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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
91           pcresample        discussion of the sample program           pcresample        discussion of the sample program
92             pcrestack         discussion of stack usage
93           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
94    
95         In  addition,  in the "man" and HTML formats, there is a short page for         In  addition,  in the "man" and HTML formats, there is a short page for
# Line 98  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 number of capturing subpatterns is 65535.         can be no more than 65535 capturing subpatterns.
116    
117         There is no limit to the number of non-capturing subpatterns,  but  the         The maximum length of name for a named subpattern is 32 characters, and
118         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         the maximum number of named subpatterns is 10000.
        including capturing subpatterns, assertions, and other types of subpat-  
        tern, is 200.  
119    
120         The  maximum  length of a subject string is the largest positive number         The  maximum  length of a subject string is the largest positive number
121         that an integer variable can hold. However, when using the  traditional         that an integer variable can hold. However, when using the  traditional
122         matching function, PCRE uses recursion to handle subpatterns and indef-         matching function, PCRE uses recursion to handle subpatterns and indef-
123         inite repetition.  This means that the available stack space may  limit         inite repetition.  This means that the available stack space may  limit
124         the size of a subject string that can be processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
125           For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
# Line 130  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-
148         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
149         general  category  properties such as Lu for an upper case letter or Nd         general  category  properties such as Lu for an upper case letter or Nd
150         for a decimal number. A full list is given in the pcrepattern  documen-         for a decimal number, the Unicode script names such as Arabic  or  Han,
151         tation. The PCRE library is increased in size by about 90K when Unicode         and  the  derived  properties  Any  and L&. A full list is given in the
152         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
153           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
154         The following comments apply when PCRE is running in UTF-8 mode:         ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
155           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
156         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         does not support this.
157         subjects  are  checked for validity on entry to the relevant functions.  
158         If an invalid UTF-8 string is passed, an error return is given. In some     Validity of UTF-8 strings
159         situations,  you  may  already  know  that  your strings are valid, and  
160         therefore want to skip these checks in order to improve performance. If         When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
161         you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,         subjects are (by default) checked for validity on entry to the relevant
162         PCRE assumes that the pattern or subject  it  is  given  (respectively)         functions. From release 7.3 of PCRE, the check is according  the  rules
163         contains  only valid UTF-8 codes. In this case, it does not diagnose an         of  RFC  3629, which are themselves derived from the Unicode specifica-
164         invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when         tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
165         PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may         allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
166         crash.         check allows only values in the range U+0 to U+10FFFF, excluding U+D800
167           to U+DFFF.
168         2. In a pattern, the escape sequence \x{...}, where the contents of the  
169         braces  is  a  string  of hexadecimal digits, is interpreted as a UTF-8         The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
170         character whose code number is the given hexadecimal number, for  exam-         which the Unicode Standard says this: "The Low Surrogate Area does  not
171         ple:  \x{1234}.  If a non-hexadecimal digit appears between the braces,         contain  any  character  assignments,  consequently  no  character code
172         the item is not recognized.  This escape sequence can be used either as         charts or namelists are provided for this area. Surrogates are reserved
173         a literal, or within a character class.         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       General comments about UTF-8 mode
201    
202         3.  The  original hexadecimal escape sequence, \xhh, matches a two-byte         1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
203         UTF-8 character if the value is greater than 127.         two-byte UTF-8 character if the value is greater than 127.
204    
205         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
206           characters for values greater than \177.
207    
208           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 184  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
237         own  character  tables when checking the case of low-valued characters,         own  character  tables when checking the case of low-valued characters,
238         so as not to degrade performance.  The Unicode property information  is         so as not to degrade performance.  The Unicode property information  is
239         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
240           support is available, PCRE supports case-insensitive matching only when
241           there  is  a  one-to-one  mapping between a letter's cases. There are a
242           small number of many-to-one mappings in Unicode;  these  are  not  sup-
243           ported by PCRE.
244    
245    
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  Last updated: 07 March 2005  REVISION
258  Copyright (c) 1997-2005 University of Cambridge.  
259           Last updated: 09 August 2007
260           Copyright (c) 1997-2007 University of Cambridge.
261  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
262    
263    
# Line 228  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 272  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 treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
334         ter. This is the normal newline character on Unix-like systems. You can         the end of a line. This is the normal newline  character  on  Unix-like
335         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
336           instead, by adding
337    
338           --enable-newline-is-cr           --enable-newline-is-cr
339    
340         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
341         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
342         line character.  
343           Alternatively, you can specify that line endings are to be indicated by
344           the two character sequence CRLF. If you want this, add
345    
346             --enable-newline-is-crlf
347    
348           to the configure command. There is a fourth option, specified by
349    
350             --enable-newline-is-anycrlf
351    
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    WHAT \R MATCHES
365    
366           By default, the sequence \R in a pattern matches  any  Unicode  newline
367           sequence,  whatever  has  been selected as the line ending sequence. If
368           you specify
369    
370             --enable-bsr-anycrlf
371    
372           the default is changed so that \R matches only CR, LF, or  CRLF.  What-
373           ever  is selected when PCRE is built can be overridden when the library
374           functions are called.
375    
376    
377  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 319  POSIX MALLOC USAGE Line 402  POSIX MALLOC USAGE
402         to the configure command.         to the configure command.
403    
404    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly  (possibly  recursively)  when  matching  a   pattern   with   the  
        pcre_exec()  function.  By controlling the maximum number of times this  
        function may be called during a single matching operation, a limit  can  
        be  placed  on  the resources used by a single call to pcre_exec(). The  
        limit can be changed at run time, as described in the pcreapi  documen-  
        tation.  The default is 10 million, but this can be changed by adding a  
        setting such as  
   
          --with-match-limit=500000  
   
        to  the  configure  command.  This  setting  has  no  effect   on   the  
        pcre_dfa_exec() matching function.  
   
   
405  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
406    
407         Within  a  compiled  pattern,  offset values are used to point from one         Within  a  compiled  pattern,  offset values are used to point from one
# Line 353  HANDLING VERY LARGE PATTERNS Line 419  HANDLING VERY LARGE PATTERNS
419         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
420         additional bytes when handling them.         additional bytes when handling them.
421    
        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.  
   
422    
423  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
424    
425         When matching with the pcre_exec() function, PCRE implements backtrack-         When matching with the pcre_exec() function, PCRE implements backtrack-
426         ing by making recursive calls to an internal function  called  match().         ing  by  making recursive calls to an internal function called match().
427         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-
428         verely limit PCRE's operation. (The Unix environment does  not  usually         verely  limit  PCRE's operation. (The Unix environment does not usually
429         suffer  from  this  problem.)  An alternative approach that uses memory         suffer from this problem, but it may sometimes be necessary to increase
430         from the heap to remember data, instead  of  using  recursive  function         the  maximum  stack size.  There is a discussion in the pcrestack docu-
431         calls,  has been implemented to work round this problem. If you want to         mentation.) An alternative approach to recursion that uses memory  from
432         build a version of PCRE that works this way, add         the  heap  to remember data, instead of using recursive function calls,
433           has been implemented to work round the problem of limited  stack  size.
