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# Line 18  INTRODUCTION Line 18  INTRODUCTION
18    
19         The  PCRE  library is a set of functions that implement regular expres-         The  PCRE  library is a set of functions that implement regular expres-
20         sion pattern matching using the same syntax and semantics as Perl, with         sion pattern matching using the same syntax and semantics as Perl, with
21         just  a  few  differences.  The current implementation of PCRE (release         just  a  few differences. (Certain features that appeared in Python and
22         6.x) corresponds approximately with Perl  5.8,  including  support  for         PCRE before they appeared in Perl are also available using  the  Python
23         UTF-8 encoded strings and Unicode general category properties. However,         syntax.)
24         this support has to be explicitly enabled; it is not the default.  
25           The  current  implementation of PCRE (release 7.x) corresponds approxi-
26         In addition to the Perl-compatible matching function,  PCRE  also  con-         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         tains  an  alternative matching function that matches the same compiled         Unicode general category properties. However, UTF-8 and Unicode support
28         patterns in a different way. In certain circumstances, the  alternative         has to be explicitly enabled; it is not the default. The Unicode tables
29         function  has  some  advantages.  For  a discussion of the two matching         correspond to Unicode release 5.0.0.
30         algorithms, see the pcrematching page.  
31           In  addition to the Perl-compatible matching function, PCRE contains an
32         PCRE is written in C and released as a C library. A  number  of  people         alternative matching function that matches the same  compiled  patterns
33         have  written  wrappers and interfaces of various kinds. In particular,         in  a different way. In certain circumstances, the alternative function
34         Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now         has some advantages. For a discussion of the two  matching  algorithms,
35           see the pcrematching page.
36    
37           PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40         included as part of the PCRE distribution. The pcrecpp page has details         included as part of the PCRE distribution. The pcrecpp page has details
41         of this interface. Other people's contributions can  be  found  in  the         of  this  interface.  Other  people's contributions can be found in the
42         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
43    
44         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
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
# Line 67  USER DOCUMENTATION Line 73  USER DOCUMENTATION
73         of searching. The sections are as follows:         of searching. The sections are as follows:
74    
75           pcre              this document           pcre              this document
76             pcre-config       show PCRE installation configuration information
77           pcreapi           details of PCRE's native C API           pcreapi           details of PCRE's native C API
78           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
79           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
# Line 77  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 99  LIMITATIONS Line 107  LIMITATIONS
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 will be slower.         of execution is slower.
111    
112           All values in repeating quantifiers must be less than 65536.
113    
114         All  values in repeating quantifiers must be less than 65536. The maxi-         There is no limit to the number of parenthesized subpatterns, but there
115         mum compiled length of subpattern with  an  explicit  repeat  count  is         can be no more than 65535 capturing subpatterns.
        30000 bytes. The maximum number of capturing subpatterns is 65535.  
   
        There  is  no limit to the number of non-capturing subpatterns, but the  
        maximum depth of nesting of  all  kinds  of  parenthesized  subpattern,  
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
116    
117         The maximum length of name for a named subpattern is 32, and the  maxi-         The maximum length of name for a named subpattern is 32 characters, and
118         mum 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
# Line 136  UTF-8 AND UNICODE PROPERTY SUPPORT Line 140  UTF-8 AND UNICODE PROPERTY SUPPORT
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 in several places, so should         is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144         not be very large.         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-
# Line 151  UTF-8 AND UNICODE PROPERTY SUPPORT Line 155  UTF-8 AND UNICODE PROPERTY SUPPORT
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
# Line 190  UTF-8 AND UNICODE PROPERTY SUPPORT Line 224  UTF-8 AND UNICODE PROPERTY SUPPORT
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           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232           acters.
233    
234         9. Case-insensitive matching applies only to  characters  whose  values         9. Case-insensitive matching applies only to  characters  whose  values
235         are  less than 128, unless PCRE is built with Unicode property support.         are  less than 128, unless PCRE is built with Unicode property support.
236         Even when Unicode property support is available, PCRE  still  uses  its         Even when Unicode property support is available, PCRE  still  uses  its
# Line 208  UTF-8 AND UNICODE PROPERTY SUPPORT Line 246  UTF-8 AND UNICODE PROPERTY SUPPORT
246  AUTHOR  AUTHOR
247    
248         Philip Hazel         Philip Hazel
249         University Computing Service,         University Computing Service
250         Cambridge CB2 3QG, 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 initial and sur-         so I've taken it away. If you want to email me, use  my  two  initials,
254         name, separated by a dot, at the domain ucs.cam.ac.uk.         followed by the two digits 10, at the domain cam.ac.uk.
255    
256    
257    REVISION
258    
259  Last updated: 05 June 2006         Last updated: 09 August 2007
260  Copyright (c) 1997-2006 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
263    
# Line 238  PCRE BUILD-TIME OPTIONS Line 279  PCRE BUILD-TIME OPTIONS
279    
280           ./configure --help           ./configure --help
281    
282         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
283         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
284         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
285         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
286         option always exists as well, but as it specifies the  default,  it  is         tary option always exists as well, but as it specifies the default,  it
287         not described.         is not described.
288    
289    
290  C++ SUPPORT  C++ SUPPORT
# Line 282  UNICODE CHARACTER PROPERTY SUPPORT Line 323  UNICODE CHARACTER PROPERTY SUPPORT
323         to the configure command. This implies UTF-8 support, even if you  have         to the configure command. This implies UTF-8 support, even if you  have
324         not explicitly requested it.         not explicitly requested it.
325    
326         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
327         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
328         gory  properties  such as Lu and Nd are supported. Details are given in         are supported. Details are given in the pcrepattern documentation.
        the pcrepattern documentation.  
329    
330    
331  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
332    
333         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
334         the  end  of  a line. This is the normal newline character on Unix-like         the end of a line. This is the normal newline  character  on  Unix-like
335         systems. You can compile PCRE to use character 13 (carriage return, CR)         systems. You can compile PCRE to use character 13 (carriage return, CR)
336         instead, by adding         instead, by adding
337    
338           --enable-newline-is-cr           --enable-newline-is-cr
339    
340         to  the  configure  command.  There  is  also  a --enable-newline-is-lf         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
341         option, which explicitly specifies linefeed as the newline character.         option, which explicitly specifies linefeed as the newline character.
342    
343         Alternatively, you can specify that line endings are to be indicated by         Alternatively, you can specify that line endings are to be indicated by
# Line 305  CODE VALUE OF NEWLINE Line 345  CODE VALUE OF NEWLINE
345    
346           --enable-newline-is-crlf           --enable-newline-is-crlf
347    
348         to  the  configure command. Whatever line ending convention is selected         to the configure command. There is a fourth option, specified by
349         when PCRE is built can be overridden when  the  library  functions  are  
350         called.  At  build time it is conventional to use the standard for your           --enable-newline-is-anycrlf
351         operating system.  
352           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
353           CRLF as indicating a line ending. Finally, a fifth option, specified by
354    
355             --enable-newline-is-any
356    
357           causes PCRE to recognize any Unicode newline sequence.
358    
359           Whatever line ending convention is selected when PCRE is built  can  be
360           overridden  when  the library functions are called. At build time it is
361           conventional to use the standard for your operating system.
362    
363    
364  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 356  HANDLING VERY LARGE PATTERNS Line 406  HANDLING VERY LARGE PATTERNS
406         longer  offsets slows down the operation of PCRE because it has to load         longer  offsets slows down the operation of PCRE because it has to load
407         additional bytes when handling them.         additional bytes when handling them.
408    
        If you build PCRE with an increased link size, test 2 (and  test  5  if  
        you  are using UTF-8) will fail. Part of the output of these tests is a  
        representation of the compiled pattern, and this changes with the  link  
        size.  
   
409    
410  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
411    
412         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
413         ing by making recursive calls to an internal function  called  match().         ing  by  making recursive calls to an internal function called match().
414         In  environments  where  the size of the stack is limited, this can se-         In environments where the size of the stack is limited,  this  can  se-
415         verely limit PCRE's operation. (The Unix environment does  not  usually         verely  limit  PCRE's operation. (The Unix environment does not usually
416         suffer from this problem, but it may sometimes be necessary to increase         suffer from this problem, but it may sometimes be necessary to increase
417         the maximum stack size.  There is a discussion in the  pcrestack  docu-         the  maximum  stack size.  There is a discussion in the pcrestack docu-
418         mentation.)  An alternative approach to recursion that uses memory from         mentation.) An alternative approach to recursion that uses memory  from
419         the heap to remember data, instead of using recursive  function  calls,         the  heap  to remember data, instead of using recursive function calls,
420         has  been  implemented to work round the problem of limited stack size.         has been implemented to work round the problem of limited  stack  size.
421         If you want to build a version of PCRE that works this way, add         If you want to build a version of PCRE that works this way, add
422    
423           --disable-stack-for-recursion           --disable-stack-for-recursion
424    
425         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
426         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
427         ment functions. Separate functions are provided because  the  usage  is         ment  functions. By default these point to malloc() and free(), but you
428         very  predictable:  the  block sizes requested are always the same, and         can replace the pointers so that your own functions are used.
429         the blocks are always freed in reverse order. A calling  program  might  
430         be  able  to implement optimized functions that perform better than the         Separate functions are  provided  rather  than  using  pcre_malloc  and
431         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         pcre_free  because  the  usage  is  very  predictable:  the block sizes
432         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
433         function; it is not relevant for the the pcre_dfa_exec() function.         reverse  order.  A calling program might be able to implement optimized
434           functions that perform better  than  malloc()  and  free().  PCRE  runs
435           noticeably more slowly when built in this way. This option affects only
436           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
437           pcre_dfa_exec() function.
438    
439    
440  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
441    
442         Internally, PCRE has a function called match(), which it calls  repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
443         edly   (sometimes   recursively)  when  matching  a  pattern  with  the         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
444         pcre_exec() function. By controlling the maximum number of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
445         function  may be called during a single matching operation, a limit can         function may be called during a single matching operation, a limit  can
446         be placed on the resources used by a single call  to  pcre_exec().  The         be  placed  on  the resources used by a single call to pcre_exec(). The
447         limit  can be changed at run time, as described in the pcreapi documen-         limit can be changed at run time, as described in the pcreapi  documen-
448         tation. The default is 10 million, but this can be changed by adding  a         tation.  The default is 10 million, but this can be changed by adding a
449         setting such as         setting such as
450    
451           --with-match-limit=500000           --with-match-limit=500000
452    
453         to   the   configure  command.  This  setting  has  no  effect  on  the         to  the  configure  command.  This  setting  has  no  effect   on   the
454         pcre_dfa_exec() matching function.         pcre_dfa_exec() matching function.
455    
456         In some environments it is desirable to limit the  depth  of  recursive         In  some  environments  it is desirable to limit the depth of recursive
457         calls of match() more strictly than the total number of calls, in order         calls of match() more strictly than the total number of calls, in order
458         to restrict the maximum amount of stack (or heap,  if  --disable-stack-         to  restrict  the maximum amount of stack (or heap, if --disable-stack-
459         for-recursion is specified) that is used. A second limit controls this;         for-recursion is specified) that is used. A second limit controls this;
460         it defaults to the value that  is  set  for  --with-match-limit,  which         it  defaults  to  the  value  that is set for --with-match-limit, which
461         imposes  no  additional constraints. However, you can set a lower limit         imposes no additional constraints. However, you can set a  lower  limit
462         by adding, for example,         by adding, for example,
463    
464           --with-match-limit-recursion=10000           --with-match-limit-recursion=10000
465    
466         to the configure command. This value can  also  be  overridden  at  run         to  the  configure  command.  This  value can also be overridden at run
467         time.         time.
468    
469    
470    CREATING CHARACTER TABLES AT BUILD TIME
471    
472           PCRE uses fixed tables for processing characters whose code values  are
473           less  than 256. By default, PCRE is built with a set of tables that are
474           distributed in the file pcre_chartables.c.dist. These  tables  are  for
475           ASCII codes only. If you add
476    
477             --enable-rebuild-chartables
478    
479           to  the  configure  command, the distributed tables are no longer used.
480           Instead, a program called dftables is compiled and  run.  This  outputs
481           the source for new set of tables, created in the default locale of your
482           C runtime system. (This method of replacing the tables does not work if
483           you  are cross compiling, because dftables is run on the local host. If
484           you need to create alternative tables when cross  compiling,  you  will
485           have to do so "by hand".)
486    
487    
488  USING EBCDIC CODE  USING EBCDIC CODE
489    
490         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
491         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
492         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by         This  is  the  case for most computer operating systems. PCRE can, how-
493         adding         ever, be compiled to run in an EBCDIC environment by adding
494    
495           --enable-ebcdic           --enable-ebcdic
496    
497         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
498           bles.  You  should  only  use  it if you know that you are in an EBCDIC
499           environment (for example, an IBM mainframe operating system).
500    
501    
502    SEE ALSO
503    
504           pcreapi(3), pcre_config(3).
505    
506    
507  Last updated: 06 June 2006  AUTHOR
508  Copyright (c) 1997-2006 University of Cambridge.  
509           Philip Hazel
510           University Computing Service
511           Cambridge CB2 3QH, England.
512    
513    
514    REVISION
515    
516           Last updated: 30 July 2007
517           Copyright (c) 1997-2007 University of Cambridge.
518  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
519    
520    
# Line 466  PCRE MATCHING ALGORITHMS Line 550  PCRE MATCHING ALGORITHMS
550           <something> <something else> <something further>           <something> <something else> <something further>
551    
552         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
553         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
554    
555    
556  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 482  REGULAR EXPRESSIONS AS TREES Line 566  REGULAR EXPRESSIONS AS TREES
566    
567  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
568    
569         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
570         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
571         depth-first search of the pattern tree. That is, it  proceeds  along  a         depth-first search of the pattern tree. That is, it  proceeds  along  a
572         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
573         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 507  THE STANDARD MATCHING ALGORITHM Line 591  THE STANDARD MATCHING ALGORITHM
591         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
592    
593    
594  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
595    
596         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
597         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
598         first search of the tree. Starting from the first matching point in the         string from left to right, once, character by character, and as it does
599         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
600         ter by character, and as it does  this,  it  remembers  all  the  paths         matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
601         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
602           keeps multiple states active simultaneously).
603         The  scan  continues until either the end of the subject is reached, or  
604         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
605         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
606         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
607           match  has  failed).   Thus,  if there is more than one possible match,
608         this algorithm finds all of them, and in particular, it finds the long-         this algorithm finds all of them, and in particular, it finds the long-
609         est. In PCRE, there is an option to stop the algorithm after the  first         est.  In PCRE, there is an option to stop the algorithm after the first
610         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
611    
612         Note that all the matches that are found start at the same point in the         Note that all the matches that are found start at the same point in the
# Line 529  THE DFA MATCHING ALGORITHM Line 614  THE DFA MATCHING ALGORITHM
614    
615           cat(er(pillar)?)           cat(er(pillar)?)
616    
617         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
618         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
619         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
620         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
621    
622         There are a number of features of PCRE regular expressions that are not         There are a number of features of PCRE regular expressions that are not
623         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
624    
625         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
626         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
627         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
628           sessive quantifiers can make a difference when what follows could  also
629           match what is quantified, for example in a pattern like this:
630    
631             ^a++\w!
632    
633           This  pattern matches "aaab!" but not "aaa!", which would be matched by
634           a non-possessive quantifier. Similarly, if an atomic group is  present,
635           it  is matched as if it were a standalone pattern at the current point,
636           and the longest match is then "locked in" for the rest of  the  overall
637           pattern.
638    
639         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
640         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
641         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
642         algorithm does not attempt to do this. This means that no captured sub-         algorithm does not attempt to do this. This means that no captured sub-
643         strings are available.         strings are available.
644    
645         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
646         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
647    
648         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
649         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
650           supported.
651    
652           5. Because many paths through the tree may be  active,  the  \K  escape
653           sequence, which resets the start of the match when encountered (but may
654           be on some paths and not on others), is not  supported.  It  causes  an
655           error if encountered.
656    
657         5. 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
658         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.
659    
660         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
661         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single  byte, even in UTF-8 mode, is not supported because the alterna-
662         rithm moves through the subject string one character at a time, for all         tive algorithm moves through the subject  string  one  character  at  a
663         active paths through the tree.         time, for all active paths through the tree.
664    
665           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
666           ported.
667    
668    
669  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
670    
671         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
672           tages:
673    
674         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-
675         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
676         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
677         things with callouts.         things with callouts.
678    
679         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
680         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-
681         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
682         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
683         able.         available.
684    
685         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
686         never needs to backtrack, it is possible  to  pass  very  long  subject         once,  and  never  needs to backtrack, it is possible to pass very long
687         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
688         tial matching each time.         for partial matching each time.
689    
690    
691  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
692    
693         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
694    
695         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
696         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
697         because it is less susceptible to optimization.         because it is less susceptible to optimization.
698    
699         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
700    
701         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
702         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
703         rithm.  
