data character in the class  (after  an  initial
3667         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3668    
3669         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
3670         mode,  the character may occupy more than one byte. A matched character         mode, the character may occupy more than one byte. A matched  character
3671         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
3672         character  in  the  class definition is a circumflex, in which case the         character in the class definition is a circumflex, in  which  case  the
3673         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
3674         circumflex  is actually required as a member of the class, ensure it is         circumflex is actually required as a member of the class, ensure it  is
3675         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3676    
3677         For example, the character class [aeiou] matches any lower case  vowel,         For  example, the character class [aeiou] matches any lower case vowel,
3678         while  [^aeiou]  matches  any character that is not a lower case vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3679         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3680         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
3681         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-
3682         sumes  a  character  from the subject string, and therefore it fails if         sumes a character from the subject string, and therefore  it  fails  if
3683         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3684    
3685         In UTF-8 mode, characters with values greater than 255 can be  included         In  UTF-8 mode, characters with values greater than 255 can be included
3686         in  a  class as a literal string of bytes, or by using the \x{ escaping         in a class as a literal string of bytes, or by using the  \x{  escaping
3687         mechanism.         mechanism.
3688    
3689         When caseless matching is set, any letters in a  class  represent  both         When  caseless  matching  is set, any letters in a class represent both
3690         their  upper  case  and lower case versions, so for example, a caseless         their upper case and lower case versions, so for  example,  a  caseless
3691         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
3692         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always
3693         understands the concept of case for characters whose  values  are  less         understands  the  concept  of case for characters whose values are less
3694         than  128, so caseless matching is always possible. For characters with         than 128, so caseless matching is always possible. For characters  with
3695         higher values, the concept of case is supported  if  PCRE  is  compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3696         with  Unicode  property support, but not otherwise.  If you want to use         with Unicode property support, but not otherwise.  If you want  to  use
3697         caseless matching for characters 128 and above, you  must  ensure  that         caseless  matching  for  characters 128 and above, you must ensure that
3698         PCRE  is  compiled  with Unicode property support as well as with UTF-8         PCRE is compiled with Unicode property support as well  as  with  UTF-8
3699         support.         support.
3700    
3701         Characters that might indicate line breaks are  never  treated  in  any         Characters  that  might  indicate  line breaks are never treated in any
3702         special  way  when  matching  character  classes,  whatever line-ending         special way  when  matching  character  classes,  whatever  line-ending
3703         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and
3704         PCRE_MULTILINE options is used. A class such as [^a] always matches one         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3705         of these characters.         of these characters.
3706    
3707         The minus (hyphen) character can be used to specify a range of  charac-         The  minus (hyphen) character can be used to specify a range of charac-
3708         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters in a character  class.  For  example,  [d-m]  matches  any  letter
3709         between d and m, inclusive. If a  minus  character  is  required  in  a         between  d  and  m,  inclusive.  If  a minus character is required in a
3710         class,  it  must  be  escaped  with a backslash or appear in a position         class, it must be escaped with a backslash  or  appear  in  a  position
3711         where it cannot be interpreted as indicating a range, typically as  the         where  it cannot be interpreted as indicating a range, typically as the
3712         first or last character in the class.         first or last character in the class.
3713    
3714         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3715         ter of a range. A pattern such as [W-]46] is interpreted as a class  of         ter  of a range. A pattern such as [W-]46] is interpreted as a class of
3716         two  characters ("W" and "-") followed by a literal string "46]", so it         two characters ("W" and "-") followed by a literal string "46]", so  it
3717         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a
3718         backslash  it is interpreted as the end of range, so [W-\]46] is inter-         backslash it is interpreted as the end of range, so [W-\]46] is  inter-
3719         preted as a class containing a range followed by two other  characters.         preted  as a class containing a range followed by two other characters.
3720         The  octal or hexadecimal representation of "]" can also be used to end         The octal or hexadecimal representation of "]" can also be used to  end
3721         a range.         a range.
3722    
3723         Ranges operate in the collating sequence of character values. They  can         Ranges  operate in the collating sequence of character values. They can
3724         also   be  used  for  characters  specified  numerically,  for  example         also  be  used  for  characters  specified  numerically,  for   example
3725         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values         [\000-\037].  In UTF-8 mode, ranges can include characters whose values
3726         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3727    
3728         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3729         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3730         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if
3731         character tables for a French locale are in  use,  [\xc8-\xcb]  matches         character  tables  for  a French locale are in use, [\xc8-\xcb] matches
3732         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented E characters in both cases. In UTF-8 mode, PCRE  supports  the
3733         concept of case for characters with values greater than 128  only  when         concept  of  case for characters with values greater than 128 only when
3734         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3735    
3736         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear
3737         in a character class, and add the characters that  they  match  to  the         in  a  character  class,  and add the characters that they match to the
3738         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3739         flex can conveniently be used with the upper case  character  types  to         flex  can  conveniently  be used with the upper case character types to
3740         specify  a  more  restricted  set of characters than the matching lower         specify a more restricted set of characters  than  the  matching  lower
3741         case type. For example, the class [^\W_] matches any letter  or  digit,         case  type.  For example, the class [^\W_] matches any letter or digit,
3742         but not underscore.         but not underscore.
3743    
3744         The  only  metacharacters  that are recognized in character classes are         The only metacharacters that are recognized in  character  classes  are
3745         backslash, hyphen (only where it can be  interpreted  as  specifying  a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
3746         range),  circumflex  (only  at the start), opening square bracket (only         range), circumflex (only at the start), opening  square  bracket  (only
3747         when it can be interpreted as introducing a POSIX class name - see  the         when  it can be interpreted as introducing a POSIX class name - see the
3748         next  section),  and  the  terminating closing square bracket. However,         next section), and the terminating  closing  square  bracket.  However,
3749         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3750    
3751    
3752  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3753    
3754         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3755         enclosed  by  [: and :] within the enclosing square brackets. PCRE also         enclosed by [: and :] within the enclosing square brackets.  PCRE  also
3756         supports this notation. For example,         supports this notation. For example,
3757    
3758           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3455  POSIX CHARACTER CLASSES Line 3775  POSIX CHARACTER CLASSES
3775           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3776           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3777    
3778         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),
3779         and space (32). Notice that this list includes the VT  character  (code         and  space  (32). Notice that this list includes the VT character (code
3780         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
3781         Perl compatibility).         Perl compatibility).
3782    
3783         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension
3784         from  Perl  5.8. Another Perl extension is negation, which is indicated         from Perl 5.8. Another Perl extension is negation, which  is  indicated
3785         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3786    
3787           [12[:^digit:]]           [12[:^digit:]]
3788    
3789         matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the         matches  "1", "2", or any non-digit. PCRE (and Perl) also recognize the
3790         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3791         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.
3792    
# Line 3486  VERTICAL BAR Line 3806  VERTICAL BAR
3806         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3807         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
3808         are  within a subpattern (defined below), "succeeds" means matching the         are  within a subpattern (defined below), "succeeds" means matching the
3809         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.