434           If you want to build a version of PCRE that works this way, add
435    
436           --disable-stack-for-recursion           --disable-stack-for-recursion
437    
438         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
439         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
440         ment functions. Separate functions are provided because  the  usage  is         ment  functions. By default these point to malloc() and free(), but you
441         very  predictable:  the  block sizes requested are always the same, and         can replace the pointers so that your own functions are used.
442         the blocks are always freed in reverse order. A calling  program  might  
443         be  able  to implement optimized functions that perform better than the         Separate functions are  provided  rather  than  using  pcre_malloc  and
444         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         pcre_free  because  the  usage  is  very  predictable:  the block sizes
445         slowly when built in this way. This option affects only the pcre_exec()         requested are always the same, and  the  blocks  are  always  freed  in
446         function; it is not relevant for the the pcre_dfa_exec() function.         reverse  order.  A calling program might be able to implement optimized
447           functions that perform better  than  malloc()  and  free().  PCRE  runs
448           noticeably more slowly when built in this way. This option affects only
449           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
450           pcre_dfa_exec() function.
451    
452    
453    LIMITING PCRE RESOURCE USAGE
454    
455           Internally,  PCRE has a function called match(), which it calls repeat-
456           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
457           pcre_exec()  function.  By controlling the maximum number of times this
458           function may be called during a single matching operation, a limit  can
459           be  placed  on  the resources used by a single call to pcre_exec(). The
460           limit can be changed at run time, as described in the pcreapi  documen-
461           tation.  The default is 10 million, but this can be changed by adding a
462           setting such as
463    
464             --with-match-limit=500000
465    
466           to  the  configure  command.  This  setting  has  no  effect   on   the
467           pcre_dfa_exec() matching function.
468    
469           In  some  environments  it is desirable to limit the depth of recursive
470           calls of match() more strictly than the total number of calls, in order
471           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
472           for-recursion is specified) that is used. A second limit controls this;
473           it  defaults  to  the  value  that is set for --with-match-limit, which
474           imposes no additional constraints. However, you can set a  lower  limit
475           by adding, for example,
476    
477             --with-match-limit-recursion=10000
478    
479           to  the  configure  command.  This  value can also be overridden at run
480           time.
481    
482    
483    CREATING CHARACTER TABLES AT BUILD TIME
484    
485           PCRE uses fixed tables for processing characters whose code values  are
486           less  than 256. By default, PCRE is built with a set of tables that are
487           distributed in the file pcre_chartables.c.dist. These  tables  are  for
488           ASCII codes only. If you add
489    
490             --enable-rebuild-chartables
491    
492           to  the  configure  command, the distributed tables are no longer used.
493           Instead, a program called dftables is compiled and  run.  This  outputs
494           the source for new set of tables, created in the default locale of your
495           C runtime system. (This method of replacing the tables does not work if
496           you  are cross compiling, because dftables is run on the local host. If
497           you need to create alternative tables when cross  compiling,  you  will
498           have to do so "by hand".)
499    
500    
501  USING EBCDIC CODE  USING EBCDIC CODE
502    
503         PCRE assumes by default that it will run in an  environment  where  the         PCRE  assumes  by  default that it will run in an environment where the
504         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
505         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by         This  is  the  case for most computer operating systems. PCRE can, how-
506         adding         ever, be compiled to run in an EBCDIC environment by adding
507    
508           --enable-ebcdic           --enable-ebcdic
509    
510         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
511           bles.  You  should  only  use  it if you know that you are in an EBCDIC
512           environment (for example, an IBM mainframe operating system).
513    
514    
515  Last updated: 15 August 2005  SEE ALSO
516  Copyright (c) 1997-2005 University of Cambridge.  
517           pcreapi(3), pcre_config(3).
518    
519    
520    AUTHOR
521    
522           Philip Hazel
523           University Computing Service
524           Cambridge CB2 3QH, England.
525    
526    
527    REVISION
528    
529           Last updated: 11 September 2007
530           Copyright (c) 1997-2007 University of Cambridge.
531  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
532    
533    
# Line 431  PCRE MATCHING ALGORITHMS Line 563  PCRE MATCHING ALGORITHMS
563           <something> <something else> <something further>           <something> <something else> <something further>
564    
565         there are three possible answers. The standard algorithm finds only one         there are three possible answers. The standard algorithm finds only one
566         of them, whereas the DFA algorithm finds all three.         of them, whereas the alternative algorithm finds all three.
567    
568    
569  REGULAR EXPRESSIONS AS TREES  REGULAR EXPRESSIONS AS TREES
# Line 440  REGULAR EXPRESSIONS AS TREES Line 572  REGULAR EXPRESSIONS AS TREES
572         resented  as  a  tree structure. An unlimited repetition in the pattern         resented  as  a  tree structure. An unlimited repetition in the pattern
573         makes the tree of infinite size, but it is still a tree.  Matching  the         makes the tree of infinite size, but it is still a tree.  Matching  the
574         pattern  to a given subject string (from a given starting point) can be         pattern  to a given subject string (from a given starting point) can be
575         thought of as a search of the tree.  There are  two  standard  ways  to         thought of as a search of the tree.  There are two  ways  to  search  a
576         search  a  tree: depth-first and breadth-first, and these correspond to         tree:  depth-first  and  breadth-first, and these correspond to the two
577         the two matching algorithms provided by PCRE.         matching algorithms provided by PCRE.
578    
579    
580  THE STANDARD MATCHING ALGORITHM  THE STANDARD MATCHING ALGORITHM
581    
582         In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
583         sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
584         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
585         single path through the tree, checking that the subject matches what is         single path through the tree, checking that the subject matches what is
586         required. When there is a mismatch, the algorithm  tries  any  alterna-         required. When there is a mismatch, the algorithm  tries  any  alterna-
# Line 472  THE STANDARD MATCHING ALGORITHM Line 604  THE STANDARD MATCHING ALGORITHM
604         This provides support for capturing parentheses and back references.         This provides support for capturing parentheses and back references.
605    
606    
607  THE DFA MATCHING ALGORITHM  THE ALTERNATIVE MATCHING ALGORITHM
608    
609         DFA stands for "deterministic finite automaton", but you do not need to         This algorithm conducts a breadth-first search of  the  tree.  Starting
610         understand the origins of that name. This algorithm conducts a breadth-         from  the  first  matching  point  in the subject, it scans the subject
611         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
612         subject,  it scans the subject string from left to right, once, charac-         this,  it remembers all the paths through the tree that represent valid
613         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",
614         through the tree that represent valid matches.         though  it is not implemented as a traditional finite state machine (it
615           keeps multiple states active simultaneously).