704    
705  Last updated: 06 June 2006  AUTHOR
706  Copyright (c) 1997-2006 University of Cambridge.  
707           Philip Hazel
708           University Computing Service
709           Cambridge CB2 3QH, England.
710    
711    
712    REVISION
713    
714           Last updated: 08 August 2007
715           Copyright (c) 1997-2007 University of Cambridge.
716  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
717    
718    
# Line 692  PCRE NATIVE API Line 806  PCRE NATIVE API
806  PCRE API OVERVIEW  PCRE API OVERVIEW
807    
808         PCRE has its own native API, which is described in this document. There         PCRE has its own native API, which is described in this document. There
809         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
810         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
811         Both of these APIs define a set of C function calls. A C++  wrapper  is         Both of these APIs define a set of C function calls. A C++  wrapper  is
812         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 715  PCRE API OVERVIEW Line 829  PCRE API OVERVIEW
829         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
830         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
831         ing. The alternative algorithm finds all possible matches (at  a  given         ing. The alternative algorithm finds all possible matches (at  a  given
832         point in the subject). However, this algorithm does not return captured         point  in  the subject), and scans the subject just once. However, this
833         substrings. A description of the  two  matching  algorithms  and  their         algorithm does not return captured substrings. A description of the two
834         advantages  and  disadvantages  is given in the pcrematching documenta-         matching  algorithms and their advantages and disadvantages is given in
835         tion.         the pcrematching documentation.
836    
837         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
838         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 779  PCRE API OVERVIEW Line 893  PCRE API OVERVIEW
893    
894    
895  NEWLINES  NEWLINES
896         PCRE supports three different conventions for indicating line breaks in  
897         strings: a single CR character, a single LF character, or the two-char-         PCRE  supports five different conventions for indicating line breaks in
898         acter  sequence  CRLF.  All  three  are used as "standard" by different         strings: a single CR (carriage return) character, a  single  LF  (line-
899         operating systems.  When PCRE is built, a default can be specified. The         feed) character, the two-character sequence CRLF, any of the three pre-
900         default  default  is  LF, which is the Unix standard. When PCRE is run,         ceding, or any Unicode newline sequence. The Unicode newline  sequences
901         the default can be overridden, either when a pattern  is  compiled,  or         are  the  three just mentioned, plus the single characters VT (vertical
902         when it is matched.         tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
903           separator, U+2028), and PS (paragraph separator, U+2029).
904    
905           Each  of  the first three conventions is used by at least one operating
906           system as its standard newline sequence. When PCRE is built, a  default
907           can  be  specified.  The default default is LF, which is the Unix stan-
908           dard. When PCRE is run, the default can be overridden,  either  when  a
909           pattern is compiled, or when it is matched.
910    
911         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-
912         acter or pair of characters that indicate a line break".         acter or pair of characters that indicate a line break". The choice  of
913           newline  convention  affects  the  handling of the dot, circumflex, and
914           dollar metacharacters, the handling of #-comments in /x mode, and, when
915           CRLF  is a recognized line ending sequence, the match position advance-
916           ment for a non-anchored pattern. The choice of newline convention  does
917           not affect the interpretation of the \n or \r escape sequences.
918    
919    
920  MULTITHREADING  MULTITHREADING
921    
922         The PCRE functions can be used in  multi-threading  applications,  with         The  PCRE  functions  can be used in multi-threading applications, with
923         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
924         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
925         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
926    
927         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
928         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
929         at once.         at once.
930    
# Line 806  MULTITHREADING Line 932  MULTITHREADING
932  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
933    
934         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
935         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
936         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
937         pcreprecompile documentation.         pcreprecompile documentation. However, compiling a  regular  expression
938           with  one version of PCRE for use with a different version is not guar-
939           anteed to work and may cause crashes.
940    
941    
942  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
943    
944         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
945    
946         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-
947         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
948         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
949         tures.         tures.
950    
951         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
952         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
953         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
954         available:         available:
955    
956           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
957    
958         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-
959         able; otherwise it is set to zero.         able; otherwise it is set to zero.
960    
961           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
962    
963         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
964         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
965    
966           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
967    
968         The  output  is  an integer whose value specifies the default character         The output is an integer whose value specifies  the  default  character
969         sequence that is recognized as meaning "newline". The three values that         sequence  that is recognized as meaning "newline". The four values that
970         are supported are: 10 for LF, 13 for CR, and 3338 for CRLF. The default         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
971         should normally be the standard sequence for your operating system.         and  -1  for  ANY. The default should normally be the standard sequence
972           for your operating system.
973    
974           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
975    
# Line 909  COMPILING A PATTERN Line 1038  COMPILING A PATTERN
1038         fully relocatable, because it may contain a copy of the tableptr  argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
1039         ment, which is an address (see below).         ment, which is an address (see below).
1040    
1041         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1042         tion. It should be zero if  no  options  are  required.  The  available         pilation. It should be zero if no options are required.  The  available
1043         options  are  described  below. Some of them, in particular, those that         options  are  described  below. Some of them, in particular, those that
1044         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
1045         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
# Line 1000  COMPILING A PATTERN Line 1129  COMPILING A PATTERN
1129         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
1130         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
1131         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
1132         newlines, independent of the setting of this option.         newline characters, independent of the setting of this option.
1133    
1134           PCRE_DUPNAMES           PCRE_DUPNAMES
1135    
# Line 1064  COMPILING A PATTERN Line 1193  COMPILING A PATTERN
1193           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1194           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1195           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1196             PCRE_NEWLINE_ANYCRLF
1197             PCRE_NEWLINE_ANY
1198    
1199         These  options  override the default newline definition that was chosen         These  options  override the default newline definition that was chosen
1200         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
1201         newline  is  indicated  by a single character (CR or LF, respectively).         newline  is  indicated  by a single character (CR or LF, respectively).
1202         Setting both of them specifies that a newline is indicated by the  two-         Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1203         character  CRLF sequence. For convenience, PCRE_NEWLINE_CRLF is defined         two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1204         to contain both bits. The only time that a line break is relevant  when         that any of the three preceding sequences should be recognized. Setting
1205         compiling a pattern is if PCRE_EXTENDED is set, and an unescaped # out-         PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1206         side a character class is encountered. This indicates  a  comment  that         recognized. The Unicode newline sequences are the three just mentioned,
1207         lasts until after the next newline.         plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1208           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1209           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1210           UTF-8 mode.
1211    
1212           The newline setting in the  options  word  uses  three  bits  that  are
1213           treated as a number, giving eight possibilities. Currently only six are
1214           used (default plus the five values above). This means that if  you  set
1215           more  than one newline option, the combination may or may not be sensi-
1216           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1217           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1218           cause an error.
1219    
1220           The only time that a line break is specially recognized when  compiling
1221           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1222           character class is encountered. This indicates  a  comment  that  lasts
1223           until  after the next line break sequence. In other circumstances, line
1224           break  sequences  are  treated  as  literal  data,   except   that   in
1225           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1226           and are therefore ignored.
1227    
1228         The newline option set at compile time becomes the default that is used         The newline option that is set at compile time becomes the default that
1229         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.
1230    
1231           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1232    
# Line 1105  COMPILING A PATTERN Line 1255  COMPILING A PATTERN
1255           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1256    
1257         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
1258         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically  checked.  There  is  a  discussion about the validity of
1259         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
1260         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
1261         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-
1262         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
1263         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
1264         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
1265         ing of subject strings.         can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1266           UTF-8 validity checking of subject strings.
1267    
1268    
1269  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1270    
1271         The following table lists the error  codes  than  may  be  returned  by         The  following  table  lists  the  error  codes than may be returned by
1272         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(), along with the error messages that may be returned  by
1273         both compiling functions.         both  compiling functions. As PCRE has developed, some error codes have
1274           fallen out of use. To avoid confusion, they have not been re-used.
1275    
1276            0  no error            0  no error
1277            1  \ at end of pattern            1  \ at end of pattern
# Line 1131  COMPILATION ERROR CODES Line 1283  COMPILATION ERROR CODES
1283            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1284            8  range out of order in character class            8  range out of order in character class
1285            9  nothing to repeat            9  nothing to repeat
1286           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1287           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1288           12  unrecognized character after (?           12  unrecognized character after (?
1289           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
# Line 1140  COMPILATION ERROR CODES Line 1292  COMPILATION ERROR CODES
1292           16  erroffset passed as NULL           16  erroffset passed as NULL
1293           17  unknown option bit(s) set           17  unknown option bit(s) set
1294           18  missing ) after comment           18  missing ) after comment
1295           19  parentheses nested too deeply           19  [this code is not in use]
1296           20  regular expression too large           20  regular expression too large
1297           21  failed to get memory           21  failed to get memory
1298           22  unmatched parentheses           22  unmatched parentheses
# Line 1150  COMPILATION ERROR CODES Line 1302  COMPILATION ERROR CODES
1302           26  malformed number or name after (?(           26  malformed number or name after (?(
1303           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1304           28  assertion expected after (?(           28  assertion expected after (?(
1305           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1306           30  unknown POSIX class name           30  unknown POSIX class name
1307           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1308           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1309           33  spare error           33  [this code is not in use]
1310           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1311           35  invalid condition (?(0)           35  invalid condition (?(0)
1312           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1163  COMPILATION ERROR CODES Line 1315  COMPILATION ERROR CODES
1315           39  closing ) for (?C expected           39  closing ) for (?C expected
1316           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1317           41  unrecognized character after (?P           41  unrecognized character after (?P
1318           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1319           43  two named subpatterns have the same name           43  two named subpatterns have the same name
1320           44  invalid UTF-8 string           44  invalid UTF-8 string
1321           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
# Line 1171  COMPILATION ERROR CODES Line 1323  COMPILATION ERROR CODES
1323           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1324           48  subpattern name is too long (maximum 32 characters)           48  subpattern name is too long (maximum 32 characters)
1325           49  too many named subpatterns (maximum 10,000)           49  too many named subpatterns (maximum 10,000)
1326           50  repeated subpattern is too long           50  [this code is not in use]
1327           51  octal value is greater than \377 (not in UTF-8 mode)           51  octal value is greater than \377 (not in UTF-8 mode)
1328             52  internal error: overran compiling workspace
1329             53  internal  error:  previously-checked  referenced  subpattern  not
1330           found
1331             54  DEFINE group contains more than one branch
1332             55  repeating a DEFINE group is not allowed
1333             56  inconsistent NEWLINE options"
1334             57  \g is not followed by a braced name or an optionally braced
1335                   non-zero number
1336             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1337    
1338    
1339  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1180  STUDYING A PATTERN Line 1341  STUDYING A PATTERN
1341         pcre_extra *pcre_study(const pcre *code, int options         pcre_extra *pcre_study(const pcre *code, int options
1342              const char **errptr);              const char **errptr);
1343    
1344         If a compiled pattern is going to be used several times,  it  is  worth         If  a  compiled  pattern is going to be used several times, it is worth
1345         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1346         matching. The function pcre_study() takes a pointer to a compiled  pat-         matching.  The function pcre_study() takes a pointer to a compiled pat-
1347         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1348         information that will help speed up matching,  pcre_study()  returns  a         information  that  will  help speed up matching, pcre_study() returns a
1349         pointer  to a pcre_extra block, in which the study_data field points to         pointer to a pcre_extra block, in which the study_data field points  to
1350         the results of the study.         the results of the study.
1351    
1352         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1353         pcre_exec().  However,  a  pcre_extra  block also contains other fields         pcre_exec(). However, a pcre_extra block  also  contains  other  fields
1354         that can be set by the caller before the block  is  passed;  these  are         that  can  be  set  by the caller before the block is passed; these are
1355         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1356    
1357         If  studying  the  pattern  does not produce any additional information         If studying the pattern does not  produce  any  additional  information
1358         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1359         wants  to  pass  any of the other fields to pcre_exec(), it must set up         wants to pass any of the other fields to pcre_exec(), it  must  set  up
1360         its own pcre_extra block.         its own pcre_extra block.
1361    
1362         The second argument of pcre_study() contains option bits.  At  present,         The  second  argument of pcre_study() contains option bits. At present,
1363         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1364    
1365         The  third argument for pcre_study() is a pointer for an error message.         The third argument for pcre_study() is a pointer for an error  message.
1366         If studying succeeds (even if no data is  returned),  the  variable  it         If  studying  succeeds  (even  if no data is returned), the variable it
1367         points  to  is  set  to NULL. Otherwise it is set to point to a textual         points to is set to NULL. Otherwise it is set to  point  to  a  textual
1368         error message. This is a static string that is part of the library. You         error message. This is a static string that is part of the library. You
1369         must  not  try  to  free it. You should test the error pointer for NULL         must not try to free it. You should test the  error  pointer  for  NULL
1370         after calling pcre_study(), to be sure that it has run successfully.         after calling pcre_study(), to be sure that it has run successfully.
1371    
1372         This is a typical call to pcre_study():         This is a typical call to pcre_study():
# Line 1217  STUDYING A PATTERN Line 1378  STUDYING A PATTERN
1378             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1379    
1380         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1381         that  do not have a single fixed starting character. A bitmap of possi-         that do not have a single fixed starting character. A bitmap of  possi-
1382         ble starting bytes is created.         ble starting bytes is created.
1383    
1384    
1385  LOCALE SUPPORT  LOCALE SUPPORT
1386    
1387         PCRE handles caseless matching, and determines whether  characters  are         PCRE  handles  caseless matching, and determines whether characters are
1388         letters  digits,  or whatever, by reference to a set of tables, indexed         letters, digits, or whatever, by reference to a set of tables,  indexed
1389         by character value. When running in UTF-8 mode, this  applies  only  to         by  character  value.  When running in UTF-8 mode, this applies only to
1390         characters  with  codes  less than 128. Higher-valued codes never match         characters with codes less than 128. Higher-valued  codes  never  match
1391         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built
1392         with  Unicode  character property support. The use of locales with Uni-         with Unicode character property support. The use of locales  with  Uni-
1393         code is discouraged.         code  is discouraged. If you are handling characters with codes greater
1394           than 128, you should either use UTF-8 and Unicode, or use locales,  but
1395         An internal set of tables is created in the default C locale when  PCRE         not try to mix the two.
1396         is  built.  This  is  used when the final argument of pcre_compile() is  
1397         NULL, and is sufficient for many applications. An  alternative  set  of         PCRE  contains  an  internal set of tables that are used when the final
1398         tables  can,  however, be supplied. These may be created in a different         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1399         locale from the default. As more and more applications change to  using         applications.  Normally, the internal tables recognize only ASCII char-
1400         Unicode, the need for this locale support is expected to die away.         acters. However, when PCRE is built, it is possible to cause the inter-
1401           nal tables to be rebuilt in the default "C" locale of the local system,
1402           which may cause them to be different.
1403    
1404           The internal tables can always be overridden by tables supplied by  the
1405           application that calls PCRE. These may be created in a different locale
1406           from the default. As more and more applications change  to  using  Uni-
1407           code, the need for this locale support is expected to die away.
1408    
1409         External  tables  are  built by calling the pcre_maketables() function,         External  tables  are  built by calling the pcre_maketables() function,
1410         which has no arguments, in the relevant locale. The result can then  be         which has no arguments, in the relevant locale. The result can then  be
# Line 1249  LOCALE SUPPORT Line 1417  LOCALE SUPPORT
1417           tables = pcre_maketables();           tables = pcre_maketables();
1418           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1419    
1420         When pcre_maketables() runs, the tables are built  in  memory  that  is         The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
1421         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         if you are using Windows, the name for the French locale is "french".
1422         that the memory containing the tables remains available for as long  as  
1423           When  pcre_maketables()  runs,  the  tables are built in memory that is
1424           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1425           that  the memory containing the tables remains available for as long as
1426         it is needed.         it is needed.
1427    
1428         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1429         pattern, and the same tables are used via this pointer by  pcre_study()         pattern,  and the same tables are used via this pointer by pcre_study()
1430         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1431         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1432         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1433    
1434         It  is  possible to pass a table pointer or NULL (indicating the use of         It is possible to pass a table pointer or NULL (indicating the  use  of
1435         the internal tables) to pcre_exec(). Although  not  intended  for  this         the  internal  tables)  to  pcre_exec(). Although not intended for this
1436         purpose,  this facility could be used to match a pattern in a different         purpose, this facility could be used to match a pattern in a  different
1437         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1438         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1439    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1443  INFORMATION ABOUT A PATTERN
1443         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1444              int what, void *where);              int what, void *where);
1445    
1446         The  pcre_fullinfo() function returns information about a compiled pat-         The pcre_fullinfo() function returns information about a compiled  pat-
1447         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1448         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1449    
1450         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1451         pattern. The second argument is the result of pcre_study(), or NULL  if         pattern.  The second argument is the result of pcre_study(), or NULL if
1452         the  pattern  was not studied. The third argument specifies which piece         the pattern was not studied. The third argument specifies  which  piece
1453         of information is required, and the fourth argument is a pointer  to  a         of  information  is required, and the fourth argument is a pointer to a
1454         variable  to  receive  the  data. The yield of the function is zero for         variable to receive the data. The yield of the  function  is  zero  for
1455         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1456    
1457           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 1288  INFORMATION ABOUT A PATTERN Line 1459  INFORMATION ABOUT A PATTERN
1459           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1460           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1461    
1462         The "magic number" is placed at the start of each compiled  pattern  as         The  "magic  number" is placed at the start of each compiled pattern as
1463         an  simple check against passing an arbitrary memory pointer. Here is a         an simple check against passing an arbitrary memory pointer. Here is  a
1464         typical call of pcre_fullinfo(), to obtain the length of  the  compiled         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1465         pattern:         pattern:
1466    
1467           int rc;           int rc;
# Line 1301  INFORMATION ABOUT A PATTERN Line 1472  INFORMATION ABOUT A PATTERN
1472             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1473             &length);         /* where to put the data */             &length);         /* where to put the data */
1474    
1475         The  possible  values for the third argument are defined in pcre.h, and         The possible values for the third argument are defined in  pcre.h,  and
1476         are as follows:         are as follows:
1477    
1478           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1479    
1480         Return the number of the highest back reference  in  the  pattern.  The         Return  the  number  of  the highest back reference in the pattern. The
1481         fourth  argument  should  point to an int variable. Zero is returned if         fourth argument should point to an int variable. Zero  is  returned  if
1482         there are no back references.         there are no back references.
