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revision 172 by ph10, Tue Jun 5 10:40:13 2007 UTC revision 231 by ph10, Tue Sep 11 11:15:33 2007 UTC
# 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.  Case-insensitive  matching  applies only to characters whose values         8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231         are less than 128, unless PCRE is built with Unicode property  support.         escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232         Even  when  Unicode  property support is available, PCRE still uses its         acters.
233         own character tables when checking the case of  low-valued  characters,  
234         so  as not to degrade performance.  The Unicode property information is         9. Case-insensitive matching applies only to  characters  whose  values
235           are  less than 128, unless PCRE is built with Unicode property support.
236           Even when Unicode property support is available, PCRE  still  uses  its
237           own  character  tables when checking the case of low-valued characters,
238           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 215  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: 18 April 2007         Last updated: 09 August 2007
260         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
# Line 327  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 390  AVOIDING EXCESSIVE STACK USAGE Line 437  AVOIDING EXCESSIVE STACK USAGE
437    
438         to  the  configure  command. With this configuration, PCRE will use the         to  the  configure  command. With this configuration, PCRE will use the
439         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
440         ment  functions.  Separate  functions are provided because the usage is         ment  functions. By default these point to malloc() and free(), but you
441         very predictable: the block sizes requested are always  the  same,  and         can replace the pointers so that your own functions are used.
442         the  blocks  are always freed in reverse order. A calling program might  
443         be able to implement optimized functions that perform better  than  the         Separate functions are  provided  rather  than  using  pcre_malloc  and
444         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more         pcre_free  because  the  usage  is  very  predictable:  the block sizes
445         slowly when built in this way. This option affects only the pcre_exec()         requested are always the same, and  the  blocks  are  always  freed  in
446         function; it is not relevant for the the pcre_dfa_exec() function.         reverse  order.  A calling program might be able to implement optimized
447           functions that perform better  than  malloc()  and  free().  PCRE  runs
448           noticeably more slowly when built in this way. This option affects only
449           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
450           pcre_dfa_exec() function.
451    
452    
453  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
# Line 451  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 474  AUTHOR Line 526  AUTHOR
526    
527  REVISION  REVISION
528    
529         Last updated: 16 April 2007         Last updated: 11 September 2007
530         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
531  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
532    
# Line 618  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 650  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 669  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    
# Line 866  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 890  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 901  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 980  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 1041  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 1154  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 1259  COMPILATION ERROR CODES Line 1341  COMPILATION ERROR CODES
1341           26  malformed number or name after (?(           26  malformed number or name after (?(
1342           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1343           28  assertion expected after (?(           28  assertion expected after (?(
1344           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1345           30  unknown POSIX class name           30  unknown POSIX class name
1346           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1347           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
# Line 1280  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
1374                   non-zero number
1375             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1376    
1377    
1378  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1476  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.
1569    
1570           PCRE_INFO_JCHANGED           PCRE_INFO_JCHANGED
1571    
1572         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
1573         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-
1574         nal option setting changes the local PCRE_DUPNAMES value.         nal option setting changes the local PCRE_DUPNAMES option.
1575    
1576           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1577    
# Line 1548  INFORMATION ABOUT A PATTERN Line 1639  INFORMATION ABOUT A PATTERN
1639         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
1640         fourth  argument  should  point to an unsigned long int variable. These         fourth  argument  should  point to an unsigned long int variable. These
1641         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1642         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1643           other words, they are the options that will be in force  when  matching
1644           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1645           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1646           and PCRE_EXTENDED.
1647    
1648         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
1649         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1751  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1846  MATCHING A PATTERN: THE TRADITIONAL FUNC
1846         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
1847         unachored at matching time.         unachored at matching time.
1848    
1849             PCRE_BSR_ANYCRLF
1850             PCRE_BSR_UNICODE
1851    
1852           These options (which are mutually exclusive) control what the \R escape
1853           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1854           or  to  match  any Unicode newline sequence. These options override the
1855           choice that was made or defaulted when the pattern was compiled.
1856    
1857           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1858           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1859           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1860           PCRE_NEWLINE_ANYCRLF           PCRE_NEWLINE_ANYCRLF
1861           PCRE_NEWLINE_ANY           PCRE_NEWLINE_ANY
1862    
1863         These  options  override  the  newline  definition  that  was chosen or         These options override  the  newline  definition  that  was  chosen  or
1864         defaulted when the pattern was compiled. For details, see the  descrip-         defaulted  when the pattern was compiled. For details, see the descrip-
1865         tion  of  pcre_compile()  above.  During  matching,  the newline choice         tion of pcre_compile()  above.  During  matching,  the  newline  choice
1866         affects the behaviour of the dot, circumflex,  and  dollar  metacharac-         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1867         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
1868         match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,         match failure for an unanchored pattern.
1869         PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt  
1870         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
1871         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-
1872         after the CRLF.         rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
1873           explicit matches for  CR  or  LF  characters,  the  match  position  is
1874           advanced by two characters instead of one, in other words, to after the
1875           CRLF.
1876    
1877           The above rule is a compromise that makes the most common cases work as
1878           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
1879           option is not set), it does not match the string "\r\nA" because, after
1880           failing  at the start, it skips both the CR and the LF before retrying.
1881           However, the pattern [\r\n]A does match that string,  because  it  con-
1882           tains an explicit CR or LF reference, and so advances only by one char-
1883           acter after the first failure.
1884    
1885           An explicit match for CR of LF is either a literal appearance of one of
1886           those  characters,  or  one  of the \r or \n escape sequences. Implicit
1887           matches such as [^X] do not count, nor does \s (which includes  CR  and
1888           LF in the characters that it matches).
1889    
1890           Notwithstanding  the above, anomalous effects may still occur when CRLF
1891           is a valid newline sequence and explicit \r or \n escapes appear in the
1892           pattern.
1893    
1894           PCRE_NOTBOL           PCRE_NOTBOL
1895    
1896         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1897         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
1898         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1899         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
1900         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1901    
1902           PCRE_NOTEOL           PCRE_NOTEOL
1903    
1904         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
1905         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
1906         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
1907         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1908         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
1909         not affect \Z or \z.         not affect \Z or \z.
1910    
1911           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1912    
1913         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
1914         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
1915         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
1916         example, if the pattern         example, if the pattern
1917    
1918           a?b?           a?b?
1919    
1920         is applied to a string not beginning with "a" or "b",  it  matches  the         is  applied  to  a string not beginning with "a" or "b", it matches the
1921         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1922         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
1923         rences of "a" or "b".         rences of "a" or "b".
1924    
1925         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1926         cial case of a pattern match of the empty  string  within  its  split()         cial  case  of  a  pattern match of the empty string within its split()
1927         function,  and  when  using  the /g modifier. It is possible to emulate         function, and when using the /g modifier. It  is  possible  to  emulate
1928         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
1929         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1930         if that fails by advancing the starting offset (see below)  and  trying         if  that  fails by advancing the starting offset (see below) and trying
1931         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
1932         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1933    
1934           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1935    
1936         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
1937         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1938         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
1939         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
1940         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
1941         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
1942         returned.         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
1943           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1944    
1945         If you already know that your subject is valid, and you  want  to  skip         If you already know that your subject is valid, and you  want  to  skip
1946         these    checks    for   performance   reasons,   you   can   set   the         these    checks    for   performance   reasons,   you   can   set   the
# Line 2039  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2163  MATCHING A PATTERN: THE TRADITIONAL FUNC
2163         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2164         description above.         description above.
2165    
          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.  
   
2166           PCRE_ERROR_BADNEWLINE     (-23)           PCRE_ERROR_BADNEWLINE     (-23)
2167    
2168         An invalid combination of PCRE_NEWLINE_xxx options was given.         An invalid combination of PCRE_NEWLINE_xxx options was given.
2169    
2170         Error numbers -16 to -20 are not used by pcre_exec().         Error numbers -16 to -20 and -22 are not used by pcre_exec().
2171    
2172    
2173  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 2199  DUPLICATE SUBPATTERN NAMES Line 2315  DUPLICATE SUBPATTERN NAMES
2315         subpatterns  are  not  required  to  be unique. Normally, patterns with         subpatterns  are  not  required  to  be unique. Normally, patterns with
2316         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
2317         subpatterns  participates. An example is shown in the pcrepattern docu-         subpatterns  participates. An example is shown in the pcrepattern docu-
2318         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2319    
2320           When   duplicates   are   present,   pcre_copy_named_substring()    and
2321         pcre_get_named_substring()  return the first substring corresponding to         pcre_get_named_substring()  return the first substring corresponding to
2322         the given name that is set.  If  none  are  set,  an  empty  string  is         the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2323         returned.  The pcre_get_stringnumber() function returns one of the num-         (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2324         bers that are associated with the name, but it is not defined which  it         function returns one of the numbers that are associated with the  name,
2325         is.         but it is not defined which it is.
2326    
2327         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
2328         name, you must use  the  pcre_get_stringtable_entries()  function.  The         name, you must use  the  pcre_get_stringtable_entries()  function.  The
# Line 2406  AUTHOR Line 2524  AUTHOR
2524    
2525  REVISION  REVISION
2526    
2527         Last updated: 04 June 2007         Last updated: 11 September 2007
2528         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2529  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2530    
# Line 2593  DIFFERENCES BETWEEN PCRE AND PERL Line 2711  DIFFERENCES BETWEEN PCRE AND PERL
2711    
2712         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2713         handle regular expressions. The differences described here  are  mainly         handle regular expressions. The differences described here  are  mainly
2714         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2715         tures that are expected to be in the forthcoming Perl 5.10.         some features that are expected to be in the forthcoming Perl 5.10.
2716    
2717         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2718         of  what  it does have are given in the section on UTF-8 support in the         of  what  it does have are given in the section on UTF-8 support in the
# Line 2659  DIFFERENCES BETWEEN PCRE AND PERL Line 2777  DIFFERENCES BETWEEN PCRE AND PERL
2777         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2778         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2779    
2780         11. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2781           (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2782           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2783           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2784           ture group; this is different to Perl.
2785    
2786           12. PCRE provides some extensions to the Perl regular expression facil-
2787         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
2788         versions, some of which (such as named parentheses) have been  in  PCRE         versions, some of which (such as named parentheses) have been  in  PCRE
2789         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 2672  DIFFERENCES BETWEEN PCRE AND PERL Line 2796  DIFFERENCES BETWEEN PCRE AND PERL
2796         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2797    
2798         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2799         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2800         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2801    
2802         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2803         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2685  DIFFERENCES BETWEEN PCRE AND PERL Line 2809  DIFFERENCES BETWEEN PCRE AND PERL
2809         (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-
2810         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2811    
2812         (g) The callout facility is PCRE-specific.         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2813           CRLF by the PCRE_BSR_ANYCRLF option.
2814    
2815         (h) The partial matching facility is PCRE-specific.         (h) The callout facility is PCRE-specific.
2816    
2817         (i) Patterns compiled by PCRE can be saved and re-used at a later time,         (i) The partial matching facility is PCRE-specific.
2818    
2819           (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2820         even on different hosts that have the other endianness.         even on different hosts that have the other endianness.
2821    
2822         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2823         different way and is not Perl-compatible.         different way and is not Perl-compatible.