616         The  scan  continues until either the end of the subject is reached, or  
617         there are no more unterminated paths. At this point,  terminated  paths         The scan continues until either the end of the subject is  reached,  or
618         represent  the different matching possibilities (if there are none, the         there  are  no more unterminated paths. At this point, terminated paths
619         match has failed).  Thus, if there is more  than  one  possible  match,         represent the different matching possibilities (if there are none,  the
620           match  has  failed).   Thus,  if there is more than one possible match,
621         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-
622         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
623         match (which is necessarily the shortest) has been found.         match (which is necessarily the shortest) has been found.
624    
625         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 494  THE DFA MATCHING ALGORITHM Line 627  THE DFA MATCHING ALGORITHM
627    
628           cat(er(pillar)?)           cat(er(pillar)?)
629    
630         is matched against the string "the caterpillar catchment",  the  result         is  matched  against the string "the caterpillar catchment", the result
631         will  be the three strings "cat", "cater", and "caterpillar" that start         will be the three strings "cat", "cater", and "caterpillar" that  start
632         at the fourth character of the subject. The algorithm does not automat-         at the fourth character of the subject. The algorithm does not automat-
633         ically move on to find matches that start at later positions.         ically move on to find matches that start at later positions.
634    
635         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
636         supported by the DFA matching algorithm. They are as follows:         supported by the alternative matching algorithm. They are as follows:
637    
638         1. Because the algorithm finds all  possible  matches,  the  greedy  or         1.  Because  the  algorithm  finds  all possible matches, the greedy or
639         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and         ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
640         ungreedy quantifiers are treated in exactly the same way.         ungreedy quantifiers are treated in exactly the same way. However, pos-
641           sessive quantifiers can make a difference when what follows could  also
642           match what is quantified, for example in a pattern like this:
643    
644             ^a++\w!
645    
646           This  pattern matches "aaab!" but not "aaa!", which would be matched by
647           a non-possessive quantifier. Similarly, if an atomic group is  present,
648           it  is matched as if it were a standalone pattern at the current point,
649           and the longest match is then "locked in" for the rest of  the  overall
650           pattern.
651    
652         2. When dealing with multiple paths through the tree simultaneously, it         2. When dealing with multiple paths through the tree simultaneously, it
653         is  not  straightforward  to  keep track of captured substrings for the         is not straightforward to keep track of  captured  substrings  for  the
654         different matching possibilities, and  PCRE's  implementation  of  this         different  matching  possibilities,  and  PCRE's implementation of this
655         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-
656         strings are available.         strings are available.
657    
658         3. Because no substrings are captured, back references within the  pat-         3.  Because no substrings are captured, back references within the pat-
659         tern are not supported, and cause errors if encountered.         tern are not supported, and cause errors if encountered.
660    
661         4.  For  the same reason, conditional expressions that use a backrefer-         4. For the same reason, conditional expressions that use  a  backrefer-
662         ence as the condition are not supported.         ence  as  the  condition or test for a specific group recursion are not
663           supported.
664    
665         5. Callouts are supported, but the value of the  capture_top  field  is         5. Because many paths through the tree may be  active,  the  \K  escape
666           sequence, which resets the start of the match when encountered (but may
667           be on some paths and not on others), is not  supported.  It  causes  an
668           error if encountered.
669    
670           6.  Callouts  are  supported, but the value of the capture_top field is
671         always 1, and the value of the capture_last field is always -1.         always 1, and the value of the capture_last field is always -1.
672    
673         6.  The \C escape sequence, which (in the standard algorithm) matches a         7. The \C escape sequence, which (in the standard algorithm) matches  a
674         single byte, even in UTF-8 mode, is not supported because the DFA algo-         single  byte, even in UTF-8 mode, is not supported because the alterna-
675         rithm moves through the subject string one character at a time, for all         tive algorithm moves through the subject  string  one  character  at  a
676         active paths through the tree.         time, for all active paths through the tree.
677    
678           8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
679           ported.
680    
681    
682  ADVANTAGES OF THE DFA ALGORITHM  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
683    
684         Using the DFA matching algorithm provides the following advantages:         Using the alternative matching algorithm provides the following  advan-
685           tages:
686    
687         1. All possible matches (at a single point in the subject) are automat-         1. All possible matches (at a single point in the subject) are automat-
688         ically  found,  and  in particular, the longest match is found. To find         ically found, and in particular, the longest match is  found.  To  find
689         more than one match using the standard algorithm, you have to do kludgy         more than one match using the standard algorithm, you have to do kludgy
690         things with callouts.         things with callouts.
691    
692         2.  There is much better support for partial matching. The restrictions         2. There is much better support for partial matching. The  restrictions
693         on the content of the pattern that apply when using the standard  algo-         on  the content of the pattern that apply when using the standard algo-
694         rithm  for partial matching do not apply to the DFA algorithm. For non-         rithm for partial matching do not apply to the  alternative  algorithm.
695         anchored patterns, the starting position of a partial match  is  avail-         For  non-anchored patterns, the starting position of a partial match is
696         able.         available.
697    
698         3.  Because  the  DFA algorithm scans the subject string just once, and         3. Because the alternative algorithm  scans  the  subject  string  just
699         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
700         strings  to  the matching function in several pieces, checking for par-         subject strings to the matching function in  several  pieces,  checking
701         tial matching each time.         for partial matching each time.
702    
703    
704  DISADVANTAGES OF THE DFA ALGORITHM  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
705    
706         The DFA algorithm suffers from a number of disadvantages:         The alternative algorithm suffers from a number of disadvantages:
707    
708         1. It is substantially slower than  the  standard  algorithm.  This  is         1.  It  is  substantially  slower  than the standard algorithm. This is
709         partly  because  it has to search for all possible matches, but is also         partly because it has to search for all possible matches, but  is  also
710         because it is less susceptible to optimization.         because it is less susceptible to optimization.
711    
712         2. Capturing parentheses and back references are not supported.         2. Capturing parentheses and back references are not supported.
713    
714         3. The "atomic group" feature of PCRE regular expressions is supported,         3. Although atomic groups are supported, their use does not provide the
715         but  does not provide the advantage that it does for the standard algo-         performance advantage that it does for the standard algorithm.
        rithm.  
716    
717  Last updated: 28 February 2005  
718  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
719    
720           Philip Hazel
721           University Computing Service
722           Cambridge CB2 3QH, England.
723    
724    
725    REVISION
726    
727           Last updated: 08 August 2007
728           Copyright (c) 1997-2007 University of Cambridge.
729  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
730    
731    
# Line 616  PCRE NATIVE API Line 778  PCRE NATIVE API
778         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
779              const char *name);              const char *name);
780    
781           int pcre_get_stringtable_entries(const pcre *code,
782                const char *name, char **first, char **last);
783    
784         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
785              int stringcount, int stringnumber,              int stringcount, int stringnumber,
786              const char **stringptr);              const char **stringptr);
# Line 654  PCRE NATIVE API Line 819  PCRE NATIVE API
819  PCRE API OVERVIEW  PCRE API OVERVIEW
820    
821         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
822         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
823         expression  API.  These  are  described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
824         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
825         distributed with PCRE. It is documented in the pcrecpp page.         distributed with PCRE. It is documented in the pcrecpp page.
