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# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few differences. (Certain features that appeared in Python and         just  a  few  differences. Certain features that appeared in Python and
22         PCRE before they appeared in Perl are also available using  the  Python         PCRE before they appeared in Perl are also available using  the  Python
23         syntax.)         syntax.  There is also some support for certain .NET and Oniguruma syn-
24           tax items, and there is an option for  requesting  some  minor  changes
25           that give better JavaScript compatibility.
26    
27         The  current  implementation of PCRE (release 7.x) corresponds approxi-         The  current  implementation of PCRE (release 7.x) corresponds approxi-
28         mately with Perl 5.10, including support for UTF-8 encoded strings  and         mately with Perl 5.10, including support for UTF-8 encoded strings  and
# Line 45  INTRODUCTION Line 47  INTRODUCTION
47    
48         Details of exactly which Perl regular expression features are  and  are         Details of exactly which Perl regular expression features are  and  are
49         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
50         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
51           page.
52    
53         Some features of PCRE can be included, excluded, or  changed  when  the         Some  features  of  PCRE can be included, excluded, or changed when the
54         library  is  built.  The pcre_config() function makes it possible for a         library is built. The pcre_config() function makes it  possible  for  a
55         client to discover which features are  available.  The  features  them-         client  to  discover  which  features are available. The features them-
56         selves  are described in the pcrebuild page. Documentation about build-         selves are described in the pcrebuild page. Documentation about  build-
57         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 file
58         in the source distribution.         in the source distribution.
59    
60         The  library  contains  a number of undocumented internal functions and         The library contains a number of undocumented  internal  functions  and
61         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
62         functions,  but  which  are  not  intended for use by external callers.         functions, but which are not intended  for  use  by  external  callers.
63         Their names all begin with "_pcre_", which hopefully will  not  provoke         Their  names  all begin with "_pcre_", which hopefully will not provoke
64         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
65         external symbols are exported when a shared library is  built,  and  in         external  symbols  are  exported when a shared library is built, and in
66         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
67    
68    
69  USER DOCUMENTATION  USER DOCUMENTATION
70    
71         The  user  documentation  for PCRE comprises a number of different sec-         The user documentation for PCRE comprises a number  of  different  sec-
72         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
73         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.
74         In the plain text format, all the sections are concatenated,  for  ease         In  the  plain text format, all the sections are concatenated, for ease
75         of searching. The sections are as follows:         of searching. The sections are as follows:
76    
77           pcre              this document           pcre              this document
# Line 83  USER DOCUMENTATION Line 86  USER DOCUMENTATION
86           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
87           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
88                               regular expressions                               regular expressions
89             pcresyntax        quick syntax reference
90           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
91           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
92           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
# Line 107  LIMITATIONS Line 111  LIMITATIONS
111         In  these  cases the limit is substantially larger.  However, the speed         In  these  cases the limit is substantially larger.  However, the speed
112         of execution is slower.         of execution is slower.
113    
114         All values in repeating quantifiers must be less than 65536. The  maxi-         All values in repeating quantifiers must be less than 65536.
        mum  compiled  length  of  subpattern  with an explicit repeat count is  
        30000 bytes. The maximum number of capturing subpatterns is 65535.  
115    
116         There is no limit to the number of parenthesized subpatterns, but there         There is no limit to the number of parenthesized subpatterns, but there
117         can be no more than 65535 capturing subpatterns.         can be no more than 65535 capturing subpatterns.
# Line 155  UTF-8 AND UNICODE PROPERTY SUPPORT Line 157  UTF-8 AND UNICODE PROPERTY SUPPORT
157         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
158         does not support this.         does not support this.
159    
160         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
161    
162           When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
163           subjects are (by default) checked for validity on entry to the relevant
164           functions.  From  release 7.3 of PCRE, the check is according the rules
165           of RFC 3629, which are themselves derived from the  Unicode  specifica-
166           tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
167           allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
168           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
169           to U+DFFF.
170    
171           The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
172           which  the Unicode Standard says this: "The Low Surrogate Area does not
173           contain any  character  assignments,  consequently  no  character  code
174           charts or namelists are provided for this area. Surrogates are reserved
175           for use with UTF-16 and then must be used in pairs."  The  code  points
176           that  are  encoded  by  UTF-16  pairs are available as independent code
177           points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
178           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
179    
180           If  an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error return
181           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
182           that your strings are valid, and therefore want to skip these checks in
183           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
184           compile  time  or at run time, PCRE assumes that the pattern or subject
185           it is given (respectively) contains only valid  UTF-8  codes.  In  this
186           case, it does not diagnose an invalid UTF-8 string.
187    
188           If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
189           what happens depends on why the string is invalid. If the  string  con-
190           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
191           string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
192           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
193           strings according to the more liberal rules of RFC  2279.  However,  if
194           the  string does not even conform to RFC 2279, the result is undefined.
195           Your program may crash.
196    
197           If you want to process strings  of  values  in  the  full  range  0  to
198           0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
199           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
200           this situation, you will have to apply your own validity check.
201    
202         1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and     General comments about UTF-8 mode
        subjects are checked for validity on entry to the  relevant  functions.  
        If an invalid UTF-8 string is passed, an error return is given. In some  
        situations, you may already know  that  your  strings  are  valid,  and  
        therefore want to skip these checks in order to improve performance. If  
        you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,  
        PCRE  assumes  that  the  pattern or subject it is given (respectively)  
        contains only valid UTF-8 codes. In this case, it does not diagnose  an  
        invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when  
        PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may  
        crash.  
203    
204         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a         1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
205         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
206    
207         3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8         2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
208         characters for values greater than \177.         characters for values greater than \177.
209    
210         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
211         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
212    
213         5. The dot metacharacter matches one UTF-8 character instead of a  sin-         4. The dot metacharacter matches one UTF-8 character instead of a  sin-
214         gle byte.         gle byte.
215    
216         6.  The  escape sequence \C can be used to match a single byte in UTF-8         5.  The  escape sequence \C can be used to match a single byte in UTF-8
217         mode, but its use can lead to some strange effects.  This  facility  is         mode, but its use can lead to some strange effects.  This  facility  is
218         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
219    
220         7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly         6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
221         test characters of any code value, but the characters that PCRE  recog-         test characters of any code value, but the characters that PCRE  recog-
222         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes  as  digits,  spaces,  or  word characters remain the same set as
223         before, all with values less than 256. This remains true even when PCRE         before, all with values less than 256. This remains true even when PCRE
224         includes  Unicode  property support, because to do otherwise would slow         includes  Unicode  property support, because to do otherwise would slow
225         down PCRE in many common cases. If you really want to test for a  wider         down PCRE in many common cases. If you really want to test for a  wider
226         sense  of,  say,  "digit",  you must use Unicode property tests such as         sense  of,  say,  "digit",  you must use Unicode property tests such as
227         \p{Nd}.         \p{Nd}. Note that this also applies to \b, because  it  is  defined  in
228           terms of \w and \W.
229    
230         8. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
231         are all low-valued characters.         are all low-valued characters.
232    
233         9.  Case-insensitive  matching  applies only to characters whose values         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
234         are less than 128, unless PCRE is built with Unicode property  support.         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
235         Even  when  Unicode  property support is available, PCRE still uses its         acters.
236         own character tables when checking the case of  low-valued  characters,  
237         so  as not to degrade performance.  The Unicode property information is         9. Case-insensitive matching applies only to  characters  whose  values
238           are  less than 128, unless PCRE is built with Unicode property support.
239           Even when Unicode property support is available, PCRE  still  uses  its
240           own  character  tables when checking the case of low-valued characters,
241           so as not to degrade performance.  The Unicode property information  is
242         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Even when Unicode property
243         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
244         there is a one-to-one mapping between a letter's  cases.  There  are  a         there  is  a  one-to-one  mapping between a letter's cases. There are a
245         small  number  of  many-to-one  mappings in Unicode; these are not sup-         small number of many-to-one mappings in Unicode;  these  are  not  sup-
246         ported by PCRE.         ported by PCRE.
247    
248    
# Line 215  AUTHOR Line 252  AUTHOR
252         University Computing Service         University Computing Service
253         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
254    
255         Putting an actual email address here seems to have been a spam  magnet,         Putting  an actual email address here seems to have been a spam magnet,
256         so  I've  taken  it away. If you want to email me, use my two initials,         so I've taken it away. If you want to email me, use  my  two  initials,
257         followed by the two digits 10, at the domain cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
258    
259    
260  REVISION  REVISION
261    
262         Last updated: 18 April 2007         Last updated: 18 March 2009
263         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
264  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
265    
266    
# Line 237  NAME Line 274  NAME
274  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
275    
276         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
277         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. It assumes use of the  configure
278         lected, by providing options to the configure script that is run before         script,  where the optional features are selected or deselected by pro-
279         the make command. The complete list of  options  for  configure  (which         viding options to configure before running the make  command.  However,
280         includes  the  standard  ones such as the selection of the installation         the  same  options  can be selected in both Unix-like and non-Unix-like
281         directory) can be obtained by running         environments using the GUI facility of  CMakeSetup  if  you  are  using
282           CMake instead of configure to build PCRE.
283    
284           The complete list of options for configure (which includes the standard
285           ones such as the  selection  of  the  installation  directory)  can  be
286           obtained by running
287    
288           ./configure --help           ./configure --help
289    
290         The following sections include  descriptions  of  options  whose  names         The  following  sections  include  descriptions  of options whose names
291         begin with --enable or --disable. These settings specify changes to the         begin with --enable or --disable. These settings specify changes to the
292         defaults for the configure command. Because of the way  that  configure         defaults  for  the configure command. Because of the way that configure
293         works,  --enable  and --disable always come in pairs, so the complemen-         works, --enable and --disable always come in pairs, so  the  complemen-
294         tary option always exists as well, but as it specifies the default,  it         tary  option always exists as well, but as it specifies the default, it
295         is not described.         is not described.
296    
297    
# Line 266  C++ SUPPORT Line 308  C++ SUPPORT
308    
309  UTF-8 SUPPORT  UTF-8 SUPPORT
310    
311         To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 Unicode character strings, add
312    
313           --enable-utf8           --enable-utf8
314    
315         to  the  configure  command.  Of  itself, this does not make PCRE treat         to the configure command. Of itself, this  does  not  make  PCRE  treat
316         strings as UTF-8. As well as compiling PCRE with this option, you  also         strings  as UTF-8. As well as compiling PCRE with this option, you also
317         have  have to set the PCRE_UTF8 option when you call the pcre_compile()         have have to set the PCRE_UTF8 option when you call the  pcre_compile()
318         function.         function.
319    
320           If  you set --enable-utf8 when compiling in an EBCDIC environment, PCRE
321           expects its input to be either ASCII or UTF-8 (depending on the runtime
322           option).  It  is not possible to support both EBCDIC and UTF-8 codes in
323           the same  version  of  the  library.  Consequently,  --enable-utf8  and
324           --enable-ebcdic are mutually exclusive.
325    
326    
327  UNICODE CHARACTER PROPERTY SUPPORT  UNICODE CHARACTER PROPERTY SUPPORT
328    
329         UTF-8 support allows PCRE to process character values greater than  255         UTF-8  support allows PCRE to process character values greater than 255
330         in  the  strings that it handles. On its own, however, it does not pro-         in the strings that it handles. On its own, however, it does  not  pro-
331         vide any facilities for accessing the properties of such characters. If         vide any facilities for accessing the properties of such characters. If
332         you  want  to  be able to use the pattern escapes \P, \p, and \X, which         you want to be able to use the pattern escapes \P, \p,  and  \X,  which
333         refer to Unicode character properties, you must add         refer to Unicode character properties, you must add
334    
335           --enable-unicode-properties           --enable-unicode-properties
336    
337         to the configure command. This implies UTF-8 support, even if you  have         to  the configure command. This implies UTF-8 support, even if you have
338         not explicitly requested it.         not explicitly requested it.
339    
340         Including  Unicode  property  support  adds around 30K of tables to the         Including Unicode property support adds around 30K  of  tables  to  the
341         PCRE library. Only the general category properties such as  Lu  and  Nd         PCRE  library.  Only  the general category properties such as Lu and Nd
342         are supported. Details are given in the pcrepattern documentation.         are supported. Details are given in the pcrepattern documentation.
343    
344    
345  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
346    
347         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating         By default, PCRE interprets the linefeed (LF) character  as  indicating
348         the end of a line. This is the normal newline  character  on  Unix-like         the  end  of  a line. This is the normal newline character on Unix-like
349         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems. You can compile PCRE to use carriage return (CR)  instead,  by
350         instead, by adding         adding
351    
352           --enable-newline-is-cr           --enable-newline-is-cr
353    
354         to the  configure  command.  There  is  also  a  --enable-newline-is-lf         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
355         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
356    
357         Alternatively, you can specify that line endings are to be indicated by         Alternatively, you can specify that line endings are to be indicated by
# Line 315  CODE VALUE OF NEWLINE Line 363  CODE VALUE OF NEWLINE
363    
364           --enable-newline-is-anycrlf           --enable-newline-is-anycrlf
365    
366         which causes PCRE to recognize any of the three sequences  CR,  LF,  or         which  causes  PCRE  to recognize any of the three sequences CR, LF, or
367         CRLF as indicating a line ending. Finally, a fifth option, specified by         CRLF as indicating a line ending. Finally, a fifth option, specified by
368    
369           --enable-newline-is-any           --enable-newline-is-any
# Line 327  CODE VALUE OF NEWLINE Line 375  CODE VALUE OF NEWLINE
375         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
376    
377    
378    WHAT \R MATCHES
379    
380           By default, the sequence \R in a pattern matches  any  Unicode  newline
381           sequence,  whatever  has  been selected as the line ending sequence. If
382           you specify
383    
384             --enable-bsr-anycrlf
385    
386           the default is changed so that \R matches only CR, LF, or  CRLF.  What-
387           ever  is selected when PCRE is built can be overridden when the library
388           functions are called.
389    
390    
391  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
392    
393         The PCRE building process uses libtool to build both shared and  static         The PCRE building process uses libtool to build both shared and  static
# Line 390  AVOIDING EXCESSIVE STACK USAGE Line 451  AVOIDING EXCESSIVE STACK USAGE
451    
452         to  the  configure  command. With this configuration, PCRE will use the         to  the  configure  command. With this configuration, PCRE will use the
453         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
454         ment  functions.  Separate  functions are provided because the usage is         ment  functions. By default these point to malloc() and free(), but you
455         very predictable: the block sizes requested are always  the  same,  and         can replace the pointers so that your own functions are used.
456         the  blocks  are always freed in reverse order. A calling program might  
457         be able to implement optimized functions that perform better  than  the         Separate functions are  provided  rather  than  using  pcre_malloc  and
458         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more         pcre_free  because  the  usage  is  very  predictable:  the block sizes
459         slowly when built in this way. This option affects only the pcre_exec()         requested are always the same, and  the  blocks  are  always  freed  in
460         function; it is not relevant for the the pcre_dfa_exec() function.         reverse  order.  A calling program might be able to implement optimized
461           functions that perform better  than  malloc()  and  free().  PCRE  runs
462           noticeably more slowly when built in this way. This option affects only
463           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
464           pcre_dfa_exec() function.
465    
466    
467  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
# Line 451  USING EBCDIC CODE Line 516  USING EBCDIC CODE
516    
517         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
518         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
519         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         This  is  the  case for most computer operating systems. PCRE can, how-
520         adding         ever, be compiled to run in an EBCDIC environment by adding
521    
522           --enable-ebcdic           --enable-ebcdic
523    
524         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
525         bles.         bles.  You  should  only  use  it if you know that you are in an EBCDIC
526           environment (for example,  an  IBM  mainframe  operating  system).  The
527           --enable-ebcdic option is incompatible with --enable-utf8.
528    
529    
530    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
531    
532           By default, pcregrep reads all files as plain text. You can build it so
533           that it recognizes files whose names end in .gz or .bz2, and reads them
534           with libz or libbz2, respectively, by adding one or both of
535    
536             --enable-pcregrep-libz
537             --enable-pcregrep-libbz2
538    
539           to the configure command. These options naturally require that the rel-
540           evant libraries are installed on your system. Configuration  will  fail
541           if they are not.
542    
543    
544    PCRETEST OPTION FOR LIBREADLINE SUPPORT
545    
546           If you add
547    
548             --enable-pcretest-libreadline
549    
550           to  the  configure  command,  pcretest  is  linked with the libreadline
551           library, and when its input is from a terminal, it reads it  using  the
552           readline() function. This provides line-editing and history facilities.
553           Note that libreadline is GPL-licenced, so if you distribute a binary of
554           pcretest linked in this way, there may be licensing issues.
555    
556           Setting  this  option  causes  the -lreadline option to be added to the
557           pcretest build. In many operating environments with  a  sytem-installed
558           libreadline this is sufficient. However, in some environments (e.g.  if
559           an unmodified distribution version of readline is in use),  some  extra
560           configuration  may  be necessary. The INSTALL file for libreadline says
561           this:
562    
563             "Readline uses the termcap functions, but does not link with the
564             termcap or curses library itself, allowing applications which link
565             with readline the to choose an appropriate library."