1483    
1484           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1485    
1486         Return the number of capturing subpatterns in the pattern.  The  fourth         Return  the  number of capturing subpatterns in the pattern. The fourth
1487         argument should point to an int variable.         argument should point to an int variable.
1488    
1489           PCRE_INFO_DEFAULT_TABLES           PCRE_INFO_DEFAULT_TABLES
1490    
1491         Return  a pointer to the internal default character tables within PCRE.         Return a pointer to the internal default character tables within  PCRE.
1492         The fourth argument should point to an unsigned char *  variable.  This         The  fourth  argument should point to an unsigned char * variable. This
1493         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1494         tion. External callers can cause PCRE to use  its  internal  tables  by         tion.  External  callers  can  cause PCRE to use its internal tables by
1495         passing a NULL table pointer.         passing a NULL table pointer.
1496    
1497           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1498    
1499         Return  information  about  the first byte of any matched string, for a         Return information about the first byte of any matched  string,  for  a
1500         non-anchored pattern. The fourth argument should point to an int  vari-         non-anchored  pattern. The fourth argument should point to an int vari-
1501         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1502         is still recognized for backwards compatibility.)         is still recognized for backwards compatibility.)
1503    
1504         If there is a fixed first byte, for example, from  a  pattern  such  as         If  there  is  a  fixed first byte, for example, from a pattern such as
1505         (cat|cow|coyote). Otherwise, if either         (cat|cow|coyote), its value is returned. Otherwise, if either
1506    
1507         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1508         branch starts with "^", or         branch starts with "^", or
1509    
1510         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1511         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1512    
1513         -1  is  returned, indicating that the pattern matches only at the start         -1 is returned, indicating that the pattern matches only at  the  start
1514         of a subject string or after any newline within the  string.  Otherwise         of  a  subject string or after any newline within the string. Otherwise
1515         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1516    
1517           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1518    
1519         If  the pattern was studied, and this resulted in the construction of a         If the pattern was studied, and this resulted in the construction of  a
1520         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1521         matching  string, a pointer to the table is returned. Otherwise NULL is         matching string, a pointer to the table is returned. Otherwise NULL  is
1522         returned. The fourth argument should point to an unsigned char *  vari-         returned.  The fourth argument should point to an unsigned char * vari-
1523         able.         able.
1524    
1525             PCRE_INFO_JCHANGED
1526    
1527           Return 1 if the (?J) option setting is used in the  pattern,  otherwise
1528           0. The fourth argument should point to an int variable. The (?J) inter-
1529           nal option setting changes the local PCRE_DUPNAMES option.
1530    
1531           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1532    
1533         Return  the  value of the rightmost literal byte that must exist in any         Return the value of the rightmost literal byte that must exist  in  any
1534         matched string, other than at its  start,  if  such  a  byte  has  been         matched  string,  other  than  at  its  start,  if such a byte has been
1535         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1536         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1537         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1538         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1539         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1540    
# Line 1365  INFORMATION ABOUT A PATTERN Line 1542  INFORMATION ABOUT A PATTERN
1542           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1543           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1544    
1545         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1546         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1547         ses, which still acquire numbers. Several convenience functions such as         ses, which still acquire numbers. Several convenience functions such as
1548         pcre_get_named_substring() are provided for  extracting  captured  sub-         pcre_get_named_substring()  are  provided  for extracting captured sub-
1549         strings  by  name. It is also possible to extract the data directly, by         strings by name. It is also possible to extract the data  directly,  by
1550         first converting the name to a number in order to  access  the  correct         first  converting  the  name to a number in order to access the correct
1551         pointers in the output vector (described with pcre_exec() below). To do         pointers in the output vector (described with pcre_exec() below). To do
1552         the conversion, you need  to  use  the  name-to-number  map,  which  is         the  conversion,  you  need  to  use  the  name-to-number map, which is
1553         described by these three values.         described by these three values.
1554    
1555         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1556         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1557         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1558         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1559         a  pointer  to  the  first  entry of the table (a pointer to char). The         a pointer to the first entry of the table  (a  pointer  to  char).  The
1560         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1561         sis,  most  significant byte first. The rest of the entry is the corre-         sis, most significant byte first. The rest of the entry is  the  corre-
1562         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1563         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1564         theses numbers. For example, consider  the  following  pattern  (assume         theses  numbers.  For  example,  consider the following pattern (assume
1565         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1566         ignored):         ignored):
1567    
1568           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1569           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1570    
1571         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1572         each  entry  in the table is eight bytes long. The table is as follows,         each entry in the table is eight bytes long. The table is  as  follows,
1573         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1574         as ??:         as ??:
1575    
# Line 1401  INFORMATION ABOUT A PATTERN Line 1578  INFORMATION ABOUT A PATTERN
1578           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1579           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1580    
1581         When  writing  code  to  extract  data from named subpatterns using the         When writing code to extract data  from  named  subpatterns  using  the
1582         name-to-number map, remember that the length of the entries  is  likely         name-to-number  map,  remember that the length of the entries is likely
1583         to be different for each compiled pattern.         to be different for each compiled pattern.
1584    
1585             PCRE_INFO_OKPARTIAL
1586    
1587           Return 1 if the pattern can be used for partial matching, otherwise  0.
1588           The  fourth  argument  should point to an int variable. The pcrepartial
1589           documentation lists the restrictions that apply to patterns  when  par-
1590           tial matching is used.
1591    
1592           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1593    
1594         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
1595         fourth argument should point to an unsigned long  int  variable.  These         fourth argument should point to an unsigned long  int  variable.  These
1596         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1597         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1598           other  words,  they are the options that will be in force when matching
1599           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1600           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1601           and PCRE_EXTENDED.
1602    
1603         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
1604         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1616  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1804  MATCHING A PATTERN: THE TRADITIONAL FUNC
1804           PCRE_NEWLINE_CR           PCRE_NEWLINE_CR
1805           PCRE_NEWLINE_LF           PCRE_NEWLINE_LF
1806           PCRE_NEWLINE_CRLF           PCRE_NEWLINE_CRLF
1807             PCRE_NEWLINE_ANYCRLF
1808             PCRE_NEWLINE_ANY
1809    
1810         These options override  the  newline  definition  that  was  chosen  or         These options override  the  newline  definition  that  was  chosen  or
1811         defaulted  when the pattern was compiled. For details, see the descrip-         defaulted  when the pattern was compiled. For details, see the descrip-
1812         tion pcre_compile() above. During matching, the newline choice  affects         tion of pcre_compile()  above.  During  matching,  the  newline  choice
1813         the behaviour of the dot, circumflex, and dollar metacharacters.         affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1814           ters. It may also alter the way the match position is advanced after  a
1815           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1816           PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt
1817           fails  when the current position is at a CRLF sequence, the match posi-
1818           tion is advanced by two characters instead of one, in other  words,  to
1819           after the CRLF.
1820    
1821           PCRE_NOTBOL           PCRE_NOTBOL
1822    
# Line 1667  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1863  MATCHING A PATTERN: THE TRADITIONAL FUNC
1863         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
1864         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1865         called.   The  value  of  startoffset is also checked to ensure that it         called.   The  value  of  startoffset is also checked to ensure that it
1866         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
1867         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
1868         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
1869         returned.         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
1870           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1871         If  you  already  know that your subject is valid, and you want to skip  
1872         these   checks   for   performance   reasons,   you   can    set    the         If you already know that your subject is valid, and you  want  to  skip
1873         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         these    checks    for   performance   reasons,   you   can   set   the
1874         do this for the second and subsequent calls to pcre_exec() if  you  are         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1875         making  repeated  calls  to  find  all  the matches in a single subject         do  this  for the second and subsequent calls to pcre_exec() if you are
1876         string. However, you should be  sure  that  the  value  of  startoffset         making repeated calls to find all  the  matches  in  a  single  subject
1877         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is         string.  However,  you  should  be  sure  that the value of startoffset
1878         set, the effect of passing an invalid UTF-8 string as a subject,  or  a         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1879         value  of startoffset that does not point to the start of a UTF-8 char-         set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1880           value of startoffset that does not point to the start of a UTF-8  char-
1881         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1882    
1883           PCRE_PARTIAL           PCRE_PARTIAL
1884    
1885         This option turns on the  partial  matching  feature.  If  the  subject         This  option  turns  on  the  partial  matching feature. If the subject
1886         string  fails to match the pattern, but at some point during the match-         string fails to match the pattern, but at some point during the  match-
1887         ing process the end of the subject was reached (that  is,  the  subject         ing  process  the  end of the subject was reached (that is, the subject
1888         partially  matches  the  pattern and the failure to match occurred only         partially matches the pattern and the failure to  match  occurred  only
1889         because there were not enough subject characters), pcre_exec()  returns         because  there were not enough subject characters), pcre_exec() returns
1890         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1891         used, there are restrictions on what may appear in the  pattern.  These         used,  there  are restrictions on what may appear in the pattern. These
1892         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1893    
1894     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1895    
1896         The  subject string is passed to pcre_exec() as a pointer in subject, a         The subject string is passed to pcre_exec() as a pointer in subject,  a
1897         length in length, and a starting byte offset in startoffset.  In  UTF-8         length  in  length, and a starting byte offset in startoffset. In UTF-8
1898         mode,  the  byte  offset  must point to the start of a UTF-8 character.         mode, the byte offset must point to the start  of  a  UTF-8  character.
1899         Unlike the pattern string, the subject may contain binary  zero  bytes.         Unlike  the  pattern string, the subject may contain binary zero bytes.
1900         When  the starting offset is zero, the search for a match starts at the         When the starting offset is zero, the search for a match starts at  the
1901         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1902    
1903         A non-zero starting offset is useful when searching for  another  match         A  non-zero  starting offset is useful when searching for another match
1904         in  the same subject by calling pcre_exec() again after a previous suc-         in the same subject by calling pcre_exec() again after a previous  suc-
1905         cess.  Setting startoffset differs from just passing over  a  shortened         cess.   Setting  startoffset differs from just passing over a shortened
1906         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1907         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1908    
1909           \Biss\B           \Biss\B
1910    
1911         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
1912         only  if  the  current position in the subject is not a word boundary.)         only if the current position in the subject is not  a  word  boundary.)
1913         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
1914         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
1915         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1916         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1917         to be a word boundary. However, if pcre_exec()  is  passed  the  entire         to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1918         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1919         rence of "iss" because it is able to look behind the starting point  to         rence  of "iss" because it is able to look behind the starting point to
1920         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1921    
1922         If  a  non-zero starting offset is passed when the pattern is anchored,         If a non-zero starting offset is passed when the pattern  is  anchored,
1923         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1924         if  the  pattern  does  not require the match to be at the start of the         if the pattern does not require the match to be at  the  start  of  the
1925         subject.         subject.
1926    
1927     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1928    
1929         In general, a pattern matches a certain portion of the subject, and  in         In  general, a pattern matches a certain portion of the subject, and in
1930         addition,  further  substrings  from  the  subject may be picked out by         addition, further substrings from the subject  may  be  picked  out  by
1931         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1932         this  is  called "capturing" in what follows, and the phrase "capturing         this is called "capturing" in what follows, and the  phrase  "capturing
1933         subpattern" is used for a fragment of a pattern that picks out  a  sub-         subpattern"  is  used for a fragment of a pattern that picks out a sub-
1934         string.  PCRE  supports several other kinds of parenthesized subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
1935         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1936    
1937         Captured substrings are returned to the caller via a vector of  integer         Captured  substrings are returned to the caller via a vector of integer
1938         offsets  whose  address is passed in ovector. The number of elements in         offsets whose address is passed in ovector. The number of  elements  in
1939         the vector is passed in ovecsize, which must be a non-negative  number.         the  vector is passed in ovecsize, which must be a non-negative number.
1940         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1941    
1942         The  first  two-thirds of the vector is used to pass back captured sub-         The first two-thirds of the vector is used to pass back  captured  sub-
1943         strings, each substring using a pair of integers. The  remaining  third         strings,  each  substring using a pair of integers. The remaining third
1944         of  the  vector is used as workspace by pcre_exec() while matching cap-         of the vector is used as workspace by pcre_exec() while  matching  cap-
1945         turing subpatterns, and is not available for passing back  information.         turing  subpatterns, and is not available for passing back information.
1946         The  length passed in ovecsize should always be a multiple of three. If         The length passed in ovecsize should always be a multiple of three.  If
1947         it is not, it is rounded down.         it is not, it is rounded down.
1948    
1949         When a match is successful, information about  captured  substrings  is         When  a  match  is successful, information about captured substrings is
1950         returned  in  pairs  of integers, starting at the beginning of ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
1951         and continuing up to two-thirds of its length at the  most.  The  first         and  continuing  up  to two-thirds of its length at the most. The first
1952         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
1953         string, and the second is set to the  offset  of  the  first  character         string,  and  the  second  is  set to the offset of the first character
1954         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1955         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1],  identify  the  portion  of  the  subject string matched by the
1956         entire  pattern.  The next pair is used for the first capturing subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1957         tern, and so on. The value returned by pcre_exec() is one more than the         tern, and so on. The value returned by pcre_exec() is one more than the
1958         highest numbered pair that has been set. For example, if two substrings         highest numbered pair that has been set. For example, if two substrings
1959         have been captured, the returned value is 3. If there are no  capturing         have  been captured, the returned value is 3. If there are no capturing
1960         subpatterns,  the return value from a successful match is 1, indicating         subpatterns, the return value from a successful match is 1,  indicating
1961         that just the first pair of offsets has been set.         that just the first pair of offsets has been set.
1962    
1963         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1964         of the string that it matched that is returned.         of the string that it matched that is returned.
1965    
1966         If  the vector is too small to hold all the captured substring offsets,         If the vector is too small to hold all the captured substring  offsets,
1967         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
1968         function  returns a value of zero. In particular, if the substring off-         function returns a value of zero. In particular, if the substring  off-
1969         sets are not of interest, pcre_exec() may be called with ovector passed         sets are not of interest, pcre_exec() may be called with ovector passed
1970         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1971         references and the ovector is not big enough to  remember  the  related         references  and  the  ovector is not big enough to remember the related
1972         substrings,  PCRE has to get additional memory for use during matching.         substrings, PCRE has to get additional memory for use during  matching.
1973         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1974    
1975         The pcre_info() function can be used to find  out  how  many  capturing         The  pcre_info()  function  can  be used to find out how many capturing
1976         subpatterns  there  are  in  a  compiled pattern. The smallest size for         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1977         ovector that will allow for n captured substrings, in addition  to  the         ovector  that  will allow for n captured substrings, in addition to the
1978         offsets of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
1979    
1980         It  is  possible for capturing subpattern number n+1 to match some part         It is possible for capturing subpattern number n+1 to match  some  part
1981         of the subject when subpattern n has not been used at all. For example,         of the subject when subpattern n has not been used at all. For example,
1982         if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the         if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1983         return from the function is 4, and subpatterns 1 and 3 are matched, but         return from the function is 4, and subpatterns 1 and 3 are matched, but
1984         2  is  not.  When  this happens, both values in the offset pairs corre-         2 is not. When this happens, both values in  the  offset  pairs  corre-
1985         sponding to unused subpatterns are set to -1.         sponding to unused subpatterns are set to -1.
1986    
1987         Offset values that correspond to unused subpatterns at the end  of  the         Offset  values  that correspond to unused subpatterns at the end of the
1988         expression  are  also  set  to  -1. For example, if the string "abc" is         expression are also set to -1. For example,  if  the  string  "abc"  is
1989         matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not         matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1990         matched.  The  return  from the function is 2, because the highest used         matched. The return from the function is 2, because  the  highest  used
1991         capturing subpattern number is 1. However, you can refer to the offsets         capturing subpattern number is 1. However, you can refer to the offsets
1992         for  the  second  and third capturing subpatterns if you wish (assuming         for the second and third capturing subpatterns if  you  wish  (assuming
1993         the vector is large enough, of course).         the vector is large enough, of course).
1994    
1995         Some convenience functions are provided  for  extracting  the  captured         Some  convenience  functions  are  provided for extracting the captured
1996         substrings as separate strings. These are described below.         substrings as separate strings. These are described below.
1997    
1998     Error return values from pcre_exec()     Error return values from pcre_exec()
1999    
2000         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
2001         defined in the header file:         defined in the header file:
2002    
2003           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1809  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2006  MATCHING A PATTERN: THE TRADITIONAL FUNC
2006    
2007           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2008    
2009         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2010         ovecsize was not zero.         ovecsize was not zero.
2011    
2012           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1818  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2015  MATCHING A PATTERN: THE TRADITIONAL FUNC
2015    
2016           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2017    
2018         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2019         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
2020         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
2021         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2022         gives when the magic number is not present.         gives when the magic number is not present.
2023    
2024           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2025    
2026         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2027         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2028         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2029    
2030           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2031    
2032         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2033         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2034         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
2035         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2036         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2037    
2038           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2039    
2040         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2041         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2042         returned by pcre_exec().         returned by pcre_exec().
2043    
2044           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2045    
2046         The  backtracking  limit,  as  specified  by the match_limit field in a         The backtracking limit, as specified by  the  match_limit  field  in  a
2047         pcre_extra structure (or defaulted) was reached.  See  the  description         pcre_extra  structure  (or  defaulted) was reached. See the description
2048         above.         above.
2049    
          PCRE_ERROR_RECURSIONLIMIT (-21)  
   
        The internal recursion limit, as specified by the match_limit_recursion  
        field in a pcre_extra structure (or defaulted)  was  reached.  See  the  
        description above.  