3810    
3811    
3812  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3813    
3814         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and
3815         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from
3816         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within the pattern by  a  sequence  of  Perl  option  letters  enclosed
3817         option letters are         between "(?" and ")".  The option letters are
3818    
3819           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3820           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3503  INTERNAL OPTION SETTING Line 3823  INTERNAL OPTION SETTING
3823    
3824         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3825         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
3826         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-
3827         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,
3828         is also permitted. If a  letter  appears  both  before  and  after  the         is  also  permitted.  If  a  letter  appears  both before and after the
3829         hyphen, the option is unset.         hyphen, the option is unset.
3830    
3831         When  an option change occurs at top level (that is, not inside subpat-         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3832         tern parentheses), the change applies to the remainder of  the  pattern         can  be changed in the same way as the Perl-compatible options by using
3833           the characters J, U and X respectively.
3834    
3835           When an option change occurs at top level (that is, not inside  subpat-
3836           tern  parentheses),  the change applies to the remainder of the pattern
3837         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
3838         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3839         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3840    
3841         An  option  change  within a subpattern (see below for a description of         An option change within a subpattern (see below for  a  description  of
3842         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
3843         it, so         it, so
3844    
3845           (a(?i)b)c           (a(?i)b)c
3846    
3847         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
3848         used).  By this means, options can be made to have  different  settings         used).   By  this means, options can be made to have different settings
3849         in  different parts of the pattern. Any changes made in one alternative         in different parts of the pattern. Any changes made in one  alternative
3850         do carry on into subsequent branches within the  same  subpattern.  For         do  carry  on  into subsequent branches within the same subpattern. For
3851         example,         example,
3852    
3853           (a(?i)b|c)           (a(?i)b|c)
3854    
3855         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the
3856         first branch is abandoned before the option setting.  This  is  because         first  branch  is  abandoned before the option setting. This is because
3857         the  effects  of option settings happen at compile time. There would be         the effects of option settings happen at compile time. There  would  be
3858         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3859    
3860         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note:  There  are  other  PCRE-specific  options that can be set by the
3861         can  be changed in the same way as the Perl-compatible options by using         application when the compile or match functions  are  called.  In  some
3862         the characters J, U and X respectively.         cases  the  pattern  can  contain special leading sequences to override
3863           what the application has set or what has been  defaulted.  Details  are
3864           given in the section entitled "Newline sequences" above.
3865    
3866    
3867  SUBPATTERNS  SUBPATTERNS
# Line 3547  SUBPATTERNS Line 3873  SUBPATTERNS
3873    
3874           cat(aract|erpillar|)           cat(aract|erpillar|)
3875    
3876         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches one of the words "cat", "cataract", or  "caterpillar".  Without
3877         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty
3878         string.         string.
3879    
3880         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2. It sets up the subpattern as  a  capturing  subpattern.  This  means
3881         that, when the whole pattern  matches,  that  portion  of  the  subject         that,  when  the  whole  pattern  matches,  that portion of the subject
3882         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
3883         ovector argument of pcre_exec(). Opening parentheses are  counted  from         ovector  argument  of pcre_exec(). Opening parentheses are counted from
3884         left  to  right  (starting  from 1) to obtain numbers for the capturing         left to right (starting from 1) to obtain  numbers  for  the  capturing
3885         subpatterns.         subpatterns.
3886    
3887         For example, if the string "the red king" is matched against  the  pat-         For  example,  if the string "the red king" is matched against the pat-
3888         tern         tern
3889    
3890           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3566  SUBPATTERNS Line 3892  SUBPATTERNS
3892         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
3893         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
3894    
3895         The fact that plain parentheses fulfil  two  functions  is  not  always         The  fact  that  plain  parentheses  fulfil two functions is not always
3896         helpful.   There are often times when a grouping subpattern is required         helpful.  There are often times when a grouping subpattern is  required
3897         without a capturing requirement. If an opening parenthesis is  followed         without  a capturing requirement. If an opening parenthesis is followed
3898         by  a question mark and a colon, the subpattern does not do any captur-         by a question mark and a colon, the subpattern does not do any  captur-
3899         ing, and is not counted when computing the  number  of  any  subsequent         ing,  and  is  not  counted when computing the number of any subsequent
3900         capturing  subpatterns. For example, if the string "the white queen" is         capturing subpatterns. For example, if the string "the white queen"  is
3901         matched against the pattern         matched against the pattern
3902    
3903           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3579  SUBPATTERNS Line 3905  SUBPATTERNS
3905         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3906         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
3907    
3908         As  a  convenient shorthand, if any option settings are required at the         As a convenient shorthand, if any option settings are required  at  the
3909         start of a non-capturing subpattern,  the  option  letters  may  appear         start  of  a  non-capturing  subpattern,  the option letters may appear
3910         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
3911    
3912           (?i:saturday|sunday)           (?i:saturday|sunday)
3913           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
3914    
3915         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
3916         tried from left to right, and options are not reset until  the  end  of         tried  from  left  to right, and options are not reset until the end of
3917         the  subpattern is reached, an option setting in one branch does affect         the subpattern is reached, an option setting in one branch does  affect
3918         subsequent branches, so the above patterns match "SUNDAY"  as  well  as         subsequent  branches,  so  the above patterns match "SUNDAY" as well as
3919         "Saturday".         "Saturday".
3920    
3921    
3922  DUPLICATE SUBPATTERN NUMBERS  DUPLICATE SUBPATTERN NUMBERS
3923    
3924         Perl 5.10 introduced a feature whereby each alternative in a subpattern         Perl 5.10 introduced a feature whereby each alternative in a subpattern
3925         uses the same numbers for its capturing parentheses. Such a  subpattern         uses  the same numbers for its capturing parentheses. Such a subpattern
3926         starts  with (?| and is itself a non-capturing subpattern. For example,         starts with (?| and is itself a non-capturing subpattern. For  example,
3927         consider this pattern:         consider this pattern:
3928    
3929           (?|(Sat)ur|(Sun))day           (?|(Sat)ur|(Sun))day
3930    
3931         Because the two alternatives are inside a (?| group, both sets of  cap-         Because  the two alternatives are inside a (?| group, both sets of cap-
3932         turing  parentheses  are  numbered one. Thus, when the pattern matches,         turing parentheses are numbered one. Thus, when  the  pattern  matches,
3933         you can look at captured substring number  one,  whichever  alternative         you  can  look  at captured substring number one, whichever alternative
3934         matched.  This  construct  is useful when you want to capture part, but         matched. This construct is useful when you want to  capture  part,  but
3935         not all, of one of a number of alternatives. Inside a (?| group, paren-         not all, of one of a number of alternatives. Inside a (?| group, paren-
3936         theses  are  numbered as usual, but the number is reset at the start of         theses are numbered as usual, but the number is reset at the  start  of
3937         each branch. The numbers of any capturing buffers that follow the  sub-         each  branch. The numbers of any capturing buffers that follow the sub-
3938         pattern  start after the highest number used in any branch. The follow-         pattern start after the highest number used in any branch. The  follow-
3939         ing example is taken from the Perl documentation.  The  numbers  under-         ing  example  is taken from the Perl documentation.  The numbers under-
3940         neath show in which buffer the captured content will be stored.         neath show in which buffer the captured content will be stored.
3941    
3942           # before  ---------------branch-reset----------- after           # before  ---------------branch-reset----------- after
3943           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3944           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
3945    
3946         A  backreference  or  a  recursive call to a numbered subpattern always         A backreference or a recursive call to  a  numbered  subpattern  always
3947         refers to the first one in the pattern with the given number.         refers to the first one in the pattern with the given number.