# Line 676  PCRE API OVERVIEW Line 841  PCRE API OVERVIEW
841    
842         A second matching function, pcre_dfa_exec(), which is not Perl-compati-         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
843         ble,  is  also provided. This uses a different algorithm for the match-         ble,  is  also provided. This uses a different algorithm for the match-
844         ing. This allows it to find all possible matches (at a given  point  in         ing. The alternative algorithm finds all possible matches (at  a  given
845         the  subject),  not  just  one. However, this algorithm does not return         point  in  the subject), and scans the subject just once. However, this
846         captured substrings. A description of the two matching  algorithms  and         algorithm does not return captured substrings. A description of the two
847         their  advantages  and disadvantages is given in the pcrematching docu-         matching  algorithms and their advantages and disadvantages is given in
848         mentation.         the pcrematching documentation.
849    
850         In addition to the main compiling and  matching  functions,  there  are         In addition to the main compiling and  matching  functions,  there  are
851         convenience functions for extracting captured substrings from a subject         convenience functions for extracting captured substrings from a subject
# Line 692  PCRE API OVERVIEW Line 857  PCRE API OVERVIEW
857           pcre_get_named_substring()           pcre_get_named_substring()
858           pcre_get_substring_list()           pcre_get_substring_list()
859           pcre_get_stringnumber()           pcre_get_stringnumber()
860             pcre_get_stringtable_entries()
861    
862         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
863         to free the memory used for extracted strings.         to free the memory used for extracted strings.
# Line 723  PCRE API OVERVIEW Line 889  PCRE API OVERVIEW
889         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
890         are used only when PCRE is compiled to use  the  heap  for  remembering         are used only when PCRE is compiled to use  the  heap  for  remembering
891         data, instead of recursive function calls, when running the pcre_exec()         data, instead of recursive function calls, when running the pcre_exec()
892         function. This is a non-standard way of building PCRE, for use in envi-         function. See the pcrebuild documentation for  details  of  how  to  do
893         ronments that have limited stacks. Because of the greater use of memory         this.  It  is  a non-standard way of building PCRE, for use in environ-
894         management, it runs more slowly.  Separate functions  are  provided  so         ments that have limited stacks. Because of the greater  use  of  memory
895         that  special-purpose  external  code  can  be used for this case. When         management,  it  runs  more  slowly. Separate functions are provided so
896         used, these functions are always called in a  stack-like  manner  (last         that special-purpose external code can be  used  for  this  case.  When
897         obtained,  first freed), and always for memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
898           obtained, first freed), and always for memory blocks of the same  size.
899           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
900           mentation.
901    
902         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
903         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 736  PCRE API OVERVIEW Line 905  PCRE API OVERVIEW
905         pcrecallout documentation.         pcrecallout documentation.
906    
907    
908    NEWLINES
909    
910           PCRE  supports five different conventions for indicating line breaks in
911           strings: a single CR (carriage return) character, a  single  LF  (line-
912           feed) character, the two-character sequence CRLF, any of the three pre-
913           ceding, or any Unicode newline sequence. The Unicode newline  sequences
914           are  the  three just mentioned, plus the single characters VT (vertical
915           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
916           separator, U+2028), and PS (paragraph separator, U+2029).
917    
918           Each  of  the first three conventions is used by at least one operating
919           system as its standard newline sequence. When PCRE is built, a  default
920           can  be  specified.  The default default is LF, which is the Unix stan-
921           dard. When PCRE is run, the default can be overridden,  either  when  a
922           pattern is compiled, or when it is matched.
923    
924           At compile time, the newline convention can be specified by the options
925           argument of pcre_compile(), or it can be specified by special  text  at
926           the start of the pattern itself; this overrides any other settings. See
927           the pcrepattern page for details of the special character sequences.
928    
929           In the PCRE documentation the word "newline" is used to mean "the char-
930           acter  or pair of characters that indicate a line break". The choice of
931           newline convention affects the handling of  the  dot,  circumflex,  and
932           dollar metacharacters, the handling of #-comments in /x mode, and, when
933           CRLF is a recognized line ending sequence, the match position  advance-
934           ment for a non-anchored pattern. There is more detail about this in the
935           section on pcre_exec() options below.
936    
937           The choice of newline convention does not affect the interpretation  of
938           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
939           which is controlled in a similar way, but by separate options.
940    
941    
942  MULTITHREADING  MULTITHREADING
943    
944         The  PCRE  functions  can be used in multi-threading applications, with         The PCRE functions can be used in  multi-threading  applications,  with
945         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
946         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
947         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
948    
949         The  compiled form of a regular expression is not altered during match-         The compiled form of a regular expression is not altered during  match-
950         ing, so the same compiled pattern can safely be used by several threads         ing, so the same compiled pattern can safely be used by several threads
951         at once.         at once.
952    
# Line 751  MULTITHREADING Line 954  MULTITHREADING
954  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
955    
956         The compiled form of a regular expression can be saved and re-used at a         The compiled form of a regular expression can be saved and re-used at a
957         later time, possibly by a different program, and even on a  host  other         later  time,  possibly by a different program, and even on a host other
958         than  the  one  on  which  it  was  compiled.  Details are given in the         than the one on which  it  was  compiled.  Details  are  given  in  the
959         pcreprecompile documentation.         pcreprecompile  documentation.  However, compiling a regular expression
960           with one version of PCRE for use with a different version is not  guar-
961           anteed to work and may cause crashes.
962    
963    
964  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
965    
966         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
967    
968         The function pcre_config() makes it possible for a PCRE client to  dis-         The  function pcre_config() makes it possible for a PCRE client to dis-
969         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
970         The pcrebuild documentation has more details about these optional  fea-         The  pcrebuild documentation has more details about these optional fea-
971         tures.         tures.
972    
973         The  first  argument  for pcre_config() is an integer, specifying which         The first argument for pcre_config() is an  integer,  specifying  which
974         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
975         into  which  the  information  is  placed. The following information is         into which the information is  placed.  The  following  information  is
976         available:         available:
977    
978           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
979    
980         The output is an integer that is set to one if UTF-8 support is  avail-         The  output is an integer that is set to one if UTF-8 support is avail-
981         able; otherwise it is set to zero.         able; otherwise it is set to zero.
982    
983           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
984    
985         The  output  is  an  integer  that is set to one if support for Unicode         The output is an integer that is set to  one  if  support  for  Unicode
986         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
987    
988           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
989    
990         The output is an integer that is set to the value of the code  that  is         The  output  is  an integer whose value specifies the default character
991         used  for the newline character. It is either linefeed (10) or carriage         sequence that is recognized as meaning "newline". The four values  that
992         return (13), and should normally be the  standard  character  for  your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
993         operating system.         and -1 for ANY. The default should normally be  the  standard  sequence
994           for your operating system.
