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# Line 2  Line 2 
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
5  synopses of each function in the library have not been included. There are  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
10    
# Line 24  INTRODUCTION Line 25  INTRODUCTION
25         tax items, and there is an option for  requesting  some  minor  changes         tax items, and there is an option for  requesting  some  minor  changes
26         that give better JavaScript compatibility.         that give better JavaScript compatibility.
27    
28         The  current  implementation of PCRE (release 7.x) corresponds approxi-         The  current implementation of PCRE (release 8.xx) corresponds approxi-
29         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
30         Unicode general category properties. However, UTF-8 and Unicode support         Unicode general category properties. However, UTF-8 and Unicode support
31         has to be explicitly enabled; it is not the default. The Unicode tables         has to be explicitly enabled; it is not the default. The Unicode tables
32         correspond to Unicode release 5.0.0.         correspond to Unicode release 5.1.
33    
34         In  addition to the Perl-compatible matching function, PCRE contains an         In  addition to the Perl-compatible matching function, PCRE contains an
35         alternative matching function that matches the same  compiled  patterns         alternative matching function that matches the same  compiled  patterns
# Line 71  USER DOCUMENTATION Line 72  USER DOCUMENTATION
72         The user documentation for PCRE comprises a number  of  different  sec-         The user documentation for PCRE comprises a number  of  different  sec-
73         tions.  In the "man" format, each of these is a separate "man page". In         tions.  In the "man" format, each of these is a separate "man page". In
74         the HTML format, each is a separate page, linked from the  index  page.         the HTML format, each is a separate page, linked from the  index  page.
75         In  the  plain text format, all the sections are concatenated, for ease         In  the  plain  text format, all the sections, except the pcredemo sec-
76         of searching. The sections are as follows:         tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79           pcre              this document           pcre              this document
80           pcre-config       show PCRE installation configuration information           pcre-config       show PCRE installation configuration information
# Line 81  USER DOCUMENTATION Line 83  USER DOCUMENTATION
83           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
84           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
85           pcrecpp           details of the C++ wrapper           pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
88           pcrematching      discussion of the two matching algorithms           pcrematching      discussion of the two matching algorithms
89           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
# Line 90  USER DOCUMENTATION Line 93  USER DOCUMENTATION
93           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
94           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
95           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
96           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
97           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
98           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
99    
# Line 136  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
142         with  the PCRE_UTF8 option flag. When you do this, both the pattern and         with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143         any subject strings that are matched against it are  treated  as  UTF-8         sequence (*UTF8). When either of these is the case,  both  the  pattern
144         strings instead of just strings of bytes.         and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of just strings of bytes.
146    
147         If  you compile PCRE with UTF-8 support, but do not use it at run time,         If you compile PCRE with UTF-8 support, but do not use it at run  time,
148         the library will be a bit bigger, but the additional run time  overhead         the  library will be a bit bigger, but the additional run time overhead
149         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150         very big.         very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
156         for a decimal number, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
158         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
159         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         does not support this.         does not support this.
163    
164     Validity of UTF-8 strings     Validity of UTF-8 strings
165    
166         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
167         subjects are (by default) checked for validity on entry to the relevant         subjects are (by default) checked for validity on entry to the relevant
168         functions. From release 7.3 of PCRE, the check is according  the  rules         functions.  From  release 7.3 of PCRE, the check is according the rules
169         of  RFC  3629, which are themselves derived from the Unicode specifica-         of RFC 3629, which are themselves derived from the  Unicode  specifica-
170         tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which         tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171         allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current         allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172         check allows only values in the range U+0 to U+10FFFF, excluding U+D800         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173         to U+DFFF.         to U+DFFF.
174    
175         The  excluded  code  points are the "Low Surrogate Area" of Unicode, of         The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176         which the Unicode Standard says this: "The Low Surrogate Area does  not         which  the Unicode Standard says this: "The Low Surrogate Area does not
177         contain  any  character  assignments,  consequently  no  character code         contain any  character  assignments,  consequently  no  character  code
178         charts or namelists are provided for this area. Surrogates are reserved         charts or namelists are provided for this area. Surrogates are reserved
179         for  use  with  UTF-16 and then must be used in pairs." The code points         for use with UTF-16 and then must be used in pairs."  The  code  points
180         that are encoded by UTF-16 pairs  are  available  as  independent  code         that  are  encoded  by  UTF-16  pairs are available as independent code
181         points  in  the  UTF-8  encoding.  (In other words, the whole surrogate         points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)         thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184         If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return         If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
185         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know         (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
186         that your strings are valid, and therefore want to skip these checks in         that your strings are valid, and therefore want to skip these checks in
187         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at         order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
188         compile time or at run time, PCRE assumes that the pattern  or  subject         compile  time  or at run time, PCRE assumes that the pattern or subject
189         it  is  given  (respectively)  contains only valid UTF-8 codes. In this         it is given (respectively) contains only valid  UTF-8  codes.  In  this
190         case, it does not diagnose an invalid UTF-8 string.         case, it does not diagnose an invalid UTF-8 string.
191    
192         If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,         If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
193         what  happens  depends on why the string is invalid. If the string con-         what happens depends on why the string is invalid. If the  string  con-
194         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a         forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
195         string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,         string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
196         apart from the initial validity test, PCRE (when in UTF-8 mode) handles         apart from the initial validity test, PCRE (when in UTF-8 mode) handles
197         strings  according  to  the more liberal rules of RFC 2279. However, if         strings according to the more liberal rules of RFC  2279.  However,  if
198         the string does not even conform to RFC 2279, the result is  undefined.         the  string does not even conform to RFC 2279, the result is undefined.
199         Your program may crash.         Your program may crash.
200    
201         If  you  want  to  process  strings  of  values  in the full range 0 to         If you want to process strings  of  values  in  the  full  range  0  to
202         0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can         0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
203         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in         set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
204         this situation, you will have to apply your own validity check.         this situation, you will have to apply your own validity check.
205    
206     General comments about UTF-8 mode     General comments about UTF-8 mode
207    
208         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a         1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
209         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
210    
211         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
212         characters for values greater than \177.         characters for values greater than \177.
213    
214         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
215         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
216    
217         4.  The dot metacharacter matches one UTF-8 character instead of a sin-         4. The dot metacharacter matches one UTF-8 character instead of a  sin-
218         gle byte.         gle byte.
219    
220         5. The escape sequence \C can be used to match a single byte  in  UTF-8         5.  The  escape sequence \C can be used to match a single byte in UTF-8
221         mode,  but  its  use can lead to some strange effects. This facility is         mode, but its use can lead to some strange effects.  This  facility  is
222         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
223    
224         6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
225         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but the characters that PCRE  recog-
226         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes  as  digits,  spaces,  or  word characters remain the same set as
227         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
228         includes Unicode property support, because to do otherwise  would  slow         includes  Unicode  property support, because to do otherwise would slow
229         down  PCRE in many common cases. If you really want to test for a wider         down PCRE in many common cases. If you really want to test for a  wider
230         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense  of,  say,  "digit",  you must use Unicode property tests such as
231         \p{Nd}.         \p{Nd}. Note that this also applies to \b, because  it  is  defined  in
232           terms of \w and \W.
233    
234         7.  Similarly,  characters that match the POSIX named character classes         7.  Similarly,  characters that match the POSIX named character classes
235         are all low-valued characters.         are all low-valued characters.
# Line 258  AUTHOR Line 263  AUTHOR
263    
264  REVISION  REVISION
265    
266         Last updated: 12 April 2008         Last updated: 01 September 2009
267         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
268  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
269    
270    
271  PCREBUILD(3)                                                      PCREBUILD(3)  PCREBUILD(3)                                                      PCREBUILD(3)
272    
273    
# Line 277  PCRE BUILD-TIME OPTIONS Line 282  PCRE BUILD-TIME OPTIONS
282         script,  where the optional features are selected or deselected by pro-         script,  where the optional features are selected or deselected by pro-
283         viding options to configure before running the make  command.  However,         viding options to configure before running the make  command.  However,
284         the  same  options  can be selected in both Unix-like and non-Unix-like         the  same  options  can be selected in both Unix-like and non-Unix-like
285         environments using the GUI facility of  CMakeSetup  if  you  are  using         environments using the GUI facility of cmake-gui if you are using CMake
286         CMake instead of configure to build PCRE.         instead of configure to build PCRE.
287    
288           There  is  a  lot more information about building PCRE in non-Unix-like
289           environments in the file called NON_UNIX_USE, which is part of the PCRE
290           distribution.  You  should consult this file as well as the README file
291           if you are building in a non-Unix-like environment.
292    
293         The complete list of options for configure (which includes the standard         The complete list of options for configure (which includes the standard
294         ones such as the  selection  of  the  installation  directory)  can  be         ones  such  as  the  selection  of  the  installation directory) can be
295         obtained by running         obtained by running
296    
297           ./configure --help           ./configure --help
298    
299         The  following  sections  include  descriptions  of options whose names         The following sections include  descriptions  of  options  whose  names
300         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
301         defaults  for  the configure command. Because of the way that configure         defaults for the configure command. Because of the way  that  configure
302         works, --enable and --disable always come in pairs, so  the  complemen-         works,  --enable  and --disable always come in pairs, so the complemen-
303         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
304         is not described.         is not described.
305    
306    
# Line 307  C++ SUPPORT Line 317  C++ SUPPORT
317    
318  UTF-8 SUPPORT  UTF-8 SUPPORT
319    
320         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
321    
322           --enable-utf8           --enable-utf8
323    
324         to the configure command. Of itself, this  does  not  make  PCRE  treat         to  the  configure  command.  Of  itself, this does not make PCRE treat
325         strings  as UTF-8. As well as compiling PCRE with this option, you also         strings as UTF-8. As well as compiling PCRE with this option, you  also
326         have have to set the PCRE_UTF8 option when you call the  pcre_compile()         have  have to set the PCRE_UTF8 option when you call the pcre_compile()
327         function.         function.
328    
329           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
330           expects its input to be either ASCII or UTF-8 (depending on the runtime
331           option). It is not possible to support both EBCDIC and UTF-8  codes  in
332           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
333           --enable-ebcdic are mutually exclusive.
334    
335    
336  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
337    
338         UTF-8  support allows PCRE to process character values greater than 255         UTF-8 support allows PCRE to process character values greater than  255
339         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-
340         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
341         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
342         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
343    
344           --enable-unicode-properties           --enable-unicode-properties
345    
346         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
347         not explicitly requested it.         not explicitly requested it.
348    
349         Including Unicode property support adds around 30K  of  tables  to  the         Including  Unicode  property  support  adds around 30K of tables to the
350         PCRE  library.  Only  the general category properties such as Lu and Nd         PCRE library. Only the general category properties such as  Lu  and  Nd
351         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
352    
353    
354  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
355    
356         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating         By  default,  PCRE interprets the linefeed (LF) character as indicating
357         the  end  of  a line. This is the normal newline character on Unix-like         the end of a line. This is the normal newline  character  on  Unix-like
358         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems.  You  can compile PCRE to use carriage return (CR) instead, by
359         instead, by adding         adding
360    
361           --enable-newline-is-cr           --enable-newline-is-cr
362    
363         to  the  configure  command.  There  is  also  a --enable-newline-is-lf         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
364         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
365    
366         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 356  CODE VALUE OF NEWLINE Line 372  CODE VALUE OF NEWLINE
372    
373           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
374    
375         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
376         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
377    
378           --enable-newline-is-any           --enable-newline-is-any
# Line 516  USING EBCDIC CODE Line 532  USING EBCDIC CODE
532    
533         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
534         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
535         environment (for example, an IBM mainframe operating system).         environment  (for  example,  an  IBM  mainframe  operating system). The
536           --enable-ebcdic option is incompatible with --enable-utf8.
537    
538    
539  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
# Line 529  PCREGREP OPTIONS FOR COMPRESSED FILE SUP Line 546  PCREGREP OPTIONS FOR COMPRESSED FILE SUP
546           --enable-pcregrep-libbz2           --enable-pcregrep-libbz2
547    
548         to the configure command. These options naturally require that the rel-         to the configure command. These options naturally require that the rel-
549         evant libraries are installed on your system. Configuration  will  fail         evant  libraries  are installed on your system. Configuration will fail
550         if they are not.         if they are not.
551    
552    
# Line 539  PCRETEST OPTION FOR LIBREADLINE SUPPORT Line 556  PCRETEST OPTION FOR LIBREADLINE SUPPORT
556    
557           --enable-pcretest-libreadline           --enable-pcretest-libreadline
558    
559         to  the  configure  command,  pcretest  is  linked with the libreadline         to the configure command,  pcretest  is  linked  with  the  libreadline
560         library, and when its input is from a terminal, it reads it  using  the         library,  and  when its input is from a terminal, it reads it using the
561         readline() function. This provides line-editing and history facilities.         readline() function. This provides line-editing and history facilities.
562         Note that libreadline is GPL-licenced, so if you distribute a binary of         Note that libreadline is GPL-licenced, so if you distribute a binary of
563         pcretest linked in this way, there may be licensing issues.         pcretest linked in this way, there may be licensing issues.
564    
565         Setting  this  option  causes  the -lreadline option to be added to the         Setting this option causes the -lreadline option to  be  added  to  the
566         pcretest build. In many operating environments with  a  sytem-installed         pcretest  build.  In many operating environments with a sytem-installed
567         libreadline this is sufficient. However, in some environments (e.g.  if         libreadline this is sufficient. However, in some environments (e.g.  if
568         an unmodified distribution version of readline is in use),  some  extra         an  unmodified  distribution version of readline is in use), some extra
569         configuration  may  be necessary. The INSTALL file for libreadline says         configuration may be necessary. The INSTALL file for  libreadline  says
570         this:         this:
571    
572           "Readline uses the termcap functions, but does not link with the           "Readline uses the termcap functions, but does not link with the
573           termcap or curses library itself, allowing applications which link           termcap or curses library itself, allowing applications which link
574           with readline the to choose an appropriate library."           with readline the to choose an appropriate library."
575    
576         If your environment has not been set up so that an appropriate  library         If  your environment has not been set up so that an appropriate library
577         is automatically included, you may need to add something like         is automatically included, you may need to add something like
578    
579           LIBS="-ncurses"           LIBS="-ncurses"
# Line 578  AUTHOR Line 595  AUTHOR
595    
596  REVISION  REVISION
597    
598         Last updated: 13 April 2008         Last updated: 06 September 2009
599         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
600  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
601    
602    
603  PCREMATCHING(3)                                                PCREMATCHING(3)  PCREMATCHING(3)                                                PCREMATCHING(3)
604    
605    
# Line 684  THE ALTERNATIVE MATCHING ALGORITHM Line 701  THE ALTERNATIVE MATCHING ALGORITHM
701         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
702         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
703    
704           Although the general principle of this matching algorithm  is  that  it
705           scans  the subject string only once, without backtracking, there is one
706           exception: when a lookbehind assertion is  encountered,  the  preceding
707           characters have to be re-inspected.
708    
709         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
710         supported by the alternative matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
711    
712         1.  Because  the  algorithm  finds  all possible matches, the greedy or         1. Because the algorithm finds all  possible  matches,  the  greedy  or
713         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
714         ungreedy quantifiers are treated in exactly the same way. However, pos-         ungreedy quantifiers are treated in exactly the same way. However, pos-
715         sessive quantifiers can make a difference when what follows could  also         sessive  quantifiers can make a difference when what follows could also
716         match what is quantified, for example in a pattern like this:         match what is quantified, for example in a pattern like this:
717    
718           ^a++\w!           ^a++\w!