2824    
2825           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2826           of a pattern that set overall options that cannot be changed within the
2827           pattern.
2828    
2829    
2830  AUTHOR  AUTHOR
2831    
# Line 2705  AUTHOR Line 2836  AUTHOR
2836    
2837  REVISION  REVISION
2838    
2839         Last updated: 06 March 2007         Last updated: 11 September 2007
2840         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2841  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2842    
# Line 2719  NAME Line 2850  NAME
2850    
2851  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2852    
2853         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2854         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2855         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2856         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2857         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2858         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2859           O'Reilly,  covers regular expressions in great detail. This description
2860           of PCRE's regular expressions is intended as reference material.
2861    
2862         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2863         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 2744  PCRE REGULAR EXPRESSION DETAILS Line 2877  PCRE REGULAR EXPRESSION DETAILS
2877         discussed in the pcrematching page.         discussed in the pcrematching page.
2878    
2879    
2880    NEWLINE CONVENTIONS
2881    
2882           PCRE  supports five different conventions for indicating line breaks in
2883           strings: a single CR (carriage return) character, a  single  LF  (line-
2884           feed) character, the two-character sequence CRLF, any of the three pre-
2885           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2886           discussion  about newlines, and shows how to set the newline convention
2887           in the options arguments for the compiling and matching functions.
2888    
2889           It is also possible to specify a newline convention by starting a  pat-
2890           tern string with one of the following five sequences:
2891    
2892             (*CR)        carriage return
2893             (*LF)        linefeed
2894             (*CRLF)      carriage return, followed by linefeed
2895             (*ANYCRLF)   any of the three above
2896             (*ANY)       all Unicode newline sequences
2897    
2898           These override the default and the options given to pcre_compile(). For
2899           example, on a Unix system where LF is the default newline sequence, the
2900           pattern
2901    
2902             (*CR)a.b
2903    
2904           changes the convention to CR. That pattern matches "a\nb" because LF is
2905           no longer a newline. Note that these special settings,  which  are  not
2906           Perl-compatible,  are  recognized  only at the very start of a pattern,
2907           and that they must be in upper case.  If  more  than  one  of  them  is
2908           present, the last one is used.
2909    
2910           The  newline  convention  does  not  affect what the \R escape sequence
2911           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2912           compatibility.  However, this can be changed; see the description of \R
2913           in the section entitled "Newline sequences" below.
2914    
2915    
2916  CHARACTERS AND METACHARACTERS  CHARACTERS AND METACHARACTERS
2917    
2918         A  regular  expression  is  a pattern that is matched against a subject         A regular expression is a pattern that is  matched  against  a  subject
2919         string from left to right. Most characters stand for  themselves  in  a         string  from  left  to right. Most characters stand for themselves in a
2920         pattern,  and  match  the corresponding characters in the subject. As a         pattern, and match the corresponding characters in the  subject.  As  a
2921         trivial example, the pattern         trivial example, the pattern
2922    
2923           The quick brown fox           The quick brown fox
2924    
2925         matches a portion of a subject string that is identical to itself. When         matches a portion of a subject string that is identical to itself. When
2926         caseless  matching is specified (the PCRE_CASELESS option), letters are         caseless matching is specified (the PCRE_CASELESS option), letters  are
2927         matched independently of case. In UTF-8 mode, PCRE  always  understands         matched  independently  of case. In UTF-8 mode, PCRE always understands
2928         the  concept  of case for characters whose values are less than 128, so         the concept of case for characters whose values are less than  128,  so
2929         caseless matching is always possible. For characters with  higher  val-         caseless  matching  is always possible. For characters with higher val-
2930         ues,  the concept of case is supported if PCRE is compiled with Unicode         ues, the concept of case is supported if PCRE is compiled with  Unicode
2931         property support, but not otherwise.   If  you  want  to  use  caseless         property  support,  but  not  otherwise.   If  you want to use caseless
2932         matching  for  characters  128  and above, you must ensure that PCRE is         matching for characters 128 and above, you must  ensure  that  PCRE  is
2933         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2934    
2935         The power of regular expressions comes  from  the  ability  to  include         The  power  of  regular  expressions  comes from the ability to include
2936         alternatives  and  repetitions in the pattern. These are encoded in the         alternatives and repetitions in the pattern. These are encoded  in  the
2937         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2938         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2939    
2940         There  are  two different sets of metacharacters: those that are recog-         There are two different sets of metacharacters: those that  are  recog-
2941         nized anywhere in the pattern except within square brackets, and  those         nized  anywhere in the pattern except within square brackets, and those
2942         that  are  recognized  within square brackets. Outside square brackets,         that are recognized within square brackets.  Outside  square  brackets,
2943         the metacharacters are as follows:         the metacharacters are as follows:
2944    
2945           \      general escape character with several uses           \      general escape character with several uses
# Line 2789  CHARACTERS AND METACHARACTERS Line 2958  CHARACTERS AND METACHARACTERS
2958                  also "possessive quantifier"                  also "possessive quantifier"
2959           {      start min/max quantifier           {      start min/max quantifier
2960    
2961         Part of a pattern that is in square brackets  is  called  a  "character         Part  of  a  pattern  that is in square brackets is called a "character
2962         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2963    
2964           \      general escape character           \      general escape character
# Line 2799  CHARACTERS AND METACHARACTERS Line 2968  CHARACTERS AND METACHARACTERS
2968                    syntax)                    syntax)
2969           ]      terminates the character class           ]      terminates the character class
2970    
2971         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the  metacharacters.
2972    
2973    
2974  BACKSLASH  BACKSLASH
2975    
2976         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2977         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
2978         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
2979         applies both inside and outside character classes.         applies both inside and outside character classes.
2980    
2981         For  example,  if  you want to match a * character, you write \* in the         For example, if you want to match a * character, you write  \*  in  the
2982         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
2983         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
2984         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
2985         that  it stands for itself. In particular, if you want to match a back-         that it stands for itself. In particular, if you want to match a  back-
2986         slash, you write \\.         slash, you write \\.
2987    
2988         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2989         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
2990         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
2991         ing  backslash  can  be  used to include a whitespace or # character as         ing backslash can be used to include a whitespace  or  #  character  as
2992         part of the pattern.         part of the pattern.
2993    
2994         If you want to remove the special meaning from a  sequence  of  charac-         If  you  want  to remove the special meaning from a sequence of charac-
2995         ters,  you can do so by putting them between \Q and \E. This is differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
2996         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
2997         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
2998         tion. Note the following examples:         tion. Note the following examples:
2999    
3000           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2835  BACKSLASH Line 3004  BACKSLASH
3004           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
3005           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
3006    
3007         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
3008         classes.         classes.
3009    
3010     Non-printing characters     Non-printing characters
3011    
3012         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
3013         acters in patterns in a visible manner. There is no restriction on  the         acters  in patterns in a visible manner. There is no restriction on the
3014         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
3015         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
3016         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is usually easier  to  use  one  of  the  following  escape
3017         sequences than the binary character it represents:         sequences than the binary character it represents:
3018    
3019           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
3020           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3021           \e        escape (hex 1B)           \e        escape (hex 1B)
3022           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3023           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3024           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3025           \t        tab (hex 09)           \t        tab (hex 09)
3026           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3027           \xhh      character with hex code hh           \xhh      character with hex code hh
3028           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
3029    
3030         The precise effect of \cx is as follows: if x is a lower  case  letter,         The  precise  effect of \cx is as follows: if x is a lower case letter,
3031         it  is converted to upper case. Then bit 6 of the character (hex 40) is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
3032         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
3033         becomes hex 7B.         becomes hex 7B.
3034    
3035         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
3036         in upper or lower case). Any number of hexadecimal  digits  may  appear         in  upper  or  lower case). Any number of hexadecimal digits may appear
3037         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
3038         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,
3039         the  maximum  hexadecimal  value is 7FFFFFFF). If characters other than         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3040         hexadecimal digits appear between \x{ and }, or if there is  no  termi-         than the largest Unicode code point, which is 10FFFF.
3041         nating  }, this form of escape is not recognized.  Instead, the initial  
3042         \x will be interpreted as a basic hexadecimal escape, with no following         If  characters  other than hexadecimal digits appear between \x{ and },
3043         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
3044           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3045           escape, with no following digits, giving a  character  whose  value  is
3046           zero.
3047    
3048         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
3049         two syntaxes for \x. There is no difference in the way  they  are  han-         two syntaxes for \x. There is no difference in the way  they  are  han-
# Line 2926  BACKSLASH Line 3098  BACKSLASH
3098    
3099     Absolute and relative back references     Absolute and relative back references
3100    
3101         The  sequence  \g followed by a positive or negative number, optionally         The  sequence  \g followed by an unsigned or a negative number, option-
3102         enclosed in braces, is an absolute or relative back reference. A  named         ally enclosed in braces, is an absolute or relative back  reference.  A
3103         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-
3104         later, following the discussion of parenthesized subpatterns.         cussed later, following the discussion of parenthesized subpatterns.
3105    
3106     Generic character types     Generic character types
3107    
# Line 2938  BACKSLASH Line 3110  BACKSLASH
3110    
3111           \d     any decimal digit           \d     any decimal digit
3112           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3113             \h     any horizontal whitespace character
3114             \H     any character that is not a horizontal whitespace character
3115           \s     any whitespace character           \s     any whitespace character
3116           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3117             \v     any vertical whitespace character
3118             \V     any character that is not a vertical whitespace character
3119           \w     any "word" character           \w     any "word" character
3120           \W     any "non-word" character           \W     any "non-word" character
3121    
# Line 2954  BACKSLASH Line 3130  BACKSLASH
3130    
3131         For compatibility with Perl, \s does not match the VT  character  (code         For compatibility with Perl, \s does not match the VT  character  (code
3132         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
3133         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
3134         "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-
3135         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
3136    
3137           In UTF-8 mode, characters with values greater than 128 never match  \d,
3138           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3139           code character property support is available.  These  sequences  retain
3140           their original meanings from before UTF-8 support was available, mainly
3141           for efficiency reasons.
3142    
3143           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3144           the  other  sequences, these do match certain high-valued codepoints in
3145           UTF-8 mode.  The horizontal space characters are:
3146    
3147             U+0009     Horizontal tab
3148             U+0020     Space
3149             U+00A0     Non-break space
3150             U+1680     Ogham space mark
3151             U+180E     Mongolian vowel separator
3152             U+2000     En quad
3153             U+2001     Em quad
3154             U+2002     En space
3155             U+2003     Em space
3156             U+2004     Three-per-em space
3157             U+2005     Four-per-em space
3158             U+2006     Six-per-em space
3159             U+2007     Figure space
3160             U+2008     Punctuation space
3161             U+2009     Thin space
3162             U+200A     Hair space
3163             U+202F     Narrow no-break space
3164             U+205F     Medium mathematical space
3165             U+3000     Ideographic space
3166    
3167           The vertical space characters are:
3168    
3169             U+000A     Linefeed
3170             U+000B     Vertical tab
3171             U+000C     Formfeed
3172             U+000D     Carriage return
3173             U+0085     Next line
3174             U+2028     Line separator
3175             U+2029     Paragraph separator
3176    
3177         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
3178         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-
# Line 2964  BACKSLASH Line 3180  BACKSLASH
3180         specific  matching is taking place (see "Locale support" in the pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3181         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
3182         systems,  or "french" in Windows, some character codes greater than 128         systems,  or "french" in Windows, some character codes greater than 128
3183         are used for accented letters, and these are matched by \w.         are used for accented letters, and these are matched by \w. The use  of
3184           locales with Unicode is discouraged.