995    
996             PCRE_CONFIG_BSR
997    
998           The output is an integer whose value indicates what character sequences
999           the \R escape sequence matches by default. A value of 0 means  that  \R
1000           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1001           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1002           tern is compiled or matched.
1003    
1004           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
1005    
# Line 808  CHECKING BUILD-TIME OPTIONS Line 1022  CHECKING BUILD-TIME OPTIONS
1022         internal  matching  function  calls in a pcre_exec() execution. Further         internal  matching  function  calls in a pcre_exec() execution. Further
1023         details are given with pcre_exec() below.         details are given with pcre_exec() below.
1024    
1025             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1026    
1027           The output is an integer that gives the default limit for the depth  of
1028           recursion  when calling the internal matching function in a pcre_exec()
1029           execution. Further details are given with pcre_exec() below.
1030    
1031           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
1032    
1033         The output is an integer that is set to one if internal recursion  when         The output is an integer that is set to one if internal recursion  when
# Line 840  COMPILING A PATTERN Line 1060  COMPILING A PATTERN
1060         obtained  via  pcre_malloc is returned. This contains the compiled code         obtained  via  pcre_malloc is returned. This contains the compiled code
1061         and related data. The pcre type is defined for the returned block; this         and related data. The pcre type is defined for the returned block; this
1062         is a typedef for a structure whose contents are not externally defined.         is a typedef for a structure whose contents are not externally defined.
1063         It is up to the caller  to  free  the  memory  when  it  is  no  longer         It is up to the caller to free the memory (via pcre_free) when it is no
1064         required.         longer required.
1065    
1066         Although  the compiled code of a PCRE regex is relocatable, that is, it         Although  the compiled code of a PCRE regex is relocatable, that is, it
1067         does not depend on memory location, the complete pcre data block is not         does not depend on memory location, the complete pcre data block is not
1068         fully  relocatable, because it may contain a copy of the tableptr argu-         fully  relocatable, because it may contain a copy of the tableptr argu-
1069         ment, which is an address (see below).         ment, which is an address (see below).
1070    
1071         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
1072         tion.  It  should  be  zero  if  no options are required. The available         pilation.  It  should be zero if no options are required. The available
1073         options are described below. Some of them, in  particular,  those  that         options are described below. Some of them, in  particular,  those  that
1074         are  compatible  with  Perl,  can also be set and unset from within the         are  compatible  with  Perl,  can also be set and unset from within the
1075         pattern (see the detailed description  in  the  pcrepattern  documenta-         pattern (see the detailed description  in  the  pcrepattern  documenta-
1076         tion).  For  these options, the contents of the options argument speci-         tion).  For  these options, the contents of the options argument speci-
1077         fies their initial settings at the start of compilation and  execution.         fies their initial settings at the start of compilation and  execution.
1078         The  PCRE_ANCHORED option can be set at the time of matching as well as         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1079         at compile time.         of matching as well as at compile time.
1080    
1081         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1082         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1083         sets the variable pointed to by errptr to point to a textual error mes-         sets the variable pointed to by errptr to point to a textual error mes-
1084         sage.  The  offset from the start of the pattern to the character where         sage. This is a static string that is part of the library. You must not
1085         the error was discovered is  placed  in  the  variable  pointed  to  by         try to free it. The offset from the start of the pattern to the charac-
1086         erroffset,  which  must  not  be  NULL. If it is, an immediate error is         ter where the error was discovered is placed in the variable pointed to
1087           by erroffset, which must not be NULL. If it is, an immediate  error  is
1088         given.         given.
1089    
1090         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1091         codeptr  argument is not NULL, a non-zero error code number is returned         codeptr argument is not NULL, a non-zero error code number is  returned
1092         via this argument in the event of an error. This is in addition to  the         via  this argument in the event of an error. This is in addition to the
1093         textual error message. Error codes and messages are listed below.         textual error message. Error codes and messages are listed below.
1094    
1095         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1096         character tables that are  built  when  PCRE  is  compiled,  using  the         character  tables  that  are  built  when  PCRE  is compiled, using the
1097         default  C  locale.  Otherwise, tableptr must be an address that is the         default C locale. Otherwise, tableptr must be an address  that  is  the
1098         result of a call to pcre_maketables(). This value is  stored  with  the         result  of  a  call to pcre_maketables(). This value is stored with the
1099         compiled  pattern,  and used again by pcre_exec(), unless another table         compiled pattern, and used again by pcre_exec(), unless  another  table
1100         pointer is passed to it. For more discussion, see the section on locale         pointer is passed to it. For more discussion, see the section on locale
1101         support below.         support below.
1102    
1103         This  code  fragment  shows a typical straightforward call to pcre_com-         This code fragment shows a typical straightforward  call  to  pcre_com-
1104         pile():         pile():
1105    
1106           pcre *re;           pcre *re;
# Line 892  COMPILING A PATTERN Line 1113  COMPILING A PATTERN
1113             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
1114             NULL);            /* use default character tables */             NULL);            /* use default character tables */
1115    
1116         The following names for option bits are defined in  the  pcre.h  header         The  following  names  for option bits are defined in the pcre.h header
1117         file:         file:
1118    
1119           PCRE_ANCHORED           PCRE_ANCHORED
1120    
1121         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
1122         is constrained to match only at the first matching point in the  string         is  constrained to match only at the first matching point in the string
1123         that  is being searched (the "subject string"). This effect can also be         that is being searched (the "subject string"). This effect can also  be
1124         achieved by appropriate constructs in the pattern itself, which is  the         achieved  by appropriate constructs in the pattern itself, which is the
1125         only way to do it in Perl.         only way to do it in Perl.
1126    
1127           PCRE_AUTO_CALLOUT           PCRE_AUTO_CALLOUT
1128    
1129         If this bit is set, pcre_compile() automatically inserts callout items,         If this bit is set, pcre_compile() automatically inserts callout items,
1130         all with number 255, before each pattern item. For  discussion  of  the         all  with  number  255, before each pattern item. For discussion of the
1131         callout facility, see the pcrecallout documentation.         callout facility, see the pcrecallout documentation.
1132    
1133             PCRE_BSR_ANYCRLF
1134             PCRE_BSR_UNICODE
1135    
1136           These options (which are mutually exclusive) control what the \R escape
1137           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1138           or to match any Unicode newline sequence. The default is specified when
1139           PCRE is built. It can be overridden from within the pattern, or by set-
1140           ting an option when a compiled pattern is matched.