   
2050           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2051    
2052         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
2053         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2054         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2055    
2056           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2057    
2058         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
2059         subject.         subject.
2060    
2061           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2062    
2063         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2064         value  of startoffset did not point to the beginning of a UTF-8 charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2065         ter.         ter.
2066    
2067           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2068    
2069         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
2070         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2071    
2072           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2073    
2074         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2075         items that are not supported for partial matching. See the  pcrepartial         items  that are not supported for partial matching. See the pcrepartial
2076         documentation for details of partial matching.         documentation for details of partial matching.
2077    
2078           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2079    
2080         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
2081         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2082    
2083           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2084    
2085         This error is given if the value of the ovecsize argument is  negative.         This  error is given if the value of the ovecsize argument is negative.
2086    
2087             PCRE_ERROR_RECURSIONLIMIT (-21)
2088    
2089           The internal recursion limit, as specified by the match_limit_recursion
2090           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2091           description above.
2092    
2093             PCRE_ERROR_BADNEWLINE     (-23)
2094    
2095           An invalid combination of PCRE_NEWLINE_xxx options was given.
2096    
2097           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2098    
2099    
2100  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1907  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2110  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2110         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2111              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2112    
2113         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2114         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2115         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2116         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2117         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2118         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2119         substrings.         substrings.
2120    
2121         A  substring that contains a binary zero is correctly extracted and has         A substring that contains a binary zero is correctly extracted and  has
2122         a further zero added on the end, but the result is not, of course, a  C         a  further zero added on the end, but the result is not, of course, a C
2123         string.   However,  you  can  process such a string by referring to the         string.  However, you can process such a string  by  referring  to  the
2124         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2125         string().  Unfortunately, the interface to pcre_get_substring_list() is         string().  Unfortunately, the interface to pcre_get_substring_list() is
2126         not adequate for handling strings containing binary zeros, because  the         not  adequate for handling strings containing binary zeros, because the
2127         end of the final string is not independently indicated.         end of the final string is not independently indicated.
2128    
2129         The  first  three  arguments  are the same for all three of these func-         The first three arguments are the same for all  three  of  these  func-
2130         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2131         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2132         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2133         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2134         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2135         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2136         it ran out of space in ovector, the value passed as stringcount  should         it  ran out of space in ovector, the value passed as stringcount should
2137         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2138    
2139         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2140         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2141         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2142         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2143         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2144         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2145         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2146         The yield of the function is the length of the  string,  not  including         The  yield  of  the function is the length of the string, not including
2147         the terminating zero, or one of         the terminating zero, or one of these error codes:
2148    
2149           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2150    
2151         The  buffer  was too small for pcre_copy_substring(), or the attempt to         The buffer was too small for pcre_copy_substring(), or the  attempt  to
2152         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2153    
2154           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2155    
2156         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2157    
2158         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2159         strings  and  builds  a list of pointers to them. All this is done in a         strings and builds a list of pointers to them. All this is  done  in  a
2160         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2161         the  memory  block  is returned via listptr, which is also the start of         the memory block is returned via listptr, which is also  the  start  of
2162         the list of string pointers. The end of the list is marked  by  a  NULL         the  list  of  string pointers. The end of the list is marked by a NULL
2163         pointer. The yield of the function is zero if all went well, or         pointer. The yield of the function is zero if all  went  well,  or  the
2164           error code
2165    
2166           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2167    
# Line 1999  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2203  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2203         To extract a substring by name, you first have to find associated  num-         To extract a substring by name, you first have to find associated  num-
2204         ber.  For example, for this pattern         ber.  For example, for this pattern
2205    
2206           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2207    
2208         the number of the subpattern called "xxx" is 2. If the name is known to         the number of the subpattern called "xxx" is 2. If the name is known to
2209         be unique (PCRE_DUPNAMES was not set), you can find the number from the         be unique (PCRE_DUPNAMES was not set), you can find the number from the
# Line 2025  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2229  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2229    
2230         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2231         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2232         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2233           behaviour may not be what you want (see the next section).
2234    
2235    
2236  DUPLICATE SUBPATTERN NAMES  DUPLICATE SUBPATTERN NAMES
# Line 2033  DUPLICATE SUBPATTERN NAMES Line 2238  DUPLICATE SUBPATTERN NAMES
2238         int pcre_get_stringtable_entries(const pcre *code,         int pcre_get_stringtable_entries(const pcre *code,
2239              const char *name, char **first, char **last);              const char *name, char **first, char **last);
2240    
2241         When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for         When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2242         subpatterns are not required to  be  unique.  Normally,  patterns  with         subpatterns  are  not  required  to  be unique. Normally, patterns with
2243         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
2244         subpatterns participates. An example is shown in the pcrepattern  docu-         subpatterns  participates. An example is shown in the pcrepattern docu-
2245         mentation. When duplicates are present, pcre_copy_named_substring() and         mentation.
2246         pcre_get_named_substring() return the first substring corresponding  to  
2247         the  given  name  that  is  set.  If  none  are set, an empty string is         When   duplicates   are   present,   pcre_copy_named_substring()    and
2248         returned.  The pcre_get_stringnumber() function returns one of the num-         pcre_get_named_substring()  return the first substring corresponding to
2249         bers  that are associated with the name, but it is not defined which it         the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2250         is.         (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2251           function returns one of the numbers that are associated with the  name,
2252           but it is not defined which it is.
2253    
2254         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
2255         name,  you  must  use  the pcre_get_stringtable_entries() function. The         name, you must use  the  pcre_get_stringtable_entries()  function.  The
2256         first argument is the compiled pattern, and the second is the name. The         first argument is the compiled pattern, and the second is the name. The
2257         third  and  fourth  are  pointers to variables which are updated by the         third and fourth are pointers to variables which  are  updated  by  the
2258         function. After it has run, they point to the first and last entries in         function. After it has run, they point to the first and last entries in
2259         the  name-to-number  table  for  the  given  name.  The function itself         the name-to-number table  for  the  given  name.  The  function  itself
2260         returns the length of each entry, or  PCRE_ERROR_NOSUBSTRING  if  there         returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2261         are  none.  The  format  of the table is described above in the section         there are none. The format of the table is described above in the  sec-
2262         entitled Information about a pattern. Given all  the  relevant  entries         tion  entitled  Information  about  a  pattern.  Given all the relevant
2263         for the name, you can extract each of their numbers, and hence the cap-         entries for the name, you can extract each of their numbers, and  hence
2264         tured data, if any.         the captured data, if any.
2265    
2266    
2267  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2268    
2269         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2270         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2271         the subject. If you want to find all possible matches, or  the  longest         the  subject.  If you want to find all possible matches, or the longest
2272         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2273         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2274         need  to  find all possible matches, you can kludge it up by making use         need to find all possible matches, you can kludge it up by  making  use
2275         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2276         tation.         tation.
2277    
2278         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2279         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2280         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2281         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2282         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2283    
2284    
# Line 2082  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2289  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2289              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2290              int *workspace, int wscount);              int *workspace, int wscount);
2291    
2292         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2293         against a compiled pattern, using a "DFA" matching algorithm. This  has         against  a  compiled pattern, using a matching algorithm that scans the
2294         different  characteristics to the normal algorithm, and is not compati-         subject string just once, and does not backtrack.  This  has  different
2295         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics  to  the  normal  algorithm, and is not compatible with
2296         Nevertheless, there are times when this kind of matching can be useful.         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2297         For a discussion of the two matching algorithms, see  the  pcrematching         theless,  there are times when this kind of matching can be useful. For
2298         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2299           mentation.
2300    
2301         The  arguments  for  the  pcre_dfa_exec()  function are the same as for         The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2302         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 2141  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2349  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2349           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2350    
2351         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2352         stop  as  soon  as  it  has found one match. Because of the way the DFA         stop as soon as it has found one match. Because of the way the alterna-
2353         algorithm works, this is necessarily the shortest possible match at the         tive algorithm works, this is necessarily the shortest  possible  match
2354         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2355    
2356           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2357    
# Line 2179  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2387  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2387         On success, the yield of the function is a number  greater  than  zero,         On success, the yield of the function is a number  greater  than  zero,
2388         which  is  the  number of matched substrings. The substrings themselves         which  is  the  number of matched substrings. The substrings themselves
2389         are returned in ovector. Each string uses two elements;  the  first  is         are returned in ovector. Each string uses two elements;  the  first  is
2390         the  offset  to the start, and the second is the offset to the end. All         the  offset  to  the start, and the second is the offset to the end. In
2391         the strings have the same start offset. (Space could have been saved by         fact, all the strings have the same start  offset.  (Space  could  have
2392         giving  this only once, but it was decided to retain some compatibility         been  saved by giving this only once, but it was decided to retain some
2393         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility with the way pcre_exec() returns data,  even  though  the
2394         strings is different.)         meaning of the strings is different.)
2395    
2396         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2397         est matching string is given first. If there were too many  matches  to         est matching string is given first. If there were too many  matches  to
# Line 2205  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2413  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2413    
2414           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2415    
2416         This  return is given if pcre_dfa_exec() encounters a condition item in         This  return  is  given  if pcre_dfa_exec() encounters a condition item
2417         a pattern that uses a back reference for the  condition.  This  is  not         that uses a back reference for the condition, or a test  for  recursion
2418         supported.         in a specific group. These are not supported.
2419    
2420           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2421    
# Line 2227  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2435  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2435         This error is given if the output vector  is  not  large  enough.  This         This error is given if the output vector  is  not  large  enough.  This
2436         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2437    
2438  Last updated: 08 June 2006  
2439  Copyright (c) 1997-2006 University of Cambridge.  SEE ALSO
2440    
2441           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2442           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2443    
2444    
2445    AUTHOR
2446    
2447           Philip Hazel
2448           University Computing Service
2449           Cambridge CB2 3QH, England.
2450    
2451    
2452    REVISION
2453    
2454           Last updated: 09 August 2007
2455           Copyright (c) 1997-2007 University of Cambridge.
2456  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2457    
2458    
# Line 2255  PCRE CALLOUTS Line 2479  PCRE CALLOUTS
2479         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2480         points:         points:
2481    
2482           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2483    
2484         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2485         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2330  THE CALLOUT INTERFACE Line 2554  THE CALLOUT INTERFACE
2554         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2555         were passed to pcre_exec().         were passed to pcre_exec().
2556    
2557         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2558         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2559         callout function may be called several times from the same point in the         sequence \K has been encountered, this value is changed to reflect  the
2560         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2561           function may be called several times from the same point in the pattern
2562           for different starting points in the subject.
2563    
2564         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2565         the current match pointer.         the current match pointer.
# Line 2386  RETURN VALUES Line 2612  RETURN VALUES
2612         reserved for use by callout functions; it will never be  used  by  PCRE         reserved for use by callout functions; it will never be  used  by  PCRE
2613         itself.         itself.
2614    
2615  Last updated: 28 February 2005  
2616  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2617    
2618           Philip Hazel
2619           University Computing Service
2620           Cambridge CB2 3QH, England.
2621    
2622    
2623    REVISION
2624    
2625           Last updated: 29 May 2007
2626           Copyright (c) 1997-2007 University of Cambridge.
2627  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2628    
2629    
# Line 2401  NAME Line 2637  NAME
2637  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2638    
2639         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2640         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2641         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2642           some features that are expected to be in the forthcoming Perl 5.10.
2643    
2644         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
2645         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
2646         main pcre page.         main pcre page.
2647    
2648         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2649         permits them, but they do not mean what you might think.  For  example,         permits  them,  but they do not mean what you might think. For example,
2650         (?!a){3} does not assert that the next three characters are not "a". It         (?!a){3} does not assert that the next three characters are not "a". It
2651         just asserts that the next character is not "a" three times.         just asserts that the next character is not "a" three times.
2652    
2653         3. Capturing subpatterns that occur inside  negative  lookahead  asser-         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2654         tions  are  counted,  but their entries in the offsets vector are never         tions are counted, but their entries in the offsets  vector  are  never
2655         set. Perl sets its numerical variables from any such patterns that  are         set.  Perl sets its numerical variables from any such patterns that are
2656         matched before the assertion fails to match something (thereby succeed-         matched before the assertion fails to match something (thereby succeed-
2657         ing), but only if the negative lookahead assertion  contains  just  one         ing),  but  only  if the negative lookahead assertion contains just one
2658         branch.         branch.
2659    
2660         4.  Though  binary zero characters are supported in the subject string,         4. Though binary zero characters are supported in the  subject  string,
2661         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2662         mal C string, terminated by zero. The escape sequence \0 can be used in         mal C string, terminated by zero. The escape sequence \0 can be used in
2663         the pattern to represent a binary zero.         the pattern to represent a binary zero.
2664    
2665         5. The following Perl escape sequences are not supported: \l,  \u,  \L,         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2666         \U, and \N. In fact these are implemented by Perl's general string-han-         \U, and \N. In fact these are implemented by Perl's general string-han-
2667         dling and are not part of its pattern matching engine. If any of  these         dling  and are not part of its pattern matching engine. If any of these
2668         are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2669    
2670         6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2671         is built with Unicode character property support. The  properties  that         is  built  with Unicode character property support. The properties that
2672         can  be tested with \p and \P are limited to the general category prop-         can be tested with \p and \P are limited to the general category  prop-
2673         erties such as Lu and Nd, script names such as Greek or  Han,  and  the         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2674         derived properties Any and L&.         derived properties Any and L&.
2675    
2676         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2677         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2678         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2679         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2680         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2681    
2682             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2449  DIFFERENCES BETWEEN PCRE AND PERL Line 2686  DIFFERENCES BETWEEN PCRE AND PERL
2686             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2687             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2688    
2689         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2690         classes.         classes.
2691    
2692         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2693         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2694         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2695         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2696         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2697    
2698         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2699         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2700         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2701    
2702           10.  There are some differences that are concerned with the settings of
2703           captured strings when part of  a  pattern  is  repeated.  For  example,
2704           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2705         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2706    
2707         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2708         ities:         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2709           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2710           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2711           ture group; this is different to Perl.
2712    
2713           12. PCRE provides some extensions to the Perl regular expression facil-
2714           ities.   Perl  5.10  will  include new features that are not in earlier
2715           versions, some of which (such as named parentheses) have been  in  PCRE
2716           for some time. This list is with respect to Perl 5.10:
2717    
2718         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2719         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2720         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2721    
2722         (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2723         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2724    
2725         (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-
2726         cial meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash  is         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2727         ignored. (Perl can be made to issue a warning.)         ignored.  (Perl can be made to issue a warning.)
2728    
2729         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2730         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-
2731         lowed by a question mark they are.         lowed by a question mark they are.
2732    
2733         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2734         tried only at the first matching position in the subject string.         tried only at the first matching position in the subject string.
2735    
2736         (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-
2737         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2738    
2739         (g)  The (?R), (?number), and (?P>name) constructs allows for recursive         (g) The callout facility is PCRE-specific.
        pattern matching (Perl can do  this  using  the  (?p{code})  construct,  
        which PCRE cannot support.)  
2740    
2741         (h)  PCRE supports named capturing substrings, using the Python syntax.         (h) The partial matching facility is PCRE-specific.
2742    
2743           (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2744           even on different hosts that have the other endianness.
2745    
2746         (i) PCRE supports the possessive quantifier  "++"  syntax,  taken  from         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2747         Sun's Java package.         different way and is not Perl-compatible.
2748    
        (j) The (R) condition, for testing recursion, is a PCRE extension.  
2749    
2750         (k) The callout facility is PCRE-specific.  AUTHOR
2751    
2752         (l) The partial matching facility is PCRE-specific.         Philip Hazel
2753           University Computing Service
2754           Cambridge CB2 3QH, England.
2755    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
2756    
2757         (n) The alternative matching function (pcre_dfa_exec())  matches  in  a  REVISION
        different way and is not Perl-compatible.  
2758    
2759  Last updated: 06 June 2006         Last updated: 08 August 2007
2760  Copyright (c) 1997-2006 University of Cambridge.         Copyright (c) 1997-2007 University of Cambridge.
2761  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2762    
2763    
# Line 2522  NAME Line 2770  NAME
2770    
2771  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2772    
2773         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2774         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2775         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2776         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2777         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2778         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2779           O'Reilly,  covers regular expressions in great detail. This description
2780           of PCRE's regular expressions is intended as reference material.
2781    
2782         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2783         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 2541  PCRE REGULAR EXPRESSION DETAILS Line 2791  PCRE REGULAR EXPRESSION DETAILS
2791         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2792         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2793         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2794         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2795         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2796         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2797           discussed in the pcrematching page.
2798         A regular expression is a pattern that is  matched  against  a  subject  
2799         string  from  left  to right. Most characters stand for themselves in a  
2800         pattern, and match the corresponding characters in the  subject.  As  a  CHARACTERS AND METACHARACTERS
2801    
2802           A  regular  expression  is  a pattern that is matched against a subject
2803           string from left to right. Most characters stand for  themselves  in  a
2804           pattern,  and  match  the corresponding characters in the subject. As a
2805         trivial example, the pattern         trivial example, the pattern
2806    
2807           The quick brown fox           The quick brown fox
2808    
2809         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
2810         caseless matching is specified (the PCRE_CASELESS option), letters  are         caseless  matching is specified (the PCRE_CASELESS option), letters are
2811         matched  independently  of case. In UTF-8 mode, PCRE always understands         matched independently of case. In UTF-8 mode, PCRE  always  understands
2812         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
2813         caseless  matching  is always possible. For characters with higher val-         caseless matching is always possible. For characters with  higher  val-
2814         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
2815         property  support,  but  not  otherwise.   If  you want to use caseless         property support, but not otherwise.   If  you  want  to  use  caseless
2816         matching for characters 128 and above, you must  ensure  that  PCRE  is         matching  for  characters  128  and above, you must ensure that PCRE is
2817         compiled with Unicode property support as well as with UTF-8 support.         compiled with Unicode property support as well as with UTF-8 support.
