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# Line 2  Line 2 
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
5  synopses of each function in the library have not been included. There are  synopses of each function in the library have not been included. Neither has
6  separate text files for the pcregrep and pcretest commands.  the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
9    
10    
# Line 18  INTRODUCTION Line 19  INTRODUCTION
19    
20         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
21         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
22         just  a  few  differences. Certain features that appeared in Python and         just  a few differences. Some features that appeared in Python and PCRE
23         PCRE before they appeared in Perl are also available using  the  Python         before they appeared in Perl are also available using the  Python  syn-
24         syntax.  There is also some support for certain .NET and Oniguruma syn-         tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25         tax items, and there is an option for  requesting  some  minor  changes         items, and there is an option for requesting some  minor  changes  that
26         that give better JavaScript compatibility.         give better JavaScript compatibility.
27    
28         The  current  implementation of PCRE (release 7.x) corresponds approxi-         The  current implementation of PCRE corresponds approximately with Perl
29         mately with Perl 5.10, including support for UTF-8 encoded strings  and         5.10, including support for UTF-8 encoded strings and  Unicode  general
30         Unicode general category properties. However, UTF-8 and Unicode support         category  properties.  However,  UTF-8  and  Unicode  support has to be
31         has to be explicitly enabled; it is not the default. The Unicode tables         explicitly enabled; it is not the default. The  Unicode  tables  corre-
32         correspond to Unicode release 5.0.0.         spond to Unicode release 5.2.0.
33    
34         In  addition to the Perl-compatible matching function, PCRE contains an         In  addition to the Perl-compatible matching function, PCRE contains an
35         alternative matching function that matches the same  compiled  patterns         alternative function that matches the same compiled patterns in a  dif-
36         in  a different way. In certain circumstances, the alternative function         ferent way. In certain circumstances, the alternative function has some
37         has some advantages. For a discussion of the two  matching  algorithms,         advantages.  For a discussion of the two matching algorithms,  see  the
38         see the pcrematching page.         pcrematching page.
39    
40         PCRE  is  written  in C and released as a C library. A number of people         PCRE  is  written  in C and released as a C library. A number of people
41         have written wrappers and interfaces of various kinds.  In  particular,         have written wrappers and interfaces of various kinds.  In  particular,
# Line 54  INTRODUCTION Line 55  INTRODUCTION
55         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
56         client  to  discover  which  features are available. The features them-         client  to  discover  which  features are available. The features them-
57         selves are described in the pcrebuild page. Documentation about  build-         selves are described in the pcrebuild page. Documentation about  build-
58         ing  PCRE for various operating systems can be found in the README file         ing  PCRE  for various operating systems can be found in the README and
59         in the source distribution.         NON-UNIX-USE files in the source distribution.
60    
61         The library contains a number of undocumented  internal  functions  and         The library contains a number of undocumented  internal  functions  and
62         data  tables  that  are  used by more than one of the exported external         data  tables  that  are  used by more than one of the exported external
# Line 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
90           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
91                               regular expressions                               regular expressions
          pcresyntax        quick syntax reference  
92           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
93           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
94           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
95           pcresample        discussion of the sample program           pcresample        discussion of the pcredemo program
96           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
99    
100         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
# Line 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 strings of 1-byte characters.
146    
147         If  you compile PCRE with UTF-8 support, but do not use it at run time,         If you compile PCRE with UTF-8 support, but do not use it at run  time,
148         the library will be a bit bigger, but the additional run time  overhead         the  library will be a bit bigger, but the additional run time overhead
149         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150         very big.         very big.
151    
152         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
153         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
155         general  category  properties such as Lu for an upper case letter or Nd         general category properties such as Lu for an upper case letter  or  Nd
156         for a decimal number, the Unicode script names such as Arabic  or  Han,         for  a  decimal number, the Unicode script names such as Arabic or Han,
157         and  the  derived  properties  Any  and L&. A full list is given in the         and the derived properties Any and L&. A full  list  is  given  in  the
158         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
159         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may         ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162         does not support this.         does not support this.
163    
164     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 March 2010
267         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
268  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
269    
270    
# 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.         or pcre_compile2() functions.
328    
329           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
330           expects its input to be either ASCII or UTF-8 (depending on the runtime
331           option). It is not possible to support both EBCDIC and UTF-8  codes  in
332           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
333           --enable-ebcdic are mutually exclusive.
334    
335    
336  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
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 416  HANDLING VERY LARGE PATTERNS Line 432  HANDLING VERY LARGE PATTERNS
432         nation metacharacter). By default, two-byte values are used  for  these         nation metacharacter). By default, two-byte values are used  for  these
433         offsets,  leading  to  a  maximum size for a compiled pattern of around         offsets,  leading  to  a  maximum size for a compiled pattern of around
434         64K. This is sufficient to handle all but the most  gigantic  patterns.         64K. This is sufficient to handle all but the most  gigantic  patterns.
435         Nevertheless,  some  people do want to process enormous patterns, so it         Nevertheless,  some  people do want to process truyl enormous patterns,
436         is possible to compile PCRE to use three-byte or four-byte  offsets  by         so it is possible to compile PCRE to use three-byte or  four-byte  off-
437         adding a setting such as         sets by adding a setting such as
438    
439           --with-link-size=3           --with-link-size=3
440    
# Line 445  AVOIDING EXCESSIVE STACK USAGE Line 461  AVOIDING EXCESSIVE STACK USAGE
461         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. With this configuration, PCRE  will  use  the
462         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
463         ment functions. By default these point to malloc() and free(), but  you         ment functions. By default these point to malloc() and free(), but  you
464         can replace the pointers so that your own functions are used.         can replace the pointers so that your own functions are used instead.
465    
466         Separate  functions  are  provided  rather  than  using pcre_malloc and         Separate  functions  are  provided  rather  than  using pcre_malloc and
467         pcre_free because the  usage  is  very  predictable:  the  block  sizes         pcre_free because the  usage  is  very  predictable:  the  block  sizes
# Line 453  AVOIDING EXCESSIVE STACK USAGE Line 469  AVOIDING EXCESSIVE STACK USAGE
469         reverse order. A calling program might be able to  implement  optimized         reverse order. A calling program might be able to  implement  optimized
470         functions  that  perform  better  than  malloc()  and free(). PCRE runs         functions  that  perform  better  than  malloc()  and free(). PCRE runs
471         noticeably more slowly when built in this way. This option affects only         noticeably more slowly when built in this way. This option affects only
472         the   pcre_exec()   function;   it   is   not   relevant  for  the  the         the pcre_exec() function; it is not relevant for pcre_dfa_exec().
        pcre_dfa_exec() function.  
473    
474    
475  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
476    
477         Internally, PCRE has a function called match(), which it calls  repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
478         edly   (sometimes   recursively)  when  matching  a  pattern  with  the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
479         pcre_exec() function. By controlling the maximum number of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
480         function  may be called during a single matching operation, a limit can         function may be called during a single matching operation, a limit  can
481         be placed on the resources used by a single call  to  pcre_exec().  The         be  placed  on  the resources used by a single call to pcre_exec(). The
482         limit  can be changed at run time, as described in the pcreapi documen-         limit can be changed at run time, as described in the pcreapi  documen-
483         tation. The default is 10 million, but this can be changed by adding  a         tation.  The default is 10 million, but this can be changed by adding a
484         setting such as         setting such as
485    
486           --with-match-limit=500000           --with-match-limit=500000
487    
488         to   the   configure  command.  This  setting  has  no  effect  on  the         to  the  configure  command.  This  setting  has  no  effect   on   the
489         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
490    
491         In some environments it is desirable to limit the  depth  of  recursive         In  some  environments  it is desirable to limit the depth of recursive
492         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
493         to restrict the maximum amount of stack (or heap,  if  --disable-stack-         to  restrict  the maximum amount of stack (or heap, if --disable-stack-
494         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
495         it defaults to the value that  is  set  for  --with-match-limit,  which         it  defaults  to  the  value  that is set for --with-match-limit, which
496         imposes  no  additional constraints. However, you can set a lower limit         imposes no additional constraints. However, you can set a  lower  limit
497         by adding, for example,         by adding, for example,
498    
499           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
500    
501         to the configure command. This value can  also  be  overridden  at  run         to  the  configure  command.  This  value can also be overridden at run
502         time.         time.
503    
504    
505  CREATING CHARACTER TABLES AT BUILD TIME  CREATING CHARACTER TABLES AT BUILD TIME
506    
507         PCRE  uses fixed tables for processing characters whose code values are         PCRE uses fixed tables for processing characters whose code values  are
508         less than 256. By default, PCRE is built with a set of tables that  are         less  than 256. By default, PCRE is built with a set of tables that are
509         distributed  in  the  file pcre_chartables.c.dist. These tables are for         distributed in the file pcre_chartables.c.dist. These  tables  are  for
510         ASCII codes only. If you add         ASCII codes only. If you add
511    
512           --enable-rebuild-chartables           --enable-rebuild-chartables
513    
514         to the configure command, the distributed tables are  no  longer  used.         to  the  configure  command, the distributed tables are no longer used.
515         Instead,  a  program  called dftables is compiled and run. This outputs         Instead, a program called dftables is compiled and  run.  This  outputs
516         the source for new set of tables, created in the default locale of your         the source for new set of tables, created in the default locale of your
517         C runtime system. (This method of replacing the tables does not work if         C runtime system. (This method of replacing the tables does not work if
518         you are cross compiling, because dftables is run on the local host.  If         you  are cross compiling, because dftables is run on the local host. If
519         you  need  to  create alternative tables when cross compiling, you will         you need to create alternative tables when cross  compiling,  you  will
520         have to do so "by hand".)         have to do so "by hand".)
521    
522    
523  USING EBCDIC CODE  USING EBCDIC CODE
524    
525         PCRE assumes by default that it will run in an  environment  where  the         PCRE  assumes  by  default that it will run in an environment where the
526         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
527         This is the case for most computer operating systems.  PCRE  can,  how-         This  is  the  case for most computer operating systems. PCRE can, how-
528         ever, be compiled to run in an EBCDIC environment by adding         ever, be compiled to run in an EBCDIC environment by adding
529    
530           --enable-ebcdic           --enable-ebcdic
531    
532         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
533         bles. You should only use it if you know that  you  are  in  an  EBCDIC         bles.  You  should  only  use  it if you know that you are in an EBCDIC
534         environment (for example, an IBM mainframe operating system).         environment (for example,  an  IBM  mainframe  operating  system).  The
535           --enable-ebcdic option is incompatible with --enable-utf8.
536    
537    
538  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT  PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
# Line 542  PCRETEST OPTION FOR LIBREADLINE SUPPORT Line 558  PCRETEST OPTION FOR LIBREADLINE SUPPORT
558         to  the  configure  command,  pcretest  is  linked with the libreadline         to  the  configure  command,  pcretest  is  linked with the libreadline
559         library, and when its input is from a terminal, it reads it  using  the         library, and when its input is from a terminal, it reads it  using  the
560         readline() function. This provides line-editing and history facilities.         readline() function. This provides line-editing and history facilities.
561         Note that libreadline is GPL-licenced, so if you distribute a binary of         Note that libreadline is GPL-licensed, so if you distribute a binary of
562         pcretest linked in this way, there may be licensing issues.         pcretest linked in this way, there may be licensing issues.
563    
564         Setting  this  option  causes  the -lreadline option to be added to the         Setting  this  option  causes  the -lreadline option to be added to the
# Line 578  AUTHOR Line 594  AUTHOR
594    
595  REVISION  REVISION
596    
597         Last updated: 13 April 2008         Last updated: 29 September 2009
598         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
599  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
600    
601    
# Line 666  THE ALTERNATIVE MATCHING ALGORITHM Line 682  THE ALTERNATIVE MATCHING ALGORITHM
682         though  it is not implemented as a traditional finite state machine (it         though  it is not implemented as a traditional finite state machine (it
683         keeps multiple states active simultaneously).         keeps multiple states active simultaneously).
684    
685           Although the general principle of this matching algorithm  is  that  it
686           scans  the subject string only once, without backtracking, there is one
687           exception: when a lookaround assertion is encountered,  the  characters
688           following  or  preceding  the  current  point  have to be independently
689           inspected.
690    
691         The scan continues until either the end of the subject is  reached,  or         The scan continues until either the end of the subject is  reached,  or
692         there  are  no more unterminated paths. At this point, terminated paths         there  are  no more unterminated paths. At this point, terminated paths
693         represent the different matching possibilities (if there are none,  the         represent the different matching possibilities (if there are none,  the
694         match  has  failed).   Thus,  if there is more than one possible match,         match  has  failed).   Thus,  if there is more than one possible match,
695         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
696         est.  In PCRE, there is an option to stop the algorithm after the first         est.  There  is  an  option to stop the algorithm after the first match
697         match (which is necessarily the shortest) has been found.         (which is necessarily the shortest) is found.
698    
699         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
700         subject. If the pattern         subject. If the pattern
# Line 742  ADVANTAGES OF THE ALTERNATIVE ALGORITHM Line 764  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
764         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
765         things with callouts.         things with callouts.
766    
767         2.  There is much better support for partial matching. The restrictions         2.  Because  the  alternative  algorithm  scans the subject string just
        on the content of the pattern that apply when using the standard  algo-  
        rithm  for  partial matching do not apply to the alternative algorithm.  
        For non-anchored patterns, the starting position of a partial match  is  
        available.  
   
        3.  Because  the  alternative  algorithm  scans the subject string just  
768         once, and never needs to backtrack, it is possible to  pass  very  long         once, and never needs to backtrack, it is possible to  pass  very  long
769         subject  strings  to  the matching function in several pieces, checking         subject  strings  to  the matching function in several pieces, checking
770         for partial matching each time.         for partial matching each time.  The  pcrepartial  documentation  gives
771           details of partial matching.
772    
773    
774  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
775    
776         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
777    
778         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
779         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
780         because it is less susceptible to optimization.         because it is less susceptible to optimization.
781    
782         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 777  AUTHOR Line 794  AUTHOR
794    
795  REVISION  REVISION
796    
797         Last updated: 19 April 2008         Last updated: 29 September 2009
798         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
799  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
800    
801    
# Line 889  PCRE API OVERVIEW Line 906  PCRE API OVERVIEW
906         pcre_exec() are used for compiling and matching regular expressions  in         pcre_exec() are used for compiling and matching regular expressions  in
907         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
908         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
909         the  source distribution. The pcresample documentation describes how to         the PCRE source distribution. A listing of this program is given in the
910         compile and run it.         pcredemo documentation, and the pcresample documentation describes  how
911           to compile and run it.
912    
913         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
914         ble,  is  also provided. This uses a different algorithm for the match-         ble, is also provided. This uses a different algorithm for  the  match-
915         ing. The alternative algorithm finds all possible matches (at  a  given         ing.  The  alternative algorithm finds all possible matches (at a given
916         point  in  the subject), and scans the subject just once. However, this         point in the subject), and scans the subject just  once  (unless  there
917         algorithm does not return captured substrings. A description of the two         are  lookbehind  assertions).  However,  this algorithm does not return
918         matching  algorithms and their advantages and disadvantages is given in         captured substrings. A description of the two matching  algorithms  and
919         the pcrematching documentation.         their  advantages  and disadvantages is given in the pcrematching docu-
920           mentation.