566    
567           If your environment has not been set up so that an appropriate  library
568           is automatically included, you may need to add something like
569    
570             LIBS="-ncurses"
571    
572           immediately before the configure command.
573    
574    
575  SEE ALSO  SEE ALSO
# Line 474  AUTHOR Line 586  AUTHOR
586    
587  REVISION  REVISION
588    
589         Last updated: 16 April 2007         Last updated: 17 March 2009
590         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
591  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
592    
593    
# Line 610  THE ALTERNATIVE MATCHING ALGORITHM Line 722  THE ALTERNATIVE MATCHING ALGORITHM
722         ence  as  the  condition or test for a specific group recursion are not         ence  as  the  condition or test for a specific group recursion are not
723         supported.         supported.
724    
725         5. Callouts are supported, but the value of the  capture_top  field  is         5. Because many paths through the tree may be  active,  the  \K  escape
726           sequence, which resets the start of the match when encountered (but may
727           be on some paths and not on others), is not  supported.  It  causes  an
728           error if encountered.
729    
730           6.  Callouts  are  supported, but the value of the capture_top field is
731         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
732    
733         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
734         single byte, even in UTF-8 mode, is not supported because the  alterna-         single  byte, even in UTF-8 mode, is not supported because the alterna-
735         tive  algorithm  moves  through  the  subject string one character at a         tive algorithm moves through the subject  string  one  character  at  a
736         time, for all active paths through the tree.         time, for all active paths through the tree.
737    
738           8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
739           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
740           negative assertion.
741    
742    
743  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
744    
745         Using the alternative matching algorithm provides the following  advan-         Using  the alternative matching algorithm provides the following advan-
746         tages:         tages:
747    
748         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
749         ically found, and in particular, the longest match is  found.  To  find         ically  found,  and  in particular, the longest match is found. To find
750         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
751         things with callouts.         things with callouts.
752    
753         2. There is much better support for partial matching. The  restrictions         2.  There is much better support for partial matching. The restrictions
754         on  the content of the pattern that apply when using the standard algo-         on the content of the pattern that apply when using the standard  algo-
755         rithm for partial matching do not apply to the  alternative  algorithm.         rithm  for  partial matching do not apply to the alternative algorithm.
756         For  non-anchored patterns, the starting position of a partial match is         For non-anchored patterns, the starting position of a partial match  is
757         available.         available.
758    
759         3. Because the alternative algorithm  scans  the  subject  string  just         3.  Because  the  alternative  algorithm  scans the subject string just
760         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
761         subject strings to the matching function in  several  pieces,  checking         subject  strings  to  the matching function in several pieces, checking
762         for partial matching each time.         for partial matching each time.
763    
764    
# Line 645  DISADVANTAGES OF THE ALTERNATIVE ALGORIT Line 766  DISADVANTAGES OF THE ALTERNATIVE ALGORIT
766    
767         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
768    
769         1.  It  is  substantially  slower  than the standard algorithm. This is         1. It is substantially slower than  the  standard  algorithm.  This  is
770         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
771         because it is less susceptible to optimization.         because it is less susceptible to optimization.
772    
773         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 664  AUTHOR Line 785  AUTHOR
785    
786  REVISION  REVISION
787    
788         Last updated: 06 March 2007         Last updated: 19 April 2008
789         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2008 University of Cambridge.
790  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
791    
792    
# Line 777  PCRE API OVERVIEW Line 898  PCRE API OVERVIEW
898         a  Perl-compatible  manner. A sample program that demonstrates the sim-         a  Perl-compatible  manner. A sample program that demonstrates the sim-
899         plest way of using them is provided in the file  called  pcredemo.c  in         plest way of using them is provided in the file  called  pcredemo.c  in
900         the  source distribution. The pcresample documentation describes how to         the  source distribution. The pcresample documentation describes how to
901         run it.         compile and run it.
902    
903         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
904         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
# Line 861  NEWLINES Line 982  NEWLINES
982         dard. When PCRE is run, the default can be overridden,  either  when  a         dard. When PCRE is run, the default can be overridden,  either  when  a
983         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
984    
985           At compile time, the newline convention can be specified by the options
986           argument of pcre_compile(), or it can be specified by special  text  at
987           the start of the pattern itself; this overrides any other settings. See
988           the pcrepattern page for details of the special character sequences.
989    
990         In the PCRE documentation the word "newline" is used to mean "the char-         In the PCRE documentation the word "newline" is used to mean "the char-
991         acter or pair of characters that indicate a line break". The choice  of         acter  or pair of characters that indicate a line break". The choice of
992         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
993         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
994         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
995         ment for a non-anchored pattern. The choice of newline convention  does         ment for a non-anchored pattern. There is more detail about this in the
996         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
997    
998           The choice of newline convention does not affect the interpretation  of
999           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1000           which is controlled in a similar way, but by separate options.
1001    
1002    
1003  MULTITHREADING  MULTITHREADING
1004    
1005         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
1006         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
1007         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1008         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
# Line 921  CHECKING BUILD-TIME OPTIONS Line 1051  CHECKING BUILD-TIME OPTIONS
1051         The output is an integer whose value specifies  the  default  character         The output is an integer whose value specifies  the  default  character
1052         sequence  that is recognized as meaning "newline". The four values that         sequence  that is recognized as meaning "newline". The four values that
1053         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1054         and  -1  for  ANY. The default should normally be the standard sequence         and  -1  for  ANY.  Though they are derived from ASCII, the same values
1055         for your operating system.         are returned in EBCDIC environments. The default should normally corre-
1056           spond to the standard sequence for your operating system.
1057    
1058             PCRE_CONFIG_BSR
1059    
1060           The output is an integer whose value indicates what character sequences
1061           the \R escape sequence matches by default. A value of 0 means  that  \R
1062           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1063           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1064           tern is compiled or matched.
1065    
1066           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1067    
1068         The output is an integer that contains the number  of  bytes  used  for         The  output  is  an  integer that contains the number of bytes used for
1069         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1070         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1071         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1072         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1073         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1074    
1075           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1076    
1077         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1078         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1079         given in the pcreposix documentation.         given in the pcreposix documentation.
1080    
1081           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1082    
1083         The output is an integer that gives the default limit for the number of         The output is a long integer that gives the default limit for the  num-
1084         internal matching function calls in a  pcre_exec()  execution.  Further         ber  of  internal  matching  function calls in a pcre_exec() execution.
1085         details are given with pcre_exec() below.         Further details are given with pcre_exec() below.
1086    
1087           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1088    
1089         The  output is an integer that gives the default limit for the depth of         The output is a long integer that gives the default limit for the depth
1090         recursion when calling the internal matching function in a  pcre_exec()         of   recursion  when  calling  the  internal  matching  function  in  a
1091         execution. Further details are given with pcre_exec() below.         pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1092           below.
1093    
1094           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1095    
# Line 1053  COMPILING A PATTERN Line 1193  COMPILING A PATTERN
1193         all with number 255, before each pattern item. For  discussion  of  the         all with number 255, before each pattern item. For  discussion  of  the
1194         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1195    
1196             PCRE_BSR_ANYCRLF
1197             PCRE_BSR_UNICODE
1198    
1199           These options (which are mutually exclusive) control what the \R escape
1200           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1201           or to match any Unicode newline sequence. The default is specified when
1202           PCRE is built. It can be overridden from within the pattern, or by set-
1203           ting an option when a compiled pattern is matched.
1204    
1205           PCRE_CASELESS           PCRE_CASELESS
1206    
1207         If  this  bit is set, letters in the pattern match both upper and lower         If  this  bit is set, letters in the pattern match both upper and lower
# Line 1126  COMPILING A PATTERN Line 1275  COMPILING A PATTERN
1275         before  or  at  the  first  newline  in  the subject string, though the         before  or  at  the  first  newline  in  the subject string, though the
1276         matched text may continue over the newline.         matched text may continue over the newline.
1277    
1278             PCRE_JAVASCRIPT_COMPAT
1279    
1280           If this option is set, PCRE's behaviour is changed in some ways so that
1281           it  is  compatible with JavaScript rather than Perl. The changes are as
1282           follows:
1283    
1284           (1) A lone closing square bracket in a pattern  causes  a  compile-time
1285           error,  because this is illegal in JavaScript (by default it is treated
1286           as a data character). Thus, the pattern AB]CD becomes illegal when this
1287           option is set.
1288    
1289           (2)  At run time, a back reference to an unset subpattern group matches
1290           an empty string (by default this causes the current  matching  alterna-
1291           tive  to  fail). A pattern such as (\1)(a) succeeds when this option is
1292           set (assuming it can find an "a" in the subject), whereas it  fails  by
1293           default, for Perl compatibility.
1294    
1295           PCRE_MULTILINE           PCRE_MULTILINE
1296    
1297         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1298         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1299         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1300         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1301         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1302         is set). This is the same as Perl.         is set). This is the same as Perl.
1303    
1304         When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1305         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1306         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1307         start and end. This is equivalent to Perl's /m option, and  it  can  be         start  and  end.  This is equivalent to Perl's /m option, and it can be
1308         changed within a pattern by a (?m) option setting. If there are no new-         changed within a pattern by a (?m) option setting. If there are no new-
1309         lines in a subject string, or no occurrences of ^ or $  in  a  pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1310         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1311    
1312           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1149  COMPILING A PATTERN Line 1315  COMPILING A PATTERN
1315           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1316           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1317    
1318         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1319         when PCRE was built. Setting the first or the second specifies  that  a         when  PCRE  was built. Setting the first or the second specifies that a
1320         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1321         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1322         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1323         that any of the three preceding sequences should be recognized. Setting         that any of the three preceding sequences should be recognized. Setting
1324         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1325         recognized. The Unicode newline sequences are the three just mentioned,         recognized. The Unicode newline sequences are the three just mentioned,
1326         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1327         U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS         U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1328         (paragraph  separator,  U+2029).  The  last  two are recognized only in         (paragraph separator, U+2029). The last  two  are  recognized  only  in
1329         UTF-8 mode.         UTF-8 mode.
1330    
1331         The newline setting in the  options  word  uses  three  bits  that  are         The  newline  setting  in  the  options  word  uses three bits that are
1332         treated as a number, giving eight possibilities. Currently only six are         treated as a number, giving eight possibilities. Currently only six are
1333         used (default plus the five values above). This means that if  you  set         used  (default  plus the five values above). This means that if you set
1334         more  than one newline option, the combination may or may not be sensi-         more than one newline option, the combination may or may not be  sensi-
1335         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to         ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1336         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1337         cause an error.         cause an error.
1338    
1339         The only time that a line break is specially recognized when  compiling         The  only time that a line break is specially recognized when compiling
1340         a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a         a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1341         character class is encountered. This indicates  a  comment  that  lasts         character  class  is  encountered.  This indicates a comment that lasts
1342         until  after the next line break sequence. In other circumstances, line         until after the next line break sequence. In other circumstances,  line
1343         break  sequences  are  treated  as  literal  data,   except   that   in         break   sequences   are   treated  as  literal  data,  except  that  in
1344         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1345         and are therefore ignored.         and are therefore ignored.
1346    
1347         The newline option that is set at compile time becomes the default that         The newline option that is set at compile time becomes the default that
1348         is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.         is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1349    
1350           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1351    
# Line 1208  COMPILING A PATTERN Line 1374  COMPILING A PATTERN
1374           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1375    
1376         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1377         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically  checked.  There  is  a  discussion about the validity of
1378         pcre_compile() returns an error. If you already know that your  pattern         UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1379         is  valid, and you want to skip this check for performance reasons, you         bytes  is  found,  pcre_compile() returns an error. If you already know
1380         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1381         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1382         your program to crash.  Note that this option can  also  be  passed  to         set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1383         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined.  It  may  cause your program to crash. Note that this option
1384         ing of subject strings.         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1385           UTF-8 validity checking of subject strings.
1386    
1387    
1388  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1389    
1390         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1391         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1392         both compiling functions. As PCRE has developed, some error codes  have         both  compiling functions. As PCRE has developed, some error codes have
1393         fallen out of use. To avoid confusion, they have not been re-used.         fallen out of use. To avoid confusion, they have not been re-used.
1394    
1395            0  no error            0  no error
# Line 1237  COMPILATION ERROR CODES Line 1404  COMPILATION ERROR CODES
1404            9  nothing to repeat            9  nothing to repeat
1405           10  [this code is not in use]           10  [this code is not in use]
1406           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1407           12  unrecognized character after (?           12  unrecognized character after (? or (?-
1408           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
1409           14  missing )           14  missing )
1410           15  reference to non-existent subpattern           15  reference to non-existent subpattern
# Line 1245  COMPILATION ERROR CODES Line 1412  COMPILATION ERROR CODES
1412           17  unknown option bit(s) set           17  unknown option bit(s) set
1413           18  missing ) after comment           18  missing ) after comment
1414           19  [this code is not in use]           19  [this code is not in use]
1415           20  regular expression too large           20  regular expression is too large
1416           21  failed to get memory           21  failed to get memory
1417           22  unmatched parentheses           22  unmatched parentheses
1418           23  internal error: code overflow           23  internal error: code overflow
# Line 1254  COMPILATION ERROR CODES Line 1421  COMPILATION ERROR CODES
1421           26  malformed number or name after (?(           26  malformed number or name after (?(
1422           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1423           28  assertion expected after (?(           28  assertion expected after (?(
1424           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1425           30  unknown POSIX class name           30  unknown POSIX class name
1426           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1427           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
# Line 1274  COMPILATION ERROR CODES Line 1441  COMPILATION ERROR CODES
1441           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1442           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1443           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1444           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10000)
1445           50  repeated subpattern is too long           50  [this code is not in use]
1446           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1447           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1448           53   internal  error:  previously-checked  referenced  subpattern not           53  internal  error:  previously-checked  referenced  subpattern  not
1449         found         found
1450           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1451           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1452           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1453             57  \g is not followed by a braced, angle-bracketed, or quoted
1454                   name/number or by a plain number
1455             58  a numbered reference must not be zero
1456             59  (*VERB) with an argument is not supported
1457             60  (*VERB) not recognized
1458             61  number is too big
1459             62  subpattern name expected
1460             63  digit expected after (?+
1461             64  ] is an invalid data character in JavaScript compatibility mode
1462    
1463           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1464           values may be used if the limits were changed when PCRE was built.
1465    
1466    
1467  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1471  INFORMATION ABOUT A PATTERN Line 1650  INFORMATION ABOUT A PATTERN
1650         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1651         able.         able.
1652    
1653             PCRE_INFO_HASCRORLF
1654    
1655           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1656           characters, otherwise 0. The fourth argument should  point  to  an  int
1657           variable.  An explicit match is either a literal CR or LF character, or
1658           \r or \n.
1659    
1660             PCRE_INFO_JCHANGED
1661    
1662           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1663           otherwise  0. The fourth argument should point to an int variable. (?J)
1664           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1665    
1666           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1667    
1668         Return  the  value of the rightmost literal byte that must exist in any         Return the value of the rightmost literal byte that must exist  in  any
1669         matched string, other than at its  start,  if  such  a  byte  has  been         matched  string,  other  than  at  its  start,  if such a byte has been
1670         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1671         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1672         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1673         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1674         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1675    
# Line 1485  INFORMATION ABOUT A PATTERN Line 1677  INFORMATION ABOUT A PATTERN
1677           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1678           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1679    
1680         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1681         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1682         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1683         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1684         strings  by  name. It is also possible to extract the data directly, by         strings by name. It is also possible to extract the data  directly,  by
1685         first converting the name to a number in order to  access  the  correct         first  converting  the  name to a number in order to access the correct
1686         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1687         the conversion, you need  to  use  the  name-to-number  map,  which  is         the  conversion,  you  need  to  use  the  name-to-number map, which is
1688         described by these three values.         described by these three values.
1689    
1690         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1691         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1692         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1693         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1694         a  pointer  to  the  first  entry of the table (a pointer to char). The         a pointer to the first entry of the table  (a  pointer  to  char).  The
1695         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1696         sis,  most  significant byte first. The rest of the entry is the corre-         sis, most significant byte first. The rest of the entry is  the  corre-
1697         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1698         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1699         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1700         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1701         ignored):         ignored):
1702    
1703           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1704           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1705    
1706         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1707         each  entry  in the table is eight bytes long. The table is as follows,         each entry in the table is eight bytes long. The table is  as  follows,
1708         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1709         as ??:         as ??:
1710    
# Line 1521  INFORMATION ABOUT A PATTERN Line 1713  INFORMATION ABOUT A PATTERN
1713           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1714           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1715    
1716         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1717         name-to-number map, remember that the length of the entries  is  likely         name-to-number  map,  remember that the length of the entries is likely
1718         to be different for each compiled pattern.         to be different for each compiled pattern.