        In UTF-8 mode, characters with values greater than 128 never match  \d,  
        \s, or \w, and always match \D, \S, and \W. This is true even when Uni-  
        code character property support is available. The use of  locales  with  
        Unicode is discouraged.  
3185    
3186     Newline sequences     Newline sequences
3187    
3188         Outside  a  character class, the escape sequence \R matches any Unicode         Outside  a  character class, by default, the escape sequence \R matches
3189         newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is         any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3190         equivalent to the following:         mode \R is equivalent to the following:
3191    
3192           (?>\r\n|\n|\x0b|\f|\r|\x85)           (?>\r\n|\n|\x0b|\f|\r|\x85)
3193    
# Line 2991  BACKSLASH Line 3203  BACKSLASH
3203         rator, U+2029).  Unicode character property support is not  needed  for         rator, U+2029).  Unicode character property support is not  needed  for
3204         these characters to be recognized.         these characters to be recognized.
3205    
3206           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3207           the complete set  of  Unicode  line  endings)  by  setting  the  option
3208           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3209           This can be made the default when PCRE is built; if this is  the  case,
3210           the  other  behaviour can be requested via the PCRE_BSR_UNICODE option.
3211           It is also possible to specify these settings  by  starting  a  pattern
3212           string with one of the following sequences:
3213    
3214             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3215             (*BSR_UNICODE)   any Unicode newline sequence
3216    
3217           These override the default and the options given to pcre_compile(), but
3218           they can be overridden by options given to pcre_exec(). Note that these
3219           special settings, which are not Perl-compatible, are recognized only at
3220           the very start of a pattern, and that they must be in  upper  case.  If
3221           more than one of them is present, the last one is used.
3222    
3223         Inside a character class, \R matches the letter "R".         Inside a character class, \R matches the letter "R".
3224    
3225     Unicode character properties     Unicode character properties
3226    
3227         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3228         tional escape sequences to match  character  properties  are  available         tional escape sequences that match characters with specific  properties
3229         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3230           limited to testing characters whose codepoints are less than  256,  but
3231           they do work in this mode.  The extra escape sequences are:
3232    
3233           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3234           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
# Line 3092  BACKSLASH Line 3323  BACKSLASH
3323         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
3324         classified as a modifier or "other".         classified as a modifier or "other".
3325    
3326           The Cs (Surrogate) property applies only to  characters  in  the  range
3327           U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3328           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3329           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3330           the pcreapi page).
3331    
3332         The long synonyms for these properties  that  Perl  supports  (such  as         The long synonyms for these properties  that  Perl  supports  (such  as
3333         \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
3334         any of these properties with "Is".         any of these properties with "Is".
# Line 3111  BACKSLASH Line 3348  BACKSLASH
3348         That is, it matches a character without the "mark"  property,  followed         That is, it matches a character without the "mark"  property,  followed
3349         by  zero  or  more  characters with the "mark" property, and treats the         by  zero  or  more  characters with the "mark" property, and treats the
3350         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3351         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3352           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3353           matches any one character.
3354    
3355         Matching  characters  by Unicode property is not fast, because PCRE has         Matching  characters  by Unicode property is not fast, because PCRE has
3356         to search a structure that contains  data  for  over  fifteen  thousand         to search a structure that contains  data  for  over  fifteen  thousand
# Line 3537  SUBPATTERNS Line 3776  SUBPATTERNS
3776         "Saturday".         "Saturday".
3777    
3778    
3779    DUPLICATE SUBPATTERN NUMBERS
3780    
3781           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3782           uses the same numbers for its capturing parentheses. Such a  subpattern
3783           starts  with (?| and is itself a non-capturing subpattern. For example,
3784           consider this pattern:
3785    
3786             (?|(Sat)ur|(Sun))day
3787    
3788           Because the two alternatives are inside a (?| group, both sets of  cap-
3789           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3790           you can look at captured substring number  one,  whichever  alternative
3791           matched.  This  construct  is useful when you want to capture part, but
3792           not all, of one of a number of alternatives. Inside a (?| group, paren-
3793           theses  are  numbered as usual, but the number is reset at the start of
3794           each branch. The numbers of any capturing buffers that follow the  sub-
3795           pattern  start after the highest number used in any branch. The follow-
3796           ing example is taken from the Perl documentation.  The  numbers  under-
3797           neath show in which buffer the captured content will be stored.
3798    
3799             # before  ---------------branch-reset----------- after
3800             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3801             # 1            2         2  3        2     3     4
3802    
3803           A  backreference  or  a  recursive call to a numbered subpattern always
3804           refers to the first one in the pattern with the given number.
3805    
3806           An alternative approach to using this "branch reset" feature is to  use
3807           duplicate named subpatterns, as described in the next section.
3808    
3809    
3810  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3811    
3812         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
# Line 3576  NAMED SUBPATTERNS Line 3846  NAMED SUBPATTERNS
3846           (?<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3847    
3848         There  are  five capturing substrings, but only one is ever set after a         There  are  five capturing substrings, but only one is ever set after a
3849         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3850         returns  the  substring  for  the first (and in this example, the only)         reset" subpattern, as described in the previous section.)
3851         subpattern of that name that matched.  This  saves  searching  to  find  
3852         which  numbered  subpattern  it  was. If you make a reference to a non-         The  convenience  function  for extracting the data by name returns the
3853         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring for the first (and in this example, the only)  subpattern  of
3854         corresponds  to  the  lowest number is used. For further details of the         that  name  that  matched.  This saves searching to find which numbered
3855         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern it was. If you make a reference to a non-unique  named  sub-
3856         tion.         pattern  from elsewhere in the pattern, the one that corresponds to the
3857           lowest number is used. For further details of the interfaces  for  han-
3858           dling named subpatterns, see the pcreapi documentation.
3859    
3860    
3861  REPETITION  REPETITION
# Line 3788  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4060  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4060    
4061           \d++foo           \d++foo
4062    
4063         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4064           example:
4065    
4066             (abc|xyz){2,3}+
4067    
4068           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4069         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4070         simpler forms of atomic group. However, there is no difference  in  the         simpler  forms  of atomic group. However, there is no difference in the
4071         meaning  of  a  possessive  quantifier and the equivalent atomic group,         meaning of a possessive quantifier and  the  equivalent  atomic  group,
4072         though there may be a performance  difference;  possessive  quantifiers         though  there  may  be a performance difference; possessive quantifiers
4073         should be slightly faster.         should be slightly faster.
4074    
4075         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-
4076         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first         tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4077         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
4078         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
4079         found its way into Perl at release 5.10.         found its way into Perl at release 5.10.
4080    
4081         PCRE has an optimization that automatically "possessifies" certain sim-         PCRE has an optimization that automatically "possessifies" certain sim-
4082         ple pattern constructs. For example, the sequence  A+B  is  treated  as         ple  pattern  constructs.  For  example, the sequence A+B is treated as
4083         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
4084         when B must follow.         when B must follow.
4085    
4086         When a pattern contains an unlimited repeat inside  a  subpattern  that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4087         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
4088         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
4089         very long time indeed. The pattern         very long time indeed. The pattern
4090    
4091           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
4092    
4093         matches  an  unlimited number of substrings that either consist of non-         matches an unlimited number of substrings that either consist  of  non-
4094         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it
4095         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
4096    
4097           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
4098    
4099         it  takes  a  long  time  before reporting failure. This is because the         it takes a long time before reporting  failure.  This  is  because  the
4100         string can be divided between the internal \D+ repeat and the  external         string  can be divided between the internal \D+ repeat and the external
4101         *  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
4102         example uses [!?] rather than a single character at  the  end,  because         example  uses  [!?]  rather than a single character at the end, because
4103         both  PCRE  and  Perl have an optimization that allows for fast failure         both PCRE and Perl have an optimization that allows  for  fast  failure
4104         when a single character is used. They remember the last single  charac-         when  a single character is used. They remember the last single charac-
4105         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
4106         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
4107         group, like this:         group, like this:
4108    
4109           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
4110    
4111         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
4112    
4113    
4114  BACK REFERENCES  BACK REFERENCES
4115    
4116         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
4117         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-
4118         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
4119         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
4120    
4121         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
4122         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
4123         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
4124         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
4125         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
4126         reference" of this type can make sense when a  repetition  is  involved         reference"  of  this  type can make sense when a repetition is involved
4127         and  the  subpattern to the right has participated in an earlier itera-         and the subpattern to the right has participated in an  earlier  itera-
4128         tion.         tion.
4129    
4130         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
4131         subpattern  whose  number  is  10  or  more using this syntax because a         subpattern whose number is 10 or  more  using  this  syntax  because  a
4132         sequence such as \50 is interpreted as a character  defined  in  octal.         sequence  such  as  \50 is interpreted as a character defined in octal.
4133         See the subsection entitled "Non-printing characters" above for further         See the subsection entitled "Non-printing characters" above for further
4134         details of the handling of digits following a backslash.  There  is  no         details  of  the  handling of digits following a backslash. There is no
4135         such  problem  when named parentheses are used. A back reference to any         such problem when named parentheses are used. A back reference  to  any
4136         subpattern is possible using named parentheses (see below).         subpattern is possible using named parentheses (see below).
4137    
4138         Another way of avoiding the ambiguity inherent in  the  use  of  digits         Another  way  of  avoiding  the ambiguity inherent in the use of digits
4139         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-
4140         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
4141         tive  or  a negative number, optionally enclosed in braces. These exam-         unsigned number or a negative number, optionally  enclosed  in  braces.
4142         ples are all identical:         These examples are all identical:
4143    
4144           (ring), \1           (ring), \1
4145           (ring), \g1           (ring), \g1
4146           (ring), \g{1}           (ring), \g{1}
4147    
4148         A positive number specifies an absolute reference without the ambiguity         An  unsigned number specifies an absolute reference without the ambigu-
4149         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
4150         digits follow the reference. A negative number is a relative reference.         digits follow the reference. A negative number is a relative reference.
4151         Consider this example:         Consider this example:
4152    
4153           (abc(def)ghi)\g{-1}           (abc(def)ghi)\g{-1}
4154    
4155         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-
4156         ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,         ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4157         \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
4158         helpful in long patterns, and also in  patterns  that  are  created  by         helpful  in  long  patterns,  and  also in patterns that are created by
4159         joining together fragments that contain references within themselves.         joining together fragments that contain references within themselves.