921    
922         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
923         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 999  MULTITHREADING Line 1018  MULTITHREADING
1018         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1019         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
1020    
1021         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
1022         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
1023         at once.         at once.
1024    
# Line 1007  MULTITHREADING Line 1026  MULTITHREADING
1026  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
1027    
1028         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
1029         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
1030         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
1031         pcreprecompile  documentation.  However, compiling a regular expression         pcreprecompile documentation. However, compiling a  regular  expression
1032         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-
1033         anteed to work and may cause crashes.         anteed to work and may cause crashes.
1034    
1035    
# Line 1018  CHECKING BUILD-TIME OPTIONS Line 1037  CHECKING BUILD-TIME OPTIONS
1037    
1038         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1039    
1040         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-
1041         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
1042         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
1043         tures.         tures.
1044    
1045         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
1046         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
1047         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
1048         available:         available:
1049    
1050           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1051    
1052         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-
1053         able; otherwise it is set to zero.         able; otherwise it is set to zero.
1054    
1055           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
1056    
1057         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
1058         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
1059    
1060           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
1061    
1062         The  output  is  an integer whose value specifies the default character         The output is an integer whose value specifies  the  default  character
1063         sequence that is recognized as meaning "newline". The four values  that         sequence  that is recognized as meaning "newline". The four values that
1064         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1065         and -1 for ANY. The default should normally be  the  standard  sequence         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1066         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1067           spond to the standard sequence for your operating system.
1068    
1069           PCRE_CONFIG_BSR           PCRE_CONFIG_BSR
1070    
# Line 1071  CHECKING BUILD-TIME OPTIONS Line 1091  CHECKING BUILD-TIME OPTIONS
1091    
1092           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1093    
1094         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1095         internal  matching  function  calls in a pcre_exec() execution. Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1096         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1097    
1098           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1099    
1100         The output is an integer that gives the default limit for the depth  of         The output is a long integer that gives the default limit for the depth
1101         recursion  when calling the internal matching function in a pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1102         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1103           below.
1104    
1105           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1106    
1107         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
1108         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1109         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
1110         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
1111         on the  heap  instead  of  recursive  function  calls.  In  this  case,         on  the  heap  instead  of  recursive  function  calls.  In  this case,
1112         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1113         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1114    
1115    
# Line 1105  COMPILING A PATTERN Line 1126  COMPILING A PATTERN
1126    
1127         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1128         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1129         the two interfaces is that pcre_compile2() has an additional  argument,         the  two interfaces is that pcre_compile2() has an additional argument,
1130         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error  code  can  be  returned.  To
1131           avoid  too  much repetition, we refer just to pcre_compile() below, but
1132           the information applies equally to pcre_compile2().
1133    
1134         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1135         the pattern argument. A pointer to a single block  of  memory  that  is         the  pattern  argument.  A  pointer to a single block of memory that is
1136         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained via pcre_malloc is returned. This contains the  compiled  code
1137         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
1138         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1139         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
1140         longer required.         longer required.
1141    
1142         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
1143         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
1144         fully  relocatable, because it may contain a copy of the tableptr argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1145         ment, which is an address (see below).         ment, which is an address (see below).
1146    
1147         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1148         pilation.  It  should be zero if no options are required. The available         pilation. It should be zero if no options are required.  The  available
1149         options are described below. Some of them, in  particular,  those  that         options  are  described  below. Some of them (in particular, those that
1150         are  compatible  with  Perl,  can also be set and unset from within the         are compatible with Perl, but some others as well) can also be set  and
1151         pattern (see the detailed description  in  the  pcrepattern  documenta-         unset  from  within  the  pattern  (see the detailed description in the
1152         tion).  For  these options, the contents of the options argument speci-         pcrepattern documentation). For those options that can be different  in
1153         fies their initial settings at the start of compilation and  execution.         different  parts  of  the pattern, the contents of the options argument
1154         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time         specifies their settings at the start of compilation and execution. The
1155         of matching as well as at compile time.         PCRE_ANCHORED, PCRE_BSR_xxx, and PCRE_NEWLINE_xxx options can be set at
1156           the time of matching as well as at compile time.
1157    
1158         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1159         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1160         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1161         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1162         try to free it. The offset from the start of the pattern to the charac-         try to free it. The byte offset from the start of the  pattern  to  the
1163         ter where the error was discovered is placed in the variable pointed to         character  that  was  being  processed when the error was discovered is
1164         by erroffset, which must not be NULL. If it is, an immediate  error  is         placed in the variable pointed to by erroffset, which must not be NULL.
1165         given.         If  it  is,  an  immediate error is given. Some errors are not detected
1166           until checks are carried out when the whole pattern has  been  scanned;
1167           in this case the offset is set to the end of the pattern.
1168    
1169         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1170         codeptr argument is not NULL, a non-zero error code number is  returned         codeptr argument is not NULL, a non-zero error code number is  returned
# Line 1335  COMPILING A PATTERN Line 1361  COMPILING A PATTERN
1361         and are therefore ignored.         and are therefore ignored.
1362    
1363         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1364         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1365    
1366           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1367    
1368         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1369         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1370         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1371         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1372         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1373    
1374           PCRE_UNGREEDY           PCRE_UNGREEDY
1375    
1376         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1377         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1378         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1379         within the pattern.         within the pattern.
1380    
1381           PCRE_UTF8           PCRE_UTF8
1382    
1383         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1384         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1385         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1386         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1387         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1388         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1389    
1390           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1391    
1392         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1393         automatically  checked.  There  is  a  discussion about the validity of         automatically checked. There is a  discussion  about  the  validity  of
1394         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
1395         bytes  is  found,  pcre_compile() returns an error. If you already know         bytes is found, pcre_compile() returns an error. If  you  already  know
1396         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-
1397         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
1398         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
1399         undefined.  It  may  cause your program to crash. Note that this option         undefined. It may cause your program to crash. Note  that  this  option
1400         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
1401         UTF-8 validity checking of subject strings.         UTF-8 validity checking of subject strings.
1402    
1403    
1404  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1405    
1406         The  following  table  lists  the  error  codes than may be returned by         The following table lists the error  codes  than  may  be  returned  by
1407         pcre_compile2(), along with the error messages that may be returned  by         pcre_compile2(),  along with the error messages that may be returned by
1408         both  compiling functions. As PCRE has developed, some error codes have         both compiling functions. As PCRE has developed, some error codes  have
1409         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.
1410    
1411            0  no error            0  no error
# Line 1435  COMPILATION ERROR CODES Line 1461  COMPILATION ERROR CODES
1461           50  [this code is not in use]           50  [this code is not in use]
1462           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1463           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1464           53  internal  error:  previously-checked  referenced  subpattern  not           53   internal  error:  previously-checked  referenced  subpattern not
1465         found         found
1466           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1467           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
# Line 1443  COMPILATION ERROR CODES Line 1469  COMPILATION ERROR CODES
1469           57  \g is not followed by a braced, angle-bracketed, or quoted           57  \g is not followed by a braced, angle-bracketed, or quoted
1470                 name/number or by a plain number                 name/number or by a plain number
1471           58  a numbered reference must not be zero           58  a numbered reference must not be zero
1472           59  (*VERB) with an argument is not supported           59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1473           60  (*VERB) not recognized           60  (*VERB) not recognized
1474           61  number is too big           61  number is too big
1475           62  subpattern name expected           62  subpattern name expected
1476           63  digit expected after (?+           63  digit expected after (?+
1477           64  ] is an invalid data character in JavaScript compatibility mode           64  ] is an invalid data character in JavaScript compatibility mode
1478             65  different names for  subpatterns  of  the  same  number  are  not
1479           allowed
1480             66  (*MARK) must have an argument
1481    
1482         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
1483         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.
# Line 1468  STUDYING A PATTERN Line 1497  STUDYING A PATTERN
1497         the results of the study.         the results of the study.
1498    
1499         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1500         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec()  or  pcre_dfa_exec(). However, a pcre_extra block also con-
1501         that can be set by the caller before the block  is  passed;  these  are         tains other fields that can be set by the caller before  the  block  is
1502         described below in the section on matching a pattern.         passed; these are described below in the section on matching a pattern.
1503    
1504         If  studying  the  pattern  does not produce any additional information         If  studying  the  pattern  does  not  produce  any useful information,
1505         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1506         wants  to  pass  any of the other fields to pcre_exec(), it must set up         wants   to   pass   any   of   the   other  fields  to  pcre_exec()  or
1507         its own pcre_extra block.         pcre_dfa_exec(), it must set up its own pcre_extra block.
1508    
1509         The second argument of pcre_study() contains option bits.  At  present,         The second argument of pcre_study() contains option bits.  At  present,
1510         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
# Line 1495  STUDYING A PATTERN Line 1524  STUDYING A PATTERN
1524             0,              /* no options exist */             0,              /* no options exist */
1525             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1526    
1527         At present, studying a pattern is useful only for non-anchored patterns         Studying a pattern does two things: first, a lower bound for the length
1528         that  do not have a single fixed starting character. A bitmap of possi-         of subject string that is needed to match the pattern is computed. This
1529         ble starting bytes is created.         does not mean that there are any strings of that length that match, but
1530           it  does  guarantee that no shorter strings match. The value is used by
1531           pcre_exec() and pcre_dfa_exec() to avoid  wasting  time  by  trying  to
1532           match  strings  that are shorter than the lower bound. You can find out
1533           the value in a calling program via the pcre_fullinfo() function.
1534    
1535           Studying a pattern is also useful for non-anchored patterns that do not
1536           have  a  single fixed starting character. A bitmap of possible starting
1537           bytes is created. This speeds up finding a position in the  subject  at
1538           which to start matching.
1539    
1540    
1541  LOCALE SUPPORT  LOCALE SUPPORT
1542    
1543         PCRE handles caseless matching, and determines whether  characters  are         PCRE  handles  caseless matching, and determines whether characters are
1544         letters,  digits, or whatever, by reference to a set of tables, indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1545         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
1546         characters  with  codes  less than 128. Higher-valued codes never match         characters with codes less than 128. Higher-valued  codes  never  match
1547         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
1548         with  Unicode  character property support. The use of locales with Uni-         with Unicode character property support. The use of locales  with  Uni-
1549         code is discouraged. If you are handling characters with codes  greater         code  is discouraged. If you are handling characters with codes greater
1550         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
1551         not try to mix the two.         not try to mix the two.
1552    
1553         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
1554         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1555         applications.  Normally, the internal tables recognize only ASCII char-         applications.  Normally, the internal tables recognize only ASCII char-
1556         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-
1557         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,
1558         which may cause them to be different.         which may cause them to be different.
1559    
1560         The  internal tables can always be overridden by tables supplied by the         The internal tables can always be overridden by tables supplied by  the
1561         application that calls PCRE. These may be created in a different locale         application that calls PCRE. These may be created in a different locale
1562         from  the  default.  As more and more applications change to using Uni-         from the default. As more and more applications change  to  using  Uni-
1563         code, the need for this locale support is expected to die away.         code, the need for this locale support is expected to die away.
1564    
1565         External tables are built by calling  the  pcre_maketables()  function,         External  tables  are  built by calling the pcre_maketables() function,
1566         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
1567         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1568         example,  to  build  and use tables that are appropriate for the French         example, to build and use tables that are appropriate  for  the  French
1569         locale (where accented characters with  values  greater  than  128  are         locale  (where  accented  characters  with  values greater than 128 are
1570         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1571    
1572           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1573           tables = pcre_maketables();           tables = pcre_maketables();
1574           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1575    
1576         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;
1577         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".
1578    
1579         When pcre_maketables() runs, the tables are built  in  memory  that  is         When  pcre_maketables()  runs,  the  tables are built in memory that is
1580         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1581         that the memory containing the tables remains available for as long  as         that  the memory containing the tables remains available for as long as
1582         it is needed.         it is needed.
1583    
1584         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
1585         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()
1586         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-
1587         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1588         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1589    
1590         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
1591         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1592         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
1593         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
1594         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1595    
# Line 1561  INFORMATION ABOUT A PATTERN Line 1599  INFORMATION ABOUT A PATTERN
1599         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1600              int what, void *where);              int what, void *where);
1601    
1602         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1603         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1604         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1605    
1606         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1607         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
1608         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1609         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
1610         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
1611         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1612    
1613           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1577  INFORMATION ABOUT A PATTERN Line 1615  INFORMATION ABOUT A PATTERN
1615           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1616           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1617    
1618         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
1619         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1620         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1621         pattern:         pattern:
1622    
1623           int rc;           int rc;
# Line 1590  INFORMATION ABOUT A PATTERN Line 1628  INFORMATION ABOUT A PATTERN
1628             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1629             &length);         /* where to put the data */             &length);         /* where to put the data */
1630    
1631         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
1632         are as follows:         are as follows:
1633    
1634           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1635    
1636         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1637         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1638         there are no back references.         there are no back references.
1639    
1640           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1641    
1642         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1643         argument should point to an int variable.         argument should point to an int variable.
1644    
1645           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1646    
1647         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1648         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1649         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1650         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1651         passing a NULL table pointer.         passing a NULL table pointer.
1652    
1653           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1654    
1655         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1656         non-anchored pattern. The fourth argument should point to an int  vari-         non-anchored  pattern. The fourth argument should point to an int vari-
1657         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
1658         is still recognized for backwards compatibility.)         is still recognized for backwards compatibility.)
1659    
1660         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
1661         (cat|cow|coyote), its value is returned. Otherwise, if either         (cat|cow|coyote), its value is returned. Otherwise, if either
1662    
1663         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1664         branch starts with "^", or         branch starts with "^", or
1665    
1666         (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
1667         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1668    
1669         -1  is  returned, indicating that the pattern matches only at the start         -1 is returned, indicating that the pattern matches only at  the  start
1670         of a subject string or after any newline within the  string.  Otherwise         of  a  subject string or after any newline within the string. Otherwise
1671         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1672    
1673           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1674    
1675         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
1676         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
1677         matching  string, a pointer to the table is returned. Otherwise NULL is         matching string, a pointer to the table is returned. Otherwise NULL  is
1678         returned. The fourth argument should point to an unsigned char *  vari-         returned.  The fourth argument should point to an unsigned char * vari-
1679         able.         able.
1680    
1681           PCRE_INFO_HASCRORLF           PCRE_INFO_HASCRORLF
1682    
1683         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
1684         characters, otherwise 0. The fourth argument should  point  to  an  int         characters,  otherwise  0.  The  fourth argument should point to an int
1685         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
1686         \r or \n.         \r or \n.