3948    
3949         An alternative approach to using this "branch reset" feature is to  use         An  alternative approach to using this "branch reset" feature is to use
3950         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
3951    
3952    
3953  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3954    
3955         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying capturing parentheses by number is simple, but  it  can  be
3956         very hard to keep track of the numbers in complicated  regular  expres-         very  hard  to keep track of the numbers in complicated regular expres-
3957         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions. Furthermore, if an  expression  is  modified,  the  numbers  may
3958         change. To help with this difficulty, PCRE supports the naming of  sub-         change.  To help with this difficulty, PCRE supports the naming of sub-
3959         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
3960         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
3961         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-
3962         tax.         tax.
3963    
3964         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>...)
3965         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
3966         to capturing parentheses from other parts of the pattern, such as back-         to capturing parentheses from other parts of the pattern, such as back-
3967         references,  recursion,  and conditions, can be made by name as well as         references, recursion, and conditions, can be made by name as  well  as
3968         by number.         by number.
3969    
3970         Names consist of up to  32  alphanumeric  characters  and  underscores.         Names  consist  of  up  to  32 alphanumeric characters and underscores.
3971         Named  capturing  parentheses  are  still  allocated numbers as well as         Named capturing parentheses are still  allocated  numbers  as  well  as
3972         names, exactly as if the names were not present. The PCRE API  provides         names,  exactly as if the names were not present. The PCRE API provides
3973         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
3974         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
3975         a captured substring by name.         a captured substring by name.
3976    
3977         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
3978         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
3979         time.  This  can  be useful for patterns where only one instance of the         time. This can be useful for patterns where only one  instance  of  the
3980         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
3981         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
3982         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
3983         the line breaks) does the job:         the line breaks) does the job:
3984    
# Line 3662  NAMED SUBPATTERNS Line 3988  NAMED SUBPATTERNS
3988           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
3989           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3990    
3991         There  are  five capturing substrings, but only one is ever set after a         There are five capturing substrings, but only one is ever set  after  a
3992         match.  (An alternative way of solving this problem is to use a "branch         match.  (An alternative way of solving this problem is to use a "branch
3993         reset" subpattern, as described in the previous section.)         reset" subpattern, as described in the previous section.)
3994    
3995         The  convenience  function  for extracting the data by name returns the         The convenience function for extracting the data by  name  returns  the
3996         substring for the first (and in this example, the only)  subpattern  of         substring  for  the first (and in this example, the only) subpattern of
3997         that  name  that  matched.  This saves searching to find which numbered         that name that matched. This saves searching  to  find  which  numbered
3998         subpattern it was. If you make a reference to a non-unique  named  sub-         subpattern  it  was. If you make a reference to a non-unique named sub-
3999         pattern  from elsewhere in the pattern, the one that corresponds to the         pattern from elsewhere in the pattern, the one that corresponds to  the
4000         lowest number is used. For further details of the interfaces  for  han-         lowest  number  is used. For further details of the interfaces for han-
4001         dling named subpatterns, see the pcreapi documentation.         dling named subpatterns, see the pcreapi documentation.
4002    
4003           Warning: You cannot use different names to distinguish between two sub-
4004           patterns  with  the same number (see the previous section) because PCRE
4005           uses only the numbers when matching.
4006    
4007    
4008  REPETITION  REPETITION
4009    
4010         Repetition  is  specified  by  quantifiers, which can follow any of the         Repetition is specified by quantifiers, which can  follow  any  of  the
4011         following items:         following items:
4012    
4013           a literal data character           a literal data character
# Line 3690  REPETITION Line 4020  REPETITION
4020           a back reference (see next section)           a back reference (see next section)
4021           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4022    
4023         The general repetition quantifier specifies a minimum and maximum  num-         The  general repetition quantifier specifies a minimum and maximum num-
4024         ber  of  permitted matches, by giving the two numbers in curly brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
4025         (braces), separated by a comma. The numbers must be  less  than  65536,         (braces),  separated  by  a comma. The numbers must be less than 65536,
4026         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
4027    
4028           z{2,4}           z{2,4}
4029    
4030         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a
4031         special character. If the second number is omitted, but  the  comma  is         special  character.  If  the second number is omitted, but the comma is
4032         present,  there  is  no upper limit; if the second number and the comma         present, there is no upper limit; if the second number  and  the  comma
4033         are both omitted, the quantifier specifies an exact number of  required         are  both omitted, the quantifier specifies an exact number of required
4034         matches. Thus         matches. Thus
4035    
4036           [aeiou]{3,}           [aeiou]{3,}
# Line 3709  REPETITION Line 4039  REPETITION
4039    
4040           \d{8}           \d{8}
4041    
4042         matches  exactly  8  digits. An opening curly bracket that appears in a         matches exactly 8 digits. An opening curly bracket that  appears  in  a
4043         position where a quantifier is not allowed, or one that does not  match         position  where a quantifier is not allowed, or one that does not match
4044         the  syntax of a quantifier, is taken as a literal character. For exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
4045         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
4046    
4047         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
# Line 3722  REPETITION Line 4052  REPETITION
4052         may be of different lengths).         may be of different lengths).
4053    
4054         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4055         the previous item and the quantifier were not present.         the previous item and the quantifier were not present. This may be use-
4056           ful for subpatterns that are referenced as subroutines  from  elsewhere
4057           in the pattern. Items other than subpatterns that have a {0} quantifier
4058           are omitted from the compiled pattern.
4059    
4060         For  convenience, the three most common quantifiers have single-charac-         For convenience, the three most common quantifiers have  single-charac-
4061         ter abbreviations:         ter abbreviations:
4062    
4063           *    is equivalent to {0,}           *    is equivalent to {0,}
4064           +    is equivalent to {1,}           +    is equivalent to {1,}
4065           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4066    
4067         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
4068         that can match no characters with a quantifier that has no upper limit,         that can match no characters with a quantifier that has no upper limit,
4069         for example:         for example:
4070    
4071           (a?)*           (a?)*
4072    
4073         Earlier versions of Perl and PCRE used to give an error at compile time         Earlier versions of Perl and PCRE used to give an error at compile time
4074         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
4075         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
4076         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
4077         ken.         ken.
4078    
4079         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
4080         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
4081         causing the rest of the pattern to fail. The classic example  of  where         causing  the  rest of the pattern to fail. The classic example of where
4082         this gives problems is in trying to match comments in C programs. These         this gives problems is in trying to match comments in C programs. These
4083         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
4084         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
4085         pattern         pattern
4086    
4087           /\*.*\*/           /\*.*\*/
# Line 3757  REPETITION Line 4090  REPETITION
4090    
4091           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4092    
4093         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
4094         the .*  item.         the .*  item.