1719    
1720             PCRE_INFO_OKPARTIAL
1721    
1722           Return 1 if the pattern can be used for partial matching, otherwise  0.
1723           The  fourth  argument  should point to an int variable. The pcrepartial
1724           documentation lists the restrictions that apply to patterns  when  par-
1725           tial matching is used.
1726    
1727           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1728    
1729         Return  a  copy of the options with which the pattern was compiled. The         Return  a  copy of the options with which the pattern was compiled. The
1730         fourth argument should point to an unsigned long  int  variable.  These         fourth argument should point to an unsigned long  int  variable.  These
1731         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1732         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1733           other  words,  they are the options that will be in force when matching
1734           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1735           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1736           and PCRE_EXTENDED.
1737    
1738         A pattern is automatically anchored by PCRE if  all  of  its  top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1739         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1610  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1813  MATCHING A PATTERN: THE TRADITIONAL FUNC
1813              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1814              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1815    
1816         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
1817         compiled pattern, which is passed in the code argument. If the  pattern         compiled  pattern, which is passed in the code argument. If the pattern
1818         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1819         argument. This function is the main matching facility of  the  library,         argument.  This  function is the main matching facility of the library,
1820         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
1821         an alternative matching function, which is described below in the  sec-         an  alternative matching function, which is described below in the sec-
1822         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1823    
1824         In  most applications, the pattern will have been compiled (and option-         In most applications, the pattern will have been compiled (and  option-
1825         ally studied) in the same process that calls pcre_exec().  However,  it         ally  studied)  in the same process that calls pcre_exec(). However, it
1826         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
1827         later in different processes, possibly even on different hosts.  For  a         later  in  different processes, possibly even on different hosts. For a
1828         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1829    
1830         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1640  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1843  MATCHING A PATTERN: THE TRADITIONAL FUNC
1843    
1844     Extra data for pcre_exec()     Extra data for pcre_exec()
1845    
1846         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
1847         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
1848         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-
1849         tional information in it. The pcre_extra block contains  the  following         tional  information  in it. The pcre_extra block contains the following
1850         fields (not necessarily in this order):         fields (not necessarily in this order):
1851    
1852           unsigned long int flags;           unsigned long int flags;
# Line 1653  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1856  MATCHING A PATTERN: THE TRADITIONAL FUNC
1856           void *callout_data;           void *callout_data;
1857           const unsigned char *tables;           const unsigned char *tables;
1858    
1859         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
1860         are set. The flag bits are:         are set. The flag bits are:
1861    
1862           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1662  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1865  MATCHING A PATTERN: THE TRADITIONAL FUNC
1865           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1866           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1867    
1868         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
1869         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1870         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
1871         add  to  the  block by setting the other fields and their corresponding         add to the block by setting the other fields  and  their  corresponding
1872         flag bits.         flag bits.
1873    
1874         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
1875         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
1876         match, but which have a very large number  of  possibilities  in  their         match,  but  which  have  a very large number of possibilities in their
1877         search  trees.  The  classic  example  is  the  use of nested unlimited         search trees. The classic  example  is  the  use  of  nested  unlimited
1878         repeats.         repeats.
1879    
1880         Internally, PCRE uses a function called match() which it calls  repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1881         edly  (sometimes  recursively). The limit set by match_limit is imposed         edly (sometimes recursively). The limit set by match_limit  is  imposed
1882         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
1883         has  the  effect  of  limiting the amount of backtracking that can take         has the effect of limiting the amount of  backtracking  that  can  take
1884         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1885         for each position in the subject string.         for each position in the subject string.
1886    
1887         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
1888         default default is 10 million, which handles all but the  most  extreme         default  default  is 10 million, which handles all but the most extreme
1889         cases.  You  can  override  the  default by suppling pcre_exec() with a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1890         pcre_extra    block    in    which    match_limit    is    set,     and         pcre_extra     block    in    which    match_limit    is    set,    and
1891         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
1892         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1893    
1894         The match_limit_recursion field is similar to match_limit, but  instead         The  match_limit_recursion field is similar to match_limit, but instead
1895         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
1896         the depth of recursion. The recursion depth is a  smaller  number  than         the  depth  of  recursion. The recursion depth is a smaller number than
1897         the  total number of calls, because not all calls to match() are recur-         the total number of calls, because not all calls to match() are  recur-
1898         sive.  This limit is of use only if it is set smaller than match_limit.         sive.  This limit is of use only if it is set smaller than match_limit.
1899    
1900         Limiting  the  recursion  depth  limits the amount of stack that can be         Limiting  the  recursion  depth  limits the amount of stack that can be
# Line 1723  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1926  MATCHING A PATTERN: THE TRADITIONAL FUNC
1926    
1927         The unused bits of the options argument for pcre_exec() must  be  zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
1928         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1929         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,    PCRE_NO_START_OPTIMIZE,
1930         PCRE_PARTIAL.         PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
1931    
1932           PCRE_ANCHORED           PCRE_ANCHORED
1933    
# Line 1733  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1936  MATCHING A PATTERN: THE TRADITIONAL FUNC
1936         turned  out to be anchored by virtue of its contents, it cannot be made         turned  out to be anchored by virtue of its contents, it cannot be made
1937         unachored at matching time.         unachored at matching time.
1938    
1939             PCRE_BSR_ANYCRLF
1940             PCRE_BSR_UNICODE
1941    
1942           These options (which are mutually exclusive) control what the \R escape
1943           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1944           or to match any Unicode newline sequence. These  options  override  the
1945           choice that was made or defaulted when the pattern was compiled.
1946    
1947           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1948           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1949           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1950           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1951           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1952    
1953         These options override  the  newline  definition  that  was  chosen  or         These  options  override  the  newline  definition  that  was chosen or
1954         defaulted  when the pattern was compiled. For details, see the descrip-         defaulted when the pattern was compiled. For details, see the  descrip-
1955         tion of pcre_compile()  above.  During  matching,  the  newline  choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1956         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1957         ters. It may also alter the way the match position is advanced after  a         ters.  It may also alter the way the match position is advanced after a
1958         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
1959         PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt  
1960         fails  when the current position is at a CRLF sequence, the match posi-         When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1961         tion is advanced by two characters instead of one, in other  words,  to         set,  and a match attempt for an unanchored pattern fails when the cur-
1962         after the CRLF.         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1963           explicit  matches  for  CR  or  LF  characters,  the  match position is
1964           advanced by two characters instead of one, in other words, to after the
1965           CRLF.
1966    
1967           The above rule is a compromise that makes the most common cases work as
1968           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1969           option is not set), it does not match the string "\r\nA" because, after
1970           failing at the start, it skips both the CR and the LF before  retrying.
1971           However,  the  pattern  [\r\n]A does match that string, because it con-
1972           tains an explicit CR or LF reference, and so advances only by one char-
1973           acter after the first failure.
1974    
1975           An explicit match for CR of LF is either a literal appearance of one of
1976           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1977           matches  such  as [^X] do not count, nor does \s (which includes CR and
1978           LF in the characters that it matches).
1979    
1980           Notwithstanding the above, anomalous effects may still occur when  CRLF
1981           is a valid newline sequence and explicit \r or \n escapes appear in the
1982           pattern.
1983    
1984           PCRE_NOTBOL           PCRE_NOTBOL
1985    
1986         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1987         the beginning of a line, so the  circumflex  metacharacter  should  not         the  beginning  of  a  line, so the circumflex metacharacter should not
1988         match  before it. Setting this without PCRE_MULTILINE (at compile time)         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1989         causes circumflex never to match. This option affects only  the  behav-         causes  circumflex  never to match. This option affects only the behav-
1990         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1991    
1992           PCRE_NOTEOL           PCRE_NOTEOL
1993    
1994         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
1995         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
1996         in  multiline mode) a newline immediately before it. Setting this with-         in multiline mode) a newline immediately before it. Setting this  with-
1997         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1998         option  affects only the behaviour of the dollar metacharacter. It does         option affects only the behaviour of the dollar metacharacter. It  does
1999         not affect \Z or \z.         not affect \Z or \z.
2000    
2001           PCRE_NOTEMPTY           PCRE_NOTEMPTY
2002    
2003         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
2004         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
2005         the alternatives match the empty string, the entire  match  fails.  For         the  alternatives  match  the empty string, the entire match fails. For
2006         example, if the pattern         example, if the pattern
2007    
2008           a?b?           a?b?
2009    
2010         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  the
2011         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
2012         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-
2013         rences of "a" or "b".         rences of "a" or "b".
2014    
2015         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
2016         cial  case  of  a  pattern match of the empty string within its split()         cial case of a pattern match of the empty  string  within  its  split()
2017         function, and when using the /g modifier. It  is  possible  to  emulate         function,  and  when  using  the /g modifier. It is possible to emulate
2018         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
2019         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
2020         if  that  fails by advancing the starting offset (see below) and trying         if that fails by advancing the starting offset (see below)  and  trying
2021         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
2022         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
2023    
2024             PCRE_NO_START_OPTIMIZE
2025    
2026           There are a number of optimizations that pcre_exec() uses at the  start
2027           of  a  match,  in  order to speed up the process. For example, if it is
2028           known that a match must start with a specific  character,  it  searches
2029           the subject for that character, and fails immediately if it cannot find
2030           it, without actually running the main matching function. When  callouts
2031           are  in  use,  these  optimizations  can cause them to be skipped. This
2032           option disables the "start-up" optimizations,  causing  performance  to
2033           suffer, but ensuring that the callouts do occur.
2034    
2035           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
2036    
2037         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
2038         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
2039         called.   The  value  of  startoffset is also checked to ensure that it         called.   The  value  of  startoffset is also checked to ensure that it
2040         points to the start of a UTF-8 character. If an invalid UTF-8  sequence         points to the start of a UTF-8 character. There is a  discussion  about
2041         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the  validity  of  UTF-8 strings in the section on UTF-8 support in the
2042         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
2043         returned.         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
2044           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2045         If  you  already  know that your subject is valid, and you want to skip  
2046         these   checks   for   performance   reasons,   you   can    set    the         If you already know that your subject is valid, and you  want  to  skip
2047         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         these    checks    for   performance   reasons,   you   can   set   the
2048         do this for the second and subsequent calls to pcre_exec() if  you  are         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
2049         making  repeated  calls  to  find  all  the matches in a single subject         do  this  for the second and subsequent calls to pcre_exec() if you are
2050         string. However, you should be  sure  that  the  value  of  startoffset         making repeated calls to find all  the  matches  in  a  single  subject
2051         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is         string.  However,  you  should  be  sure  that the value of startoffset
2052         set, the effect of passing an invalid UTF-8 string as a subject,  or  a         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
2053         value  of startoffset that does not point to the start of a UTF-8 char-         set,  the  effect of passing an invalid UTF-8 string as a subject, or a
2054           value of startoffset that does not point to the start of a UTF-8  char-
2055         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
2056    
2057           PCRE_PARTIAL           PCRE_PARTIAL
2058    
2059         This option turns on the  partial  matching  feature.  If  the  subject         This  option  turns  on  the  partial  matching feature. If the subject
2060         string  fails to match the pattern, but at some point during the match-         string fails to match the pattern, but at some point during the  match-
2061         ing process the end of the subject was reached (that  is,  the  subject         ing  process  the  end of the subject was reached (that is, the subject
2062         partially  matches  the  pattern and the failure to match occurred only         partially matches the pattern and the failure to  match  occurred  only
2063         because there were not enough subject characters), pcre_exec()  returns         because  there were not enough subject characters), pcre_exec() returns
2064         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
2065         used, there are restrictions on what may appear in the  pattern.  These         used,  there  are restrictions on what may appear in the pattern. These
2066         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
2067    
2068     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
2069    
2070         The  subject string is passed to pcre_exec() as a pointer in subject, a         The subject string is passed to pcre_exec() as a pointer in subject,  a
2071         length in length, and a starting byte offset in startoffset.  In  UTF-8         length (in bytes) in length, and a starting byte offset in startoffset.
2072         mode,  the  byte  offset  must point to the start of a UTF-8 character.         In UTF-8 mode, the byte offset must point to the start of a UTF-8 char-
2073         Unlike the pattern string, the subject may contain binary  zero  bytes.         acter.  Unlike  the pattern string, the subject may contain binary zero
2074         When  the starting offset is zero, the search for a match starts at the         bytes. When the starting offset is zero, the search for a match  starts
2075         beginning of the subject, and this is by far the most common case.         at  the  beginning  of  the subject, and this is by far the most common
2076           case.
2077    
2078         A non-zero starting offset is useful when searching for  another  match         A non-zero starting offset is useful when searching for  another  match
2079         in  the same subject by calling pcre_exec() again after a previous suc-         in  the same subject by calling pcre_exec() again after a previous suc-
# Line 1865  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2109  MATCHING A PATTERN: THE TRADITIONAL FUNC
2109         string.  PCRE  supports several other kinds of parenthesized subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2110         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2111    
2112         Captured substrings are returned to the caller via a vector of  integer         Captured substrings are returned to the caller via a vector of integers
2113         offsets  whose  address is passed in ovector. The number of elements in         whose  address is passed in ovector. The number of elements in the vec-
2114         the vector is passed in ovecsize, which must be a non-negative  number.         tor is passed in ovecsize, which must be a non-negative  number.  Note:
2115         Note: this argument is NOT the size of ovector in bytes.         this argument is NOT the size of ovector in bytes.
2116    
2117         The  first  two-thirds of the vector is used to pass back captured sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2118         strings, each substring using a pair of integers. The  remaining  third         strings, each substring using a pair of integers. The  remaining  third
2119         of  the  vector is used as workspace by pcre_exec() while matching cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2120         turing subpatterns, and is not available for passing back  information.         turing subpatterns, and is not available for passing back  information.
2121         The  length passed in ovecsize should always be a multiple of three. If         The  number passed in ovecsize should always be a multiple of three. If
2122         it is not, it is rounded down.         it is not, it is rounded down.
2123    
2124         When a match is successful, information about  captured  substrings  is         When a match is successful, information about  captured  substrings  is
2125         returned  in  pairs  of integers, starting at the beginning of ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2126         and continuing up to two-thirds of its length at the  most.  The  first         and continuing up to two-thirds of its length at the  most.  The  first
2127         element of a pair is set to the offset of the first character in a sub-         element  of  each pair is set to the byte offset of the first character
2128         string, and the second is set to the  offset  of  the  first  character         in a substring, and the second is set to the byte offset of  the  first
2129         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-         character  after  the end of a substring. Note: these values are always
2130         tor[1], identify the portion of  the  subject  string  matched  by  the         byte offsets, even in UTF-8 mode. They are not character counts.
2131         entire  pattern.  The next pair is used for the first capturing subpat-  
2132         tern, and so on. The value returned by pcre_exec() is one more than the         The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2133         highest numbered pair that has been set. For example, if two substrings         portion  of  the subject string matched by the entire pattern. The next
2134         have been captured, the returned value is 3. If there are no  capturing         pair is used for the first capturing subpattern, and so on.  The  value
2135         subpatterns,  the return value from a successful match is 1, indicating         returned by pcre_exec() is one more than the highest numbered pair that
2136         that just the first pair of offsets has been set.         has been set.  For example, if two substrings have been  captured,  the
2137           returned  value is 3. If there are no capturing subpatterns, the return
2138           value from a successful match is 1, indicating that just the first pair
2139           of offsets has been set.
2140    
2141         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2142         of the string that it matched that is returned.         of the string that it matched that is returned.
2143    
2144         If  the vector is too small to hold all the captured substring offsets,         If the vector is too small to hold all the captured substring  offsets,
2145         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2146         function  returns a value of zero. In particular, if the substring off-         function returns a value of zero. If the substring offsets are  not  of
2147         sets are not of interest, pcre_exec() may be called with ovector passed         interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2148         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         ovecsize as zero. However, if the pattern contains back references  and
2149         references and the ovector is not big enough to  remember  the  related         the  ovector is not big enough to remember the related substrings, PCRE
2150         substrings,  PCRE has to get additional memory for use during matching.         has to get additional memory for use during matching. Thus it  is  usu-
2151         Thus it is usually advisable to supply an ovector.         ally advisable to supply an ovector.
2152    
2153         The pcre_info() function can be used to find  out  how  many  capturing         The  pcre_info()  function  can  be used to find out how many capturing
2154         subpatterns  there  are  in  a  compiled pattern. The smallest size for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2155         ovector that will allow for n captured substrings, in addition  to  the         ovector  that  will allow for n captured substrings, in addition to the
2156         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.