2818    
2819         The  power  of  regular  expressions  comes from the ability to include         The power of regular expressions comes  from  the  ability  to  include
2820         alternatives and repetitions in the pattern. These are encoded  in  the         alternatives  and  repetitions in the pattern. These are encoded in the
2821         pattern by the use of metacharacters, which do not stand for themselves         pattern by the use of metacharacters, which do not stand for themselves
2822         but instead are interpreted in some special way.         but instead are interpreted in some special way.
2823    
2824         There are two different sets of metacharacters: those that  are  recog-         There  are  two different sets of metacharacters: those that are recog-
2825         nized  anywhere in the pattern except within square brackets, and those         nized anywhere in the pattern except within square brackets, and  those
2826         that are recognized in square brackets. Outside  square  brackets,  the         that  are  recognized  within square brackets. Outside square brackets,
2827         metacharacters are as follows:         the metacharacters are as follows:
2828    
2829           \      general escape character with several uses           \      general escape character with several uses
2830           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2588  PCRE REGULAR EXPRESSION DETAILS Line 2842  PCRE REGULAR EXPRESSION DETAILS
2842                  also "possessive quantifier"                  also "possessive quantifier"
2843           {      start min/max quantifier           {      start min/max quantifier
2844    
2845         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
2846         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2847    
2848           \      general escape character           \      general escape character
# Line 2598  PCRE REGULAR EXPRESSION DETAILS Line 2852  PCRE REGULAR EXPRESSION DETAILS
2852                    syntax)                    syntax)
2853           ]      terminates the character class           ]      terminates the character class
2854    
2855         The following sections describe the use of each of the  metacharacters.         The  following sections describe the use of each of the metacharacters.
2856    
2857    
2858  BACKSLASH  BACKSLASH
2859    
2860         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2861         a non-alphanumeric character, it takes away any  special  meaning  that         a  non-alphanumeric  character,  it takes away any special meaning that
2862         character  may  have.  This  use  of  backslash  as an escape character         character may have. This  use  of  backslash  as  an  escape  character
2863         applies both inside and outside character classes.         applies both inside and outside character classes.
2864    
2865         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
2866         pattern.   This  escaping  action  applies whether or not the following         pattern.  This escaping action applies whether  or  not  the  following
2867         character would otherwise be interpreted as a metacharacter, so  it  is         character  would  otherwise be interpreted as a metacharacter, so it is
2868         always  safe  to  precede  a non-alphanumeric with backslash to specify         always safe to precede a non-alphanumeric  with  backslash  to  specify
2869         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-
2870         slash, you write \\.         slash, you write \\.
2871    
2872         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in
2873         the pattern (other than in a character class) and characters between  a         the  pattern (other than in a character class) and characters between a
2874         # outside a character class and the next newline are ignored. An escap-         # outside a character class and the next newline are ignored. An escap-
2875         ing backslash can be used to include a whitespace  or  #  character  as         ing  backslash  can  be  used to include a whitespace or # character as
2876         part of the pattern.         part of the pattern.
2877    
2878         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-
2879         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-
2880         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
2881         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-
2882         tion. Note the following examples:         tion. Note the following examples:
2883    
2884           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 2634  BACKSLASH Line 2888  BACKSLASH
2888           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2889           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2890    
2891         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2892         classes.         classes.
2893    
2894     Non-printing characters     Non-printing characters
2895    
2896         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-
2897         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
2898         appearance of non-printing characters, apart from the binary zero  that         appearance  of non-printing characters, apart from the binary zero that
2899         terminates  a  pattern,  but  when  a pattern is being prepared by text         terminates a pattern, but when a pattern  is  being  prepared  by  text
2900         editing, it is usually easier  to  use  one  of  the  following  escape         editing,  it  is  usually  easier  to  use  one of the following escape
2901         sequences than the binary character it represents:         sequences than the binary character it represents:
2902    
2903           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 2657  BACKSLASH Line 2911  BACKSLASH
2911           \xhh      character with hex code hh           \xhh      character with hex code hh
2912           \x{hhh..} character with hex code hhh..           \x{hhh..} character with hex code hhh..
2913    
2914         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,
2915         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
2916         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;
2917         becomes hex 7B.         becomes hex 7B.
2918    
2919         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
2920         in  upper  or  lower case). Any number of hexadecimal digits may appear         in upper or lower case). Any number of hexadecimal  digits  may  appear
2921         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
2922         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,
2923         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than         the  maximum value in hexadecimal is 7FFFFFFF. Note that this is bigger
2924         hexadecimal  digits  appear between \x{ and }, or if there is no termi-         than the largest Unicode code point, which is 10FFFF.
2925         nating }, this form of escape is not recognized.  Instead, the  initial  
2926         \x will be interpreted as a basic hexadecimal escape, with no following         If characters other than hexadecimal digits appear between \x{  and  },
2927         digits, giving a character whose value is zero.         or if there is no terminating }, this form of escape is not recognized.
2928           Instead, the initial \x will be  interpreted  as  a  basic  hexadecimal
2929           escape,  with  no  following  digits, giving a character whose value is
2930           zero.
2931    
2932         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
2933         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 2692  BACKSLASH Line 2949  BACKSLASH
2949    
2950         Inside a character class, or if the decimal number is  greater  than  9         Inside a character class, or if the decimal number is  greater  than  9
2951         and  there have not been that many capturing subpatterns, PCRE re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2952         up to three octal digits following the backslash, ane uses them to gen-         up to three octal digits following the backslash, and uses them to gen-
2953         erate  a data character. Any subsequent digits stand for themselves. In         erate  a data character. Any subsequent digits stand for themselves. In
2954         non-UTF-8 mode, the value of a character specified  in  octal  must  be         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2955         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
# Line 2719  BACKSLASH Line 2976  BACKSLASH
2976         All the sequences that define a single character value can be used both         All the sequences that define a single character value can be used both
2977         inside and outside character classes. In addition, inside  a  character         inside and outside character classes. In addition, inside  a  character
2978         class,  the  sequence \b is interpreted as the backspace character (hex         class,  the  sequence \b is interpreted as the backspace character (hex
2979         08), and the sequence \X is interpreted as the character "X". Outside a         08), and the sequences \R and \X are interpreted as the characters  "R"
2980         character class, these sequences have different meanings (see below).         and  "X", respectively. Outside a character class, these sequences have
2981           different meanings (see below).
2982    
2983       Absolute and relative back references
2984    
2985           The sequence \g followed by an unsigned or a negative  number,  option-
2986           ally  enclosed  in braces, is an absolute or relative back reference. A
2987           named back reference can be coded as \g{name}. Back references are dis-
2988           cussed later, following the discussion of parenthesized subpatterns.
2989    
2990     Generic character types     Generic character types
2991    
2992         The  third  use of backslash is for specifying generic character types.         Another use of backslash is for specifying generic character types. The
2993         The following are always recognized:         following are always recognized:
2994    
2995           \d     any decimal digit           \d     any decimal digit
2996           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
2997             \h     any horizontal whitespace character
2998             \H     any character that is not a horizontal whitespace character
2999           \s     any whitespace character           \s     any whitespace character
3000           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3001             \v     any vertical whitespace character
3002             \V     any character that is not a vertical whitespace character
3003           \w     any "word" character           \w     any "word" character
3004           \W     any "non-word" character           \W     any "non-word" character
3005    
# Line 2745  BACKSLASH Line 3014  BACKSLASH
3014    
3015         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
3016         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
3017         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
3018         "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-
3019         ter. In PCRE, it never does.)         ter. In PCRE, it never does.
3020    
3021           In  UTF-8 mode, characters with values greater than 128 never match \d,
3022           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3023           code  character  property  support is available. These sequences retain
3024           their original meanings from before UTF-8 support was available, mainly
3025           for efficiency reasons.
3026    
3027           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3028           the other sequences, these do match certain high-valued  codepoints  in
3029           UTF-8 mode.  The horizontal space characters are:
3030    
3031             U+0009     Horizontal tab
3032             U+0020     Space
3033             U+00A0     Non-break space
3034             U+1680     Ogham space mark
3035             U+180E     Mongolian vowel separator
3036             U+2000     En quad
3037             U+2001     Em quad
3038             U+2002     En space
3039             U+2003     Em space
3040             U+2004     Three-per-em space
3041             U+2005     Four-per-em space
3042             U+2006     Six-per-em space
3043             U+2007     Figure space
3044             U+2008     Punctuation space
3045             U+2009     Thin space
3046             U+200A     Hair space
3047             U+202F     Narrow no-break space
3048             U+205F     Medium mathematical space
3049             U+3000     Ideographic space
3050    
3051           The vertical space characters are:
3052    
3053             U+000A     Linefeed
3054             U+000B     Vertical tab
3055             U+000C     Formfeed
3056             U+000D     Carriage return
3057             U+0085     Next line
3058             U+2028     Line separator
3059             U+2029     Paragraph separator
3060    
3061         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
3062         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-
3063         trolled  by PCRE's low-valued character tables, and may vary if locale-         trolled  by PCRE's low-valued character tables, and may vary if locale-
3064         specific matching is taking place (see "Locale support" in the  pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
3065         page).  For  example,  in  the  "fr_FR" (French) locale, some character         page).  For  example,  in  a French locale such as "fr_FR" in Unix-like
3066         codes greater than 128 are used for accented  letters,  and  these  are         systems, or "french" in Windows, some character codes greater than  128
3067         matched by \w.         are  used for accented letters, and these are matched by \w. The use of
3068           locales with Unicode is discouraged.
3069    
3070       Newline sequences
3071    
3072           Outside a character class, the escape sequence \R matches  any  Unicode
3073           newline  sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \R is
3074           equivalent to the following:
3075    
3076             (?>\r\n|\n|\x0b|\f|\r|\x85)
3077    
3078           This is an example of an "atomic group", details  of  which  are  given
3079           below.  This particular group matches either the two-character sequence
3080           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
3081           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3082           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3083           is treated as a single unit that cannot be split.
3084    
3085           In  UTF-8  mode, two additional characters whose codepoints are greater
3086           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3087           rator,  U+2029).   Unicode character property support is not needed for
3088           these characters to be recognized.
3089    
3090         In  UTF-8 mode, characters with values greater than 128 never match \d,         Inside a character class, \R matches the letter "R".
        \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.  
3091    
3092     Unicode character properties     Unicode character properties
3093    
3094         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3095         tional  escape  sequences  to  match character properties are available         tional  escape sequences that match characters with specific properties
3096         when UTF-8 mode is selected. They are:         are available.  When not in UTF-8 mode, these sequences are  of  course
3097           limited  to  testing characters whose codepoints are less than 256, but
3098           they do work in this mode.  The extra escape sequences are:
3099    
3100           \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
3101           \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
# Line 2788  BACKSLASH Line 3117  BACKSLASH
3117         Those that are not part of an identified script are lumped together  as         Those that are not part of an identified script are lumped together  as
3118         "Common". The current list of scripts is:         "Common". The current list of scripts is:
3119    
3120         Arabic,  Armenian,  Bengali,  Bopomofo, Braille, Buginese, Buhid, Cana-         Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3121         dian_Aboriginal, Cherokee, Common, Coptic, Cypriot, Cyrillic,  Deseret,         Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
3122         Devanagari,  Ethiopic,  Georgian,  Glagolitic, Gothic, Greek, Gujarati,         Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3123         Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana,  Inherited,  Kannada,         Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
3124         Katakana,  Kharoshthi,  Khmer,  Lao, Latin, Limbu, Linear_B, Malayalam,         gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
3125         Mongolian, Myanmar, New_Tai_Lue, Ogham, Old_Italic, Old_Persian, Oriya,         Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3126         Osmanya,  Runic,  Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tag-         Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
3127         banwa,  Tai_Le,  Tamil,  Telugu,  Thaana,  Thai,   Tibetan,   Tifinagh,         Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3128         Ugaritic, Yi.         Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3129    
3130         Each  character has exactly one general category property, specified by         Each  character has exactly one general category property, specified by
3131         a two-letter abbreviation. For compatibility with Perl, negation can be         a two-letter abbreviation. For compatibility with Perl, negation can be
# Line 2861  BACKSLASH Line 3190  BACKSLASH
3190         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
3191         classified as a modifier or "other".         classified as a modifier or "other".
3192    
3193           The  Cs  (Surrogate)  property  applies only to characters in the range
3194           U+D800 to U+DFFF. Such characters are not valid in UTF-8  strings  (see
3195           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3196           ing has been turned off (see the discussion  of  PCRE_NO_UTF8_CHECK  in
3197           the pcreapi page).
3198    
3199         The  long  synonyms  for  these  properties that Perl supports (such as         The  long  synonyms  for  these  properties that Perl supports (such as
3200         \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
3201         any of these properties with "Is".         any of these properties with "Is".
# Line 2880  BACKSLASH Line 3215  BACKSLASH
3215         That  is,  it matches a character without the "mark" property, followed         That  is,  it matches a character without the "mark" property, followed
3216         by zero or more characters with the "mark"  property,  and  treats  the         by zero or more characters with the "mark"  property,  and  treats  the
3217         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3218         property are typically accents that affect the preceding character.         property are typically accents that  affect  the  preceding  character.
3219           None  of  them  have  codepoints less than 256, so in non-UTF-8 mode \X
3220           matches any one character.
3221    
3222         Matching characters by Unicode property is not fast, because  PCRE  has         Matching characters by Unicode property is not fast, because  PCRE  has
3223         to  search  a  structure  that  contains data for over fifteen thousand         to  search  a  structure  that  contains data for over fifteen thousand
3224         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3225         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3226    
3227       Resetting the match start
3228    
3229           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3230           ously matched characters not  to  be  included  in  the  final  matched
3231           sequence. For example, the pattern:
3232    
3233             foo\Kbar
3234    
3235           matches  "foobar",  but reports that it has matched "bar". This feature
3236           is similar to a lookbehind assertion (described  below).   However,  in
3237           this  case, the part of the subject before the real match does not have
3238           to be of fixed length, as lookbehind assertions do. The use of \K  does
3239           not  interfere  with  the setting of captured substrings.  For example,
3240           when the pattern
3241    
3242             (foo)\Kbar
3243    
3244           matches "foobar", the first substring is still set to "foo".
3245    
3246     Simple assertions     Simple assertions
3247    
3248         The fourth use of backslash is for certain simple assertions. An asser-         The final use of backslash is for certain simple assertions. An  asser-
3249         tion specifies a condition that has to be met at a particular point  in         tion  specifies a condition that has to be met at a particular point in
3250         a  match, without consuming any characters from the subject string. The         a match, without consuming any characters from the subject string.  The
3251         use of subpatterns for more complicated assertions is described  below.         use  of subpatterns for more complicated assertions is described below.
3252         The backslashed assertions are:         The backslashed assertions are:
3253    
3254           \b     matches at a word boundary           \b     matches at a word boundary
3255           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3256           \A     matches at start of subject           \A     matches at the start of the subject
3257           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3258           \z     matches at end of subject                   also matches before a newline at the end of the subject
3259           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3260             \G     matches at the first matching position in the subject
3261    
3262         These  assertions may not appear in character classes (but note that \b         These assertions may not appear in character classes (but note that  \b
3263         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3264         acter class).         acter class).
3265    
3266         A  word  boundary is a position in the subject string where the current         A word boundary is a position in the subject string where  the  current
3267         character and the previous character do not both match \w or  \W  (i.e.         character  and  the previous character do not both match \w or \W (i.e.
3268         one  matches  \w  and the other matches \W), or the start or end of the         one matches \w and the other matches \W), or the start or  end  of  the
3269         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3270    
3271         The \A, \Z, and \z assertions differ from  the  traditional  circumflex         The  \A,  \Z,  and \z assertions differ from the traditional circumflex
3272         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3273         at the very start and end of the subject string, whatever  options  are         at  the  very start and end of the subject string, whatever options are
3274         set.  Thus,  they are independent of multiline mode. These three asser-         set. Thus, they are independent of multiline mode. These  three  asser-
3275         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3276         affect  only the behaviour of the circumflex and dollar metacharacters.         affect only the behaviour of the circumflex and dollar  metacharacters.
3277         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However,  if the startoffset argument of pcre_exec() is non-zero, indi-
3278         cating that matching is to start at a point other than the beginning of         cating that matching is to start at a point other than the beginning of
3279         the subject, \A can never match. The difference between \Z  and  \z  is         the  subject,  \A  can never match. The difference between \Z and \z is
3280         that \Z matches before a newline at the end of the string as well as at         that \Z matches before a newline at the end of the string as well as at
3281         the very end, whereas \z matches only at the end.         the very end, whereas \z matches only at the end.
3282    
3283         The \G assertion is true only when the current matching position is  at         The  \G assertion is true only when the current matching position is at
3284         the  start point of the match, as specified by the startoffset argument         the start point of the match, as specified by the startoffset  argument
3285         of pcre_exec(). It differs from \A when the  value  of  startoffset  is         of  pcre_exec().  It  differs  from \A when the value of startoffset is
3286         non-zero.  By calling pcre_exec() multiple times with appropriate argu-         non-zero. By calling pcre_exec() multiple times with appropriate  argu-
3287         ments, you can mimic Perl's /g option, and it is in this kind of imple-         ments, you can mimic Perl's /g option, and it is in this kind of imple-
3288         mentation where \G can be useful.         mentation where \G can be useful.