1687    
1688           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1689    
1690         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,
1691         otherwise  0. The fourth argument should point to an int variable. (?J)         otherwise 0. The fourth argument should point to an int variable.  (?J)
1692         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1693    
1694           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1695    
1696         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
1697         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
1698         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1699         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
1700         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1701         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
1702         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1703    
1704             PCRE_INFO_MINLENGTH
1705    
1706           If  the  pattern  was studied and a minimum length for matching subject
1707           strings was computed, its value is  returned.  Otherwise  the  returned
1708           value  is  -1. The value is a number of characters, not bytes (this may
1709           be relevant in UTF-8 mode). The fourth argument should point to an  int
1710           variable.  A  non-negative  value is a lower bound to the length of any
1711           matching string. There may not be any strings of that  length  that  do
1712           actually match, but every string that does match is at least that long.
1713    
1714           PCRE_INFO_NAMECOUNT           PCRE_INFO_NAMECOUNT
1715           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1716           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1717    
1718         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1719         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1720         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1721         pcre_get_named_substring()  are  provided  for extracting captured sub-         pcre_get_named_substring() are provided for  extracting  captured  sub-
1722         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
1723         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
1724         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1725         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
1726         described by these three values.         described by these three values.
1727    
1728         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
1729         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1730         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
1731         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1732         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
1733         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-
1734         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-
1735         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated.
1736         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-  
1737         theses  numbers.  For  example,  consider the following pattern (assume         The names are in alphabetical order. Duplicate names may appear if  (?|
1738         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is         is used to create multiple groups with the same number, as described in
1739         ignored):         the section on duplicate subpattern numbers in  the  pcrepattern  page.
1740           Duplicate  names  for  subpatterns with different numbers are permitted
1741           only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
1742           appear  in  the table in the order in which they were found in the pat-
1743           tern. In the absence of (?| this is the  order  of  increasing  number;
1744           when (?| is used this is not necessarily the case because later subpat-
1745           terns may have lower numbers.
1746    
1747           As a simple example of the name/number table,  consider  the  following
1748           pattern  (assume  PCRE_EXTENDED is set, so white space - including new-
1749           lines - is ignored):
1750    
1751           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1752           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1753    
1754         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1755         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,
1756         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1757         as ??:         as ??:
1758    
# Line 1703  INFORMATION ABOUT A PATTERN Line 1761  INFORMATION ABOUT A PATTERN
1761           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1762           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1763    
1764         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1765         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
1766         to be different for each compiled pattern.         to be different for each compiled pattern.
1767    
1768           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1769    
1770         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
1771         The  fourth  argument  should point to an int variable. The pcrepartial         pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
1772         documentation lists the restrictions that apply to patterns  when  par-         variable.  From  release  8.00,  this  always  returns  1,  because the
1773         tial matching is used.         restrictions that previously applied  to  partial  matching  have  been
1774           lifted.  The  pcrepartial documentation gives details of partial match-
1775           ing.
1776    
1777           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1778    
1779         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
1780         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1781         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1782         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
1783         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
1784         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
1785         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1786         and PCRE_EXTENDED.         and PCRE_EXTENDED.
1787    
1788         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
1789         alternatives begin with one of the following:         alternatives begin with one of the following:
1790    
1791           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1739  INFORMATION ABOUT A PATTERN Line 1799  INFORMATION ABOUT A PATTERN
1799    
1800           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1801    
1802         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
1803         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
1804         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
1805         size_t variable.         size_t variable.
# Line 1747  INFORMATION ABOUT A PATTERN Line 1807  INFORMATION ABOUT A PATTERN
1807           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1808    
1809         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
1810         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
1811         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
1812         created by pcre_study(). The fourth argument should point to  a  size_t         created  by  pcre_study().  If pcre_extra is NULL, or there is no study
1813           data, zero is returned. The fourth argument should point  to  a  size_t
1814         variable.         variable.
1815    
1816    
# Line 1803  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1864  MATCHING A PATTERN: THE TRADITIONAL FUNC
1864              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1865              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1866    
1867         The  function pcre_exec() is called to match a subject string against a         The function pcre_exec() is called to match a subject string against  a
1868         compiled pattern, which is passed in the code argument. If the  pattern         compiled  pattern, which is passed in the code argument. If the pattern
1869         has been studied, the result of the study should be passed in the extra         was studied, the result of the study should  be  passed  in  the  extra
1870         argument. This function is the main matching facility of  the  library,         argument.  This  function is the main matching facility of the library,
1871         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1872         an alternative matching function, which is described below in the  sec-         an  alternative matching function, which is described below in the sec-
1873         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1874    
1875         In  most applications, the pattern will have been compiled (and option-         In most applications, the pattern will have been compiled (and  option-
1876         ally studied) in the same process that calls pcre_exec().  However,  it         ally  studied)  in the same process that calls pcre_exec(). However, it
1877         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1878         later in different processes, possibly even on different hosts.  For  a         later  in  different processes, possibly even on different hosts. For a
1879         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1880    
1881         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1833  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1894  MATCHING A PATTERN: THE TRADITIONAL FUNC
1894    
1895     Extra data for pcre_exec()     Extra data for pcre_exec()
1896    
1897         If  the  extra argument is not NULL, it must point to a pcre_extra data         If the extra argument is not NULL, it must point to a  pcre_extra  data
1898         block. The pcre_study() function returns such a block (when it  doesn't         block.  The pcre_study() function returns such a block (when it doesn't
1899         return  NULL), but you can also create one for yourself, and pass addi-         return NULL), but you can also create one for yourself, and pass  addi-
1900         tional information in it. The pcre_extra block contains  the  following         tional  information  in it. The pcre_extra block contains the following
1901         fields (not necessarily in this order):         fields (not necessarily in this order):
1902    
1903           unsigned long int flags;           unsigned long int flags;
# Line 1845  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1906  MATCHING A PATTERN: THE TRADITIONAL FUNC
1906           unsigned long int match_limit_recursion;           unsigned long int match_limit_recursion;
1907           void *callout_data;           void *callout_data;
1908           const unsigned char *tables;           const unsigned char *tables;
1909             unsigned char **mark;
1910    
1911         The  flags  field  is a bitmap that specifies which of the other fields         The flags field is a bitmap that specifies which of  the  other  fields
1912         are set. The flag bits are:         are set. The flag bits are:
1913    
1914           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1854  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1916  MATCHING A PATTERN: THE TRADITIONAL FUNC
1916           PCRE_EXTRA_MATCH_LIMIT_RECURSION           PCRE_EXTRA_MATCH_LIMIT_RECURSION
1917           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1918           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1919             PCRE_EXTRA_MARK
1920    
1921         Other flag bits should be set to zero. The study_data field is  set  in         Other  flag  bits should be set to zero. The study_data field is set in
1922         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1923         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1924         add  to  the  block by setting the other fields and their corresponding         add to the block by setting the other fields  and  their  corresponding
1925         flag bits.         flag bits.
1926    
1927         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1928         a  vast amount of resources when running patterns that are not going to         a vast amount of resources when running patterns that are not going  to
1929         match, but which have a very large number  of  possibilities  in  their         match,  but  which  have  a very large number of possibilities in their
1930         search  trees.  The  classic  example  is  the  use of nested unlimited         search trees. The classic example is a pattern that uses nested  unlim-
1931         repeats.         ited repeats.
1932    
1933         Internally, PCRE uses a function called match() which it calls  repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1934         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly (sometimes recursively). The limit set by match_limit  is  imposed
1935         on the number of times this function is called during  a  match,  which         on  the  number  of times this function is called during a match, which
1936         has  the  effect  of  limiting the amount of backtracking that can take         has the effect of limiting the amount of  backtracking  that  can  take
1937         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1938         for each position in the subject string.         for each position in the subject string.
1939    
1940         The  default  value  for  the  limit can be set when PCRE is built; the         The default value for the limit can be set  when  PCRE  is  built;  the
1941         default default is 10 million, which handles all but the  most  extreme         default  default  is 10 million, which handles all but the most extreme
1942         cases.  You  can  override  the  default by suppling pcre_exec() with a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1943         pcre_extra    block    in    which    match_limit    is    set,     and         pcre_extra     block    in    which    match_limit    is    set,    and
1944         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
1945         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1946    
1947         The match_limit_recursion field is similar to match_limit, but  instead         The  match_limit_recursion field is similar to match_limit, but instead
1948         of limiting the total number of times that match() is called, it limits         of limiting the total number of times that match() is called, it limits
1949         the depth of recursion. The recursion depth is a  smaller  number  than         the  depth  of  recursion. The recursion depth is a smaller number than
1950         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-
1951         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.
1952    
1953         Limiting  the  recursion  depth  limits the amount of stack that can be         Limiting  the  recursion  depth  limits the amount of stack that can be
# Line 1898  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1961  MATCHING A PATTERN: THE TRADITIONAL FUNC
1961         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
1962         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1963    
1964         The pcre_callout field is used in conjunction with the  "callout"  fea-         The callout_data field is used in conjunction with the  "callout"  fea-
1965         ture, which is described in the pcrecallout documentation.         ture, and is described in the pcrecallout documentation.
1966    
1967         The  tables  field  is  used  to  pass  a  character  tables pointer to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1968         pcre_exec(); this overrides the value that is stored with the  compiled         pcre_exec(); this overrides the value that is stored with the  compiled
# Line 1912  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1975  MATCHING A PATTERN: THE TRADITIONAL FUNC
1975         address  when  pcre_exec() is called. See the pcreprecompile documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1976         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1977    
1978           If PCRE_EXTRA_MARK is set in the flags field, the mark  field  must  be
1979           set  to  point  to a char * variable. If the pattern contains any back-
1980           tracking control verbs such as (*MARK:NAME), and the execution ends  up
1981           with  a  name  to  pass back, a pointer to the name string (zero termi-
1982           nated) is placed in the variable pointed to  by  the  mark  field.  The
1983           names  are  within  the  compiled pattern; if you wish to retain such a
1984           name you must copy it before freeing the memory of a compiled  pattern.
1985           If  there  is no name to pass back, the variable pointed to by the mark
1986           field set to NULL. For details of the backtracking control  verbs,  see
1987           the section entitled "Backtracking control" in the pcrepattern documen-
1988           tation.
1989    
1990     Option bits for pcre_exec()     Option bits for pcre_exec()
1991    
1992         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.
1993         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,
1994         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,    PCRE_NOTEMPTY,    PCRE_NOTEMPTY_ATSTART,
1995         PCRE_PARTIAL.         PCRE_NO_START_OPTIMIZE,   PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,  and
1996           PCRE_PARTIAL_HARD.
1997    
1998           PCRE_ANCHORED           PCRE_ANCHORED
1999    
2000         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
2001         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
2002         turned  out to be anchored by virtue of its contents, it cannot be made         turned out to be anchored by virtue of its contents, it cannot be  made
2003         unachored at matching time.         unachored at matching time.
2004    
2005           PCRE_BSR_ANYCRLF           PCRE_BSR_ANYCRLF
2006           PCRE_BSR_UNICODE           PCRE_BSR_UNICODE
2007    
2008         These options (which are mutually exclusive) control what the \R escape         These options (which are mutually exclusive) control what the \R escape
2009         sequence  matches.  The choice is either to match only CR, LF, or CRLF,         sequence matches. The choice is either to match only CR, LF,  or  CRLF,
2010         or to match any Unicode newline sequence. These  options  override  the         or  to  match  any Unicode newline sequence. These options override the
2011         choice that was made or defaulted when the pattern was compiled.         choice that was made or defaulted when the pattern was compiled.
2012    
2013           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1940  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2016  MATCHING A PATTERN: THE TRADITIONAL FUNC
2016           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
2017           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
2018    
2019         These  options  override  the  newline  definition  that  was chosen or         These options override  the  newline  definition  that  was  chosen  or
2020         defaulted when the pattern was compiled. For details, see the  descrip-         defaulted  when the pattern was compiled. For details, see the descrip-
2021         tion  of  pcre_compile()  above.  During  matching,  the newline choice         tion of pcre_compile()  above.  During  matching,  the  newline  choice
2022         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
2023         ters.  It may also alter the way the match position is advanced after a         ters. It may also alter the way the match position is advanced after  a
2024         match failure for an unanchored pattern.         match failure for an unanchored pattern.
2025    
2026         When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is         When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
2027         set,  and a match attempt for an unanchored pattern fails when the cur-         set, and a match attempt for an unanchored pattern fails when the  cur-
2028         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no         rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
2029         explicit  matches  for  CR  or  LF  characters,  the  match position is         explicit matches for  CR  or  LF  characters,  the  match  position  is
2030         advanced by two characters instead of one, in other words, to after the         advanced by two characters instead of one, in other words, to after the
2031         CRLF.         CRLF.
2032    
2033         The above rule is a compromise that makes the most common cases work as         The above rule is a compromise that makes the most common cases work as
2034         expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL         expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
2035         option is not set), it does not match the string "\r\nA" because, after         option is not set), it does not match the string "\r\nA" because, after
2036         failing at the start, it skips both the CR and the LF before  retrying.         failing  at the start, it skips both the CR and the LF before retrying.
2037         However,  the  pattern  [\r\n]A does match that string, because it con-         However, the pattern [\r\n]A does match that string,  because  it  con-
2038         tains an explicit CR or LF reference, and so advances only by one char-         tains an explicit CR or LF reference, and so advances only by one char-
2039         acter after the first failure.         acter after the first failure.
2040    
2041         An explicit match for CR of LF is either a literal appearance of one of         An explicit match for CR of LF is either a literal appearance of one of
2042         those characters, or one of the \r or  \n  escape  sequences.  Implicit         those  characters,  or  one  of the \r or \n escape sequences. Implicit
2043         matches  such  as [^X] do not count, nor does \s (which includes CR and         matches such as [^X] do not count, nor does \s (which includes  CR  and
2044         LF in the characters that it matches).         LF in the characters that it matches).
2045    
2046         Notwithstanding the above, anomalous effects may still occur when  CRLF         Notwithstanding  the above, anomalous effects may still occur when CRLF
2047         is a valid newline sequence and explicit \r or \n escapes appear in the         is a valid newline sequence and explicit \r or \n escapes appear in the
2048         pattern.         pattern.
2049    
2050           PCRE_NOTBOL           PCRE_NOTBOL
2051    
2052         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
2053         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
2054         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
2055         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
2056         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
2057    
2058           PCRE_NOTEOL           PCRE_NOTEOL
2059    
2060         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
2061         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
2062         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
2063         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2064         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
2065         not affect \Z or \z.         not affect \Z or \z.
2066    
2067           PCRE_NOTEMPTY           PCRE_NOTEMPTY
2068    
2069         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
2070         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
2071         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
2072         example, if the pattern         example, if the pattern
2073    
2074           a?b?           a?b?
2075    
2076         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
2077         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
2078         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-
2079         rences of "a" or "b".         rences of "a" or "b".
2080    
2081         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-           PCRE_NOTEMPTY_ATSTART
2082         cial case of a pattern match of the empty  string  within  its  split()  
2083         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
2084         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
2085         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.