1141    
1142           PCRE_CASELESS           PCRE_CASELESS
1143    
1144         If  this  bit is set, letters in the pattern match both upper and lower         If this bit is set, letters in the pattern match both upper  and  lower
1145         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1146         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1147         always understands the concept of case for characters whose values  are         always  understands the concept of case for characters whose values are
1148         less  than 128, so caseless matching is always possible. For characters         less than 128, so caseless matching is always possible. For  characters
1149         with higher values, the concept of case is supported if  PCRE  is  com-         with  higher  values,  the concept of case is supported if PCRE is com-
1150         piled  with Unicode property support, but not otherwise. If you want to         piled with Unicode property support, but not otherwise. If you want  to
1151         use caseless matching for characters 128 and  above,  you  must  ensure         use  caseless  matching  for  characters 128 and above, you must ensure
1152         that  PCRE  is  compiled  with Unicode property support as well as with         that PCRE is compiled with Unicode property support  as  well  as  with
1153         UTF-8 support.         UTF-8 support.
1154    
1155           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1156    
1157         If this bit is set, a dollar metacharacter in the pattern matches  only         If  this bit is set, a dollar metacharacter in the pattern matches only
1158         at  the  end  of the subject string. Without this option, a dollar also         at the end of the subject string. Without this option,  a  dollar  also
1159         matches immediately before the final character if it is a newline  (but         matches  immediately before a newline at the end of the string (but not
1160         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1161         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1162         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1163    
1164           PCRE_DOTALL           PCRE_DOTALL
1165    
1166         If this bit is set, a dot metacharater in the pattern matches all char-         If this bit is set, a dot metacharater in the pattern matches all char-
1167         acters, including newlines. Without it,  newlines  are  excluded.  This         acters,  including  those that indicate newline. Without it, a dot does
1168         option  is equivalent to Perl's /s option, and it can be changed within         not match when the current position is at a  newline.  This  option  is
1169         a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]         equivalent  to Perl's /s option, and it can be changed within a pattern
1170         always  matches a newline character, independent of the setting of this         by a (?s) option setting. A negative class such as [^a] always  matches
1171         option.         newline characters, independent of the setting of this option.
1172    
1173             PCRE_DUPNAMES
1174    
1175           If  this  bit is set, names used to identify capturing subpatterns need
1176           not be unique. This can be helpful for certain types of pattern when it
1177           is  known  that  only  one instance of the named subpattern can ever be
1178           matched. There are more details of named subpatterns  below;  see  also
1179           the pcrepattern documentation.
1180    
1181           PCRE_EXTENDED           PCRE_EXTENDED
1182    
1183         If this bit is set, whitespace  data  characters  in  the  pattern  are         If  this  bit  is  set,  whitespace  data characters in the pattern are
1184         totally ignored except when escaped or inside a character class. White-         totally ignored except when escaped or inside a character class. White-
1185         space does not include the VT character (code 11). In addition, charac-         space does not include the VT character (code 11). In addition, charac-
1186         ters between an unescaped # outside a character class and the next new-         ters between an unescaped # outside a character class and the next new-
1187         line character, inclusive, are also  ignored.  This  is  equivalent  to         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1188         Perl's  /x  option,  and  it  can be changed within a pattern by a (?x)         option, and it can be changed within a pattern by a  (?x)  option  set-
1189         option setting.         ting.
1190    
1191         This option makes it possible to include  comments  inside  complicated         This  option  makes  it possible to include comments inside complicated
1192         patterns.   Note,  however,  that this applies only to data characters.         patterns.  Note, however, that this applies only  to  data  characters.
1193         Whitespace  characters  may  never  appear  within  special   character         Whitespace   characters  may  never  appear  within  special  character
1194         sequences  in  a  pattern,  for  example  within the sequence (?( which         sequences in a pattern, for  example  within  the  sequence  (?(  which
1195         introduces a conditional subpattern.         introduces a conditional subpattern.
1196    
1197           PCRE_EXTRA           PCRE_EXTRA
1198    
1199         This option was invented in order to turn on  additional  functionality         This  option  was invented in order to turn on additional functionality
1200         of  PCRE  that  is  incompatible with Perl, but it is currently of very         of PCRE that is incompatible with Perl, but it  is  currently  of  very
1201         little use. When set, any backslash in a pattern that is followed by  a         little  use. When set, any backslash in a pattern that is followed by a
1202         letter  that  has  no  special  meaning causes an error, thus reserving         letter that has no special meaning  causes  an  error,  thus  reserving
1203         these combinations for future expansion. By  default,  as  in  Perl,  a         these  combinations  for  future  expansion.  By default, as in Perl, a
1204         backslash  followed by a letter with no special meaning is treated as a         backslash followed by a letter with no special meaning is treated as  a
1205         literal. There are at present no  other  features  controlled  by  this         literal.  (Perl can, however, be persuaded to give a warning for this.)
1206         option. It can also be set by a (?X) option setting within a pattern.         There are at present no other features controlled by  this  option.  It
1207           can also be set by a (?X) option setting within a pattern.
1208    
1209           PCRE_FIRSTLINE           PCRE_FIRSTLINE
1210    
1211         If  this  option  is  set,  an  unanchored pattern is required to match         If  this  option  is  set,  an  unanchored pattern is required to match
1212         before or at the first newline character in the subject string,  though         before or at the first  newline  in  the  subject  string,  though  the
1213         the matched text may continue over the newline.         matched text may continue over the newline.
1214    
1215           PCRE_MULTILINE           PCRE_MULTILINE
1216    
# Line 983  COMPILING A PATTERN Line 1222  COMPILING A PATTERN
1222         is set). This is the same as Perl.         is set). This is the same as Perl.
1223    
1224         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"         When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1225         constructs  match  immediately following or immediately before any new-         constructs  match  immediately following or immediately before internal
1226         line in the subject string, respectively, as well as at the very  start         newlines in the subject string, respectively, as well as  at  the  very
1227         and  end. This is equivalent to Perl's /m option, and it can be changed         start  and  end.  This is equivalent to Perl's /m option, and it can be
1228         within a pattern by a (?m) option setting. If there are no "\n" charac-         changed within a pattern by a (?m) option setting. If there are no new-
1229         ters  in  a  subject  string, or no occurrences of ^ or $ in a pattern,         lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1230         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1231    
1232             PCRE_NEWLINE_CR
1233             PCRE_NEWLINE_LF
1234             PCRE_NEWLINE_CRLF
1235             PCRE_NEWLINE_ANYCRLF
1236             PCRE_NEWLINE_ANY
1237    
1238           These options override the default newline definition that  was  chosen
1239           when  PCRE  was built. Setting the first or the second specifies that a
1240           newline is indicated by a single character (CR  or  LF,  respectively).
1241           Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1242           two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1243           that any of the three preceding sequences should be recognized. Setting
1244           PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1245           recognized. The Unicode newline sequences are the three just mentioned,
1246           plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1247           U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1248           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1249           UTF-8 mode.
1250    
1251           The  newline  setting  in  the  options  word  uses three bits that are
1252           treated as a number, giving eight possibilities. Currently only six are
1253           used  (default  plus the five values above). This means that if you set
1254           more than one newline option, the combination may or may not be  sensi-
1255           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1256           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1257           cause an error.