2157    
2158         It  is  possible for capturing subpattern number n+1 to match some part         It is possible for capturing subpattern number n+1 to match  some  part
2159         of the subject when subpattern n has not been used at all. For example,         of the subject when subpattern n has not been used at all. For example,
2160         if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the         if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2161         return from the function is 4, and subpatterns 1 and 3 are matched, but         return from the function is 4, and subpatterns 1 and 3 are matched, but
2162         2  is  not.  When  this happens, both values in the offset pairs corre-         2 is not. When this happens, both values in  the  offset  pairs  corre-
2163         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2164    
2165         Offset values that correspond to unused subpatterns at the end  of  the         Offset  values  that correspond to unused subpatterns at the end of the
2166         expression  are  also  set  to  -1. For example, if the string "abc" is         expression are also set to -1. For example,  if  the  string  "abc"  is
2167         matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not         matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2168         matched.  The  return  from the function is 2, because the highest used         matched. The return from the function is 2, because  the  highest  used
2169         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2170         for  the  second  and third capturing subpatterns if you wish (assuming         for the second and third capturing subpatterns if  you  wish  (assuming
2171         the vector is large enough, of course).         the vector is large enough, of course).
2172    
2173         Some convenience functions are provided  for  extracting  the  captured         Some  convenience  functions  are  provided for extracting the captured
2174         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2175    
2176     Error return values from pcre_exec()     Error return values from pcre_exec()
2177    
2178         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
2179         defined in the header file:         defined in the header file:
2180    
2181           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1937  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2184  MATCHING A PATTERN: THE TRADITIONAL FUNC
2184    
2185           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2186    
2187         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2188         ovecsize was not zero.         ovecsize was not zero.
2189    
2190           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1946  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2193  MATCHING A PATTERN: THE TRADITIONAL FUNC
2193    
2194           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2195    
2196         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2197         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
2198         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
2199         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2200         gives when the magic number is not present.         gives when the magic number is not present.
2201    
2202           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2203    
2204         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2205         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2206         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2207    
2208           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2209    
2210         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2211         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2212         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
2213         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2214         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2215    
2216           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2217    
2218         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2219         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2220         returned by pcre_exec().         returned by pcre_exec().
2221    
2222           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2223    
2224         The  backtracking  limit,  as  specified  by the match_limit field in a         The backtracking limit, as specified by  the  match_limit  field  in  a
2225         pcre_extra structure (or defaulted) was reached.  See  the  description         pcre_extra  structure  (or  defaulted) was reached. See the description
2226         above.         above.
2227    
2228           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2229    
2230         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
2231         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2232         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2233    
2234           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2235    
2236         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
2237         subject.         subject.
2238    
2239           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2240    
2241         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2242         value  of startoffset did not point to the beginning of a UTF-8 charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2243         ter.         ter.
2244    
2245           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2246    
2247         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
2248         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2249    
2250           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2251    
2252         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2253         items that are not supported for partial matching. See the  pcrepartial         items  that are not supported for partial matching. See the pcrepartial
2254         documentation for details of partial matching.         documentation for details of partial matching.
2255    
2256           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2257    
2258         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
2259         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2260    
2261           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2262    
2263         This error is given if the value of the ovecsize argument is  negative.         This error is given if the value of the ovecsize argument is negative.
2264    
2265           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2266    
# Line 2021  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2268  MATCHING A PATTERN: THE TRADITIONAL FUNC
2268         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2269         description above.         description above.
2270    
          PCRE_ERROR_NULLWSLIMIT    (-22)  
   
        When  a  group  that  can  match an empty substring is repeated with an  
        unbounded upper limit, the subject position at the start of  the  group  
        must be remembered, so that a test for an empty string can be made when  
        the end of the group is reached. Some workspace is required  for  this;  
        if it runs out, this error is given.  
   
2271           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2272    
2273         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2274    
2275         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2276    
2277    
2278  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2171  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2410  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2410         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2411         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2412    
2413           Warning:  If the pattern uses the "(?|" feature to set up multiple sub-
2414           patterns with the same number, you  cannot  use  names  to  distinguish
2415           them, because names are not included in the compiled code. The matching
2416           process uses only numbers.
2417    
2418    
2419  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
2420    
2421         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2422              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2423    
2424         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2425         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns  are  not  required  to  be unique. Normally, patterns with
2426         duplicate  names  are such that in any one match, only one of the named         duplicate names are such that in any one match, only one of  the  named
2427         subpatterns participates. An example is shown in the pcrepattern  docu-         subpatterns  participates. An example is shown in the pcrepattern docu-
2428         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2429         pcre_get_named_substring() return the first substring corresponding  to  
2430         the  given  name  that  is  set.  If  none  are set, an empty string is         When   duplicates   are   present,   pcre_copy_named_substring()    and
2431         returned.  The pcre_get_stringnumber() function returns one of the num-         pcre_get_named_substring()  return the first substring corresponding to
2432         bers  that are associated with the name, but it is not defined which it         the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2433         is.         (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2434           function returns one of the numbers that are associated with the  name,
2435           but it is not defined which it is.
2436    
2437         If you want to get full details of all captured substrings for a  given         If  you want to get full details of all captured substrings for a given
2438         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name, you must use  the  pcre_get_stringtable_entries()  function.  The
2439         first argument is the compiled pattern, and the second is the name. The         first argument is the compiled pattern, and the second is the name. The
2440         third  and  fourth  are  pointers to variables which are updated by the         third and fourth are pointers to variables which  are  updated  by  the
2441         function. After it has run, they point to the first and last entries in         function. After it has run, they point to the first and last entries in
2442         the  name-to-number  table  for  the  given  name.  The function itself         the name-to-number table  for  the  given  name.  The  function  itself
2443         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2444         there  are none. The format of the table is described above in the sec-         there are none. The format of the table is described above in the  sec-
2445         tion entitled Information about a  pattern.   Given  all  the  relevant         tion  entitled  Information  about  a  pattern.  Given all the relevant
2446         entries  for the name, you can extract each of their numbers, and hence         entries for the name, you can extract each of their numbers, and  hence
2447         the captured data, if any.         the captured data, if any.
2448    
2449    
2450  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2451    
2452         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2453         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2454         the subject. If you want to find all possible matches, or  the  longest         the  subject.  If you want to find all possible matches, or the longest
2455         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2456         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2457         need  to  find all possible matches, you can kludge it up by making use         need to find all possible matches, you can kludge it up by  making  use
2458         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2459         tation.         tation.
2460    
2461         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2462         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2463         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2464         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2465         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2466    
2467    
# Line 2226  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2472  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2472              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2473              int *workspace, int wscount);              int *workspace, int wscount);
2474    
2475         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2476         against a compiled pattern, using a matching algorithm that  scans  the         against  a  compiled pattern, using a matching algorithm that scans the
2477         subject  string  just  once, and does not backtrack. This has different         subject string just once, and does not backtrack.  This  has  different
2478         characteristics to the normal algorithm, and  is  not  compatible  with         characteristics  to  the  normal  algorithm, and is not compatible with
2479         Perl.  Some  of the features of PCRE patterns are not supported. Never-         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2480         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
2481         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, see the pcrematching docu-
2482         mentation.         mentation.
2483    
2484         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
2485         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-
2486         ent way, and this is described below. The other  common  arguments  are         ent  way,  and  this is described below. The other common arguments are
2487         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
2488         repeated here.         repeated here.
2489    
2490         The two additional arguments provide workspace for  the  function.  The         The  two  additional  arguments provide workspace for the function. The
2491         workspace  vector  should  contain at least 20 elements. It is used for         workspace vector should contain at least 20 elements. It  is  used  for
2492         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2493         workspace  will  be  needed for patterns and subjects where there are a         workspace will be needed for patterns and subjects where  there  are  a
2494         lot of potential matches.         lot of potential matches.
2495    
2496         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 2266  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2512  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2512    
2513     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2514    
2515         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
2516         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-
2517         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2518         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2519         three of these are the same as for pcre_exec(), so their description is         three of these are the same as for pcre_exec(), so their description is
2520         not repeated here.         not repeated here.
2521    
2522           PCRE_PARTIAL           PCRE_PARTIAL
2523    
2524         This  has  the  same general effect as it does for pcre_exec(), but the         This has the same general effect as it does for  pcre_exec(),  but  the
2525         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2526         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2527         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2528         been no complete matches, but there is still at least one matching pos-         been no complete matches, but there is still at least one matching pos-
2529         sibility. The portion of the string that provided the partial match  is         sibility.  The portion of the string that provided the partial match is
2530         set as the first matching string.         set as the first matching string.
2531    
2532           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2533    
2534         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2535         stop as soon as it has found one match. Because of the way the alterna-         stop as soon as it has found one match. Because of the way the alterna-
2536         tive  algorithm  works, this is necessarily the shortest possible match         tive algorithm works, this is necessarily the shortest  possible  match
2537         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2538    
2539           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2540    
2541         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2542         returns  a  partial  match, it is possible to call it again, with addi-         returns a partial match, it is possible to call it  again,  with  addi-
2543         tional subject characters, and have it continue with  the  same  match.         tional  subject  characters,  and have it continue with the same match.
2544         The  PCRE_DFA_RESTART  option requests this action; when it is set, the         The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2545         workspace and wscount options must reference the same vector as  before         workspace  and wscount options must reference the same vector as before
2546         because  data  about  the  match so far is left in them after a partial         because data about the match so far is left in  them  after  a  partial
2547         match. There is more discussion of this  facility  in  the  pcrepartial         match.  There  is  more  discussion of this facility in the pcrepartial
2548         documentation.         documentation.
2549    
2550     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2551    
2552         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-
2553         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
2554         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
2555         matches are all initial substrings of the longer matches. For  example,         matches  are all initial substrings of the longer matches. For example,
2556         if the pattern         if the pattern
2557    
2558           <.*>           <.*>
# Line 2321  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2567  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2567           <something> <something else>           <something> <something else>
2568           <something> <something else> <something further>           <something> <something else> <something further>
2569    
2570         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,
2571         which is the number of matched substrings.  The  substrings  themselves         which  is  the  number of matched substrings. The substrings themselves
2572         are  returned  in  ovector. Each string uses two elements; the first is         are returned in ovector. Each string uses two elements;  the  first  is
2573         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
2574         fact,  all  the  strings  have the same start offset. (Space could have         fact, all the strings have the same start  offset.  (Space  could  have
2575         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
2576         compatibility  with  the  way pcre_exec() returns data, even though the         compatibility with the way pcre_exec() returns data,  even  though  the
2577         meaning of the strings is different.)         meaning of the strings is different.)
2578    
2579         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-
2580         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
2581         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
2582         filled with the longest matches.         filled with the longest matches.
2583    
2584     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2585    
2586         The  pcre_dfa_exec()  function returns a negative number when it fails.         The pcre_dfa_exec() function returns a negative number when  it  fails.
2587         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
2588         described  above.   There are in addition the following errors that are         described above.  There are in addition the following errors  that  are
2589         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2590    
2591           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2592    
2593         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-
2594         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
2595         reference.         reference.
2596    
2597           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2598    
2599         This return is given if pcre_dfa_exec()  encounters  a  condition  item         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2600         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
2601         in a specific group. These are not supported.         in a specific group. These are not supported.
2602    
2603           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2604    
2605         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
2606         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
2607         (it is meaningless).         (it is meaningless).
2608    
2609           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2610    
2611         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
2612         workspace vector.         workspace vector.
2613    
2614           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2615    
2616         When  a  recursive subpattern is processed, the matching function calls         When a recursive subpattern is processed, the matching  function  calls
2617         itself recursively, using private vectors for  ovector  and  workspace.         itself  recursively,  using  private vectors for ovector and workspace.
2618         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
2619         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2620    
2621    
2622  SEE ALSO  SEE ALSO
2623    
2624         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2625         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2626    
2627    
2628  AUTHOR  AUTHOR
# Line 2388  AUTHOR Line 2634  AUTHOR
2634    
2635  REVISION  REVISION
2636    
2637         Last updated: 24 April 2007         Last updated: 17 March 2009
2638         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2639  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2640    
2641    
# Line 2440  PCRE CALLOUTS Line 2686  PCRE CALLOUTS
2686  MISSING CALLOUTS  MISSING CALLOUTS
2687    
2688         You  should  be  aware  that,  because of optimizations in the way PCRE         You  should  be  aware  that,  because of optimizations in the way PCRE
2689         matches patterns, callouts sometimes do not happen. For example, if the         matches patterns by default, callouts  sometimes  do  not  happen.  For
2690         pattern is         example, if the pattern is
2691    
2692           ab(?C4)cd           ab(?C4)cd
2693    
# Line 2450  MISSING CALLOUTS Line 2696  MISSING CALLOUTS
2696         ever  start,  and  the  callout is never reached. However, with "abyd",         ever  start,  and  the  callout is never reached. However, with "abyd",
2697         though the result is still no match, the callout is obeyed.         though the result is still no match, the callout is obeyed.
2698    
2699           You can disable these optimizations by passing the  PCRE_NO_START_OPTI-
2700           MIZE  option  to  pcre_exec()  or  pcre_dfa_exec(). This slows down the
2701           matching process, but does ensure that callouts  such  as  the  example
2702           above are obeyed.
2703    
2704    
2705  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2706    
2707         During matching, when PCRE reaches a callout point, the external  func-         During  matching, when PCRE reaches a callout point, the external func-
2708         tion  defined by pcre_callout is called (if it is set). This applies to         tion defined by pcre_callout is called (if it is set). This applies  to
2709         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The         both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
2710         only  argument  to  the callout function is a pointer to a pcre_callout         only argument to the callout function is a pointer  to  a  pcre_callout
2711         block. This structure contains the following fields:         block. This structure contains the following fields:
2712    
2713           int          version;           int          version;
# Line 2472  THE CALLOUT INTERFACE Line 2723  THE CALLOUT INTERFACE
2723           int          pattern_position;           int          pattern_position;
2724           int          next_item_length;           int          next_item_length;
2725    
2726         The version field is an integer containing the version  number  of  the         The  version  field  is an integer containing the version number of the
2727         block  format. The initial version was 0; the current version is 1. The         block format. The initial version was 0; the current version is 1.  The
2728         version number will change again in future  if  additional  fields  are         version  number  will  change  again in future if additional fields are
2729         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2730    
2731         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
# Line 2491  THE CALLOUT INTERFACE Line 2742  THE CALLOUT INTERFACE
2742         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2743         were passed to pcre_exec().         were passed to pcre_exec().
2744    
2745         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2746         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2747         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
2748         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2749           function may be called several times from the same point in the pattern
2750           for different starting points in the subject.
2751    
2752         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2753         the current match pointer.         the current match pointer.
# Line 2557  AUTHOR Line 2810  AUTHOR
2810    
2811  REVISION  REVISION
2812    
2813         Last updated: 06 March 2007         Last updated: 15 March 2009
2814         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2009 University of Cambridge.
2815  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2816    
2817    
# Line 2573  DIFFERENCES BETWEEN PCRE AND PERL Line 2826  DIFFERENCES BETWEEN PCRE AND PERL
2826    
2827         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2828         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2829         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2830         tures that are expected to be in the forthcoming Perl 5.10.         some features that are expected to be in the forthcoming Perl 5.10.
2831    
2832         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
2833         of  what  it does have are given in the section on UTF-8 support in the         of  what  it does have are given in the section on UTF-8 support in the
# Line 2639  DIFFERENCES BETWEEN PCRE AND PERL Line 2892  DIFFERENCES BETWEEN PCRE AND PERL
2892         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2893         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2894    
2895         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2896           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2897           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2898           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2899           ture group; this is different to Perl.
2900    
2901           12. PCRE provides some extensions to the Perl regular expression facil-
2902         ities.   Perl  5.10  will  include new features that are not in earlier         ities.   Perl  5.10  will  include new features that are not in earlier
2903         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2904         for some time. This list is with respect to Perl 5.10:         for some time. This list is with respect to Perl 5.10:
# Line 2652  DIFFERENCES BETWEEN PCRE AND PERL Line 2911  DIFFERENCES BETWEEN PCRE AND PERL
2911         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2912    
2913         (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-
2914         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2915         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2916    
2917         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2918         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-
# Line 2665  DIFFERENCES BETWEEN PCRE AND PERL Line 2924  DIFFERENCES BETWEEN PCRE AND PERL
2924         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2925         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2926    
2927         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2928           CRLF by the PCRE_BSR_ANYCRLF option.
2929    
2930           (h) The callout facility is PCRE-specific.
2931    
2932         (h) The partial matching facility is PCRE-specific.         (i) The partial matching facility is PCRE-specific.
2933    
2934         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2935         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2936    
2937         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2938         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2939    
2940           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2941           of a pattern that set overall options that cannot be changed within the
2942           pattern.
2943    
2944    
2945  AUTHOR  AUTHOR
2946    
# Line 2685  AUTHOR Line 2951  AUTHOR
2951    
2952  REVISION  REVISION
2953    
2954         Last updated: 06 March 2007         Last updated: 11 September 2007
2955         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2956  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2957    
# Line 2699  NAME Line 2965  NAME
2965    
2966  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2967    
2968         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2969         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2970         documentation  and  in  a  number  of books, some of which have copious         tax summary in the pcresyntax page. PCRE tries to match Perl syntax and
2971         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         semantics as closely as it can. PCRE  also  supports  some  alternative
2972         by  O'Reilly, covers regular expressions in great detail. This descrip-         regular  expression  syntax (which does not conflict with the Perl syn-
2973         tion of PCRE's regular expressions is intended as reference material.         tax) in order to provide some compatibility with regular expressions in
2974           Python, .NET, and Oniguruma.
2975    
2976           Perl's  regular expressions are described in its own documentation, and
2977           regular expressions in general are covered in a number of  books,  some
2978           of  which  have  copious  examples. Jeffrey Friedl's "Mastering Regular
2979           Expressions", published by  O'Reilly,  covers  regular  expressions  in
2980           great  detail.  This  description  of  PCRE's  regular  expressions  is
2981           intended as reference material.