3289    
3290         Note,  however,  that  PCRE's interpretation of \G, as the start of the         Note, however, that PCRE's interpretation of \G, as the  start  of  the
3291         current match, is subtly different from Perl's, which defines it as the         current match, is subtly different from Perl's, which defines it as the
3292         end  of  the  previous  match. In Perl, these can be different when the         end of the previous match. In Perl, these can  be  different  when  the
3293         previously matched string was empty. Because PCRE does just  one  match         previously  matched  string was empty. Because PCRE does just one match
3294         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3295    
3296         If  all  the alternatives of a pattern begin with \G, the expression is         If all the alternatives of a pattern begin with \G, the  expression  is
3297         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3298         in the compiled regular expression.         in the compiled regular expression.
3299    
# Line 2944  BACKSLASH Line 3301  BACKSLASH
3301  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3302    
3303         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3304         character is an assertion that is true only  if  the  current  matching         character  is  an  assertion  that is true only if the current matching
3305         point  is  at the start of the subject string. If the startoffset argu-         point is at the start of the subject string. If the  startoffset  argu-
3306         ment of pcre_exec() is non-zero, circumflex  can  never  match  if  the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
3307         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
3308         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3309    
3310         Circumflex need not be the first character of the pattern if  a  number         Circumflex  need  not be the first character of the pattern if a number
3311         of  alternatives are involved, but it should be the first thing in each         of alternatives are involved, but it should be the first thing in  each
3312         alternative in which it appears if the pattern is ever  to  match  that         alternative  in  which  it appears if the pattern is ever to match that
3313         branch.  If all possible alternatives start with a circumflex, that is,         branch. If all possible alternatives start with a circumflex, that  is,
3314         if the pattern is constrained to match only at the start  of  the  sub-         if  the  pattern  is constrained to match only at the start of the sub-
3315         ject,  it  is  said  to be an "anchored" pattern. (There are also other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
3316         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3317    
3318         A dollar character is an assertion that is true  only  if  the  current         A  dollar  character  is  an assertion that is true only if the current
3319         matching  point  is  at  the  end of the subject string, or immediately         matching point is at the end of  the  subject  string,  or  immediately
3320         before a newline at the end of the string (by default). Dollar need not         before a newline at the end of the string (by default). Dollar need not
3321         be  the  last  character of the pattern if a number of alternatives are         be the last character of the pattern if a number  of  alternatives  are
3322         involved, but it should be the last item in  any  branch  in  which  it         involved,  but  it  should  be  the last item in any branch in which it
3323         appears. Dollar has no special meaning in a character class.         appears. Dollar has no special meaning in a character class.
3324    
3325         The  meaning  of  dollar  can be changed so that it matches only at the         The meaning of dollar can be changed so that it  matches  only  at  the
3326         very end of the string, by setting the  PCRE_DOLLAR_ENDONLY  option  at         very  end  of  the string, by setting the PCRE_DOLLAR_ENDONLY option at
3327         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3328    
3329         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3330         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex         PCRE_MULTILINE  option  is  set.  When  this  is the case, a circumflex
3331         matches  immediately after internal newlines as well as at the start of         matches immediately after internal newlines as well as at the start  of
3332         the subject string. It does not match after a  newline  that  ends  the         the  subject  string.  It  does not match after a newline that ends the
3333         string.  A dollar matches before any newlines in the string, as well as         string. A dollar matches before any newlines in the string, as well  as
3334         at the very end, when PCRE_MULTILINE is set. When newline is  specified         at  the very end, when PCRE_MULTILINE is set. When newline is specified
3335         as  the  two-character  sequence CRLF, isolated CR and LF characters do         as the two-character sequence CRLF, isolated CR and  LF  characters  do
3336         not indicate newlines.         not indicate newlines.
3337    
3338         For example, the pattern /^abc$/ matches the subject string  "def\nabc"         For  example, the pattern /^abc$/ matches the subject string "def\nabc"
3339         (where  \n  represents a newline) in multiline mode, but not otherwise.         (where \n represents a newline) in multiline mode, but  not  otherwise.
3340         Consequently, patterns that are anchored in single  line  mode  because         Consequently,  patterns  that  are anchored in single line mode because
3341         all  branches  start  with  ^ are not anchored in multiline mode, and a         all branches start with ^ are not anchored in  multiline  mode,  and  a
3342         match for circumflex is  possible  when  the  startoffset  argument  of         match  for  circumflex  is  possible  when  the startoffset argument of
3343         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if         pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is  ignored  if
3344         PCRE_MULTILINE is set.         PCRE_MULTILINE is set.
3345    
3346         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note  that  the sequences \A, \Z, and \z can be used to match the start
3347         and  end of the subject in both modes, and if all branches of a pattern         and end of the subject in both modes, and if all branches of a  pattern
3348         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is         start  with  \A it is always anchored, whether or not PCRE_MULTILINE is
3349         set.         set.
3350    
3351    
3352  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3353    
3354         Outside a character class, a dot in the pattern matches any one charac-         Outside a character class, a dot in the pattern matches any one charac-
3355         ter in the subject string except (by default) a character  that  signi-         ter  in  the subject string except (by default) a character that signi-
3356         fies  the  end  of  a line. In UTF-8 mode, the matched character may be         fies the end of a line. In UTF-8 mode, the  matched  character  may  be
3357         more than one byte long. When a line ending  is  defined  as  a  single         more than one byte long.
3358         character  (CR  or LF), dot never matches that character; when the two-  
3359         character sequence CRLF is used, dot does not match CR if it is immedi-         When  a line ending is defined as a single character, dot never matches
3360         ately  followed by LF, but otherwise it matches all characters (includ-         that character; when the two-character sequence CRLF is used, dot  does
3361         ing isolated CRs and LFs).         not  match  CR  if  it  is immediately followed by LF, but otherwise it
3362           matches all characters (including isolated CRs and LFs). When any  Uni-
3363           code  line endings are being recognized, dot does not match CR or LF or
3364           any of the other line ending characters.
3365    
3366         The behaviour of dot with regard to newlines can  be  changed.  If  the         The behaviour of dot with regard to newlines can  be  changed.  If  the
3367         PCRE_DOTALL  option  is  set,  a dot matches any one character, without         PCRE_DOTALL  option  is  set,  a dot matches any one character, without
3368         exception. If newline is defined as the two-character sequence CRLF, it         exception. If the two-character sequence CRLF is present in the subject
3369         takes two dots to match it.         string, it takes two dots to match it.
3370    
3371         The  handling of dot is entirely independent of the handling of circum-         The  handling of dot is entirely independent of the handling of circum-
3372         flex and dollar, the only relationship being  that  they  both  involve         flex and dollar, the only relationship being  that  they  both  involve
# Line 3016  FULL STOP (PERIOD, DOT) Line 3376  FULL STOP (PERIOD, DOT)
3376  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3377    
3378         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3379         both in and out of UTF-8 mode. Unlike a dot, it always matches  CR  and         both in and out of UTF-8 mode. Unlike a  dot,  it  always  matches  any
3380         LF.  The feature is provided in Perl in order to match individual bytes         line-ending  characters.  The  feature  is provided in Perl in order to
3381         in UTF-8 mode.  Because it breaks up UTF-8 characters  into  individual         match individual bytes in UTF-8 mode. Because it breaks up UTF-8  char-
3382         bytes,  what remains in the string may be a malformed UTF-8 string. For         acters  into individual bytes, what remains in the string may be a mal-
3383         this reason, the \C escape sequence is best avoided.         formed UTF-8 string. For this reason, the \C escape  sequence  is  best
3384           avoided.
3385    
3386         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE  does  not  allow \C to appear in lookbehind assertions (described
3387         below),  because  in UTF-8 mode this would make it impossible to calcu-         below), because in UTF-8 mode this would make it impossible  to  calcu-
3388         late the length of the lookbehind.         late the length of the lookbehind.
3389    
3390    
# Line 3032  SQUARE BRACKETS AND CHARACTER CLASSES Line 3393  SQUARE BRACKETS AND CHARACTER CLASSES
3393         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3394         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3395         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3396         it  should  be  the first data character in the class (after an initial         it should be the first data character in the class  (after  an  initial
3397         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3398    
3399         A character class matches a single character in the subject.  In  UTF-8         A  character  class matches a single character in the subject. In UTF-8
3400         mode,  the character may occupy more than one byte. A matched character         mode, the character may occupy more than one byte. A matched  character
3401         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3402         character  in  the  class definition is a circumflex, in which case the         character in the class definition is a circumflex, in  which  case  the
3403         subject character must not be in the set defined by  the  class.  If  a         subject  character  must  not  be in the set defined by the class. If a
3404         circumflex  is actually required as a member of the class, ensure it is         circumflex is actually required as a member of the class, ensure it  is
3405         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3406    
3407         For example, the character class [aeiou] matches any lower case  vowel,         For  example, the character class [aeiou] matches any lower case vowel,
3408         while  [^aeiou]  matches  any character that is not a lower case vowel.         while [^aeiou] matches any character that is not a  lower  case  vowel.
3409         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3410         characters  that  are in the class by enumerating those that are not. A         characters that are in the class by enumerating those that are  not.  A
3411         class that starts with a circumflex is not an assertion: it still  con-         class  that starts with a circumflex is not an assertion: it still con-
3412         sumes  a  character  from the subject string, and therefore it fails if         sumes a character from the subject string, and therefore  it  fails  if
3413         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3414    
3415         In UTF-8 mode, characters with values greater than 255 can be  included         In  UTF-8 mode, characters with values greater than 255 can be included
3416         in  a  class as a literal string of bytes, or by using the \x{ escaping         in a class as a literal string of bytes, or by using the  \x{  escaping
3417         mechanism.         mechanism.
3418    
3419         When caseless matching is set, any letters in a  class  represent  both         When  caseless  matching  is set, any letters in a class represent both
3420         their  upper  case  and lower case versions, so for example, a caseless         their upper case and lower case versions, so for  example,  a  caseless
3421         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not
3422         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always         match "A", whereas a caseful version would. In UTF-8 mode, PCRE  always
3423         understands the concept of case for characters whose  values  are  less         understands  the  concept  of case for characters whose values are less
3424         than  128, so caseless matching is always possible. For characters with         than 128, so caseless matching is always possible. For characters  with
3425         higher values, the concept of case is supported  if  PCRE  is  compiled         higher  values,  the  concept  of case is supported if PCRE is compiled
3426         with  Unicode  property support, but not otherwise.  If you want to use         with Unicode property support, but not otherwise.  If you want  to  use
3427         caseless matching for characters 128 and above, you  must  ensure  that         caseless  matching  for  characters 128 and above, you must ensure that
3428         PCRE  is  compiled  with Unicode property support as well as with UTF-8         PCRE is compiled with Unicode property support as well  as  with  UTF-8
3429         support.         support.
3430    
3431         Characters that might indicate  line  breaks  (CR  and  LF)  are  never         Characters  that  might  indicate  line breaks are never treated in any
3432         treated  in  any  special way when matching character classes, whatever         special way  when  matching  character  classes,  whatever  line-ending
3433         line-ending sequence is in use, and whatever setting of the PCRE_DOTALL         sequence  is  in  use,  and  whatever  setting  of  the PCRE_DOTALL and
3434         and PCRE_MULTILINE options is used. A class such as [^a] always matches         PCRE_MULTILINE options is used. A class such as [^a] always matches one
3435         one of these characters.         of these characters.
3436    
3437         The minus (hyphen) character can be used to specify a range of  charac-         The  minus (hyphen) character can be used to specify a range of charac-
3438         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters in a character  class.  For  example,  [d-m]  matches  any  letter
3439         between d and m, inclusive. If a  minus  character  is  required  in  a         between  d  and  m,  inclusive.  If  a minus character is required in a
3440         class,  it  must  be  escaped  with a backslash or appear in a position         class, it must be escaped with a backslash  or  appear  in  a  position
3441         where it cannot be interpreted as indicating a range, typically as  the         where  it cannot be interpreted as indicating a range, typically as the
3442         first or last character in the class.         first or last character in the class.
3443    
3444         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
3445         ter of a range. A pattern such as [W-]46] is interpreted as a class  of         ter  of a range. A pattern such as [W-]46] is interpreted as a class of
3446         two  characters ("W" and "-") followed by a literal string "46]", so it         two characters ("W" and "-") followed by a literal string "46]", so  it
3447         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a
3448         backslash  it is interpreted as the end of range, so [W-\]46] is inter-         backslash it is interpreted as the end of range, so [W-\]46] is  inter-
3449         preted as a class containing a range followed by two other  characters.         preted  as a class containing a range followed by two other characters.
3450         The  octal or hexadecimal representation of "]" can also be used to end         The octal or hexadecimal representation of "]" can also be used to  end
3451         a range.         a range.
3452    
3453         Ranges operate in the collating sequence of character values. They  can         Ranges  operate in the collating sequence of character values. They can
3454         also   be  used  for  characters  specified  numerically,  for  example         also  be  used  for  characters  specified  numerically,  for   example
3455         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values         [\000-\037].  In UTF-8 mode, ranges can include characters whose values
3456         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
3457    
3458         If a range that includes letters is used when caseless matching is set,         If a range that includes letters is used when caseless matching is set,
3459         it matches the letters in either case. For example, [W-c] is equivalent         it matches the letters in either case. For example, [W-c] is equivalent
3460         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to [][\\^_`wxyzabc], matched caselessly,  and  in  non-UTF-8  mode,  if
3461         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches         character  tables  for  a French locale are in use, [\xc8-\xcb] matches
3462         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the         accented E characters in both cases. In UTF-8 mode, PCRE  supports  the
3463         concept of case for characters with values greater than 128  only  when         concept  of  case for characters with values greater than 128 only when
3464         it is compiled with Unicode property support.         it is compiled with Unicode property support.
3465    
3466         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear         The character types \d, \D, \p, \P, \s, \S, \w, and \W may also  appear
3467         in a character class, and add the characters that  they  match  to  the         in  a  character  class,  and add the characters that they match to the
3468         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
3469         flex can conveniently be used with the upper case  character  types  to         flex  can  conveniently  be used with the upper case character types to
3470         specify  a  more  restricted  set of characters than the matching lower         specify a more restricted set of characters  than  the  matching  lower
3471         case type. For example, the class [^\W_] matches any letter  or  digit,         case  type.  For example, the class [^\W_] matches any letter or digit,
3472         but not underscore.         but not underscore.
3473    
3474         The  only  metacharacters  that are recognized in character classes are         The only metacharacters that are recognized in  character  classes  are
3475         backslash, hyphen (only where it can be  interpreted  as  specifying  a         backslash,  hyphen  (only  where  it can be interpreted as specifying a
3476         range),  circumflex  (only  at the start), opening square bracket (only         range), circumflex (only at the start), opening  square  bracket  (only
3477         when it can be interpreted as introducing a POSIX class name - see  the         when  it can be interpreted as introducing a POSIX class name - see the
3478         next  section),  and  the  terminating closing square bracket. However,         next section), and the terminating  closing  square  bracket.  However,
3479         escaping other non-alphanumeric characters does no harm.         escaping other non-alphanumeric characters does no harm.
3480    
3481    
3482  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
3483    
3484         Perl supports the POSIX notation for character classes. This uses names         Perl supports the POSIX notation for character classes. This uses names
3485         enclosed  by  [: and :] within the enclosing square brackets. PCRE also         enclosed by [: and :] within the enclosing square brackets.  PCRE  also
3486         supports this notation. For example,         supports this notation. For example,
3487    
3488           [01[:alpha:]%]           [01[:alpha:]%]
# Line 3144  POSIX CHARACTER CLASSES Line 3505  POSIX CHARACTER CLASSES
3505           word     "word" characters (same as \w)           word     "word" characters (same as \w)
3506           xdigit   hexadecimal digits           xdigit   hexadecimal digits
3507    
3508         The  "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),         The "space" characters are HT (9), LF (10), VT (11), FF (12), CR  (13),
3509         and space (32). Notice that this list includes the VT  character  (code         and  space  (32). Notice that this list includes the VT character (code
3510         11). This makes "space" different to \s, which does not include VT (for         11). This makes "space" different to \s, which does not include VT (for
3511         Perl compatibility).         Perl compatibility).
3512    
3513         The name "word" is a Perl extension, and "blank"  is  a  GNU  extension         The  name  "word"  is  a Perl extension, and "blank" is a GNU extension
3514         from  Perl  5.8. Another Perl extension is negation, which is indicated         from Perl 5.8. Another Perl extension is negation, which  is  indicated
3515         by a ^ character after the colon. For example,         by a ^ character after the colon. For example,
3516    
3517           [12[:^digit:]]           [12[:^digit:]]
3518    
3519         matches "1", "2", or any non-digit. PCRE (and Perl) also recognize  the         matches  "1", "2", or any non-digit. PCRE (and Perl) also recognize the
3520         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
3521         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
3522    
# Line 3165  POSIX CHARACTER CLASSES Line 3526  POSIX CHARACTER CLASSES
3526    
3527  VERTICAL BAR  VERTICAL BAR
3528    
3529         Vertical bar characters are used to separate alternative patterns.  For         Vertical  bar characters are used to separate alternative patterns. For
3530         example, the pattern         example, the pattern
3531    
3532           gilbert|sullivan           gilbert|sullivan
3533    
3534         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches either "gilbert" or "sullivan". Any number of alternatives  may
3535         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear,  and  an  empty  alternative  is  permitted (matching the empty
3536         string). The matching process tries each alternative in turn, from left         string). The matching process tries each alternative in turn, from left
3537         to right, and the first one that succeeds is used. If the  alternatives         to  right, and the first one that succeeds is used. If the alternatives
3538         are  within a subpattern (defined below), "succeeds" means matching the         are within a subpattern (defined below), "succeeds" means matching  the
3539         rest of the main pattern as well as the alternative in the  subpattern.         rest  of the main pattern as well as the alternative in the subpattern.
