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# Line 45  INTRODUCTION Line 45  INTRODUCTION
45    
46         Details of exactly which Perl regular expression features are  and  are         Details of exactly which Perl regular expression features are  and  are
47         not supported by PCRE are given in separate documents. See the pcrepat-         not supported by PCRE are given in separate documents. See the pcrepat-
48         tern and pcrecompat pages.         tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
49           page.
50    
51         Some features of PCRE can be included, excluded, or  changed  when  the         Some  features  of  PCRE can be included, excluded, or changed when the
52         library  is  built.  The pcre_config() function makes it possible for a         library is built. The pcre_config() function makes it  possible  for  a
53         client to discover which features are  available.  The  features  them-         client  to  discover  which  features are available. The features them-
54         selves  are described in the pcrebuild page. Documentation about build-         selves are described in the pcrebuild page. Documentation about  build-
55         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
56         in the source distribution.         in the source distribution.
57    
58         The  library  contains  a number of undocumented internal functions and         The library contains a number of undocumented  internal  functions  and
59         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
60         functions,  but  which  are  not  intended for use by external callers.         functions, but which are not intended  for  use  by  external  callers.
61         Their names all begin with "_pcre_", which hopefully will  not  provoke         Their  names  all begin with "_pcre_", which hopefully will not provoke
62         any name clashes. In some environments, it is possible to control which         any name clashes. In some environments, it is possible to control which
63         external symbols are exported when a shared library is  built,  and  in         external  symbols  are  exported when a shared library is built, and in
64         these cases the undocumented symbols are not exported.         these cases the undocumented symbols are not exported.
65    
66    
67  USER DOCUMENTATION  USER DOCUMENTATION
68    
69         The  user  documentation  for PCRE comprises a number of different sec-         The user documentation for PCRE comprises a number  of  different  sec-
70         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
71         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.
72         In the plain text format, all the sections are concatenated,  for  ease         In  the  plain text format, all the sections are concatenated, for ease
73         of searching. The sections are as follows:         of searching. The sections are as follows:
74    
75           pcre              this document           pcre              this document
# Line 83  USER DOCUMENTATION Line 84  USER DOCUMENTATION
84           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
85           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
86                               regular expressions                               regular expressions
87             pcresyntax        quick syntax reference
88           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
89           pcreposix         the POSIX-compatible C API           pcreposix         the POSIX-compatible C API
90           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
# Line 90  USER DOCUMENTATION Line 92  USER DOCUMENTATION
92           pcrestack         discussion of stack usage           pcrestack         discussion of stack usage
93           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
94    
95         In addition, in the "man" and HTML formats, there is a short  page  for         In  addition,  in the "man" and HTML formats, there is a short page for
96         each C library function, listing its arguments and results.         each C library function, listing its arguments and results.
97    
98    
99  LIMITATIONS  LIMITATIONS
100    
101         There  are some size limitations in PCRE but it is hoped that they will         There are some size limitations in PCRE but it is hoped that they  will
102         never in practice be relevant.         never in practice be relevant.
103    
104         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
105         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
106         process regular expressions that are truly enormous,  you  can  compile         process  regular  expressions  that are truly enormous, you can compile
107         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in         PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
108         the source distribution and the pcrebuild documentation  for  details).         the  source  distribution and the pcrebuild documentation for details).
109         In  these  cases the limit is substantially larger.  However, the speed         In these cases the limit is substantially larger.  However,  the  speed
110         of execution is slower.         of execution is slower.
111    
112         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.  
113    
114         There is no limit to the number of parenthesized subpatterns, but there         There is no limit to the number of parenthesized subpatterns, but there
115         can be no more than 65535 capturing subpatterns.         can be no more than 65535 capturing subpatterns.
# Line 117  LIMITATIONS Line 117  LIMITATIONS
117         The maximum length of name for a named subpattern is 32 characters, and         The maximum length of name for a named subpattern is 32 characters, and
118         the maximum number of named subpatterns is 10000.         the maximum number of named subpatterns is 10000.
119    
120         The maximum length of a subject string is the largest  positive  number         The  maximum  length of a subject string is the largest positive number
121         that  an integer variable can hold. However, when using the traditional         that an integer variable can hold. However, when using the  traditional
122         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         inite  repetition.  This means that the available stack space may limit         inite repetition.  This means that the available stack space may  limit
124         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
125         For a discussion of stack issues, see the pcrestack documentation.         For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130         From  release  3.3,  PCRE  has  had  some support for character strings         From release 3.3, PCRE has  had  some  support  for  character  strings
131         encoded in the UTF-8 format. For release 4.0 this was greatly  extended         encoded  in the UTF-8 format. For release 4.0 this was greatly extended
132         to  cover  most common requirements, and in release 5.0 additional sup-         to cover most common requirements, and in release 5.0  additional  sup-
133         port for Unicode general category properties was added.         port for Unicode general category properties was added.
134    
135         In order process UTF-8 strings, you must build PCRE  to  include  UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
136         support  in  the  code,  and, in addition, you must call pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
137         with the PCRE_UTF8 option flag. When you do this, both the pattern  and         with  the PCRE_UTF8 option flag. When you do this, both the pattern and
138         any  subject  strings  that are matched against it are treated as UTF-8         any subject strings that are matched against it are  treated  as  UTF-8
139         strings instead of just strings of bytes.         strings instead of just strings of bytes.
140    
141         If you compile PCRE with UTF-8 support, but do not use it at run  time,         If  you compile PCRE with UTF-8 support, but do not use it at run time,
142         the  library will be a bit bigger, but the additional run time overhead         the library will be a bit bigger, but the additional run time  overhead
143         is limited to testing the PCRE_UTF8 flag occasionally, so should not be         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144         very big.         very big.
145    
146         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
147         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
148         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
149         general category properties such as Lu for an upper case letter  or  Nd         general  category  properties such as Lu for an upper case letter or Nd
150         for  a  decimal number, the Unicode script names such as Arabic or Han,         for a decimal number, the Unicode script names such as Arabic  or  Han,
151         and the derived properties Any and L&. A full  list  is  given  in  the         and  the  derived  properties  Any  and L&. A full list is given in the
152         pcrepattern documentation. Only the short names for properties are sup-         pcrepattern documentation. Only the short names for properties are sup-
153         ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-         ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
154         ter},  is  not  supported.   Furthermore,  in Perl, many properties may         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
155         optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE         optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
156         does not support this.         does not support this.
157    
158         The following comments apply when PCRE is running in UTF-8 mode:     Validity of UTF-8 strings
159    
160           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
161           subjects are (by default) checked for validity on entry to the relevant
162           functions. From release 7.3 of PCRE, the check is according  the  rules
163           of  RFC  3629, which are themselves derived from the Unicode specifica-
164           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
165           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
166           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
167           to U+DFFF.
168    
169           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
170           which the Unicode Standard says this: "The Low Surrogate Area does  not
171           contain  any  character  assignments,  consequently  no  character code
172           charts or namelists are provided for this area. Surrogates are reserved
173           for  use  with  UTF-16 and then must be used in pairs." The code points
174           that are encoded by UTF-16 pairs  are  available  as  independent  code
175           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
176           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
177    
178           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
179           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
180           that your strings are valid, and therefore want to skip these checks in
181           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
182           compile time or at run time, PCRE assumes that the pattern  or  subject
183           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
184           case, it does not diagnose an invalid UTF-8 string.
185    
186           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
187           what  happens  depends on why the string is invalid. If the string con-
188           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
189           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
190           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
191           strings  according  to  the more liberal rules of RFC 2279. However, if
192           the string does not even conform to RFC 2279, the result is  undefined.
193           Your program may crash.
194    
195           If  you  want  to  process  strings  of  values  in the full range 0 to
196           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
197           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
198           this situation, you will have to apply your own validity check.
199    
200         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.  
201    
202         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
203         two-byte UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
204    
205         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
206         characters for values greater than \177.         characters for values greater than \177.
207    
208         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
209         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
210    
211         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-
212         gle byte.         gle byte.
213    
214         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
215         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
216         not available in the alternative matching function, pcre_dfa_exec().         not available in the alternative matching function, pcre_dfa_exec().
217    
218         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
219         test characters of any code value, but the characters that PCRE  recog-         test  characters of any code value, but the characters that PCRE recog-
220         nizes  as  digits,  spaces,  or  word characters remain the same set as         nizes as digits, spaces, or word characters  remain  the  same  set  as
221         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
222         includes  Unicode  property support, because to do otherwise would slow         includes Unicode property support, because to do otherwise  would  slow
223         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
224         sense  of,  say,  "digit",  you must use Unicode property tests such as         sense of, say, "digit", you must use Unicode  property  tests  such  as
225         \p{Nd}.         \p{Nd}.
226    
227         8. Similarly, characters that match the POSIX named  character  classes         7.  Similarly,  characters that match the POSIX named character classes
228         are all low-valued characters.         are all low-valued characters.
229    
230         9.  However,  the Perl 5.10 horizontal and vertical whitespace matching         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232         acters.         acters.
233    
234         10.  Case-insensitive  matching applies only to characters whose values         9. Case-insensitive matching applies only to  characters  whose  values
235         are less than 128, unless PCRE is built with Unicode property  support.         are  less than 128, unless PCRE is built with Unicode property support.
236         Even  when  Unicode  property support is available, PCRE still uses its         Even when Unicode property support is available, PCRE  still  uses  its
237         own character tables when checking the case of  low-valued  characters,         own  character  tables when checking the case of low-valued characters,
238         so  as not to degrade performance.  The Unicode property information is         so as not to degrade performance.  The Unicode property information  is
239         used only for characters with higher values. Even when Unicode property         used only for characters with higher values. Even when Unicode property
240         support is available, PCRE supports case-insensitive matching only when         support is available, PCRE supports case-insensitive matching only when
241         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
242         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-
243         ported by PCRE.         ported by PCRE.
244    
245    
# Line 219  AUTHOR Line 249  AUTHOR
249         University Computing Service         University Computing Service
250         Cambridge CB2 3QH, England.         Cambridge CB2 3QH, England.
251    
252         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,
253         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,
254         followed by the two digits 10, at the domain cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
255    
256    
257  REVISION  REVISION
258    
259         Last updated: 13 June 2007         Last updated: 09 August 2007
260         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
263    
264  PCREBUILD(3)                                                      PCREBUILD(3)  PCREBUILD(3)                                                      PCREBUILD(3)
265    
266    
# Line 331  CODE VALUE OF NEWLINE Line 361  CODE VALUE OF NEWLINE
361         conventional to use the standard for your operating system.         conventional to use the standard for your operating system.
362    
363    
364    WHAT \R MATCHES
365    
366           By default, the sequence \R in a pattern matches  any  Unicode  newline
367           sequence,  whatever  has  been selected as the line ending sequence. If
368           you specify
369    
370             --enable-bsr-anycrlf
371    
372           the default is changed so that \R matches only CR, LF, or  CRLF.  What-
373           ever  is selected when PCRE is built can be overridden when the library
374           functions are called.
375    
376    
377  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
378    
379         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 459  USING EBCDIC CODE Line 502  USING EBCDIC CODE
502    
503         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
504         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
505         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         This  is  the  case for most computer operating systems. PCRE can, how-
506         adding         ever, be compiled to run in an EBCDIC environment by adding
507    
508           --enable-ebcdic           --enable-ebcdic
509    
510         to the configure command. This setting implies --enable-rebuild-charta-         to the configure command. This setting implies --enable-rebuild-charta-
511         bles.         bles.  You  should  only  use  it if you know that you are in an EBCDIC
512           environment (for example, an IBM mainframe operating system).
513    
514    
515  SEE ALSO  SEE ALSO
# Line 482  AUTHOR Line 526  AUTHOR
526    
527  REVISION  REVISION
528    
529         Last updated: 05 June 2007         Last updated: 11 September 2007
530         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
531  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
532    
533    
534  PCREMATCHING(3)                                                PCREMATCHING(3)  PCREMATCHING(3)                                                PCREMATCHING(3)
535    
536    
# Line 626  THE ALTERNATIVE MATCHING ALGORITHM Line 670  THE ALTERNATIVE MATCHING ALGORITHM
670         6.  Callouts  are  supported, but the value of the capture_top field is         6.  Callouts  are  supported, but the value of the capture_top field is
671         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.
672    
673         7.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
674         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-
675         tive algorithm moves through the subject  string  one  character  at  a         tive algorithm moves through the subject  string  one  character  at  a
676         time, for all active paths through the tree.         time, for all active paths through the tree.
677    
678           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
679           ported.
680    
681    
682  ADVANTAGES OF THE ALTERNATIVE ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
683    
684         Using  the alternative matching algorithm provides the following advan-         Using the alternative matching algorithm provides the following  advan-
685         tages:         tages:
686    
687         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-
688         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
689         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
690         things with callouts.         things with callouts.
691    
692         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
693         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-
694         rithm  for  partial matching do not apply to the alternative algorithm.         rithm for partial matching do not apply to the  alternative  algorithm.
695         For non-anchored patterns, the starting position of a partial match  is         For  non-anchored patterns, the starting position of a partial match is
696         available.         available.