719    
720         This  pattern matches "aaab!" but not "aaa!", which would be matched by         This pattern matches "aaab!" but not "aaa!", which would be matched  by
721         a non-possessive quantifier. Similarly, if an atomic group is  present,         a  non-possessive quantifier. Similarly, if an atomic group is present,
722         it  is matched as if it were a standalone pattern at the current point,         it is matched as if it were a standalone pattern at the current  point,
723         and the longest match is then "locked in" for the rest of  the  overall         and  the  longest match is then "locked in" for the rest of the overall
724         pattern.         pattern.
725    
726         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
727         is not straightforward to keep track of  captured  substrings  for  the         is  not  straightforward  to  keep track of captured substrings for the
728         different  matching  possibilities,  and  PCRE's implementation of this         different matching possibilities, and  PCRE's  implementation  of  this
729         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
730         strings are available.         strings are available.
731    
732         3.  Because no substrings are captured, back references within the pat-         3. Because no substrings are captured, back references within the  pat-
733         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
734    
735         4. For the same reason, conditional expressions that use  a  backrefer-         4.  For  the same reason, conditional expressions that use a backrefer-
736         ence  as  the  condition or test for a specific group recursion are not         ence as the condition or test for a specific group  recursion  are  not
737         supported.         supported.
738    
739         5. Because many paths through the tree may be  active,  the  \K  escape         5.  Because  many  paths  through the tree may be active, the \K escape
740         sequence, which resets the start of the match when encountered (but may         sequence, which resets the start of the match when encountered (but may
741         be on some paths and not on others), is not  supported.  It  causes  an         be  on  some  paths  and not on others), is not supported. It causes an
742         error if encountered.         error if encountered.
743    
744         6.  Callouts  are  supported, but the value of the capture_top field is         6. Callouts are supported, but the value of the  capture_top  field  is
745         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
746    
747         7. The \C escape sequence, which (in the standard algorithm) matches  a         7.  The \C escape sequence, which (in the standard algorithm) matches a
748         single  byte, even in UTF-8 mode, is not supported because the alterna-         single byte, even in UTF-8 mode, is not supported because the  alterna-
749         tive algorithm moves through the subject  string  one  character  at  a         tive  algorithm  moves  through  the  subject string one character at a
750         time, for all active paths through the tree.         time, for all active paths through the tree.
751    
752         8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)         8. Except for (*FAIL), the backtracking control verbs such as  (*PRUNE)
753         are not supported. (*FAIL) is supported, and  behaves  like  a  failing         are  not  supported.  (*FAIL)  is supported, and behaves like a failing
754         negative assertion.         negative assertion.
755    
756    
757  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
758    
759         Using  the alternative matching algorithm provides the following advan-         Using the alternative matching algorithm provides the following  advan-
760         tages:         tages:
761    
762         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
763         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
764         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
765         things with callouts.         things with callouts.
766    
767         2.  There is much better support for partial matching. The restrictions         2. Because the alternative algorithm  scans  the  subject  string  just
768         on the content of the pattern that apply when using the standard  algo-         once,  and  never  needs to backtrack, it is possible to pass very long
769         rithm  for  partial matching do not apply to the alternative algorithm.         subject strings to the matching function in  several  pieces,  checking
        For non-anchored patterns, the starting position of a partial match  is  
        available.  
   
        3.  Because  the  alternative  algorithm  scans the subject string just  
        once, and never needs to backtrack, it is possible to  pass  very  long  
        subject  strings  to  the matching function in several pieces, checking  
770         for partial matching each time.         for partial matching each time.
771    
772    
# Line 758  DISADVANTAGES OF THE ALTERNATIVE ALGORIT Line 774  DISADVANTAGES OF THE ALTERNATIVE ALGORIT
774    
775         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
776    
777         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
778         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
779         because it is less susceptible to optimization.         because it is less susceptible to optimization.
780    
781         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 777  AUTHOR Line 793  AUTHOR
793    
794  REVISION  REVISION
795    
796         Last updated: 19 April 2008         Last updated: 05 September 2009
797         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
798  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
799    
800    
801  PCREAPI(3)                                                          PCREAPI(3)  PCREAPI(3)                                                          PCREAPI(3)
802    
803    
# Line 889  PCRE API OVERVIEW Line 905  PCRE API OVERVIEW
905         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
906         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
907         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
908         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
909         compile and run it.         pcredemo documentation, and the pcresample documentation describes  how
910           to compile and run it.
911    
912         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
913         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
914         ing. The alternative algorithm finds all possible matches (at  a  given         ing.  The  alternative algorithm finds all possible matches (at a given
915         point  in  the subject), and scans the subject just once. However, this         point in the subject), and scans the subject just  once  (unless  there
916         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
917         matching  algorithms and their advantages and disadvantages is given in         captured substrings. A description of the two matching  algorithms  and
918         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
919           mentation.
920    
921         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
922         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 999  MULTITHREADING Line 1017  MULTITHREADING
1017         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
1018         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1019    
1020         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
1021         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
1022         at once.         at once.
1023    
# Line 1007  MULTITHREADING Line 1025  MULTITHREADING
1025  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
1026    
1027         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
1028         later  time,  possibly by a different program, and even on a host other         later time, possibly by a different program, and even on a  host  other
1029         than the one on which  it  was  compiled.  Details  are  given  in  the         than  the  one  on  which  it  was  compiled.  Details are given in the
1030         pcreprecompile  documentation.  However, compiling a regular expression         pcreprecompile documentation. However, compiling a  regular  expression
1031         with one version of PCRE for use with a different version is not  guar-         with  one version of PCRE for use with a different version is not guar-
1032         anteed to work and may cause crashes.         anteed to work and may cause crashes.
1033    
1034    
# Line 1018  CHECKING BUILD-TIME OPTIONS Line 1036  CHECKING BUILD-TIME OPTIONS
1036    
1037         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1038    
1039         The  function pcre_config() makes it possible for a PCRE client to dis-         The function pcre_config() makes it possible for a PCRE client to  dis-
1040         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1041         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
1042         tures.         tures.
1043    
1044         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
1045         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1046         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
1047         available:         available:
1048    
1049           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1050    
1051         The  output is an integer that is set to one if UTF-8 support is avail-         The output is an integer that is set to one if UTF-8 support is  avail-
1052         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1053    
1054           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1055    
1056         The output is an integer that is set to  one  if  support  for  Unicode         The  output  is  an  integer  that is set to one if support for Unicode
1057         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1058    
1059           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1060    
1061         The  output  is  an integer whose value specifies the default character         The output is an integer whose value specifies  the  default  character
1062         sequence that is recognized as meaning "newline". The four values  that         sequence  that is recognized as meaning "newline". The four values that
1063         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,
1064         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
1065         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1066           spond to the standard sequence for your operating system.
1067    
1068           PCRE_CONFIG_BSR           PCRE_CONFIG_BSR
1069    
# Line 1071  CHECKING BUILD-TIME OPTIONS Line 1090  CHECKING BUILD-TIME OPTIONS
1090    
1091           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1092    
1093         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-
1094         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1095         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1096    
1097           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1098    
1099         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
1100         recursion  when calling the internal matching function in a pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1101         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1102           below.
1103    
1104           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1105    
1106         The output is an integer that is set to one if internal recursion  when         The  output is an integer that is set to one if internal recursion when
1107         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1108         the stack to remember their state. This is the usual way that  PCRE  is         the  stack  to remember their state. This is the usual way that PCRE is
1109         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1110         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1111         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1112         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1113    
1114    
# Line 1105  COMPILING A PATTERN Line 1125  COMPILING A PATTERN
1125    
1126         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1127         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1128         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1129         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1130    
1131         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1132         the pattern argument. A pointer to a single block  of  memory  that  is         the  pattern  argument.  A  pointer to a single block of memory that is
1133         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1134         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1135         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1136         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1137         longer required.         longer required.
1138    
1139         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although the compiled code of a PCRE regex is relocatable, that is,  it
1140         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1141         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1142         ment, which is an address (see below).         ment, which is an address (see below).
1143    
1144         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1145         pilation.  It  should be zero if no options are required. The available         pilation. It should be zero if no options are required.  The  available
1146         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1147         are  compatible  with  Perl,  can also be set and unset from within the         are compatible with Perl, but also some others) can  also  be  set  and
1148         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1149         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1150         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1151         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time         specifies their initial settings at the start of compilation and execu-
1152         of matching as well as at compile time.         tion.  The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at the
1153           time of matching as well as at compile time.
1154    
1155         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1156         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
# Line 1335  COMPILING A PATTERN Line 1356  COMPILING A PATTERN
1356         and are therefore ignored.         and are therefore ignored.
1357    
1358         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
1359         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.
1360    
1361           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1362    
1363         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1364         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1365         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1366         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1367         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1368    
1369           PCRE_UNGREEDY           PCRE_UNGREEDY
1370    
1371         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1372         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1373         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1374         within the pattern.         within the pattern.
1375    
1376           PCRE_UTF8           PCRE_UTF8
1377    
1378         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1379         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1380         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1381         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1382         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1383         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1384    
1385           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1386    
1387         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
1388         automatically  checked.  There  is  a  discussion about the validity of         automatically checked. There is a  discussion  about  the  validity  of
1389         UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1390         bytes  is  found,  pcre_compile() returns an error. If you already know         bytes is found, pcre_compile() returns an error. If  you  already  know
1391         that your pattern is valid, and you want to skip this check for perfor-         that your pattern is valid, and you want to skip this check for perfor-
1392         mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1393         set, the effect of passing an invalid UTF-8  string  as  a  pattern  is         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1394         undefined.  It  may  cause your program to crash. Note that this option         undefined. It may cause your program to crash. Note  that  this  option
1395         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1396         UTF-8 validity checking of subject strings.         UTF-8 validity checking of subject strings.
1397    
1398    
1399  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1400    
1401         The  following  table  lists  the  error  codes than may be returned by         The following table lists the error  codes  than  may  be  returned  by
1402         pcre_compile2(), along with the error messages that may be returned  by         pcre_compile2(),  along with the error messages that may be returned by
1403         both  compiling functions. As PCRE has developed, some error codes have         both compiling functions. As PCRE has developed, some error codes  have
1404         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.
1405    
1406            0  no error            0  no error
# Line 1435  COMPILATION ERROR CODES Line 1456  COMPILATION ERROR CODES
1456           50  [this code is not in use]           50  [this code is not in use]
1457           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1458           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1459           53  internal  error:  previously-checked  referenced  subpattern  not           53   internal  error:  previously-checked  referenced  subpattern not
1460         found         found
1461           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1462           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
# Line 1450  COMPILATION ERROR CODES Line 1471  COMPILATION ERROR CODES
1471           63  digit expected after (?+           63  digit expected after (?+
1472           64  ] is an invalid data character in JavaScript compatibility mode           64  ] is an invalid data character in JavaScript compatibility mode
1473    
1474         The  numbers  32  and 10000 in errors 48 and 49 are defaults; different         The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
1475         values may be used if the limits were changed when PCRE was built.         values may be used if the limits were changed when PCRE was built.
1476    
1477    
# Line 1459  STUDYING A PATTERN Line 1480  STUDYING A PATTERN
1480         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1481              const char **errptr);              const char **errptr);
1482    
1483         If a compiled pattern is going to be used several times,  it  is  worth         If  a  compiled  pattern is going to be used several times, it is worth
1484         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1485         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1486         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1487         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1488         pointer  to a pcre_extra block, in which the study_data field points to         pointer to a pcre_extra block, in which the study_data field points  to
1489         the results of the study.         the results of the study.
1490    
1491         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1492         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec(). However, a pcre_extra block  also  contains  other  fields
1493         that can be set by the caller before the block  is  passed;  these  are         that  can  be  set  by the caller before the block is passed; these are
1494         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1495    
1496         If  studying  the  pattern  does not produce any additional information         If studying the pattern does not  produce  any  additional  information
1497         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1498         wants  to  pass  any of the other fields to pcre_exec(), it must set up         wants to pass any of the other fields to pcre_exec(), it  must  set  up
1499         its own pcre_extra block.         its own pcre_extra block.
1500    
1501         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1502         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1503    
1504         The  third argument for pcre_study() is a pointer for an error message.         The third argument for pcre_study() is a pointer for an error  message.
1505         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1506         points  to  is  set  to NULL. Otherwise it is set to point to a textual         points to is set to NULL. Otherwise it is set to  point  to  a  textual
1507         error message. This is a static string that is part of the library. You         error message. This is a static string that is part of the library. You
1508         must  not  try  to  free it. You should test the error pointer for NULL         must not try to free it. You should test the  error  pointer  for  NULL
1509         after calling pcre_study(), to be sure that it has run successfully.         after calling pcre_study(), to be sure that it has run successfully.
1510    
1511         This is a typical call to pcre_study():         This is a typical call to pcre_study():
# Line 1496  STUDYING A PATTERN Line 1517  STUDYING A PATTERN
1517             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1518    
1519         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1520         that  do not have a single fixed starting character. A bitmap of possi-         that do not have a single fixed starting character. A bitmap of  possi-
1521         ble starting bytes is created.         ble starting bytes is created.
1522    
1523    
1524  LOCALE SUPPORT  LOCALE SUPPORT
1525    
1526         PCRE handles caseless matching, and determines whether  characters  are         PCRE  handles  caseless matching, and determines whether characters are
1527         letters,  digits, or whatever, by reference to a set of tables, indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1528         by character value. When running in UTF-8 mode, this  applies  only  to         by  character  value.  When running in UTF-8 mode, this applies only to
1529         characters  with  codes  less than 128. Higher-valued codes never match         characters with codes less than 128. Higher-valued  codes  never  match
1530         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built
1531         with  Unicode  character property support. The use of locales with Uni-         with Unicode character property support. The use of locales  with  Uni-
1532         code is discouraged. If you are handling characters with codes  greater         code  is discouraged. If you are handling characters with codes greater
1533         than  128, you should either use UTF-8 and Unicode, or use locales, but         than 128, you should either use UTF-8 and Unicode, or use locales,  but
1534         not try to mix the two.         not try to mix the two.
1535    
1536         PCRE contains an internal set of tables that are used  when  the  final         PCRE  contains  an  internal set of tables that are used when the final
1537         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1538         applications.  Normally, the internal tables recognize only ASCII char-         applications.  Normally, the internal tables recognize only ASCII char-
1539         acters. However, when PCRE is built, it is possible to cause the inter-         acters. However, when PCRE is built, it is possible to cause the inter-
1540         nal tables to be rebuilt in the default "C" locale of the local system,         nal tables to be rebuilt in the default "C" locale of the local system,
1541         which may cause them to be different.         which may cause them to be different.
1542    
1543         The  internal tables can always be overridden by tables supplied by the         The internal tables can always be overridden by tables supplied by  the
1544         application that calls PCRE. These may be created in a different locale         application that calls PCRE. These may be created in a different locale
1545         from  the  default.  As more and more applications change to using Uni-         from the default. As more and more applications change  to  using  Uni-
1546         code, the need for this locale support is expected to die away.         code, the need for this locale support is expected to die away.
1547    
1548         External tables are built by calling  the  pcre_maketables()  function,         External  tables  are  built by calling the pcre_maketables() function,
1549         which  has no arguments, in the relevant locale. The result can then be         which has no arguments, in the relevant locale. The result can then  be
1550         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1551         example,  to  build  and use tables that are appropriate for the French         example, to build and use tables that are appropriate  for  the  French
1552         locale (where accented characters with  values  greater  than  128  are         locale  (where  accented  characters  with  values greater than 128 are
1553         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1554    
1555           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1556           tables = pcre_maketables();           tables = pcre_maketables();
1557           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1558    
1559         The  locale  name "fr_FR" is used on Linux and other Unix-like systems;         The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
1560         if you are using Windows, the name for the French locale is "french".         if you are using Windows, the name for the French locale is "french".