3540    
3541    
3542  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3543    
3544         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The settings of the  PCRE_CASELESS,  PCRE_MULTILINE,  PCRE_DOTALL,  and
3545         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED  options  can  be  changed  from  within the pattern by a
3546         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         sequence of Perl option letters enclosed  between  "(?"  and  ")".  The
3547         option letters are         option letters are
3548    
3549           i  for PCRE_CASELESS           i  for PCRE_CASELESS
# Line 3192  INTERNAL OPTION SETTING Line 3553  INTERNAL OPTION SETTING
3553    
3554         For example, (?im) sets caseless, multiline matching. It is also possi-         For example, (?im) sets caseless, multiline matching. It is also possi-
3555         ble to unset these options by preceding the letter with a hyphen, and a         ble to unset these options by preceding the letter with a hyphen, and a
3556         combined setting and unsetting such as (?im-sx), which sets  PCRE_CASE-         combined  setting and unsetting such as (?im-sx), which sets PCRE_CASE-
3557         LESS  and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,         LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and  PCRE_EXTENDED,
3558         is also permitted. If a  letter  appears  both  before  and  after  the         is  also  permitted.  If  a  letter  appears  both before and after the
3559         hyphen, the option is unset.         hyphen, the option is unset.
3560    
3561         When  an option change occurs at top level (that is, not inside subpat-         When an option change occurs at top level (that is, not inside  subpat-
3562         tern parentheses), the change applies to the remainder of  the  pattern         tern  parentheses),  the change applies to the remainder of the pattern
3563         that follows.  If the change is placed right at the start of a pattern,         that follows.  If the change is placed right at the start of a pattern,
3564         PCRE extracts it into the global options (and it will therefore show up         PCRE extracts it into the global options (and it will therefore show up
3565         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3566    
3567         An option change within a subpattern affects only that part of the cur-         An option change within a subpattern (see below for  a  description  of
3568         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3569           it, so
3570    
3571           (a(?i)b)c           (a(?i)b)c
3572    
# Line 3236  SUBPATTERNS Line 3598  SUBPATTERNS
3598           cat(aract|erpillar|)           cat(aract|erpillar|)
3599    
3600         matches one of the words "cat", "cataract", or  "caterpillar".  Without         matches one of the words "cat", "cataract", or  "caterpillar".  Without
3601         the  parentheses,  it  would  match "cataract", "erpillar" or the empty         the  parentheses,  it  would  match  "cataract", "erpillar" or an empty
3602         string.         string.
3603    
3604         2. It sets up the subpattern as  a  capturing  subpattern.  This  means         2. It sets up the subpattern as  a  capturing  subpattern.  This  means
# Line 3265  SUBPATTERNS Line 3627  SUBPATTERNS
3627           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3628    
3629         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3630         1 and 2. The maximum number of capturing subpatterns is 65535, and  the         1 and 2. The maximum number of capturing subpatterns is 65535.
        maximum  depth  of  nesting of all subpatterns, both capturing and non-  
        capturing, is 200.  
3631    
3632         As a convenient shorthand, if any option settings are required  at  the         As a convenient shorthand, if any option settings are required  at  the
3633         start  of  a  non-capturing  subpattern,  the option letters may appear         start  of  a  non-capturing  subpattern,  the option letters may appear
# Line 3283  SUBPATTERNS Line 3643  SUBPATTERNS
3643         "Saturday".         "Saturday".
3644    
3645    
3646    DUPLICATE SUBPATTERN NUMBERS
3647    
3648           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3649           uses  the same numbers for its capturing parentheses. Such a subpattern
3650           starts with (?| and is itself a non-capturing subpattern. For  example,
3651           consider this pattern:
3652    
3653             (?|(Sat)ur|(Sun))day
3654    
3655           Because  the two alternatives are inside a (?| group, both sets of cap-
3656           turing parentheses are numbered one. Thus, when  the  pattern  matches,
3657           you  can  look  at captured substring number one, whichever alternative
3658           matched. This construct is useful when you want to  capture  part,  but
3659           not all, of one of a number of alternatives. Inside a (?| group, paren-
3660           theses are numbered as usual, but the number is reset at the  start  of
3661           each  branch. The numbers of any capturing buffers that follow the sub-
3662           pattern start after the highest number used in any branch. The  follow-
3663           ing  example  is taken from the Perl documentation.  The numbers under-
3664           neath show in which buffer the captured content will be stored.
3665    
3666             # before  ---------------branch-reset----------- after
3667             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3668             # 1            2         2  3        2     3     4
3669    
3670           A backreference or a recursive call to  a  numbered  subpattern  always
3671           refers to the first one in the pattern with the given number.
3672    
3673           An  alternative approach to using this "branch reset" feature is to use
3674           duplicate named subpatterns, as described in the next section.
3675    
3676    
3677  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3678    
3679         Identifying capturing parentheses by number is simple, but  it  can  be         Identifying capturing parentheses by number is simple, but  it  can  be
3680         very  hard  to keep track of the numbers in complicated regular expres-         very  hard  to keep track of the numbers in complicated regular expres-
3681         sions. Furthermore, if an  expression  is  modified,  the  numbers  may         sions. Furthermore, if an  expression  is  modified,  the  numbers  may
3682         change.  To help with this difficulty, PCRE supports the naming of sub-         change.  To help with this difficulty, PCRE supports the naming of sub-
3683         patterns, something that Perl  does  not  provide.  The  Python  syntax         patterns. This feature was not added to Perl until release 5.10. Python
3684         (?P<name>...)  is  used. References to capturing parentheses from other         had  the  feature earlier, and PCRE introduced it at release 4.0, using
3685         parts of the pattern, such as  backreferences,  recursion,  and  condi-         the Python syntax. PCRE now supports both the Perl and the Python  syn-
3686         tions, can be made by name as well as by number.         tax.
3687    
3688           In  PCRE,  a subpattern can be named in one of three ways: (?<name>...)
3689           or (?'name'...) as in Perl, or (?P<name>...) as in  Python.  References
3690           to capturing parentheses from other parts of the pattern, such as back-
3691           references, recursion, and conditions, can be made by name as  well  as
3692           by number.
3693    
3694         Names  consist  of  up  to  32 alphanumeric characters and underscores.         Names  consist  of  up  to  32 alphanumeric characters and underscores.
3695         Named capturing parentheses are still  allocated  numbers  as  well  as         Named capturing parentheses are still  allocated  numbers  as  well  as
3696         names. The PCRE API provides function calls for extracting the name-to-         names,  exactly as if the names were not present. The PCRE API provides
3697         number translation table from a compiled pattern. There is also a  con-         function calls for extracting the name-to-number translation table from
3698         venience function for extracting a captured substring by name.         a compiled pattern. There is also a convenience function for extracting
3699           a captured substring by name.
3700    
3701         By  default, a name must be unique within a pattern, but it is possible         By default, a name must be unique within a pattern, but it is  possible
3702         to relax this constraint by setting the PCRE_DUPNAMES option at compile         to relax this constraint by setting the PCRE_DUPNAMES option at compile
3703         time.  This  can  be useful for patterns where only one instance of the         time. This can be useful for patterns where only one  instance  of  the
3704         named parentheses can match. Suppose you want to match the  name  of  a         named  parentheses  can  match. Suppose you want to match the name of a
3705         weekday,  either as a 3-letter abbreviation or as the full name, and in         weekday, either as a 3-letter abbreviation or as the full name, and  in
3706         both cases you want to extract the abbreviation. This pattern (ignoring         both cases you want to extract the abbreviation. This pattern (ignoring
3707         the line breaks) does the job:         the line breaks) does the job:
3708    
3709           (?P<DN>Mon|Fri|Sun)(?:day)?|           (?<DN>Mon|Fri|Sun)(?:day)?|
3710           (?P<DN>Tue)(?:sday)?|           (?<DN>Tue)(?:sday)?|
3711           (?P<DN>Wed)(?:nesday)?|           (?<DN>Wed)(?:nesday)?|
3712           (?P<DN>Thu)(?:rsday)?|           (?<DN>Thu)(?:rsday)?|
3713           (?P<DN>Sat)(?:urday)?           (?<DN>Sat)(?:urday)?
3714    
3715         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
3716         match.  The convenience  function  for  extracting  the  data  by  name         match.  (An alternative way of solving this problem is to use a "branch
3717         returns  the  substring  for  the first, and in this example, the only,         reset" subpattern, as described in the previous section.)
3718         subpattern of that name that matched.  This  saves  searching  to  find  
3719         which  numbered  subpattern  it  was. If you make a reference to a non-         The convenience function for extracting the data by  name  returns  the
3720         unique named subpattern from elsewhere in the  pattern,  the  one  that         substring  for  the first (and in this example, the only) subpattern of
3721         corresponds  to  the  lowest number is used. For further details of the         that name that matched. This saves searching  to  find  which  numbered
3722         interfaces for handling named subpatterns, see the  pcreapi  documenta-         subpattern  it  was. If you make a reference to a non-unique named sub-
3723         tion.         pattern from elsewhere in the pattern, the one that corresponds to  the
3724           lowest  number  is used. For further details of the interfaces for han-
3725           dling named subpatterns, see the pcreapi documentation.
3726    
3727    
3728  REPETITION  REPETITION
3729    
3730         Repetition  is  specified  by  quantifiers, which can follow any of the         Repetition is specified by quantifiers, which can  follow  any  of  the
3731         following items:         following items:
3732    
3733           a literal data character           a literal data character
3734           the . metacharacter           the dot metacharacter
3735           the \C escape sequence           the \C escape sequence
3736           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3737             the \R escape sequence
3738           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3739           a character class           a character class
3740           a back reference (see next section)           a back reference (see next section)
3741           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
3742    
3743         The general repetition quantifier specifies a minimum and maximum  num-         The  general repetition quantifier specifies a minimum and maximum num-
3744         ber  of  permitted matches, by giving the two numbers in curly brackets         ber of permitted matches, by giving the two numbers in  curly  brackets
3745         (braces), separated by a comma. The numbers must be  less  than  65536,         (braces),  separated  by  a comma. The numbers must be less than 65536,
3746         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
3747    
3748           z{2,4}           z{2,4}
3749    
3750         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a
3751         special character. If the second number is omitted, but  the  comma  is         special  character.  If  the second number is omitted, but the comma is
3752         present,  there  is  no upper limit; if the second number and the comma         present, there is no upper limit; if the second number  and  the  comma
3753         are both omitted, the quantifier specifies an exact number of  required         are  both omitted, the quantifier specifies an exact number of required
3754         matches. Thus         matches. Thus
3755    
3756           [aeiou]{3,}           [aeiou]{3,}
# Line 3358  REPETITION Line 3759  REPETITION
3759    
3760           \d{8}           \d{8}
3761    
3762         matches  exactly  8  digits. An opening curly bracket that appears in a         matches exactly 8 digits. An opening curly bracket that  appears  in  a
3763         position where a quantifier is not allowed, or one that does not  match         position  where a quantifier is not allowed, or one that does not match
3764         the  syntax of a quantifier, is taken as a literal character. For exam-         the syntax of a quantifier, is taken as a literal character. For  exam-
3765         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
3766    
3767         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to         In UTF-8 mode, quantifiers apply to UTF-8  characters  rather  than  to
3768         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
3769         acters, each of which is represented by a two-byte sequence. Similarly,         acters, each of which is represented by a two-byte sequence. Similarly,
3770         when Unicode property support is available, \X{3} matches three Unicode         when Unicode property support is available, \X{3} matches three Unicode
3771         extended  sequences,  each of which may be several bytes long (and they         extended sequences, each of which may be several bytes long  (and  they
3772         may be of different lengths).         may be of different lengths).
3773    
3774         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3775         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3776    
3777         For  convenience  (and  historical compatibility) the three most common         For convenience, the three most common quantifiers have  single-charac-
3778         quantifiers have single-character abbreviations:         ter abbreviations:
3779    
3780           *    is equivalent to {0,}           *    is equivalent to {0,}
3781           +    is equivalent to {1,}           +    is equivalent to {1,}
3782           ?    is equivalent to {0,1}           ?    is equivalent to {0,1}
3783    
3784         It is possible to construct infinite loops by  following  a  subpattern         It  is  possible  to construct infinite loops by following a subpattern
3785         that can match no characters with a quantifier that has no upper limit,         that can match no characters with a quantifier that has no upper limit,
3786         for example:         for example:
3787    
3788           (a?)*           (a?)*
3789    
3790         Earlier versions of Perl and PCRE used to give an error at compile time         Earlier versions of Perl and PCRE used to give an error at compile time
3791         for  such  patterns. However, because there are cases where this can be         for such patterns. However, because there are cases where this  can  be
3792         useful, such patterns are now accepted, but if any  repetition  of  the         useful,  such  patterns  are now accepted, but if any repetition of the
3793         subpattern  does in fact match no characters, the loop is forcibly bro-         subpattern does in fact match no characters, the loop is forcibly  bro-
3794         ken.         ken.
3795    
3796         By default, the quantifiers are "greedy", that is, they match  as  much         By  default,  the quantifiers are "greedy", that is, they match as much
3797         as  possible  (up  to  the  maximum number of permitted times), without         as possible (up to the maximum  number  of  permitted  times),  without
3798         causing the rest of the pattern to fail. The classic example  of  where         causing  the  rest of the pattern to fail. The classic example of where
3799         this gives problems is in trying to match comments in C programs. These         this gives problems is in trying to match comments in C programs. These
3800         appear between /* and */ and within the comment,  individual  *  and  /         appear  between  /*  and  */ and within the comment, individual * and /
3801         characters  may  appear. An attempt to match C comments by applying the         characters may appear. An attempt to match C comments by  applying  the
3802         pattern         pattern
3803    
3804           /\*.*\*/           /\*.*\*/
# Line 3406  REPETITION Line 3807  REPETITION
3807    
3808           /* first comment */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
3809    
3810         fails, because it matches the entire string owing to the greediness  of         fails,  because it matches the entire string owing to the greediness of
3811         the .*  item.         the .*  item.
3812    
3813         However,  if  a quantifier is followed by a question mark, it ceases to         However, if a quantifier is followed by a question mark, it  ceases  to
3814         be greedy, and instead matches the minimum number of times possible, so         be greedy, and instead matches the minimum number of times possible, so
3815         the pattern         the pattern
3816    
3817           /\*.*?\*/           /\*.*?\*/
3818    
3819         does  the  right  thing with the C comments. The meaning of the various         does the right thing with the C comments. The meaning  of  the  various
3820         quantifiers is not otherwise changed,  just  the  preferred  number  of         quantifiers  is  not  otherwise  changed,  just the preferred number of
3821         matches.   Do  not  confuse this use of question mark with its use as a         matches.  Do not confuse this use of question mark with its  use  as  a
3822         quantifier in its own right. Because it has two uses, it can  sometimes         quantifier  in its own right. Because it has two uses, it can sometimes
3823         appear doubled, as in         appear doubled, as in
3824    
3825           \d??\d           \d??\d
# Line 3426  REPETITION Line 3827  REPETITION
3827         which matches one digit by preference, but can match two if that is the         which matches one digit by preference, but can match two if that is the
3828         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3829    
3830         If the PCRE_UNGREEDY option is set (an option which is not available in         If  the PCRE_UNGREEDY option is set (an option that is not available in
3831         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl), the quantifiers are not greedy by default, but  individual  ones
3832         can be made greedy by following them with a  question  mark.  In  other         can  be  made  greedy  by following them with a question mark. In other
3833         words, it inverts the default behaviour.         words, it inverts the default behaviour.
3834    
3835         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When a parenthesized subpattern is quantified  with  a  minimum  repeat
3836         count that is greater than 1 or with a limited maximum, more memory  is         count  that is greater than 1 or with a limited maximum, more memory is
3837         required  for  the  compiled  pattern, in proportion to the size of the         required for the compiled pattern, in proportion to  the  size  of  the
3838         minimum or maximum.         minimum or maximum.
3839    
3840         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-         If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equiv-
3841         alent  to Perl's /s) is set, thus allowing the . to match newlines, the         alent to Perl's /s) is set, thus allowing the dot  to  match  newlines,
3842         pattern is implicitly anchored, because whatever follows will be  tried         the  pattern  is  implicitly anchored, because whatever follows will be
3843         against  every character position in the subject string, so there is no         tried against every character position in the subject string, so  there
3844         point in retrying the overall match at any position  after  the  first.         is  no  point  in  retrying the overall match at any position after the
3845         PCRE normally treats such a pattern as though it were preceded by \A.         first. PCRE normally treats such a pattern as though it  were  preceded
3846           by \A.
3847    
3848         In  cases  where  it  is known that the subject string contains no new-         In  cases  where  it  is known that the subject string contains no new-
3849         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-         lines, it is worth setting PCRE_DOTALL in order to  obtain  this  opti-
# Line 3449  REPETITION Line 3851  REPETITION
3851    
3852         However,  there is one situation where the optimization cannot be used.         However,  there is one situation where the optimization cannot be used.