2086         if that fails by advancing the starting offset (see below)  and  trying  
2087         an ordinary match again. There is some code that demonstrates how to do         Perl    has    no    direct    equivalent    of    PCRE_NOTEMPTY     or
2088         this in the pcredemo.c sample program.         PCRE_NOTEMPTY_ATSTART,  but  it  does  make a special case of a pattern
2089           match of the empty string within its split() function, and  when  using
2090           the  /g  modifier.  It  is  possible  to emulate Perl's behaviour after
2091           matching a null string by first trying the match again at the same off-
2092           set  with  PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED,  and then if that
2093           fails, by advancing the starting offset (see below) and trying an ordi-
2094           nary  match  again. There is some code that demonstrates how to do this
2095           in the pcredemo sample program.
2096    
2097             PCRE_NO_START_OPTIMIZE
2098    
2099           There are a number of optimizations that pcre_exec() uses at the  start
2100           of  a  match,  in  order to speed up the process. For example, if it is
2101           known that a match must start with a specific  character,  it  searches
2102           the subject for that character, and fails immediately if it cannot find
2103           it, without actually running the main matching function. When  callouts
2104           are  in  use,  these  optimizations  can cause them to be skipped. This
2105           option disables the "start-up" optimizations,  causing  performance  to
2106           suffer, but ensuring that the callouts do occur.
2107    
2108           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2109    
2110         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
2111         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
2112         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
2113         points  to  the start of a UTF-8 character. There is a discussion about         points to the start of a UTF-8 character. There is a  discussion  about
2114         the validity of UTF-8 strings in the section on UTF-8  support  in  the         the  validity  of  UTF-8 strings in the section on UTF-8 support in the
2115         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
2116         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
2117         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.         tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2118    
2119         If  you  already  know that your subject is valid, and you want to skip         If you already know that your subject is valid, and you  want  to  skip
2120         these   checks   for   performance   reasons,   you   can    set    the         these    checks    for   performance   reasons,   you   can   set   the
2121         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
2122         do this for the second and subsequent calls to pcre_exec() if  you  are         do  this  for the second and subsequent calls to pcre_exec() if you are
2123         making  repeated  calls  to  find  all  the matches in a single subject         making repeated calls to find all  the  matches  in  a  single  subject
2124         string. However, you should be  sure  that  the  value  of  startoffset         string.  However,  you  should  be  sure  that the value of startoffset
2125         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
2126         set, the effect of passing an invalid UTF-8 string as a subject,  or  a         set,  the  effect of passing an invalid UTF-8 string as a subject, or a
2127         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-
2128         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2129    
2130           PCRE_PARTIAL           PCRE_PARTIAL_HARD
2131             PCRE_PARTIAL_SOFT
2132    
2133         This option turns on the  partial  matching  feature.  If  the  subject         These  options turn on the partial matching feature. For backwards com-
2134         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
2135         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,
2136         partially  matches  the  pattern and the failure to match occurred only         but there are not enough subject characters to complete the  match.  If
2137         because there were not enough subject characters), pcre_exec()  returns         this  happens  when  PCRE_PARTIAL_HARD  is set, pcre_exec() immediately
2138         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         returns PCRE_ERROR_PARTIAL. Otherwise,  if  PCRE_PARTIAL_SOFT  is  set,
2139         used, there are restrictions on what may appear in the  pattern.  These         matching  continues by testing any other alternatives. Only if they all
2140         are discussed in the pcrepartial documentation.         fail is PCRE_ERROR_PARTIAL returned  (instead  of  PCRE_ERROR_NOMATCH).
2141           The portion of the string that was inspected when the partial match was
2142           found is set as the first matching string. There  is  a  more  detailed
2143           discussion in the pcrepartial documentation.
2144    
2145     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2146    
2147         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
2148         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.
2149         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-
2150         Unlike the pattern string, the subject may contain binary  zero  bytes.         acter. Unlike the pattern string, the subject may contain  binary  zero
2151         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
2152         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
2153           case.
2154         A non-zero starting offset is useful when searching for  another  match  
2155         in  the same subject by calling pcre_exec() again after a previous suc-         A  non-zero  starting offset is useful when searching for another match
2156         cess.  Setting startoffset differs from just passing over  a  shortened         in the same subject by calling pcre_exec() again after a previous  suc-
2157         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins         cess.   Setting  startoffset differs from just passing over a shortened
2158           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
2159         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
2160    
2161           \Biss\B           \Biss\B
2162    
2163         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
2164         only  if  the  current position in the subject is not a word boundary.)         only if the current position in the subject is not  a  word  boundary.)
2165         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
2166         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
2167         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
2168         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
2169         to be a word boundary. However, if pcre_exec()  is  passed  the  entire         to  be  a  word  boundary. However, if pcre_exec() is passed the entire
2170         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
2171         rence of "iss" because it is able to look behind the starting point  to         rence  of "iss" because it is able to look behind the starting point to
2172         discover that it is preceded by a letter.         discover that it is preceded by a letter.
2173    
2174         If  a  non-zero starting offset is passed when the pattern is anchored,         If a non-zero starting offset is passed when the pattern  is  anchored,
2175         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
2176         if  the  pattern  does  not require the match to be at the start of the         if the pattern does not require the match to be at  the  start  of  the
2177         subject.         subject.
2178    
2179     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2180    
2181         In general, a pattern matches a certain portion of the subject, and  in         In  general, a pattern matches a certain portion of the subject, and in
2182         addition,  further  substrings  from  the  subject may be picked out by         addition, further substrings from the subject  may  be  picked  out  by
2183         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
2184         this  is  called "capturing" in what follows, and the phrase "capturing         this is called "capturing" in what follows, and the  phrase  "capturing
2185         subpattern" is used for a fragment of a pattern that picks out  a  sub-         subpattern"  is  used for a fragment of a pattern that picks out a sub-
2186         string.  PCRE  supports several other kinds of parenthesized subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
2187         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2188    
2189         Captured substrings are returned to the caller via a vector of  integer         Captured substrings are returned to the caller via a vector of integers
2190         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-
2191         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:
2192         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2193    
2194         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-
2195         strings, each substring using a pair of integers. The  remaining  third         strings,  each  substring using a pair of integers. The remaining third
2196         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-
2197         turing subpatterns, and is not available for passing back  information.         turing  subpatterns, and is not available for passing back information.
2198         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
2199         it is not, it is rounded down.         it is not, it is rounded down.
2200    
2201         When a match is successful, information about  captured  substrings  is         When  a  match  is successful, information about captured substrings is
2202         returned  in  pairs  of integers, starting at the beginning of ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
2203         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
2204         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
2205         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
2206         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
2207         tor[1], identify the portion of  the  subject  string  matched  by  the         byte offsets, even in UTF-8 mode. They are not character counts.
2208         entire  pattern.  The next pair is used for the first capturing subpat-  
2209         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
2210         highest numbered pair that has been set. For example, if two substrings         portion of the subject string matched by the entire pattern.  The  next
2211         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
2212         subpatterns,  the return value from a successful match is 1, indicating         returned by pcre_exec() is one more than the highest numbered pair that
2213         that just the first pair of offsets has been set.         has  been  set.  For example, if two substrings have been captured, the
2214           returned value is 3. If there are no capturing subpatterns, the  return
2215           value from a successful match is 1, indicating that just the first pair
2216           of offsets has been set.
2217    
2218         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2219         of the string that it matched that is returned.         of the string that it matched that is returned.
2220    
2221         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,
2222         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
2223         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
2224         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
2225         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize  as zero. However, if the pattern contains back references and
2226         references and the ovector is not big enough to  remember  the  related         the ovector is not big enough to remember the related substrings,  PCRE
2227         substrings,  PCRE has to get additional memory for use during matching.         has  to  get additional memory for use during matching. Thus it is usu-
2228         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2229    
2230         The pcre_info() function can be used to find  out  how  many  capturing         The pcre_fullinfo() function can be used to find out how many capturing
2231         subpatterns  there  are  in  a  compiled pattern. The smallest size for         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2232         ovector that will allow for n captured substrings, in addition  to  the         ovector that will allow for n captured substrings, in addition  to  the
2233         offsets of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
# Line 2224  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2326  MATCHING A PATTERN: THE TRADITIONAL FUNC
2326    
2327           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2328    
2329         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         This  code  is  no  longer  in  use.  It was formerly returned when the
2330         items that are not supported for partial matching. See the  pcrepartial         PCRE_PARTIAL option was used with a compiled pattern  containing  items
2331         documentation for details of partial matching.         that  were  not  supported  for  partial  matching.  From  release 8.00
2332           onwards, there are no restrictions on partial matching.
2333    
2334           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2335    
2336         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
2337         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2338    
2339           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2340    
2341         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.
2342    
2343           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2344    
# Line 2385  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2488  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2488         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
2489         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2490    
2491           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2492           terns with the same number, as described in the  section  on  duplicate
2493           subpattern  numbers  in  the  pcrepattern page, you cannot use names to
2494           distinguish the different subpatterns, because names are  not  included
2495           in  the compiled code. The matching process uses only numbers. For this
2496           reason, the use of different names for subpatterns of the  same  number
2497           causes an error at compile time.
2498    
2499    
2500  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2501    
# Line 2392  DUPLICATE SUBPATTERN NAMES Line 2503  DUPLICATE SUBPATTERN NAMES
2503              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2504    
2505         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2506         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns are not required to be unique. (Duplicate names are  always
2507         duplicate  names  are such that in any one match, only one of the named         allowed  for subpatterns with the same number, created by using the (?|
2508         subpatterns participates. An example is shown in the pcrepattern  docu-         feature. Indeed, if such subpatterns are named, they  are  required  to
2509         mentation.         use the same names.)
2510    
2511           Normally, patterns with duplicate names are such that in any one match,
2512           only one of the named subpatterns participates. An example is shown  in
2513           the pcrepattern documentation.
2514    
2515         When    duplicates   are   present,   pcre_copy_named_substring()   and         When    duplicates   are   present,   pcre_copy_named_substring()   and
2516         pcre_get_named_substring() return the first substring corresponding  to         pcre_get_named_substring() return the first substring corresponding  to
# Line 2448  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2563  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2563         characteristics to the normal algorithm, and  is  not  compatible  with         characteristics to the normal algorithm, and  is  not  compatible  with
2564         Perl.  Some  of the features of PCRE patterns are not supported. Never-         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2565         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
2566         a discussion of the two matching algorithms, see the pcrematching docu-         a  discussion  of  the  two matching algorithms, and a list of features
2567         mentation.         that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2568           tion.
2569    
2570         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
2571         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-
2572         ent way, and this is described below. The other  common  arguments  are         ent  way,  and  this is described below. The other common arguments are
2573         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
2574         repeated here.         repeated here.
2575    
2576         The two additional arguments provide workspace for  the  function.  The         The  two  additional  arguments provide workspace for the function. The
2577         workspace  vector  should  contain at least 20 elements. It is used for         workspace vector should contain at least 20 elements. It  is  used  for
2578         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2579         workspace  will  be  needed for patterns and subjects where there are a         workspace will be needed for patterns and subjects where  there  are  a
2580         lot of potential matches.         lot of potential matches.
2581    
2582         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 2598  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2598    
2599     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2600    
2601         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
2602         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-
2603         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,         LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2604         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-
2605         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
2606         not repeated here.         four of these are  exactly  the  same  as  for  pcre_exec(),  so  their
2607           description is not repeated here.
2608           PCRE_PARTIAL  
2609             PCRE_PARTIAL_HARD
2610         This  has  the  same general effect as it does for pcre_exec(), but the           PCRE_PARTIAL_SOFT
2611         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for  
2612         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
2613         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have         details are slightly  different.  When  PCRE_PARTIAL_HARD  is  set  for
2614         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-
2615         sibility. The portion of the string that provided the partial match  is         ject is reached and there is still at least  one  matching  possibility
2616         set as the first matching string.         that requires additional characters. This happens even if some complete
2617           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2618           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2619           of the subject is reached, there have been  no  complete  matches,  but
2620           there  is  still  at least one matching possibility. The portion of the
2621           string that was inspected when the longest partial match was  found  is
2622           set as the first matching string in both cases.
2623    
2624           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2625    
# Line 2508  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2630  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2630    
2631           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2632    
2633         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
2634         returns  a  partial  match, it is possible to call it again, with addi-         again,  with  additional  subject characters, and have it continue with
2635         tional subject characters, and have it continue with  the  same  match.         the same match. The PCRE_DFA_RESTART option requests this action;  when
2636         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
2637         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
2638         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
2639         match. There is more discussion of this  facility  in  the  pcrepartial         pcrepartial documentation.
        documentation.  
2640    
2641     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2642    
2643         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-
2644         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
2645         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
2646         matches are all initial substrings of the longer matches. For  example,         matches  are all initial substrings of the longer matches. For example,
2647         if the pattern         if the pattern
2648    
2649           <.*>           <.*>
# Line 2537  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2658  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2658           <something> <something else>           <something> <something else>
2659           <something> <something else> <something further>           <something> <something else> <something further>
2660    
2661         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,
2662         which is the number of matched substrings.  The  substrings  themselves         which  is  the  number of matched substrings. The substrings themselves
2663         are  returned  in  ovector. Each string uses two elements; the first is         are returned in ovector. Each string uses two elements;  the  first  is
2664         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
2665         fact,  all  the  strings  have the same start offset. (Space could have         fact, all the strings have the same start  offset.  (Space  could  have
2666         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
2667         compatibility  with  the  way pcre_exec() returns data, even though the         compatibility with the way pcre_exec() returns data,  even  though  the
2668         meaning of the strings is different.)         meaning of the strings is different.)
2669    
2670         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-
2671         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
2672         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
2673         filled with the longest matches.         filled with the longest matches.
2674    
2675     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2676    
2677         The  pcre_dfa_exec()  function returns a negative number when it fails.         The pcre_dfa_exec() function returns a negative number when  it  fails.
2678         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
2679         described  above.   There are in addition the following errors that are         described above.  There are in addition the following errors  that  are
2680         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2681    
2682           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2683    
2684         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-
2685         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
2686         reference.         reference.
2687    
2688           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2689    
2690         This return is given if pcre_dfa_exec()  encounters  a  condition  item         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2691         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
2692         in a specific group. These are not supported.         in a specific group. These are not supported.
2693    
2694           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2695    
2696         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
2697         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
2698         (it is meaningless).         (it is meaningless).
2699    
2700           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2701    
2702         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
2703         workspace vector.         workspace vector.
2704    
2705           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2706    
2707         When  a  recursive subpattern is processed, the matching function calls         When a recursive subpattern is processed, the matching  function  calls
2708         itself recursively, using private vectors for  ovector  and  workspace.         itself  recursively,  using  private vectors for ovector and workspace.