697    
698         3.  Because  the  alternative  algorithm  scans the subject string just         3. Because the alternative algorithm  scans  the  subject  string  just
699         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
700         subject  strings  to  the matching function in several pieces, checking         subject strings to the matching function in  several  pieces,  checking
701         for partial matching each time.         for partial matching each time.
702    
703    
# Line 658  DISADVANTAGES OF THE ALTERNATIVE ALGORIT Line 705  DISADVANTAGES OF THE ALTERNATIVE ALGORIT
705    
706         The alternative algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
707    
708         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
709         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
710         because it is less susceptible to optimization.         because it is less susceptible to optimization.
711    
712         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
# Line 677  AUTHOR Line 724  AUTHOR
724    
725  REVISION  REVISION
726    
727         Last updated: 29 May 2007         Last updated: 08 August 2007
728         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
729  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
730    
731    
732  PCREAPI(3)                                                          PCREAPI(3)  PCREAPI(3)                                                          PCREAPI(3)
733    
734    
# Line 874  NEWLINES Line 921  NEWLINES
921         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
922         pattern is compiled, or when it is matched.         pattern is compiled, or when it is matched.
923    
924           At compile time, the newline convention can be specified by the options
925           argument of pcre_compile(), or it can be specified by special  text  at
926           the start of the pattern itself; this overrides any other settings. See
927           the pcrepattern page for details of the special character sequences.
928    
929         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-
930         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
931         newline  convention  affects  the  handling of the dot, circumflex, and         newline convention affects the handling of  the  dot,  circumflex,  and
932         dollar metacharacters, the handling of #-comments in /x mode, and, when         dollar metacharacters, the handling of #-comments in /x mode, and, when
933         CRLF  is a recognized line ending sequence, the match position advance-         CRLF is a recognized line ending sequence, the match position  advance-
934         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
935         not affect the interpretation of the \n or \r escape sequences.         section on pcre_exec() options below.
936    
937           The choice of newline convention does not affect the interpretation  of
938           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
939           which is controlled in a similar way, but by separate options.
940    
941    
942  MULTITHREADING  MULTITHREADING
943    
944         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
945         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
946         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
947         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
948    
949         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
950         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
951         at once.         at once.
952    
# Line 898  MULTITHREADING Line 954  MULTITHREADING
954  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
955    
956         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
957         later time, possibly by a different program, and even on a  host  other         later  time,  possibly by a different program, and even on a host other
958         than  the  one  on  which  it  was  compiled.  Details are given in the         than the one on which  it  was  compiled.  Details  are  given  in  the
959         pcreprecompile documentation. However, compiling a  regular  expression         pcreprecompile  documentation.  However, compiling a regular expression
960         with  one version of PCRE for use with a different version is not guar-         with one version of PCRE for use with a different version is not  guar-
961         anteed to work and may cause crashes.         anteed to work and may cause crashes.
962    
963    
# Line 909  CHECKING BUILD-TIME OPTIONS Line 965  CHECKING BUILD-TIME OPTIONS
965    
966         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
967    
968         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
969         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
970         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
971         tures.         tures.
972    
973         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
974         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
975         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
976         available:         available:
977    
978           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
979    
980         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
981         able; otherwise it is set to zero.         able; otherwise it is set to zero.
982    
983           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
984    
985         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
986         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
987    
988           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
989    
990         The output is an integer whose value specifies  the  default  character         The  output  is  an integer whose value specifies the default character
991         sequence  that is recognized as meaning "newline". The four values that         sequence that is recognized as meaning "newline". The four values  that
992         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,
993         and  -1  for  ANY. The default should normally be the standard sequence         and -1 for ANY. The default should normally be  the  standard  sequence
994         for your operating system.         for your operating system.
995    
996             PCRE_CONFIG_BSR
997    
998           The output is an integer whose value indicates what character sequences
999           the \R escape sequence matches by default. A value of 0 means  that  \R
1000           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1001           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1002           tern is compiled or matched.
1003    
1004           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1005    
1006         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
1007         internal linkage in compiled regular expressions. The value is 2, 3, or         internal linkage in compiled regular expressions. The value is 2, 3, or
1008         4. Larger values allow larger regular expressions to  be  compiled,  at         4.  Larger  values  allow larger regular expressions to be compiled, at
1009         the  expense  of  slower matching. The default value of 2 is sufficient         the expense of slower matching. The default value of  2  is  sufficient
1010         for all but the most massive patterns, since  it  allows  the  compiled         for  all  but  the  most massive patterns, since it allows the compiled
1011         pattern to be up to 64K in size.         pattern to be up to 64K in size.
1012    
1013           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1014    
1015         The  output  is  an integer that contains the threshold above which the         The output is an integer that contains the threshold  above  which  the
1016         POSIX interface uses malloc() for output vectors. Further  details  are         POSIX  interface  uses malloc() for output vectors. Further details are
1017         given in the pcreposix documentation.         given in the pcreposix documentation.
1018    
1019           PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
1020    
1021         The output is an integer that gives the default limit for the number of         The output is an integer that gives the default limit for the number of
1022         internal matching function calls in a  pcre_exec()  execution.  Further         internal  matching  function  calls in a pcre_exec() execution. Further
1023         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1024    
1025           PCRE_CONFIG_MATCH_LIMIT_RECURSION           PCRE_CONFIG_MATCH_LIMIT_RECURSION
1026    
1027         The  output is an integer that gives the default limit for the depth of         The output is an integer that gives the default limit for the depth  of
1028         recursion when calling the internal matching function in a  pcre_exec()         recursion  when calling the internal matching function in a pcre_exec()
1029         execution. Further details are given with pcre_exec() below.         execution. Further details are given with pcre_exec() below.
1030    
1031           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1032    
1033         The  output is an integer that is set to one if internal recursion when         The output is an integer that is set to one if internal recursion  when
1034         running pcre_exec() is implemented by recursive function calls that use         running pcre_exec() is implemented by recursive function calls that use
1035         the  stack  to remember their state. This is the usual way that PCRE is         the stack to remember their state. This is the usual way that  PCRE  is
1036         compiled. The output is zero if PCRE was compiled to use blocks of data         compiled. The output is zero if PCRE was compiled to use blocks of data
1037         on  the  heap  instead  of  recursive  function  calls.  In  this case,         on the  heap  instead  of  recursive  function  calls.  In  this  case,
1038         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory         pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1039         blocks on the heap, thus avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
1040    
1041    
# Line 988  COMPILING A PATTERN Line 1052  COMPILING A PATTERN
1052    
1053         Either of the functions pcre_compile() or pcre_compile2() can be called         Either of the functions pcre_compile() or pcre_compile2() can be called
1054         to compile a pattern into an internal form. The only difference between         to compile a pattern into an internal form. The only difference between
1055         the  two interfaces is that pcre_compile2() has an additional argument,         the two interfaces is that pcre_compile2() has an additional  argument,
1056         errorcodeptr, via which a numerical error code can be returned.         errorcodeptr, via which a numerical error code can be returned.
1057    
1058         The pattern is a C string terminated by a binary zero, and is passed in         The pattern is a C string terminated by a binary zero, and is passed in
1059         the  pattern  argument.  A  pointer to a single block of memory that is         the pattern argument. A pointer to a single block  of  memory  that  is
1060         obtained via pcre_malloc is returned. This contains the  compiled  code         obtained  via  pcre_malloc is returned. This contains the compiled code
1061         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1062         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1063         It is up to the caller to free the memory (via pcre_free) when it is no         It is up to the caller to free the memory (via pcre_free) when it is no
1064         longer required.         longer required.
1065    
1066         Although the compiled code of a PCRE regex is relocatable, that is,  it         Although  the compiled code of a PCRE regex is relocatable, that is, it
1067         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1068         fully relocatable, because it may contain a copy of the tableptr  argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1069         ment, which is an address (see below).         ment, which is an address (see below).
1070    
1071         The options argument contains various bit settings that affect the com-         The options argument contains various bit settings that affect the com-
1072         pilation. It should be zero if no options are required.  The  available         pilation.  It  should be zero if no options are required. The available
1073         options  are  described  below. Some of them, in particular, those that         options are described below. Some of them, in  particular,  those  that
1074         are compatible with Perl, can also be set and  unset  from  within  the         are  compatible  with  Perl,  can also be set and unset from within the
1075         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1076         tion). For these options, the contents of the options  argument  speci-         tion).  For  these options, the contents of the options argument speci-
1077         fies  their initial settings at the start of compilation and execution.         fies their initial settings at the start of compilation and  execution.
1078         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1079         of matching as well as at compile time.         of matching as well as at compile time.
1080    
1081         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1082         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1083         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1084         sage. This is a static string that is part of the library. You must not         sage. This is a static string that is part of the library. You must not
1085         try to free it. The offset from the start of the pattern to the charac-         try to free it. The offset from the start of the pattern to the charac-
1086         ter where the error was discovered is placed in the variable pointed to         ter where the error was discovered is placed in the variable pointed to
1087         by  erroffset,  which must not be NULL. If it is, an immediate error is         by erroffset, which must not be NULL. If it is, an immediate  error  is
1088         given.         given.
1089    
1090         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1091         codeptr  argument is not NULL, a non-zero error code number is returned         codeptr argument is not NULL, a non-zero error code number is  returned
1092         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1093         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1094    
1095         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1096         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1097         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1098         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1099         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1100         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1101         support below.         support below.
1102    
1103         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1104         pile():         pile():
1105    
1106           pcre *re;           pcre *re;
# Line 1049  COMPILING A PATTERN Line 1113  COMPILING A PATTERN
1113             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1114             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1115    
1116         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1117         file:         file:
1118    
1119           PCRE_ANCHORED           PCRE_ANCHORED
1120    
1121         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1122         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1123         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1124         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1125         only way to do it in Perl.         only way to do it in Perl.
1126    
1127           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1128    
1129         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1130         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1131         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1132    
1133             PCRE_BSR_ANYCRLF
1134             PCRE_BSR_UNICODE
1135    
1136           These options (which are mutually exclusive) control what the \R escape
1137           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1138           or to match any Unicode newline sequence. The default is specified when
1139           PCRE is built. It can be overridden from within the pattern, or by set-
1140           ting an option when a compiled pattern is matched.
1141    
1142           PCRE_CASELESS           PCRE_CASELESS
1143    
1144         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
1145         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1146         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1147         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1148         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1149         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1150         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1151         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1152         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1153         UTF-8 support.         UTF-8 support.
1154    
1155           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1156    
1157         If this bit is set, a dollar metacharacter in the pattern matches  only         If  this bit is set, a dollar metacharacter in the pattern matches only
1158         at  the  end  of the subject string. Without this option, a dollar also         at the end of the subject string. Without this option,  a  dollar  also
1159         matches immediately before a newline at the end of the string (but  not         matches  immediately before a newline at the end of the string (but not
1160         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1161         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1162         Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1163    
1164           PCRE_DOTALL           PCRE_DOTALL
1165    
1166         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1167         acters, including those that indicate newline. Without it, a  dot  does         acters,  including  those that indicate newline. Without it, a dot does
1168         not  match  when  the  current position is at a newline. This option is         not match when the current position is at a  newline.  This  option  is
1169         equivalent to Perl's /s option, and it can be changed within a  pattern         equivalent  to Perl's /s option, and it can be changed within a pattern
1170         by  a (?s) option setting. A negative class such as [^a] always matches         by a (?s) option setting. A negative class such as [^a] always  matches
1171         newline characters, independent of the setting of this option.         newline characters, independent of the setting of this option.
1172    
1173           PCRE_DUPNAMES           PCRE_DUPNAMES
1174    
1175         If this bit is set, names used to identify capturing  subpatterns  need         If  this  bit is set, names used to identify capturing subpatterns need
1176         not be unique. This can be helpful for certain types of pattern when it         not be unique. This can be helpful for certain types of pattern when it
1177         is known that only one instance of the named  subpattern  can  ever  be         is  known  that  only  one instance of the named subpattern can ever be
1178         matched.  There  are  more details of named subpatterns below; see also         matched. There are more details of named subpatterns  below;  see  also
1179         the pcrepattern documentation.         the pcrepattern documentation.
1180    
1181           PCRE_EXTENDED           PCRE_EXTENDED
1182    
1183         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1184         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1185         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1186         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1187         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1188         option,  and  it  can be changed within a pattern by a (?x) option set-         option, and it can be changed within a pattern by a  (?x)  option  set-
1189         ting.         ting.
1190    
1191         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1192         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1193         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1194         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1195         introduces a conditional subpattern.         introduces a conditional subpattern.
1196    
1197           PCRE_EXTRA           PCRE_EXTRA
1198    
1199         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1200         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1201         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1202         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1203         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1204         backslash  followed by a letter with no special meaning is treated as a         backslash followed by a letter with no special meaning is treated as  a
1205         literal. (Perl can, however, be persuaded to give a warning for  this.)         literal.  (Perl can, however, be persuaded to give a warning for this.)
1206         There  are  at  present no other features controlled by this option. It         There are at present no other features controlled by  this  option.  It
1207         can also be set by a (?X) option setting within a pattern.         can also be set by a (?X) option setting within a pattern.