4160    
4161         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
4162         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
4163         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
4164         of doing that). So the pattern         of doing that). So the pattern
4165    
4166           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4167    
4168         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4169         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
4170         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-
4171         ple,         ple,
4172    
4173           ((?i)rah)\s+\1           ((?i)rah)\s+\1
4174    
4175         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
4176         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4177    
4178         There are several different ways of writing back  references  to  named         There  are  several  different ways of writing back references to named
4179         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
4180         \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
4181         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
4182         and named references, is also supported. We  could  rewrite  the  above         and  named  references,  is  also supported. We could rewrite the above
4183         example in any of the following ways:         example in any of the following ways:
4184    
4185           (?<p1>(?i)rah)\s+\k<p1>           (?<p1>(?i)rah)\s+\k<p1>
# Line 3910  BACK REFERENCES Line 4187  BACK REFERENCES
4187           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4188           (?<p1>(?i)rah)\s+\g{p1}           (?<p1>(?i)rah)\s+\g{p1}
4189    
4190         A  subpattern  that  is  referenced  by  name may appear in the pattern         A subpattern that is referenced by  name  may  appear  in  the  pattern
4191         before or after the reference.         before or after the reference.
4192    
4193         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
4194         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
4195         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4196    
4197           (a|(bc))\2           (a|(bc))\2
4198    
4199         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
4200         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
4201         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
4202         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4203         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
4204         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
4205         ments" below) can be used.         ments" below) can be used.
4206    
4207         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
4208         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
4209         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
4210         patterns. For example, the pattern         patterns. For example, the pattern
4211    
4212           (a|b\1)+           (a|b\1)+
4213    
4214         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-
4215         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4216         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4217         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
4218         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
4219         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4220    
4221    
4222  ASSERTIONS  ASSERTIONS
4223    
4224         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
4225         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
4226         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
4227         described above.         described above.
4228    
4229         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two
4230         kinds: those that look ahead of the current  position  in  the  subject         kinds:  those  that  look  ahead of the current position in the subject
4231         string,  and  those  that  look  behind  it. An assertion subpattern is         string, and those that look  behind  it.  An  assertion  subpattern  is
4232         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
4233         matching position to be changed.         matching position to be changed.
4234    
4235         Assertion  subpatterns  are  not  capturing subpatterns, and may not be         Assertion subpatterns are not capturing subpatterns,  and  may  not  be
4236         repeated, because it makes no sense to assert the  same  thing  several         repeated,  because  it  makes no sense to assert the same thing several
4237         times.  If  any kind of assertion contains capturing subpatterns within         times. If any kind of assertion contains capturing  subpatterns  within
4238         it, these are counted for the purposes of numbering the capturing  sub-         it,  these are counted for the purposes of numbering the capturing sub-
4239         patterns in the whole pattern.  However, substring capturing is carried         patterns in the whole pattern.  However, substring capturing is carried
4240         out only for positive assertions, because it does not  make  sense  for         out  only  for  positive assertions, because it does not make sense for
4241         negative assertions.         negative assertions.
4242    
4243     Lookahead assertions     Lookahead assertions
# Line 3970  ASSERTIONS Line 4247  ASSERTIONS
4247    
4248           \w+(?=;)           \w+(?=;)
4249    
4250         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-
4251         colon in the match, and         colon in the match, and
4252    
4253           foo(?!bar)           foo(?!bar)
4254    
4255         matches  any  occurrence  of  "foo" that is not followed by "bar". Note         matches any occurrence of "foo" that is not  followed  by  "bar".  Note
4256         that the apparently similar pattern         that the apparently similar pattern
4257    
4258           (?!foo)bar           (?!foo)bar
4259    
4260         does not find an occurrence of "bar"  that  is  preceded  by  something         does  not  find  an  occurrence  of "bar" that is preceded by something
4261         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other than "foo"; it finds any occurrence of "bar" whatsoever,  because
4262         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
4263         "bar". A lookbehind assertion is needed to achieve the other effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
4264    
4265         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
4266         most convenient way to do it is  with  (?!)  because  an  empty  string         most  convenient  way  to  do  it  is with (?!) because an empty string
4267         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
4268         string must always fail.         string must always fail.
4269    
4270     Lookbehind assertions     Lookbehind assertions
4271    
4272         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind  assertions start with (?<= for positive assertions and (?<!
4273         for negative assertions. For example,         for negative assertions. For example,
4274    
4275           (?<!foo)bar           (?<!foo)bar
4276    
4277         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
4278         contents of a lookbehind assertion are restricted  such  that  all  the         contents  of  a  lookbehind  assertion are restricted such that all the
4279         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-
4280         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
4281         fixed length. Thus         fixed length. Thus
4282    
4283           (?<=bullock|donkey)           (?<=bullock|donkey)
# Line 4009  ASSERTIONS Line 4286  ASSERTIONS
4286    
4287           (?<!dogs?|cats?)           (?<!dogs?|cats?)
4288    
4289         causes  an  error at compile time. Branches that match different length         causes an error at compile time. Branches that match  different  length
4290         strings are permitted only at the top level of a lookbehind  assertion.         strings  are permitted only at the top level of a lookbehind assertion.
4291         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
4292         requires all branches to match the same length of string. An  assertion         requires  all branches to match the same length of string. An assertion
4293         such as         such as
4294    
4295           (?<=ab(c|de))           (?<=ab(c|de))
4296    
4297         is  not  permitted,  because  its single top-level branch can match two         is not permitted, because its single top-level  branch  can  match  two
4298         different lengths, but it is acceptable if rewritten to  use  two  top-         different  lengths,  but  it is acceptable if rewritten to use two top-
4299         level branches:         level branches:
4300    
4301           (?<=abc|abde)           (?<=abc|abde)
4302    
4303         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
4304         instead of a lookbehind assertion; this is not restricted to  a  fixed-         instead  of  a lookbehind assertion; this is not restricted to a fixed-
4305         length.         length.
4306    
4307         The  implementation  of lookbehind assertions is, for each alternative,         The implementation of lookbehind assertions is, for  each  alternative,
4308         to temporarily move the current position back by the fixed  length  and         to  temporarily  move the current position back by the fixed length and
4309         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4310         rent position, the assertion fails.         rent position, the assertion fails.
4311    
4312         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
4313         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode) to appear in lookbehind assertions, because it makes it  impossi-
4314         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,
4315         which can match different numbers of bytes, are also not permitted.         which can match different numbers of bytes, are also not permitted.
4316    
4317         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind         Possessive quantifiers can  be  used  in  conjunction  with  lookbehind
4318         assertions to specify efficient matching at  the  end  of  the  subject         assertions  to  specify  efficient  matching  at the end of the subject
4319         string. Consider a simple pattern such as         string. Consider a simple pattern such as
4320    
4321           abcd$           abcd$
4322    
4323         when  applied  to  a  long string that does not match. Because matching         when applied to a long string that does  not  match.  Because  matching
4324         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
4325         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
4326         pattern is specified as         pattern is specified as
4327    
4328           ^.*abcd$           ^.*abcd$
4329    
4330         the initial .* matches the entire string at first, but when this  fails         the  initial .* matches the entire string at first, but when this fails
4331         (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
4332         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
4333         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,
4334         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
4335    
4336           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4337    
4338         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
4339         entire  string.  The subsequent lookbehind assertion does a single test         entire string. The subsequent lookbehind assertion does a  single  test
4340         on the last four characters. If it fails, the match fails  immediately.         on  the last four characters. If it fails, the match fails immediately.
4341         For  long  strings, this approach makes a significant difference to the         For long strings, this approach makes a significant difference  to  the
4342         processing time.         processing time.
4343    
4344     Using multiple assertions     Using multiple assertions
# Line 4070  ASSERTIONS Line 4347  ASSERTIONS
4347    
4348           (?<=\d{3})(?<!999)foo           (?<=\d{3})(?<!999)foo
4349    
4350         matches "foo" preceded by three digits that are not "999". Notice  that         matches  "foo" preceded by three digits that are not "999". Notice that
4351         each  of  the  assertions is applied independently at the same point in         each of the assertions is applied independently at the  same  point  in
4352         the subject string. First there is a  check  that  the  previous  three         the  subject  string.  First  there  is a check that the previous three
4353         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
4354         three characters are not "999".  This pattern does not match "foo" pre-         three characters are not "999".  This pattern does not match "foo" pre-
4355         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
4356         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-
4357         foo". A pattern to do that is         foo". A pattern to do that is
4358    
4359           (?<=\d{3}...)(?<!999)foo           (?<=\d{3}...)(?<!999)foo
4360    
4361         This  time  the  first assertion looks at the preceding six characters,         This time the first assertion looks at the  preceding  six  characters,
4362         checking that the first three are digits, and then the second assertion         checking that the first three are digits, and then the second assertion
4363         checks that the preceding three characters are not "999".         checks that the preceding three characters are not "999".
4364    
# Line 4089  ASSERTIONS Line 4366  ASSERTIONS
4366    
4367           (?<=(?<!foo)bar)baz           (?<=(?<!foo)bar)baz
4368    
4369         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
4370         is not preceded by "foo", while         is not preceded by "foo", while
4371    
4372           (?<=\d{3}(?!999)...)foo           (?<=\d{3}(?!999)...)foo
4373    
4374         is another pattern that matches "foo" preceded by three digits and  any         is  another pattern that matches "foo" preceded by three digits and any
4375         three characters that are not "999".         three characters that are not "999".
4376    
4377    
4378  CONDITIONAL SUBPATTERNS  CONDITIONAL SUBPATTERNS
4379    
4380         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-
4381         ditionally or to choose between two alternative subpatterns,  depending         ditionally  or to choose between two alternative subpatterns, depending
4382         on  the result of an assertion, or whether a previous capturing subpat-         on the result of an assertion, or whether a previous capturing  subpat-
4383         tern matched or not. The two possible forms of  conditional  subpattern         tern  matched  or not. The two possible forms of conditional subpattern
4384         are         are
4385    
4386           (?(condition)yes-pattern)           (?(condition)yes-pattern)
4387           (?(condition)yes-pattern|no-pattern)           (?(condition)yes-pattern|no-pattern)
4388    
4389         If  the  condition is satisfied, the yes-pattern is used; otherwise the         If the condition is satisfied, the yes-pattern is used;  otherwise  the
4390         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-
4391         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4392    
4393         There  are  four  kinds of condition: references to subpatterns, refer-         There are four kinds of condition: references  to  subpatterns,  refer-
4394         ences to recursion, a pseudo-condition called DEFINE, and assertions.         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4395    
4396     Checking for a used subpattern by number     Checking for a used subpattern by number
4397    
4398         If the text between the parentheses consists of a sequence  of  digits,         If  the  text between the parentheses consists of a sequence of digits,
4399         the  condition  is  true if the capturing subpattern of that number has         the condition is true if the capturing subpattern of  that  number  has
4400         previously matched. An alternative notation is to  precede  the  digits         previously  matched.  An  alternative notation is to precede the digits
4401         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-
4402         tive rather than absolute.  The most recently opened parentheses can be         tive rather than absolute.  The most recently opened parentheses can be
4403         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
4404         looping constructs it can also make sense to refer to subsequent groups         looping constructs it can also make sense to refer to subsequent groups
4405         with constructs such as (?(+2).         with constructs such as (?(+2).