1561    
1562         When pcre_maketables() runs, the tables are built  in  memory  that  is         When  pcre_maketables()  runs,  the  tables are built in memory that is
1563         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1564         that the memory containing the tables remains available for as long  as         that  the memory containing the tables remains available for as long as
1565         it is needed.         it is needed.
1566    
1567         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1568         pattern, and the same tables are used via this pointer by  pcre_study()         pattern,  and the same tables are used via this pointer by pcre_study()
1569         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1570         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1571         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1572    
1573         It  is  possible to pass a table pointer or NULL (indicating the use of         It is possible to pass a table pointer or NULL (indicating the  use  of
1574         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1575         purpose,  this facility could be used to match a pattern in a different         purpose, this facility could be used to match a pattern in a  different
1576         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1577         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1578    
# Line 1561  INFORMATION ABOUT A PATTERN Line 1582  INFORMATION ABOUT A PATTERN
1582         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1583              int what, void *where);              int what, void *where);
1584    
1585         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1586         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1587         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1588    
1589         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1590         pattern. The second argument is the result of pcre_study(), or NULL  if         pattern.  The second argument is the result of pcre_study(), or NULL if
1591         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1592         of information is required, and the fourth argument is a pointer  to  a         of  information  is required, and the fourth argument is a pointer to a
1593         variable  to  receive  the  data. The yield of the function is zero for         variable to receive the data. The yield of the  function  is  zero  for
1594         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1595    
1596           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1577  INFORMATION ABOUT A PATTERN Line 1598  INFORMATION ABOUT A PATTERN
1598           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1599           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1600    
1601         The "magic number" is placed at the start of each compiled  pattern  as         The  "magic  number" is placed at the start of each compiled pattern as
1602         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1603         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1604         pattern:         pattern:
1605    
1606           int rc;           int rc;
# Line 1590  INFORMATION ABOUT A PATTERN Line 1611  INFORMATION ABOUT A PATTERN
1611             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1612             &length);         /* where to put the data */             &length);         /* where to put the data */
1613    
1614         The  possible  values for the third argument are defined in pcre.h, and         The possible values for the third argument are defined in  pcre.h,  and
1615         are as follows:         are as follows:
1616    
1617           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1618    
1619         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1620         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1621         there are no back references.         there are no back references.
1622    
1623           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1624    
1625         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1626         argument should point to an int variable.         argument should point to an int variable.
1627    
1628           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1629    
1630         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1631         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1632         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1633         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1634         passing a NULL table pointer.         passing a NULL table pointer.
1635    
1636           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1637    
1638         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1639         non-anchored pattern. The fourth argument should point to an int  vari-         non-anchored  pattern. The fourth argument should point to an int vari-
1640         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1641         is still recognized for backwards compatibility.)         is still recognized for backwards compatibility.)
1642    
1643         If there is a fixed first byte, for example, from  a  pattern  such  as         If  there  is  a  fixed first byte, for example, from a pattern such as
1644         (cat|cow|coyote), its value is returned. Otherwise, if either         (cat|cow|coyote), its value is returned. Otherwise, if either
1645    
1646         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1647         branch starts with "^", or         branch starts with "^", or
1648    
1649         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1650         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1651    
1652         -1  is  returned, indicating that the pattern matches only at the start         -1 is returned, indicating that the pattern matches only at  the  start
1653         of a subject string or after any newline within the  string.  Otherwise         of  a  subject string or after any newline within the string. Otherwise
1654         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1655    
1656           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1657    
1658         If  the pattern was studied, and this resulted in the construction of a         If the pattern was studied, and this resulted in the construction of  a
1659         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1660         matching  string, a pointer to the table is returned. Otherwise NULL is         matching string, a pointer to the table is returned. Otherwise NULL  is
1661         returned. The fourth argument should point to an unsigned char *  vari-         returned.  The fourth argument should point to an unsigned char * vari-
1662         able.         able.
1663    
1664           PCRE_INFO_HASCRORLF           PCRE_INFO_HASCRORLF
1665    
1666         Return  1  if  the  pattern  contains any explicit matches for CR or LF         Return 1 if the pattern contains any explicit  matches  for  CR  or  LF
1667         characters, otherwise 0. The fourth argument should  point  to  an  int         characters,  otherwise  0.  The  fourth argument should point to an int
1668         variable.  An explicit match is either a literal CR or LF character, or         variable. An explicit match is either a literal CR or LF character,  or
1669         \r or \n.         \r or \n.
1670    
1671           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1672    
1673         Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,         Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
1674         otherwise  0. The fourth argument should point to an int variable. (?J)         otherwise 0. The fourth argument should point to an int variable.  (?J)
1675         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1676    
1677           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1678    
1679         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
1680         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
1681         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1682         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
1683         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1684         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
1685         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1686    
# Line 1667  INFORMATION ABOUT A PATTERN Line 1688  INFORMATION ABOUT A PATTERN
1688           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1689           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1690    
1691         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1692         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1693         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1694         pcre_get_named_substring()  are  provided  for extracting captured sub-         pcre_get_named_substring() are provided for  extracting  captured  sub-
1695         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
1696         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
1697         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1698         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
1699         described by these three values.         described by these three values.
1700    
1701         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
1702         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1703         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
1704         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1705         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
1706         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-
1707         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-
1708         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1709         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-
1710         theses  numbers.  For  example,  consider the following pattern (assume         theses numbers. For example, consider  the  following  pattern  (assume
1711         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1712         ignored):         ignored):
1713    
1714           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1715           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1716    
1717         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1718         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,
1719         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1720         as ??:         as ??:
1721    
# Line 1703  INFORMATION ABOUT A PATTERN Line 1724  INFORMATION ABOUT A PATTERN
1724           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1725           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1726    
1727         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1728         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
1729         to be different for each compiled pattern.         to be different for each compiled pattern.
1730    
1731           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1732    
1733         Return 1 if the pattern can be used for partial matching, otherwise  0.         Return  1  if  the  pattern  can  be  used  for  partial  matching with
1734         The  fourth  argument  should point to an int variable. The pcrepartial         pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1735         documentation lists the restrictions that apply to patterns  when  par-         variable.  From  release  8.00,  this  always  returns  1,  because the
1736         tial matching is used.         restrictions that previously applied  to  partial  matching  have  been
1737           lifted.  The  pcrepartial documentation gives details of partial match-
1738           ing.
1739    
1740           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1741    
1742         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
1743         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1744         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1745         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
1746         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
1747         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
1748         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1749         and PCRE_EXTENDED.         and PCRE_EXTENDED.
1750    
1751         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
1752         alternatives begin with one of the following:         alternatives begin with one of the following:
1753    
1754           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1739  INFORMATION ABOUT A PATTERN Line 1762  INFORMATION ABOUT A PATTERN
1762    
1763           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1764    
1765         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
1766         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
1767         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
1768         size_t variable.         size_t variable.
# Line 1747  INFORMATION ABOUT A PATTERN Line 1770  INFORMATION ABOUT A PATTERN
1770           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1771    
1772         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
1773         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
1774         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
1775         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
1776         variable.         variable.
1777    
1778    
# Line 1757  OBSOLETE INFO FUNCTION Line 1780  OBSOLETE INFO FUNCTION
1780    
1781         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1782    
1783         The  pcre_info()  function is now obsolete because its interface is too         The pcre_info() function is now obsolete because its interface  is  too
1784         restrictive to return all the available data about a compiled  pattern.         restrictive  to return all the available data about a compiled pattern.
1785         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1786         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-
1787         lowing negative numbers:         lowing negative numbers:
1788    
1789           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1790           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1791    
1792         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
1793         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
1794         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1795    
1796         If  the  pattern  is  not anchored and the firstcharptr argument is not         If the pattern is not anchored and the  firstcharptr  argument  is  not
1797         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
1798         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1799    
1800    
# Line 1779  REFERENCE COUNTS Line 1802  REFERENCE COUNTS
1802    
1803         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1804    
1805         The  pcre_refcount()  function is used to maintain a reference count in         The pcre_refcount() function is used to maintain a reference  count  in
1806         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
1807         benefit  of  applications  that  operate  in an object-oriented manner,         benefit of applications that  operate  in  an  object-oriented  manner,
1808         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1809         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.
1810    
1811         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1812         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
1813         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
1814         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
1815         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
1816         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1817    
1818         Except when it is zero, the reference count is not correctly  preserved         Except  when it is zero, the reference count is not correctly preserved
1819         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
1820         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1821    
1822    
# Line 1887  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1910  MATCHING A PATTERN: THE TRADITIONAL FUNC
1910         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-
1911         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.
1912    
1913         Limiting  the  recursion  depth  limits the amount of stack that can be         Limiting the recursion depth limits the amount of  stack  that  can  be
1914         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
1915         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1916    
1917         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
1918         built; the default default  is  the  same  value  as  the  default  for         built;  the  default  default  is  the  same  value  as the default for
1919         match_limit.  You can override the default by suppling pcre_exec() with         match_limit. You can override the default by suppling pcre_exec()  with
1920         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1921         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
1922         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1923    
1924         The pcre_callout field is used in conjunction with the  "callout"  fea-         The  callout_data  field is used in conjunction with the "callout" fea-
1925         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
1926    
1927         The  tables  field  is  used  to  pass  a  character  tables pointer to         The tables field  is  used  to  pass  a  character  tables  pointer  to
1928         pcre_exec(); this overrides the value that is stored with the  compiled         pcre_exec();  this overrides the value that is stored with the compiled
1929         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
1930         custom tables were supplied to pcre_compile() via  its  tableptr  argu-         custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1931         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
1932         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-
1933         using  patterns  that  have been saved after compiling with an external         using patterns that have been saved after compiling  with  an  external
1934         set of tables, because the external tables  might  be  at  a  different         set  of  tables,  because  the  external tables might be at a different
1935         address  when  pcre_exec() is called. See the pcreprecompile documenta-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
1936         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1937    
1938     Option bits for pcre_exec()     Option bits for pcre_exec()
1939    
1940         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.
1941         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,
1942         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
1943         PCRE_PARTIAL.         PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
1944           PCRE_PARTIAL_HARD.
1945    
1946           PCRE_ANCHORED           PCRE_ANCHORED
1947    
# Line 1997  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2021  MATCHING A PATTERN: THE TRADITIONAL FUNC
2021    
2022           a?b?           a?b?
2023    
2024         is applied to a string not beginning with "a" or "b",  it  matches  the         is applied to a string not beginning with "a" or  "b",  it  matches  an
2025         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2026         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
2027         rences of "a" or "b".         rences of "a" or "b".
2028    
2029         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2030         cial case of a pattern match of the empty  string  within  its  split()  
2031         function,  and  when  using  the /g modifier. It is possible to emulate         This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2032         Perl's behaviour after matching a null string by first trying the match         not at the start of  the  subject  is  permitted.  If  the  pattern  is
2033         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         anchored, such a match can occur only if the pattern contains \K.
2034         if that fails by advancing the starting offset (see below)  and  trying  
2035         an ordinary match again. There is some code that demonstrates how to do         Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2036         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2037           match  of  the empty string within its split() function, and when using
2038           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2039           matching a null string by first trying the match again at the same off-
2040           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2041           fails, by advancing the starting offset (see below) and trying an ordi-
2042           nary match again. There is some code that demonstrates how to  do  this
2043           in the pcredemo sample program.
2044    
2045             PCRE_NO_START_OPTIMIZE
2046    
2047           There  are a number of optimizations that pcre_exec() uses at the start
2048           of a match, in order to speed up the process. For  example,  if  it  is
2049           known  that  a  match must start with a specific character, it searches
2050           the subject for that character, and fails immediately if it cannot find
2051           it,  without actually running the main matching function. When callouts
2052           are in use, these optimizations can cause  them  to  be  skipped.  This
2053           option  disables  the  "start-up" optimizations, causing performance to
2054           suffer, but ensuring that the callouts do occur.
2055    
2056           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2057    
# Line 2033  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2075  MATCHING A PATTERN: THE TRADITIONAL FUNC
2075         value  of startoffset that does not point to the start of a UTF-8 char-         value  of startoffset that does not point to the start of a UTF-8 char-
2076         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2077    
2078           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2079             PCRE_PARTIAL_SOFT
2080    
2081         This option turns on the  partial  matching  feature.  If  the  subject         These options turn on the partial matching feature. For backwards  com-
2082         string  fails to match the pattern, but at some point during the match-         patibility,  PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial
2083         ing process the end of the subject was reached (that  is,  the  subject         match occurs if the end of the subject string is reached  successfully,
2084         partially  matches  the  pattern and the failure to match occurred only         but  there  are not enough subject characters to complete the match. If
2085         because there were not enough subject characters), pcre_exec()  returns         this happens when PCRE_PARTIAL_HARD  is  set,  pcre_exec()  immediately
2086         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         returns  PCRE_ERROR_PARTIAL.  Otherwise,  if  PCRE_PARTIAL_SOFT is set,
2087         used, there are restrictions on what may appear in the  pattern.  These         matching continues by testing any other alternatives. Only if they  all
2088         are discussed in the pcrepartial documentation.         fail  is  PCRE_ERROR_PARTIAL  returned (instead of PCRE_ERROR_NOMATCH).
2089           The portion of the string that was inspected when the partial match was
2090           found  is  set  as  the first matching string. There is a more detailed
2091           discussion in the pcrepartial documentation.
2092    
2093     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2094    
2095         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
2096         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.
2097         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-
2098         Unlike the pattern string, the subject may contain binary  zero  bytes.         acter.  Unlike  the pattern string, the subject may contain binary zero
2099         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
2100         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
2101           case.
2102    
2103         A non-zero starting offset is useful when searching for  another  match         A non-zero starting offset is useful when searching for  another  match
2104         in  the same subject by calling pcre_exec() again after a previous suc-         in  the same subject by calling pcre_exec() again after a previous suc-
# Line 2087  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2134  MATCHING A PATTERN: THE TRADITIONAL FUNC
2134         string.  PCRE  supports several other kinds of parenthesized subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2135         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2136    
2137         Captured substrings are returned to the caller via a vector of  integer         Captured substrings are returned to the caller via a vector of integers
2138         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-
2139         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:
2140         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2141    
2142         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-
2143         strings, each substring using a pair of integers. The  remaining  third         strings, each substring using a pair of integers. The  remaining  third
2144         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-
2145         turing subpatterns, and is not available for passing back  information.         turing subpatterns, and is not available for passing back  information.
2146         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
2147         it is not, it is rounded down.         it is not, it is rounded down.
2148    
2149         When a match is successful, information about  captured  substrings  is         When a match is successful, information about  captured  substrings  is
2150         returned  in  pairs  of integers, starting at the beginning of ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2151         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
2152         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
2153         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
2154         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
2155         tor[1], identify the portion of  the  subject  string  matched  by  the         byte offsets, even in UTF-8 mode. They are not character counts.
2156         entire  pattern.  The next pair is used for the first capturing subpat-  
2157         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
2158         highest numbered pair that has been set. For example, if two substrings         portion  of  the subject string matched by the entire pattern. The next
2159         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
2160         subpatterns,  the return value from a successful match is 1, indicating         returned by pcre_exec() is one more than the highest numbered pair that
2161         that just the first pair of offsets has been set.         has been set.  For example, if two substrings have been  captured,  the
2162           returned  value is 3. If there are no capturing subpatterns, the return
2163           value from a successful match is 1, indicating that just the first pair
2164           of offsets has been set.
2165    
2166         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2167         of the string that it matched that is returned.         of the string that it matched that is returned.