1208    
1209           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1210    
1211         If this option is set, an  unanchored  pattern  is  required  to  match         If  this  option  is  set,  an  unanchored pattern is required to match
1212         before  or  at  the  first  newline  in  the subject string, though the         before or at the first  newline  in  the  subject  string,  though  the
1213         matched text may continue over the newline.         matched text may continue over the newline.
1214    
1215           PCRE_MULTILINE           PCRE_MULTILINE
1216    
1217         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
1218         line  of characters (even if it actually contains newlines). The "start         line of characters (even if it actually contains newlines). The  "start
1219         of line" metacharacter (^) matches only at the  start  of  the  string,         of  line"  metacharacter  (^)  matches only at the start of the string,
1220         while  the  "end  of line" metacharacter ($) matches only at the end of         while the "end of line" metacharacter ($) matches only at  the  end  of
1221         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1222         is set). This is the same as Perl.         is set). This is the same as Perl.
1223    
1224         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"
1225         constructs match immediately following or immediately  before  internal         constructs  match  immediately following or immediately before internal
1226         newlines  in  the  subject string, respectively, as well as at the very         newlines in the subject string, respectively, as well as  at  the  very
1227         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
1228         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-
1229         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,
1230         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1231    
1232           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
# Line 1162  COMPILING A PATTERN Line 1235  COMPILING A PATTERN
1235           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1236           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1237    
1238         These  options  override the default newline definition that was chosen         These options override the default newline definition that  was  chosen
1239         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
1240         newline  is  indicated  by a single character (CR or LF, respectively).         newline is indicated by a single character (CR  or  LF,  respectively).
1241         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the         Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1242         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies         two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1243         that any of the three preceding sequences should be recognized. Setting         that any of the three preceding sequences should be recognized. Setting
1244         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be         PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1245         recognized. The Unicode newline sequences are the three just mentioned,         recognized. The Unicode newline sequences are the three just mentioned,
1246         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,         plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1247         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
1248         (paragraph  separator,  U+2029).  The  last  two are recognized only in         (paragraph separator, U+2029). The last  two  are  recognized  only  in
1249         UTF-8 mode.         UTF-8 mode.
1250    
1251         The newline setting in the  options  word  uses  three  bits  that  are         The  newline  setting  in  the  options  word  uses three bits that are
1252         treated as a number, giving eight possibilities. Currently only six are         treated as a number, giving eight possibilities. Currently only six are
1253         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
1254         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-
1255         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
1256         PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and         PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1257         cause an error.         cause an error.
1258    
1259         The only time that a line break is specially recognized when  compiling         The  only time that a line break is specially recognized when compiling
1260         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
1261         character class is encountered. This indicates  a  comment  that  lasts         character  class  is  encountered.  This indicates a comment that lasts
1262         until  after the next line break sequence. In other circumstances, line         until after the next line break sequence. In other circumstances,  line
1263         break  sequences  are  treated  as  literal  data,   except   that   in         break   sequences   are   treated  as  literal  data,  except  that  in
1264         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters         PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1265         and are therefore ignored.         and are therefore ignored.
1266    
1267         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
1268         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.
1269    
1270           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1271    
1272         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1273         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1274         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1275         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1276         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1277    
1278           PCRE_UNGREEDY           PCRE_UNGREEDY
1279    
1280         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1281         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1282         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1283         within the pattern.         within the pattern.
1284    
1285           PCRE_UTF8           PCRE_UTF8
1286    
1287         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1288         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1289         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1290         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1291         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1292         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1293    
1294           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1295    
1296         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
1297         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1298         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
1299         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
1300         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-
1301         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
1302         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
1303         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
1304         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1305           UTF-8 validity checking of subject strings.
1306    
1307    
1308  COMPILATION ERROR CODES  COMPILATION ERROR CODES
# Line 1288  COMPILATION ERROR CODES Line 1362  COMPILATION ERROR CODES
1362           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1363           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1364           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10,000)
1365           50  repeated subpattern is too long           50  [this code is not in use]
1366           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1367           52  internal error: overran compiling workspace           52  internal error: overran compiling workspace
1368           53   internal  error:  previously-checked  referenced  subpattern not           53   internal  error:  previously-checked  referenced  subpattern not
1369         found         found
1370           54  DEFINE group contains more than one branch           54  DEFINE group contains more than one branch
1371           55  repeating a DEFINE group is not allowed           55  repeating a DEFINE group is not allowed
1372           56  inconsistent NEWLINE options"           56  inconsistent NEWLINE options
1373           57  \g is not followed by a braced name or an optionally braced           57  \g is not followed by a braced name or an optionally braced
1374                 non-zero number                 non-zero number
1375           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number           58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
# Line 1487  INFORMATION ABOUT A PATTERN Line 1561  INFORMATION ABOUT A PATTERN
1561         returned. The fourth argument should point to an unsigned char *  vari-         returned. The fourth argument should point to an unsigned char *  vari-
1562         able.         able.
1563    
1564             PCRE_INFO_HASCRORLF
1565    
1566           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1567           characters, otherwise 0. The fourth argument should  point  to  an  int
1568           variable.  An explicit match is either a literal CR or LF character, or
1569           \r or \n.
1570    
1571           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1572    
1573         Return  1  if the (?J) option setting is used in the pattern, otherwise         Return 1 if the (?J) option setting is used in the  pattern,  otherwise
1574         0. The fourth argument should point to an int variable. The (?J) inter-         0. The fourth argument should point to an int variable. The (?J) inter-
1575         nal option setting changes the local PCRE_DUPNAMES option.         nal option setting changes the local PCRE_DUPNAMES option.
1576    
1577           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1578    
1579         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
1580         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
1581         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1582         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
1583         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1584         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
1585         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1586    
# Line 1507  INFORMATION ABOUT A PATTERN Line 1588  INFORMATION ABOUT A PATTERN
1588           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1589           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1590    
1591         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1592         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1593         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1594         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1595         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
1596         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
1597         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1598         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
1599         described by these three values.         described by these three values.
1600    
1601         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
1602         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1603         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
1604         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1605         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
1606         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-
1607         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-
1608         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1609         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-
1610         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1611         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1612         ignored):         ignored):
1613    
1614           (?<date> (?<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1615           (?<month>\d\d) - (?<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1616    
1617         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1618         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,
1619         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1620         as ??:         as ??:
1621    
# Line 1543  INFORMATION ABOUT A PATTERN Line 1624  INFORMATION ABOUT A PATTERN
1624           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1625           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1626    
1627         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1628         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
1629         to be different for each compiled pattern.         to be different for each compiled pattern.
1630    
1631           PCRE_INFO_OKPARTIAL           PCRE_INFO_OKPARTIAL
1632    
1633         Return  1 if the pattern can be used for partial matching, otherwise 0.         Return 1 if the pattern can be used for partial matching, otherwise  0.
1634         The fourth argument should point to an int  variable.  The  pcrepartial         The  fourth  argument  should point to an int variable. The pcrepartial
1635         documentation  lists  the restrictions that apply to patterns when par-         documentation lists the restrictions that apply to patterns  when  par-
1636         tial matching is used.         tial matching is used.
1637    
1638           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1639    
1640         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
1641         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1642         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1643         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1644           other  words,  they are the options that will be in force when matching
1645           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1646           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1647           and PCRE_EXTENDED.
1648    
1649         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
1650         alternatives begin with one of the following:         alternatives begin with one of the following:
1651    
1652           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1575  INFORMATION ABOUT A PATTERN Line 1660  INFORMATION ABOUT A PATTERN
1660    
1661           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1662    
1663         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1664         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1665         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1666         size_t variable.         size_t variable.
# Line 1583  INFORMATION ABOUT A PATTERN Line 1668  INFORMATION ABOUT A PATTERN
1668           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1669    
1670         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1671         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1672         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1673         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1674         variable.         variable.
1675    
1676    
# Line 1593  OBSOLETE INFO FUNCTION Line 1678  OBSOLETE INFO FUNCTION
1678    
1679         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1680    
1681         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1682         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1683         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1684         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1685         lowing negative numbers:         lowing negative numbers:
1686    
1687           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1688           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1689    
1690         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1691         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1692         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1693    
1694         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1695         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1696         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1697    
1698    
# Line 1615  REFERENCE COUNTS Line 1700  REFERENCE COUNTS
1700    
1701         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1702    
1703         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1704         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1705         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1706         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1707         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1708    
1709         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1710         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1711         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1712         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1713         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1714         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1715    
1716         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1717         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1718         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1719    
1720    
# Line 1639  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1724  MATCHING A PATTERN: THE TRADITIONAL FUNC
1724              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1725              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1726    
1727         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
1728         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1729         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
1730         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1731         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
1732         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1733         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1734    
1735         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1736         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1737         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
1738         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1739         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1740    
1741         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1669  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1754  MATCHING A PATTERN: THE TRADITIONAL FUNC
1754    
1755     Extra data for pcre_exec()     Extra data for pcre_exec()
1756    
1757         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
1758         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
1759         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-
1760         tional  information  in it. The pcre_extra block contains the following         tional information in it. The pcre_extra block contains  the  following
1761         fields (not necessarily in this order):         fields (not necessarily in this order):
1762    
1763           unsigned long int flags;           unsigned long int flags;
# Line 1682  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1767  MATCHING A PATTERN: THE TRADITIONAL FUNC
1767           void *callout_data;           void *callout_data;
1768           const unsigned char *tables;           const unsigned char *tables;
1769    
1770         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
1771         are set. The flag bits are:         are set. The flag bits are:
1772    
1773           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1776  MATCHING A PATTERN: THE TRADITIONAL FUNC
1776           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1777           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1778    
1779         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
1780         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1781         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
1782         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1783         flag bits.         flag bits.
1784    
1785         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
1786         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
1787         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1788         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1789         repeats.         repeats.
1790    
1791         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1792         edly (sometimes recursively). The limit set by match_limit  is  imposed         edly  (sometimes  recursively). The limit set by match_limit is imposed
1793         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
1794         has the effect of limiting the amount of  backtracking  that  can  take         has  the  effect  of  limiting the amount of backtracking that can take
1795         place. For patterns that are not anchored, the count restarts from zero         place. For patterns that are not anchored, the count restarts from zero
1796         for each position in the subject string.         for each position in the subject string.
1797    
1798         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
1799         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1800         cases. You can override the default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1801         pcre_extra     block    in    which    match_limit    is    set,    and         pcre_extra    block    in    which    match_limit    is    set,     and
1802         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
1803         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1804    
1805         The  match_limit_recursion field is similar to match_limit, but instead         The match_limit_recursion field is similar to match_limit, but  instead
1806         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
1807         the  depth  of  recursion. The recursion depth is a smaller number than         the depth of recursion. The recursion depth is a  smaller  number  than
1808         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-
1809         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.
1810    
1811         Limiting the recursion depth limits the amount of  stack  that  can  be         Limiting  the  recursion  depth  limits the amount of stack that can be
1812         used, or, when PCRE has been compiled to use memory on the heap instead         used, or, when PCRE has been compiled to use memory on the heap instead
1813         of the stack, the amount of heap memory that can be used.         of the stack, the amount of heap memory that can be used.
1814    
1815         The default value for match_limit_recursion can be  set  when  PCRE  is         The  default  value  for  match_limit_recursion can be set when PCRE is
1816         built;  the  default  default  is  the  same  value  as the default for         built; the default default  is  the  same  value  as  the  default  for
1817         match_limit. You can override the default by suppling pcre_exec()  with         match_limit.  You can override the default by suppling pcre_exec() with
1818         a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and         a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1819         PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the         PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1820         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.         limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1821    
1822         The  pcre_callout  field is used in conjunction with the "callout" fea-         The pcre_callout field is used in conjunction with the  "callout"  fea-
1823         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1824    
1825         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1826         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1827         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1828         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1829         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1830         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1831         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1832         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1833         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1834         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1835    
1836     Option bits for pcre_exec()     Option bits for pcre_exec()
1837    
1838         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.
1839         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,
1840         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1841         PCRE_PARTIAL.         PCRE_PARTIAL.
1842    
1843           PCRE_ANCHORED           PCRE_ANCHORED
1844    
1845         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1846         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1847         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
1848         unachored at matching time.         unachored at matching time.
1849    
1850             PCRE_BSR_ANYCRLF
1851             PCRE_BSR_UNICODE
1852    
1853           These options (which are mutually exclusive) control what the \R escape
1854           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1855           or to match any Unicode newline sequence. These  options  override  the
1856           choice that was made or defaulted when the pattern was compiled.
1857    
1858           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1859           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1860           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
# Line 1773  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1866  MATCHING A PATTERN: THE TRADITIONAL FUNC
1866         tion  of  pcre_compile()  above.  During  matching,  the newline choice         tion  of  pcre_compile()  above.  During  matching,  the newline choice
1867         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1868         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
1869         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
1870         PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt  
1871         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
1872         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-
1873         after the CRLF.         rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1874           explicit  matches  for  CR  or  LF  characters,  the  match position is
1875           advanced by two characters instead of one, in other words, to after the
1876           CRLF.
1877    
1878           The above rule is a compromise that makes the most common cases work as
1879           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1880           option is not set), it does not match the string "\r\nA" because, after
1881           failing at the start, it skips both the CR and the LF before  retrying.