4406    
4407         Consider  the  following  pattern, which contains non-significant white         Consider the following pattern, which  contains  non-significant  white
4408         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
4409         divide it into three parts for ease of discussion:         divide it into three parts for ease of discussion:
4410    
4411           ( \( )?    [^()]+    (?(1) \) )           ( \( )?    [^()]+    (?(1) \) )
4412    
4413         The  first  part  matches  an optional opening parenthesis, and if that         The first part matches an optional opening  parenthesis,  and  if  that
4414         character is present, sets it as the first captured substring. The sec-         character is present, sets it as the first captured substring. The sec-
4415         ond  part  matches one or more characters that are not parentheses. The         ond part matches one or more characters that are not  parentheses.  The
4416         third part is a conditional subpattern that tests whether the first set         third part is a conditional subpattern that tests whether the first set
4417         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
4418         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-
4419         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern is executed and a  closing  parenthesis  is  required.  Otherwise,
4420         since no-pattern is not present, the  subpattern  matches  nothing.  In         since  no-pattern  is  not  present, the subpattern matches nothing. In
4421         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other words,  this  pattern  matches  a  sequence  of  non-parentheses,
4422         optionally enclosed in parentheses.         optionally enclosed in parentheses.
4423    
4424         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
4425         relative reference:         relative reference:
4426    
4427           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...           ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4428    
4429         This  makes  the  fragment independent of the parentheses in the larger         This makes the fragment independent of the parentheses  in  the  larger
4430         pattern.         pattern.
4431    
4432     Checking for a used subpattern by name     Checking for a used subpattern by name
4433    
4434         Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a         Perl  uses  the  syntax  (?(<name>)...) or (?('name')...) to test for a
4435         used  subpattern  by  name.  For compatibility with earlier versions of         used subpattern by name. For compatibility  with  earlier  versions  of
4436         PCRE, which had this facility before Perl, the syntax  (?(name)...)  is         PCRE,  which  had this facility before Perl, the syntax (?(name)...) is
4437         also  recognized. However, there is a possible ambiguity with this syn-         also recognized. However, there is a possible ambiguity with this  syn-
4438         tax, because subpattern names may  consist  entirely  of  digits.  PCRE         tax,  because  subpattern  names  may  consist entirely of digits. PCRE
4439         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
4440         consists entirely of digits, PCRE looks for a subpattern of  that  num-         consists  entirely  of digits, PCRE looks for a subpattern of that num-
4441         ber,  which must be greater than zero. Using subpattern names that con-         ber, which must be greater than zero. Using subpattern names that  con-
4442         sist entirely of digits is not recommended.         sist entirely of digits is not recommended.
4443    
4444         Rewriting the above example to use a named subpattern gives this:         Rewriting the above example to use a named subpattern gives this:
# Line 4172  CONDITIONAL SUBPATTERNS Line 4449  CONDITIONAL SUBPATTERNS
4449     Checking for pattern recursion     Checking for pattern recursion
4450    
4451         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
4452         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
4453         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-
4454         sand follow the letter R, for example:         sand follow the letter R, for example:
4455    
4456           (?(R3)...) or (?(R&name)...)           (?(R3)...) or (?(R&name)...)
4457    
4458         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-
4459         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
4460         entire recursion stack.         entire recursion stack.
4461    
4462         At  "top  level", all these recursion test conditions are false. Recur-         At "top level", all these recursion test conditions are  false.  Recur-
4463         sive patterns are described below.         sive patterns are described below.
4464    
4465     Defining subpatterns for use by reference only     Defining subpatterns for use by reference only
4466    
4467         If the condition is the string (DEFINE), and  there  is  no  subpattern         If  the  condition  is  the string (DEFINE), and there is no subpattern
4468         with  the  name  DEFINE,  the  condition is always false. In this case,         with the name DEFINE, the condition is  always  false.  In  this  case,
4469         there may be only one alternative  in  the  subpattern.  It  is  always         there  may  be  only  one  alternative  in the subpattern. It is always
4470         skipped  if  control  reaches  this  point  in the pattern; the idea of         skipped if control reaches this point  in  the  pattern;  the  idea  of
4471         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-
4472         erenced  from elsewhere. (The use of "subroutines" is described below.)         erenced from elsewhere. (The use of "subroutines" is described  below.)
4473         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
4474         this (ignore whitespace and line breaks):         this (ignore whitespace and line breaks):
4475    
4476           (?(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) )
4477           \b (?&byte) (\.(?&byte)){3} \b           \b (?&byte) (\.(?&byte)){3} \b
4478    
4479         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
4480         group named "byte" is defined. This matches an individual component  of         group  named "byte" is defined. This matches an individual component of
4481         an  IPv4  address  (a number less than 256). When matching takes place,         an IPv4 address (a number less than 256). When  matching  takes  place,
4482         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
4483         condition.         condition.
4484    
4485         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
4486         four dot-separated components of an IPv4 address, insisting on  a  word         four  dot-separated  components of an IPv4 address, insisting on a word
4487         boundary at each end.         boundary at each end.
4488    
4489     Assertion conditions     Assertion conditions
4490    
4491         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
4492         assertion.  This may be a positive or negative lookahead or  lookbehind         assertion.   This may be a positive or negative lookahead or lookbehind
4493         assertion.  Consider  this  pattern,  again  containing non-significant         assertion. Consider  this  pattern,  again  containing  non-significant
4494         white space, and with the two alternatives on the second line:         white space, and with the two alternatives on the second line:
4495    
4496           (?(?=[^a-z]*[a-z])           (?(?=[^a-z]*[a-z])
4497           \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} )
4498    
4499         The condition  is  a  positive  lookahead  assertion  that  matches  an         The  condition  is  a  positive  lookahead  assertion  that  matches an
4500         optional  sequence of non-letters followed by a letter. In other words,         optional sequence of non-letters followed by a letter. In other  words,
4501         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
4502         letter  is found, the subject is matched against the first alternative;         letter is found, the subject is matched against the first  alternative;
4503         otherwise it is  matched  against  the  second.  This  pattern  matches         otherwise  it  is  matched  against  the  second.  This pattern matches
4504         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
4505         letters and dd are digits.         letters and dd are digits.
4506    
4507    
4508  COMMENTS  COMMENTS
4509    
4510         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
4511         next  closing  parenthesis.  Nested  parentheses are not permitted. The         next closing parenthesis. Nested parentheses  are  not  permitted.  The
4512         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
4513         at all.         at all.
4514    
4515         If  the PCRE_EXTENDED option is set, an unescaped # character outside a         If the PCRE_EXTENDED option is set, an unescaped # character outside  a
4516         character class introduces a  comment  that  continues  to  immediately         character  class  introduces  a  comment  that continues to immediately
4517         after the next newline in the pattern.         after the next newline in the pattern.
4518    
4519    
4520  RECURSIVE PATTERNS  RECURSIVE PATTERNS
4521    
4522         Consider  the problem of matching a string in parentheses, allowing for         Consider the problem of matching a string in parentheses, allowing  for
4523         unlimited nested parentheses. Without the use of  recursion,  the  best         unlimited  nested  parentheses.  Without the use of recursion, the best
4524         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
4525         depth of nesting. It is not possible to  handle  an  arbitrary  nesting         depth  of  nesting.  It  is not possible to handle an arbitrary nesting
4526         depth.         depth.
4527    
4528         For some time, Perl has provided a facility that allows regular expres-         For some time, Perl has provided a facility that allows regular expres-
4529         sions to recurse (amongst other things). It does this by  interpolating         sions  to recurse (amongst other things). It does this by interpolating
4530         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
4531         expression itself. A Perl pattern using code interpolation to solve the         expression itself. A Perl pattern using code interpolation to solve the
4532         parentheses problem can be created like this:         parentheses problem can be created like this:
4533    
# Line 4260  RECURSIVE PATTERNS Line 4537  RECURSIVE PATTERNS
4537         refers recursively to the pattern in which it appears.         refers recursively to the pattern in which it appears.
4538    
4539         Obviously, PCRE cannot support the interpolation of Perl code. Instead,         Obviously, PCRE cannot support the interpolation of Perl code. Instead,
4540         it  supports  special  syntax  for recursion of the entire pattern, and         it supports special syntax for recursion of  the  entire  pattern,  and
4541         also for individual subpattern recursion.  After  its  introduction  in         also  for  individual  subpattern  recursion. After its introduction in
4542         PCRE  and  Python,  this  kind of recursion was introduced into Perl at         PCRE and Python, this kind of recursion was  introduced  into  Perl  at
4543         release 5.10.         release 5.10.
4544    
4545         A special item that consists of (? followed by a  number  greater  than         A  special  item  that consists of (? followed by a number greater than
4546         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
4547         the given number, provided that it occurs inside that  subpattern.  (If         the  given  number, provided that it occurs inside that subpattern. (If
4548         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-
4549         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
4550         regular expression.         regular expression.
4551    
4552         In  PCRE (like Python, but unlike Perl), a recursive subpattern call is         In PCRE (like Python, but unlike Perl), a recursive subpattern call  is
4553         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
4554         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
4555         alternatives and there is a subsequent matching failure.         alternatives and there is a subsequent matching failure.
4556    
4557         This PCRE pattern solves the nested  parentheses  problem  (assume  the         This  PCRE  pattern  solves  the nested parentheses problem (assume the
4558         PCRE_EXTENDED option is set so that white space is ignored):         PCRE_EXTENDED option is set so that white space is ignored):
4559    
4560           \( ( (?>[^()]+) | (?R) )* \)           \( ( (?>[^()]+) | (?R) )* \)
4561    
4562         First  it matches an opening parenthesis. Then it matches any number of         First it matches an opening parenthesis. Then it matches any number  of
4563         substrings which can either be a  sequence  of  non-parentheses,  or  a         substrings  which  can  either  be  a sequence of non-parentheses, or a
4564         recursive  match  of the pattern itself (that is, a correctly parenthe-         recursive match of the pattern itself (that is, a  correctly  parenthe-
4565         sized substring).  Finally there is a closing parenthesis.         sized substring).  Finally there is a closing parenthesis.
4566    
4567         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
4568         the entire pattern, so instead you could use this:         the entire pattern, so instead you could use this:
4569    
4570           ( \( ( (?>[^()]+) | (?1) )* \) )           ( \( ( (?>[^()]+) | (?1) )* \) )
4571    
4572         We  have  put the pattern into parentheses, and caused the recursion to         We have put the pattern into parentheses, and caused the  recursion  to
4573         refer to them instead of the whole pattern.         refer to them instead of the whole pattern.
4574    
4575         In a larger pattern,  keeping  track  of  parenthesis  numbers  can  be         In  a  larger  pattern,  keeping  track  of  parenthesis numbers can be
4576         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
4577         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
4578         (?-2) to refer to the second most recently opened parentheses preceding         (?-2) to refer to the second most recently opened parentheses preceding
4579         the recursion. In other  words,  a  negative  number  counts  capturing         the  recursion.  In  other  words,  a  negative number counts capturing
4580         parentheses leftwards from the point at which it is encountered.         parentheses leftwards from the point at which it is encountered.
4581    
4582         It  is  also  possible  to refer to subsequently opened parentheses, by         It is also possible to refer to  subsequently  opened  parentheses,  by
4583         writing references such as (?+2). However, these  cannot  be  recursive         writing  references  such  as (?+2). However, these cannot be recursive
4584         because  the  reference  is  not inside the parentheses that are refer-         because the reference is not inside the  parentheses  that  are  refer-
4585         enced. They are always "subroutine" calls, as  described  in  the  next         enced.  They  are  always  "subroutine" calls, as described in the next
4586         section.         section.