2168    
2169         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,
2170         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
2171         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
2172         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
2173         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize as zero. However, if the pattern contains back references  and
2174         references and the ovector is not big enough to  remember  the  related         the  ovector is not big enough to remember the related substrings, PCRE
2175         substrings,  PCRE has to get additional memory for use during matching.         has to get additional memory for use during matching. Thus it  is  usu-
2176         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2177    
2178         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
2179         subpatterns  there  are  in  a  compiled pattern. The smallest size for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2180         ovector that will allow for n captured substrings, in addition  to  the         ovector  that  will allow for n captured substrings, in addition to the
2181         offsets of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
2182    
2183         It  is  possible for capturing subpattern number n+1 to match some part         It is possible for capturing subpattern number n+1 to match  some  part
2184         of the subject when subpattern n has not been used at all. For example,         of the subject when subpattern n has not been used at all. For example,
2185         if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the         if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2186         return from the function is 4, and subpatterns 1 and 3 are matched, but         return from the function is 4, and subpatterns 1 and 3 are matched, but
2187         2  is  not.  When  this happens, both values in the offset pairs corre-         2 is not. When this happens, both values in  the  offset  pairs  corre-
2188         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2189    
2190         Offset values that correspond to unused subpatterns at the end  of  the         Offset  values  that correspond to unused subpatterns at the end of the
2191         expression  are  also  set  to  -1. For example, if the string "abc" is         expression are also set to -1. For example,  if  the  string  "abc"  is
2192         matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not         matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2193         matched.  The  return  from the function is 2, because the highest used         matched. The return from the function is 2, because  the  highest  used
2194         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2195         for  the  second  and third capturing subpatterns if you wish (assuming         for the second and third capturing subpatterns if  you  wish  (assuming
2196         the vector is large enough, of course).         the vector is large enough, of course).
2197    
2198         Some convenience functions are provided  for  extracting  the  captured         Some  convenience  functions  are  provided for extracting the captured
2199         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2200    
2201     Error return values from pcre_exec()     Error return values from pcre_exec()
2202    
2203         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
2204         defined in the header file:         defined in the header file:
2205    
2206           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 2159  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2209  MATCHING A PATTERN: THE TRADITIONAL FUNC
2209    
2210           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2211    
2212         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2213         ovecsize was not zero.         ovecsize was not zero.
2214    
2215           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 2168  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2218  MATCHING A PATTERN: THE TRADITIONAL FUNC
2218    
2219           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2220    
2221         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2222         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
2223         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
2224         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2225         gives when the magic number is not present.         gives when the magic number is not present.
2226    
2227           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2228    
2229         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2230         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2231         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2232    
2233           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2234    
2235         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2236         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2237         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
2238         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2239         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2240    
2241           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2242    
2243         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2244         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2245         returned by pcre_exec().         returned by pcre_exec().
2246    
2247           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2248    
2249         The  backtracking  limit,  as  specified  by the match_limit field in a         The backtracking limit, as specified by  the  match_limit  field  in  a
2250         pcre_extra structure (or defaulted) was reached.  See  the  description         pcre_extra  structure  (or  defaulted) was reached. See the description
2251         above.         above.
2252    
2253           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2254    
2255         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
2256         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2257         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2258    
2259           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2260    
2261         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
2262         subject.         subject.
2263    
2264           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2265    
2266         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2267         value  of startoffset did not point to the beginning of a UTF-8 charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2268         ter.         ter.
2269    
2270           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2271    
2272         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
2273         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2274    
2275           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2276    
2277         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This code is no longer in  use.  It  was  formerly  returned  when  the
2278         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL  option  was used with a compiled pattern containing items
2279         documentation for details of partial matching.         that were  not  supported  for  partial  matching.  From  release  8.00
2280           onwards, there are no restrictions on partial matching.
2281    
2282           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2283    
# Line 2235  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2286  MATCHING A PATTERN: THE TRADITIONAL FUNC
2286    
2287           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2288    
2289         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.
2290    
2291           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2292    
2293         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2294         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2295         description above.         description above.
2296    
2297           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
# Line 2263  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2314  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2314         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2315              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2316    
2317         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2318         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2319         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2320         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2321         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2322         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2323         substrings.         substrings.
2324    
2325         A  substring that contains a binary zero is correctly extracted and has         A substring that contains a binary zero is correctly extracted and  has
2326         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
2327         string.   However,  you  can  process such a string by referring to the         string.  However, you can process such a string  by  referring  to  the
2328         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2329         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2330         not adequate for handling strings containing binary zeros, because  the         not  adequate for handling strings containing binary zeros, because the
2331         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2332    
2333         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-
2334         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2335         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
2336         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2337         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2338         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2339         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2340         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
2341         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2342    
2343         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2344         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2345         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2346         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2347         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2348         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2349         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2350         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
2351         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2352    
2353           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2354    
2355         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
2356         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2357    
2358           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2359    
2360         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2361    
2362         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2363         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
2364         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
2365         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
2366         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
2367         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
2368         error code         error code
2369    
2370           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2371    
2372         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2373    
2374         When any of these functions encounter a substring that is unset,  which         When  any of these functions encounter a substring that is unset, which
2375         can  happen  when  capturing subpattern number n+1 matches some part of         can happen when capturing subpattern number n+1 matches  some  part  of
2376         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
2377         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2378         string by inspecting the appropriate offset in ovector, which is  nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2379         tive for unset substrings.         tive for unset substrings.
2380    
2381         The  two convenience functions pcre_free_substring() and pcre_free_sub-         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2382         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
2383         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2384         tively. They do nothing more than  call  the  function  pointed  to  by         tively.  They  do  nothing  more  than  call the function pointed to by
2385         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.
2386         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-
2387         cial   interface  to  another  programming  language  that  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2388         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-
2389         vided.         vided.
2390    
2391    
# Line 2353  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2404  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2404              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2405              const char **stringptr);              const char **stringptr);
2406    
2407         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-
2408         ber.  For example, for this pattern         ber.  For example, for this pattern
2409    
2410           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2362  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2413  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2413         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
2414         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2415         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
2416         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2417         subpattern of that name.         subpattern of that name.
2418    
2419         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
2420         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2421         are also two functions that do the whole job.         are also two functions that do the whole job.
2422    
2423         Most    of    the    arguments   of   pcre_copy_named_substring()   and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2424         pcre_get_named_substring() are the same  as  those  for  the  similarly         pcre_get_named_substring()  are  the  same  as  those for the similarly
2425         named  functions  that extract by number. As these are described in the         named functions that extract by number. As these are described  in  the
2426         previous section, they are not re-described here. There  are  just  two         previous  section,  they  are not re-described here. There are just two
2427         differences:         differences:
2428    
2429         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2430         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
2431         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
2432         name-to-number translation table.         name-to-number translation table.
2433    
2434         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2435         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2436         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
2437         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2438    
2439           Warning: If the pattern uses the "(?|" feature to set up multiple  sub-
2440           patterns  with  the  same  number,  you cannot use names to distinguish
2441           them, because names are not included in the compiled code. The matching
2442           process uses only numbers.
2443    
2444    
2445  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2446    
# Line 2448  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2504  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2504         characteristics to the normal algorithm, and  is  not  compatible  with         characteristics to the normal algorithm, and  is  not  compatible  with
2505         Perl.  Some  of the features of PCRE patterns are not supported. Never-         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2506         theless, there are times when this kind of matching can be useful.  For         theless, there are times when this kind of matching can be useful.  For
2507         a discussion of the two matching algorithms, see the pcrematching docu-         a  discussion  of  the  two matching algorithms, and a list of features
2508         mentation.         that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2509           tion.
2510    
2511         The arguments for the pcre_dfa_exec() function  are  the  same  as  for         The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2512         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
2513         ent way, and this is described below. The other  common  arguments  are         ent  way,  and  this is described below. The other common arguments are
2514         used  in  the  same way as for pcre_exec(), so their description is not         used in the same way as for pcre_exec(), so their  description  is  not
2515         repeated here.         repeated here.
2516    
2517         The two additional arguments provide workspace for  the  function.  The         The  two  additional  arguments provide workspace for the function. The
2518         workspace  vector  should  contain at least 20 elements. It is used for         workspace vector should contain at least 20 elements. It  is  used  for
2519         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2520         workspace  will  be  needed for patterns and subjects where there are a         workspace will be needed for patterns and subjects where  there  are  a
2521         lot of potential matches.         lot of potential matches.
2522    
2523         Here is an example of a simple call to pcre_dfa_exec():         Here is an example of a simple call to pcre_dfa_exec():
# Line 2482  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2539  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2539    
2540     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2541    
2542         The unused bits of the options argument  for  pcre_dfa_exec()  must  be         The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2543         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-         zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2544         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2545         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_NOTEMPTY_ATSTART, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_HARD, PCRE_PAR-
2546         three of these are the same as for pcre_exec(), so their description is         TIAL_SOFT,  PCRE_DFA_SHORTEST,  and  PCRE_DFA_RESTART. All but the last
2547         not repeated here.         four of these are  exactly  the  same  as  for  pcre_exec(),  so  their
2548           description is not repeated here.
2549           PCRE_PARTIAL  
2550             PCRE_PARTIAL_HARD
2551         This  has  the  same general effect as it does for pcre_exec(), but the           PCRE_PARTIAL_SOFT
2552         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for  
2553         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into         These  have the same general effect as they do for pcre_exec(), but the
2554         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for
2555         been no complete matches, but there is still at least one matching pos-         pcre_dfa_exec(),  it  returns PCRE_ERROR_PARTIAL if the end of the sub-
2556         sibility. The portion of the string that provided the partial match  is         ject is reached and there is still at least  one  matching  possibility
2557         set as the first matching string.         that requires additional characters. This happens even if some complete
2558           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2559           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2560           of the subject is reached, there have been  no  complete  matches,  but
2561           there  is  still  at least one matching possibility. The portion of the
2562           string that was inspected when the longest partial match was  found  is
2563           set as the first matching string in both cases.
2564    
2565           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2566    
# Line 2508  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2571  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2571    
2572           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2573    
2574         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and         When pcre_dfa_exec() returns a partial match, it is possible to call it
2575         returns  a  partial  match, it is possible to call it again, with addi-         again,  with  additional  subject characters, and have it continue with
2576         tional subject characters, and have it continue with  the  same  match.         the same match. The PCRE_DFA_RESTART option requests this action;  when
2577         The  PCRE_DFA_RESTART  option requests this action; when it is set, the         it  is  set,  the workspace and wscount options must reference the same
2578         workspace and wscount options must reference the same vector as  before         vector as before because data about the match so far is  left  in  them
2579         because  data  about  the  match so far is left in them after a partial         after a partial match. There is more discussion of this facility in the
2580         match. There is more discussion of this  facility  in  the  pcrepartial         pcrepartial documentation.
        documentation.  
2581    
2582     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2583    
2584         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2585         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2586         of  the  function  start  at the same point in the subject. The shorter         of the function start at the same point in  the  subject.  The  shorter
2587         matches are all initial substrings of the longer matches. For  example,         matches  are all initial substrings of the longer matches. For example,
2588         if the pattern         if the pattern
2589    
2590           <.*>           <.*>
# Line 2537  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2599  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2599           <something> <something else>           <something> <something else>
2600           <something> <something else> <something further>           <something> <something else> <something further>
2601    
2602         On  success,  the  yield of the function is a number greater than zero,         On success, the yield of the function is a number  greater  than  zero,
2603         which is the number of matched substrings.  The  substrings  themselves         which  is  the  number of matched substrings. The substrings themselves
2604         are  returned  in  ovector. Each string uses two elements; the first is         are returned in ovector. Each string uses two elements;  the  first  is
2605         the offset to the start, and the second is the offset to  the  end.  In         the  offset  to  the start, and the second is the offset to the end. In
2606         fact,  all  the  strings  have the same start offset. (Space could have         fact, all the strings have the same start  offset.  (Space  could  have
2607         been saved by giving this only once, but it was decided to retain  some         been  saved by giving this only once, but it was decided to retain some
2608         compatibility  with  the  way pcre_exec() returns data, even though the         compatibility with the way pcre_exec() returns data,  even  though  the
2609         meaning of the strings is different.)         meaning of the strings is different.)
2610    
2611         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2612         est  matching  string is given first. If there were too many matches to         est matching string is given first. If there were too many  matches  to
2613         fit into ovector, the yield of the function is zero, and the vector  is         fit  into ovector, the yield of the function is zero, and the vector is
2614         filled with the longest matches.         filled with the longest matches.
2615    
2616     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2617    
2618         The  pcre_dfa_exec()  function returns a negative number when it fails.         The pcre_dfa_exec() function returns a negative number when  it  fails.
2619         Many of the errors are the same  as  for  pcre_exec(),  and  these  are         Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2620         described  above.   There are in addition the following errors that are         described above.  There are in addition the following errors  that  are
2621         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2622    
2623           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2624    
2625         This return is given if pcre_dfa_exec() encounters an item in the  pat-         This  return is given if pcre_dfa_exec() encounters an item in the pat-
2626         tern  that  it  does not support, for instance, the use of \C or a back         tern that it does not support, for instance, the use of \C  or  a  back
2627         reference.         reference.
2628    
2629           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2630    
2631         This return is given if pcre_dfa_exec()  encounters  a  condition  item         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2632         that  uses  a back reference for the condition, or a test for recursion         that uses a back reference for the condition, or a test  for  recursion
2633         in a specific group. These are not supported.         in a specific group. These are not supported.
2634    
2635           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2636    
2637         This return is given if pcre_dfa_exec() is called with an  extra  block         This  return  is given if pcre_dfa_exec() is called with an extra block
2638         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2639         (it is meaningless).         (it is meaningless).
2640    
2641           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2642    
2643         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2644         workspace vector.         workspace vector.
2645    
2646           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2647    
2648         When  a  recursive subpattern is processed, the matching function calls         When a recursive subpattern is processed, the matching  function  calls
2649         itself recursively, using private vectors for  ovector  and  workspace.         itself  recursively,  using  private vectors for ovector and workspace.
2650         This  error  is  given  if  the output vector is not large enough. This         This error is given if the output vector  is  not  large  enough.  This
2651         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2652    
2653    
2654  SEE ALSO  SEE ALSO
2655    
2656         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2657         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2658    
2659    
2660  AUTHOR  AUTHOR
# Line 2604  AUTHOR Line 2666  AUTHOR
2666    
2667  REVISION  REVISION
2668    
2669         Last updated: 12 April 2008         Last updated: 11 September 2009
2670         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2671  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2672    
2673    
2674  PCRECALLOUT(3)                                                  PCRECALLOUT(3)  PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2675    
2676    
# Line 2656  PCRE CALLOUTS Line 2718  PCRE CALLOUTS
2718  MISSING CALLOUTS  MISSING CALLOUTS
2719    
2720         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2721         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2722         pattern is         example, if the pattern is
2723    
2724           ab(?C4)cd           ab(?C4)cd
2725    
# Line 2666  MISSING CALLOUTS Line 2728  MISSING CALLOUTS
2728         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2729         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2730    
2731           You can disable these optimizations by passing the  PCRE_NO_START_OPTI-
2732           MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the
2733           matching process, but does ensure that callouts  such  as  the  example
2734           above are obeyed.
2735    
2736    
2737  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2738    
2739         During matching, when PCRE reaches a callout point, the external  func-         During  matching, when PCRE reaches a callout point, the external func-
2740         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
2741         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
2742         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
2743         block. This structure contains the following fields:         block. This structure contains the following fields:
2744    
2745           int          version;           int          version;
# Line 2688  THE CALLOUT INTERFACE Line 2755  THE CALLOUT INTERFACE
2755           int          pattern_position;           int          pattern_position;
2756           int          next_item_length;           int          next_item_length;
2757    
2758         The version field is an integer containing the version  number  of  the         The  version  field  is an integer containing the version number of the
2759         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
2760         version number will change again in future  if  additional  fields  are         version  number  will  change  again in future if additional fields are
2761         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.