1882           However,  the  pattern  [\r\n]A does match that string, because it con-
1883           tains an explicit CR or LF reference, and so advances only by one char-
1884           acter after the first failure.
1885    
1886           An explicit match for CR of LF is either a literal appearance of one of
1887           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1888           matches  such  as [^X] do not count, nor does \s (which includes CR and
1889           LF in the characters that it matches).
1890    
1891           Notwithstanding the above, anomalous effects may still occur when  CRLF
1892           is a valid newline sequence and explicit \r or \n escapes appear in the
1893           pattern.
1894    
1895           PCRE_NOTBOL           PCRE_NOTBOL
1896    
# Line 1824  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1937  MATCHING A PATTERN: THE TRADITIONAL FUNC
1937         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
1938         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1939         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
1940         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
1941         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
1942         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
1943         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
1944           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1945         If you already know that your subject is valid, and you  want  to  skip  
1946         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
1947         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
1948         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
1949         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
1950         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
1951         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
1952         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
1953         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
1954           value  of startoffset that does not point to the start of a UTF-8 char-
1955         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1956    
1957           PCRE_PARTIAL           PCRE_PARTIAL
1958    
1959         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1960         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-
1961         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
1962         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1963         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1964         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1965         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1966         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1967    
1968     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1969    
1970         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
1971         length  in  length, and a starting byte offset in startoffset. In UTF-8         length in length, and a starting byte offset in startoffset.  In  UTF-8
1972         mode, the byte offset must point to the start  of  a  UTF-8  character.         mode,  the  byte  offset  must point to the start of a UTF-8 character.
1973         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
1974         When the starting offset is zero, the search for a match starts at  the         When  the starting offset is zero, the search for a match starts at the
1975         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1976    
1977         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
1978         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-
1979         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
1980         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1981         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1982    
1983           \Biss\B           \Biss\B
1984    
1985         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1986         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
1987         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
1988         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
1989         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1990         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1991         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1992         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1993         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
1994         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1995    
1996         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
1997         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1998         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
1999         subject.         subject.
2000    
2001     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2002    
2003         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2004         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2005         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2006         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2007         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2008         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2009         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2010    
2011         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2012         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2013         the  vector is passed in ovecsize, which must be a non-negative number.         the vector is passed in ovecsize, which must be a non-negative  number.
2014         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
2015    
2016         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-
2017         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2018         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-
2019         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2020         The length passed in ovecsize should always be a multiple of three.  If         The  length passed in ovecsize should always be a multiple of three. If
2021         it is not, it is rounded down.         it is not, it is rounded down.
2022    
2023         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2024         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2025         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
2026         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
2027         string,  and  the  second  is  set to the offset of the first character         string, and the second is set to the  offset  of  the  first  character
2028         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2029         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
2030         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2031         tern, and so on. The value returned by pcre_exec() is one more than the         tern, and so on. The value returned by pcre_exec() is one more than the
2032         highest numbered pair that has been set. For example, if two substrings         highest numbered pair that has been set. For example, if two substrings
2033         have  been captured, the returned value is 3. If there are no capturing         have been captured, the returned value is 3. If there are no  capturing
2034         subpatterns, the return value from a successful match is 1,  indicating         subpatterns,  the return value from a successful match is 1, indicating
2035         that just the first pair of offsets has been set.         that just the first pair of offsets has been set.
2036    
2037         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2038         of the string that it matched that is returned.         of the string that it matched that is returned.
2039    
2040         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,
2041         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
2042         function returns a value of zero. In particular, if the substring  off-         function  returns a value of zero. In particular, if the substring off-
2043         sets are not of interest, pcre_exec() may be called with ovector passed         sets are not of interest, pcre_exec() may be called with ovector passed
2044         as NULL and ovecsize as zero. However, if  the  pattern  contains  back         as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2045         references  and  the  ovector is not big enough to remember the related         references and the ovector is not big enough to  remember  the  related
2046         substrings, PCRE has to get additional memory for use during  matching.         substrings,  PCRE has to get additional memory for use during matching.
2047         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2048    
2049         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
2050         subpatterns there are in a compiled  pattern.  The  smallest  size  for         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2051         ovector  that  will allow for n captured substrings, in addition to the         ovector that will allow for n captured substrings, in addition  to  the
2052         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.
2053    
2054         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
2055         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,
2056         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
2057         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
2058         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-
2059         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
2060    
2061         Offset  values  that correspond to unused subpatterns at the end of the         Offset values that correspond to unused subpatterns at the end  of  the
2062         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
2063         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
2064         matched. The return from the function is 2, because  the  highest  used         matched.  The  return  from the function is 2, because the highest used
2065         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
2066         for the second and third capturing subpatterns if  you  wish  (assuming         for  the  second  and third capturing subpatterns if you wish (assuming
2067         the vector is large enough, of course).         the vector is large enough, of course).
2068    
2069         Some  convenience  functions  are  provided for extracting the captured         Some convenience functions are provided  for  extracting  the  captured
2070         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
2071    
2072     Error return values from pcre_exec()     Error return values from pcre_exec()
2073    
2074         If pcre_exec() fails, it returns a negative number. The  following  are         If  pcre_exec()  fails, it returns a negative number. The following are
2075         defined in the header file:         defined in the header file:
2076    
2077           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1966  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2080  MATCHING A PATTERN: THE TRADITIONAL FUNC
2080    
2081           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2082    
2083         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
2084         ovecsize was not zero.         ovecsize was not zero.
2085    
2086           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1975  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2089  MATCHING A PATTERN: THE TRADITIONAL FUNC
2089    
2090           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2091    
2092         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,
2093         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
2094         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
2095         an  environment  with the other endianness. This is the error that PCRE         an environment with the other endianness. This is the error  that  PCRE
2096         gives when the magic number is not present.         gives when the magic number is not present.
2097    
2098           PCRE_ERROR_UNKNOWN_OPCODE (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2099    
2100         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2101         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
2102         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2103    
2104           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2105    
2106         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
2107         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2108         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
2109         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
2110         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2111    
2112           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2113    
2114         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2115         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2116         returned by pcre_exec().         returned by pcre_exec().
2117    
2118           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2119    
2120         The backtracking limit, as specified by  the  match_limit  field  in  a         The  backtracking  limit,  as  specified  by the match_limit field in a
2121         pcre_extra  structure  (or  defaulted) was reached. See the description         pcre_extra structure (or defaulted) was reached.  See  the  description
2122         above.         above.
2123    
2124           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2125    
2126         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
2127         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
2128         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2129    
2130           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2131    
2132         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
2133         subject.         subject.
2134    
2135           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2136    
2137         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
2138         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-
2139         ter.         ter.
2140    
2141           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2142    
2143         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
2144         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2145    
2146           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2147    
2148         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2149         items  that are not supported for partial matching. See the pcrepartial         items that are not supported for partial matching. See the  pcrepartial
2150         documentation for details of partial matching.         documentation for details of partial matching.
2151    
2152           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2153    
2154         An unexpected internal error has occurred. This error could  be  caused         An  unexpected  internal error has occurred. This error could be caused
2155         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2156    
2157           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2158    
2159         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.
2160    
2161           PCRE_ERROR_RECURSIONLIMIT (-21)           PCRE_ERROR_RECURSIONLIMIT (-21)
2162    
2163         The internal recursion limit, as specified by the match_limit_recursion         The internal recursion limit, as specified by the match_limit_recursion
2164         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2165         description above.         description above.
2166    
          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.  
   
2167           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2168    
2169         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2170    
2171         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2172    
2173    
2174  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2078  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2184  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2184         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2185              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2186    
2187         Captured substrings can be  accessed  directly  by  using  the  offsets         Captured  substrings  can  be  accessed  directly  by using the offsets
2188         returned  by  pcre_exec()  in  ovector.  For convenience, the functions         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2189         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2190         string_list()  are  provided for extracting captured substrings as new,         string_list() are provided for extracting captured substrings  as  new,
2191         separate, zero-terminated strings. These functions identify  substrings         separate,  zero-terminated strings. These functions identify substrings
2192         by  number.  The  next section describes functions for extracting named         by number. The next section describes functions  for  extracting  named
2193         substrings.         substrings.
2194    
2195         A substring that contains a binary zero is correctly extracted and  has         A  substring that contains a binary zero is correctly extracted and has
2196         a  further zero added on the end, but the result is not, of course, a C         a further zero added on the end, but the result is not, of course, a  C
2197         string.  However, you can process such a string  by  referring  to  the         string.   However,  you  can  process such a string by referring to the
2198         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2199         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2200         not  adequate for handling strings containing binary zeros, because the         not adequate for handling strings containing binary zeros, because  the
2201         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2202    
2203         The first three arguments are the same for all  three  of  these  func-         The  first  three  arguments  are the same for all three of these func-
2204         tions:  subject  is  the subject string that has just been successfully         tions: subject is the subject string that has  just  been  successfully
2205         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2206         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2207         were captured by the match, including the substring  that  matched  the         were  captured  by  the match, including the substring that matched the
2208         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2209         it is greater than zero. If pcre_exec() returned zero, indicating  that         it  is greater than zero. If pcre_exec() returned zero, indicating that
2210         it  ran out of space in ovector, the value passed as stringcount should         it ran out of space in ovector, the value passed as stringcount  should
2211         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2212    
2213         The functions pcre_copy_substring() and pcre_get_substring() extract  a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2214         single  substring,  whose  number  is given as stringnumber. A value of         single substring, whose number is given as  stringnumber.  A  value  of
2215         zero extracts the substring that matched the  entire  pattern,  whereas         zero  extracts  the  substring that matched the entire pattern, whereas
2216         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2217         string(), the string is placed in buffer,  whose  length  is  given  by         string(),  the  string  is  placed  in buffer, whose length is given by
2218         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2219         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2220         The  yield  of  the function is the length of the string, not including         The yield of the function is the length of the  string,  not  including
2221         the terminating zero, or one of these error codes:         the terminating zero, or one of these error codes:
2222    
2223           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2224    
2225         The buffer was too small for pcre_copy_substring(), or the  attempt  to         The  buffer  was too small for pcre_copy_substring(), or the attempt to
2226         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2227    
2228           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2229    
2230         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2231    
2232         The  pcre_get_substring_list()  function  extracts  all  available sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
2233         strings and builds a list of pointers to them. All this is  done  in  a         strings  and  builds  a list of pointers to them. All this is done in a
2234         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2235         the memory block is returned via listptr, which is also  the  start  of         the  memory  block  is returned via listptr, which is also the start of
2236         the  list  of  string pointers. The end of the list is marked by a NULL         the list of string pointers. The end of the list is marked  by  a  NULL
2237         pointer. The yield of the function is zero if all  went  well,  or  the         pointer.  The  yield  of  the function is zero if all went well, or the
2238         error code         error code
2239    
2240           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2241    
2242         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2243    
2244         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2245         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2246         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2247         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2248         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2249         tive for unset substrings.         tive for unset substrings.
2250    
2251         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2252         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2253         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2254         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2255         pcre_free, which of course could be called directly from a  C  program.         pcre_free,  which  of course could be called directly from a C program.
2256         However,  PCRE is used in some situations where it is linked via a spe-         However, PCRE is used in some situations where it is linked via a  spe-
2257         cial  interface  to  another  programming  language  that  cannot   use         cial   interface  to  another  programming  language  that  cannot  use
2258         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free directly; it is for these cases that the functions  are  pro-
2259         vided.         vided.
2260    
2261    
# Line 2168  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2274  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2274              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2275              const char **stringptr);              const char **stringptr);
2276    
2277         To extract a substring by name, you first have to find associated  num-         To  extract a substring by name, you first have to find associated num-
2278         ber.  For example, for this pattern         ber.  For example, for this pattern
2279    
2280           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
# Line 2177  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2283  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2283         be unique (PCRE_DUPNAMES was not set), you can find the number from the         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2284         name by calling pcre_get_stringnumber(). The first argument is the com-         name by calling pcre_get_stringnumber(). The first argument is the com-
2285         piled pattern, and the second is the name. The yield of the function is         piled pattern, and the second is the name. The yield of the function is
2286         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2287         subpattern of that name.         subpattern of that name.
2288    
2289         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2290         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2291         are also two functions that do the whole job.         are also two functions that do the whole job.
2292    
2293         Most   of   the   arguments    of    pcre_copy_named_substring()    and         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2294         pcre_get_named_substring()  are  the  same  as  those for the similarly         pcre_get_named_substring() are the same  as  those  for  the  similarly
2295         named functions that extract by number. As these are described  in  the         named  functions  that extract by number. As these are described in the
2296         previous  section,  they  are not re-described here. There are just two         previous section, they are not re-described here. There  are  just  two
2297         differences:         differences:
2298    
2299         First, instead of a substring number, a substring name is  given.  Sec-         First,  instead  of a substring number, a substring name is given. Sec-
2300         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2301         to the compiled pattern. This is needed in order to gain access to  the         to  the compiled pattern. This is needed in order to gain access to the
2302         name-to-number translation table.         name-to-number translation table.
2303    
2304         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2305         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2306         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
2307         behaviour may not be what you want (see the next section).         behaviour may not be what you want (see the next section).