4587    
4588         An  alternative  approach is to use named parentheses instead. The Perl         An alternative approach is to use named parentheses instead.  The  Perl
4589         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
4590         supported. We could rewrite the above example as follows:         supported. We could rewrite the above example as follows:
4591    
4592           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )           (?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
4593    
4594         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
4595         one is used.         one is used.
4596    
4597         This particular example pattern that we have been looking  at  contains         This  particular  example pattern that we have been looking at contains
4598         nested  unlimited repeats, and so the use of atomic grouping for match-         nested unlimited repeats, and so the use of atomic grouping for  match-
4599         ing strings of non-parentheses is important when applying  the  pattern         ing  strings  of non-parentheses is important when applying the pattern
4600         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
4601         to         to
4602    
4603           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()           (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
4604    
4605         it yields "no match" quickly. However, if atomic grouping is not  used,         it  yields "no match" quickly. However, if atomic grouping is not used,
4606         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
4607         different ways the + and * repeats can carve up the  subject,  and  all         different  ways  the  + and * repeats can carve up the subject, and all
4608         have to be tested before failure can be reported.         have to be tested before failure can be reported.
4609    
4610         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
4611         those from the outermost level of the recursion at which the subpattern         those from the outermost level of the recursion at which the subpattern
4612         value  is  set.   If  you want to obtain intermediate values, a callout         value is set.  If you want to obtain  intermediate  values,  a  callout
4613         function can be used (see below and the pcrecallout documentation).  If         function  can be used (see below and the pcrecallout documentation). If
4614         the pattern above is matched against         the pattern above is matched against
4615    
4616           (ab(cd)ef)           (ab(cd)ef)
4617    
4618         the  value  for  the  capturing  parentheses is "ef", which is the last         the value for the capturing parentheses is  "ef",  which  is  the  last
4619         value taken on at the top level. If additional parentheses  are  added,         value  taken  on at the top level. If additional parentheses are added,
4620         giving         giving
4621    
4622           \( ( ( (?>[^()]+) | (?R) )* ) \)           \( ( ( (?>[^()]+) | (?R) )* ) \)
4623              ^                        ^              ^                        ^
4624              ^                        ^              ^                        ^
4625    
4626         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
4627         parentheses. If there are more than 15 capturing parentheses in a  pat-         parentheses.  If there are more than 15 capturing parentheses in a pat-
4628         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,
4629         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-
4630         wards.  If  no  memory  can  be  obtained,  the  match  fails  with the         wards. If  no  memory  can  be  obtained,  the  match  fails  with  the
4631         PCRE_ERROR_NOMEMORY error.         PCRE_ERROR_NOMEMORY error.
4632    
4633         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
4634         recursion.   Consider  this pattern, which matches text in angle brack-         recursion.  Consider this pattern, which matches text in  angle  brack-
4635         ets, allowing for arbitrary nesting. Only digits are allowed in  nested         ets,  allowing for arbitrary nesting. Only digits are allowed in nested
4636         brackets  (that is, when recursing), whereas any characters are permit-         brackets (that is, when recursing), whereas any characters are  permit-
4637         ted at the outer level.         ted at the outer level.
4638    
4639           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >           < (?: (?(R) \d++  | [^<>]*+) | (?R)) * >
4640    
4641         In this pattern, (?(R) is the start of a conditional  subpattern,  with         In  this  pattern, (?(R) is the start of a conditional subpattern, with
4642         two  different  alternatives for the recursive and non-recursive cases.         two different alternatives for the recursive and  non-recursive  cases.
4643         The (?R) item is the actual recursive call.         The (?R) item is the actual recursive call.
4644    
4645    
4646  SUBPATTERNS AS SUBROUTINES  SUBPATTERNS AS SUBROUTINES
4647    
4648         If the syntax for a recursive subpattern reference (either by number or         If the syntax for a recursive subpattern reference (either by number or
4649         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-
4650         ates like a subroutine in a programming language. The "called"  subpat-         ates  like a subroutine in a programming language. The "called" subpat-
4651         tern may be defined before or after the reference. A numbered reference         tern may be defined before or after the reference. A numbered reference
4652         can be absolute or relative, as in these examples:         can be absolute or relative, as in these examples:
4653    
# Line 4382  SUBPATTERNS AS SUBROUTINES Line 4659  SUBPATTERNS AS SUBROUTINES
4659    
4660           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
4661    
4662         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
4663         not "sense and responsibility". If instead the pattern         not "sense and responsibility". If instead the pattern
4664    
4665           (sens|respons)e and (?1)ibility           (sens|respons)e and (?1)ibility
4666    
4667         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
4668         two strings. Another example is  given  in  the  discussion  of  DEFINE         two  strings.  Another  example  is  given  in the discussion of DEFINE
4669         above.         above.
4670    
4671         Like recursive subpatterns, a "subroutine" call is always treated as an         Like recursive subpatterns, a "subroutine" call is always treated as an
4672         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,
4673         it  is  never  re-entered, even if it contains untried alternatives and         it is never re-entered, even if it contains  untried  alternatives  and
4674         there is a subsequent matching failure.         there is a subsequent matching failure.
4675    
4676         When a subpattern is used as a subroutine, processing options  such  as         When  a  subpattern is used as a subroutine, processing options such as
4677         case-independence are fixed when the subpattern is defined. They cannot         case-independence are fixed when the subpattern is defined. They cannot
4678         be changed for different calls. For example, consider this pattern:         be changed for different calls. For example, consider this pattern:
4679    
4680           (abc)(?i:(?-1))           (abc)(?i:(?-1))
4681    
4682         It matches "abcabc". It does not match "abcABC" because the  change  of         It  matches  "abcabc". It does not match "abcABC" because the change of
4683         processing option does not affect the called subpattern.         processing option does not affect the called subpattern.
4684    
4685    
4686  CALLOUTS  CALLOUTS
4687    
4688         Perl has a feature whereby using the sequence (?{...}) causes arbitrary         Perl has a feature whereby using the sequence (?{...}) causes arbitrary
4689         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.
4690         This makes it possible, amongst other things, to extract different sub-         This makes it possible, amongst other things, to extract different sub-
4691         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-
4692         tion.         tion.
4693    
4694         PCRE provides a similar feature, but of course it cannot obey arbitrary         PCRE provides a similar feature, but of course it cannot obey arbitrary
4695         Perl code. The feature is called "callout". The caller of PCRE provides         Perl code. The feature is called "callout". The caller of PCRE provides
4696         an  external function by putting its entry point in the global variable         an external function by putting its entry point in the global  variable
4697         pcre_callout.  By default, this variable contains NULL, which  disables         pcre_callout.   By default, this variable contains NULL, which disables
4698         all calling out.         all calling out.
4699    
4700         Within  a  regular  expression,  (?C) indicates the points at which the         Within a regular expression, (?C) indicates the  points  at  which  the
4701         external function is to be called. If you want  to  identify  different         external  function  is  to be called. If you want to identify different
4702         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.
4703         The default value is zero.  For example, this pattern has  two  callout         The  default  value is zero.  For example, this pattern has two callout
4704         points:         points:
4705    
4706           (?C1)abc(?C2)def           (?C1)abc(?C2)def
4707    
4708         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
4709         automatically installed before each item in the pattern. They  are  all         automatically  installed  before each item in the pattern. They are all
4710         numbered 255.         numbered 255.
4711    
4712         During matching, when PCRE reaches a callout point (and pcre_callout is         During matching, when PCRE reaches a callout point (and pcre_callout is
4713         set), the external function is called. It is provided with  the  number         set),  the  external function is called. It is provided with the number
4714         of  the callout, the position in the pattern, and, optionally, one item         of the callout, the position in the pattern, and, optionally, one  item
4715         of data originally supplied by the caller of pcre_exec().  The  callout         of  data  originally supplied by the caller of pcre_exec(). The callout
4716         function  may cause matching to proceed, to backtrack, or to fail alto-         function may cause matching to proceed, to backtrack, or to fail  alto-
4717         gether. A complete description of the interface to the callout function         gether. A complete description of the interface to the callout function
4718         is given in the pcrecallout documentation.         is given in the pcrecallout documentation.
4719    
4720    
4721    BACTRACKING CONTROL
4722    
4723           Perl 5.10 introduced a number of "Special Backtracking Control  Verbs",
4724           which are described in the Perl documentation as "experimental and sub-
4725           ject to change or removal in a future version of Perl". It goes  on  to
4726           say:  "Their usage in production code should be noted to avoid problems
4727           during upgrades." The same remarks apply to the PCRE features described
4728           in this section.
4729    
4730           Since these verbs are specifically related to backtracking, they can be
4731           used only when the pattern is to be matched  using  pcre_exec(),  which
4732           uses  a  backtracking  algorithm. They cause an error if encountered by
4733           pcre_dfa_exec().
4734    
4735           The new verbs make use of what was previously invalid syntax: an  open-
4736           ing parenthesis followed by an asterisk. In Perl, they are generally of
4737           the form (*VERB:ARG) but PCRE does not support the use of arguments, so
4738           its  general  form is just (*VERB). Any number of these verbs may occur
4739           in a pattern. There are two kinds:
4740    
4741       Verbs that act immediately
4742    
4743           The following verbs act as soon as they are encountered:
4744    
4745              (*ACCEPT)
4746    
4747           This verb causes the match to end successfully, skipping the  remainder
4748           of  the pattern. When inside a recursion, only the innermost pattern is
4749           ended immediately. PCRE differs  from  Perl  in  what  happens  if  the
4750           (*ACCEPT)  is inside capturing parentheses. In Perl, the data so far is
4751           captured: in PCRE no data is captured. For example:
4752    
4753             A(A|B(*ACCEPT)|C)D
4754    
4755           This matches "AB", "AAD", or "ACD", but when it matches "AB",  no  data
4756           is captured.
4757    
4758             (*FAIL) or (*F)
4759    
4760           This  verb  causes the match to fail, forcing backtracking to occur. It
4761           is equivalent to (?!) but easier to read. The Perl documentation  notes
4762           that  it  is  probably  useful only when combined with (?{}) or (??{}).
4763           Those are, of course, Perl features that are not present in  PCRE.  The
4764           nearest  equivalent is the callout feature, as for example in this pat-
4765           tern:
4766    
4767             a+(?C)(*FAIL)
4768    
4769           A match with the string "aaaa" always fails, but the callout  is  taken
4770           before each backtrack happens (in this example, 10 times).
4771    
4772       Verbs that act after backtracking
4773    
4774           The following verbs do nothing when they are encountered. Matching con-
4775           tinues with what follows, but if there is no subsequent match, a  fail-
4776           ure  is  forced.   The  verbs  differ  in  exactly what kind of failure
4777           occurs.
4778    
4779             (*COMMIT)
4780    
4781           This verb causes the whole match to fail outright if the  rest  of  the
4782           pattern  does  not match. Even if the pattern is unanchored, no further
4783           attempts to find a match by advancing the start point take place.  Once
4784           (*COMMIT)  has been passed, pcre_exec() is committed to finding a match
4785           at the current starting point, or not at all. For example:
4786    
4787             a+(*COMMIT)b
4788    
4789           This matches "xxaab" but not "aacaab". It can be thought of as  a  kind
4790           of dynamic anchor, or "I've started, so I must finish."