2762    
2763         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 2775  AUTHOR Line 2842  AUTHOR
2842    
2843  REVISION  REVISION
2844    
2845         Last updated: 29 May 2007         Last updated: 15 March 2009
2846         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2847  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2848    
2849    
2850  PCRECOMPAT(3)                                                    PCRECOMPAT(3)  PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2851    
2852    
# Line 2792  DIFFERENCES BETWEEN PCRE AND PERL Line 2859  DIFFERENCES BETWEEN PCRE AND PERL
2859         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2860         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2861         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2862         some features that are expected to be in the forthcoming Perl 5.10.         some features that are in Perl 5.10.
2863    
2864         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2865         of  what  it does have are given in the section on UTF-8 support in the         of  what  it does have are given in the section on UTF-8 support in the
# Line 2824  DIFFERENCES BETWEEN PCRE AND PERL Line 2891  DIFFERENCES BETWEEN PCRE AND PERL
2891         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2892         can be tested with \p and \P are limited to the general category  prop-         can be tested with \p and \P are limited to the general category  prop-
2893         erties  such  as  Lu and Nd, script names such as Greek or Han, and the         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2894         derived properties Any and L&.         derived properties Any and L&. PCRE does  support  the  Cs  (surrogate)
2895           property,  which  Perl  does  not; the Perl documentation says "Because
2896           Perl hides the need for the user to understand the internal representa-
2897           tion  of Unicode characters, there is no need to implement the somewhat
2898           messy concept of surrogates."
2899    
2900         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2901         ters  in  between  are  treated as literals. This is slightly different         ters  in  between  are  treated as literals. This is slightly different
# Line 2844  DIFFERENCES BETWEEN PCRE AND PERL Line 2915  DIFFERENCES BETWEEN PCRE AND PERL
2915    
2916         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2917         constructions. However, there is support for recursive  patterns.  This         constructions. However, there is support for recursive  patterns.  This
2918         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE         is  not  available  in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
2919         "callout" feature allows an external function to be called during  pat-         "callout" feature allows an external function to be called during  pat-
2920         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2921    
2922         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2923         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2924         unlike Perl.         unlike  Perl. There is a discussion of an example that explains this in
2925           more detail in the section on recursion differences from  Perl  in  the
2926           pcrecompat page.
2927    
2928         10.  There are some differences that are concerned with the settings of         10.  There are some differences that are concerned with the settings of
2929         captured strings when part of  a  pattern  is  repeated.  For  example,         captured strings when part of  a  pattern  is  repeated.  For  example,
# Line 2859  DIFFERENCES BETWEEN PCRE AND PERL Line 2932  DIFFERENCES BETWEEN PCRE AND PERL
2932    
2933         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2934         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2935         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If         the forms without an argument. PCRE does not support (*MARK).
        (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-  
        ture group; this is different to Perl.  
2936    
2937         12. PCRE provides some extensions to the Perl regular expression facil-         12. PCRE provides some extensions to the Perl regular expression facil-
2938         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
# Line 2886  DIFFERENCES BETWEEN PCRE AND PERL Line 2957  DIFFERENCES BETWEEN PCRE AND PERL
2957         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2958         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
2959    
2960         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
2961         TURE options for pcre_exec() have no Perl equivalents.         and PCRE_NO_AUTO_CAPTURE options for pcre_exec() have no  Perl  equiva-
2962           lents.
2963    
2964         (g) The \R escape sequence can be restricted to match only CR,  LF,  or         (g)  The  \R escape sequence can be restricted to match only CR, LF, or
2965         CRLF by the PCRE_BSR_ANYCRLF option.         CRLF by the PCRE_BSR_ANYCRLF option.
2966    
2967         (h) The callout facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
# Line 2899  DIFFERENCES BETWEEN PCRE AND PERL Line 2971  DIFFERENCES BETWEEN PCRE AND PERL
2971         (j) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2972         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2973    
2974         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a         (k)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2975         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2976    
2977         (l)  PCRE  recognizes some special sequences such as (*CR) at the start         (l) PCRE recognizes some special sequences such as (*CR) at  the  start
2978         of a pattern that set overall options that cannot be changed within the         of a pattern that set overall options that cannot be changed within the
2979         pattern.         pattern.
2980    
# Line 2916  AUTHOR Line 2988  AUTHOR
2988    
2989  REVISION  REVISION
2990    
2991         Last updated: 11 September 2007         Last updated: 18 September 2009
2992         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2993  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2994    
2995    
2996  PCREPATTERN(3)                                                  PCREPATTERN(3)  PCREPATTERN(3)                                                  PCREPATTERN(3)
2997    
2998    
# Line 2948  PCRE REGULAR EXPRESSION DETAILS Line 3020  PCRE REGULAR EXPRESSION DETAILS
3020         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3021         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
3022         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, you must build PCRE to  include  UTF-8  support,  and  then  call
3023         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  with  the  PCRE_UTF8  option.  There  is also a special
3024         matching is mentioned in several places below. There is also a  summary         sequence that can be given at the start of a pattern:
3025         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3026         page.           (*UTF8)
3027    
3028           Starting a pattern with this sequence  is  equivalent  to  setting  the
3029           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3030           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3031           below.  There  is  also  a  summary of UTF-8 features in the section on
3032           UTF-8 support in the main pcre page.
3033    
3034         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3035         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
# Line 3055  CHARACTERS AND METACHARACTERS Line 3133  CHARACTERS AND METACHARACTERS
3133                    syntax)                    syntax)
3134           ]      terminates the character class           ]      terminates the character class
3135    
3136         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the metacharacters.
3137    
3138    
3139  BACKSLASH  BACKSLASH
3140    
3141         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3142         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
3143         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
3144         applies both inside and outside character classes.         applies both inside and outside character classes.
3145    
3146         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
3147         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
3148         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
3149         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
3150         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-
3151         slash, you write \\.         slash, you write \\.
3152    
3153         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3154         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
3155         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3156         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
3157         part of the pattern.         part of the pattern.
3158    
3159         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-
3160         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-
3161         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
3162         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
3163         tion. Note the following examples:         tion. Note the following examples:
3164    
3165           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 3091  BACKSLASH Line 3169  BACKSLASH
3169           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3170           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3171    
3172         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3173         classes.         classes.
3174    
3175     Non-printing characters     Non-printing characters
3176    
3177         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-
3178         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
3179         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3180         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3181         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is usually easier  to  use  one  of  the  following  escape
3182         sequences than the binary character it represents:         sequences than the binary character it represents:
3183    
3184           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 3114  BACKSLASH Line 3192  BACKSLASH
3192           \xhh      character with hex code hh           \xhh      character with hex code hh
3193           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3194    
3195         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,
3196         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
3197         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;
3198         becomes hex 7B.         becomes hex 7B.
3199    
3200         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
3201         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3202         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
3203         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,
3204         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3205         than the largest Unicode code point, which is 10FFFF.         than the largest Unicode code point, which is 10FFFF.
3206    
3207         If characters other than hexadecimal digits appear between \x{  and  },         If  characters  other than hexadecimal digits appear between \x{ and },
3208         or if there is no terminating }, this form of escape is not recognized.         or if there is no terminating }, this form of escape is not recognized.
3209         Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal         Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3210         escape,  with  no  following  digits, giving a character whose value is         escape, with no following digits, giving a  character  whose  value  is
3211         zero.         zero.
3212    
3213         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
3214         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-
3215         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3216    
3217         After \0 up to two further octal digits are read. If  there  are  fewer         After  \0  up  to two further octal digits are read. If there are fewer
3218         than  two  digits,  just  those  that  are  present  are used. Thus the         than two digits, just  those  that  are  present  are  used.  Thus  the
3219         sequence \0\x\07 specifies two binary zeros followed by a BEL character         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3220         (code  value 7). Make sure you supply two digits after the initial zero         (code value 7). Make sure you supply two digits after the initial  zero
3221         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3222    
3223         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
3224         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3225         its as a decimal number. If the number is less than  10,  or  if  there         its  as  a  decimal  number. If the number is less than 10, or if there
3226         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3227         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3228         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3229         of parenthesized subpatterns.         of parenthesized subpatterns.
3230    
3231         Inside a character class, or if the decimal number is  greater  than  9         Inside  a  character  class, or if the decimal number is greater than 9
3232         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3233         up to three octal digits following the backslash, and uses them to gen-         up to three octal digits following the backslash, and uses them to gen-
3234         erate  a data character. Any subsequent digits stand for themselves. In         erate a data character. Any subsequent digits stand for themselves.  In
3235         non-UTF-8 mode, the value of a character specified  in  octal  must  be         non-UTF-8  mode,  the  value  of a character specified in octal must be
3236         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For         less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3237         example:         example:
3238    
3239           \040   is another way of writing a space           \040   is another way of writing a space
# Line 3173  BACKSLASH Line 3251  BACKSLASH
3251           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3252                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3253    
3254         Note that octal values of 100 or greater must not be  introduced  by  a         Note  that  octal  values of 100 or greater must not be introduced by a
3255         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3256    
3257         All the sequences that define a single character value can be used both         All the sequences that define a single character value can be used both
3258         inside and outside character classes. In addition, inside  a  character         inside  and  outside character classes. In addition, inside a character
3259         class,  the  sequence \b is interpreted as the backspace character (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3260         08), and the sequences \R and \X are interpreted as the characters  "R"         08),  and the sequences \R and \X are interpreted as the characters "R"
3261         and  "X", respectively. Outside a character class, these sequences have         and "X", respectively. Outside a character class, these sequences  have
3262         different meanings (see below).         different meanings (see below).
3263    
3264     Absolute and relative back references     Absolute and relative back references
3265    
3266         The sequence \g followed by an unsigned or a negative  number,  option-         The  sequence  \g followed by an unsigned or a negative number, option-
3267         ally  enclosed  in braces, is an absolute or relative back reference. A         ally enclosed in braces, is an absolute or relative back  reference.  A
3268         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-
3269         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3270    
3271     Absolute and relative subroutine calls     Absolute and relative subroutine calls
3272    
3273         For  compatibility with Oniguruma, the non-Perl syntax \g followed by a         For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3274         name or a number enclosed either in angle brackets or single quotes, is         name or a number enclosed either in angle brackets or single quotes, is
3275         an  alternative  syntax for referencing a subpattern as a "subroutine".         an alternative syntax for referencing a subpattern as  a  "subroutine".
3276         Details are discussed later.   Note  that  \g{...}  (Perl  syntax)  and         Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3277         \g<...>  (Oniguruma  syntax)  are  not synonymous. The former is a back         \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3278         reference; the latter is a subroutine call.         reference; the latter is a subroutine call.
3279    
3280     Generic character types     Generic character types
# Line 3216  BACKSLASH Line 3294  BACKSLASH
3294           \W     any "non-word" character           \W     any "non-word" character
3295    
3296         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3297         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3298         of each pair.         of each pair.
3299    
3300         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3301         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3302         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
3303         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3304    
3305         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3306         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
3307         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
3308         "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-
3309         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3310    
3311         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,
3312         \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-
3313         code character property support is available.  These  sequences  retain         code  character  property  support is available. These sequences retain
3314         their original meanings from before UTF-8 support was available, mainly         their original meanings from before UTF-8 support was available, mainly
3315         for efficiency reasons.         for  efficiency  reasons. Note that this also affects \b, because it is
3316           defined in terms of \w and \W.
3317    
3318         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
3319         the  other  sequences, these do match certain high-valued codepoints in         the  other  sequences, these do match certain high-valued codepoints in
# Line 3428  BACKSLASH Line 3507  BACKSLASH
3507         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see         U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3508         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-         RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3509         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in         ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3510         the pcreapi page).         the pcreapi page). Perl does not support the Cs property.
3511    
3512         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  property  names  that  Perl supports (such as
3513         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3514         any of these properties with "Is".         any of these properties with "Is".
3515    
# Line 3760  POSIX CHARACTER CLASSES Line 3839  POSIX CHARACTER CLASSES
3839    
3840  VERTICAL BAR  VERTICAL BAR
3841    
3842         Vertical  bar characters are used to separate alternative patterns. For         Vertical bar characters are used to separate alternative patterns.  For
3843         example, the pattern         example, the pattern
3844    
3845           gilbert|sullivan           gilbert|sullivan
3846    
3847         matches either "gilbert" or "sullivan". Any number of alternatives  may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3848         appear,  and  an  empty  alternative  is  permitted (matching the empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3849         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3850         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
3851         are within a subpattern (defined below), "succeeds" means matching  the         are  within a subpattern (defined below), "succeeds" means matching the
3852         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.
3853    
3854    
3855  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 3796  INTERNAL OPTION SETTING Line 3875  INTERNAL OPTION SETTING
3875         can  be changed in the same way as the Perl-compatible options by using         can  be changed in the same way as the Perl-compatible options by using
3876         the characters J, U and X respectively.         the characters J, U and X respectively.
3877    
3878         When an option change occurs at top level (that is, not inside  subpat-         When one of these option changes occurs at  top  level  (that  is,  not
3879         tern  parentheses),  the change applies to the remainder of the pattern         inside  subpattern parentheses), the change applies to the remainder of
3880         that follows.  If the change is placed right at the start of a pattern,         the pattern that follows. If the change is placed right at the start of
3881         PCRE extracts it into the global options (and it will therefore show up         a pattern, PCRE extracts it into the global options (and it will there-
3882         in data extracted by the pcre_fullinfo() function).         fore show up in data extracted by the pcre_fullinfo() function).
3883    
3884         An option change within a subpattern (see below for  a  description  of         An option change within a subpattern (see below for  a  description  of
3885         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
# Line 3823  INTERNAL OPTION SETTING Line 3902  INTERNAL OPTION SETTING
3902    
3903         Note:  There  are  other  PCRE-specific  options that can be set by the         Note:  There  are  other  PCRE-specific  options that can be set by the
3904         application when the compile or match functions  are  called.  In  some         application when the compile or match functions  are  called.  In  some
3905         cases  the  pattern  can  contain special leading sequences to override         cases the pattern can contain special leading sequences such as (*CRLF)
3906         what the application has set or what has been  defaulted.  Details  are         to override what the application has set or what  has  been  defaulted.
3907         given in the section entitled "Newline sequences" above.         Details  are  given  in the section entitled "Newline sequences" above.
3908           There is also the (*UTF8) leading sequence that  can  be  used  to  set
3909           UTF-8 mode; this is equivalent to setting the PCRE_UTF8 option.
3910    
3911    
3912  SUBPATTERNS  SUBPATTERNS
# Line 3964  NAMED SUBPATTERNS Line 4045  NAMED SUBPATTERNS
4045         lowest  number  is used. For further details of the interfaces for han-         lowest  number  is used. For further details of the interfaces for han-
4046         dling named subpatterns, see the pcreapi documentation.         dling named subpatterns, see the pcreapi documentation.
4047    
4048           Warning: You cannot use different names to distinguish between two sub-
4049           patterns  with  the same number (see the previous section) because PCRE
4050           uses only the numbers when matching.
4051    
4052    
4053  REPETITION  REPETITION
4054    
# Line 4004  REPETITION Line 4089  REPETITION
4089         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-
4090         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.
4091    
4092         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
4093         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
4094         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
4095         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
4096         extended sequences, each of which may be several bytes long  (and  they         extended  sequences,  each of which may be several bytes long (and they
4097         may be of different lengths).         may be of different lengths).