2982    
2983         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2984         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
# Line 2718  PCRE REGULAR EXPRESSION DETAILS Line 2992  PCRE REGULAR EXPRESSION DETAILS
2992         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2993         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2994         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2995         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2996         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2997         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2998           discussed in the pcrematching page.
2999    
3000    
3001    NEWLINE CONVENTIONS
3002    
3003           PCRE  supports five different conventions for indicating line breaks in
3004           strings: a single CR (carriage return) character, a  single  LF  (line-
3005           feed) character, the two-character sequence CRLF, any of the three pre-
3006           ceding, or any Unicode newline sequence. The pcreapi page  has  further
3007           discussion  about newlines, and shows how to set the newline convention
3008           in the options arguments for the compiling and matching functions.
3009    
3010           It is also possible to specify a newline convention by starting a  pat-
3011           tern string with one of the following five sequences:
3012    
3013             (*CR)        carriage return
3014             (*LF)        linefeed
3015             (*CRLF)      carriage return, followed by linefeed
3016             (*ANYCRLF)   any of the three above
3017             (*ANY)       all Unicode newline sequences
3018    
3019           These override the default and the options given to pcre_compile(). For
3020           example, on a Unix system where LF is the default newline sequence, the
3021           pattern
3022    
3023             (*CR)a.b
3024    
3025           changes the convention to CR. That pattern matches "a\nb" because LF is
3026           no longer a newline. Note that these special settings,  which  are  not
3027           Perl-compatible,  are  recognized  only at the very start of a pattern,
3028           and that they must be in upper case.  If  more  than  one  of  them  is
3029           present, the last one is used.
3030    
3031           The  newline  convention  does  not  affect what the \R escape sequence
3032           matches. By default, this is any Unicode  newline  sequence,  for  Perl
3033           compatibility.  However, this can be changed; see the description of \R
3034           in the section entitled "Newline sequences" below. A change of \R  set-
3035           ting can be combined with a change of newline convention.
3036    
3037    
3038  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
3039    
3040         A regular expression is a pattern that is  matched  against  a  subject         A  regular  expression  is  a pattern that is matched against a subject
3041         string  from  left  to right. Most characters stand for themselves in a         string from left to right. Most characters stand for  themselves  in  a
3042         pattern, and match the corresponding characters in the  subject.  As  a         pattern,  and  match  the corresponding characters in the subject. As a
3043         trivial example, the pattern         trivial example, the pattern
3044    
3045           The quick brown fox           The quick brown fox
3046    
3047         matches a portion of a subject string that is identical to itself. When         matches a portion of a subject string that is identical to itself. When
3048         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
3049         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
3050         the concept of case for characters whose values are less than  128,  so         the  concept  of case for characters whose values are less than 128, so
3051         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
3052         ues, the concept of case is supported if PCRE is compiled with  Unicode         ues,  the concept of case is supported if PCRE is compiled with Unicode
3053         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
3054         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
3055         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
3056    
3057         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
3058         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
3059         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
3060         but instead are interpreted in some special way.         but instead are interpreted in some special way.
3061    
3062         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
3063         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
3064         that are recognized within square brackets.  Outside  square  brackets,         that  are  recognized  within square brackets. Outside square brackets,
3065         the metacharacters are as follows:         the metacharacters are as follows:
3066    
3067           \      general escape character with several uses           \      general escape character with several uses
# Line 2768  CHARACTERS AND METACHARACTERS Line 3080  CHARACTERS AND METACHARACTERS
3080                  also "possessive quantifier"                  also "possessive quantifier"
3081           {      start min/max quantifier           {      start min/max quantifier
3082    
3083         Part  of  a  pattern  that is in square brackets is called a "character         Part of a pattern that is in square brackets  is  called  a  "character
3084         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
3085    
3086           \      general escape character           \      general escape character
# Line 2778  CHARACTERS AND METACHARACTERS Line 3090  CHARACTERS AND METACHARACTERS
3090                    syntax)                    syntax)
3091           ]      terminates the character class           ]      terminates the character class
3092    
3093         The following sections describe the use of each of the  metacharacters.         The following sections describe the use of each of the metacharacters.
3094    
3095    
3096  BACKSLASH  BACKSLASH
# Line 2830  BACKSLASH Line 3142  BACKSLASH
3142           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3143           \e        escape (hex 1B)           \e        escape (hex 1B)
3144           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3145           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3146           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3147           \t        tab (hex 09)           \t        tab (hex 09)
3148           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
# Line 2845  BACKSLASH Line 3157  BACKSLASH
3157         After \x, from zero to two hexadecimal digits are read (letters can  be         After \x, from zero to two hexadecimal digits are read (letters can  be
3158         in  upper  or  lower case). Any number of hexadecimal digits may appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3159         between \x{ and }, but the value of the character  code  must  be  less         between \x{ and }, but the value of the character  code  must  be  less
3160         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3161         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3162         hexadecimal  digits  appear between \x{ and }, or if there is no termi-         than the largest Unicode code point, which is 10FFFF.
3163         nating }, this form of escape is not recognized.  Instead, the  initial  
3164         \x will be interpreted as a basic hexadecimal escape, with no following         If  characters  other than hexadecimal digits appear between \x{ and },
3165         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3166           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3167           escape, with no following digits, giving a  character  whose  value  is
3168           zero.
3169    
3170         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
3171         two  syntaxes  for  \x. There is no difference in the way they are han-         two syntaxes for \x. There is no difference in the way  they  are  han-
3172         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3173    
3174         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
3175         than  two  digits,  just  those  that  are  present  are used. Thus the         than two digits, just  those  that  are  present  are  used.  Thus  the
3176         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
3177         (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
3178         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3179    
3180         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-
3181         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3182         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
3183         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3184         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3185         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3186         of parenthesized subpatterns.         of parenthesized subpatterns.
3187    
3188         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
3189         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3190         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-
3191         erate  a data character. Any subsequent digits stand for themselves. In         erate a data character. Any subsequent digits stand for themselves.  In
3192         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
3193         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
3194         example:         example:
3195    
3196           \040   is another way of writing a space           \040   is another way of writing a space
# Line 2893  BACKSLASH Line 3208  BACKSLASH
3208           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3209                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3210    
3211         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
3212         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3213    
3214         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
3215         inside and outside character classes. In addition, inside  a  character         inside  and  outside character classes. In addition, inside a character
3216         class,  the  sequence \b is interpreted as the backspace character (hex         class, the sequence \b is interpreted as the backspace  character  (hex
3217         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"
3218         and  "X", respectively. Outside a character class, these sequences have         and "X", respectively. Outside a character class, these sequences  have
3219         different meanings (see below).         different meanings (see below).
3220    
3221     Absolute and relative back references     Absolute and relative back references
3222    
3223         The sequence \g followed by a positive or negative  number,  optionally         The  sequence  \g followed by an unsigned or a negative number, option-
3224         enclosed  in  braces,  is  an absolute or relative back reference. Back         ally enclosed in braces, is an absolute or relative back  reference.  A
3225         references are discussed later, following the discussion  of  parenthe-         named back reference can be coded as \g{name}. Back references are dis-
3226         sized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3227    
3228       Absolute and relative subroutine calls
3229    
3230           For compatibility with Oniguruma, the non-Perl syntax \g followed by  a
3231           name or a number enclosed either in angle brackets or single quotes, is
3232           an alternative syntax for referencing a subpattern as  a  "subroutine".
3233           Details  are  discussed  later.   Note  that  \g{...} (Perl syntax) and
3234           \g<...> (Oniguruma syntax) are not synonymous. The  former  is  a  back
3235           reference; the latter is a subroutine call.
3236    
3237     Generic character types     Generic character types
3238    
# Line 2917  BACKSLASH Line 3241  BACKSLASH
3241    
3242           \d     any decimal digit           \d     any decimal digit
3243           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3244             \h     any horizontal whitespace character
3245             \H     any character that is not a horizontal whitespace character
3246           \s     any whitespace character           \s     any whitespace character
3247           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3248             \v     any vertical whitespace character
3249             \V     any character that is not a vertical whitespace character
3250           \w     any "word" character           \w     any "word" character
3251           \W     any "non-word" character           \W     any "non-word" character
3252    
# Line 2933  BACKSLASH Line 3261  BACKSLASH
3261    
3262         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3263         11).  This makes it different from the the POSIX "space" class. The  \s         11).  This makes it different from the the POSIX "space" class. The  \s
3264         characters  are  HT (9), LF (10), FF (12), CR (13), and space (32). (If         characters  are  HT  (9), LF (10), FF (12), CR (13), and space (32). If
3265         "use locale;" is included in a Perl script, \s may match the VT charac-         "use locale;" is included in a Perl script, \s may match the VT charac-
3266         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
   
        A "word" character is an underscore or any character less than 256 that  
        is a letter or digit. The definition of  letters  and  digits  is  con-  
        trolled  by PCRE's low-valued character tables, and may vary if locale-  
        specific matching is taking place (see "Locale support" in the  pcreapi  
        page).  For  example,  in  a French locale such as "fr_FR" in Unix-like  
        systems, or "french" in Windows, some character codes greater than  128  
        are used for accented letters, and these are matched by \w.  
3267    
3268         In  UTF-8 mode, characters with values greater than 128 never match \d,         In  UTF-8 mode, characters with values greater than 128 never match \d,
3269         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3270         code  character  property support is available. The use of locales with         code  character  property  support is available. These sequences retain
3271         Unicode is discouraged.         their original meanings from before UTF-8 support was available, mainly
3272           for  efficiency  reasons. Note that this also affects \b, because it is
3273           defined in terms of \w and \W.
3274    
3275           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3276           the  other  sequences, these do match certain high-valued codepoints in
3277           UTF-8 mode.  The horizontal space characters are:
3278    
3279             U+0009     Horizontal tab
3280             U+0020     Space
3281             U+00A0     Non-break space
3282             U+1680     Ogham space mark
3283             U+180E     Mongolian vowel separator
3284             U+2000     En quad
3285             U+2001     Em quad
3286             U+2002     En space
3287             U+2003     Em space
3288             U+2004     Three-per-em space
3289             U+2005     Four-per-em space
3290             U+2006     Six-per-em space
3291             U+2007     Figure space
3292             U+2008     Punctuation space
3293             U+2009     Thin space
3294             U+200A     Hair space
3295             U+202F     Narrow no-break space
3296             U+205F     Medium mathematical space
3297             U+3000     Ideographic space
3298    
3299           The vertical space characters are:
3300    
3301             U+000A     Linefeed
3302             U+000B     Vertical tab
3303             U+000C     Formfeed
3304             U+000D     Carriage return
3305             U+0085     Next line
3306             U+2028     Line separator
3307             U+2029     Paragraph separator
3308    
3309           A "word" character is an underscore or any character less than 256 that
3310           is  a  letter  or  digit.  The definition of letters and digits is con-
3311           trolled by PCRE's low-valued character tables, and may vary if  locale-
3312           specific  matching is taking place (see "Locale support" in the pcreapi
3313           page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
3314           systems,  or "french" in Windows, some character codes greater than 128
3315           are used for accented letters, and these are matched by \w. The use  of
3316           locales with Unicode is discouraged.
3317    
3318     Newline sequences     Newline sequences
3319    
3320         Outside a character class, the escape sequence \R matches  any  Unicode         Outside  a  character class, by default, the escape sequence \R matches
3321         newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3322         equivalent to the following:         mode \R is equivalent to the following:
3323    
3324           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3325    
3326         This is an example of an "atomic group", details  of  which  are  given         This  is  an  example  of an "atomic group", details of which are given
3327         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3328         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3329         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage         U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3330         return, U+000D), or NEL (next line, U+0085). The two-character sequence         return, U+000D), or NEL (next line, U+0085). The two-character sequence
3331         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3332    
3333         In  UTF-8  mode, two additional characters whose codepoints are greater         In UTF-8 mode, two additional characters whose codepoints  are  greater
3334         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-         than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3335         rator,  U+2029).   Unicode character property support is not needed for         rator, U+2029).  Unicode character property support is not  needed  for
3336         these characters to be recognized.         these characters to be recognized.
3337    
3338           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3339           the complete set  of  Unicode  line  endings)  by  setting  the  option
3340           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3341           (BSR is an abbrevation for "backslash R".) This can be made the default
3342           when  PCRE  is  built;  if this is the case, the other behaviour can be
3343           requested via the PCRE_BSR_UNICODE option.   It  is  also  possible  to
3344           specify  these  settings  by  starting a pattern string with one of the
3345           following sequences:
3346    
3347             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3348             (*BSR_UNICODE)   any Unicode newline sequence
3349    
3350           These override the default and the options given to pcre_compile(), but
3351           they can be overridden by options given to pcre_exec(). Note that these
3352           special settings, which are not Perl-compatible, are recognized only at
3353           the  very  start  of a pattern, and that they must be in upper case. If
3354           more than one of them is present, the last one is  used.  They  can  be
3355           combined  with  a  change of newline convention, for example, a pattern
3356           can start with:
3357    
3358             (*ANY)(*BSR_ANYCRLF)
3359    
3360         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3361    
3362     Unicode character properties     Unicode character properties
3363    
3364         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3365         tional  escape  sequences  to  match character properties are available         tional  escape sequences that match characters with specific properties
3366         when UTF-8 mode is selected. They are:         are available.  When not in UTF-8 mode, these sequences are  of  course
3367           limited  to  testing characters whose codepoints are less than 256, but
3368           they do work in this mode.  The extra escape sequences are:
3369    
3370           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3371           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
# Line 3071  BACKSLASH Line 3460  BACKSLASH
3460         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3461         classified as a modifier or "other".         classified as a modifier or "other".
3462    
3463           The  Cs  (Surrogate)  property  applies only to characters in the range
3464           U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3465           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3466           ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3467           the pcreapi page).
3468    
3469         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  these  properties that Perl supports (such as
3470         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix         \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3471         any of these properties with "Is".         any of these properties with "Is".
# Line 3090  BACKSLASH Line 3485  BACKSLASH
3485         That  is,  it matches a character without the "mark" property, followed         That  is,  it matches a character without the "mark" property, followed
3486         by zero or more characters with the "mark"  property,  and  treats  the         by zero or more characters with the "mark"  property,  and  treats  the
3487         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3488         property are typically accents that affect the preceding character.         property are typically accents that  affect  the  preceding  character.
3489           None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X
3490           matches any one character.
3491    
3492         Matching characters by Unicode property is not fast, because  PCRE  has         Matching characters by Unicode property is not fast, because  PCRE  has
3493         to  search  a  structure  that  contains data for over fifteen thousand         to  search  a  structure  that  contains data for over fifteen thousand
3494         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3495         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3496    
3497       Resetting the match start
3498    
3499           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3500           ously matched characters not  to  be  included  in  the  final  matched
3501           sequence. For example, the pattern:
3502    
3503             foo\Kbar
3504    
3505           matches  "foobar",  but reports that it has matched "bar". This feature
3506           is similar to a lookbehind assertion (described  below).   However,  in
3507           this  case, the part of the subject before the real match does not have
3508           to be of fixed length, as lookbehind assertions do. The use of \K  does
3509           not  interfere  with  the setting of captured substrings.  For example,
3510           when the pattern
3511    
3512             (foo)\Kbar
3513    
3514           matches "foobar", the first substring is still set to "foo".
3515    
3516     Simple assertions     Simple assertions
3517    
3518         The  final use of backslash is for certain simple assertions. An asser-         The final use of backslash is for certain simple assertions. An  asser-
3519         tion specifies a condition that has to be met at a particular point  in         tion  specifies a condition that has to be met at a particular point in
3520         a  match, without consuming any characters from the subject string. The         a match, without consuming any characters from the subject string.  The
3521         use of subpatterns for more complicated assertions is described  below.         use  of subpatterns for more complicated assertions is described below.
3522         The backslashed assertions are:         The backslashed assertions are:
3523    
3524           \b     matches at a word boundary           \b     matches at a word boundary
# Line 3113  BACKSLASH Line 3529  BACKSLASH
3529           \z     matches only at the end of the subject           \z     matches only at the end of the subject
3530           \G     matches at the first matching position in the subject           \G     matches at the first matching position in the subject
3531    
3532         These  assertions may not appear in character classes (but note that \b         These assertions may not appear in character classes (but note that  \b
3533         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3534         acter class).         acter class).
3535    
3536         A  word  boundary is a position in the subject string where the current         A word boundary is a position in the subject string where  the  current
3537         character and the previous character do not both match \w or  \W  (i.e.         character  and  the previous character do not both match \w or \W (i.e.