3853         When .*  is inside capturing parentheses that  are  the  subject  of  a         When .*  is inside capturing parentheses that  are  the  subject  of  a
3854         backreference  elsewhere in the pattern, a match at the start may fail,         backreference  elsewhere  in the pattern, a match at the start may fail
3855         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3856    
3857           (.*)abc\1           (.*)abc\1
3858    
# Line 3474  REPETITION Line 3876  REPETITION
3876    
3877  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3878    
3879         With both maximizing and minimizing repetition, failure of what follows         With  both  maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
3880         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition, failure of what follows normally causes the  repeated  item
3881         ferent number of repeats allows the rest of the pattern to match. Some-         to  be  re-evaluated to see if a different number of repeats allows the
3882         times it is useful to prevent this, either to change the nature of  the         rest of the pattern to match. Sometimes it is useful to  prevent  this,
3883         match,  or  to  cause it fail earlier than it otherwise might, when the         either  to  change the nature of the match, or to cause it fail earlier
3884         author of the pattern knows there is no point in carrying on.         than it otherwise might, when the author of the pattern knows there  is
3885           no point in carrying on.
3886    
3887         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider,  for  example, the pattern \d+foo when applied to the subject
3888         line         line
3889    
3890           123456bar           123456bar
3891    
3892         After matching all 6 digits and then failing to match "foo", the normal         After matching all 6 digits and then failing to match "foo", the normal
3893         action of the matcher is to try again with only 5 digits  matching  the         action  of  the matcher is to try again with only 5 digits matching the
3894         \d+  item,  and  then  with  4,  and  so on, before ultimately failing.         \d+ item, and then with  4,  and  so  on,  before  ultimately  failing.
3895         "Atomic grouping" (a term taken from Jeffrey  Friedl's  book)  provides         "Atomic  grouping"  (a  term taken from Jeffrey Friedl's book) provides
3896         the  means for specifying that once a subpattern has matched, it is not         the means for specifying that once a subpattern has matched, it is  not
3897         to be re-evaluated in this way.         to be re-evaluated in this way.
3898    
3899         If we use atomic grouping for the previous example, the  matcher  would         If  we  use atomic grouping for the previous example, the matcher gives
3900         give up immediately on failing to match "foo" the first time. The nota-         up immediately on failing to match "foo" the first time.  The  notation
3901         tion is a kind of special parenthesis, starting with  (?>  as  in  this         is a kind of special parenthesis, starting with (?> as in this example:
        example:  
3902    
3903           (?>\d+)foo           (?>\d+)foo
3904    
3905         This  kind  of  parenthesis "locks up" the  part of the pattern it con-         This kind of parenthesis "locks up" the  part of the  pattern  it  con-
3906         tains once it has matched, and a failure further into  the  pattern  is         tains  once  it  has matched, and a failure further into the pattern is
3907         prevented  from  backtracking into it. Backtracking past it to previous         prevented from backtracking into it. Backtracking past it  to  previous
3908         items, however, works as normal.         items, however, works as normal.
3909    
3910         An alternative description is that a subpattern of  this  type  matches         An  alternative  description  is that a subpattern of this type matches
3911         the  string  of  characters  that an identical standalone pattern would         the string of characters that an  identical  standalone  pattern  would
3912         match, if anchored at the current point in the subject string.         match, if anchored at the current point in the subject string.
3913    
3914         Atomic grouping subpatterns are not capturing subpatterns. Simple cases         Atomic grouping subpatterns are not capturing subpatterns. Simple cases
3915         such as the above example can be thought of as a maximizing repeat that         such as the above example can be thought of as a maximizing repeat that
3916         must swallow everything it can. So, while both \d+ and  \d+?  are  pre-         must  swallow  everything  it can. So, while both \d+ and \d+? are pre-
3917         pared  to  adjust  the number of digits they match in order to make the         pared to adjust the number of digits they match in order  to  make  the
3918         rest of the pattern match, (?>\d+) can only match an entire sequence of         rest of the pattern match, (?>\d+) can only match an entire sequence of
3919         digits.         digits.
3920    
3921         Atomic  groups in general can of course contain arbitrarily complicated         Atomic groups in general can of course contain arbitrarily  complicated
3922         subpatterns, and can be nested. However, when  the  subpattern  for  an         subpatterns,  and  can  be  nested. However, when the subpattern for an
3923         atomic group is just a single repeated item, as in the example above, a         atomic group is just a single repeated item, as in the example above, a
3924         simpler notation, called a "possessive quantifier" can  be  used.  This         simpler  notation,  called  a "possessive quantifier" can be used. This
3925         consists  of  an  additional  + character following a quantifier. Using         consists of an additional + character  following  a  quantifier.  Using
3926         this notation, the previous example can be rewritten as         this notation, the previous example can be rewritten as
3927    
3928           \d++foo           \d++foo
3929    
3930           Note that a possessive quantifier can be used with an entire group, for
3931           example:
3932    
3933             (abc|xyz){2,3}+
3934    
3935         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3936         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3937         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3938         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3939         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3940           should be slightly faster.
3941         The possessive quantifier syntax is an extension to  the  Perl  syntax.  
3942         Jeffrey  Friedl originated the idea (and the name) in the first edition         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3943         of his book.  Mike McCloskey liked it, so implemented it when he  built         tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3944         Sun's Java package, and PCRE copied it from there.         edition of his book. Mike McCloskey liked it, so implemented it when he
3945           built Sun's Java package, and PCRE copied it from there. It  ultimately
3946         When  a  pattern  contains an unlimited repeat inside a subpattern that         found its way into Perl at release 5.10.
3947         can itself be repeated an unlimited number of  times,  the  use  of  an  
3948         atomic  group  is  the  only way to avoid some failing matches taking a         PCRE has an optimization that automatically "possessifies" certain sim-
3949           ple pattern constructs. For example, the sequence  A+B  is  treated  as
3950           A++B  because  there is no point in backtracking into a sequence of A's
3951           when B must follow.
3952    
3953           When a pattern contains an unlimited repeat inside  a  subpattern  that
3954           can  itself  be  repeated  an  unlimited number of times, the use of an
3955           atomic group is the only way to avoid some  failing  matches  taking  a
3956         very long time indeed. The pattern         very long time indeed. The pattern
3957    
3958           (\D+|<\d+>)*[!?]           (\D+|<\d+>)*[!?]
3959    
3960         matches an unlimited number of substrings that either consist  of  non-         matches  an  unlimited number of substrings that either consist of non-
3961         digits,  or  digits  enclosed in <>, followed by either ! or ?. When it         digits, or digits enclosed in <>, followed by either ! or  ?.  When  it
3962         matches, it runs quickly. However, if it is applied to         matches, it runs quickly. However, if it is applied to
3963    
3964           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3965    
3966         it takes a long time before reporting  failure.  This  is  because  the         it  takes  a  long  time  before reporting failure. This is because the
3967         string  can be divided between the internal \D+ repeat and the external         string can be divided between the internal \D+ repeat and the  external
3968         * 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
3969         example  uses  [!?]  rather than a single character at the end, because         example uses [!?] rather than a single character at  the  end,  because
3970         both PCRE and Perl have an optimization that allows  for  fast  failure         both  PCRE  and  Perl have an optimization that allows for fast failure
3971         when  a single character is used. They remember the last single charac-         when a single character is used. They remember the last single  charac-
3972         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
3973         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
3974         group, like this:         group, like this:
3975    
3976           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3977    
3978         sequences of non-digits cannot be broken, and failure happens  quickly.         sequences  of non-digits cannot be broken, and failure happens quickly.
3979    
3980    
3981  BACK REFERENCES  BACK REFERENCES
3982    
3983         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3984         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-
3985         pattern  earlier  (that is, to its left) in the pattern, provided there         pattern earlier (that is, to its left) in the pattern,  provided  there
3986         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3987    
3988         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3989         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
3990         there are not that many capturing left parentheses in the  entire  pat-         there  are  not that many capturing left parentheses in the entire pat-
3991         tern.  In  other words, the parentheses that are referenced need not be         tern. In other words, the parentheses that are referenced need  not  be
3992         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
3993         reference"  of  this  type can make sense when a repetition is involved         reference" of this type can make sense when a  repetition  is  involved
3994         and the subpattern to the right has participated in an  earlier  itera-         and  the  subpattern to the right has participated in an earlier itera-
3995         tion.         tion.
3996    
3997         It is not possible to have a numerical "forward back reference" to sub-         It is not possible to have a numerical "forward back  reference"  to  a
3998         pattern whose number is 10 or more. However, a back  reference  to  any         subpattern  whose  number  is  10  or  more using this syntax because a
3999         subpattern  is  possible  using named parentheses (see below). See also         sequence such as \50 is interpreted as a character  defined  in  octal.
4000         the subsection entitled "Non-printing  characters"  above  for  further         See the subsection entitled "Non-printing characters" above for further
4001         details of the handling of digits following a backslash.         details of the handling of digits following a backslash.  There  is  no
4002           such  problem  when named parentheses are used. A back reference to any
4003           subpattern is possible using named parentheses (see below).
4004    
4005           Another way of avoiding the ambiguity inherent in  the  use  of  digits
4006           following a backslash is to use the \g escape sequence, which is a fea-
4007           ture introduced in Perl 5.10.  This  escape  must  be  followed  by  an
4008           unsigned  number  or  a negative number, optionally enclosed in braces.
4009           These examples are all identical:
4010    
4011             (ring), \1
4012             (ring), \g1
4013             (ring), \g{1}
4014    
4015           An unsigned number specifies an absolute reference without the  ambigu-
4016           ity that is present in the older syntax. It is also useful when literal
4017           digits follow the reference. A negative number is a relative reference.
4018           Consider this example:
4019    
4020             (abc(def)ghi)\g{-1}
4021    
4022           The sequence \g{-1} is a reference to the most recently started captur-
4023           ing subpattern before \g, that is, is it equivalent to  \2.  Similarly,
4024           \g{-2} would be equivalent to \1. The use of relative references can be
4025           helpful in long patterns, and also in  patterns  that  are  created  by
4026           joining together fragments that contain references within themselves.
4027    
4028         A  back  reference matches whatever actually matched the capturing sub-         A  back  reference matches whatever actually matched the capturing sub-
4029         pattern in the current subject string, rather  than  anything  matching         pattern in the current subject string, rather  than  anything  matching
# Line 3603  BACK REFERENCES Line 4042  BACK REFERENCES
4042         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
4043         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4044    
4045         Back references to named subpatterns use the Python  syntax  (?P=name).         There are several different ways of writing back  references  to  named
4046         We could rewrite the above example as follows:         subpatterns.  The  .NET syntax \k{name} and the Perl syntax \k<name> or
4047           \k'name' are supported, as is the Python syntax (?P=name). Perl  5.10's
4048           unified back reference syntax, in which \g can be used for both numeric
4049           and named references, is also supported. We  could  rewrite  the  above
4050           example in any of the following ways:
4051    
4052             (?<p1>(?i)rah)\s+\k<p1>
4053             (?'p1'(?i)rah)\s+\k{p1}
4054           (?P<p1>(?i)rah)\s+(?P=p1)           (?P<p1>(?i)rah)\s+(?P=p1)
4055             (?<p1>(?i)rah)\s+\g{p1}
4056    
4057         A  subpattern  that  is  referenced  by  name may appear in the pattern         A  subpattern  that  is  referenced  by  name may appear in the pattern
4058         before or after the reference.         before or after the reference.
# Line 3721  ASSERTIONS Line 4167  ASSERTIONS
4167    
4168           (?<=abc|abde)           (?<=abc|abde)
4169    
4170           In some cases, the Perl 5.10 escape sequence \K (see above) can be used
4171           instead of a lookbehind assertion; this is not restricted to  a  fixed-
4172           length.
4173    
4174         The  implementation  of lookbehind assertions is, for each alternative,         The  implementation  of lookbehind assertions is, for each alternative,
4175         to temporarily move the current position back by the  fixed  width  and         to temporarily move the current position back by the fixed  length  and
4176         then try to match. If there are insufficient characters before the cur-         then try to match. If there are insufficient characters before the cur-
4177         rent position, the match is deemed to fail.         rent position, the assertion fails.
4178    
4179         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
4180         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
4181         ble to calculate the length of the lookbehind. The \X escape, which can         ble to calculate the length of the lookbehind. The \X and  \R  escapes,
4182         match different numbers of bytes, is also not permitted.         which can match different numbers of bytes, are also not permitted.
4183    
4184         Atomic  groups can be used in conjunction with lookbehind assertions to         Possessive  quantifiers  can  be  used  in  conjunction with lookbehind
4185         specify efficient matching at the end of the subject string. Consider a         assertions to specify efficient matching at  the  end  of  the  subject
4186         simple pattern such as         string. Consider a simple pattern such as
4187    
4188           abcd$           abcd$
4189    
# Line 3750  ASSERTIONS Line 4200  ASSERTIONS
4200         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,
4201         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
4202    
          ^(?>.*)(?<=abcd)  
   
        or, equivalently, using the possessive quantifier syntax,  
   
4203           ^.*+(?<=abcd)           ^.*+(?<=abcd)
4204    
4205         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
4206         entire  string.  The subsequent lookbehind assertion does a single test         entire  string.  The subsequent lookbehind assertion does a single test
4207         on the last four characters. If it fails, the match fails  immediately.         on the last four characters. If it fails, the match fails  immediately.
4208         For  long  strings, this approach makes a significant difference to the         For  long  strings, this approach makes a significant difference to the
# Line 3811  CONDITIONAL SUBPATTERNS Line 4257  CONDITIONAL SUBPATTERNS
4257         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-
4258         tives in the subpattern, a compile-time error occurs.         tives in the subpattern, a compile-time error occurs.
4259    
4260         There are three kinds of condition. If the text between the parentheses         There  are  four  kinds of condition: references to subpatterns, refer-
4261         consists of a sequence of digits, or a sequence of alphanumeric charac-         ences to recursion, a pseudo-condition called DEFINE, and assertions.
4262         ters  and underscores, the condition is satisfied if the capturing sub-  
4263         pattern of that number or name has previously matched. There is a  pos-     Checking for a used subpattern by number
4264         sible  ambiguity here, because subpattern names may consist entirely of  
4265         digits. PCRE looks first for a named subpattern; if it cannot find  one         If the text between the parentheses consists of a sequence  of  digits,
4266         and  the text consists entirely of digits, it looks for a subpattern of         the  condition  is  true if the capturing subpattern of that number has
4267         that number, which must be greater than zero.  Using  subpattern  names         previously matched. An alternative notation is to  precede  the  digits
4268         that consist entirely of digits is not recommended.         with a plus or minus sign. In this case, the subpattern number is rela-
4269           tive rather than absolute.  The most recently opened parentheses can be
4270           referenced  by  (?(-1),  the  next most recent by (?(-2), and so on. In
4271           looping constructs it can also make sense to refer to subsequent groups
4272           with constructs such as (?(+2).
4273    
4274         Consider  the  following  pattern, which contains non-significant white         Consider  the  following  pattern, which contains non-significant white
4275         space to make it more readable (assume the PCRE_EXTENDED option) and to         space to make it more readable (assume the PCRE_EXTENDED option) and to
# Line 3836  CONDITIONAL SUBPATTERNS Line 4286  CONDITIONAL SUBPATTERNS
4286         tern  is  executed  and  a  closing parenthesis is required. Otherwise,         tern  is  executed  and  a  closing parenthesis is required. Otherwise,
4287         since no-pattern is not present, the  subpattern  matches  nothing.  In         since no-pattern is not present, the  subpattern  matches  nothing.  In
4288         other  words,  this  pattern  matches  a  sequence  of non-parentheses,         other  words,  this  pattern  matches  a  sequence  of non-parentheses,
4289         optionally enclosed in parentheses. Rewriting it to use a named subpat-         optionally enclosed in parentheses.
4290         tern gives this:  
4291           If you were embedding this pattern in a larger one,  you  could  use  a
4292           relative reference:
4293    
4294             ...other stuff... ( \( )?    [^()]+    (?(-1) \) ) ...
4295    
4296           This  makes  the  fragment independent of the parentheses in the larger
4297           pattern.
4298    
4299           (?P<OPEN> \( )?    [^()]+    (?(OPEN) \) )     Checking for a used subpattern by name
4300    
4301           Perl uses the syntax (?(<name>)...) or (?('name')...)  to  test  for  a
4302           used  subpattern  by  name.  For compatibility with earlier versions of
4303           PCRE, which had this facility before Perl, the syntax  (?(name)...)  is
4304           also  recognized. However, there is a possible ambiguity with this syn-
4305           tax, because subpattern names may  consist  entirely  of  digits.  PCRE
4306           looks  first for a named subpattern; if it cannot find one and the name
4307           consists entirely of digits, PCRE looks for a subpattern of  that  num-
4308           ber,  which must be greater than zero. Using subpattern names that con-
4309           sist entirely of digits is not recommended.
4310    
4311           Rewriting the above example to use a named subpattern gives this:
4312    
4313             (?<OPEN> \( )?    [^()]+    (?(<OPEN>) \) )
4314    
4315    
4316       Checking for pattern recursion
4317    
4318         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
4319         name R, the condition is satisfied if a recursive call to  the  pattern         name  R, the condition is true if a recursive call to the whole pattern
4320         or  subpattern  has  been made. At "top level", the condition is false.         or any subpattern has been made. If digits or a name preceded by amper-
4321         This is a PCRE extension.  Recursive patterns are described in the next         sand follow the letter R, for example:
4322         section.  
4323             (?(R3)...) or (?(R&name)...)
4324    
4325           the  condition is true if the most recent recursion is into the subpat-
4326           tern whose number or name is given. This condition does not  check  the
4327           entire recursion stack.
4328    
4329           At  "top  level", all these recursion test conditions are false. Recur-
4330           sive patterns are described below.
4331    
4332       Defining subpatterns for use by reference only
4333    
4334           If the condition is the string (DEFINE), and  there  is  no  subpattern