4098    
4099         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4100         the previous item and the quantifier were not present. This may be use-         the previous item and the quantifier were not present. This may be use-
4101         ful  for  subpatterns that are referenced as subroutines from elsewhere         ful for subpatterns that are referenced as subroutines  from  elsewhere
4102         in the pattern. Items other than subpatterns that have a {0} quantifier         in the pattern. Items other than subpatterns that have a {0} quantifier
4103         are omitted from the compiled pattern.         are omitted from the compiled pattern.
4104    
4105         For  convenience, the three most common quantifiers have single-charac-         For convenience, the three most common quantifiers have  single-charac-
4106         ter abbreviations:         ter abbreviations:
4107    
4108           *    is equivalent to {0,}           *    is equivalent to {0,}
4109           +    is equivalent to {1,}           +    is equivalent to {1,}
4110           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4111    
4112         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
4113         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,
4114         for example:         for example:
4115    
4116           (a?)*           (a?)*
4117    
4118         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
4119         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
4120         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
4121         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
4122         ken.         ken.
4123    
4124         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
4125         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
4126         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
4127         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
4128         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
4129         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
4130         pattern         pattern
4131    
4132           /\*.*\*/           /\*.*\*/
# Line 4050  REPETITION Line 4135  REPETITION
4135    
4136           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4137    
4138         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
4139         the .*  item.         the .*  item.
4140    
4141         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
4142         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4143         the pattern         the pattern
4144    
4145           /\*.*?\*/           /\*.*?\*/
4146    
4147         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
4148         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
4149         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
4150         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
4151         appear doubled, as in         appear doubled, as in
4152    
4153           \d??\d           \d??\d
# Line 4070  REPETITION Line 4155  REPETITION
4155         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
4156         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4157    
4158         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
4159         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
4160         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
4161         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4162    
4163         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
4164         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
4165         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
4166         minimum or maximum.         minimum or maximum.
4167    
4168         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-
4169         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,
4170         the pattern is implicitly anchored, because whatever  follows  will  be         the  pattern  is  implicitly anchored, because whatever follows will be
4171         tried  against every character position in the subject string, so there         tried against every character position in the subject string, so  there
4172         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
4173         first.  PCRE  normally treats such a pattern as though it were preceded         first. PCRE normally treats such a pattern as though it  were  preceded
4174         by \A.         by \A.
4175    
4176         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-
4177         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-
4178         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4179    
4180         However, there is one situation where the optimization cannot be  used.         However,  there is one situation where the optimization cannot be used.
4181         When  .*   is  inside  capturing  parentheses that are the subject of a         When .*  is inside capturing parentheses that  are  the  subject  of  a
4182         backreference elsewhere in the pattern, a match at the start  may  fail         backreference  elsewhere  in the pattern, a match at the start may fail
4183         where a later one succeeds. Consider, for example:         where a later one succeeds. Consider, for example:
4184    
4185           (.*)abc\1           (.*)abc\1
4186    
4187         If  the subject is "xyz123abc123" the match point is the fourth charac-         If the subject is "xyz123abc123" the match point is the fourth  charac-
4188         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4189    
4190         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 4108  REPETITION Line 4193  REPETITION
4193           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4194    
4195         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4196         is "tweedledee". However, if there are  nested  capturing  subpatterns,         is  "tweedledee".  However,  if there are nested capturing subpatterns,
4197         the  corresponding captured values may have been set in previous itera-         the corresponding captured values may have been set in previous  itera-
4198         tions. For example, after         tions. For example, after
4199    
4200           /(a|(b))+/           /(a|(b))+/
# Line 4119  REPETITION Line 4204  REPETITION
4204    
4205  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4206    
4207         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
4208         repetition,  failure  of what follows normally causes the repeated item         repetition, failure of what follows normally causes the  repeated  item
4209         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
4210         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,
4211         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
4212         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
4213         no point in carrying on.         no point in carrying on.
4214    
4215         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider,  for  example, the pattern \d+foo when applied to the subject
4216         line         line
4217    
4218           123456bar           123456bar
4219    
4220         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
4221         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
4222         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.
4223         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides
4224         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
4225         to be re-evaluated in this way.         to be re-evaluated in this way.
4226    
4227         If we use atomic grouping for the previous example, the  matcher  gives         If  we  use atomic grouping for the previous example, the matcher gives
4228         up  immediately  on failing to match "foo" the first time. The notation         up immediately on failing to match "foo" the first time.  The  notation
4229         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4230    
4231           (?>\d+)foo           (?>\d+)foo
# Line 4218  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4303  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4303    
4304           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4305    
4306         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences of non-digits cannot be broken, and failure happens quickly.
4307    
4308    
4309  BACK REFERENCES  BACK REFERENCES
4310    
4311         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4312         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-
4313         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
4314         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4315    
4316         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4317         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
4318         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
4319         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
4320         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
4321         reference"  of  this  type can make sense when a repetition is involved         reference" of this type can make sense when a  repetition  is  involved
4322         and the subpattern to the right has participated in an  earlier  itera-         and  the  subpattern to the right has participated in an earlier itera-
4323         tion.         tion.
4324    
4325         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
4326         subpattern whose number is 10 or  more  using  this  syntax  because  a         subpattern  whose  number  is  10  or  more using this syntax because a
4327         sequence  such  as  \50 is interpreted as a character defined in octal.         sequence such as \50 is interpreted as a character  defined  in  octal.
4328         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4329         details  of  the  handling of digits following a backslash. There is no         details of the handling of digits following a backslash.  There  is  no
4330         such problem when named parentheses are used. A back reference  to  any         such  problem  when named parentheses are used. A back reference to any
4331         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4332    
4333         Another  way  of  avoiding  the ambiguity inherent in the use of digits         Another way of avoiding the ambiguity inherent in  the  use  of  digits
4334         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-
4335         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
4336         unsigned number or a negative number, optionally  enclosed  in  braces.         unsigned  number  or  a negative number, optionally enclosed in braces.
4337         These examples are all identical:         These examples are all identical:
4338    
4339           (ring), \1           (ring), \1
4340           (ring), \g1           (ring), \g1
4341           (ring), \g{1}           (ring), \g{1}
4342    
4343         An  unsigned number specifies an absolute reference without the ambigu-         An unsigned number specifies an absolute reference without the  ambigu-
4344         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
4345         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4346         Consider this example:         Consider this example:
# Line 4263  BACK REFERENCES Line 4348  BACK REFERENCES
4348           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4349    
4350         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-
4351         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
4352         \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
4353         helpful  in  long  patterns,  and  also in patterns that are created by         helpful in long patterns, and also in  patterns  that  are  created  by
4354         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4355    
4356         A back reference matches whatever actually matched the  capturing  sub-         A  back  reference matches whatever actually matched the capturing sub-
4357         pattern  in  the  current subject string, rather than anything matching         pattern in the current subject string, rather  than  anything  matching
4358         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4359         of doing that). So the pattern         of doing that). So the pattern
4360    
4361           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4362    
4363         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
4364         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
4365         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-
4366         ple,         ple,
4367    
4368           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4369    
4370         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
4371         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4372    
4373         There  are  several  different ways of writing back references to named         There are several different ways of writing back  references  to  named
4374         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
4375         \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
4376         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
4377         and  named  references,  is  also supported. We could rewrite the above         and named references, is also supported. We  could  rewrite  the  above
4378         example in any of the following ways:         example in any of the following ways:
4379    
4380           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 4297  BACK REFERENCES Line 4382  BACK REFERENCES
4382           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4383           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4384    
4385         A subpattern that is referenced by  name  may  appear  in  the  pattern         A  subpattern  that  is  referenced  by  name may appear in the pattern
4386         before or after the reference.         before or after the reference.
4387    
4388         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
4389         subpattern has not actually been used in a particular match,  any  back         subpattern  has  not actually been used in a particular match, any back
4390         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4391    
4392           (a|(bc))\2           (a|(bc))\2
4393    
4394         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
4395         may be many capturing parentheses in a pattern,  all  digits  following         may  be  many  capturing parentheses in a pattern, all digits following
4396         the  backslash  are taken as part of a potential back reference number.         the backslash are taken as part of a potential back  reference  number.
4397         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4398         used  to  terminate  the back reference. If the PCRE_EXTENDED option is         used to terminate the back reference. If the  PCRE_EXTENDED  option  is
4399         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-
4400         ments" below) can be used.         ments" below) can be used.
4401    
4402         A  back reference that occurs inside the parentheses to which it refers         A back reference that occurs inside the parentheses to which it  refers
4403         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
4404         matches.   However,  such references can be useful inside repeated sub-         matches.  However, such references can be useful inside  repeated  sub-
4405         patterns. For example, the pattern         patterns. For example, the pattern
4406    
4407           (a|b\1)+           (a|b\1)+
4408    
4409         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-
4410         ation  of  the  subpattern,  the  back  reference matches the character         ation of the subpattern,  the  back  reference  matches  the  character
4411         string corresponding to the previous iteration. In order  for  this  to         string  corresponding  to  the previous iteration. In order for this to
4412         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
4413         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
4414         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4415    
4416    
4417  ASSERTIONS  ASSERTIONS
4418    
4419         An  assertion  is  a  test on the characters following or preceding the         An assertion is a test on the characters  following  or  preceding  the
4420         current matching point that does not actually consume  any  characters.         current  matching  point that does not actually consume any characters.
4421         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
4422         described above.         described above.
4423    
4424         More complicated assertions are coded as  subpatterns.  There  are  two         More  complicated  assertions  are  coded as subpatterns. There are two
4425         kinds:  those  that  look  ahead of the current position in the subject         kinds: those that look ahead of the current  position  in  the  subject
4426         string, and those that look  behind  it.  An  assertion  subpattern  is         string,  and  those  that  look  behind  it. An assertion subpattern is
4427         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
4428         matching position to be changed.         matching position to be changed.
4429    
4430         Assertion subpatterns are not capturing subpatterns,  and  may  not  be         Assertion  subpatterns  are  not  capturing subpatterns, and may not be
4431         repeated,  because  it  makes no sense to assert the same thing several         repeated, because it makes no sense to assert the  same  thing  several
4432         times. If any kind of assertion contains capturing  subpatterns  within         times.  If  any kind of assertion contains capturing subpatterns within
4433         it,  these are counted for the purposes of numbering the capturing sub-         it, these are counted for the purposes of numbering the capturing  sub-
4434         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4435         out  only  for  positive assertions, because it does not make sense for         out only for positive assertions, because it does not  make  sense  for
4436         negative assertions.         negative assertions.
4437    
4438     Lookahead assertions     Lookahead assertions
# Line 4357  ASSERTIONS Line 4442  ASSERTIONS
4442    
4443           \w+(?=;)           \w+(?=;)
4444    
4445         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-
4446         colon in the match, and         colon in the match, and
4447    
4448           foo(?!bar)           foo(?!bar)
4449    
4450         matches any occurrence of "foo" that is not  followed  by  "bar".  Note         matches  any  occurrence  of  "foo" that is not followed by "bar". Note
4451         that the apparently similar pattern         that the apparently similar pattern
4452    
4453           (?!foo)bar           (?!foo)bar
4454    
4455         does  not  find  an  occurrence  of "bar" that is preceded by something         does not find an occurrence of "bar"  that  is  preceded  by  something
4456         other than "foo"; it finds any occurrence of "bar" whatsoever,  because         other  than "foo"; it finds any occurrence of "bar" whatsoever, because
4457         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4458         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4459    
4460         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
4461         most  convenient  way  to  do  it  is with (?!) because an empty string         most convenient way to do it is  with  (?!)  because  an  empty  string
4462         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
4463         string must always fail.         string must always fail.
4464    
4465     Lookbehind assertions     Lookbehind assertions
4466    
4467         Lookbehind  assertions start with (?<= for positive assertions and (?<!         Lookbehind assertions start with (?<= for positive assertions and  (?<!
4468         for negative assertions. For example,         for negative assertions. For example,
4469    
4470           (?<!foo)bar           (?<!foo)bar
4471    
4472         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
4473         contents  of  a  lookbehind  assertion are restricted such that all the         contents of a lookbehind assertion are restricted  such  that  all  the
4474         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-
4475         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
4476         fixed length. Thus         fixed length. Thus
4477    
4478           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4396  ASSERTIONS Line 4481  ASSERTIONS
4481    
4482           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4483    
4484         causes an error at compile time. Branches that match  different  length         causes  an  error at compile time. Branches that match different length
4485         strings  are permitted only at the top level of a lookbehind assertion.         strings are permitted only at the top level of a lookbehind  assertion.
4486         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
4487         requires  all branches to match the same length of string. An assertion         requires all branches to match the same length of string. An  assertion
4488         such as         such as
4489    
4490           (?<=ab(c|de))           (?<=ab(c|de))
4491    
4492         is not permitted, because its single top-level  branch  can  match  two         is  not  permitted,  because  its single top-level branch can match two
4493         different  lengths,  but  it is acceptable if rewritten to use two top-         different lengths, but it is acceptable if rewritten to  use  two  top-
4494         level branches:         level branches:
4495    
4496           (?<=abc|abde)           (?<=abc|abde)
4497    
4498         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
4499         instead  of  a lookbehind assertion; this is not restricted to a fixed-         instead of a lookbehind assertion; this is not restricted to  a  fixed-
4500         length.         length.
4501    
4502         The implementation of lookbehind assertions is, for  each  alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4503         to  temporarily  move the current position back by the fixed length and         to temporarily move the current position back by the fixed  length  and
4504         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4505         rent position, the assertion fails.         rent position, the assertion fails.
4506    
4507         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
4508         mode) to appear in lookbehind assertions, because it makes it  impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
4509         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,
4510         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4511    
4512         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4513         assertions  to  specify  efficient  matching  at the end of the subject         assertions to specify efficient matching at  the  end  of  the  subject
4514         string. Consider a simple pattern such as         string. Consider a simple pattern such as
4515    
4516           abcd$           abcd$
4517    
4518         when applied to a long string that does  not  match.  Because  matching         when  applied  to  a  long string that does not match. Because matching
4519         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
4520         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
4521         pattern is specified as         pattern is specified as
4522    
4523           ^.*abcd$           ^.*abcd$
4524    
4525         the  initial .* matches the entire string at first, but when this fails         the initial .* matches the entire string at first, but when this  fails
4526         (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
4527         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
4528         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,
4529         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
4530    
4531           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4532    
4533         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
4534         entire string. The subsequent lookbehind assertion does a  single  test         entire  string.  The subsequent lookbehind assertion does a single test
4535         on  the last four characters. If it fails, the match fails immediately.         on the last four characters. If it fails, the match fails  immediately.
4536         For long strings, this approach makes a significant difference  to  the         For  long  strings, this approach makes a significant difference to the
4537         processing time.         processing time.
4538    
4539     Using multiple assertions     Using multiple assertions
# Line 4457  ASSERTIONS Line 4542  ASSERTIONS
4542    
4543           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4544    
4545         matches  "foo" preceded by three digits that are not "999". Notice that         matches "foo" preceded by three digits that are not "999". Notice  that
4546         each of the assertions is applied independently at the  same  point  in         each  of  the  assertions is applied independently at the same point in
4547         the  subject  string.  First  there  is a check that the previous three         the subject string. First there is a  check  that  the  previous  three
4548         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
4549         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4550         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
4551         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-
4552         foo". A pattern to do that is         foo". A pattern to do that is
4553    
4554           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4555    
4556         This time the first assertion looks at the  preceding  six  characters,         This  time  the  first assertion looks at the preceding six characters,
4557         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4558         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4559    
# Line 4476  ASSERTIONS Line 4561  ASSERTIONS
4561    
4562           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4563    
4564         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
4565         is not preceded by "foo", while         is not preceded by "foo", while
4566    
4567           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4568    
4569         is  another pattern that matches "foo" preceded by three digits and any         is another pattern that matches "foo" preceded by three digits and  any
4570         three characters that are not "999".         three characters that are not "999".