3538         one  matches  \w  and the other matches \W), or the start or end of the         one matches \w and the other matches \W), or the start or  end  of  the
3539         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3540    
3541         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3542         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3543         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3544         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3545         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3546         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3547         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3548         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3549         the subject, \A can never match. The difference between \Z  and  \z  is         the  subject,  \A  can never match. The difference between \Z and \z is
3550         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3551         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3552    
3553         The \G assertion is true only when the current matching position is  at         The  \G assertion is true only when the current matching position is at
3554         the  start point of the match, as specified by the startoffset argument         the start point of the match, as specified by the startoffset  argument
3555         of pcre_exec(). It differs from \A when the  value  of  startoffset  is         of  pcre_exec().  It  differs  from \A when the value of startoffset is
3556         non-zero.  By calling pcre_exec() multiple times with appropriate argu-         non-zero. By calling pcre_exec() multiple times with appropriate  argu-
3557         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3558         mentation where \G can be useful.         mentation where \G can be useful.
3559    
3560         Note,  however,  that  PCRE's interpretation of \G, as the start of the         Note, however, that PCRE's interpretation of \G, as the  start  of  the
3561         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3562         end  of  the  previous  match. In Perl, these can be different when the         end of the previous match. In Perl, these can  be  different  when  the
3563         previously matched string was empty. Because PCRE does just  one  match         previously  matched  string was empty. Because PCRE does just one match
3564         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3565    
3566         If  all  the alternatives of a pattern begin with \G, the expression is         If all the alternatives of a pattern begin with \G, the  expression  is
3567         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3568         in the compiled regular expression.         in the compiled regular expression.
3569    
# Line 3155  BACKSLASH Line 3571  BACKSLASH
3571  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3572    
3573         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3574         character is an assertion that is true only  if  the  current  matching         character  is  an  assertion  that is true only if the current matching
3575         point  is  at the start of the subject string. If the startoffset argu-         point is at the start of the subject string. If the  startoffset  argu-
3576         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
3577         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
3578         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3579    
3580         Circumflex need not be the first character of the pattern if  a  number         Circumflex  need  not be the first character of the pattern if a number
3581         of  alternatives are involved, but it should be the first thing in each         of alternatives are involved, but it should be the first thing in  each
3582         alternative in which it appears if the pattern is ever  to  match  that         alternative  in  which  it appears if the pattern is ever to match that
3583         branch.  If all possible alternatives start with a circumflex, that is,         branch. If all possible alternatives start with a circumflex, that  is,
3584         if the pattern is constrained to match only at the start  of  the  sub-         if  the  pattern  is constrained to match only at the start of the sub-
3585         ject,  it  is  said  to be an "anchored" pattern. (There are also other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
3586         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3587    
3588         A dollar character is an assertion that is true  only  if  the  current         A  dollar  character  is  an assertion that is true only if the current
3589         matching  point  is  at  the  end of the subject string, or immediately         matching point is at the end of  the  subject  string,  or  immediately
3590         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3591         be  the  last  character of the pattern if a number of alternatives are         be the last character of the pattern if a number  of  alternatives  are
3592         involved, but it should be the last item in  any  branch  in  which  it         involved,  but  it  should  be  the last item in any branch in which it
3593         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3594    
3595         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3596         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3597         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3598    
3599         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3600         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3601         matches  immediately after internal newlines as well as at the start of         matches immediately after internal newlines as well as at the start  of
3602         the subject string. It does not match after a  newline  that  ends  the         the  subject  string.  It  does not match after a newline that ends the
3603         string.  A dollar matches before any newlines in the string, as well as         string. A dollar matches before any newlines in the string, as well  as
3604         at the very end, when PCRE_MULTILINE is set. When newline is  specified         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3605         as  the  two-character  sequence CRLF, isolated CR and LF characters do         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3606         not indicate newlines.         not indicate newlines.
3607    
3608         For example, the pattern /^abc$/ matches the subject string  "def\nabc"         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3609         (where  \n  represents a newline) in multiline mode, but not otherwise.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3610         Consequently, patterns that are anchored in single  line  mode  because         Consequently,  patterns  that  are anchored in single line mode because
3611         all  branches  start  with  ^ are not anchored in multiline mode, and a         all branches start with ^ are not anchored in  multiline  mode,  and  a
3612         match for circumflex is  possible  when  the  startoffset  argument  of         match  for  circumflex  is  possible  when  the startoffset argument of
3613         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3614         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3615    
3616         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3617         and  end of the subject in both modes, and if all branches of a pattern         and end of the subject in both modes, and if all branches of a  pattern
3618         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3619         set.         set.
3620    
3621    
3622  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3623    
3624         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3625         ter in the subject string except (by default) a character  that  signi-         ter  in  the subject string except (by default) a character that signi-
3626         fies  the  end  of  a line. In UTF-8 mode, the matched character may be         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3627         more than one byte long.         more than one byte long.
3628    
3629         When a line ending is defined as a single character, dot never  matches         When  a line ending is defined as a single character, dot never matches
3630         that  character; when the two-character sequence CRLF is used, dot does         that character; when the two-character sequence CRLF is used, dot  does
3631         not match CR if it is immediately followed  by  LF,  but  otherwise  it         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3632         matches  all characters (including isolated CRs and LFs). When any Uni-         matches all characters (including isolated CRs and LFs). When any  Uni-
3633         code line endings are being recognized, dot does not match CR or LF  or         code  line endings are being recognized, dot does not match CR or LF or
3634         any of the other line ending characters.         any of the other line ending characters.
3635    
3636         The  behaviour  of  dot  with regard to newlines can be changed. If the         The behaviour of dot with regard to newlines can  be  changed.  If  the
3637         PCRE_DOTALL option is set, a dot matches  any  one  character,  without         PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3638         exception. If the two-character sequence CRLF is present in the subject         exception. If the two-character sequence CRLF is present in the subject
3639         string, it takes two dots to match it.         string, it takes two dots to match it.
3640    
3641         The handling of dot is entirely independent of the handling of  circum-         The  handling of dot is entirely independent of the handling of circum-
3642         flex  and  dollar,  the  only relationship being that they both involve         flex and dollar, the only relationship being  that  they  both  involve
3643         newlines. Dot has no special meaning in a character class.         newlines. Dot has no special meaning in a character class.
3644    
3645    
3646  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3647    
3648         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3649         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3650         line-ending characters. The feature is provided in  Perl  in  order  to         line-ending  characters.  The  feature  is provided in Perl in order to
3651         match  individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3652         acters into individual bytes, what remains in the string may be a  mal-         acters  into individual bytes, what remains in the string may be a mal-
3653         formed  UTF-8  string.  For this reason, the \C escape sequence is best         formed UTF-8 string. For this reason, the \C escape  sequence  is  best
3654         avoided.         avoided.
3655    
3656         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3657         below),  because  in UTF-8 mode this would make it impossible to calcu-         below), because in UTF-8 mode this would make it impossible  to  calcu-
3658         late the length of the lookbehind.         late the length of the lookbehind.
3659    
3660    
# Line 3247  SQUARE BRACKETS AND CHARACTER CLASSES Line 3663  SQUARE BRACKETS AND CHARACTER CLASSES
3663         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3664         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3665         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3666         it  should  be  the first data character in the class (after an initial         it should be the first data character in the class  (after  an  initial
3667         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3668    
3669         A character class matches a single character in the subject.  In  UTF-8         A  character  class matches a single character in the subject. In UTF-8
3670         mode,  the character may occupy more than one byte. A matched character         mode, the character may occupy more than one byte. A matched  character
3671         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3672         character  in  the  class definition is a circumflex, in which case the         character in the class definition is a circumflex, in  which  case  the
3673         subject character must not be in the set defined by  the  class.  If  a         subject  character  must  not  be in the set defined by the class. If a
3674         circumflex  is actually required as a member of the class, ensure it is         circumflex is actually required as a member of the class, ensure it  is
3675         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3676    
3677         For example, the character class [aeiou] matches any lower case  vowel,         For  example, the character class [aeiou] matches any lower case vowel,
3678         while  [^aeiou]  matches  any character that is not a lower case vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3679         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3680         characters  that  are in the class by enumerating those that are not. A         characters that are in the class by enumerating those that are  not.  A
3681         class that starts with a circumflex is not an assertion: it still  con-         class  that starts with a circumflex is not an assertion: it still con-
3682         sumes  a  character  from the subject string, and therefore it fails if         sumes a character from the subject string, and therefore  it  fails  if
3683         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3684    
3685         In UTF-8 mode, characters with values greater than 255 can be  included         In  UTF-8 mode, characters with values greater than 255 can be included
3686         in  a  class as a literal string of bytes, or by using the \x{ escaping         in a class as a literal string of bytes, or by using the  \x{  escaping
3687         mechanism.         mechanism.
3688    
3689         When caseless matching is set, any letters in a  class  represent  both         When  caseless  matching  is set, any letters in a class represent both
3690         their  upper  case  and lower case versions, so for example, a caseless         their upper case and lower case versions, so for  example,  a  caseless
3691         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
3692         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always
3693         understands the concept of case for characters whose  values  are  less         understands  the  concept  of case for characters whose values are less
3694         than  128, so caseless matching is always possible. For characters with         than 128, so caseless matching is always possible. For characters  with
3695         higher values, the concept of case is supported  if  PCRE  is  compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3696         with  Unicode  property support, but not otherwise.  If you want to use         with Unicode property support, but not otherwise.  If you want  to  use
3697         caseless matching for characters 128 and above, you  must  ensure  that         caseless  matching  for  characters 128 and above, you must ensure that
3698         PCRE  is  compiled  with Unicode property support as well as with UTF-8         PCRE is compiled with Unicode property support as well  as  with  UTF-8
3699         support.         support.
3700    
3701         Characters that might indicate line breaks are  never  treated  in  any         Characters  that  might  indicate  line breaks are never treated in any
3702         special  way  when  matching  character  classes,  whatever line-ending         special way  when  matching  character  classes,  whatever  line-ending
3703         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and
3704         PCRE_MULTILINE options is used. A class such as [^a] always matches one         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3705         of these characters.         of these characters.
3706    
3707         The minus (hyphen) character can be used to specify a range of  charac-         The  minus (hyphen) character can be used to specify a range of charac-
3708         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters in a character  class.  For  example,  [d-m]  matches  any  letter
3709         between d and m, inclusive. If a  minus  character  is  required  in  a         between  d  and  m,  inclusive.  If  a minus character is required in a
3710         class,  it  must  be  escaped  with a backslash or appear in a position         class, it must be escaped with a backslash  or  appear  in  a  position
3711         where it cannot be interpreted as indicating a range, typically as  the         where  it cannot be interpreted as indicating a range, typically as the
3712         first or last character in the class.         first or last character in the class.
3713    
3714         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3715         ter of a range. A pattern such as [W-]46] is interpreted as a class  of         ter  of a range. A pattern such as [W-]46] is interpreted as a class of
3716         two  characters ("W" and "-") followed by a literal string "46]", so it         two characters ("W" and "-") followed by a literal string "46]", so  it
3717         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a
3718         backslash  it is interpreted as the end of range, so [W-\]46] is inter-         backslash it is interpreted as the end of range, so [W-\]46] is  inter-
3719         preted as a class containing a range followed by two other  characters.         preted  as a class containing a range followed by two other characters.
3720         The  octal or hexadecimal representation of "]" can also be used to end         The octal or hexadecimal representation of "]" can also be used to  end
3721         a range.         a range.
3722    
3723         Ranges operate in the collating sequence of character values. They  can         Ranges  operate in the collating sequence of character values. They can
3724         also   be  used  for  characters  specified  numerically,  for  example         also  be  used  for  characters  specified  numerically,  for   example
3725         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values         [\000-\037].  In UTF-8 mode, ranges can include characters whose values
3726         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3727    
3728         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3729         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3730         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if
3731         character tables for a French locale are in  use,  [\xc8-\xcb]  matches         character  tables  for  a French locale are in use, [\xc8-\xcb] matches
3732         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented E characters in both cases. In UTF-8 mode, PCRE  supports  the
3733         concept of case for characters with values greater than 128  only  when         concept  of  case for characters with values greater than 128 only when
3734         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3735    
3736         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear
3737         in a character class, and add the characters that  they  match  to  the         in  a  character  class,  and add the characters that they match to the
3738         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3739         flex can conveniently be used with the upper case  character  types  to         flex  can  conveniently  be used with the upper case character types to
3740         specify  a  more  restricted  set of characters than the matching lower         specify a more restricted set of characters  than  the  matching  lower
3741         case type. For example, the class [^\W_] matches any letter  or  digit,         case  type.  For example, the class [^\W_] matches any letter or digit,
3742         but not underscore.         but not underscore.
3743    
3744         The  only  metacharacters  that are recognized in character classes are         The only metacharacters that are recognized in  character  classes  are
3745         backslash, hyphen (only where it can be  interpreted  as  specifying  a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
3746         range),  circumflex  (only  at the start), opening square bracket (only         range), circumflex (only at the start), opening  square  bracket  (only
3747         when it can be interpreted as introducing a POSIX class name - see  the         when  it can be interpreted as introducing a POSIX class name - see the
3748         next  section),  and  the  terminating closing square bracket. However,         next section), and the terminating  closing  square  bracket.  However,
3749         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3750    
3751    
3752  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3753    
3754         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3755         enclosed  by  [: and :] within the enclosing square brackets. PCRE also         enclosed by [: and :] within the enclosing square brackets.  PCRE  also
3756         supports this notation. For example,         supports this notation. For example,
3757    
3758           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3359  POSIX CHARACTER CLASSES Line 3775  POSIX CHARACTER CLASSES
3775           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3776           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3777    
3778         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),
3779         and space (32). Notice that this list includes the VT  character  (code         and  space  (32). Notice that this list includes the VT character (code
3780         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
3781         Perl compatibility).         Perl compatibility).
3782    
3783         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension
3784         from  Perl  5.8. Another Perl extension is negation, which is indicated         from Perl 5.8. Another Perl extension is negation, which  is  indicated
3785         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3786    
3787           [12[:^digit:]]           [12[:^digit:]]
3788    
3789         matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the         matches  "1", "2", or any non-digit. PCRE (and Perl) also recognize the
3790         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3791         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
3792    
# Line 3390  VERTICAL BAR Line 3806  VERTICAL BAR
3806         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3807         to right, and the first one that succeeds is used. If the  alternatives         to right, and the first one that succeeds is used. If the  alternatives
3808         are  within a subpattern (defined below), "succeeds" means matching the         are  within a subpattern (defined below), "succeeds" means matching the
3809         rest of the main pattern as well as the alternative in the  subpattern.         rest of the main pattern as well as the alternative in the subpattern.
3810    
3811    
3812  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3813    
3814         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and
3815         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED  options  (which are Perl-compatible) can be changed from
3816         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within the pattern by  a  sequence  of  Perl  option  letters  enclosed
3817         option letters are         between "(?" and ")".  The option letters are
3818    
3819           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3820           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3407  INTERNAL OPTION SETTING Line 3823  INTERNAL OPTION SETTING
3823    
3824         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3825         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
3826         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-
3827         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,
3828         is also permitted. If a  letter  appears  both  before  and  after  the         is  also  permitted.  If  a  letter  appears  both before and after the
3829         hyphen, the option is unset.         hyphen, the option is unset.
3830    
3831         When  an option change occurs at top level (that is, not inside subpat-         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3832         tern parentheses), the change applies to the remainder of  the  pattern         can  be changed in the same way as the Perl-compatible options by using
3833           the characters J, U and X respectively.
3834    
3835           When an option change occurs at top level (that is, not inside  subpat-
3836           tern  parentheses),  the change applies to the remainder of the pattern
3837         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
3838         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3839         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3840    
3841         An  option  change  within a subpattern (see below for a description of         An option change within a subpattern (see below for  a  description  of
3842         subpatterns) affects only that part of the current pattern that follows         subpatterns) affects only that part of the current pattern that follows
3843         it, so         it, so
3844    
3845           (a(?i)b)c           (a(?i)b)c
3846    
3847         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3848         used).  By this means, options can be made to have  different  settings         used).   By  this means, options can be made to have different settings
3849         in  different parts of the pattern. Any changes made in one alternative         in different parts of the pattern. Any changes made in one  alternative
3850         do carry on into subsequent branches within the  same  subpattern.  For         do  carry  on  into subsequent branches within the same subpattern. For
3851         example,         example,
3852    
3853           (a(?i)b|c)           (a(?i)b|c)
3854    
3855         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the
3856         first branch is abandoned before the option setting.  This  is  because         first  branch  is  abandoned before the option setting. This is because
3857         the  effects  of option settings happen at compile time. There would be         the effects of option settings happen at compile time. There  would  be
3858         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3859    
3860         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note:  There  are  other  PCRE-specific  options that can be set by the
3861         can  be changed in the same way as the Perl-compatible options by using         application when the compile or match functions  are  called.  In  some
3862         the characters J, U and X respectively.         cases  the  pattern  can  contain special leading sequences to override
3863           what the application has set or what has been  defaulted.  Details  are
3864           given in the section entitled "Newline sequences" above.