4095    
4096         However,  if  a quantifier is followed by a question mark, it ceases to         However, if a quantifier is followed by a question mark, it  ceases  to
4097         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4098         the pattern         the pattern
4099    
4100           /\*.*?\*/           /\*.*?\*/
4101    
4102         does  the  right  thing with the C comments. The meaning of the various         does the right thing with the C comments. The meaning  of  the  various
4103         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
4104         matches.   Do  not  confuse this use of question mark with its use as a         matches.  Do not confuse this use of question mark with its  use  as  a
4105         quantifier in its own right. Because it has two uses, it can  sometimes         quantifier  in its own right. Because it has two uses, it can sometimes
4106         appear doubled, as in         appear doubled, as in
4107    
4108           \d??\d           \d??\d
# Line 3777  REPETITION Line 4110  REPETITION
4110         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
4111         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4112    
4113         If the PCRE_UNGREEDY option is set (an option that is not available  in         If  the PCRE_UNGREEDY option is set (an option that is not available in
4114         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
4115         can be made greedy by following them with a  question  mark.  In  other         can  be  made  greedy  by following them with a question mark. In other
4116         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4117    
4118         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
4119         count that is greater than 1 or with a limited maximum, more memory  is         count  that is greater than 1 or with a limited maximum, more memory is
4120         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
4121         minimum or maximum.         minimum or maximum.
4122    
4123         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
4124         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,         alent to Perl's /s) is set, thus allowing the dot  to  match  newlines,
4125         the pattern is implicitly anchored, because whatever  follows  will  be         the  pattern  is  implicitly anchored, because whatever follows will be
4126         tried  against every character position in the subject string, so there         tried against every character position in the subject string, so  there
4127         is no point in retrying the overall match at  any  position  after  the         is  no  point  in  retrying the overall match at any position after the
4128         first.  PCRE  normally treats such a pattern as though it were preceded         first. PCRE normally treats such a pattern as though it  were  preceded
4129         by \A.         by \A.
4130    
4131         In cases where it is known that the subject  string  contains  no  new-         In  cases  where  it  is known that the subject string contains no new-
4132         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-
4133         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4134    
4135         However, there is one situation where the optimization cannot be  used.         However,  there is one situation where the optimization cannot be used.
4136         When  .*   is  inside  capturing  parentheses that are the subject of a         When .*  is inside capturing parentheses that  are  the  subject  of  a
4137         backreference elsewhere in the pattern, a match at the start  may  fail         backreference  elsewhere  in the pattern, a match at the start may fail
4138         where a later one succeeds. Consider, for example:         where a later one succeeds. Consider, for example:
4139    
4140           (.*)abc\1           (.*)abc\1
4141    
4142         If  the subject is "xyz123abc123" the match point is the fourth charac-         If the subject is "xyz123abc123" the match point is the fourth  charac-
4143         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4144    
4145         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3815  REPETITION Line 4148  REPETITION
4148           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4149    
4150         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4151         is "tweedledee". However, if there are  nested  capturing  subpatterns,         is  "tweedledee".  However,  if there are nested capturing subpatterns,
4152         the  corresponding captured values may have been set in previous itera-         the corresponding captured values may have been set in previous  itera-
4153         tions. For example, after         tions. For example, after
4154    
4155           /(a|(b))+/           /(a|(b))+/
# Line 3826  REPETITION Line 4159  REPETITION
4159    
4160  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4161    
4162         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
4163         repetition,  failure  of what follows normally causes the repeated item         repetition, failure of what follows normally causes the  repeated  item
4164         to be re-evaluated to see if a different number of repeats  allows  the         to  be  re-evaluated to see if a different number of repeats allows the
4165         rest  of  the pattern to match. Sometimes it is useful to prevent this,         rest of the pattern to match. Sometimes it is useful to  prevent  this,
4166         either to change the nature of the match, or to cause it  fail  earlier         either  to  change the nature of the match, or to cause it fail earlier
4167         than  it otherwise might, when the author of the pattern knows there is         than it otherwise might, when the author of the pattern knows there  is
4168         no point in carrying on.         no point in carrying on.
4169    
4170         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider,  for  example, the pattern \d+foo when applied to the subject
4171         line         line
4172    
4173           123456bar           123456bar
4174    
4175         After matching all 6 digits and then failing to match "foo", the normal         After matching all 6 digits and then failing to match "foo", the normal
4176         action of the matcher is to try again with only 5 digits  matching  the         action  of  the matcher is to try again with only 5 digits matching the
4177         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.
4178         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides
4179         the  means for specifying that once a subpattern has matched, it is not         the means for specifying that once a subpattern has matched, it is  not
4180         to be re-evaluated in this way.         to be re-evaluated in this way.
4181    
4182         If we use atomic grouping for the previous example, the  matcher  gives         If  we  use atomic grouping for the previous example, the matcher gives
4183         up  immediately  on failing to match "foo" the first time. The notation         up immediately on failing to match "foo" the first time.  The  notation
4184         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4185    
4186           (?>\d+)foo           (?>\d+)foo
# Line 3925  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4258  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4258    
4259           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4260    
4261         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences of non-digits cannot be broken, and failure happens quickly.
4262    
4263    
4264  BACK REFERENCES  BACK REFERENCES
4265    
4266         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4267         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
4268         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
4269         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4270    
4271         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4272         it  is  always  taken  as a back reference, and causes an error only if         it is always taken as a back reference, and causes  an  error  only  if
4273         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
4274         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
4275         to the left of the reference for numbers less than 10. A "forward  back         to  the left of the reference for numbers less than 10. A "forward back
4276         reference"  of  this  type can make sense when a repetition is involved         reference" of this type can make sense when a  repetition  is  involved
4277         and the subpattern to the right has participated in an  earlier  itera-         and  the  subpattern to the right has participated in an earlier itera-
4278         tion.         tion.
4279    
4280         It  is  not  possible to have a numerical "forward back reference" to a         It is not possible to have a numerical "forward back  reference"  to  a
4281         subpattern whose number is 10 or  more  using  this  syntax  because  a         subpattern  whose  number  is  10  or  more using this syntax because a
4282         sequence  such  as  \50 is interpreted as a character defined in octal.         sequence such as \50 is interpreted as a character  defined  in  octal.
4283         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4284         details  of  the  handling of digits following a backslash. There is no         details of the handling of digits following a backslash.  There  is  no
4285         such problem when named parentheses are used. A back reference  to  any         such  problem  when named parentheses are used. A back reference to any
4286         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4287    
4288         Another  way  of  avoiding  the ambiguity inherent in the use of digits         Another way of avoiding the ambiguity inherent in  the  use  of  digits
4289         following a backslash is to use the \g escape sequence, which is a fea-         following a backslash is to use the \g escape sequence, which is a fea-
4290         ture  introduced  in  Perl  5.10.  This  escape  must be followed by an         ture introduced in Perl 5.10.  This  escape  must  be  followed  by  an
4291         unsigned number or a negative number, optionally  enclosed  in  braces.         unsigned  number  or  a negative number, optionally enclosed in braces.