1258    
1259           The  only time that a line break is specially recognized when compiling
1260           a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1261           character  class  is  encountered.  This indicates a comment that lasts
1262           until after the next line break sequence. In other circumstances,  line
1263           break   sequences   are   treated  as  literal  data,  except  that  in
1264           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1265           and are therefore ignored.
1266    
1267           The newline option that is set at compile time becomes the default that
1268           is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
1269    
1270           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1271    
1272         If this option is set, it disables the use of numbered capturing paren-         If this option is set, it disables the use of numbered capturing paren-
1273         theses  in the pattern. Any opening parenthesis that is not followed by         theses in the pattern. Any opening parenthesis that is not followed  by
1274         ? behaves as if it were followed by ?: but named parentheses can  still         ?  behaves as if it were followed by ?: but named parentheses can still
1275         be  used  for  capturing  (and  they acquire numbers in the usual way).         be used for capturing (and they acquire  numbers  in  the  usual  way).
1276         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1277    
1278           PCRE_UNGREEDY           PCRE_UNGREEDY
1279    
1280         This option inverts the "greediness" of the quantifiers  so  that  they         This  option  inverts  the "greediness" of the quantifiers so that they
1281         are  not greedy by default, but become greedy if followed by "?". It is         are not greedy by default, but become greedy if followed by "?". It  is
1282         not compatible with Perl. It can also be set by a (?U)  option  setting         not  compatible  with Perl. It can also be set by a (?U) option setting
1283         within the pattern.         within the pattern.
1284    
1285           PCRE_UTF8           PCRE_UTF8
1286    
1287         This  option  causes PCRE to regard both the pattern and the subject as         This option causes PCRE to regard both the pattern and the  subject  as
1288         strings of UTF-8 characters instead of single-byte  character  strings.         strings  of  UTF-8 characters instead of single-byte character strings.
1289         However,  it is available only when PCRE is built to include UTF-8 sup-         However, it is available only when PCRE is built to include UTF-8  sup-
1290         port. If not, the use of this option provokes an error. Details of  how         port.  If not, the use of this option provokes an error. Details of how
1291         this  option  changes the behaviour of PCRE are given in the section on         this option changes the behaviour of PCRE are given in the  section  on
1292         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1293    
1294           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1295    
1296         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is         When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1297         automatically  checked. If an invalid UTF-8 sequence of bytes is found,         automatically checked. There is a  discussion  about  the  validity  of
1298         pcre_compile() returns an error. If you already know that your  pattern         UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1299         is  valid, and you want to skip this check for performance reasons, you         bytes is found, pcre_compile() returns an error. If  you  already  know
1300         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of         that your pattern is valid, and you want to skip this check for perfor-
1301         passing an invalid UTF-8 string as a pattern is undefined. It may cause         mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1302         your program to crash.  Note that this option can  also  be  passed  to         set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1303         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-         undefined. It may cause your program to crash. Note  that  this  option
1304         ing of subject strings.         can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1305           UTF-8 validity checking of subject strings.
1306    
1307    
1308  COMPILATION ERROR CODES  COMPILATION ERROR CODES
1309    
1310         The following table lists the error  codes  than  may  be  returned  by         The following table lists the error  codes  than  may  be  returned  by
1311         pcre_compile2(),  along with the error messages that may be returned by         pcre_compile2(),  along with the error messages that may be returned by
1312         both compiling functions.         both compiling functions. As PCRE has developed, some error codes  have
1313           fallen out of use. To avoid confusion, they have not been re-used.
1314    
1315            0  no error            0  no error
1316            1  \ at end of pattern            1  \ at end of pattern
# Line 1043  COMPILATION ERROR CODES Line 1322  COMPILATION ERROR CODES
1322            7  invalid escape sequence in character class            7  invalid escape sequence in character class
1323            8  range out of order in character class            8  range out of order in character class
1324            9  nothing to repeat            9  nothing to repeat
1325           10  operand of unlimited repeat could match the empty string           10  [this code is not in use]
1326           11  internal error: unexpected repeat           11  internal error: unexpected repeat
1327           12  unrecognized character after (?           12  unrecognized character after (?
1328           13  POSIX named classes are supported only within a class           13  POSIX named classes are supported only within a class
# Line 1052  COMPILATION ERROR CODES Line 1331  COMPILATION ERROR CODES
1331           16  erroffset passed as NULL           16  erroffset passed as NULL
1332           17  unknown option bit(s) set           17  unknown option bit(s) set
1333           18  missing ) after comment           18  missing ) after comment
1334           19  parentheses nested too deeply           19  [this code is not in use]
1335           20  regular expression too large           20  regular expression too large
1336           21  failed to get memory           21  failed to get memory
1337           22  unmatched parentheses           22  unmatched parentheses
1338           23  internal error: code overflow           23  internal error: code overflow
1339           24  unrecognized character after (?<           24  unrecognized character after (?<
1340           25  lookbehind assertion is not fixed length           25  lookbehind assertion is not fixed length
1341           26  malformed number after (?(           26  malformed number or name after (?(
1342           27  conditional group contains more than two branches           27  conditional group contains more than two branches
1343           28  assertion expected after (?(           28  assertion expected after (?(
1344           29  (?R or (?digits must be followed by )           29  (?R or (?[+-]digits must be followed by )
1345           30  unknown POSIX class name           30  unknown POSIX class name
1346           31  POSIX collating elements are not supported           31  POSIX collating elements are not supported
1347           32  this version of PCRE is not compiled with PCRE_UTF8 support           32  this version of PCRE is not compiled with PCRE_UTF8 support
1348           33  spare error           33  [this code is not in use]
1349           34  character value in \x{...} sequence is too large           34  character value in \x{...} sequence is too large
1350           35  invalid condition (?(0)           35  invalid condition (?(0)
1351           36  \C not allowed in lookbehind assertion           36  \C not allowed in lookbehind assertion
# Line 1075  COMPILATION ERROR CODES Line 1354  COMPILATION ERROR CODES
1354           39  closing ) for (?C expected           39  closing ) for (?C expected
1355           40  recursive call could loop indefinitely           40  recursive call could loop indefinitely
1356           41  unrecognized character after (?P           41  unrecognized character after (?P
1357           42  syntax error after (?P           42  syntax error in subpattern name (missing terminator)
1358           43  two named groups have the same name           43  two named subpatterns have the same name
1359           44  invalid UTF-8 string           44  invalid UTF-8 string
1360           45  support for \P, \p, and \X has not been compiled           45  support for \P, \p, and \X has not been compiled
1361           46  malformed \P or \p sequence           46  malformed \P or \p sequence
1362           47  unknown property name after \P or \p           47  unknown property name after \P or \p
1363             48  subpattern name is too long (maximum 32 characters)
1364             49  too many named subpatterns (maximum 10,000)
1365             50  [this code is not in use]
1366             51  octal value is greater than \377 (not in UTF-8 mode)
1367             52  internal error: overran compiling workspace
1368             53   internal  error:  previously-checked  referenced  subpattern not
1369           found
1370             54  DEFINE group contains more than one branch
1371             55  repeating a DEFINE group is not allowed
1372             56  inconsistent NEWLINE options
1373             57  \g is not followed by a braced name or an optionally braced
1374                   non-zero number
1375             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1376    
1377    
1378  STUDYING A PATTERN  STUDYING A PATTERN
# Line 1111  STUDYING A PATTERN Line 1403  STUDYING A PATTERN
1403    
1404         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.