2709         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
2710         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2711    
2712    
2713  SEE ALSO  SEE ALSO
2714    
2715         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2716         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2717    
2718    
2719  AUTHOR  AUTHOR
# Line 2604  AUTHOR Line 2725  AUTHOR
2725    
2726  REVISION  REVISION
2727    
2728         Last updated: 12 April 2008         Last updated: 26 March 2010
2729         Copyright (c) 1997-2008 University of Cambridge.         Copyright (c) 1997-2010 University of Cambridge.
2730  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2731    
2732    
# Line 2634  PCRE CALLOUTS Line 2755  PCRE CALLOUTS
2755    
2756           (?C1)abc(?C2)def           (?C1)abc(?C2)def
2757    
2758         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
2759         called, PCRE automatically  inserts  callouts,  all  with  number  255,         pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
2760         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is         with  number  255,  before  each  item  in the pattern. For example, if
2761         used with the pattern         PCRE_AUTO_CALLOUT is used with the pattern
2762    
2763           A(\d{2}|--)           A(\d{2}|--)
2764    
# Line 2656  PCRE CALLOUTS Line 2777  PCRE CALLOUTS
2777  MISSING CALLOUTS  MISSING CALLOUTS
2778    
2779         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2780         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2781         pattern is         example, if the pattern is
2782    
2783           ab(?C4)cd           ab(?C4)cd
2784    
# Line 2666  MISSING CALLOUTS Line 2787  MISSING CALLOUTS
2787         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2788         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2789    
2790           If the pattern is studied, PCRE knows the minimum length of a  matching
2791           string,  and will immediately give a "no match" return without actually
2792           running a match if the subject is not long enough, or,  for  unanchored
2793           patterns, if it has been scanned far enough.
2794    
2795           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
2796           MIZE option to pcre_exec() or  pcre_dfa_exec().  This  slows  down  the
2797           matching  process,  but  does  ensure that callouts such as the example
2798           above are obeyed.
2799    
2800    
2801  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2802    
# Line 2693  THE CALLOUT INTERFACE Line 2824  THE CALLOUT INTERFACE
2824         version number will change again in future  if  additional  fields  are         version number will change again in future  if  additional  fields  are
2825         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.
2826    
2827         The callout_number field contains the number of the  callout,  as  com-         The  callout_number  field  contains the number of the callout, as com-
2828         piled  into  the pattern (that is, the number after ?C for manual call-         piled into the pattern (that is, the number after ?C for  manual  call-
2829         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2830    
2831         The offset_vector field is a pointer to the vector of offsets that  was         The  offset_vector field is a pointer to the vector of offsets that was
2832         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When         passed  by  the  caller  to  pcre_exec()   or   pcre_dfa_exec().   When
2833         pcre_exec() is used, the contents can be inspected in order to  extract         pcre_exec()  is used, the contents can be inspected in order to extract
2834         substrings  that  have  been  matched  so  far,  in the same way as for         substrings that have been matched so  far,  in  the  same  way  as  for
2835         extracting substrings after a match has completed. For  pcre_dfa_exec()         extracting  substrings after a match has completed. For pcre_dfa_exec()
2836         this field is not useful.         this field is not useful.
2837    
2838         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2839         were passed to pcre_exec().         were passed to pcre_exec().
2840    
2841         The start_match field normally contains the offset within  the  subject         The  start_match  field normally contains the offset within the subject
2842         at  which  the  current  match  attempt started. However, if the escape         at which the current match attempt  started.  However,  if  the  escape
2843         sequence \K has been encountered, this value is changed to reflect  the         sequence  \K has been encountered, this value is changed to reflect the
2844         modified  starting  point.  If the pattern is not anchored, the callout         modified starting point. If the pattern is not  anchored,  the  callout
2845         function may be called several times from the same point in the pattern         function may be called several times from the same point in the pattern
2846         for different starting points in the subject.         for different starting points in the subject.
2847    
2848         The  current_position  field  contains the offset within the subject of         The current_position field contains the offset within  the  subject  of
2849         the current match pointer.         the current match pointer.
2850    
2851         When the pcre_exec() function is used, the capture_top  field  contains         When  the  pcre_exec() function is used, the capture_top field contains
2852         one  more than the number of the highest numbered captured substring so         one more than the number of the highest numbered captured substring  so
2853         far. If no substrings have been captured, the value of  capture_top  is         far.  If  no substrings have been captured, the value of capture_top is
2854         one.  This  is always the case when pcre_dfa_exec() is used, because it         one. This is always the case when pcre_dfa_exec() is used,  because  it
2855         does not support captured substrings.         does not support captured substrings.
2856    
2857         The capture_last field contains the number of the  most  recently  cap-         The  capture_last  field  contains the number of the most recently cap-
2858         tured  substring. If no substrings have been captured, its value is -1.         tured substring. If no substrings have been captured, its value is  -1.
2859         This is always the case when pcre_dfa_exec() is used.         This is always the case when pcre_dfa_exec() is used.
2860    
2861         The callout_data field contains a value that is passed  to  pcre_exec()         The  callout_data  field contains a value that is passed to pcre_exec()
2862         or  pcre_dfa_exec() specifically so that it can be passed back in call-         or pcre_dfa_exec() specifically so that it can be passed back in  call-
2863         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data         outs.  It  is  passed  in the pcre_callout field of the pcre_extra data
2864         structure.  If  no such data was passed, the value of callout_data in a         structure. If no such data was passed, the value of callout_data  in  a
2865         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout  block  is  NULL. There is a description of the pcre_extra
2866         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2867    
2868         The  pattern_position field is present from version 1 of the pcre_call-         The pattern_position field is present from version 1 of the  pcre_call-
2869         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2870         the pattern string.         the pattern string.
2871    
2872         The  next_item_length field is present from version 1 of the pcre_call-         The next_item_length field is present from version 1 of the  pcre_call-
2873         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2874         the  pattern  string. When the callout immediately precedes an alterna-         the pattern string. When the callout immediately precedes  an  alterna-
2875         tion bar, a closing parenthesis, or the end of the pattern, the  length         tion  bar, a closing parenthesis, or the end of the pattern, the length
2876         is  zero.  When the callout precedes an opening parenthesis, the length         is zero. When the callout precedes an opening parenthesis,  the  length
2877         is that of the entire subpattern.         is that of the entire subpattern.
2878    
2879         The pattern_position and next_item_length fields are intended  to  help         The  pattern_position  and next_item_length fields are intended to help
2880         in  distinguishing between different automatic callouts, which all have         in distinguishing between different automatic callouts, which all  have
2881         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2882    
2883    
2884  RETURN VALUES  RETURN VALUES
2885    
2886         The external callout function returns an integer to PCRE. If the  value         The  external callout function returns an integer to PCRE. If the value
2887         is  zero,  matching  proceeds  as  normal. If the value is greater than         is zero, matching proceeds as normal. If  the  value  is  greater  than
2888         zero, matching fails at the current point, but  the  testing  of  other         zero,  matching  fails  at  the current point, but the testing of other
2889         matching possibilities goes ahead, just as if a lookahead assertion had         matching possibilities goes ahead, just as if a lookahead assertion had
2890         failed. If the value is less than zero, the  match  is  abandoned,  and         failed.  If  the  value  is less than zero, the match is abandoned, and
2891         pcre_exec() (or pcre_dfa_exec()) returns the negative value.         pcre_exec() or pcre_dfa_exec() returns the negative value.
2892    
2893         Negative   values   should   normally   be   chosen  from  the  set  of         Negative  values  should  normally  be   chosen   from   the   set   of
2894         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2895         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is
2896         reserved for use by callout functions; it will never be  used  by  PCRE         reserved  for  use  by callout functions; it will never be used by PCRE
2897         itself.         itself.
2898    
2899    
# Line 2775  AUTHOR Line 2906  AUTHOR
2906    
2907  REVISION  REVISION
2908    
2909         Last updated: 29 May 2007         Last updated: 29 September 2009
2910         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2911  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2912    
2913    
# Line 2790  NAME Line 2921  NAME
2921  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2922    
2923         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2924         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences  described  here  are  with
2925         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain         respect to Perl 5.10.
        some features that are expected to be in the forthcoming Perl 5.10.  
2926    
2927         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
2928         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
2929         main pcre page.         main pcre page.
2930    
2931         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2932         permits  them,  but they do not mean what you might think. For example,         permits them, but they do not mean what you might think.  For  example,
2933         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
2934         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
2935    
2936         3.  Capturing  subpatterns  that occur inside negative lookahead asser-         3. Capturing subpatterns that occur inside  negative  lookahead  asser-
2937         tions are counted, but their entries in the offsets  vector  are  never         tions  are  counted,  but their entries in the offsets vector are never
2938         set.  Perl sets its numerical variables from any such patterns that are         set. Perl sets its numerical variables from any such patterns that  are
2939         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
2940         ing),  but  only  if the negative lookahead assertion contains just one         ing), but only if the negative lookahead assertion  contains  just  one
2941         branch.         branch.
2942    
2943         4. Though binary zero characters are supported in the  subject  string,         4.  Though  binary zero characters are supported in the subject string,
2944         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2945         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
2946         the pattern to represent a binary zero.         the pattern to represent a binary zero.
2947    
2948         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5. The following Perl escape sequences are not supported: \l,  \u,  \L,
2949         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
2950         dling  and are not part of its pattern matching engine. If any of these         dling and are not part of its pattern matching engine. If any of  these
2951         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2952    
2953         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE         6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE
2954         is  built  with Unicode character property support. The properties that         is built with Unicode character property support. The  properties  that
2955         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-
2956         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
2957         derived properties Any and L&.         derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
2958           property, which Perl does not; the  Perl  documentation  says  "Because
2959           Perl hides the need for the user to understand the internal representa-
2960           tion of Unicode characters, there is no need to implement the  somewhat
2961           messy concept of surrogates."
2962    
2963         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2964         ters  in  between  are  treated as literals. This is slightly different         ters in between are treated as literals.  This  is  slightly  different
2965         from Perl in that $ and @ are  also  handled  as  literals  inside  the         from  Perl  in  that  $  and  @ are also handled as literals inside the
2966         quotes.  In Perl, they cause variable interpolation (but of course PCRE         quotes. In Perl, they cause variable interpolation (but of course  PCRE
2967         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2968    
2969             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2839  DIFFERENCES BETWEEN PCRE AND PERL Line 2973  DIFFERENCES BETWEEN PCRE AND PERL
2973             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2974             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2975    
2976         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
2977         classes.         classes.
2978    
2979         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2980         constructions. However, there is support for recursive  patterns.  This         constructions.  However,  there is support for recursive patterns. This
2981         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
2982         "callout" feature allows an external function to be called during  pat-         "callout"  feature allows an external function to be called during pat-
2983         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2984    
2985         9.  Subpatterns  that  are  called  recursively or as "subroutines" are         9. Subpatterns that are called  recursively  or  as  "subroutines"  are
2986         always treated as atomic groups in  PCRE.  This  is  like  Python,  but         always  treated  as  atomic  groups  in  PCRE. This is like Python, but
2987         unlike Perl.         unlike Perl. There is a discussion of an example that explains this  in
2988           more  detail  in  the section on recursion differences from Perl in the
2989         10.  There are some differences that are concerned with the settings of         pcrepattern page.
2990         captured strings when part of  a  pattern  is  repeated.  For  example,  
2991         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         10. There are some differences that are concerned with the settings  of
2992           captured  strings  when  part  of  a  pattern is repeated. For example,
2993           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
2994         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2995    
2996         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2997         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in         (*FAIL), (*F), (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but  only  in
2998         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If         the forms without an argument. PCRE does not support (*MARK).
2999         (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-  
3000         ture group; this is different to Perl.         12.  PCRE's handling of duplicate subpattern numbers and duplicate sub-
3001           pattern names is not as general as Perl's. This is a consequence of the
3002         12. PCRE provides some extensions to the Perl regular expression facil-         fact the PCRE works internally just with numbers, using an external ta-
3003         ities.   Perl  5.10  will  include new features that are not in earlier         ble to translate between numbers and names. In  particular,  a  pattern
3004         versions, some of which (such as named parentheses) have been  in  PCRE         such  as  (?|(?<a>A)|(?<b)B),  where the two capturing parentheses have
3005         for some time. This list is with respect to Perl 5.10:         the same number but different names, is not supported,  and  causes  an
3006           error  at compile time. If it were allowed, it would not be possible to
3007         (a)  Although  lookbehind  assertions  must match fixed length strings,         distinguish which parentheses matched, because both names map  to  cap-
3008         each alternative branch of a lookbehind assertion can match a different         turing subpattern number 1. To avoid this confusing situation, an error
3009         length of string. Perl requires them all to have the same length.         is given at compile time.
3010    
3011           13. PCRE provides some extensions to the Perl regular expression facil-
3012           ities.   Perl  5.10  includes new features that are not in earlier ver-
3013           sions of Perl, some of which (such as named parentheses) have  been  in
3014           PCRE for some time. This list is with respect to Perl 5.10:
3015    
3016           (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3017           strings, each alternative branch of a lookbehind assertion can match  a
3018           different  length  of  string.  Perl requires them all to have the same
3019           length.
3020    
3021         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
3022         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
3023    
3024         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
3025         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3026         ignored.  (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
3027    
3028         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3029         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
3030         lowed by a question mark they are.         lowed by a question mark they are.
3031    
3032         (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
3033         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
3034    
3035         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3036         TURE options for pcre_exec() have no Perl equivalents.         and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3037           lents.
3038    
3039         (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
3040         CRLF by the PCRE_BSR_ANYCRLF option.         CRLF by the PCRE_BSR_ANYCRLF option.
# Line 2916  AUTHOR Line 3063  AUTHOR
3063    
3064  REVISION  REVISION
3065    
3066         Last updated: 11 September 2007         Last updated: 04 October 2009
3067         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
3068  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
3069    
3070    
# Line 2947  PCRE REGULAR EXPRESSION DETAILS Line 3094  PCRE REGULAR EXPRESSION DETAILS
3094    
3095         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
3096         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
3097         this, you must build PCRE to  include  UTF-8  support,  and  then  call         this, PCRE must be built to include UTF-8 support, and  you  must  call
3098         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern         pcre_compile()  or  pcre_compile2() with the PCRE_UTF8 option. There is
3099         matching is mentioned in several places below. There is also a  summary         also a special sequence that can be given at the start of a pattern:
3100         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre  
3101         page.           (*UTF8)
3102    
3103           Starting a pattern with this sequence  is  equivalent  to  setting  the
3104           PCRE_UTF8  option.  This  feature  is  not Perl-compatible. How setting
3105           UTF-8 mode affects pattern matching  is  mentioned  in  several  places
3106           below.  There  is  also  a  summary of UTF-8 features in the section on
3107           UTF-8 support in the main pcre page.
3108    
3109         The remainder of this document discusses the  patterns  that  are  sup-         The remainder of this document discusses the  patterns  that  are  sup-
3110         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 2981  NEWLINE CONVENTIONS Line 3134  NEWLINE CONVENTIONS
3134           (*ANYCRLF)   any of the three above           (*ANYCRLF)   any of the three above
3135           (*ANY)       all Unicode newline sequences           (*ANY)       all Unicode newline sequences
3136    
3137         These override the default and the options given to pcre_compile(). For         These  override  the default and the options given to pcre_compile() or
3138         example, on a Unix system where LF is the default newline sequence, the         pcre_compile2(). For example, on a Unix system where LF is the  default
3139         pattern         newline sequence, the pattern
3140    
3141           (*CR)a.b           (*CR)a.b
3142    
# Line 3055  CHARACTERS AND METACHARACTERS Line 3208  CHARACTERS AND METACHARACTERS
3208                    syntax)                    syntax)
3209           ]      terminates the character class           ]      terminates the character class
3210    
3211         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the metacharacters.