4292         These examples are all identical:         These examples are all identical:
4293    
4294           (ring), \1           (ring), \1
4295           (ring), \g1           (ring), \g1
4296           (ring), \g{1}           (ring), \g{1}
4297    
4298         An  unsigned number specifies an absolute reference without the ambigu-         An unsigned number specifies an absolute reference without the  ambigu-
4299         ity that is present in the older syntax. It is also useful when literal         ity that is present in the older syntax. It is also useful when literal
4300         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4301         Consider this example:         Consider this example:
# Line 3970  BACK REFERENCES Line 4303  BACK REFERENCES
4303           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4304    
4305         The sequence \g{-1} is a reference to the most recently started captur-         The sequence \g{-1} is a reference to the most recently started captur-
4306         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
4307         \g{-2} would be equivalent to \1. The use of relative references can be         \g{-2} would be equivalent to \1. The use of relative references can be
4308         helpful  in  long  patterns,  and  also in patterns that are created by         helpful in long patterns, and also in  patterns  that  are  created  by
4309         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4310    
4311         A back reference matches whatever actually matched the  capturing  sub-         A  back  reference matches whatever actually matched the capturing sub-
4312         pattern  in  the  current subject string, rather than anything matching         pattern in the current subject string, rather  than  anything  matching
4313         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4314         of doing that). So the pattern         of doing that). So the pattern
4315    
4316           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4317    
4318         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
4319         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
4320         time  of the back reference, the case of letters is relevant. For exam-         time of the back reference, the case of letters is relevant. For  exam-
4321         ple,         ple,
4322    
4323           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4324    
4325         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the
4326         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4327    
4328         There  are  several  different ways of writing back references to named         There are several different ways of writing back  references  to  named
4329         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or
4330         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's         \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's
4331         unified back reference syntax, in which \g can be used for both numeric         unified back reference syntax, in which \g can be used for both numeric
4332         and  named  references,  is  also supported. We could rewrite the above         and named references, is also supported. We  could  rewrite  the  above
4333         example in any of the following ways:         example in any of the following ways:
4334    
4335           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 4004  BACK REFERENCES Line 4337  BACK REFERENCES
4337           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4338           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4339    
4340         A subpattern that is referenced by  name  may  appear  in  the  pattern         A  subpattern  that  is  referenced  by  name may appear in the pattern
4341         before or after the reference.         before or after the reference.
4342    
4343         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
4344         subpattern has not actually been used in a particular match,  any  back         subpattern  has  not actually been used in a particular match, any back
4345         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4346    
4347           (a|(bc))\2           (a|(bc))\2
4348    
4349         always  fails if it starts to match "a" rather than "bc". Because there         always fails if it starts to match "a" rather than "bc". Because  there
4350         may be many capturing parentheses in a pattern,  all  digits  following         may  be  many  capturing parentheses in a pattern, all digits following
4351         the  backslash  are taken as part of a potential back reference number.         the backslash are taken as part of a potential back  reference  number.
4352         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4353         used  to  terminate  the back reference. If the PCRE_EXTENDED option is         used to terminate the back reference. If the  PCRE_EXTENDED  option  is
4354         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-
4355         ments" below) can be used.         ments" below) can be used.
4356    
4357         A  back reference that occurs inside the parentheses to which it refers         A back reference that occurs inside the parentheses to which it  refers
4358         fails when the subpattern is first used, so, for example,  (a\1)  never         fails  when  the subpattern is first used, so, for example, (a\1) never
4359         matches.   However,  such references can be useful inside repeated sub-         matches.  However, such references can be useful inside  repeated  sub-
4360         patterns. For example, the pattern         patterns. For example, the pattern
4361    
4362           (a|b\1)+           (a|b\1)+
4363    
4364         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-
4365         ation  of  the  subpattern,  the  back  reference matches the character         ation of the subpattern,  the  back  reference  matches  the  character
4366         string corresponding to the previous iteration. In order  for  this  to         string  corresponding  to  the previous iteration. In order for this to
4367         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
4368         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
4369         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4370    
4371    
4372  ASSERTIONS  ASSERTIONS
4373    
4374         An  assertion  is  a  test on the characters following or preceding the         An assertion is a test on the characters  following  or  preceding  the
4375         current matching point that does not actually consume  any  characters.         current  matching  point that does not actually consume any characters.
4376         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are
4377         described above.         described above.
4378    
4379         More complicated assertions are coded as  subpatterns.  There  are  two         More  complicated  assertions  are  coded as subpatterns. There are two
4380         kinds:  those  that  look  ahead of the current position in the subject         kinds: those that look ahead of the current  position  in  the  subject
4381         string, and those that look  behind  it.  An  assertion  subpattern  is         string,  and  those  that  look  behind  it. An assertion subpattern is
4382         matched  in  the  normal way, except that it does not cause the current         matched in the normal way, except that it does not  cause  the  current
4383         matching position to be changed.         matching position to be changed.
4384    
4385         Assertion subpatterns are not capturing subpatterns,  and  may  not  be         Assertion  subpatterns  are  not  capturing subpatterns, and may not be
4386         repeated,  because  it  makes no sense to assert the same thing several         repeated, because it makes no sense to assert the  same  thing  several
4387         times. If any kind of assertion contains capturing  subpatterns  within         times.  If  any kind of assertion contains capturing subpatterns within
4388         it,  these are counted for the purposes of numbering the capturing sub-         it, these are counted for the purposes of numbering the capturing  sub-
4389         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4390         out  only  for  positive assertions, because it does not make sense for         out only for positive assertions, because it does not  make  sense  for
4391         negative assertions.         negative assertions.
4392    
4393     Lookahead assertions     Lookahead assertions
# Line 4064  ASSERTIONS Line 4397  ASSERTIONS
4397    
4398           \w+(?=;)           \w+(?=;)
4399    
4400         matches  a word followed by a semicolon, but does not include the semi-         matches a word followed by a semicolon, but does not include the  semi-
4401         colon in the match, and         colon in the match, and
4402    
4403           foo(?!bar)           foo(?!bar)
4404    
4405         matches any occurrence of "foo" that is not  followed  by  "bar".  Note         matches  any  occurrence  of  "foo" that is not followed by "bar". Note
4406         that the apparently similar pattern         that the apparently similar pattern
4407    
4408           (?!foo)bar           (?!foo)bar
4409    
4410         does  not  find  an  occurrence  of "bar" that is preceded by something         does not find an occurrence of "bar"  that  is  preceded  by  something
4411         other than "foo"; it finds any occurrence of "bar" whatsoever,  because         other  than "foo"; it finds any occurrence of "bar" whatsoever, because
4412         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4413         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4414    
4415         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
4416         most  convenient  way  to  do  it  is with (?!) because an empty string         most convenient way to do it is  with  (?!)  because  an  empty  string
4417         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
4418         string must always fail.         string must always fail.
4419    
4420     Lookbehind assertions     Lookbehind assertions
4421    
4422         Lookbehind  assertions start with (?<= for positive assertions and (?<!         Lookbehind assertions start with (?<= for positive assertions and  (?<!
4423         for negative assertions. For example,         for negative assertions. For example,
4424    
4425           (?<!foo)bar           (?<!foo)bar
4426    
4427         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
4428         contents  of  a  lookbehind  assertion are restricted such that all the         contents of a lookbehind assertion are restricted  such  that  all  the
4429         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-
4430         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
4431         fixed length. Thus         fixed length. Thus
4432    
4433           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4103  ASSERTIONS Line 4436  ASSERTIONS
4436    
4437           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4438    
4439         causes an error at compile time. Branches that match  different  length         causes  an  error at compile time. Branches that match different length
4440         strings  are permitted only at the top level of a lookbehind assertion.         strings are permitted only at the top level of a lookbehind  assertion.