4571    
4572    
4573  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4574    
4575         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-
4576         ditionally  or to choose between two alternative subpatterns, depending         ditionally or to choose between two alternative subpatterns,  depending
4577         on the result of an assertion, or whether a previous capturing  subpat-         on  the result of an assertion, or whether a previous capturing subpat-
4578         tern  matched  or not. The two possible forms of conditional subpattern         tern matched or not. The two possible forms of  conditional  subpattern
4579         are         are
4580    
4581           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4582           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4583    
4584         If the condition is satisfied, the yes-pattern is used;  otherwise  the         If  the  condition is satisfied, the yes-pattern is used; otherwise the
4585         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-
4586         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4587    
4588         There are four kinds of condition: references  to  subpatterns,  refer-         There  are  four  kinds of condition: references to subpatterns, refer-
4589         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4590    
4591     Checking for a used subpattern by number     Checking for a used subpattern by number
4592    
4593         If  the  text between the parentheses consists of a sequence of digits,         If the text between the parentheses consists of a sequence  of  digits,
4594         the condition is true if the capturing subpattern of  that  number  has         the  condition  is  true if the capturing subpattern of that number has
4595         previously  matched.  An  alternative notation is to precede the digits         previously matched. An alternative notation is to  precede  the  digits
4596         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-
4597         tive rather than absolute.  The most recently opened parentheses can be         tive rather than absolute.  The most recently opened parentheses can be
4598         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
4599         looping constructs it can also make sense to refer to subsequent groups         looping constructs it can also make sense to refer to subsequent groups
4600         with constructs such as (?(+2).         with constructs such as (?(+2).
4601    
4602         Consider the following pattern, which  contains  non-significant  white         Consider  the  following  pattern, which contains non-significant white
4603         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
4604         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4605    
4606           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4607    
4608         The first part matches an optional opening  parenthesis,  and  if  that         The  first  part  matches  an optional opening parenthesis, and if that
4609         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4610         ond part matches one or more characters that are not  parentheses.  The         ond  part  matches one or more characters that are not parentheses. The
4611         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4612         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
4613         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-
4614         tern is executed and a  closing  parenthesis  is  required.  Otherwise,         tern  is  executed  and  a  closing parenthesis is required. Otherwise,
4615         since  no-pattern  is  not  present, the subpattern matches nothing. In         since no-pattern is not present, the  subpattern  matches  nothing.  In
4616         other words,  this  pattern  matches  a  sequence  of  non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4617         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4618    
4619         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
4620         relative reference:         relative reference:
4621    
4622           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4623    
4624         This makes the fragment independent of the parentheses  in  the  larger         This  makes  the  fragment independent of the parentheses in the larger
4625         pattern.         pattern.
4626    
4627     Checking for a used subpattern by name     Checking for a used subpattern by name
4628    
4629         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4630         used subpattern by name. For compatibility  with  earlier  versions  of         used  subpattern  by  name.  For compatibility with earlier versions of
4631         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4632         also recognized. However, there is a possible ambiguity with this  syn-         also  recognized. However, there is a possible ambiguity with this syn-
4633         tax,  because  subpattern  names  may  consist entirely of digits. PCRE         tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4634         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
4635         consists  entirely  of digits, PCRE looks for a subpattern of that num-         consists entirely of digits, PCRE looks for a subpattern of  that  num-
4636         ber, which must be greater than zero. Using subpattern names that  con-         ber,  which must be greater than zero. Using subpattern names that con-
4637         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4638    
4639         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4559  CONDITIONAL SUBPATTERNS Line 4644  CONDITIONAL SUBPATTERNS
4644     Checking for pattern recursion     Checking for pattern recursion
4645    
4646         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
4647         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
4648         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-
4649         sand follow the letter R, for example:         sand follow the letter R, for example:
4650    
4651           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4652    
4653         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-
4654         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
4655         entire recursion stack.         entire recursion stack.
4656    
4657         At "top level", all these recursion test conditions are  false.  Recur-         At  "top  level", all these recursion test conditions are false. Recur-
4658         sive patterns are described below.         sive patterns are described below.
4659    
4660     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4661    
4662         If  the  condition  is  the string (DEFINE), and there is no subpattern         If the condition is the string (DEFINE), and  there  is  no  subpattern
4663         with the name DEFINE, the condition is  always  false.  In  this  case,         with  the  name  DEFINE,  the  condition is always false. In this case,
4664         there  may  be  only  one  alternative  in the subpattern. It is always         there may be only one alternative  in  the  subpattern.  It  is  always
4665         skipped if control reaches this point  in  the  pattern;  the  idea  of         skipped  if  control  reaches  this  point  in the pattern; the idea of
4666         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-
4667         erenced from elsewhere. (The use of "subroutines" is described  below.)         erenced  from elsewhere. (The use of "subroutines" is described below.)
4668         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
4669         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4670    
4671           (?(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) )
4672           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4673    
4674         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
4675         group  named "byte" is defined. This matches an individual component of         group named "byte" is defined. This matches an individual component  of
4676         an IPv4 address (a number less than 256). When  matching  takes  place,         an  IPv4  address  (a number less than 256). When matching takes place,
4677         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
4678         condition.         condition.
4679    
4680         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
4681         four  dot-separated  components of an IPv4 address, insisting on a word         four dot-separated components of an IPv4 address, insisting on  a  word
4682         boundary at each end.         boundary at each end.
4683    
4684     Assertion conditions     Assertion conditions
4685    
4686         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
4687         assertion.   This may be a positive or negative lookahead or lookbehind         assertion.  This may be a positive or negative lookahead or  lookbehind
4688         assertion. Consider  this  pattern,  again  containing  non-significant         assertion.  Consider  this  pattern,  again  containing non-significant
4689         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4690    
4691           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4692           \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} )
4693    
4694         The  condition  is  a  positive  lookahead  assertion  that  matches an         The condition  is  a  positive  lookahead  assertion  that  matches  an
4695         optional sequence of non-letters followed by a letter. In other  words,         optional  sequence of non-letters followed by a letter. In other words,
4696         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
4697         letter is found, the subject is matched against the first  alternative;         letter  is found, the subject is matched against the first alternative;
4698         otherwise  it  is  matched  against  the  second.  This pattern matches         otherwise it is  matched  against  the  second.  This  pattern  matches
4699         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
4700         letters and dd are digits.         letters and dd are digits.
4701    
4702    
4703  COMMENTS  COMMENTS
4704    
4705         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
4706         next closing parenthesis. Nested parentheses  are  not  permitted.  The         next  closing  parenthesis.  Nested  parentheses are not permitted. The
4707         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
4708         at all.         at all.
4709    
4710         If the PCRE_EXTENDED option is set, an unescaped # character outside  a         If  the PCRE_EXTENDED option is set, an unescaped # character outside a
4711         character  class  introduces  a  comment  that continues to immediately         character class introduces a  comment  that  continues  to  immediately
4712         after the next newline in the pattern.         after the next newline in the pattern.
4713    
4714    
4715  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4716    
4717         Consider the problem of matching a string in parentheses, allowing  for         Consider  the problem of matching a string in parentheses, allowing for
4718         unlimited  nested  parentheses.  Without the use of recursion, the best         unlimited nested parentheses. Without the use of  recursion,  the  best
4719         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
4720         depth  of  nesting.  It  is not possible to handle an arbitrary nesting         depth of nesting. It is not possible to  handle  an  arbitrary  nesting
4721         depth.         depth.
4722    
4723         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4724         sions  to recurse (amongst other things). It does this by interpolating         sions to recurse (amongst other things). It does this by  interpolating
4725         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
4726         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4727         parentheses problem can be created like this:         parentheses problem can be created like this:
4728    
# Line 4647  RECURSIVE PATTERNS Line 4732  RECURSIVE PATTERNS
4732         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4733    
4734         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4735         it supports special syntax for recursion of  the  entire  pattern,  and         it  supports  special  syntax  for recursion of the entire pattern, and
4736         also  for  individual  subpattern  recursion. After its introduction in         also for individual subpattern recursion.  After  its  introduction  in
4737         PCRE and Python, this kind of recursion was  introduced  into  Perl  at         PCRE  and  Python,  this  kind of recursion was subsequently introduced
4738         release 5.10.         into Perl at release 5.10.
4739    
4740         A  special  item  that consists of (? followed by a number greater than         A special item that consists of (? followed by a  number  greater  than
4741         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
4742         the  given  number, provided that it occurs inside that subpattern. (If         the given number, provided that it occurs inside that  subpattern.  (If
4743         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-
4744         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
4745         regular expression.         regular expression.
4746    
        In PCRE (like Python, but unlike Perl), a recursive subpattern call  is  
        always treated as an atomic group. That is, once it has matched some of  
        the subject string, it is never re-entered, even if it contains untried  
        alternatives and there is a subsequent matching failure.  
   
4747         This  PCRE  pattern  solves  the nested parentheses problem (assume the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4748         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4749    
# Line 4752  RECURSIVE PATTERNS Line 4832  RECURSIVE PATTERNS
4832         two different alternatives for the recursive and  non-recursive  cases.         two different alternatives for the recursive and  non-recursive  cases.
4833         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4834    
4835       Recursion difference from Perl
4836    
4837           In  PCRE (like Python, but unlike Perl), a recursive subpattern call is
4838           always treated as an atomic group. That is, once it has matched some of
4839           the subject string, it is never re-entered, even if it contains untried
4840           alternatives and there is a subsequent matching failure.  This  can  be
4841           illustrated  by the following pattern, which purports to match a palin-
4842           dromic string that contains an odd number of characters  (for  example,
4843           "a", "aba", "abcba", "abcdcba"):
4844    
4845             ^(.|(.)(?1)\2)$
4846    
4847           The idea is that it either matches a single character, or two identical
4848           characters surrounding a sub-palindrome. In Perl, this  pattern  works;
4849           in  PCRE  it  does  not if the pattern is longer than three characters.
4850           Consider the subject string "abcba":
4851    
4852           At the top level, the first character is matched, but as it is  not  at
4853           the end of the string, the first alternative fails; the second alterna-
4854           tive is taken and the recursion kicks in. The recursive call to subpat-
4855           tern  1  successfully  matches the next character ("b"). (Note that the
4856           beginning and end of line tests are not part of the recursion).
4857    
4858           Back at the top level, the next character ("c") is compared  with  what
4859           subpattern  2 matched, which was "a". This fails. Because the recursion
4860           is treated as an atomic group, there are now  no  backtracking  points,
4861           and  so  the  entire  match fails. (Perl is able, at this point, to re-
4862           enter the recursion and try the second alternative.)  However,  if  the
4863           pattern is written with the alternatives in the other order, things are
4864           different:
4865    
4866             ^((.)(?1)\2|.)$
4867    
4868           This time, the recursing alternative is tried first, and  continues  to
4869           recurse  until  it runs out of characters, at which point the recursion
4870           fails. But this time we do have  another  alternative  to  try  at  the
4871           higher  level.  That  is  the  big difference: in the previous case the
4872           remaining alternative is at a deeper recursion level, which PCRE cannot
4873           use.
4874    
4875           To change the pattern so that matches all palindromic strings, not just
4876           those with an odd number of characters, it is tempting  to  change  the
4877           pattern to this:
4878    
4879             ^((.)(?1)\2|.?)$
4880    
4881           Again,  this  works  in Perl, but not in PCRE, and for the same reason.
4882           When a deeper recursion has matched a single character,  it  cannot  be
4883           entered  again  in  order  to match an empty string. The solution is to
4884           separate the two cases, and write out the odd and even cases as  alter-
4885           natives at the higher level:
4886    
4887             ^(?:((.)(?1)\2|)|((.)(?3)\4|.))
4888    
4889           If  you  want  to match typical palindromic phrases, the pattern has to
4890           ignore all non-word characters, which can be done like this:
4891    
4892             ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+4|\W*+.\W*+))\W*+$
4893    
4894           If run with the PCRE_CASELESS option, this pattern matches phrases such
4895           as "A man, a plan, a canal: Panama!" and it works well in both PCRE and
4896           Perl. Note the use of the possessive quantifier *+ to avoid  backtrack-
4897           ing  into  sequences of non-word characters. Without this, PCRE takes a
4898           great deal longer (ten times or more) to  match  typical  phrases,  and
4899           Perl takes so long that you think it has gone into a loop.
4900    
4901    
4902  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4903    
# Line 4864  BACKTRACKING CONTROL Line 5010  BACKTRACKING CONTROL
5010         (*FAIL), which behaves like a failing negative assertion, they cause an         (*FAIL), which behaves like a failing negative assertion, they cause an
5011         error if encountered by pcre_dfa_exec().         error if encountered by pcre_dfa_exec().
5012    
5013         The new verbs make use of what was previously invalid syntax: an  open-         If any of these verbs are used in an assertion subpattern, their effect
5014           is  confined  to that subpattern; it does not extend to the surrounding
5015           pattern.  Note that assertion subpatterns are processed as anchored  at
5016           the point where they are tested.
5017    
5018           The  new verbs make use of what was previously invalid syntax: an open-
5019         ing parenthesis followed by an asterisk. In Perl, they are generally of         ing parenthesis followed by an asterisk. In Perl, they are generally of
5020         the form (*VERB:ARG) but PCRE does not support the use of arguments, so         the form (*VERB:ARG) but PCRE does not support the use of arguments, so
5021         its  general  form is just (*VERB). Any number of these verbs may occur         its general form is just (*VERB). Any number of these verbs  may  occur
5022         in a pattern. There are two kinds:         in a pattern. There are two kinds:
5023    
5024     Verbs that act immediately     Verbs that act immediately
# Line 4876  BACKTRACKING CONTROL Line 5027  BACKTRACKING CONTROL
5027    
5028            (*ACCEPT)            (*ACCEPT)
5029    
5030         This verb causes the match to end successfully, skipping the  remainder         This  verb causes the match to end successfully, skipping the remainder
5031         of  the pattern. When inside a recursion, only the innermost pattern is         of the pattern. When inside a recursion, only the innermost pattern  is
5032         ended immediately. PCRE differs  from  Perl  in  what  happens  if  the         ended  immediately.  If  the (*ACCEPT) is inside capturing parentheses,
5033         (*ACCEPT)  is inside capturing parentheses. In Perl, the data so far is         the data so far is captured. (This feature was added to PCRE at release
5034         captured: in PCRE no data is captured. For example:         8.00.) For example:
5035    
5036           A(A|B(*ACCEPT)|C)D           A((?:A|B(*ACCEPT)|C)D)
5037    
5038         This matches "AB", "AAD", or "ACD", but when it matches "AB",  no  data         This  matches  "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-
5039         is captured.         tured by the outer parentheses.
5040    
5041           (*FAIL) or (*F)           (*FAIL) or (*F)
5042    
5043         This  verb  causes the match to fail, forcing backtracking to occur. It         This verb causes the match to fail, forcing backtracking to  occur.  It
5044         is equivalent to (?!) but easier to read. The Perl documentation  notes         is  equivalent to (?!) but easier to read. The Perl documentation notes
5045         that  it  is  probably  useful only when combined with (?{}) or (??{}).         that it is probably useful only when combined  with  (?{})  or  (??{}).