2308    
2309    
# Line 2206  DUPLICATE SUBPATTERN NAMES Line 2312  DUPLICATE SUBPATTERN NAMES
2312         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2313              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2314    
2315         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2316         subpatterns  are  not  required  to  be unique. Normally, patterns with         subpatterns are not required to  be  unique.  Normally,  patterns  with
2317         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
2318         subpatterns  participates. An example is shown in the pcrepattern docu-         subpatterns participates. An example is shown in the pcrepattern  docu-
2319         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2320         pcre_get_named_substring()  return the first substring corresponding to  
2321         the given name that is set.  If  none  are  set,  an  empty  string  is         When    duplicates   are   present,   pcre_copy_named_substring()   and
2322         returned.  The pcre_get_stringnumber() function returns one of the num-         pcre_get_named_substring() return the first substring corresponding  to
2323         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
2324         is.         (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2325           function  returns one of the numbers that are associated with the name,
2326           but it is not defined which it is.
2327    
2328         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
2329         name, you must use  the  pcre_get_stringtable_entries()  function.  The         name,  you  must  use  the pcre_get_stringtable_entries() function. The
2330         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
2331         third and fourth are pointers to variables which  are  updated  by  the         third  and  fourth  are  pointers to variables which are updated by the
2332         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
2333         the name-to-number table  for  the  given  name.  The  function  itself         the  name-to-number  table  for  the  given  name.  The function itself
2334         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if         returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2335         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-
2336         tion  entitled  Information  about  a  pattern.  Given all the relevant         tion entitled Information about a  pattern.   Given  all  the  relevant
2337         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
2338         the captured data, if any.         the captured data, if any.
2339    
2340    
2341  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2342    
2343         The  traditional  matching  function  uses a similar algorithm to Perl,         The traditional matching function uses a  similar  algorithm  to  Perl,
2344         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
2345         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
2346         possible match, consider using the alternative matching  function  (see         possible  match,  consider using the alternative matching function (see
2347         below)  instead.  If you cannot use the alternative function, but still         below) instead. If you cannot use the alternative function,  but  still
2348         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
2349         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2350         tation.         tation.
2351    
2352         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-
2353         tern.   When your callout function is called, extract and save the cur-         tern.  When your callout function is called, extract and save the  cur-
2354         rent matched substring. Then return  1,  which  forces  pcre_exec()  to         rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2355         backtrack  and  try other alternatives. Ultimately, when it runs out of         backtrack and try other alternatives. Ultimately, when it runs  out  of
2356         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2357    
2358    
# Line 2255  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2363  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2363              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2364              int *workspace, int wscount);              int *workspace, int wscount);
2365    
2366         The function pcre_dfa_exec()  is  called  to  match  a  subject  string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2367         against  a  compiled pattern, using a matching algorithm that scans the         against a compiled pattern, using a matching algorithm that  scans  the
2368         subject string just once, and does not backtrack.  This  has  different         subject  string  just  once, and does not backtrack. This has different
2369         characteristics  to  the  normal  algorithm, and is not compatible with         characteristics to the normal algorithm, and  is  not  compatible  with
2370         Perl. Some of the features of PCRE patterns are not  supported.  Never-         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2371         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
2372         a discussion of the two matching algorithms, see the pcrematching docu-         a discussion of the two matching algorithms, see the pcrematching docu-
2373         mentation.         mentation.
2374    
2375         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
2376         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-
2377         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2378         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
2379         repeated here.         repeated here.
2380    
2381         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2382         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2383         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2384         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2385         lot of potential matches.         lot of potential matches.
2386    
2387         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 2295  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2403  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2403    
2404     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2405    
2406         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
2407         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-
2408         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2409         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
2410         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
2411         not repeated here.         not repeated here.
2412    
2413           PCRE_PARTIAL           PCRE_PARTIAL
2414    
2415         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
2416         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2417         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2418         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
2419         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-
2420         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2421         set as the first matching string.         set as the first matching string.
2422    
2423           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2424    
2425         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2426         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-
2427         tive algorithm works, this is necessarily the shortest  possible  match         tive  algorithm  works, this is necessarily the shortest possible match
2428         at the first possible matching point in the subject string.         at the first possible matching point in the subject string.
2429    
2430           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2431    
2432         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2433         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-
2434         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2435         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
2436         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2437         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
2438         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2439         documentation.         documentation.
2440    
2441     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2442    
2443         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-
2444         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
2445         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
2446         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2447         if the pattern         if the pattern
2448    
2449           <.*>           <.*>
# Line 2350  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2458  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2458           <something> <something else>           <something> <something else>
2459           <something> <something else> <something further>           <something> <something else> <something further>
2460    
2461         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,
2462         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2463         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2464         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
2465         fact, all the strings have the same start  offset.  (Space  could  have         fact,  all  the  strings  have the same start offset. (Space could have
2466         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
2467         compatibility with the way pcre_exec() returns data,  even  though  the         compatibility  with  the  way pcre_exec() returns data, even though the
2468         meaning of the strings is different.)         meaning of the strings is different.)
2469    
2470         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-
2471         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
2472         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
2473         filled with the longest matches.         filled with the longest matches.
2474    
2475     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2476    
2477         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2478         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
2479         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2480         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2481    
2482           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2483    
2484         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-
2485         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
2486         reference.         reference.
2487    
2488           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2489    
2490         This  return  is  given  if pcre_dfa_exec() encounters a condition item         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2491         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
2492         in a specific group. These are not supported.         in a specific group. These are not supported.
2493    
2494           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2495    
2496         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
2497         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
2498         (it is meaningless).         (it is meaningless).
2499    
2500           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2501    
2502         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
2503         workspace vector.         workspace vector.
2504    
2505           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2506    
2507         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2508         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2509         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
2510         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2511    
2512    
2513  SEE ALSO  SEE ALSO
2514    
2515         pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-         pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2516         tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).         tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2517    
2518    
2519  AUTHOR  AUTHOR
# Line 2417  AUTHOR Line 2525  AUTHOR
2525    
2526  REVISION  REVISION
2527    
2528         Last updated: 13 June 2007         Last updated: 11 September 2007
2529         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2530  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2531    
2532    
2533  PCRECALLOUT(3)                                                  PCRECALLOUT(3)  PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2534    
2535    
# Line 2591  REVISION Line 2699  REVISION
2699         Last updated: 29 May 2007         Last updated: 29 May 2007
2700         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2701  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2702    
2703    
2704  PCRECOMPAT(3)                                                    PCRECOMPAT(3)  PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2705    
2706    
# Line 2670  DIFFERENCES BETWEEN PCRE AND PERL Line 2778  DIFFERENCES BETWEEN PCRE AND PERL
2778         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2779         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2780    
2781         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2782           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2783           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2784           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2785           ture group; this is different to Perl.
2786    
2787           12. PCRE provides some extensions to the Perl regular expression facil-
2788         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
2789         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2790         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 2696  DIFFERENCES BETWEEN PCRE AND PERL Line 2810  DIFFERENCES BETWEEN PCRE AND PERL
2810         (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-
2811         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2812    
2813         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2814           CRLF by the PCRE_BSR_ANYCRLF option.
2815    
2816         (h) The partial matching facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
2817    
2818         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (i) The partial matching facility is PCRE-specific.
2819    
2820           (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2821         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2822    
2823         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2824         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2825    
2826           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2827           of a pattern that set overall options that cannot be changed within the
2828           pattern.
2829    
2830    
2831  AUTHOR  AUTHOR
2832    
# Line 2716  AUTHOR Line 2837  AUTHOR
2837    
2838  REVISION  REVISION
2839    
2840         Last updated: 13 June 2007         Last updated: 11 September 2007
2841         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2842  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2843    
2844    
2845  PCREPATTERN(3)                                                  PCREPATTERN(3)  PCREPATTERN(3)                                                  PCREPATTERN(3)
2846    
2847    
# Line 2730  NAME Line 2851  NAME
2851    
2852  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2853    
2854         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2855         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2856         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2857         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2858         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2859         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2860           O'Reilly,  covers regular expressions in great detail. This description
2861           of PCRE's regular expressions is intended as reference material.
2862    
2863         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2864         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 2755  PCRE REGULAR EXPRESSION DETAILS Line 2878  PCRE REGULAR EXPRESSION DETAILS
2878         discussed in the pcrematching page.         discussed in the pcrematching page.
2879    
2880    
2881    NEWLINE CONVENTIONS
2882    
2883           PCRE  supports five different conventions for indicating line breaks in
2884           strings: a single CR (carriage return) character, a  single  LF  (line-
2885           feed) character, the two-character sequence CRLF, any of the three pre-
2886           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2887           discussion  about newlines, and shows how to set the newline convention
2888           in the options arguments for the compiling and matching functions.
2889    
2890           It is also possible to specify a newline convention by starting a  pat-
2891           tern string with one of the following five sequences:
2892    
2893             (*CR)        carriage return
2894             (*LF)        linefeed
2895             (*CRLF)      carriage return, followed by linefeed
2896             (*ANYCRLF)   any of the three above
2897             (*ANY)       all Unicode newline sequences
2898    
2899           These override the default and the options given to pcre_compile(). For
2900           example, on a Unix system where LF is the default newline sequence, the
2901           pattern
2902    
2903             (*CR)a.b
2904    
2905           changes the convention to CR. That pattern matches "a\nb" because LF is
2906           no longer a newline. Note that these special settings,  which  are  not
2907           Perl-compatible,  are  recognized  only at the very start of a pattern,
2908           and that they must be in upper case.  If  more  than  one  of  them  is
2909           present, the last one is used.
2910    
2911           The  newline  convention  does  not  affect what the \R escape sequence
2912           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2913           compatibility.  However, this can be changed; see the description of \R
2914           in the section entitled "Newline sequences" below. A change of \R  set-
2915           ting can be combined with a change of newline convention.
2916    
2917    
2918  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
2919    
2920         A  regular  expression  is  a pattern that is matched against a subject         A  regular  expression  is  a pattern that is matched against a subject
# Line 2862  BACKSLASH Line 3022  BACKSLASH
3022           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3023           \e        escape (hex 1B)           \e        escape (hex 1B)
3024           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3025           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3026           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3027           \t        tab (hex 09)           \t        tab (hex 09)
3028           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
# Line 2877  BACKSLASH Line 3037  BACKSLASH
3037         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
3038         in upper or lower case). Any number of hexadecimal  digits  may  appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
3039         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
3040         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,
3041         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
3042         hexadecimal digits appear between \x{ and }, or if there is  no  termi-         than the largest Unicode code point, which is 10FFFF.
3043         nating  }, this form of escape is not recognized.  Instead, the initial  
3044         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
3045         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3046           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
3047           escape,  with  no  following  digits, giving a character whose value is
3048           zero.
3049    
3050         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
3051         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-
3052         dled. For example, \xdc is exactly the same as \x{dc}.         dled. For example, \xdc is exactly the same as \x{dc}.
3053    
3054         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
3055         than two digits, just  those  that  are  present  are  used.  Thus  the         than  two  digits,  just  those  that  are  present  are used. Thus the
3056         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
3057         (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
3058         if the pattern character that follows is itself an octal digit.         if the pattern character that follows is itself an octal digit.
3059    
3060         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-
3061         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3062         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
3063         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3064         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
3065         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
3066         of parenthesized subpatterns.         of parenthesized subpatterns.
3067    
3068         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
3069         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
3070         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-
3071         erate a data character. Any subsequent digits stand for themselves.  In         erate  a data character. Any subsequent digits stand for themselves. In
3072         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
3073         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
3074         example:         example:
3075    
3076           \040   is another way of writing a space           \040   is another way of writing a space
# Line 2925  BACKSLASH Line 3088  BACKSLASH
3088           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3089                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3090    
3091         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
3092         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3093    
3094         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
3095         inside  and  outside character classes. In addition, inside a character         inside and outside character classes. In addition, inside  a  character
3096         class, the sequence \b is interpreted as the backspace  character  (hex         class,  the  sequence \b is interpreted as the backspace character (hex
3097         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"
3098         and "X", respectively. Outside a character class, these sequences  have         and  "X", respectively. Outside a character class, these sequences have
3099         different meanings (see below).         different meanings (see below).
3100    
3101     Absolute and relative back references     Absolute and relative back references
3102    
3103         The  sequence  \g followed by a positive or negative number, optionally         The sequence \g followed by an unsigned or a negative  number,  option-
3104         enclosed in braces, is an absolute or relative back reference. A  named         ally  enclosed  in braces, is an absolute or relative back reference. A
3105         back  reference can be coded as \g{name}. Back references are discussed         named back reference can be coded as \g{name}. Back references are dis-
3106         later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3107    
3108     Generic character types     Generic character types
3109    
# Line 2959  BACKSLASH Line 3122  BACKSLASH
3122           \W     any "non-word" character           \W     any "non-word" character
3123    
3124         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
3125         into two disjoint sets. Any given character matches one, and only  one,         into  two disjoint sets. Any given character matches one, and only one,
3126         of each pair.         of each pair.
3127    
3128         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
3129         acter classes. They each match one character of the  appropriate  type.         acter  classes.  They each match one character of the appropriate type.
3130         If  the current matching point is at the end of the subject string, all         If the current matching point is at the end of the subject string,  all
3131         of them fail, since there is no character to match.         of them fail, since there is no character to match.