4791    
4792             (*PRUNE)
4793    
4794           This  verb causes the match to fail at the current position if the rest
4795           of the pattern does not match. If the pattern is unanchored, the normal
4796           "bumpalong"  advance to the next starting character then happens. Back-
4797           tracking can occur as usual to the left of (*PRUNE), or  when  matching
4798           to  the right of (*PRUNE), but if there is no match to the right, back-
4799           tracking cannot cross (*PRUNE).  In simple cases, the use  of  (*PRUNE)
4800           is just an alternative to an atomic group or possessive quantifier, but
4801           there are some uses of (*PRUNE) that cannot be expressed in  any  other
4802           way.
4803    
4804             (*SKIP)
4805    
4806           This  verb  is like (*PRUNE), except that if the pattern is unanchored,
4807           the "bumpalong" advance is not to the next character, but to the  posi-
4808           tion  in  the  subject where (*SKIP) was encountered. (*SKIP) signifies
4809           that whatever text was matched leading up to it cannot  be  part  of  a
4810           successful match. Consider:
4811    
4812             a+(*SKIP)b
4813    
4814           If  the  subject  is  "aaaac...",  after  the first match attempt fails
4815           (starting at the first character in the  string),  the  starting  point
4816           skips on to start the next attempt at "c". Note that a possessive quan-
4817           tifer does not have the same effect in this example; although it  would
4818           suppress  backtracking  during  the  first  match  attempt,  the second
4819           attempt would start at the second character instead of skipping  on  to
4820           "c".
4821    
4822             (*THEN)
4823    
4824           This verb causes a skip to the next alternation if the rest of the pat-
4825           tern does not match. That is, it cancels pending backtracking, but only
4826           within  the  current  alternation.  Its name comes from the observation
4827           that it can be used for a pattern-based if-then-else block:
4828    
4829             ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
4830    
4831           If the COND1 pattern matches, FOO is tried (and possibly further  items
4832           after  the  end  of  the group if FOO succeeds); on failure the matcher
4833           skips to the second alternative and tries COND2,  without  backtracking
4834           into  COND1.  If  (*THEN)  is  used outside of any alternation, it acts
4835           exactly like (*PRUNE).
4836    
4837    
4838  SEE ALSO  SEE ALSO
4839    
4840         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).         pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).
# Line 4455  AUTHOR Line 4849  AUTHOR
4849    
4850  REVISION  REVISION
4851    
4852         Last updated: 29 May 2007         Last updated: 11 September 2007
4853           Copyright (c) 1997-2007 University of Cambridge.
4854    ------------------------------------------------------------------------------
4855    
4856    
4857    PCRESYNTAX(3)                                                    PCRESYNTAX(3)
4858    
4859    
4860    NAME
4861           PCRE - Perl-compatible regular expressions
4862    
4863    
4864    PCRE REGULAR EXPRESSION SYNTAX SUMMARY
4865    
4866           The  full syntax and semantics of the regular expressions that are sup-
4867           ported by PCRE are described in  the  pcrepattern  documentation.  This
4868           document contains just a quick-reference summary of the syntax.
4869    
4870    
4871    QUOTING
4872    
4873             \x         where x is non-alphanumeric is a literal x
4874             \Q...\E    treat enclosed characters as literal
4875    
4876    
4877    CHARACTERS
4878    
4879             \a         alarm, that is, the BEL character (hex 07)
4880             \cx        "control-x", where x is any character
4881             \e         escape (hex 1B)
4882             \f         formfeed (hex 0C)
4883             \n         newline (hex 0A)
4884             \r         carriage return (hex 0D)
4885             \t         tab (hex 09)
4886             \ddd       character with octal code ddd, or backreference
4887             \xhh       character with hex code hh
4888             \x{hhh..}  character with hex code hhh..
4889    
4890    
4891    CHARACTER TYPES
4892    
4893             .          any character except newline;
4894                          in dotall mode, any character whatsoever
4895             \C         one byte, even in UTF-8 mode (best avoided)
4896             \d         a decimal digit
4897             \D         a character that is not a decimal digit
4898             \h         a horizontal whitespace character
4899             \H         a character that is not a horizontal whitespace character
4900             \p{xx}     a character with the xx property
4901             \P{xx}     a character without the xx property
4902             \R         a newline sequence
4903             \s         a whitespace character
4904             \S         a character that is not a whitespace character
4905             \v         a vertical whitespace character
4906             \V         a character that is not a vertical whitespace character
4907             \w         a "word" character
4908             \W         a "non-word" character
4909             \X         an extended Unicode sequence
4910    
4911           In PCRE, \d, \D, \s, \S, \w, and \W recognize only ASCII characters.
4912    
4913    
4914    GENERAL CATEGORY PROPERTY CODES FOR \p and \P
4915    
4916             C          Other
4917             Cc         Control
4918             Cf         Format
4919             Cn         Unassigned
4920             Co         Private use
4921             Cs         Surrogate
4922    
4923             L          Letter
4924             Ll         Lower case letter
4925             Lm         Modifier letter
4926             Lo         Other letter
4927             Lt         Title case letter
4928             Lu         Upper case letter
4929             L&         Ll, Lu, or Lt
4930    
4931             M          Mark
4932             Mc         Spacing mark
4933             Me         Enclosing mark
4934             Mn         Non-spacing mark
4935    
4936             N          Number
4937             Nd         Decimal number
4938             Nl         Letter number
4939             No         Other number
4940    
4941             P          Punctuation
4942             Pc         Connector punctuation
4943             Pd         Dash punctuation
4944             Pe         Close punctuation
4945             Pf         Final punctuation
4946             Pi         Initial punctuation
4947             Po         Other punctuation
4948             Ps         Open punctuation
4949    
4950             S          Symbol
4951             Sc         Currency symbol
4952             Sk         Modifier symbol
4953             Sm         Mathematical symbol
4954             So         Other symbol
4955    
4956             Z          Separator
4957             Zl         Line separator
4958             Zp         Paragraph separator
4959             Zs         Space separator
4960    
4961    
4962    SCRIPT NAMES FOR \p AND \P
4963    
4964           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
4965           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
4966           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
4967           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
4968           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
4969           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
4970           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
4971           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
4972           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
4973    
4974    
4975    CHARACTER CLASSES
4976    
4977             [...]       positive character class
4978             [^...]      negative character class
4979             [x-y]       range (can be used for hex characters)
4980             [[:xxx:]]   positive POSIX named set
4981             [[^:xxx:]]  negative POSIX named set
4982    
4983             alnum       alphanumeric
4984             alpha       alphabetic
4985             ascii       0-127
4986             blank       space or tab
4987             cntrl       control character
4988             digit       decimal digit
4989             graph       printing, excluding space
4990             lower       lower case letter
4991             print       printing, including space
4992             punct       printing, excluding alphanumeric
4993             space       whitespace
4994             upper       upper case letter
4995             word        same as \w
4996             xdigit      hexadecimal digit
4997    
4998           In PCRE, POSIX character set names recognize only ASCII characters. You
4999           can use \Q...\E inside a character class.
5000    
5001    
5002    QUANTIFIERS
5003    
5004             ?           0 or 1, greedy
5005             ?+          0 or 1, possessive
5006             ??          0 or 1, lazy
5007             *           0 or more, greedy
5008             *+          0 or more, possessive
5009             *?          0 or more, lazy
5010             +           1 or more, greedy
5011             ++          1 or more, possessive
5012             +?          1 or more, lazy
5013             {n}         exactly n
5014             {n,m}       at least n, no more than m, greedy
5015             {n,m}+      at least n, no more than m, possessive
5016             {n,m}?      at least n, no more than m, lazy
5017             {n,}        n or more, greedy
5018             {n,}+       n or more, possessive
5019             {n,}?       n or more, lazy
5020    
5021    
5022    ANCHORS AND SIMPLE ASSERTIONS
5023    
5024             \b          word boundary
5025             \B          not a word boundary
5026             ^           start of subject
5027                          also after internal newline in multiline mode
5028             \A          start of subject
5029             $           end of subject
5030                          also before newline at end of subject
5031                          also before internal newline in multiline mode
5032             \Z          end of subject
5033                          also before newline at end of subject
5034             \z          end of subject
5035             \G          first matching position in subject
5036    
5037    
5038    MATCH POINT RESET
5039    
5040             \K          reset start of match
5041    
5042    
5043    ALTERNATION
5044    
5045             expr|expr|expr...
5046    
5047    
5048    CAPTURING
5049    
5050             (...)          capturing group
5051             (?<name>...)   named capturing group (Perl)
5052             (?'name'...)   named capturing group (Perl)
5053             (?P<name>...)  named capturing group (Python)
5054             (?:...)        non-capturing group
5055             (?|...)        non-capturing group; reset group numbers for
5056                             capturing groups in each alternative
5057    
5058    
5059    ATOMIC GROUPS
5060    
5061             (?>...)        atomic, non-capturing group
5062    
5063    
5064    COMMENT
5065    
5066             (?#....)       comment (not nestable)
5067    
5068    
5069    OPTION SETTING
5070    
5071             (?i)           caseless
5072             (?J)           allow duplicate names
5073             (?m)           multiline
5074             (?s)           single line (dotall)
5075             (?U)           default ungreedy (lazy)
5076             (?x)           extended (ignore white space)
5077             (?-...)        unset option(s)
5078    
5079    
5080    LOOKAHEAD AND LOOKBEHIND ASSERTIONS
5081    
5082             (?=...)        positive look ahead
5083             (?!...)        negative look ahead
5084             (?<=...)       positive look behind
5085             (?<!...)       negative look behind
5086    
5087           Each top-level branch of a look behind must be of a fixed length.
5088    
5089    
5090    BACKREFERENCES
5091    
5092             \n             reference by number (can be ambiguous)
5093             \gn            reference by number
5094             \g{n}          reference by number
5095             \g{-n}         relative reference by number
5096             \k<name>       reference by name (Perl)
5097             \k'name'       reference by name (Perl)
5098             \g{name}       reference by name (Perl)
5099             \k{name}       reference by name (.NET)
5100             (?P=name)      reference by name (Python)
5101    
5102    
5103    SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)
5104    
5105             (?R)           recurse whole pattern
5106             (?n)           call subpattern by absolute number
5107             (?+n)          call subpattern by relative number
5108             (?-n)          call subpattern by relative number
5109             (?&name)       call subpattern by name (Perl)
5110             (?P>name)      call subpattern by name (Python)
5111    
5112    
5113    CONDITIONAL PATTERNS
5114    
5115             (?(condition)yes-pattern)
5116             (?(condition)yes-pattern|no-pattern)
5117    
5118             (?(n)...       absolute reference condition
5119             (?(+n)...      relative reference condition
5120             (?(-n)...      relative reference condition
5121             (?(<name>)...  named reference condition (Perl)
5122             (?('name')...  named reference condition (Perl)
5123             (?(name)...    named reference condition (PCRE)
5124             (?(R)...       overall recursion condition
5125             (?(Rn)...      specific group recursion condition
5126             (?(R&name)...  specific recursion condition
5127             (?(DEFINE)...  define subpattern for reference
5128             (?(assert)...  assertion condition
5129    
5130    
5131    BACKTRACKING CONTROL
5132    
5133           The following act immediately they are reached:
5134    
5135             (*ACCEPT)      force successful match
5136             (*FAIL)        force backtrack; synonym (*F)
5137    
5138           The following act only when a subsequent match failure causes  a  back-
5139           track to reach them. They all force a match failure, but they differ in
5140           what happens afterwards. Those that advance the start-of-match point do
5141           so only if the pattern is not anchored.