4441         This is an extension compared with  Perl  (at  least  for  5.8),  which         This  is  an  extension  compared  with  Perl (at least for 5.8), which
4442         requires  all branches to match the same length of string. An assertion         requires all branches to match the same length of string. An  assertion
4443         such as         such as
4444    
4445           (?<=ab(c|de))           (?<=ab(c|de))
4446    
4447         is not permitted, because its single top-level  branch  can  match  two         is  not  permitted,  because  its single top-level branch can match two
4448         different  lengths,  but  it is acceptable if rewritten to use two top-         different lengths, but it is acceptable if rewritten to  use  two  top-
4449         level branches:         level branches:
4450    
4451           (?<=abc|abde)           (?<=abc|abde)
4452    
4453         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
4454         instead  of  a lookbehind assertion; this is not restricted to a fixed-         instead of a lookbehind assertion; this is not restricted to  a  fixed-
4455         length.         length.
4456    
4457         The implementation of lookbehind assertions is, for  each  alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4458         to  temporarily  move the current position back by the fixed length and         to temporarily move the current position back by the fixed  length  and
4459         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4460         rent position, the assertion fails.         rent position, the assertion fails.
4461    
4462         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
4463         mode) to appear in lookbehind assertions, because it makes it  impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
4464         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,
4465         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4466    
4467         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4468         assertions  to  specify  efficient  matching  at the end of the subject         assertions to specify efficient matching at  the  end  of  the  subject
4469         string. Consider a simple pattern such as         string. Consider a simple pattern such as
4470    
4471           abcd$           abcd$
4472    
4473         when applied to a long string that does  not  match.  Because  matching         when  applied  to  a  long string that does not match. Because matching
4474         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
4475         and then see if what follows matches the rest of the  pattern.  If  the         and  then  see  if what follows matches the rest of the pattern. If the
4476         pattern is specified as         pattern is specified as
4477    
4478           ^.*abcd$           ^.*abcd$
4479    
4480         the  initial .* matches the entire string at first, but when this fails         the initial .* matches the entire string at first, but when this  fails
4481         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
4482         last  character,  then all but the last two characters, and so on. Once         last character, then all but the last two characters, and so  on.  Once
4483         again the search for "a" covers the entire string, from right to  left,         again  the search for "a" covers the entire string, from right to left,
4484         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
4485    
4486           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4487    
4488         there  can  be  no backtracking for the .*+ item; it can match only the         there can be no backtracking for the .*+ item; it can  match  only  the
4489         entire string. The subsequent lookbehind assertion does a  single  test         entire  string.  The subsequent lookbehind assertion does a single test
4490         on  the last four characters. If it fails, the match fails immediately.         on the last four characters. If it fails, the match fails  immediately.
4491         For long strings, this approach makes a significant difference  to  the         For  long  strings, this approach makes a significant difference to the
4492         processing time.         processing time.
4493    
4494     Using multiple assertions     Using multiple assertions
# Line 4164  ASSERTIONS Line 4497  ASSERTIONS
4497    
4498           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4499    
4500         matches  "foo" preceded by three digits that are not "999". Notice that         matches "foo" preceded by three digits that are not "999". Notice  that
4501         each of the assertions is applied independently at the  same  point  in         each  of  the  assertions is applied independently at the same point in
4502         the  subject  string.  First  there  is a check that the previous three         the subject string. First there is a  check  that  the  previous  three
4503         characters are all digits, and then there is  a  check  that  the  same         characters  are  all  digits,  and  then there is a check that the same
4504         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4505         ceded by six characters, the first of which are  digits  and  the  last         ceded  by  six  characters,  the first of which are digits and the last
4506         three  of  which  are not "999". For example, it doesn't match "123abc-         three of which are not "999". For example, it  doesn't  match  "123abc-
4507         foo". A pattern to do that is         foo". A pattern to do that is
4508    
4509           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4510    
4511         This time the first assertion looks at the  preceding  six  characters,         This  time  the  first assertion looks at the preceding six characters,
4512         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4513         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4514    
# Line 4183  ASSERTIONS Line 4516  ASSERTIONS
4516    
4517           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4518    
4519         matches an occurrence of "baz" that is preceded by "bar" which in  turn         matches  an occurrence of "baz" that is preceded by "bar" which in turn
4520         is not preceded by "foo", while         is not preceded by "foo", while
4521    
4522           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4523    
4524         is  another pattern that matches "foo" preceded by three digits and any         is another pattern that matches "foo" preceded by three digits and  any
4525         three characters that are not "999".         three characters that are not "999".
4526    
4527    
4528  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4529    
4530         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-
4531         ditionally  or to choose between two alternative subpatterns, depending         ditionally or to choose between two alternative subpatterns,  depending
4532         on the result of an assertion, or whether a previous capturing  subpat-         on  the result of an assertion, or whether a previous capturing subpat-
4533         tern  matched  or not. The two possible forms of conditional subpattern         tern matched or not. The two possible forms of  conditional  subpattern
4534         are         are
4535    
4536           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4537           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4538    
4539         If the condition is satisfied, the yes-pattern is used;  otherwise  the         If  the  condition is satisfied, the yes-pattern is used; otherwise the
4540         no-pattern  (if  present)  is used. If there are more than two alterna-         no-pattern (if present) is used. If there are more  than  two  alterna-
4541         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4542    
4543         There are four kinds of condition: references  to  subpatterns,  refer-         There  are  four  kinds of condition: references to subpatterns, refer-
4544         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4545    
4546     Checking for a used subpattern by number     Checking for a used subpattern by number
4547    
4548         If  the  text between the parentheses consists of a sequence of digits,         If the text between the parentheses consists of a sequence  of  digits,
4549         the condition is true if the capturing subpattern of  that  number  has         the  condition  is  true if the capturing subpattern of that number has
4550         previously  matched.  An  alternative notation is to precede the digits         previously matched. An alternative notation is to  precede  the  digits
4551         with a plus or minus sign. In this case, the subpattern number is rela-         with a plus or minus sign. In this case, the subpattern number is rela-
4552         tive rather than absolute.  The most recently opened parentheses can be         tive rather than absolute.  The most recently opened parentheses can be
4553         referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In         referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In
4554         looping constructs it can also make sense to refer to subsequent groups         looping constructs it can also make sense to refer to subsequent groups
4555         with constructs such as (?(+2).         with constructs such as (?(+2).
4556    
4557         Consider the following pattern, which  contains  non-significant  white         Consider  the  following  pattern, which contains non-significant white
4558         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
4559         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4560    
4561           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4562    
4563         The first part matches an optional opening  parenthesis,  and  if  that         The  first  part  matches  an optional opening parenthesis, and if that
4564         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4565         ond part matches one or more characters that are not  parentheses.  The         ond  part  matches one or more characters that are not parentheses. The
4566         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4567         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
4568         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-
4569         tern is executed and a  closing  parenthesis  is  required.  Otherwise,         tern  is  executed  and  a  closing parenthesis is required. Otherwise,
4570         since  no-pattern  is  not  present, the subpattern matches nothing. In         since no-pattern is not present, the  subpattern  matches  nothing.  In
4571         other words,  this  pattern  matches  a  sequence  of  non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4572         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4573    
4574         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
4575         relative reference:         relative reference:
4576    
4577           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4578    
4579         This makes the fragment independent of the parentheses  in  the  larger         This  makes  the  fragment independent of the parentheses in the larger
4580         pattern.         pattern.