3132    
3133         For compatibility with Perl, \s does not match the VT  character  (code         For  compatibility  with Perl, \s does not match the VT character (code
3134         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
3135         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
3136         "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-
3137         ter. In PCRE, it never does.         ter. In PCRE, it never does.
3138    
3139         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,
3140         \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-
3141         code character property support is available.  These  sequences  retain         code  character  property  support is available. These sequences retain
3142         their original meanings from before UTF-8 support was available, mainly         their original meanings from before UTF-8 support was available, mainly
3143         for efficiency reasons.         for efficiency reasons.
3144    
3145         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to         The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3146         the  other  sequences, these do match certain high-valued codepoints in         the other sequences, these do match certain high-valued  codepoints  in
3147         UTF-8 mode.  The horizontal space characters are:         UTF-8 mode.  The horizontal space characters are:
3148    
3149           U+0009     Horizontal tab           U+0009     Horizontal tab
# Line 3014  BACKSLASH Line 3177  BACKSLASH
3177           U+2029     Paragraph separator           U+2029     Paragraph separator
3178    
3179         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
3180         is  a  letter  or  digit.  The definition of letters and digits is con-         is a letter or digit. The definition of  letters  and  digits  is  con-
3181         trolled by PCRE's low-valued character tables, and may vary if  locale-         trolled  by PCRE's low-valued character tables, and may vary if locale-
3182         specific  matching is taking place (see "Locale support" in the pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
3183         page). For example, in a French locale such  as  "fr_FR"  in  Unix-like         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3184         systems,  or "french" in Windows, some character codes greater than 128         systems, or "french" in Windows, some character codes greater than  128
3185         are used for accented letters, and these are matched by \w. The use  of         are  used for accented letters, and these are matched by \w. The use of
3186         locales with Unicode is discouraged.         locales with Unicode is discouraged.
3187    
3188     Newline sequences     Newline sequences
3189    
3190         Outside  a  character class, the escape sequence \R matches any Unicode         Outside a character class, by default, the escape sequence  \R  matches
3191         newline sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R  is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3192         equivalent to the following:         mode \R is equivalent to the following:
3193    
3194           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3195    
3196         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
3197         below.  This particular group matches either the two-character sequence         below.  This particular group matches either the two-character sequence
3198         CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,         CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
3199         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
3200         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
3201         is treated as a single unit that cannot be split.         is treated as a single unit that cannot be split.
3202    
3203         In UTF-8 mode, two additional characters whose codepoints  are  greater         In  UTF-8  mode, two additional characters whose codepoints are greater
3204         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-
3205         rator, U+2029).  Unicode character property support is not  needed  for         rator,  U+2029).   Unicode character property support is not needed for
3206         these characters to be recognized.         these characters to be recognized.
3207    
3208           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3209           the  complete  set  of  Unicode  line  endings)  by  setting the option
3210           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3211           (BSR is an abbrevation for "backslash R".) This can be made the default
3212           when PCRE is built; if this is the case, the  other  behaviour  can  be
3213           requested  via  the  PCRE_BSR_UNICODE  option.   It is also possible to
3214           specify these settings by starting a pattern string  with  one  of  the
3215           following sequences:
3216    
3217             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3218             (*BSR_UNICODE)   any Unicode newline sequence
3219    
3220           These override the default and the options given to pcre_compile(), but
3221           they can be overridden by options given to pcre_exec(). Note that these
3222           special settings, which are not Perl-compatible, are recognized only at
3223           the very start of a pattern, and that they must be in  upper  case.  If
3224           more  than  one  of  them is present, the last one is used. They can be
3225           combined with a change of newline convention, for  example,  a  pattern
3226           can start with:
3227    
3228             (*ANY)(*BSR_ANYCRLF)
3229    
3230         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3231    
3232     Unicode character properties     Unicode character properties
3233    
3234         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3235         tional escape sequences to match  character  properties  are  available         tional escape sequences that match characters with specific  properties
3236         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3237           limited to testing characters whose codepoints are less than  256,  but
3238           they do work in this mode.  The extra escape sequences are:
3239    
3240           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3241           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
# Line 3143  BACKSLASH Line 3330  BACKSLASH
3330         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
3331         classified as a modifier or "other".         classified as a modifier or "other".
3332    
3333           The Cs (Surrogate) property applies only to  characters  in  the  range
3334           U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3335           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3336           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3337           the pcreapi page).
3338    
3339         The long synonyms for these properties  that  Perl  supports  (such  as         The long synonyms for these properties  that  Perl  supports  (such  as
3340         \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
3341         any of these properties with "Is".         any of these properties with "Is".
# Line 3162  BACKSLASH Line 3355  BACKSLASH
3355         That is, it matches a character without the "mark"  property,  followed         That is, it matches a character without the "mark"  property,  followed
3356         by  zero  or  more  characters with the "mark" property, and treats the         by  zero  or  more  characters with the "mark" property, and treats the
3357         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3358         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3359           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3360           matches any one character.
3361    
3362         Matching  characters  by Unicode property is not fast, because PCRE has         Matching  characters  by Unicode property is not fast, because PCRE has
3363         to search a structure that contains  data  for  over  fifteen  thousand         to search a structure that contains  data  for  over  fifteen  thousand
# Line 3487  VERTICAL BAR Line 3682  VERTICAL BAR
3682  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3683    
3684         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3685         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3686         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3687         option letters are         between "(?" and ")".  The option letters are
3688    
3689           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3690           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 3503  INTERNAL OPTION SETTING Line 3698  INTERNAL OPTION SETTING
3698         is also permitted. If a  letter  appears  both  before  and  after  the         is also permitted. If a  letter  appears  both  before  and  after  the
3699         hyphen, the option is unset.         hyphen, the option is unset.
3700    
3701           The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3702           can be changed in the same way as the Perl-compatible options by  using
3703           the characters J, U and X respectively.
3704    
3705         When  an option change occurs at top level (that is, not inside subpat-         When  an option change occurs at top level (that is, not inside subpat-
3706         tern parentheses), the change applies to the remainder of  the  pattern         tern parentheses), the change applies to the remainder of  the  pattern
3707         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,
# Line 3528  INTERNAL OPTION SETTING Line 3727  INTERNAL OPTION SETTING
3727         the  effects  of option settings happen at compile time. There would be         the  effects  of option settings happen at compile time. There would be
3728         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3729    
3730         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA         Note: There are other PCRE-specific options that  can  be  set  by  the
3731         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
3732         the characters J, U and X respectively.         cases the pattern can contain special  leading  sequences  to  override
3733           what  the  application  has set or what has been defaulted. Details are
3734           given in the section entitled "Newline sequences" above.
3735    
3736    
3737  SUBPATTERNS  SUBPATTERNS
# Line 3872  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4073  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4073    
4074           \d++foo           \d++foo
4075    
4076         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4077           example:
4078    
4079             (abc|xyz){2,3}+
4080    
4081           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4082         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4083         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4084         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4085         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4086         should be slightly faster.         should be slightly faster.
4087    
4088         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-
4089         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4090         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
4091         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
4092         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4093    
4094         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4095         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4096         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
4097         when B must follow.         when B must follow.
4098    
4099         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4100         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
4101         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
4102         very long time indeed. The pattern         very long time indeed. The pattern
4103    
4104           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4105    
4106         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4107         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4108         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4109    
4110           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4111    
4112         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4113         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4114         *  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
4115         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4116         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4117         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4118         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
4119         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
4120         group, like this:         group, like this:
4121    
4122           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4123    
4124         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4125    
4126    
4127  BACK REFERENCES  BACK REFERENCES
4128    
4129         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4130         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
4131         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4132         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4133    
4134         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4135         it is always taken as a back reference, and causes  an  error  only  if         it  is  always  taken  as a back reference, and causes an error only if
4136         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4137         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4138         to  the left of the reference for numbers less than 10. A "forward back         to the left of the reference for numbers less than 10. A "forward  back
4139         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4140         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4141         tion.         tion.
4142    
4143         It is not possible to have a numerical "forward back  reference"  to  a         It  is  not  possible to have a numerical "forward back reference" to a
4144         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4145         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4146         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4147         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4148         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4149         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4150    
4151         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4152         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-
4153         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
4154         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned number or a negative number, optionally  enclosed  in  braces.
4155         ples are all identical:         These examples are all identical:
4156    
4157           (ring), \1           (ring), \1
4158           (ring), \g1           (ring), \g1
4159           (ring), \g{1}           (ring), \g{1}
4160    
4161         A positive number specifies an absolute reference without the ambiguity         An  unsigned number specifies an absolute reference without the ambigu-
4162         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
4163         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4164         Consider this example:         Consider this example:
4165    
4166           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4167    
4168         The sequence \g{-1} is a reference to the most recently started captur-         The sequence \g{-1} is a reference to the most recently started captur-
4169         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4170         \g{-2} would be equivalent to \1. The use of relative references can be         \g{-2} would be equivalent to \1. The use of relative references can be
4171         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4172         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4173    
4174         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4175         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4176         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4177         of doing that). So the pattern         of doing that). So the pattern
4178    
4179           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4180    
4181         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4182         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4183         time of the back reference, the case of letters is relevant. For  exam-         time  of the back reference, the case of letters is relevant. For exam-
4184         ple,         ple,
4185    
4186           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4187    
4188         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
4189         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4190    
4191         There are several different ways of writing back  references  to  named         There  are  several  different ways of writing back references to named
4192         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or
4193         \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's         \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4194         unified back reference syntax, in which \g can be used for both numeric         unified back reference syntax, in which \g can be used for both numeric
4195         and named references, is also supported. We  could  rewrite  the  above         and  named  references,  is  also supported. We could rewrite the above
4196         example in any of the following ways:         example in any of the following ways:
4197    
4198           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 3994  BACK REFERENCES Line 4200  BACK REFERENCES
4200           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4201           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4202    
4203         A  subpattern  that  is  referenced  by  name may appear in the pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4204         before or after the reference.         before or after the reference.
4205    
4206         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
4207         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
4208         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4209    
4210           (a|(bc))\2           (a|(bc))\2
4211    
4212         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
4213         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
4214         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
4215         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4216         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
4217         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
4218         ments" below) can be used.         ments" below) can be used.
4219    
4220         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
4221         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
4222         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
4223         patterns. For example, the pattern         patterns. For example, the pattern
4224    
4225           (a|b\1)+           (a|b\1)+
4226    
4227         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-
4228         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4229         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4230         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
4231         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
4232         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4233    
4234    
4235  ASSERTIONS  ASSERTIONS
4236    
4237         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
4238         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
4239         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
4240         described above.         described above.
4241    
4242         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
4243         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
4244         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
4245         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
4246         matching position to be changed.         matching position to be changed.
4247    
4248         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
4249         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
4250         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
4251         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
4252         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4253         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
4254         negative assertions.         negative assertions.
4255    
4256     Lookahead assertions     Lookahead assertions
# Line 4054  ASSERTIONS Line 4260  ASSERTIONS
4260    
4261           \w+(?=;)           \w+(?=;)
4262    
4263         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-
4264         colon in the match, and         colon in the match, and
4265    
4266           foo(?!bar)           foo(?!bar)
4267    
4268         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
4269         that the apparently similar pattern         that the apparently similar pattern
4270    
4271           (?!foo)bar           (?!foo)bar
4272    
4273         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
4274         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
4275         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4276         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4277    
4278         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
4279         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
4280         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
4281         string must always fail.         string must always fail.
4282    
4283     Lookbehind assertions     Lookbehind assertions
4284    
4285         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4286         for negative assertions. For example,         for negative assertions. For example,
4287    
4288           (?<!foo)bar           (?<!foo)bar
4289    
4290         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
4291         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4292         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-
4293         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
4294         fixed length. Thus         fixed length. Thus
4295    
4296           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4093  ASSERTIONS Line 4299  ASSERTIONS
4299    
4300           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4301    
4302         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4303         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4304         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
4305         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
4306         such as         such as
4307    
4308           (?<=ab(c|de))           (?<=ab(c|de))
4309    
4310         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
4311         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
4312         level branches:         level branches:
4313    
4314           (?<=abc|abde)           (?<=abc|abde)
4315    
4316         In some cases, the Perl 5.10 escape sequence \K (see above) can be used         In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4317         instead of a lookbehind assertion; this is not restricted to  a  fixed-         instead  of  a lookbehind assertion; this is not restricted to a fixed-
4318         length.         length.
4319    
4320         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4321         to temporarily move the current position back by the fixed  length  and         to  temporarily  move the current position back by the fixed length and
4322         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4323         rent position, the assertion fails.         rent position, the assertion fails.
4324    
4325         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
4326         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
4327         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,
4328         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4329    
4330         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
4331         assertions to specify efficient matching at  the  end  of  the  subject         assertions  to  specify  efficient  matching  at the end of the subject
4332         string. Consider a simple pattern such as         string. Consider a simple pattern such as
4333    
4334           abcd$           abcd$
4335    
4336         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
4337         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
4338         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
4339         pattern is specified as         pattern is specified as
4340    
4341           ^.*abcd$           ^.*abcd$
4342    
4343         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
4344         (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
4345         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
4346         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,
4347         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
4348    
4349           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4350    
4351         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
4352         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4353         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4354         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4355         processing time.         processing time.