3212    
3213    
3214  BACKSLASH  BACKSLASH
3215    
3216         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
3217         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
3218         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
3219         applies both inside and outside character classes.         applies both inside and outside character classes.
3220    
3221         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
3222         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
3223         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
3224         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
3225         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-
3226         slash, you write \\.         slash, you write \\.
3227    
3228         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
3229         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
3230         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
3231         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
3232         part of the pattern.         part of the pattern.
3233    
3234         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-
3235         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-
3236         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
3237         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
3238         tion. Note the following examples:         tion. Note the following examples:
3239    
3240           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 3091  BACKSLASH Line 3244  BACKSLASH
3244           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3245           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3246    
3247         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3248         classes.         classes.
3249    
3250     Non-printing characters     Non-printing characters
3251    
3252         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-
3253         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
3254         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3255         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3256         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is  often  easier  to  use  one  of  the  following  escape
3257         sequences than the binary character it represents:         sequences than the binary character it represents:
3258    
3259           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 3110  BACKSLASH Line 3263  BACKSLASH
3263           \n        linefeed (hex 0A)           \n        linefeed (hex 0A)
3264           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3265           \t        tab (hex 09)           \t        tab (hex 09)
3266           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or back reference
3267           \xhh      character with hex code hh           \xhh      character with hex code hh
3268           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3269    
3270         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,
3271         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
3272         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;
3273         becomes hex 7B.         becomes hex 7B.
3274    
3275         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
3276         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3277         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
3278         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,
3279         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3280         than the largest Unicode code point, which is 10FFFF.         than the largest Unicode code point, which is 10FFFF.
3281    
3282         If characters other than hexadecimal digits appear between \x{  and  },         If  characters  other than hexadecimal digits appear between \x{ and },
3283         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.
3284         Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal         Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3285         escape,  with  no  following  digits, giving a character whose value is         escape, with no following digits, giving a  character  whose  value  is
3286         zero.         zero.
3287    
3288         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
3289         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-
3290         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3291    
3292         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
3293         than  two  digits,  just  those  that  are  present  are used. Thus the         than two digits, just  those  that  are  present  are  used.  Thus  the
3294         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
3295         (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
3296         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3297    
3298         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-
3299         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3300         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
3301         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3302         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3303         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3304         of parenthesized subpatterns.         of parenthesized subpatterns.
3305    
3306         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
3307         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3308         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-
3309         erate  a data character. Any subsequent digits stand for themselves. In         erate a data character. Any subsequent digits stand for themselves.  In
3310         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
3311         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
3312         example:         example:
3313    
3314           \040   is another way of writing a space           \040   is another way of writing a space
# Line 3173  BACKSLASH Line 3326  BACKSLASH
3326           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3327                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3328    
3329         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
3330         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3331    
3332         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
3333         inside and outside character classes. In addition, inside  a  character         inside  and  outside character classes. In addition, inside a character
3334         class,  the  sequence \b is interpreted as the backspace character (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3335         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"
3336         and  "X", respectively. Outside a character class, these sequences have         and "X", respectively. Outside a character class, these sequences  have
3337         different meanings (see below).         different meanings (see below).
3338    
3339     Absolute and relative back references     Absolute and relative back references
3340    
3341         The sequence \g followed by an unsigned or a negative  number,  option-         The  sequence  \g followed by an unsigned or a negative number, option-
3342         ally  enclosed  in braces, is an absolute or relative back reference. A         ally enclosed in braces, is an absolute or relative back  reference.  A
3343         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-
3344         cussed later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3345    
3346     Absolute and relative subroutine calls     Absolute and relative subroutine calls
3347    
3348         For  compatibility with Oniguruma, the non-Perl syntax \g followed by a         For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3349         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
3350         an  alternative  syntax for referencing a subpattern as a "subroutine".         an alternative syntax for referencing a subpattern as  a  "subroutine".
3351         Details are discussed later.   Note  that  \g{...}  (Perl  syntax)  and         Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3352         \g<...>  (Oniguruma  syntax)  are  not synonymous. The former is a back         \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3353         reference; the latter is a subroutine call.         reference; the latter is a subroutine call.
3354    
3355     Generic character types     Generic character types
# Line 3216  BACKSLASH Line 3369  BACKSLASH
3369           \W     any "non-word" character           \W     any "non-word" character
3370    
3371         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3372         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3373         of each pair.         of each pair.
3374    
3375         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3376         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3377         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
3378         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3379    
3380         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3381         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
3382         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
3383         "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-
3384         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3385    
3386         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,
3387         \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-
3388         code character property support is available.  These  sequences  retain         code  character  property  support is available. These sequences retain
3389         their original meanings from before UTF-8 support was available, mainly         their original meanings from before UTF-8 support was available, mainly
3390         for efficiency reasons.         for  efficiency  reasons. Note that this also affects \b, because it is
3391           defined in terms of \w and \W.
3392    
3393         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
3394         the  other  sequences, these do match certain high-valued codepoints in         the  other  sequences, these do match certain high-valued codepoints in
# Line 3311  BACKSLASH Line 3465  BACKSLASH
3465           (*BSR_ANYCRLF)   CR, LF, or CRLF only           (*BSR_ANYCRLF)   CR, LF, or CRLF only
3466           (*BSR_UNICODE)   any Unicode newline sequence           (*BSR_UNICODE)   any Unicode newline sequence
3467    
3468         These override the default and the options given to pcre_compile(), but         These override the default and the options given to  pcre_compile()  or
3469         they can be overridden by options given to pcre_exec(). Note that these         pcre_compile2(),  but  they  can  be  overridden  by  options  given to
3470         special settings, which are not Perl-compatible, are recognized only at         pcre_exec() or pcre_dfa_exec(). Note that these special settings, which
3471         the  very  start  of a pattern, and that they must be in upper case. If         are  not  Perl-compatible,  are  recognized only at the very start of a
3472         more than one of them is present, the last one is  used.  They  can  be         pattern, and that they must be in upper case. If more than one of  them
3473         combined  with  a  change of newline convention, for example, a pattern         is present, the last one is used. They can be combined with a change of
3474         can start with:         newline convention, for example, a pattern can start with:
3475    
3476           (*ANY)(*BSR_ANYCRLF)           (*ANY)(*BSR_ANYCRLF)
3477    
# Line 3351  BACKSLASH Line 3505  BACKSLASH
3505         Those that are not part of an identified script are lumped together  as         Those that are not part of an identified script are lumped together  as
3506         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3507    
3508         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,         Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille,
3509         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,         Buginese, Buhid, Canadian_Aboriginal, Carian, Cham,  Cherokee,  Common,
3510         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,         Coptic,   Cuneiform,  Cypriot,  Cyrillic,  Deseret,  Devanagari,  Egyp-
3511         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-         tian_Hieroglyphs,  Ethiopic,  Georgian,  Glagolitic,   Gothic,   Greek,
3512         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,         Gujarati,  Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana, Impe-
3513         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,         rial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian,
3514         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,         Javanese,  Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao,
3515         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,         Latin,  Lepcha,  Limbu,  Linear_B,  Lisu,  Lycian,  Lydian,  Malayalam,
3516         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.         Meetei_Mayek,  Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic,
3517           Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki,  Oriya,  Osmanya,
3518           Phags_Pa,  Phoenician,  Rejang,  Runic, Samaritan, Saurashtra, Shavian,
3519           Sinhala, Sundanese, Syloti_Nagri, Syriac,  Tagalog,  Tagbanwa,  Tai_Le,
3520           Tai_Tham,  Tai_Viet,  Tamil,  Telugu,  Thaana, Thai, Tibetan, Tifinagh,
3521           Ugaritic, Vai, Yi.
3522    
3523         Each  character has exactly one general category property, specified by         Each character has exactly one general category property, specified  by
3524         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
3525         specified  by  including a circumflex between the opening brace and the         specified by including a circumflex between the opening brace  and  the
3526         property name. For example, \p{^Lu} is the same as \P{Lu}.         property name. For example, \p{^Lu} is the same as \P{Lu}.
3527    
3528         If only one letter is specified with \p or \P, it includes all the gen-         If only one letter is specified with \p or \P, it includes all the gen-
3529         eral  category properties that start with that letter. In this case, in         eral category properties that start with that letter. In this case,  in
3530         the absence of negation, the curly brackets in the escape sequence  are         the  absence of negation, the curly brackets in the escape sequence are
3531         optional; these two examples have the same effect:         optional; these two examples have the same effect:
3532    
3533           \p{L}           \p{L}
# Line 3420  BACKSLASH Line 3579  BACKSLASH
3579           Zp    Paragraph separator           Zp    Paragraph separator
3580           Zs    Space separator           Zs    Space separator
3581    
3582         The  special property L& is also supported: it matches a character that         The special property L& is also supported: it matches a character  that
3583         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3584         classified as a modifier or "other".         classified as a modifier or "other".
3585    
3586         The  Cs  (Surrogate)  property  applies only to characters in the range         The Cs (Surrogate) property applies only to  characters  in  the  range
3587         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
3588         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-
3589         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
3590         the pcreapi page).         the pcreapi page). Perl does not support the Cs property.
3591    
3592         The  long  synonyms  for  these  properties that Perl supports (such as         The long synonyms for  property  names  that  Perl  supports  (such  as
3593         \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
3594         any of these properties with "Is".         any of these properties with "Is".
3595    
3596         No character that is in the Unicode table has the Cn (unassigned) prop-         No character that is in the Unicode table has the Cn (unassigned) prop-
3597         erty.  Instead, this property is assumed for any code point that is not         erty.  Instead, this property is assumed for any code point that is not
3598         in the Unicode table.         in the Unicode table.
3599    
3600         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3601         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3602    
3603         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3604         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3605    
3606           (?>\PM\pM*)           (?>\PM\pM*)
3607    
3608         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3609         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3610         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3611         property are typically accents that  affect  the  preceding  character.         property  are  typically  accents  that affect the preceding character.
3612         None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X         None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3613         matches any one character.         matches any one character.
3614    
3615         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3616         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3617         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3618         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3619    
3620     Resetting the match start     Resetting the match start
3621    
3622         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-         The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3623         ously matched characters not  to  be  included  in  the  final  matched         ously  matched  characters  not  to  be  included  in the final matched
3624         sequence. For example, the pattern:         sequence. For example, the pattern:
3625    
3626           foo\Kbar           foo\Kbar
3627    
3628         matches  "foobar",  but reports that it has matched "bar". This feature         matches "foobar", but reports that it has matched "bar".  This  feature
3629         is similar to a lookbehind assertion (described  below).   However,  in         is  similar  to  a lookbehind assertion (described below).  However, in
3630         this  case, the part of the subject before the real match does not have         this case, the part of the subject before the real match does not  have
3631         to be of fixed length, as lookbehind assertions do. The use of \K  does         to  be of fixed length, as lookbehind assertions do. The use of \K does
3632         not  interfere  with  the setting of captured substrings.  For example,         not interfere with the setting of captured  substrings.   For  example,
3633         when the pattern         when the pattern
3634    
3635           (foo)\Kbar           (foo)\Kbar
3636    
3637         matches "foobar", the first substring is still set to "foo".         matches "foobar", the first substring is still set to "foo".
3638    
3639           Perl  documents  that  the  use  of  \K  within assertions is "not well
3640           defined". In PCRE, \K is acted upon  when  it  occurs  inside  positive
3641           assertions, but is ignored in negative assertions.
3642    
3643     Simple assertions     Simple assertions
3644    
3645         The final use of backslash is for certain simple assertions. An  asser-         The  final use of backslash is for certain simple assertions. An asser-
3646         tion  specifies a condition that has to be met at a particular point in         tion specifies a condition that has to be met at a particular point  in
3647         a match, without consuming any characters from the subject string.  The         a  match, without consuming any characters from the subject string. The
3648         use  of subpatterns for more complicated assertions is described below.         use of subpatterns for more complicated assertions is described  below.
3649         The backslashed assertions are:         The backslashed assertions are:
3650    
3651           \b     matches at a word boundary           \b     matches at a word boundary
# Line 3493  BACKSLASH Line 3656  BACKSLASH
3656           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3657           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3658    
3659         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
3660         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3661         acter class).         acter class).
3662    
3663         A word boundary is a position in the subject string where  the  current         A  word  boundary is a position in the subject string where the current
3664         character  and  the previous character do not both match \w or \W (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3665         one matches \w and the other matches \W), or the start or  end  of  the         one  matches  \w  and the other matches \W), or the start or end of the
3666         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively. Neither
3667           PCRE  nor  Perl  has a separte "start of word" or "end of word" metase-
3668           quence. However, whatever follows \b normally determines which  it  is.
3669           For example, the fragment \ba matches "a" at the start of a word.
3670    
3671         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3672         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
# Line 3626  SQUARE BRACKETS AND CHARACTER CLASSES Line 3792  SQUARE BRACKETS AND CHARACTER CLASSES
3792    
3793         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3794         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3795         cial. If a closing square bracket is required as a member of the class,         cial by default.  However, if the PCRE_JAVASCRIPT_COMPAT option is set,
3796         it should be the first data character in the class  (after  an  initial         a lone closing square bracket causes a compile-time error. If a closing
3797         circumflex, if present) or escaped with a backslash.         square  bracket  is required as a member of the class, it should be the
3798           first data character in the class  (after  an  initial  circumflex,  if
3799           present) or escaped with a backslash.
3800    
3801         A  character  class matches a single character in the subject. In UTF-8         A  character  class matches a single character in the subject. In UTF-8
3802         mode, the character may occupy more than one byte. A matched  character         mode, the character may be more than one byte long. A matched character
3803         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3804         character in the class definition is a circumflex, in  which  case  the         character in the class definition is a circumflex, in  which  case  the
3805         subject  character  must  not  be in the set defined by the class. If a         subject  character  must  not  be in the set defined by the class. If a
# Line 3642  SQUARE BRACKETS AND CHARACTER CLASSES Line 3810  SQUARE BRACKETS AND CHARACTER CLASSES
3810         while [^aeiou] matches any character that is not a  lower  case  vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3811         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3812         characters that are in the class by enumerating those that are  not.  A         characters that are in the class by enumerating those that are  not.  A
3813         class  that starts with a circumflex is not an assertion: it still con-         class  that starts with a circumflex is not an assertion; it still con-
3814         sumes a character from the subject string, and therefore  it  fails  if         sumes a character from the subject string, and therefore  it  fails  if
3815         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3816    
# Line 3658  SQUARE BRACKETS AND CHARACTER CLASSES Line 3826  SQUARE BRACKETS AND CHARACTER CLASSES
3826         than 128, so caseless matching is always possible. For characters  with         than 128, so caseless matching is always possible. For characters  with
3827         higher  values,  the  concept  of case is supported if PCRE is compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3828         with Unicode property support, but not otherwise.  If you want  to  use         with Unicode property support, but not otherwise.  If you want  to  use
3829         caseless  matching  for  characters 128 and above, you must ensure that         caseless  matching  in UTF8-mode for characters 128 and above, you must
3830         PCRE is compiled with Unicode property support as well  as  with  UTF-8         ensure that PCRE is compiled with Unicode property support as  well  as
3831         support.         with UTF-8 support.