4581    
4582     Checking for a used subpattern by name     Checking for a used subpattern by name
4583    
4584         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4585         used subpattern by name. For compatibility  with  earlier  versions  of         used  subpattern  by  name.  For compatibility with earlier versions of
4586         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4587         also recognized. However, there is a possible ambiguity with this  syn-         also  recognized. However, there is a possible ambiguity with this syn-
4588         tax,  because  subpattern  names  may  consist entirely of digits. PCRE         tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4589         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
4590         consists  entirely  of digits, PCRE looks for a subpattern of that num-         consists entirely of digits, PCRE looks for a subpattern of  that  num-
4591         ber, which must be greater than zero. Using subpattern names that  con-         ber,  which must be greater than zero. Using subpattern names that con-
4592         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4593    
4594         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4266  CONDITIONAL SUBPATTERNS Line 4599  CONDITIONAL SUBPATTERNS
4599     Checking for pattern recursion     Checking for pattern recursion
4600    
4601         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
4602         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
4603         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-
4604         sand follow the letter R, for example:         sand follow the letter R, for example:
4605    
4606           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4607    
4608         the condition is true if the most recent recursion is into the  subpat-         the  condition is true if the most recent recursion is into the subpat-
4609         tern  whose  number or name is given. This condition does not check the         tern whose number or name is given. This condition does not  check  the
4610         entire recursion stack.         entire recursion stack.
4611    
4612         At "top level", all these recursion test conditions are  false.  Recur-         At  "top  level", all these recursion test conditions are false. Recur-
4613         sive patterns are described below.         sive patterns are described below.
4614    
4615     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4616    
4617         If  the  condition  is  the string (DEFINE), and there is no subpattern         If the condition is the string (DEFINE), and  there  is  no  subpattern
4618         with the name DEFINE, the condition is  always  false.  In  this  case,         with  the  name  DEFINE,  the  condition is always false. In this case,
4619         there  may  be  only  one  alternative  in the subpattern. It is always         there may be only one alternative  in  the  subpattern.  It  is  always
4620         skipped if control reaches this point  in  the  pattern;  the  idea  of         skipped  if  control  reaches  this  point  in the pattern; the idea of
4621         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-
4622         erenced from elsewhere. (The use of "subroutines" is described  below.)         erenced  from elsewhere. (The use of "subroutines" is described below.)
4623         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
4624         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4625    
4626           (?(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) )
4627           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4628    
4629         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
4630         group  named "byte" is defined. This matches an individual component of         group named "byte" is defined. This matches an individual component  of
4631         an IPv4 address (a number less than 256). When  matching  takes  place,         an  IPv4  address  (a number less than 256). When matching takes place,
4632         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
4633         condition.         condition.
4634    
4635         The rest of the pattern uses references to the named group to match the         The rest of the pattern uses references to the named group to match the
4636         four  dot-separated  components of an IPv4 address, insisting on a word         four dot-separated components of an IPv4 address, insisting on  a  word
4637         boundary at each end.         boundary at each end.
4638    
4639     Assertion conditions     Assertion conditions
4640    
4641         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
4642         assertion.   This may be a positive or negative lookahead or lookbehind         assertion.  This may be a positive or negative lookahead or  lookbehind
4643         assertion. Consider  this  pattern,  again  containing  non-significant         assertion.  Consider  this  pattern,  again  containing non-significant
4644         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4645    
4646           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4647           \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} )
4648    
4649         The  condition  is  a  positive  lookahead  assertion  that  matches an         The condition  is  a  positive  lookahead  assertion  that  matches  an
4650         optional sequence of non-letters followed by a letter. In other  words,         optional  sequence of non-letters followed by a letter. In other words,
4651         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
4652         letter is found, the subject is matched against the first  alternative;         letter  is found, the subject is matched against the first alternative;
4653         otherwise  it  is  matched  against  the  second.  This pattern matches         otherwise it is  matched  against  the  second.  This  pattern  matches
4654         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
4655         letters and dd are digits.         letters and dd are digits.
4656    
4657    
4658  COMMENTS  COMMENTS
4659    
4660         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
4661         next closing parenthesis. Nested parentheses  are  not  permitted.  The         next  closing  parenthesis.  Nested  parentheses are not permitted. The
4662         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
4663         at all.         at all.
4664    
4665         If the PCRE_EXTENDED option is set, an unescaped # character outside  a         If  the PCRE_EXTENDED option is set, an unescaped # character outside a
4666         character  class  introduces  a  comment  that continues to immediately         character class introduces a  comment  that  continues  to  immediately
4667         after the next newline in the pattern.         after the next newline in the pattern.
4668    
4669    
4670  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4671    
4672         Consider the problem of matching a string in parentheses, allowing  for         Consider  the problem of matching a string in parentheses, allowing for
4673         unlimited  nested  parentheses.  Without the use of recursion, the best         unlimited nested parentheses. Without the use of  recursion,  the  best
4674         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
4675         depth  of  nesting.  It  is not possible to handle an arbitrary nesting         depth of nesting. It is not possible to  handle  an  arbitrary  nesting
4676         depth.         depth.
4677    
4678         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4679         sions  to recurse (amongst other things). It does this by interpolating         sions to recurse (amongst other things). It does this by  interpolating
4680         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
4681         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4682         parentheses problem can be created like this:         parentheses problem can be created like this:
4683    
# Line 4354  RECURSIVE PATTERNS Line 4687  RECURSIVE PATTERNS
4687         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4688    
4689         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4690         it supports special syntax for recursion of  the  entire  pattern,  and         it  supports  special  syntax  for recursion of the entire pattern, and
4691         also  for  individual  subpattern  recursion. After its introduction in         also for individual subpattern recursion.  After  its  introduction  in
4692         PCRE and Python, this kind of recursion was  introduced  into  Perl  at         PCRE  and  Python,  this  kind of recursion was introduced into Perl at
4693         release 5.10.         release 5.10.
4694    
4695         A  special  item  that consists of (? followed by a number greater than         A special item that consists of (? followed by a  number  greater  than
4696         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
4697         the  given  number, provided that it occurs inside that subpattern. (If         the given number, provided that it occurs inside that  subpattern.  (If
4698         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-
4699         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
4700         regular expression.         regular expression.
4701    
4702         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is
4703         always treated as an atomic group. That is, once it has matched some of         always treated as an atomic group. That is, once it has matched some of
4704         the subject string, it is never re-entered, even if it contains untried         the subject string, it is never re-entered, even if it contains untried
4705         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4706    
4707         This  PCRE  pattern  solves  the nested parentheses problem (assume the         This PCRE pattern solves the nested  parentheses  problem  (assume  the
4708         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4709    
4710           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4711    
4712         First it matches an opening parenthesis. Then it matches any number  of         First  it matches an opening parenthesis. Then it matches any number of
4713         substrings  which  can  either  be  a sequence of non-parentheses, or a         substrings which can either be a  sequence  of  non-parentheses,  or  a
4714         recursive match of the pattern itself (that is, a  correctly  parenthe-         recursive  match  of the pattern itself (that is, a correctly parenthe-
4715         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4716    
4717         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
4718         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4719    
4720           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4721    
4722         We have put the pattern into parentheses, and caused the  recursion  to         We  have  put the pattern into parentheses, and caused the recursion to
4723         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
4724    
4725         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be
4726         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
4727         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
4728         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
4729         the  recursion.  In  other  words,  a  negative number counts capturing         the recursion. In other  words,  a  negative  number  counts  capturing
4730         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
4731    
4732         It is also possible to refer to  subsequently  opened  parentheses,  by         It  is  also  possible  to refer to subsequently opened parentheses, by
4733         writing  references  such  as (?+2). However, these cannot be recursive         writing references such as (?+2). However, these  cannot  be  recursive
4734         because the reference is not inside the  parentheses  that  are  refer-         because  the  reference  is  not inside the parentheses that are refer-
4735         enced.  They  are  always  "subroutine" calls, as described in the next         enced. They are always "subroutine" calls, as  described  in  the  next
4736         section.         section.