3865    
3866    
3867  SUBPATTERNS  SUBPATTERNS
# Line 3451  SUBPATTERNS Line 3873  SUBPATTERNS
3873    
3874           cat(aract|erpillar|)           cat(aract|erpillar|)
3875    
3876         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches one of the words "cat", "cataract", or  "caterpillar".  Without
3877         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty
3878         string.         string.
3879    
3880         2.  It  sets  up  the  subpattern as a capturing subpattern. This means         2. It sets up the subpattern as  a  capturing  subpattern.  This  means
3881         that, when the whole pattern  matches,  that  portion  of  the  subject         that,  when  the  whole  pattern  matches,  that portion of the subject
3882         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
3883         ovector argument of pcre_exec(). Opening parentheses are  counted  from         ovector  argument  of pcre_exec(). Opening parentheses are counted from
3884         left  to  right  (starting  from 1) to obtain numbers for the capturing         left to right (starting from 1) to obtain  numbers  for  the  capturing
3885         subpatterns.         subpatterns.
3886    
3887         For example, if the string "the red king" is matched against  the  pat-         For  example,  if the string "the red king" is matched against the pat-
3888         tern         tern
3889    
3890           the ((red|white) (king|queen))           the ((red|white) (king|queen))
# Line 3470  SUBPATTERNS Line 3892  SUBPATTERNS
3892         the captured substrings are "red king", "red", and "king", and are num-         the captured substrings are "red king", "red", and "king", and are num-
3893         bered 1, 2, and 3, respectively.         bered 1, 2, and 3, respectively.
3894    
3895         The fact that plain parentheses fulfil  two  functions  is  not  always         The  fact  that  plain  parentheses  fulfil two functions is not always
3896         helpful.   There are often times when a grouping subpattern is required         helpful.  There are often times when a grouping subpattern is  required
3897         without a capturing requirement. If an opening parenthesis is  followed         without  a capturing requirement. If an opening parenthesis is followed
3898         by  a question mark and a colon, the subpattern does not do any captur-         by a question mark and a colon, the subpattern does not do any  captur-
3899         ing, and is not counted when computing the  number  of  any  subsequent         ing,  and  is  not  counted when computing the number of any subsequent
3900         capturing  subpatterns. For example, if the string "the white queen" is         capturing subpatterns. For example, if the string "the white queen"  is
3901         matched against the pattern         matched against the pattern
3902    
3903           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
# Line 3483  SUBPATTERNS Line 3905  SUBPATTERNS
3905         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3906         1 and 2. The maximum number of capturing subpatterns is 65535.         1 and 2. The maximum number of capturing subpatterns is 65535.
3907    
3908         As  a  convenient shorthand, if any option settings are required at the         As a convenient shorthand, if any option settings are required  at  the
3909         start of a non-capturing subpattern,  the  option  letters  may  appear         start  of  a  non-capturing  subpattern,  the option letters may appear
3910         between the "?" and the ":". Thus the two patterns         between the "?" and the ":". Thus the two patterns
3911    
3912           (?i:saturday|sunday)           (?i:saturday|sunday)
3913           (?:(?i)saturday|sunday)           (?:(?i)saturday|sunday)
3914    
3915         match exactly the same set of strings. Because alternative branches are         match exactly the same set of strings. Because alternative branches are
3916         tried from left to right, and options are not reset until  the  end  of         tried  from  left  to right, and options are not reset until the end of
3917         the  subpattern is reached, an option setting in one branch does affect         the subpattern is reached, an option setting in one branch does  affect
3918         subsequent branches, so the above patterns match "SUNDAY"  as  well  as         subsequent  branches,  so  the above patterns match "SUNDAY" as well as
3919         "Saturday".         "Saturday".
3920    
3921    
3922    DUPLICATE SUBPATTERN NUMBERS
3923    
3924           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3925           uses  the same numbers for its capturing parentheses. Such a subpattern
3926           starts with (?| and is itself a non-capturing subpattern. For  example,
3927           consider this pattern:
3928    
3929             (?|(Sat)ur|(Sun))day
3930    
3931           Because  the two alternatives are inside a (?| group, both sets of cap-
3932           turing parentheses are numbered one. Thus, when  the  pattern  matches,
3933           you  can  look  at captured substring number one, whichever alternative
3934           matched. This construct is useful when you want to  capture  part,  but
3935           not all, of one of a number of alternatives. Inside a (?| group, paren-
3936           theses are numbered as usual, but the number is reset at the  start  of
3937           each  branch. The numbers of any capturing buffers that follow the sub-
3938           pattern start after the highest number used in any branch. The  follow-
3939           ing  example  is taken from the Perl documentation.  The numbers under-
3940           neath show in which buffer the captured content will be stored.
3941    
3942             # before  ---------------branch-reset----------- after
3943             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3944             # 1            2         2  3        2     3     4
3945    
3946           A backreference or a recursive call to  a  numbered  subpattern  always
3947           refers to the first one in the pattern with the given number.
3948    
3949           An  alternative approach to using this "branch reset" feature is to use
3950           duplicate named subpatterns, as described in the next section.
3951    
3952    
3953  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3954    
3955         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying capturing parentheses by number is simple, but  it  can  be
3956         very hard to keep track of the numbers in complicated  regular  expres-         very  hard  to keep track of the numbers in complicated regular expres-
3957         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions. Furthermore, if an  expression  is  modified,  the  numbers  may
3958         change. To help with this difficulty, PCRE supports the naming of  sub-         change.  To help with this difficulty, PCRE supports the naming of sub-
3959         patterns. This feature was not added to Perl until release 5.10. Python         patterns. This feature was not added to Perl until release 5.10. Python
3960         had the feature earlier, and PCRE introduced it at release  4.0,  using         had  the  feature earlier, and PCRE introduced it at release 4.0, using
3961         the  Python syntax. PCRE now supports both the Perl and the Python syn-         the Python syntax. PCRE now supports both the Perl and the Python  syn-
3962         tax.         tax.
3963    
3964         In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)         In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
3965         or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References         or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
3966         to capturing parentheses from other parts of the pattern, such as back-         to capturing parentheses from other parts of the pattern, such as back-
3967         references,  recursion,  and conditions, can be made by name as well as         references, recursion, and conditions, can be made by name as  well  as
3968         by number.         by number.
3969    
3970         Names consist of up to  32  alphanumeric  characters  and  underscores.         Names  consist  of  up  to  32 alphanumeric characters and underscores.
3971         Named  capturing  parentheses  are  still  allocated numbers as well as         Named capturing parentheses are still  allocated  numbers  as  well  as
3972         names, exactly as if the names were not present. The PCRE API  provides         names,  exactly as if the names were not present. The PCRE API provides
3973         function calls for extracting the name-to-number translation table from         function calls for extracting the name-to-number translation table from
3974         a compiled pattern. There is also a convenience function for extracting         a compiled pattern. There is also a convenience function for extracting
3975         a captured substring by name.         a captured substring by name.
3976    
3977         By  default, a name must be unique within a pattern, but it is possible         By default, a name must be unique within a pattern, but it is  possible
3978         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
3979         time.  This  can  be useful for patterns where only one instance of the         time. This can be useful for patterns where only one  instance  of  the
3980         named parentheses can match. Suppose you want to match the  name  of  a         named  parentheses  can  match. Suppose you want to match the name of a
3981         weekday,  either as a 3-letter abbreviation or as the full name, and in         weekday, either as a 3-letter abbreviation or as the full name, and  in
3982         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
3983         the line breaks) does the job:         the line breaks) does the job:
3984    
# Line 3535  NAMED SUBPATTERNS Line 3988  NAMED SUBPATTERNS
3988           (?<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
3989           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3990    
3991         There  are  five capturing substrings, but only one is ever set after a         There are five capturing substrings, but only one is ever set  after  a
3992         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3993         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3994         subpattern of that name that matched.  This  saves  searching  to  find  
3995         which  numbered  subpattern  it  was. If you make a reference to a non-         The convenience function for extracting the data by  name  returns  the
3996         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring  for  the first (and in this example, the only) subpattern of
3997         corresponds  to  the  lowest number is used. For further details of the         that name that matched. This saves searching  to  find  which  numbered
3998         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern  it  was. If you make a reference to a non-unique named sub-
3999         tion.         pattern from elsewhere in the pattern, the one that corresponds to  the
4000           lowest  number  is used. For further details of the interfaces for han-
4001           dling named subpatterns, see the pcreapi documentation.
4002    
4003           Warning: You cannot use different names to distinguish between two sub-
4004           patterns  with  the same number (see the previous section) because PCRE
4005           uses only the numbers when matching.
4006    
4007    
4008  REPETITION  REPETITION
4009    
4010         Repetition  is  specified  by  quantifiers, which can follow any of the         Repetition is specified by quantifiers, which can  follow  any  of  the
4011         following items:         following items:
4012    
4013           a literal data character           a literal data character
# Line 3561  REPETITION Line 4020  REPETITION
4020           a back reference (see next section)           a back reference (see next section)
4021           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
4022    
4023         The general repetition quantifier specifies a minimum and maximum  num-         The  general repetition quantifier specifies a minimum and maximum num-
4024         ber  of  permitted matches, by giving the two numbers in curly brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
4025         (braces), separated by a comma. The numbers must be  less  than  65536,         (braces),  separated  by  a comma. The numbers must be less than 65536,
4026         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
4027    
4028           z{2,4}           z{2,4}
4029    
4030         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a
4031         special character. If the second number is omitted, but  the  comma  is         special  character.  If  the second number is omitted, but the comma is
4032         present,  there  is  no upper limit; if the second number and the comma         present, there is no upper limit; if the second number  and  the  comma
4033         are both omitted, the quantifier specifies an exact number of  required         are  both omitted, the quantifier specifies an exact number of required
4034         matches. Thus         matches. Thus
4035    
4036           [aeiou]{3,}           [aeiou]{3,}
# Line 3580  REPETITION Line 4039  REPETITION
4039    
4040           \d{8}           \d{8}
4041    
4042         matches  exactly  8  digits. An opening curly bracket that appears in a         matches exactly 8 digits. An opening curly bracket that  appears  in  a
4043         position where a quantifier is not allowed, or one that does not  match         position  where a quantifier is not allowed, or one that does not match
4044         the  syntax of a quantifier, is taken as a literal character. For exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
4045         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
4046    
4047         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
# Line 3593  REPETITION Line 4052  REPETITION
4052         may be of different lengths).         may be of different lengths).
4053    
4054         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
4055         the previous item and the quantifier were not present.         the previous item and the quantifier were not present. This may be use-
4056           ful for subpatterns that are referenced as subroutines  from  elsewhere
4057           in the pattern. Items other than subpatterns that have a {0} quantifier
4058           are omitted from the compiled pattern.
4059    
4060         For  convenience, the three most common quantifiers have single-charac-         For convenience, the three most common quantifiers have  single-charac-
4061         ter abbreviations:         ter abbreviations:
4062    
4063           *    is equivalent to {0,}           *    is equivalent to {0,}
4064           +    is equivalent to {1,}           +    is equivalent to {1,}
4065           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
4066    
4067         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
4068         that can match no characters with a quantifier that has no upper limit,         that can match no characters with a quantifier that has no upper limit,
4069         for example:         for example:
4070    
4071           (a?)*           (a?)*
4072    
4073         Earlier versions of Perl and PCRE used to give an error at compile time         Earlier versions of Perl and PCRE used to give an error at compile time
4074         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
4075         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
4076         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
4077         ken.         ken.
4078    
4079         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
4080         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
4081         causing the rest of the pattern to fail. The classic example  of  where         causing  the  rest of the pattern to fail. The classic example of where
4082         this gives problems is in trying to match comments in C programs. These         this gives problems is in trying to match comments in C programs. These
4083         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
4084         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
4085         pattern         pattern
4086    
4087           /\*.*\*/           /\*.*\*/
# Line 3628  REPETITION Line 4090  REPETITION
4090    
4091           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
4092    
4093         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
4094         the .*  item.         the .*  item.
4095    
4096         However,  if  a quantifier is followed by a question mark, it ceases to         However, if a quantifier is followed by a question mark, it  ceases  to
4097         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
4098         the pattern         the pattern
4099    
4100           /\*.*?\*/           /\*.*?\*/
4101    
4102         does  the  right  thing with the C comments. The meaning of the various         does the right thing with the C comments. The meaning  of  the  various
4103         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
4104         matches.   Do  not  confuse this use of question mark with its use as a         matches.  Do not confuse this use of question mark with its  use  as  a
4105         quantifier in its own right. Because it has two uses, it can  sometimes         quantifier  in its own right. Because it has two uses, it can sometimes
4106         appear doubled, as in         appear doubled, as in
4107    
4108           \d??\d           \d??\d
# Line 3648  REPETITION Line 4110  REPETITION
4110         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
4111         only way the rest of the pattern matches.         only way the rest of the pattern matches.
4112    
4113         If the PCRE_UNGREEDY option is set (an option that is not available  in         If  the PCRE_UNGREEDY option is set (an option that is not available in
4114         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
4115         can be made greedy by following them with a  question  mark.  In  other         can  be  made  greedy  by following them with a question mark. In other
4116         words, it inverts the default behaviour.         words, it inverts the default behaviour.
4117    
4118         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
4119         count that is greater than 1 or with a limited maximum, more memory  is         count  that is greater than 1 or with a limited maximum, more memory is
4120         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
4121         minimum or maximum.         minimum or maximum.
4122    
4123         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
4124         alent  to  Perl's  /s) is set, thus allowing the dot to match newlines,         alent to Perl's /s) is set, thus allowing the dot  to  match  newlines,
4125         the pattern is implicitly anchored, because whatever  follows  will  be         the  pattern  is  implicitly anchored, because whatever follows will be
4126         tried  against every character position in the subject string, so there         tried against every character position in the subject string, so  there
4127         is no point in retrying the overall match at  any  position  after  the         is  no  point  in  retrying the overall match at any position after the
4128         first.  PCRE  normally treats such a pattern as though it were preceded         first. PCRE normally treats such a pattern as though it  were  preceded
4129         by \A.         by \A.
4130    
4131         In cases where it is known that the subject  string  contains  no  new-         In  cases  where  it  is known that the subject string contains no new-
4132         lines,  it  is  worth setting PCRE_DOTALL in order to obtain this opti-         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-
4133         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
4134    
4135         However, there is one situation where the optimization cannot be  used.         However,  there is one situation where the optimization cannot be used.
4136         When  .*   is  inside  capturing  parentheses that are the subject of a         When .*  is inside capturing parentheses that  are  the  subject  of  a
4137         backreference elsewhere in the pattern, a match at the start  may  fail         backreference  elsewhere  in the pattern, a match at the start may fail
4138         where a later one succeeds. Consider, for example:         where a later one succeeds. Consider, for example:
4139    
4140           (.*)abc\1           (.*)abc\1
4141    
4142         If  the subject is "xyz123abc123" the match point is the fourth charac-         If the subject is "xyz123abc123" the match point is the fourth  charac-
4143         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
4144    
4145         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3686  REPETITION Line 4148  REPETITION
4148           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4149    
4150         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4151         is "tweedledee". However, if there are  nested  capturing  subpatterns,         is  "tweedledee".  However,  if there are nested capturing subpatterns,
4152         the  corresponding captured values may have been set in previous itera-         the corresponding captured values may have been set in previous  itera-
4153         tions. For example, after         tions. For example, after
4154    
4155           /(a|(b))+/           /(a|(b))+/
# Line 3697  REPETITION Line 4159  REPETITION
4159    
4160  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4161    
4162         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
4163         repetition,  failure  of what follows normally causes the repeated item         repetition, failure of what follows normally causes the  repeated  item
4164         to be re-evaluated to see if a different number of repeats  allows  the         to  be  re-evaluated to see if a different number of repeats allows the
4165         rest  of  the pattern to match. Sometimes it is useful to prevent this,         rest of the pattern to match. Sometimes it is useful to  prevent  this,
4166         either to change the nature of the match, or to cause it  fail  earlier         either  to  change the nature of the match, or to cause it fail earlier
4167         than  it otherwise might, when the author of the pattern knows there is         than it otherwise might, when the author of the pattern knows there  is
4168         no point in carrying on.         no point in carrying on.
4169    
4170         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider,  for  example, the pattern \d+foo when applied to the subject
4171         line         line
4172    
4173           123456bar           123456bar
4174    
4175         After matching all 6 digits and then failing to match "foo", the normal         After matching all 6 digits and then failing to match "foo", the normal
4176         action of the matcher is to try again with only 5 digits  matching  the         action  of  the matcher is to try again with only 5 digits matching the
4177         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.
4178         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides
4179         the  means for specifying that once a subpattern has matched, it is not         the means for specifying that once a subpattern has matched, it is  not
4180         to be re-evaluated in this way.         to be re-evaluated in this way.