3832    
3833         Characters  that  might  indicate  line breaks are never treated in any         Characters  that  might  indicate  line breaks are never treated in any
3834         special way  when  matching  character  classes,  whatever  line-ending         special way  when  matching  character  classes,  whatever  line-ending
# Line 3760  POSIX CHARACTER CLASSES Line 3928  POSIX CHARACTER CLASSES
3928    
3929  VERTICAL BAR  VERTICAL BAR
3930    
3931         Vertical  bar characters are used to separate alternative patterns. For         Vertical bar characters are used to separate alternative patterns.  For
3932         example, the pattern         example, the pattern
3933    
3934           gilbert|sullivan           gilbert|sullivan
3935    
3936         matches either "gilbert" or "sullivan". Any number of alternatives  may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3937         appear,  and  an  empty  alternative  is  permitted (matching the empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3938         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3939         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
3940         are within a subpattern (defined below), "succeeds" means matching  the         are  within a subpattern (defined below), "succeeds" means matching the
3941         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.
3942    
3943    
3944  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 3796  INTERNAL OPTION SETTING Line 3964  INTERNAL OPTION SETTING
3964         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
3965         the characters J, U and X respectively.         the characters J, U and X respectively.
3966    
3967         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
3968         tern  parentheses),  the change applies to the remainder of the pattern         inside  subpattern parentheses), the change applies to the remainder of
3969         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
3970         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-
3971         in data extracted by the pcre_fullinfo() function).         fore show up in data extracted by the pcre_fullinfo() function).
3972    
3973         An option change within a subpattern (see below for  a  description  of         An option change within a subpattern (see below for  a  description  of
3974         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 3991  INTERNAL OPTION SETTING
3991    
3992         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
3993         application when the compile or match functions  are  called.  In  some         application when the compile or match functions  are  called.  In  some
3994         cases  the  pattern  can  contain special leading sequences to override         cases the pattern can contain special leading sequences such as (*CRLF)
3995         what the application has set or what has been  defaulted.  Details  are         to override what the application has set or what  has  been  defaulted.
3996         given in the section entitled "Newline sequences" above.         Details  are  given  in the section entitled "Newline sequences" above.
3997           There is also the (*UTF8) leading sequence that  can  be  used  to  set
3998           UTF-8 mode; this is equivalent to setting the PCRE_UTF8 option.
3999    
4000    
4001  SUBPATTERNS  SUBPATTERNS
# Line 3907  DUPLICATE SUBPATTERN NUMBERS Line 4077  DUPLICATE SUBPATTERN NUMBERS
4077           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x           / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
4078           # 1            2         2  3        2     3     4           # 1            2         2  3        2     3     4
4079    
4080         A backreference or a recursive call to  a  numbered  subpattern  always         A back reference to a numbered subpattern uses the  most  recent  value
4081         refers to the first one in the pattern with the given number.         that  is  set  for that number by any subpattern. The following pattern
4082           matches "abcabc" or "defdef":
4083    
4084             /(?|(abc)|(def))\1/
4085    
4086           In contrast, a recursive or "subroutine" call to a numbered  subpattern
4087           always  refers  to  the first one in the pattern with the given number.
4088           The following pattern matches "abcabc" or "defabc":
4089    
4090             /(?|(abc)|(def))(?1)/
4091    
4092           If a condition test for a subpattern's having matched refers to a  non-
4093           unique  number, the test is true if any of the subpatterns of that num-
4094           ber have matched.
4095    
4096         An  alternative approach to using this "branch reset" feature is to use         An alternative approach to using this "branch reset" feature is to  use
4097         duplicate named subpatterns, as described in the next section.         duplicate named subpatterns, as described in the next section.
4098    
4099    
4100  NAMED SUBPATTERNS  NAMED SUBPATTERNS
4101    
4102         Identifying capturing parentheses by number is simple, but  it  can  be         Identifying  capturing  parentheses  by number is simple, but it can be
4103         very  hard  to keep track of the numbers in complicated regular expres-         very hard to keep track of the numbers in complicated  regular  expres-
4104         sions. Furthermore, if an  expression  is  modified,  the  numbers  may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
4105         change.  To help with this difficulty, PCRE supports the naming of sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
4106         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
4107         had  the  feature earlier, and PCRE introduced it at release 4.0, using         had the feature earlier, and PCRE introduced it at release  4.0,  using
4108         the Python syntax. PCRE now supports both the Perl and the Python  syn-         the  Python syntax. PCRE now supports both the Perl and the Python syn-
4109         tax.         tax. Perl allows identically numbered  subpatterns  to  have  different
4110           names, but PCRE does not.
4111    
4112         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
4113         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
4114         to capturing parentheses from other parts of the pattern, such as back-         to  capturing parentheses from other parts of the pattern, such as back
4115         references, recursion, and conditions, can be made by name as  well  as         references, recursion, and conditions, can be made by name as  well  as
4116         by number.         by number.
4117    
# Line 3940  NAMED SUBPATTERNS Line 4124  NAMED SUBPATTERNS
4124    
4125         By default, a name must be unique within a pattern, but it is  possible         By default, a name must be unique within a pattern, but it is  possible
4126         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
4127         time. This can be useful for patterns where only one  instance  of  the         time. (Duplicate names are also always permitted for  subpatterns  with
4128           the  same  number, set up as described in the previous section.) Dupli-
4129           cate names can be useful for patterns where only one  instance  of  the
4130         named  parentheses  can  match. Suppose you want to match the name of a         named  parentheses  can  match. Suppose you want to match the name of a
4131         weekday, either as a 3-letter abbreviation or as the full name, and  in         weekday, either as a 3-letter abbreviation or as the full name, and  in
4132         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
# Line 3959  NAMED SUBPATTERNS Line 4145  NAMED SUBPATTERNS
4145         The convenience function for extracting the data by  name  returns  the         The convenience function for extracting the data by  name  returns  the
4146         substring  for  the first (and in this example, the only) subpattern of         substring  for  the first (and in this example, the only) subpattern of
4147         that name that matched. This saves searching  to  find  which  numbered         that name that matched. This saves searching  to  find  which  numbered
4148         subpattern  it  was. If you make a reference to a non-unique named sub-         subpattern it was.
4149         pattern from elsewhere in the pattern, the one that corresponds to  the  
4150         lowest  number  is used. For further details of the interfaces for han-         If  you  make  a  back  reference to a non-unique named subpattern from
4151         dling named subpatterns, see the pcreapi documentation.         elsewhere in the pattern, the one that corresponds to the first  occur-
4152           rence of the name is used. In the absence of duplicate numbers (see the
4153           previous section) this is the one with the lowest number. If you use  a
4154           named  reference  in a condition test (see the section about conditions
4155           below), either to check whether a subpattern has matched, or  to  check
4156           for  recursion,  all  subpatterns with the same name are tested. If the
4157           condition is true for any one of them, the overall condition  is  true.
4158           This is the same behaviour as testing by number. For further details of
4159           the interfaces for handling named subpatterns, see the pcreapi documen-
4160           tation.
4161    
4162           Warning: You cannot use different names to distinguish between two sub-
4163           patterns with the same number because PCRE uses only the  numbers  when
4164           matching. For this reason, an error is given at compile time if differ-
4165           ent names are given to subpatterns with the same number.  However,  you
4166           can  give  the same name to subpatterns with the same number, even when
4167           PCRE_DUPNAMES is not set.
4168    
4169    
4170  REPETITION  REPETITION
# Line 3979  REPETITION Line 4181  REPETITION
4181           a character class           a character class
4182           a back reference (see next section)           a back reference (see next section)
4183           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4184             a recursive or "subroutine" call to a subpattern
4185    
4186         The  general repetition quantifier specifies a minimum and maximum num-         The  general repetition quantifier specifies a minimum and maximum num-
4187         ber of permitted matches, by giving the two numbers in  curly  brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
# Line 4004  REPETITION Line 4207  REPETITION
4207         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-
4208         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.
4209    
4210         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
4211         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-
4212         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
4213         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
4214         extended sequences, each of which may be several bytes long  (and  they         extended  sequences,  each of which may be several bytes long (and they
4215         may be of different lengths).         may be of different lengths).
4216    
4217         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4218         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-
4219         ful  for  subpatterns that are referenced as subroutines from elsewhere         ful for subpatterns that are referenced as subroutines  from  elsewhere
4220         in the pattern. Items other than subpatterns that have a {0} quantifier         in the pattern. Items other than subpatterns that have a {0} quantifier
4221         are omitted from the compiled pattern.         are omitted from the compiled pattern.
4222    
4223         For  convenience, the three most common quantifiers have single-charac-         For convenience, the three most common quantifiers have  single-charac-
4224         ter abbreviations:         ter abbreviations:
4225    
4226           *    is equivalent to {0,}           *    is equivalent to {0,}
4227           +    is equivalent to {1,}           +    is equivalent to {1,}
4228           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4229    
4230         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
4231         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,
4232         for example:         for example:
4233    
4234           (a?)*           (a?)*
4235    
4236         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
4237         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
4238         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
4239         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
4240         ken.         ken.
4241    
4242         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
4243         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
4244         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
4245         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
4246         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
4247         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
4248         pattern         pattern
4249    
4250           /\*.*\*/           /\*.*\*/
# Line 4050  REPETITION Line 4253  REPETITION
4253    
4254           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4255    
4256         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
4257         the .*  item.         the .*  item.
4258    
4259         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
4260         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4261         the pattern         the pattern
4262    
4263           /\*.*?\*/           /\*.*?\*/
4264    
4265         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
4266         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
4267         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
4268         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
4269         appear doubled, as in         appear doubled, as in
4270    
4271           \d??\d           \d??\d
# Line 4070  REPETITION Line 4273  REPETITION
4273         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
4274         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4275    
4276         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
4277         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
4278         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
4279         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4280    
4281         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
4282         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
4283         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
4284         minimum or maximum.         minimum or maximum.
4285    
4286         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-
4287         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,
4288         the pattern is implicitly anchored, because whatever  follows  will  be         the  pattern  is  implicitly anchored, because whatever follows will be
4289         tried  against every character position in the subject string, so there         tried against every character position in the subject string, so  there
4290         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
4291         first.  PCRE  normally treats such a pattern as though it were preceded         first. PCRE normally treats such a pattern as though it  were  preceded
4292         by \A.         by \A.
4293    
4294         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-
4295         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-
4296         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4297    
4298         However, there is one situation where the optimization cannot be  used.         However,  there is one situation where the optimization cannot be used.
4299         When  .*   is  inside  capturing  parentheses that are the subject of a         When .*  is inside capturing parentheses that are the subject of a back
4300         backreference elsewhere in the pattern, a match at the start  may  fail         reference elsewhere in the pattern, a match at the start may fail where
4301         where a later one succeeds. Consider, for example:         a later one succeeds. Consider, for example:
4302    
4303           (.*)abc\1           (.*)abc\1
4304    
4305         If  the subject is "xyz123abc123" the match point is the fourth charac-         If the subject is "xyz123abc123" the match point is the fourth  charac-
4306         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4307    
4308         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 4311  REPETITION
4311           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4312    
4313         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4314         is "tweedledee". However, if there are  nested  capturing  subpatterns,         is  "tweedledee".  However,  if there are nested capturing subpatterns,
4315         the  corresponding captured values may have been set in previous itera-         the corresponding captured values may have been set in previous  itera-
4316         tions. For example, after         tions. For example, after
4317    
4318           /(a|(b))+/           /(a|(b))+/
# Line 4119  REPETITION Line 4322  REPETITION
4322    
4323  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4324    
4325         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
4326         repetition,  failure  of what follows normally causes the repeated item         repetition, failure of what follows normally causes the  repeated  item
4327         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
4328         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,
4329         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
4330         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
4331         no point in carrying on.         no point in carrying on.
4332    
4333         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider,  for  example, the pattern \d+foo when applied to the subject
4334         line         line
4335    
4336           123456bar           123456bar
4337    
4338         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
4339         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
4340         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.
4341         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides
4342         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
4343         to be re-evaluated in this way.         to be re-evaluated in this way.
4344    
4345         If we use atomic grouping for the previous example, the  matcher  gives         If  we  use atomic grouping for the previous example, the matcher gives
4346         up  immediately  on failing to match "foo" the first time. The notation         up immediately on failing to match "foo" the first time.  The  notation
4347         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4348    
4349           (?>\d+)foo           (?>\d+)foo
# Line 4218  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4421  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4421    
4422           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4423    
4424         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences of non-digits cannot be broken, and failure happens quickly.
4425    
4426    
4427  BACK REFERENCES  BACK REFERENCES
4428    
4429         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4430         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-
4431         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
4432         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4433    
4434         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4435         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
4436         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
4437         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
4438         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
4439         reference"  of  this  type can make sense when a repetition is involved         reference" of this type can make sense when a  repetition  is  involved
4440         and the subpattern to the right has participated in an  earlier  itera-         and  the  subpattern to the right has participated in an earlier itera-
4441         tion.         tion.
4442    
4443         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
4444         subpattern whose number is 10 or  more  using  this  syntax  because  a         subpattern  whose  number  is  10  or  more using this syntax because a
4445         sequence  such  as  \50 is interpreted as a character defined in octal.         sequence such as \50 is interpreted as a character  defined  in  octal.
4446         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4447         details  of  the  handling of digits following a backslash. There is no         details of the handling of digits following a backslash.  There  is  no
4448         such problem when named parentheses are used. A back reference  to  any         such  problem  when named parentheses are used. A back reference to any
4449         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4450    
4451         Another  way  of  avoiding  the ambiguity inherent in the use of digits         Another way of avoiding the ambiguity inherent in  the  use  of  digits
4452         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-
4453         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
4454         unsigned number or a negative number, optionally  enclosed  in  braces.         unsigned  number  or  a negative number, optionally enclosed in braces.