4737    
4738         An alternative approach is to use named parentheses instead.  The  Perl         An  alternative  approach is to use named parentheses instead. The Perl
4739         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
4740         supported. We could rewrite the above example as follows:         supported. We could rewrite the above example as follows:
4741    
4742           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4743    
4744         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
4745         one is used.         one is used.
4746    
4747         This  particular  example pattern that we have been looking at contains         This particular example pattern that we have been looking  at  contains
4748         nested unlimited repeats, and so the use of atomic grouping for  match-         nested  unlimited repeats, and so the use of atomic grouping for match-
4749         ing  strings  of non-parentheses is important when applying the pattern         ing strings of non-parentheses is important when applying  the  pattern
4750         to strings that do not match. For example, when this pattern is applied         to strings that do not match. For example, when this pattern is applied
4751         to         to
4752    
4753           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4754    
4755         it  yields "no match" quickly. However, if atomic grouping is not used,         it yields "no match" quickly. However, if atomic grouping is not  used,
4756         the match runs for a very long time indeed because there  are  so  many         the  match  runs  for a very long time indeed because there are so many
4757         different  ways  the  + and * repeats can carve up the subject, and all         different ways the + and * repeats can carve up the  subject,  and  all
4758         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4759    
4760         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4761         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4762         value is set.  If you want to obtain  intermediate  values,  a  callout         value  is  set.   If  you want to obtain intermediate values, a callout
4763         function  can be used (see below and the pcrecallout documentation). If         function can be used (see below and the pcrecallout documentation).  If
4764         the pattern above is matched against         the pattern above is matched against
4765    
4766           (ab(cd)ef)           (ab(cd)ef)
4767    
4768         the value for the capturing parentheses is  "ef",  which  is  the  last         the  value  for  the  capturing  parentheses is "ef", which is the last
4769         value  taken  on at the top level. If additional parentheses are added,         value taken on at the top level. If additional parentheses  are  added,
4770         giving         giving
4771    
4772           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4773              ^                        ^              ^                        ^
4774              ^                        ^              ^                        ^
4775    
4776         the string they capture is "ab(cd)ef", the contents of  the  top  level         the  string  they  capture is "ab(cd)ef", the contents of the top level
4777         parentheses.  If there are more than 15 capturing parentheses in a pat-         parentheses. If there are more than 15 capturing parentheses in a  pat-
4778         tern, PCRE has to obtain extra memory to store data during a recursion,         tern, PCRE has to obtain extra memory to store data during a recursion,
4779         which  it  does  by  using pcre_malloc, freeing it via pcre_free after-         which it does by using pcre_malloc, freeing  it  via  pcre_free  after-
4780         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the
4781         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4782    
4783         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
4784         recursion.  Consider this pattern, which matches text in  angle  brack-         recursion.   Consider  this pattern, which matches text in angle brack-
4785         ets,  allowing for arbitrary nesting. Only digits are allowed in nested         ets, allowing for arbitrary nesting. Only digits are allowed in  nested
4786         brackets (that is, when recursing), whereas any characters are  permit-         brackets  (that is, when recursing), whereas any characters are permit-
4787         ted at the outer level.         ted at the outer level.
4788    
4789           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4790    
4791         In  this  pattern, (?(R) is the start of a conditional subpattern, with         In this pattern, (?(R) is the start of a conditional  subpattern,  with
4792         two different alternatives for the recursive and  non-recursive  cases.         two  different  alternatives for the recursive and non-recursive cases.
4793         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4794    
4795    
4796  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4797    
4798         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4799         by name) is used outside the parentheses to which it refers,  it  oper-         by  name)  is used outside the parentheses to which it refers, it oper-
4800         ates  like a subroutine in a programming language. The "called" subpat-         ates like a subroutine in a programming language. The "called"  subpat-
4801         tern may be defined before or after the reference. A numbered reference         tern may be defined before or after the reference. A numbered reference
4802         can be absolute or relative, as in these examples:         can be absolute or relative, as in these examples:
4803    
# Line 4476  SUBPATTERNS AS SUBROUTINES Line 4809  SUBPATTERNS AS SUBROUTINES
4809    
4810           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4811    
4812         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
4813         not "sense and responsibility". If instead the pattern         not "sense and responsibility". If instead the pattern
4814    
4815           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4816    
4817         is used, it does match "sense and responsibility" as well as the  other         is  used, it does match "sense and responsibility" as well as the other
4818         two  strings.  Another  example  is  given  in the discussion of DEFINE         two strings. Another example is  given  in  the  discussion  of  DEFINE
4819         above.         above.
4820    
4821         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4822         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,
4823         it is never re-entered, even if it contains  untried  alternatives  and         it  is  never  re-entered, even if it contains untried alternatives and
4824         there is a subsequent matching failure.         there is a subsequent matching failure.
4825    
4826         When  a  subpattern is used as a subroutine, processing options such as         When a subpattern is used as a subroutine, processing options  such  as
4827         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
4828         be changed for different calls. For example, consider this pattern:         be changed for different calls. For example, consider this pattern:
4829    
4830           (abc)(?i:(?-1))           (abc)(?i:(?-1))
4831    
4832         It  matches  "abcabc". It does not match "abcABC" because the change of         It matches "abcabc". It does not match "abcABC" because the  change  of
4833         processing option does not affect the called subpattern.         processing option does not affect the called subpattern.
4834    
4835    
4836    ONIGURUMA SUBROUTINE SYNTAX
4837    
4838           For  compatibility with Oniguruma, the non-Perl syntax \g followed by a
4839           name or a number enclosed either in angle brackets or single quotes, is
4840           an  alternative  syntax  for  referencing a subpattern as a subroutine,
4841           possibly recursively. Here are two of the examples used above,  rewrit-
4842           ten using this syntax:
4843    
4844             (?<pn> \( ( (?>[^()]+) | \g<pn> )* \) )
4845             (sens|respons)e and \g'1'ibility
4846    
4847           PCRE  supports  an extension to Oniguruma: if a number is preceded by a
4848           plus or a minus sign it is taken as a relative reference. For example:
4849    
4850             (abc)(?i:\g<-1>)
4851    
4852           Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are  not
4853           synonymous.  The former is a back reference; the latter is a subroutine
4854           call.
4855    
4856    
4857  CALLOUTS  CALLOUTS
4858    
4859         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
# Line 4535  CALLOUTS Line 4889  CALLOUTS
4889         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4890    
4891    
4892    BACKTRACKING CONTROL
4893    
4894           Perl 5.10 introduced a number of "Special Backtracking Control  Verbs",