4356    
4357     Using multiple assertions     Using multiple assertions
# Line 4154  ASSERTIONS Line 4360  ASSERTIONS
4360    
4361           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4362    
4363         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4364         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4365         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4366         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
4367         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4368         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
4369         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-
4370         foo". A pattern to do that is         foo". A pattern to do that is
4371    
4372           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4373    
4374         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4375         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4376         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4377    
# Line 4173  ASSERTIONS Line 4379  ASSERTIONS
4379    
4380           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4381    
4382         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
4383         is not preceded by "foo", while         is not preceded by "foo", while
4384    
4385           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4386    
4387         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4388         three characters that are not "999".         three characters that are not "999".
4389    
4390    
4391  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4392    
4393         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-
4394         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4395         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4396         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4397         are         are
4398    
4399           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4400           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4401    
4402         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4403         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-
4404         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4405    
4406         There  are  four  kinds of condition: references to subpatterns, refer-         There are four kinds of condition: references  to  subpatterns,  refer-
4407         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4408    
4409     Checking for a used subpattern by number     Checking for a used subpattern by number
4410    
4411         If the text between the parentheses consists of a sequence  of  digits,         If  the  text between the parentheses consists of a sequence of digits,
4412         the  condition  is  true if the capturing subpattern of that number has         the condition is true if the capturing subpattern of  that  number  has
4413         previously matched. An alternative notation is to  precede  the  digits         previously  matched.  An  alternative notation is to precede the digits
4414         with a plus or minus sign. In this case, the subpattern number is rela-         with a plus or minus sign. In this case, the subpattern number is rela-
4415         tive rather than absolute.  The most recently opened parentheses can be         tive rather than absolute.  The most recently opened parentheses can be
4416         referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In         referenced by (?(-1), the next most recent by (?(-2),  and  so  on.  In
4417         looping constructs it can also make sense to refer to subsequent groups         looping constructs it can also make sense to refer to subsequent groups
4418         with constructs such as (?(+2).         with constructs such as (?(+2).
4419    
4420         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4421         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
4422         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4423    
4424           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4425    
4426         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4427         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4428         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4429         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4430         of parentheses matched or not. If they did, that is, if subject started         of parentheses matched or not. If they did, that is, if subject started
4431         with an opening parenthesis, the condition is true, and so the yes-pat-         with an opening parenthesis, the condition is true, and so the yes-pat-
4432         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4433         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4434         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4435         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4436    
4437         If you were embedding this pattern in a larger one,  you  could  use  a         If  you  were  embedding  this pattern in a larger one, you could use a
4438         relative reference:         relative reference:
4439    
4440           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4441    
4442         This  makes  the  fragment independent of the parentheses in the larger         This makes the fragment independent of the parentheses  in  the  larger
4443         pattern.         pattern.
4444    
4445     Checking for a used subpattern by name     Checking for a used subpattern by name
4446    
4447         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4448         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4449         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4450         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4451         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4452         looks  first for a named subpattern; if it cannot find one and the name         looks first for a named subpattern; if it cannot find one and the  name
4453         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4454         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4455         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4456    
4457         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4256  CONDITIONAL SUBPATTERNS Line 4462  CONDITIONAL SUBPATTERNS
4462     Checking for pattern recursion     Checking for pattern recursion
4463    
4464         If the condition is the string (R), and there is no subpattern with the         If the condition is the string (R), and there is no subpattern with the
4465         name  R, the condition is true if a recursive call to the whole pattern         name R, the condition is true if a recursive call to the whole  pattern
4466         or any subpattern has been made. If digits or a name preceded by amper-         or any subpattern has been made. If digits or a name preceded by amper-
4467         sand follow the letter R, for example:         sand follow the letter R, for example:
4468    
4469           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4470    
4471         the  condition is true if the most recent recursion is into the subpat-         the condition is true if the most recent recursion is into the  subpat-
4472         tern whose number or name is given. This condition does not  check  the         tern  whose  number or name is given. This condition does not check the
4473         entire recursion stack.         entire recursion stack.
4474    
4475         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test conditions are  false.  Recur-
4476         sive patterns are described below.         sive patterns are described below.
4477    
4478     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4479    
4480         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4481         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4482         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4483         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4484         DEFINE is that it can be used to define "subroutines" that can be  ref-         DEFINE  is that it can be used to define "subroutines" that can be ref-
4485         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4486         For example, a pattern to match an IPv4 address could be  written  like         For  example,  a pattern to match an IPv4 address could be written like
4487         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4488    
4489           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )           (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
4490           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4491    
4492         The  first part of the pattern is a DEFINE group inside which a another         The first part of the pattern is a DEFINE group inside which a  another
4493         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4494         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4495         this part of the pattern is skipped because DEFINE acts  like  a  false         this  part  of  the pattern is skipped because DEFINE acts like a false
4496         condition.         condition.
4497    
4498         The rest of the pattern uses references to the named group to match the         The rest of the pattern uses references to the named group to match the
4499         four dot-separated components of an IPv4 address, insisting on  a  word         four  dot-separated  components of an IPv4 address, insisting on a word
4500         boundary at each end.         boundary at each end.
4501    
4502     Assertion conditions     Assertion conditions
4503    
4504         If  the  condition  is  not  in any of the above formats, it must be an         If the condition is not in any of the above  formats,  it  must  be  an
4505         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4506         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4507         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4508    
4509           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4510           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )           \d{2}-[a-z]{3}-\d{2}  |  \d{2}-\d{2}-\d{2} )
4511    
4512         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4513         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4514         it tests for the presence of at least one letter in the subject.  If  a         it  tests  for the presence of at least one letter in the subject. If a
4515         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4516         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4517         strings  in  one  of the two forms dd-aaa-dd or dd-dd-dd, where aaa are         strings in one of the two forms dd-aaa-dd or dd-dd-dd,  where  aaa  are
4518         letters and dd are digits.         letters and dd are digits.
4519    
4520    
4521  COMMENTS  COMMENTS
4522    
4523         The sequence (?# marks the start of a comment that continues up to  the         The  sequence (?# marks the start of a comment that continues up to the
4524         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4525         characters that make up a comment play no part in the pattern  matching         characters  that make up a comment play no part in the pattern matching
4526         at all.         at all.
4527    
4528         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4529         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4530         after the next newline in the pattern.         after the next newline in the pattern.
4531    
4532    
4533  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4534    
4535         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4536         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4537         that  can  be  done  is  to use a pattern that matches up to some fixed         that can be done is to use a pattern that  matches  up  to  some  fixed
4538         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4539         depth.         depth.
4540    
4541         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4542         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4543         Perl  code in the expression at run time, and the code can refer to the         Perl code in the expression at run time, and the code can refer to  the
4544         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4545         parentheses problem can be created like this:         parentheses problem can be created like this:
4546    
# Line 4344  RECURSIVE PATTERNS Line 4550  RECURSIVE PATTERNS
4550         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4551    
4552         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4553         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4554         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4555         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of recursion was  introduced  into  Perl  at
4556         release 5.10.         release 5.10.
4557    
4558         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4559         zero and a closing parenthesis is a recursive call of the subpattern of         zero and a closing parenthesis is a recursive call of the subpattern of
4560         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4561         not,  it  is  a  "subroutine" call, which is described in the next sec-         not, it is a "subroutine" call, which is described  in  the  next  sec-
4562         tion.) The special item (?R) or (?0) is a recursive call of the  entire         tion.)  The special item (?R) or (?0) is a recursive call of the entire
4563         regular expression.         regular expression.
4564    
4565         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
4566         always treated as an atomic group. That is, once it has matched some of         always treated as an atomic group. That is, once it has matched some of
4567         the subject string, it is never re-entered, even if it contains untried         the subject string, it is never re-entered, even if it contains untried
4568         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4569    
4570         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4571         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4572    
4573           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4574    
4575         First  it matches an opening parenthesis. Then it matches any number of         First it matches an opening parenthesis. Then it matches any number  of
4576         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings  which  can  either  be  a sequence of non-parentheses, or a
4577         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive match of the pattern itself (that is, a  correctly  parenthe-
4578         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4579    
4580         If this were part of a larger pattern, you would not  want  to  recurse         If  this  were  part of a larger pattern, you would not want to recurse
4581         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4582    
4583           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4584    
4585         We  have  put the pattern into parentheses, and caused the recursion to         We have put the pattern into parentheses, and caused the  recursion  to
4586         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
4587    
4588         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
4589         tricky.  This is made easier by the use of relative references. (A Perl         tricky. This is made easier by the use of relative references. (A  Perl
4590         5.10 feature.)  Instead of (?1) in the  pattern  above  you  can  write         5.10  feature.)   Instead  of  (?1)  in the pattern above you can write
4591         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
4592         the recursion. In other  words,  a  negative  number  counts  capturing         the  recursion.  In  other  words,  a  negative number counts capturing
4593         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
4594    
4595         It  is  also  possible  to refer to subsequently opened parentheses, by         It is also possible to refer to  subsequently  opened  parentheses,  by
4596         writing references such as (?+2). However, these  cannot  be  recursive         writing  references  such  as (?+2). However, these cannot be recursive
4597         because  the  reference  is  not inside the parentheses that are refer-         because the reference is not inside the  parentheses  that  are  refer-
4598         enced. They are always "subroutine" calls, as  described  in  the  next         enced.  They  are  always  "subroutine" calls, as described in the next
4599         section.         section.
4600    
4601         An  alternative  approach is to use named parentheses instead. The Perl         An alternative approach is to use named parentheses instead.  The  Perl
4602         syntax for this is (?&name); PCRE's earlier syntax  (?P>name)  is  also         syntax  for  this  is (?&name); PCRE's earlier syntax (?P>name) is also
4603         supported. We could rewrite the above example as follows:         supported. We could rewrite the above example as follows:
4604    
4605           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4606    
4607         If  there  is more than one subpattern with the same name, the earliest         If there is more than one subpattern with the same name,  the  earliest
4608         one is used.         one is used.
4609    
4610         This particular example pattern that we have been looking  at  contains         This  particular  example pattern that we have been looking at contains
4611         nested  unlimited repeats, and so the use of atomic grouping for match-         nested unlimited repeats, and so the use of atomic grouping for  match-
4612         ing strings of non-parentheses is important when applying  the  pattern         ing  strings  of non-parentheses is important when applying the pattern
4613         to strings that do not match. For example, when this pattern is applied         to strings that do not match. For example, when this pattern is applied
4614         to         to
4615    
4616           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4617    
4618         it yields "no match" quickly. However, if atomic grouping is not  used,         it  yields "no match" quickly. However, if atomic grouping is not used,
4619         the  match  runs  for a very long time indeed because there are so many         the match runs for a very long time indeed because there  are  so  many
4620         different ways the + and * repeats can carve up the  subject,  and  all         different  ways  the  + and * repeats can carve up the subject, and all
4621         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4622    
4623         At the end of a match, the values set for any capturing subpatterns are         At the end of a match, the values set for any capturing subpatterns are
4624         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4625         value  is  set.   If  you want to obtain intermediate values, a callout         value is set.  If you want to obtain  intermediate  values,  a  callout
4626         function can be used (see below and the pcrecallout documentation).  If         function  can be used (see below and the pcrecallout documentation). If
4627         the pattern above is matched against         the pattern above is matched against
4628    
4629           (ab(cd)ef)           (ab(cd)ef)
4630    
4631         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the capturing parentheses is  "ef",  which  is  the  last
4632         value taken on at the top level. If additional parentheses  are  added,         value  taken  on at the top level. If additional parentheses are added,
4633         giving         giving
4634    
4635           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4636              ^                        ^              ^                        ^
4637              ^                        ^              ^                        ^
4638    
4639         the  string  they  capture is "ab(cd)ef", the contents of the top level         the string they capture is "ab(cd)ef", the contents of  the  top  level
4640         parentheses. If there are more than 15 capturing parentheses in a  pat-         parentheses.  If there are more than 15 capturing parentheses in a pat-
4641         tern, PCRE has to obtain extra memory to store data during a recursion,         tern, PCRE has to obtain extra memory to store data during a recursion,
4642         which it does by using pcre_malloc, freeing  it  via  pcre_free  after-         which  it  does  by  using pcre_malloc, freeing it via pcre_free after-
4643         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the
4644         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4645    
4646         Do not confuse the (?R) item with the condition (R),  which  tests  for         Do  not  confuse  the (?R) item with the condition (R), which tests for
4647         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.  Consider this pattern, which matches text in  angle  brack-
4648         ets, allowing for arbitrary nesting. Only digits are allowed in  nested         ets,  allowing for arbitrary nesting. Only digits are allowed in nested
4649         brackets  (that is, when recursing), whereas any characters are permit-         brackets (that is, when recursing), whereas any characters are  permit-
4650         ted at the outer level.         ted at the outer level.
4651    
4652           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4653    
4654         In this pattern, (?(R) is the start of a conditional  subpattern,  with         In  this  pattern, (?(R) is the start of a conditional subpattern, with
4655         two  different  alternatives for the recursive and non-recursive cases.         two different alternatives for the recursive and  non-recursive  cases.