5142    
5143             (*COMMIT)      overall failure, no advance of starting point
5144             (*PRUNE)       advance to next starting character
5145             (*SKIP)        advance start to current matching position
5146             (*THEN)        local failure, backtrack to next alternation
5147    
5148    
5149    NEWLINE CONVENTIONS
5150    
5151           These are recognized only at the very start of a pattern.
5152    
5153             (*CR)
5154             (*LF)
5155             (*CRLF)
5156             (*ANYCRLF)
5157             (*ANY)
5158    
5159    
5160    WHAT \R MATCHES
5161    
5162           These are recognized only at the very start of a pattern.
5163    
5164             (*BSR_ANYCRLF)
5165             (*BSR_UNICODE)
5166    
5167    
5168    CALLOUTS
5169    
5170             (?C)      callout
5171             (?Cn)     callout with data n
5172    
5173    
5174    SEE ALSO
5175    
5176           pcrepattern(3), pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).
5177    
5178    
5179    AUTHOR
5180    
5181           Philip Hazel
5182           University Computing Service
5183           Cambridge CB2 3QH, England.
5184    
5185    
5186    REVISION
5187    
5188           Last updated: 11 September 2007
5189         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
5190  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
5191    
# Line 4786  RE-USING A PRECOMPILED PATTERN Line 5516  RE-USING A PRECOMPILED PATTERN
5516    
5517  COMPATIBILITY WITH DIFFERENT PCRE RELEASES  COMPATIBILITY WITH DIFFERENT PCRE RELEASES
5518    
5519         The layout of the control block that is at the start of the  data  that         In general, it is safest to  recompile  all  saved  patterns  when  you
5520         makes  up  a  compiled pattern was changed for release 5.0. If you have         update  to  a new PCRE release, though not all updates actually require
5521         any saved patterns that were compiled with  previous  releases  (not  a         this. Recompiling is definitely needed for release 7.2.
        facility  that  was  previously advertised), you will have to recompile  
        them for release 5.0 and above.  
   
        If you have any saved patterns in UTF-8 mode that use  \p  or  \P  that  
        were  compiled  with any release up to and including 6.4, you will have  
        to recompile them for release 6.5 and above.  
   
        All saved patterns from earlier releases must be recompiled for release  
        7.0  or  higher,  because  there was an internal reorganization at that  
        release.  
5522    
5523    
5524  AUTHOR  AUTHOR
# Line 4810  AUTHOR Line 5530  AUTHOR
5530    
5531  REVISION  REVISION
5532    
5533         Last updated: 24 April 2007         Last updated: 13 June 2007
5534         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
5535  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
5536    
# Line 5545  PCRE SAMPLE PROGRAM Line 6265  PCRE SAMPLE PROGRAM
6265         bility  of  matching an empty string. Comments in the code explain what         bility  of  matching an empty string. Comments in the code explain what
6266         is going on.         is going on.
6267    
6268         If PCRE is installed in the standard include  and  library  directories         The demonstration program is automatically built if you use  "./config-
6269         for  your  system, you should be able to compile the demonstration pro-         ure;make"  to  build PCRE. Otherwise, if PCRE is installed in the stan-
6270         gram using this command:         dard include and library directories for your  system,  you  should  be
6271           able to compile the demonstration program using this command:
6272    
6273           gcc -o pcredemo pcredemo.c -lpcre           gcc -o pcredemo pcredemo.c -lpcre
6274    
6275         If PCRE is installed elsewhere, you may need to add additional  options         If  PCRE is installed elsewhere, you may need to add additional options
6276         to  the  command line. For example, on a Unix-like system that has PCRE         to the command line. For example, on a Unix-like system that  has  PCRE
6277         installed in /usr/local, you  can  compile  the  demonstration  program         installed  in  /usr/local,  you  can  compile the demonstration program
6278         using a command like this:         using a command like this:
6279    
6280           gcc -o pcredemo -I/usr/local/include pcredemo.c \           gcc -o pcredemo -I/usr/local/include pcredemo.c \
6281               -L/usr/local/lib -lpcre               -L/usr/local/lib -lpcre
6282    
6283         Once  you  have  compiled the demonstration program, you can run simple         Once you have compiled the demonstration program, you  can  run  simple
6284         tests like this:         tests like this:
6285    
6286           ./pcredemo 'cat|dog' 'the cat sat on the mat'           ./pcredemo 'cat|dog' 'the cat sat on the mat'
6287           ./pcredemo -g 'cat|dog' 'the dog sat on the cat'           ./pcredemo -g 'cat|dog' 'the dog sat on the cat'
6288    
6289         Note that there is a  much  more  comprehensive  test  program,  called         Note  that  there  is  a  much  more comprehensive test program, called
6290         pcretest,  which  supports  many  more  facilities  for testing regular         pcretest, which supports  many  more  facilities  for  testing  regular
6291         expressions and the PCRE library. The pcredemo program is provided as a         expressions and the PCRE library. The pcredemo program is provided as a
6292         simple coding example.         simple coding example.
6293    
# Line 5574  PCRE SAMPLE PROGRAM Line 6295  PCRE SAMPLE PROGRAM
6295         the standard library directory, you may get an error like this when you         the standard library directory, you may get an error like this when you
6296         try to run pcredemo:         try to run pcredemo:
6297    
6298           ld.so.1:  a.out:  fatal:  libpcre.so.0:  open failed: No such file or           ld.so.1: a.out: fatal: libpcre.so.0: open failed:  No  such  file  or
6299         directory         directory
6300    
6301         This is caused by the way shared library support works  on  those  sys-         This  is  caused  by the way shared library support works on those sys-
6302         tems. You need to add         tems. You need to add
6303    
6304           -R/usr/local/lib           -R/usr/local/lib
# Line 5594  AUTHOR Line 6315  AUTHOR
6315    
6316  REVISION  REVISION
6317    
6318         Last updated: 06 March 2007         Last updated: 13 June 2007
6319         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
6320  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
6321  PCRESTACK(3)                                                      PCRESTACK(3)  PCRESTACK(3)                                                      PCRESTACK(3)
# Line 5664  PCRE DISCUSSION OF STACK USAGE Line 6385  PCRE DISCUSSION OF STACK USAGE
6385         In environments where stack memory is constrained, you  might  want  to         In environments where stack memory is constrained, you  might  want  to
6386         compile  PCRE to use heap memory instead of stack for remembering back-         compile  PCRE to use heap memory instead of stack for remembering back-
6387         up points. This makes it run a lot more slowly, however. Details of how         up points. This makes it run a lot more slowly, however. Details of how
6388         to do this are given in the pcrebuild documentation.         to do this are given in the pcrebuild documentation. When built in this
6389           way, instead of using the stack, PCRE obtains and frees memory by call-
6390         In  Unix-like environments, there is not often a problem with the stack         ing  the  functions  that  are  pointed to by the pcre_stack_malloc and
6391         unless very long strings are involved,  though  the  default  limit  on         pcre_stack_free variables. By default,  these  point  to  malloc()  and
6392         stack  size  varies  from system to system. Values from 8Mb to 64Mb are         free(),  but you can replace the pointers to cause PCRE to use your own
6393           functions. Since the block sizes are always the same,  and  are  always
6394           freed in reverse order, it may be possible to implement customized mem-
6395           ory handlers that are more efficient than the standard functions.
6396    
6397           In Unix-like environments, there is not often a problem with the  stack
6398           unless  very  long  strings  are  involved, though the default limit on
6399           stack size varies from system to system. Values from 8Mb  to  64Mb  are
6400         common. You can find your default limit by running the command:         common. You can find your default limit by running the command:
6401    
6402           ulimit -s           ulimit -s
6403    
6404         Unfortunately, the effect of running out of  stack  is  often  SIGSEGV,         Unfortunately,  the  effect  of  running out of stack is often SIGSEGV,
6405         though  sometimes  a more explicit error message is given. You can nor-         though sometimes a more explicit error message is given. You  can  nor-
6406         mally increase the limit on stack size by code such as this:         mally increase the limit on stack size by code such as this:
6407    
6408           struct rlimit rlim;           struct rlimit rlim;
# Line 5682  PCRE DISCUSSION OF STACK USAGE Line 6410  PCRE DISCUSSION OF STACK USAGE
6410           rlim.rlim_cur = 100*1024*1024;           rlim.rlim_cur = 100*1024*1024;
6411           setrlimit(RLIMIT_STACK, &rlim);           setrlimit(RLIMIT_STACK, &rlim);
6412    
6413         This reads the current limits (soft and hard) using  getrlimit(),  then         This  reads  the current limits (soft and hard) using getrlimit(), then
6414         attempts  to  increase  the  soft limit to 100Mb using setrlimit(). You         attempts to increase the soft limit to  100Mb  using  setrlimit().  You
6415         must do this before calling pcre_exec().         must do this before calling pcre_exec().
6416    
6417         PCRE has an internal counter that can be used to  limit  the  depth  of         PCRE  has  an  internal  counter that can be used to limit the depth of
6418         recursion,  and  thus cause pcre_exec() to give an error code before it         recursion, and thus cause pcre_exec() to give an error code  before  it
6419         runs out of stack. By default, the limit is very  large,  and  unlikely         runs  out  of  stack. By default, the limit is very large, and unlikely
6420         ever  to operate. It can be changed when PCRE is built, and it can also         ever to operate. It can be changed when PCRE is built, and it can  also
6421         be set when pcre_exec() is called. For details of these interfaces, see         be set when pcre_exec() is called. For details of these interfaces, see
6422         the pcrebuild and pcreapi documentation.         the pcrebuild and pcreapi documentation.
6423    
6424         As a very rough rule of thumb, you should reckon on about 500 bytes per         As a very rough rule of thumb, you should reckon on about 500 bytes per
6425         recursion. Thus, if you want to limit your  stack  usage  to  8Mb,  you         recursion.  Thus,  if  you  want  to limit your stack usage to 8Mb, you
6426         should  set  the  limit at 16000 recursions. A 64Mb stack, on the other         should set the limit at 16000 recursions. A 64Mb stack,  on  the  other
6427         hand, can support around 128000 recursions. The pcretest  test  program         hand,  can  support around 128000 recursions. The pcretest test program
6428         has a command line option (-S) that can be used to increase the size of         has a command line option (-S) that can be used to increase the size of
6429         its stack.         its stack.
6430    
# Line 5710  AUTHOR Line 6438  AUTHOR
6438    
6439  REVISION  REVISION
6440    
6441         Last updated: 12 March 2007         Last updated: 05 June 2007
6442         Copyright (c) 1997-2007 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
6443  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
6444    

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