4455         These examples are all identical:         These examples are all identical:
4456    
4457           (ring), \1           (ring), \1
4458           (ring), \g1           (ring), \g1
4459           (ring), \g{1}           (ring), \g{1}
4460    
4461         An  unsigned number specifies an absolute reference without the ambigu-         An unsigned number specifies an absolute reference without the  ambigu-
4462         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
4463         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4464         Consider this example:         Consider this example:
# Line 4263  BACK REFERENCES Line 4466  BACK REFERENCES
4466           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4467    
4468         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-
4469         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
4470         \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
4471         helpful  in  long  patterns,  and  also in patterns that are created by         helpful in long patterns, and also in  patterns  that  are  created  by
4472         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4473    
4474         A back reference matches whatever actually matched the  capturing  sub-         A  back  reference matches whatever actually matched the capturing sub-
4475         pattern  in  the  current subject string, rather than anything matching         pattern in the current subject string, rather  than  anything  matching
4476         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4477         of doing that). So the pattern         of doing that). So the pattern
4478    
4479           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4480    
4481         matches  "sense and sensibility" and "response and responsibility", but         matches "sense and sensibility" and "response and responsibility",  but
4482         not "sense and responsibility". If caseful matching is in force at  the         not  "sense and responsibility". If caseful matching is in force at the
4483         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-
4484         ple,         ple,
4485    
4486           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4487    
4488         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
4489         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4490    
4491         There  are  several  different ways of writing back references to named         There are several different ways of writing back  references  to  named
4492         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
4493         \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
4494         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
4495         and  named  references,  is  also supported. We could rewrite the above         and named references, is also supported. We  could  rewrite  the  above
4496         example in any of the following ways:         example in any of the following ways:
4497    
4498           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 4297  BACK REFERENCES Line 4500  BACK REFERENCES
4500           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4501           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4502    
4503         A subpattern that is referenced by  name  may  appear  in  the  pattern         A  subpattern  that  is  referenced  by  name may appear in the pattern
4504         before or after the reference.         before or after the reference.
4505    
4506         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
4507         subpattern has not actually been used in a particular match,  any  back         subpattern  has  not actually been used in a particular match, any back
4508         references to it always fail. For example, the pattern         references to it always fail by default. For example, the pattern
4509    
4510           (a|(bc))\2           (a|(bc))\2
4511    
4512         always  fails if it starts to match "a" rather than "bc". Because there         always fails if it starts to match "a" rather than  "bc".  However,  if
4513         may be many capturing parentheses in a pattern,  all  digits  following         the PCRE_JAVASCRIPT_COMPAT option is set at compile time, a back refer-
4514         the  backslash  are taken as part of a potential back reference number.         ence to an unset value matches an empty string.
4515         If the pattern continues with a digit character, some delimiter must be  
4516         used  to  terminate  the back reference. If the PCRE_EXTENDED option is         Because there may be many capturing parentheses in a pattern, all  dig-
4517         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-         its  following a backslash are taken as part of a potential back refer-
4518         ments" below) can be used.         ence number.  If the pattern continues with  a  digit  character,  some
4519           delimiter  must  be  used  to  terminate  the  back  reference.  If the
4520           PCRE_EXTENDED option is set, this can be whitespace. Otherwise, the \g{
4521           syntax or an empty comment (see "Comments" below) can be used.
4522    
4523       Recursive back references
4524    
4525         A  back reference that occurs inside the parentheses to which it refers         A  back reference that occurs inside the parentheses to which it refers
4526         fails when the subpattern is first used, so, for example,  (a\1)  never         fails when the subpattern is first used, so, for example,  (a\1)  never
# Line 4328  BACK REFERENCES Line 4536  BACK REFERENCES
4536         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
4537         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4538    
4539           Back  references of this type cause the group that they reference to be
4540           treated as an atomic group.  Once the whole group has been  matched,  a
4541           subsequent  matching  failure cannot cause backtracking into the middle
4542           of the group.
4543    
4544    
4545  ASSERTIONS  ASSERTIONS
4546    
4547         An  assertion  is  a  test on the characters following or preceding the         An assertion is a test on the characters  following  or  preceding  the
4548         current matching point that does not actually consume  any  characters.         current  matching  point that does not actually consume any characters.
4549         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
4550         described above.         described above.
4551    
4552         More complicated assertions are coded as  subpatterns.  There  are  two         More  complicated  assertions  are  coded as subpatterns. There are two
4553         kinds:  those  that  look  ahead of the current position in the subject         kinds: those that look ahead of the current  position  in  the  subject
4554         string, and those that look  behind  it.  An  assertion  subpattern  is         string,  and  those  that  look  behind  it. An assertion subpattern is
4555         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
4556         matching position to be changed.         matching position to be changed.
4557    
4558         Assertion subpatterns are not capturing subpatterns,  and  may  not  be         Assertion  subpatterns  are  not  capturing subpatterns, and may not be
4559         repeated,  because  it  makes no sense to assert the same thing several         repeated, because it makes no sense to assert the  same  thing  several
4560         times. If any kind of assertion contains capturing  subpatterns  within         times.  If  any kind of assertion contains capturing subpatterns within
4561         it,  these are counted for the purposes of numbering the capturing sub-         it, these are counted for the purposes of numbering the capturing  sub-
4562         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4563         out  only  for  positive assertions, because it does not make sense for         out only for positive assertions, because it does not  make  sense  for
4564         negative assertions.         negative assertions.
4565    
4566     Lookahead assertions     Lookahead assertions
# Line 4357  ASSERTIONS Line 4570  ASSERTIONS
4570    
4571           \w+(?=;)           \w+(?=;)
4572    
4573         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-
4574         colon in the match, and         colon in the match, and
4575    
4576           foo(?!bar)           foo(?!bar)
4577    
4578         matches any occurrence of "foo" that is not  followed  by  "bar".  Note         matches  any  occurrence  of  "foo" that is not followed by "bar". Note
4579         that the apparently similar pattern         that the apparently similar pattern
4580    
4581           (?!foo)bar           (?!foo)bar
4582    
4583         does  not  find  an  occurrence  of "bar" that is preceded by something         does not find an occurrence of "bar"  that  is  preceded  by  something
4584         other than "foo"; it finds any occurrence of "bar" whatsoever,  because         other  than "foo"; it finds any occurrence of "bar" whatsoever, because
4585         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4586         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4587    
4588         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
4589         most  convenient  way  to  do  it  is with (?!) because an empty string         most convenient way to do it is  with  (?!)  because  an  empty  string
4590         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
4591         string must always fail.         string must always fail.   The  Perl  5.10  backtracking  control  verb
4592           (*FAIL) or (*F) is essentially a synonym for (?!).
4593    
4594     Lookbehind assertions     Lookbehind assertions
4595    
# Line 4398  ASSERTIONS Line 4612  ASSERTIONS
4612    
4613         causes an error at compile time. Branches that match  different  length         causes an error at compile time. Branches that match  different  length
4614         strings  are permitted only at the top level of a lookbehind assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4615         This is an extension compared with  Perl  (at  least  for  5.8),  which         This is an extension compared with Perl (5.8 and 5.10), which  requires
4616         requires  all branches to match the same length of string. An assertion         all branches to match the same length of string. An assertion such as
        such as  
4617    
4618           (?<=ab(c|de))           (?<=ab(c|de))
4619    
4620         is not permitted, because its single top-level  branch  can  match  two         is  not  permitted,  because  its single top-level branch can match two
4621         different  lengths,  but  it is acceptable if rewritten to use two top-         different lengths, but it is acceptable to PCRE if rewritten to use two
4622         level branches:         top-level branches:
4623    
4624           (?<=abc|abde)           (?<=abc|abde)
4625    
4626         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
4627         instead  of  a lookbehind assertion; this is not restricted to a fixed-         instead of  a  lookbehind  assertion  to  get  round  the  fixed-length
4628         length.         restriction.
4629    
4630         The implementation of lookbehind assertions is, for  each  alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4631         to  temporarily  move the current position back by the fixed length and         to temporarily move the current position back by the fixed  length  and
4632         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4633         rent position, the assertion fails.         rent position, the assertion fails.
4634    
4635         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
4636         mode) to appear in lookbehind assertions, because it makes it  impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
4637         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,
4638         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4639    
4640         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind         "Subroutine"  calls  (see below) such as (?2) or (?&X) are permitted in
4641         assertions  to  specify  efficient  matching  at the end of the subject         lookbehinds, as long as the subpattern matches a  fixed-length  string.
4642         string. Consider a simple pattern such as         Recursion, however, is not supported.
4643    
4644           Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4645           assertions to specify efficient matching of fixed-length strings at the
4646           end of subject strings. Consider a simple pattern such as
4647    
4648           abcd$           abcd$
4649    
4650         when applied to a long string that does  not  match.  Because  matching         when  applied  to  a  long string that does not match. Because matching
4651         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
4652         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
4653         pattern is specified as         pattern is specified as
4654    
4655           ^.*abcd$           ^.*abcd$
4656    
4657         the  initial .* matches the entire string at first, but when this fails         the initial .* matches the entire string at first, but when this  fails
4658         (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
4659         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
4660         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,
4661         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
4662    
4663           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4664    
4665         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
4666         entire string. The subsequent lookbehind assertion does a  single  test         entire  string.  The subsequent lookbehind assertion does a single test
4667         on  the last four characters. If it fails, the match fails immediately.         on the last four characters. If it fails, the match fails  immediately.
4668         For long strings, this approach makes a significant difference  to  the         For  long  strings, this approach makes a significant difference to the
4669         processing time.         processing time.
4670    
4671     Using multiple assertions     Using multiple assertions
# Line 4457  ASSERTIONS Line 4674  ASSERTIONS
4674    
4675           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4676    
4677         matches  "foo" preceded by three digits that are not "999". Notice that         matches "foo" preceded by three digits that are not "999". Notice  that
4678         each of the assertions is applied independently at the  same  point  in         each  of  the  assertions is applied independently at the same point in
4679         the  subject  string.  First  there  is a check that the previous three         the subject string. First there is a  check  that  the  previous  three
4680         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
4681         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4682         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
4683         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-
4684         foo". A pattern to do that is         foo". A pattern to do that is
4685    
4686           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4687    
4688         This time the first assertion looks at the  preceding  six  characters,         This  time  the  first assertion looks at the preceding six characters,
4689         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4690         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4691    
# Line 4476  ASSERTIONS Line 4693  ASSERTIONS
4693    
4694           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4695    
4696         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
4697         is not preceded by "foo", while         is not preceded by "foo", while
4698    
4699           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4700    
4701         is  another pattern that matches "foo" preceded by three digits and any         is another pattern that matches "foo" preceded by three digits and  any
4702         three characters that are not "999".         three characters that are not "999".
4703    
4704    
4705  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4706    
4707         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-
4708         ditionally  or to choose between two alternative subpatterns, depending         ditionally or to choose between two alternative subpatterns,  depending
4709         on the result of an assertion, or whether a previous capturing  subpat-         on  the result of an assertion, or whether a specific capturing subpat-
4710         tern  matched  or not. The two possible forms of conditional subpattern         tern has already been matched. The two possible  forms  of  conditional
4711         are         subpattern are:
4712    
4713           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4714           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4715    
4716         If the condition is satisfied, the yes-pattern is used;  otherwise  the         If  the  condition is satisfied, the yes-pattern is used; otherwise the
4717         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-
4718         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4719    
4720         There are four kinds of condition: references  to  subpatterns,  refer-         There  are  four  kinds of condition: references to subpatterns, refer-
4721         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4722    
4723     Checking for a used subpattern by number     Checking for a used subpattern by number
4724    
4725         If  the  text between the parentheses consists of a sequence of digits,         If the text between the parentheses consists of a sequence  of  digits,
4726         the condition is true if the capturing subpattern of  that  number  has         the condition is true if a capturing subpattern of that number has pre-
4727         previously  matched.  An  alternative notation is to precede the digits         viously matched. If there is more than one  capturing  subpattern  with
4728         with a plus or minus sign. In this case, the subpattern number is rela-         the  same  number  (see  the earlier section about duplicate subpattern
4729         tive rather than absolute.  The most recently opened parentheses can be         numbers), the condition is true if any of them have been set. An alter-
4730         referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In         native  notation is to precede the digits with a plus or minus sign. In
4731         looping constructs it can also make sense to refer to subsequent groups         this case, the subpattern number is relative rather than absolute.  The
4732         with constructs such as (?(+2).         most  recently opened parentheses can be referenced by (?(-1), the next
4733           most recent by (?(-2), and so on. In looping  constructs  it  can  also
4734           make  sense  to  refer  to  subsequent  groups  with constructs such as
4735           (?(+2).
4736    
4737         Consider the following pattern, which  contains  non-significant  white         Consider the following pattern, which  contains  non-significant  white
4738         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
# Line 4555  CONDITIONAL SUBPATTERNS Line 4775  CONDITIONAL SUBPATTERNS
4775    
4776           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )           (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4777    
4778           If  the  name used in a condition of this kind is a duplicate, the test
4779           is applied to all subpatterns of the same name, and is true if any  one
4780           of them has matched.
4781    
4782     Checking for pattern recursion     Checking for pattern recursion
4783    
# Line 4565  CONDITIONAL SUBPATTERNS Line 4788  CONDITIONAL SUBPATTERNS
4788    
4789           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4790    
4791         the condition is true if the most recent recursion is into the  subpat-         the condition is true if the most recent recursion is into a subpattern
4792         tern  whose  number or name is given. This condition does not check the         whose number or name is given. This condition does not check the entire
4793         entire recursion stack.         recursion stack. If the name used in a condition  of  this  kind  is  a
4794           duplicate, the test is applied to all subpatterns of the same name, and
4795           is true if any one of them is the most recent recursion.
4796    
4797         At "top level", all these recursion test conditions are  false.  Recur-         At "top level", all these recursion test  conditions  are  false.   The
4798         sive patterns are described below.         syntax for recursive patterns is described below.
4799    
4800     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4801    
# Line 4590  CONDITIONAL SUBPATTERNS Line 4815  CONDITIONAL SUBPATTERNS
4815         group  named "byte" is defined. This matches an individual component of         group  named "byte" is defined. This matches an individual component of
4816         an IPv4 address (a number less than 256). When  matching  takes  place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4817         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
4818         condition.         condition. The rest of the pattern uses references to the  named  group
4819           to  match the four dot-separated components of an IPv4 address, insist-
4820         The rest of the pattern uses references to the named group to match the         ing on a word boundary at each end.
        four  dot-separated  components of an IPv4 address, insisting on a word  
        boundary at each end.  
4821    
4822     Assertion conditions     Assertion conditions
4823    
# Line 4649  RECURSIVE PATTERNS Line 4872  RECURSIVE PATTERNS
4872         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4873         it supports special syntax for recursion of  the  entire  pattern,  and         it supports special syntax for recursion of  the  entire  pattern,  and
4874         also  for  individual  subpattern  recursion. After its introduction in         also  for  individual  subpattern  recursion. After its introduction in
4875         PCRE and Python, this kind of recursion was  introduced  into  Perl  at         PCRE and Python, this kind of  recursion  was  subsequently  introduced
4876         release 5.10.         into Perl at release 5.10.
4877    
4878         A  special  item  that consists of (? followed by a number greater than         A  special  item  that consists of (? followed by a number greater than
4879         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
# Line 4659  RECURSIVE PATTERNS Line 4882  RECURSIVE PATTERNS
4882         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
4883         regular expression.         regular expression.
4884    
4885         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is         This PCRE pattern solves the nested  parentheses  problem  (assume  the
        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.  
   
        This  PCRE  pattern  solves  the nested parentheses problem (assume the  
4886         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4887    
4888           \( ( (?>[^()]+) | (?R) )* \)           \( ( [^()]++ | (?R) )* \)
4889    
4890         First it matches an opening parenthesis. Then it matches any number  of         First  it matches an opening parenthesis. Then it matches any number of