4656         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4657    
4658    
4659  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4660    
4661         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4662         by  name)  is used outside the parentheses to which it refers, it oper-         by name) is used outside the parentheses to which it refers,  it  oper-
4663         ates like a subroutine in a programming language. The "called"  subpat-         ates  like a subroutine in a programming language. The "called" subpat-
4664         tern may be defined before or after the reference. A numbered reference         tern may be defined before or after the reference. A numbered reference
4665         can be absolute or relative, as in these examples:         can be absolute or relative, as in these examples:
4666    
# Line 4466  SUBPATTERNS AS SUBROUTINES Line 4672  SUBPATTERNS AS SUBROUTINES
4672    
4673           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4674    
4675         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4676         not "sense and responsibility". If instead the pattern         not "sense and responsibility". If instead the pattern
4677    
4678           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4679    
4680         is  used, it does match "sense and responsibility" as well as the other         is used, it does match "sense and responsibility" as well as the  other
4681         two strings. Another example is  given  in  the  discussion  of  DEFINE         two  strings.  Another  example  is  given  in the discussion of DEFINE
4682         above.         above.
4683    
4684         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4685         atomic group. That is, once it has matched some of the subject  string,         atomic  group. That is, once it has matched some of the subject string,
4686         it  is  never  re-entered, even if it contains untried alternatives and         it is never re-entered, even if it contains  untried  alternatives  and
4687         there is a subsequent matching failure.         there is a subsequent matching failure.
4688    
4689         When a subpattern is used as a subroutine, processing options  such  as         When  a  subpattern is used as a subroutine, processing options such as
4690         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
4691         be changed for different calls. For example, consider this pattern:         be changed for different calls. For example, consider this pattern:
4692    
4693           (abc)(?i:(?-1))           (abc)(?i:(?-1))
4694    
4695         It matches "abcabc". It does not match "abcABC" because the  change  of         It  matches  "abcabc". It does not match "abcABC" because the change of
4696         processing option does not affect the called subpattern.         processing option does not affect the called subpattern.
4697    
4698    
4699  CALLOUTS  CALLOUTS
4700    
4701         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
4702         Perl code to be obeyed in the middle of matching a regular  expression.         Perl  code to be obeyed in the middle of matching a regular expression.
4703         This makes it possible, amongst other things, to extract different sub-         This makes it possible, amongst other things, to extract different sub-
4704         strings that match the same pair of parentheses when there is a repeti-         strings that match the same pair of parentheses when there is a repeti-
4705         tion.         tion.
4706    
4707         PCRE provides a similar feature, but of course it cannot obey arbitrary         PCRE provides a similar feature, but of course it cannot obey arbitrary
4708         Perl code. The feature is called "callout". The caller of PCRE provides         Perl code. The feature is called "callout". The caller of PCRE provides
4709         an  external function by putting its entry point in the global variable         an external function by putting its entry point in the global  variable
4710         pcre_callout.  By default, this variable contains NULL, which  disables         pcre_callout.   By default, this variable contains NULL, which disables
4711         all calling out.         all calling out.
4712    
4713         Within  a  regular  expression,  (?C) indicates the points at which the         Within a regular expression, (?C) indicates the  points  at  which  the
4714         external function is to be called. If you want  to  identify  different         external  function  is  to be called. If you want to identify different
4715         callout  points, you can put a number less than 256 after the letter C.         callout points, you can put a number less than 256 after the letter  C.
4716         The default value is zero.  For example, this pattern has  two  callout         The  default  value is zero.  For example, this pattern has two callout
4717         points:         points:
4718    
4719           (?C1)abc(?C2)def           (?C1)abc(?C2)def
4720    
4721         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are         If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are
4722         automatically installed before each item in the pattern. They  are  all         automatically  installed  before each item in the pattern. They are all
4723         numbered 255.         numbered 255.
4724    
4725         During matching, when PCRE reaches a callout point (and pcre_callout is         During matching, when PCRE reaches a callout point (and pcre_callout is
4726         set), the external function is called. It is provided with  the  number         set),  the  external function is called. It is provided with the number
4727         of  the callout, the position in the pattern, and, optionally, one item         of the callout, the position in the pattern, and, optionally, one  item
4728         of data originally supplied by the caller of pcre_exec().  The  callout         of  data  originally supplied by the caller of pcre_exec(). The callout
4729         function  may cause matching to proceed, to backtrack, or to fail alto-         function may cause matching to proceed, to backtrack, or to fail  alto-
4730         gether. A complete description of the interface to the callout function         gether. A complete description of the interface to the callout function
4731         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4732    
4733    
4734    BACKTRACKING CONTROL
4735    
4736           Perl 5.10 introduced a number of "Special Backtracking Control  Verbs",
4737           which are described in the Perl documentation as "experimental and sub-
4738           ject to change or removal in a future version of Perl". It goes  on  to
4739           say:  "Their usage in production code should be noted to avoid problems
4740           during upgrades." The same remarks apply to the PCRE features described
4741           in this section.
4742    
4743           Since these verbs are specifically related to backtracking, they can be
4744           used only when the pattern is to be matched  using  pcre_exec(),  which
4745           uses  a  backtracking  algorithm. They cause an error if encountered by
4746           pcre_dfa_exec().
4747    
4748           The new verbs make use of what was previously invalid syntax: an  open-
4749           ing parenthesis followed by an asterisk. In Perl, they are generally of
4750           the form (*VERB:ARG) but PCRE does not support the use of arguments, so
4751           its  general  form is just (*VERB). Any number of these verbs may occur
4752           in a pattern. There are two kinds:
4753    
4754       Verbs that act immediately
4755    
4756           The following verbs act as soon as they are encountered:
4757    
4758              (*ACCEPT)
4759    
4760           This verb causes the match to end successfully, skipping the  remainder
4761           of  the pattern. When inside a recursion, only the innermost pattern is
4762           ended immediately. PCRE differs  from  Perl  in  what  happens  if  the
4763           (*ACCEPT)  is inside capturing parentheses. In Perl, the data so far is
4764           captured: in PCRE no data is captured. For example:
4765    
4766             A(A|B(*ACCEPT)|C)D
4767    
4768           This matches "AB", "AAD", or "ACD", but when it matches "AB",  no  data
4769           is captured.
4770    
4771             (*FAIL) or (*F)
4772    
4773           This  verb  causes the match to fail, forcing backtracking to occur. It
4774           is equivalent to (?!) but easier to read. The Perl documentation  notes
4775           that  it  is  probably  useful only when combined with (?{}) or (??{}).
4776           Those are, of course, Perl features that are not present in  PCRE.  The
4777           nearest  equivalent is the callout feature, as for example in this pat-
4778           tern:
4779    
4780             a+(?C)(*FAIL)
4781    
4782           A match with the string "aaaa" always fails, but the callout  is  taken
4783           before each backtrack happens (in this example, 10 times).
4784    
4785       Verbs that act after backtracking
4786    
4787           The following verbs do nothing when they are encountered. Matching con-
4788           tinues with what follows, but if there is no subsequent match, a  fail-
4789           ure  is  forced.   The  verbs  differ  in  exactly what kind of failure
4790           occurs.
4791    
4792             (*COMMIT)
4793    
4794           This verb causes the whole match to fail outright if the  rest  of  the
4795           pattern  does  not match. Even if the pattern is unanchored, no further
4796           attempts to find a match by advancing the start point take place.  Once
4797           (*COMMIT)  has been passed, pcre_exec() is committed to finding a match
4798           at the current starting point, or not at all. For example:
4799    
4800             a+(*COMMIT)b
4801    
4802           This matches "xxaab" but not "aacaab". It can be thought of as  a  kind
4803           of dynamic anchor, or "I've started, so I must finish."
4804    
4805             (*PRUNE)
4806    
4807           This  verb causes the match to fail at the current position if the rest
4808           of the pattern does not match. If the pattern is unanchored, the normal
4809           "bumpalong"  advance to the next starting character then happens. Back-
4810           tracking can occur as usual to the left of (*PRUNE), or  when  matching
4811           to  the right of (*PRUNE), but if there is no match to the right, back-
4812           tracking cannot cross (*PRUNE).  In simple cases, the use  of  (*PRUNE)
4813           is just an alternative to an atomic group or possessive quantifier, but
4814           there are some uses of (*PRUNE) that cannot be expressed in  any  other
4815           way.
4816    
4817             (*SKIP)
4818    
4819           This  verb  is like (*PRUNE), except that if the pattern is unanchored,
4820           the "bumpalong" advance is not to the next character, but to the  posi-
4821           tion  in  the  subject where (*SKIP) was encountered. (*SKIP) signifies
4822           that whatever text was matched leading up to it cannot  be  part  of  a
4823           successful match. Consider:
4824    
4825             a+(*SKIP)b
4826    
4827           If  the  subject  is  "aaaac...",  after  the first match attempt fails
4828           (starting at the first character in the  string),  the  starting  point
4829           skips on to start the next attempt at "c". Note that a possessive quan-
4830           tifer does not have the same effect in this example; although it  would
4831           suppress  backtracking  during  the  first  match  attempt,  the second
4832           attempt would start at the second character instead of skipping  on  to
4833           "c".
4834    
4835             (*THEN)
4836    
4837           This verb causes a skip to the next alternation if the rest of the pat-
4838           tern does not match. That is, it cancels pending backtracking, but only
4839           within  the  current  alternation.  Its name comes from the observation
4840           that it can be used for a pattern-based if-then-else block:
4841    
4842             ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
4843    
4844           If the COND1 pattern matches, FOO is tried (and possibly further  items
4845           after  the  end  of  the group if FOO succeeds); on failure the matcher
4846           skips to the second alternative and tries COND2,  without  backtracking
4847           into  COND1.  If  (*THEN)  is  used outside of any alternation, it acts
4848           exactly like (*PRUNE).
4849    
4850    
4851  SEE ALSO  SEE ALSO
4852    
4853         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).
# Line 4539  AUTHOR Line 4862  AUTHOR
4862    
4863  REVISION  REVISION
4864    
4865         Last updated: 13 June 2007         Last updated: 17 September 2007
4866         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
4867  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
4868    
4869    
4870    PCRESYNTAX(3)                                                    PCRESYNTAX(3)
4871    
4872    
4873    NAME
4874           PCRE - Perl-compatible regular expressions
4875    
4876    
4877    PCRE REGULAR EXPRESSION SYNTAX SUMMARY
4878    
4879           The  full syntax and semantics of the regular expressions that are sup-
4880           ported by PCRE are described in  the  pcrepattern  documentation.  This
4881           document contains just a quick-reference summary of the syntax.
4882    
4883    
4884    QUOTING
4885    
4886             \x         where x is non-alphanumeric is a literal x
4887             \Q...\E    treat enclosed characters as literal
4888    
4889    
4890    CHARACTERS
4891    
4892             \a         alarm, that is, the BEL character (hex 07)
4893             \cx        "control-x", where x is any character
4894             \e         escape (hex 1B)
4895             \f         formfeed (hex 0C)
4896             \n         newline (hex 0A)
4897             \r         carriage return (hex 0D)
4898             \t         tab (hex 09)
4899             \ddd       character with octal code ddd, or backreference
4900             \xhh       character with hex code hh
4901             \x{hhh..}  character with hex code hhh..
4902    
4903    
4904    CHARACTER TYPES
4905    
4906             .          any character except newline;
4907                          in dotall mode, any character whatsoever
4908             \C         one byte, even in UTF-8 mode (best avoided)
4909             \d         a decimal digit
4910             \D         a character that is not a decimal digit
4911             \h         a horizontal whitespace character
4912             \H         a character that is not a horizontal whitespace character
4913             \p{xx}     a character with the xx property
4914             \P{xx}     a character without the xx property
4915             \R         a newline sequence
4916             \s         a whitespace character
4917             \S         a character that is not a whitespace character
4918             \v         a vertical whitespace character
4919             \V         a character that is not a vertical whitespace character
4920             \w         a "word" character
4921             \W         a "non-word" character
4922             \X         an extended Unicode sequence
4923    
4924           In PCRE, \d, \D, \s, \S, \w, and \W recognize only ASCII characters.
4925    
4926    
4927    GENERAL CATEGORY PROPERTY CODES FOR \p and \P
4928    
4929             C          Other
4930             Cc         Control
4931             Cf         Format
4932             Cn         Unassigned
4933             Co         Private use
4934             Cs         Surrogate
4935    
4936             L          Letter
4937             Ll         Lower case letter
4938             Lm         Modifier letter
4939             Lo         Other letter
4940             Lt         Title case letter
4941             Lu         Upper case letter
4942             L&         Ll, Lu, or Lt
4943    
4944             M          Mark
4945             Mc         Spacing mark
4946             Me         Enclosing mark
4947             Mn         Non-spacing mark
4948    
4949             N          Number
4950             Nd         Decimal number
4951             Nl         Letter number
4952             No         Other number
4953    
4954             P          Punctuation
4955             Pc         Connector punctuation
4956             Pd         Dash punctuation
4957             Pe         Close punctuation
4958             Pf         Final punctuation
4959             Pi         Initial punctuation
4960             Po         Other punctuation
4961             Ps         Open punctuation
4962    
4963             S          Symbol
4964             Sc     &nbs