5046         Those are, of course, Perl features that are not present in  PCRE.  The         Those  are,  of course, Perl features that are not present in PCRE. The
5047         nearest  equivalent is the callout feature, as for example in this pat-         nearest equivalent is the callout feature, as for example in this  pat-
5048         tern:         tern:
5049    
5050           a+(?C)(*FAIL)           a+(?C)(*FAIL)
5051    
5052         A match with the string "aaaa" always fails, but the callout  is  taken         A  match  with the string "aaaa" always fails, but the callout is taken
5053         before each backtrack happens (in this example, 10 times).         before each backtrack happens (in this example, 10 times).
5054    
5055     Verbs that act after backtracking     Verbs that act after backtracking
5056    
5057         The following verbs do nothing when they are encountered. Matching con-         The following verbs do nothing when they are encountered. Matching con-
5058         tinues with what follows, but if there is no subsequent match, a  fail-         tinues  with what follows, but if there is no subsequent match, a fail-
5059         ure  is  forced.   The  verbs  differ  in  exactly what kind of failure         ure is forced.  The verbs  differ  in  exactly  what  kind  of  failure
5060         occurs.         occurs.
5061    
5062           (*COMMIT)           (*COMMIT)
5063    
5064         This verb causes the whole match to fail outright if the  rest  of  the         This  verb  causes  the whole match to fail outright if the rest of the
5065         pattern  does  not match. Even if the pattern is unanchored, no further         pattern does not match. Even if the pattern is unanchored,  no  further
5066         attempts to find a match by advancing the start point take place.  Once         attempts  to find a match by advancing the start point take place. Once
5067         (*COMMIT)  has been passed, pcre_exec() is committed to finding a match         (*COMMIT) has been passed, pcre_exec() is committed to finding a  match
5068         at the current starting point, or not at all. For example:         at the current starting point, or not at all. For example:
5069    
5070           a+(*COMMIT)b           a+(*COMMIT)b
5071    
5072         This matches "xxaab" but not "aacaab". It can be thought of as  a  kind         This  matches  "xxaab" but not "aacaab". It can be thought of as a kind
5073         of dynamic anchor, or "I've started, so I must finish."         of dynamic anchor, or "I've started, so I must finish."
5074    
5075           (*PRUNE)           (*PRUNE)
5076    
5077         This  verb causes the match to fail at the current position if the rest         This verb causes the match to fail at the current position if the  rest
5078         of the pattern does not match. If the pattern is unanchored, the normal         of the pattern does not match. If the pattern is unanchored, the normal
5079         "bumpalong"  advance to the next starting character then happens. Back-         "bumpalong" advance to the next starting character then happens.  Back-
5080         tracking can occur as usual to the left of (*PRUNE), or  when  matching         tracking  can  occur as usual to the left of (*PRUNE), or when matching
5081         to  the right of (*PRUNE), but if there is no match to the right, back-         to the right of (*PRUNE), but if there is no match to the right,  back-
5082         tracking cannot cross (*PRUNE).  In simple cases, the use  of  (*PRUNE)         tracking  cannot  cross (*PRUNE).  In simple cases, the use of (*PRUNE)
5083         is just an alternative to an atomic group or possessive quantifier, but         is just an alternative to an atomic group or possessive quantifier, but
5084         there are some uses of (*PRUNE) that cannot be expressed in  any  other         there  are  some uses of (*PRUNE) that cannot be expressed in any other
5085         way.         way.
5086    
5087           (*SKIP)           (*SKIP)
5088    
5089         This  verb  is like (*PRUNE), except that if the pattern is unanchored,         This verb is like (*PRUNE), except that if the pattern  is  unanchored,
5090         the "bumpalong" advance is not to the next character, but to the  posi-         the  "bumpalong" advance is not to the next character, but to the posi-
5091         tion  in  the  subject where (*SKIP) was encountered. (*SKIP) signifies         tion in the subject where (*SKIP) was  encountered.  (*SKIP)  signifies
5092         that whatever text was matched leading up to it cannot  be  part  of  a         that  whatever  text  was  matched leading up to it cannot be part of a
5093         successful match. Consider:         successful match. Consider:
5094    
5095           a+(*SKIP)b           a+(*SKIP)b
5096    
5097         If  the  subject  is  "aaaac...",  after  the first match attempt fails         If the subject is "aaaac...",  after  the  first  match  attempt  fails
5098         (starting at the first character in the  string),  the  starting  point         (starting  at  the  first  character in the string), the starting point
5099         skips on to start the next attempt at "c". Note that a possessive quan-         skips on to start the next attempt at "c". Note that a possessive quan-
5100         tifer does not have the same effect in this example; although it  would         tifer  does not have the same effect in this example; although it would
5101         suppress  backtracking  during  the  first  match  attempt,  the second         suppress backtracking  during  the  first  match  attempt,  the  second
5102         attempt would start at the second character instead of skipping  on  to         attempt  would  start at the second character instead of skipping on to
5103         "c".         "c".
5104    
5105           (*THEN)           (*THEN)
5106    
5107         This verb causes a skip to the next alternation if the rest of the pat-         This verb causes a skip to the next alternation if the rest of the pat-
5108         tern does not match. That is, it cancels pending backtracking, but only         tern does not match. That is, it cancels pending backtracking, but only
5109         within  the  current  alternation.  Its name comes from the observation         within the current alternation. Its name  comes  from  the  observation
5110         that it can be used for a pattern-based if-then-else block:         that it can be used for a pattern-based if-then-else block:
5111    
5112           ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...           ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
5113    
5114         If the COND1 pattern matches, FOO is tried (and possibly further  items         If  the COND1 pattern matches, FOO is tried (and possibly further items
5115         after  the  end  of  the group if FOO succeeds); on failure the matcher         after the end of the group if FOO succeeds);  on  failure  the  matcher
5116         skips to the second alternative and tries COND2,  without  backtracking         skips  to  the second alternative and tries COND2, without backtracking
5117         into  COND1.  If  (*THEN)  is  used outside of any alternation, it acts         into COND1. If (*THEN) is used outside  of  any  alternation,  it  acts
5118         exactly like (*PRUNE).         exactly like (*PRUNE).
5119    
5120    
# Line 4981  AUTHOR Line 5132  AUTHOR
5132    
5133  REVISION  REVISION
5134    
5135         Last updated: 19 April 2008         Last updated: 18 September 2009
5136         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
5137  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
5138    
5139    
5140  PCRESYNTAX(3)                                                    PCRESYNTAX(3)  PCRESYNTAX(3)                                                    PCRESYNTAX(3)
5141    
5142    
# Line 5094  GENERAL CATEGORY PROPERTY CODES FOR \p a Line 5245  GENERAL CATEGORY PROPERTY CODES FOR \p a
5245  SCRIPT NAMES FOR \p AND \P  SCRIPT NAMES FOR \p AND \P
5246    
5247         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
5248         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, Coptic, Cu-
5249         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         neiform,  Cypriot,  Cyrillic,  Deseret, Devanagari, Ethiopic, Georgian,
5250         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         Glagolitic, Gothic, Greek, Gujarati, Gurmukhi,  Han,  Hangul,  Hanunoo,
5251         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         Hebrew,  Hiragana,  Inherited, Kannada, Katakana, Kayah_Li, Kharoshthi,
5252         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lycian, Lydian,  Malayalam,
5253         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Mongolian,  Myanmar,  New_Tai_Lue, Nko, Ogham, Old_Italic, Old_Persian,
5254         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Saurash-
5255         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         tra,  Shavian,  Sinhala,  Sudanese, Syloti_Nagri, Syriac, Tagalog, Tag-
5256           banwa,  Tai_Le,  Tamil,  Telugu,  Thaana,  Thai,   Tibetan,   Tifinagh,
5257           Ugaritic, Vai, Yi.
5258    
5259    
5260  CHARACTER CLASSES  CHARACTER CLASSES
# Line 5153  QUANTIFIERS Line 5306  QUANTIFIERS
5306    
5307  ANCHORS AND SIMPLE ASSERTIONS  ANCHORS AND SIMPLE ASSERTIONS
5308    
5309           \b          word boundary           \b          word boundary (only ASCII letters recognized)
5310           \B          not a word boundary           \B          not a word boundary
5311           ^           start of subject           ^           start of subject
5312                        also after internal newline in multiline mode                        also after internal newline in multiline mode
# Line 5179  ALTERNATION Line 5332  ALTERNATION
5332    
5333  CAPTURING  CAPTURING
5334    
5335           (...)          capturing group           (...)           capturing group
5336           (?<name>...)   named capturing group (Perl)           (?<name>...)    named capturing group (Perl)
5337           (?'name'...)   named capturing group (Perl)           (?'name'...)    named capturing group (Perl)
5338           (?P<name>...)  named capturing group (Python)           (?P<name>...)   named capturing group (Python)
5339           (?:...)        non-capturing group           (?:...)         non-capturing group
5340           (?|...)        non-capturing group; reset group numbers for           (?|...)         non-capturing group; reset group numbers for
5341                           capturing groups in each alternative                            capturing groups in each alternative
5342    
5343    
5344  ATOMIC GROUPS  ATOMIC GROUPS
5345    
5346           (?>...)        atomic, non-capturing group           (?>...)         atomic, non-capturing group
5347    
5348    
5349  COMMENT  COMMENT
5350    
5351           (?#....)       comment (not nestable)           (?#....)        comment (not nestable)
5352    
5353    
5354  OPTION SETTING  OPTION SETTING
5355    
5356           (?i)           caseless           (?i)            caseless
5357           (?J)           allow duplicate names           (?J)            allow duplicate names
5358           (?m)           multiline           (?m)            multiline
5359           (?s)           single line (dotall)           (?s)            single line (dotall)
5360           (?U)           default ungreedy (lazy)           (?U)            default ungreedy (lazy)
5361           (?x)           extended (ignore white space)           (?x)            extended (ignore white space)
5362           (?-...)        unset option(s)           (?-...)         unset option(s)
5363    
5364           The following is recognized only at the start of a pattern or after one
5365           of the newline-setting options with similar syntax:
5366    
5367             (*UTF8)         set UTF-8 mode
5368    
5369    
5370  LOOKAHEAD AND LOOKBEHIND ASSERTIONS  LOOKAHEAD AND LOOKBEHIND ASSERTIONS
5371    
5372           (?=...)        positive look ahead           (?=...)         positive look ahead
5373           (?!...)        negative look ahead           (?!...)         negative look ahead
5374           (?<=...)       positive look behind           (?<=...)        positive look behind
5375           (?<!...)       negative look behind           (?<!...)        negative look behind
5376    
5377         Each top-level branch of a look behind must be of a fixed length.         Each top-level branch of a look behind must be of a fixed length.
5378    
5379    
5380  BACKREFERENCES  BACKREFERENCES
5381    
5382           \n             reference by number (can be ambiguous)           \n              reference by number (can be ambiguous)
5383           \gn            reference by number           \gn             reference by number
5384           \g{n}          reference by number           \g{n}           reference by number
5385           \g{-n}         relative reference by number           \g{-n}          relative reference by number
5386           \k<name>       reference by name (Perl)           \k<name>        reference by name (Perl)
5387           \k'name'       reference by name (Perl)           \k'name'        reference by name (Perl)
5388           \g{name}       reference by name (Perl)           \g{name}        reference by name (Perl)
5389           \k{name}       reference by name (.NET)           \k{name}        reference by name (.NET)
5390           (?P=name)      reference by name (Python)           (?P=name)       reference by name (Python)
5391    
5392    
5393  SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)  SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)
5394    
5395           (?R)           recurse whole pattern           (?R)            recurse whole pattern
5396           (?n)           call subpattern by absolute number           (?n)            call subpattern by absolute number
5397           (?+n)          call subpattern by relative number           (?+n)           call subpattern by relative number
5398           (?-n)          call subpattern by relative number           (?-n)           call subpattern by relative number
5399           (?&name)       call subpattern by name (Perl)           (?&name)        call subpattern by name (Perl)
5400           (?P>name)      call subpattern by name (Python)           (?P>name)       call subpattern by name (Python)
5401           \g<name>       call subpattern by name (Oniguruma)           \g<name>        call subpattern by name (Oniguruma)
5402           \g'name'       call subpattern by name (Oniguruma)           \g'name'        call subpattern by name (Oniguruma)
5403           \g<n>          call subpattern by absolute number (Oniguruma)           \g<n>           call subpattern by absolute number (Oniguruma)
5404           \g'n'          call subpattern by absolute number (Oniguruma)           \g'n'           call subpattern by absolute number (Oniguruma)
5405           \g<+n>         call subpattern by relative number (PCRE extension)           \g<+n>          call subpattern by relative number (PCRE extension)
5406           \g'+n'         call subpattern by relative number (PCRE extension)           \g'+n'          call subpattern by relative number (PCRE extension)
5407           \g<-n>         call subpattern by relative number (PCRE extension)           \g<-n>          call subpattern by relative number (PCRE extension)
5408           \g'-n'         call subpattern by relative number (PCRE extension)           \g'-n'          call subpattern by relative number (PCRE extension)
5409    
5410    
5411  CONDITIONAL PATTERNS  CONDITIONAL PATTERNS
# Line 5255  CONDITIONAL PATTERNS Line 5413  CONDITIONAL PATTERNS
5413           (?(condition)yes-pattern)           (?(condition)yes-pattern)
5414           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
5415    
5416           (?(n)...       absolute reference condition           (?(n)...        absolute reference condition
5417           (?(+n)...      relative reference condition           (?(+n)...       relative reference condition
5418           (?(-n)...      relative reference condition           (?(-n)...       relative reference condition
5419           (?(<name>)...  named reference condition (Perl)           (?(<name>)...   named reference condition (Perl)
5420           (?('name')...  named reference condition (Perl)           (?('name')...   named reference condition (Perl)
5421           (?(name)...    named reference condition (PCRE)           (?(name)...     named reference condition (PCRE)
5422           (?(R)...       overall recursion condition           (?(R)...        overall recursion condition
5423           (?(Rn)...      specific group recursion condition           (?(Rn)...       specific group recursion condition
5424           (?(R&name)...  specific recursion condition           (?(R&name)...   specific recursion condition
5425           (?(DEFINE)...  define subpattern for reference           (?(DEFINE)...   define subpattern for reference
5426           (?(assert)...  assertion condition           (?(assert)...   assertion condition
5427    
5428    
5429  BACKTRACKING CONTROL  BACKTRACKING CONTROL
5430    
5431         The following act immediately they are reached:         The following act immediately they are reached:
5432    
5433           (*ACCEPT)      force successful match           (*ACCEPT)       force successful match
5434           (*FAIL)        force backtrack; synonym (*F)           (*FAIL)         force backtrack; synonym (*F)
5435    
5436         The following act only when a subsequent match failure causes  a  back-         The  following  act only when a subsequent match failure causes a back-
5437         track to reach them. They all force a match failure, but they differ in         track to reach them. They all force a match failure, but they differ in
5438         what happens afterwards. Those that advance the start-of-match point do         what happens afterwards. Those that advance the start-of-match point do
5439         so only if the pattern is not anchored.         so only if the pattern is not anchored.
5440    
5441           (*COMMIT)      overall failure, no advance of starting point           (*COMMIT)       overall failure, no advance of starting point
5442           (*PRUNE)       advance to next starting character           (*PRUNE)        advance to next starting character
5443           (*SKIP)        advance start to current matching position           (*SKIP)         advance start to current matching position
5444           (*THEN)        local failure, backtrack to next alternation           (*THEN)         local failure, backtrack to next alternation
5445    
5446    
5447  NEWLINE CONVENTIONS  NEWLINE CONVENTIONS
5448    
5449         These  are  recognized only at the very start of the pattern or after a         These are recognized only at the very start of the pattern or  after  a
5450         (*BSR_...) option.         (*BSR_...) or (*UTF8) option.
5451