4181    
4182         If we use atomic grouping for the previous example, the  matcher  gives         If  we  use atomic grouping for the previous example, the matcher gives
4183         up  immediately  on failing to match "foo" the first time. The notation         up immediately on failing to match "foo" the first time.  The  notation
4184         is a kind of special parenthesis, starting with (?> as in this example:         is a kind of special parenthesis, starting with (?> as in this example:
4185    
4186           (?>\d+)foo           (?>\d+)foo
# Line 3748  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4210  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4210    
4211           \d++foo           \d++foo
4212    
4213         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4214           example:
4215    
4216             (abc|xyz){2,3}+
4217    
4218           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4219         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4220         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4221         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4222         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4223         should be slightly faster.         should be slightly faster.
4224    
4225         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-         The possessive quantifier syntax is an extension to the Perl  5.8  syn-
4226         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4227         edition of his book. Mike McCloskey liked it, so implemented it when he         edition of his book. Mike McCloskey liked it, so implemented it when he
4228         built Sun's Java package, and PCRE copied it from there. It  ultimately         built  Sun's Java package, and PCRE copied it from there. It ultimately
4229         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4230    
4231         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4232         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4233         A++B  because  there is no point in backtracking into a sequence of A's         A++B because there is no point in backtracking into a sequence  of  A's
4234         when B must follow.         when B must follow.
4235    
4236         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4237         can  itself  be  repeated  an  unlimited number of times, the use of an         can itself be repeated an unlimited number of  times,  the  use  of  an
4238         atomic group is the only way to avoid some  failing  matches  taking  a         atomic  group  is  the  only way to avoid some failing matches taking a
4239         very long time indeed. The pattern         very long time indeed. The pattern
4240    
4241           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4242    
4243         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4244         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4245         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4246    
4247           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4248    
4249         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4250         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4251         *  repeat  in  a  large  number of ways, and all have to be tried. (The         * repeat in a large number of ways, and all  have  to  be  tried.  (The
4252         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4253         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4254         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4255         ter  that  is required for a match, and fail early if it is not present         ter that is required for a match, and fail early if it is  not  present
4256         in the string.) If the pattern is changed so that  it  uses  an  atomic         in  the  string.)  If  the pattern is changed so that it uses an atomic
4257         group, like this:         group, like this:
4258    
4259           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4260    
4261         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens quickly.
4262    
4263    
4264  BACK REFERENCES  BACK REFERENCES
# Line 3820  BACK REFERENCES Line 4287  BACK REFERENCES
4287    
4288         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another way of avoiding the ambiguity inherent in  the  use  of  digits
4289         following a backslash is to use the \g escape sequence, which is a fea-         following a backslash is to use the \g escape sequence, which is a fea-
4290         ture introduced in Perl 5.10. This escape must be followed by  a  posi-         ture introduced in Perl 5.10.  This  escape  must  be  followed  by  an
4291         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned  number  or  a negative number, optionally enclosed in braces.
4292         ples are all identical:         These examples are all identical:
4293    
4294           (ring), \1           (ring), \1
4295           (ring), \g1           (ring), \g1
4296           (ring), \g{1}           (ring), \g{1}
4297    
4298         A positive number specifies an absolute reference without the ambiguity         An unsigned number specifies an absolute reference without the  ambigu-
4299         that  is  present  in  the older syntax. It is also useful when literal         ity that is present in the older syntax. It is also useful when literal
4300         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4301         Consider this example:         Consider this example:
4302    
# Line 3858  BACK REFERENCES Line 4325  BACK REFERENCES
4325         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the
4326         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4327    
4328         Back references to named subpatterns use the Perl  syntax  \k<name>  or         There are several different ways of writing back  references  to  named
4329         \k'name'  or  the  Python  syntax (?P=name). We could rewrite the above         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or
4330         example in either of the following ways:         \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's
4331           unified back reference syntax, in which \g can be used for both numeric
4332           and named references, is also supported. We  could  rewrite  the  above
4333           example in any of the following ways:
4334    
4335           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
4336             (?'p1'(?i)rah)\s+\k{p1}
4337           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4338             (?<p1>(?i)rah)\s+\g{p1}
4339    
4340         A subpattern that is referenced by  name  may  appear  in  the  pattern         A  subpattern  that  is  referenced  by  name may appear in the pattern
4341         before or after the reference.         before or after the reference.
4342    
4343         There  may be more than one back reference to the same subpattern. If a         There may be more than one back reference to the same subpattern. If  a
4344         subpattern has not actually been used in a particular match,  any  back         subpattern  has  not actually been used in a particular match, any back
4345         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4346    
4347           (a|(bc))\2           (a|(bc))\2
4348    
4349         always  fails if it starts to match "a" rather than "bc". Because there         always fails if it starts to match "a" rather than "bc". Because  there
4350         may be many capturing parentheses in a pattern,  all  digits  following         may  be  many  capturing parentheses in a pattern, all digits following
4351         the  backslash  are taken as part of a potential back reference number.         the backslash are taken as part of a potential back  reference  number.
4352         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4353         used  to  terminate  the back reference. If the PCRE_EXTENDED option is         used to terminate the back reference. If the  PCRE_EXTENDED  option  is
4354         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-
4355         ments" below) can be used.         ments" below) can be used.
4356    
4357         A  back reference that occurs inside the parentheses to which it refers         A back reference that occurs inside the parentheses to which it  refers
4358         fails when the subpattern is first used, so, for example,  (a\1)  never         fails  when  the subpattern is first used, so, for example, (a\1) never
4359         matches.   However,  such references can be useful inside repeated sub-         matches.  However, such references can be useful inside  repeated  sub-
4360         patterns. For example, the pattern         patterns. For example, the pattern
4361    
4362           (a|b\1)+           (a|b\1)+
4363    
4364         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
4365         ation  of  the  subpattern,  the  back  reference matches the character         ation of the subpattern,  the  back  reference  matches  the  character
4366         string corresponding to the previous iteration. In order  for  this  to         string  corresponding  to  the previous iteration. In order for this to
4367         work,  the  pattern must be such that the first iteration does not need         work, the pattern must be such that the first iteration does  not  need
4368         to match the back reference. This can be done using alternation, as  in         to  match the back reference. This can be done using alternation, as in
4369         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4370    
4371    
4372  ASSERTIONS  ASSERTIONS
4373    
4374         An  assertion  is  a  test on the characters following or preceding the         An assertion is a test on the characters  following  or  preceding  the
4375         current matching point that does not actually consume  any  characters.         current  matching  point that does not actually consume any characters.
4376         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are
4377         described above.         described above.
4378    
4379         More complicated assertions are coded as  subpatterns.  There  are  two         More  complicated  assertions  are  coded as subpatterns. There are two
4380         kinds:  those  that  look  ahead of the current position in the subject         kinds: those that look ahead of the current  position  in  the  subject
4381         string, and those that look  behind  it.  An  assertion  subpattern  is         string,  and  those  that  look  behind  it. An assertion subpattern is
4382         matched  in  the  normal way, except that it does not cause the current         matched in the normal way, except that it does not  cause  the  current
4383         matching position to be changed.         matching position to be changed.
4384    
4385         Assertion subpatterns are not capturing subpatterns,  and  may  not  be         Assertion  subpatterns  are  not  capturing subpatterns, and may not be
4386         repeated,  because  it  makes no sense to assert the same thing several         repeated, because it makes no sense to assert the  same  thing  several
4387         times. If any kind of assertion contains capturing  subpatterns  within         times.  If  any kind of assertion contains capturing subpatterns within
4388         it,  these are counted for the purposes of numbering the capturing sub-         it, these are counted for the purposes of numbering the capturing  sub-
4389         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4390         out  only  for  positive assertions, because it does not make sense for         out only for positive assertions, because it does not  make  sense  for
4391         negative assertions.         negative assertions.
4392    
4393     Lookahead assertions     Lookahead assertions
# Line 3925  ASSERTIONS Line 4397  ASSERTIONS
4397    
4398           \w+(?=;)           \w+(?=;)
4399    
4400         matches  a word followed by a semicolon, but does not include the semi-         matches a word followed by a semicolon, but does not include the  semi-
4401         colon in the match, and         colon in the match, and
4402    
4403           foo(?!bar)           foo(?!bar)
4404    
4405         matches any occurrence of "foo" that is not  followed  by  "bar".  Note         matches  any  occurrence  of  "foo" that is not followed by "bar". Note
4406         that the apparently similar pattern         that the apparently similar pattern
4407    
4408           (?!foo)bar           (?!foo)bar
4409    
4410         does  not  find  an  occurrence  of "bar" that is preceded by something         does not find an occurrence of "bar"  that  is  preceded  by  something
4411         other than "foo"; it finds any occurrence of "bar" whatsoever,  because         other  than "foo"; it finds any occurrence of "bar" whatsoever, because
4412         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4413         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4414    
4415         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
4416         most  convenient  way  to  do  it  is with (?!) because an empty string         most convenient way to do it is  with  (?!)  because  an  empty  string
4417         always matches, so an assertion that requires there not to be an  empty         always  matches, so an assertion that requires there not to be an empty
4418         string must always fail.         string must always fail.
4419    
4420     Lookbehind assertions     Lookbehind assertions
4421    
4422         Lookbehind  assertions start with (?<= for positive assertions and (?<!         Lookbehind assertions start with (?<= for positive assertions and  (?<!
4423         for negative assertions. For example,         for negative assertions. For example,
4424    
4425           (?<!foo)bar           (?<!foo)bar
4426    
4427         does find an occurrence of "bar" that is not  preceded  by  "foo".  The         does  find  an  occurrence  of "bar" that is not preceded by "foo". The
4428         contents  of  a  lookbehind  assertion are restricted such that all the         contents of a lookbehind assertion are restricted  such  that  all  the
4429         strings it matches must have a fixed length. However, if there are sev-         strings it matches must have a fixed length. However, if there are sev-
4430         eral  top-level  alternatives,  they  do  not all have to have the same         eral top-level alternatives, they do not all  have  to  have  the  same
4431         fixed length. Thus         fixed length. Thus
4432    
4433           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 3964  ASSERTIONS Line 4436  ASSERTIONS
4436    
4437           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4438    
4439         causes an error at compile time. Branches that match  different  length         causes  an  error at compile time. Branches that match different length
4440         strings  are permitted only at the top level of a lookbehind assertion.         strings are permitted only at the top level of a lookbehind  assertion.
4441         This is an extension compared with  Perl  (at  least  for  5.8),  which         This  is  an  extension  compared  with  Perl (at least for 5.8), which
4442         requires  all branches to match the same length of string. An assertion         requires all branches to match the same length of string. An  assertion
4443         such as         such as
4444    
4445           (?<=ab(c|de))           (?<=ab(c|de))
4446    
4447         is not permitted, because its single top-level  branch  can  match  two         is  not  permitted,  because  its single top-level branch can match two
4448         different  lengths,  but  it is acceptable if rewritten to use two top-         different lengths, but it is acceptable if rewritten to  use  two  top-
4449         level branches:         level branches:
4450    
4451           (?<=abc|abde)           (?<=abc|abde)
4452    
4453         The implementation of lookbehind assertions is, for  each  alternative,         In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4454         to  temporarily  move the current position back by the fixed length and         instead of a lookbehind assertion; this is not restricted to  a  fixed-
4455           length.
4456    
4457           The  implementation  of lookbehind assertions is, for each alternative,
4458           to temporarily move the current position back by the fixed  length  and
4459         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4460         rent position, the assertion fails.         rent position, the assertion fails.
4461    
4462         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
4463         mode) to appear in lookbehind assertions, because it makes it  impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
4464         ble  to  calculate the length of the lookbehind. The \X and \R escapes,         ble to calculate the length of the lookbehind. The \X and  \R  escapes,
4465         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4466    
4467         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4468         assertions  to  specify  efficient  matching  at the end of the subject         assertions to specify efficient matching at  the  end  of  the  subject
4469         string. Consider a simple pattern such as         string. Consider a simple pattern such as
4470    
4471           abcd$           abcd$
4472    
4473         when applied to a long string that does  not  match.  Because  matching         when  applied  to  a  long string that does not match. Because matching
4474         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
4475         and then see if what follows matches the rest of the  pattern.  If  the         and  then  see  if what follows matches the rest of the pattern. If the
4476         pattern is specified as         pattern is specified as
4477    
4478           ^.*abcd$           ^.*abcd$
4479    
4480         the  initial .* matches the entire string at first, but when this fails         the initial .* matches the entire string at first, but when this  fails
4481         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
4482         last  character,  then all but the last two characters, and so on. Once         last character, then all but the last two characters, and so  on.  Once
4483         again the search for "a" covers the entire string, from right to  left,         again  the search for "a" covers the entire string, from right to left,
4484         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
4485    
4486           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4487    
4488         there  can  be  no backtracking for the .*+ item; it can match only the         there can be no backtracking for the .*+ item; it can  match  only  the
4489         entire string. The subsequent lookbehind assertion does a  single  test         entire  string.  The subsequent lookbehind assertion does a single test
4490         on  the last four characters. If it fails, the match fails immediately.         on the last four characters. If it fails, the match fails  immediately.
4491         For long strings, this approach makes a significant difference  to  the         For  long  strings, this approach makes a significant difference to the
4492         processing time.         processing time.
4493    
4494     Using multiple assertions     Using multiple assertions
# Line 4021  ASSERTIONS Line 4497  ASSERTIONS
4497    
4498           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4499    
4500         matches  "foo" preceded by three digits that are not "999". Notice that         matches "foo" preceded by three digits that are not "999". Notice  that
4501         each of the assertions is applied independently at the  same  point  in         each  of  the  assertions is applied independently at the same point in
4502         the  subject  string.  First  there  is a check that the previous three         the subject string. First there is a  check  that  the  previous  three
4503         characters are all digits, and then there is  a  check  that  the  same         characters  are  all  digits,  and  then there is a check that the same
4504         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4505         ceded by six characters, the first of which are  digits  and  the  last         ceded  by  six  characters,  the first of which are digits and the last
4506         three  of  which  are not "999". For example, it doesn't match "123abc-         three of which are not "999". For example, it  doesn't  match  "123abc-
4507         foo". A pattern to do that is         foo". A pattern to do that is
4508    
4509           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4510    
4511         This time the first assertion looks at the  preceding  six  characters,         This  time  the  first assertion looks at the preceding six characters,
4512         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4513         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4514    
# Line 4040  ASSERTIONS Line 4516  ASSERTIONS
4516    
4517           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4518    
4519         matches an occurrence of "baz" that is preceded by "bar" which in  turn         matches  an occurrence of "baz" that is preceded by "bar" which in turn
4520         is not preceded by "foo", while         is not preceded by "foo", while
4521    
4522           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4523    
4524         is  another pattern that matches "foo" preceded by three digits and any         is another pattern that matches "foo" preceded by three digits and  any
4525         three characters that are not "999".         three characters that are not "999".
4526    
4527    
4528  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4529    
4530         It is possible to cause the matching process to obey a subpattern  con-         It  is possible to cause the matching process to obey a subpattern con-
4531         ditionally  or to choose between two alternative subpatterns, depending         ditionally or to choose between two alternative subpatterns,  depending
4532         on the result of an assertion, or whether a previous capturing  subpat-         on  the result of an assertion, or whether a previous capturing subpat-
4533         tern  matched  or not. The two possible forms of conditional subpattern         tern matched or not. The two possible forms of  conditional  subpattern
4534         are         are
4535    
4536           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4537           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4538    
4539         If the condition is satisfied, the yes-pattern is used;  otherwise  the         If  the  condition is satisfied, the yes-pattern is used; otherwise the
4540         no-pattern  (if  present)  is used. If there are more than two alterna-         no-pattern (if present) is used. If there are more  than  two  alterna-
4541         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4542    
4543         There are four kinds of condition: references  to  subpatterns,  refer-         There  are  four  kinds of condition: references to subpatterns, refer-
4544         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4545    
4546     Checking for a used subpattern by number     Checking for a used subpattern by number
4547    
4548         If  the  text between the parentheses consists of a sequence of digits,         If the text between the parentheses consists of a sequence  of  digits,
4549         the condition is true if the capturing subpattern of  that  number  has         the  condition  is  true if the capturing subpattern of that number has
4550         previously matched.         previously matched. An alternative notation is to  precede  the  digits
4551           with a plus or minus sign. In this case, the subpattern number is rela-
4552           tive rather than absolute.  The most recently opened parentheses can be
4553           referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In
4554           looping constructs it can also make sense to refer to subsequent groups
4555           with constructs such as (?(+2).
4556    
4557         Consider  the  following  pattern, which contains non-significant white         Consider  the  following  pattern, which contains non-significant white
4558         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
# Line 4090  CONDITIONAL SUBPATTERNS Line 4571  CONDITIONAL SUBPATTERNS
4571         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4572         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4573    
4574           If you were embedding this pattern in a larger one,  you  could  use  a
4575           relative reference:
4576    
4577             ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...