1405         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
1406         points  to  is set to NULL. Otherwise it points to a textual error mes-         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1407         sage. You should therefore test the error pointer for NULL after  call-         error message. This is a static string that is part of the library. You
1408         ing pcre_study(), to be sure that it has run successfully.         must  not  try  to  free it. You should test the error pointer for NULL
1409           after calling pcre_study(), to be sure that it has run successfully.
1410    
1411         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1412    
# Line 1124  STUDYING A PATTERN Line 1417  STUDYING A PATTERN
1417             &error);        /* set to NULL or points to a message */             &error);        /* set to NULL or points to a message */
1418    
1419         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1420         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-
1421         ble starting bytes is created.         ble starting bytes is created.
1422    
1423    
1424  LOCALE SUPPORT  LOCALE SUPPORT
1425    
1426         PCRE  handles  caseless matching, and determines whether characters are         PCRE handles caseless matching, and determines whether  characters  are
1427         letters digits, or whatever, by reference to a set of  tables,  indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1428         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
1429         characters with codes less than 128. Higher-valued  codes  never  match         characters  with  codes  less than 128. Higher-valued codes never match
1430         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
1431         with Unicode character property support.         with  Unicode  character property support. The use of locales with Uni-
1432           code is discouraged. If you are handling characters with codes  greater
1433         An internal set of tables is created in the default C locale when  PCRE         than  128, you should either use UTF-8 and Unicode, or use locales, but
1434         is  built.  This  is  used when the final argument of pcre_compile() is         not try to mix the two.
1435         NULL, and is sufficient for many applications. An  alternative  set  of  
1436         tables  can,  however, be supplied. These may be created in a different         PCRE contains an internal set of tables that are used  when  the  final
1437         locale from the default. As more and more applications change to  using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1438         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1439           acters. However, when PCRE is built, it is possible to cause the inter-
1440         External  tables  are  built by calling the pcre_maketables() function,         nal tables to be rebuilt in the default "C" locale of the local system,
1441         which has no arguments, in the relevant locale. The result can then  be         which may cause them to be different.
1442         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For  
1443         example, to build and use tables that are appropriate  for  the  French         The  internal tables can always be overridden by tables supplied by the
1444         locale  (where  accented  characters  with  values greater than 128 are         application that calls PCRE. These may be created in a different locale
1445           from  the  default.  As more and more applications change to using Uni-
1446           code, the need for this locale support is expected to die away.
1447    
1448           External tables are built by calling  the  pcre_maketables()  function,
1449           which  has no arguments, in the relevant locale. The result can then be
1450           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1451           example,  to  build  and use tables that are appropriate for the French
1452           locale (where accented characters with  values  greater  than  128  are
1453         treated as letters), the following code could be used:         treated as letters), the following code could be used:
1454    
1455           setlocale(LC_CTYPE, "fr_FR");           setlocale(LC_CTYPE, "fr_FR");
1456           tables = pcre_maketables();           tables = pcre_maketables();
1457           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1458    
1459           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1460           if you are using Windows, the name for the French locale is "french".
1461    
1462         When pcre_maketables() runs, the tables are built  in  memory  that  is         When pcre_maketables() runs, the tables are built  in  memory  that  is
1463         obtained  via  pcre_malloc. It is the caller's responsibility to ensure         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1464         that the memory containing the tables remains available for as long  as         that the memory containing the tables remains available for as long  as
# Line 1200  INFORMATION ABOUT A PATTERN Line 1504  INFORMATION ABOUT A PATTERN
1504         pattern:         pattern:
1505    
1506           int rc;           int rc;
1507           unsigned long int length;           size_t length;
1508           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1509             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1510             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
# Line 1232  INFORMATION ABOUT A PATTERN Line 1536  INFORMATION ABOUT A PATTERN
1536           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1537    
1538         Return  information  about  the first byte of any matched string, for a         Return  information  about  the first byte of any matched string, for a
1539         non-anchored   pattern.   (This    option    used    to    be    called         non-anchored pattern. The fourth argument should point to an int  vari-
1540         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1541         compatibility.)         is still recognized for backwards compatibility.)
1542    
1543         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
1544         (cat|cow|coyote),  it  is  returned in the integer pointed to by where.         (cat|cow|coyote), its value is returned. Otherwise, if either
        Otherwise, if either  
1545    
1546         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1547         branch starts with "^", or         branch starts with "^", or
1548    
1549         (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
1550         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1551    
1552         -1 is returned, indicating that the pattern matches only at  the  start         -1  is  returned, indicating that the pattern matches only at the start
1553         of  a  subject string or after any newline within the string. Otherwise         of a subject string or after any newline within the  string.  Otherwise
1554         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1555    
1556           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1557    
1558         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
1559         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
1560         matching string, a pointer to the table is returned. Otherwise NULL  is         matching  string, a pointer to the table is returned. Otherwise NULL is
1561         returned.  The fourth argument should point to an unsigned char * vari-         returned. The fourth argument should point to an unsigned char *  vari-
1562         able.         able.
1563    
1564             PCRE_INFO_HASCRORLF
1565    
1566           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1567           characters, otherwise 0. The fourth argument should  point  to  an  int
1568           variable.  An explicit match is either a literal CR or LF character, or
1569           \r or \n.
1570    
1571             PCRE_INFO_JCHANGED
1572    
1573           Return 1 if the (?J) option setting is used in the  pattern,  otherwise
1574           0. The fourth argument should point to an int variable. The (?J) inter-
1575           nal option setting changes the local PCRE_DUPNAMES option.
1576    
1577           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1578    
1579         Return the value of the rightmost literal byte that must exist  in  any         Return the value of the rightmost literal byte that must exist  in  any
# Line 1274  INFORMATION ABOUT A PATTERN Line 1590  INFORMATION ABOUT A PATTERN
1590    
1591         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1592         ses.  The names are just an additional way of identifying the parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1593         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1594         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring()  are  provided  for extracting captured sub-
1595         captured substring by name. It is also possible  to  extract  the  data         strings by name. It is also possible to extract the data  directly,  by
1596         directly,  by  first converting the name to a number in order to access         first  converting  the  name to a number in order to access the correct
1597         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1598         below).  To  do the conversion, you need to use the name-to-number map,         the  conversion,  you  need  to  use  the  name-to-number map, which is
1599         which is described by these three values.         described by these three values.
1600    
1601         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1602         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 1290  INFORMATION ABOUT A PATTERN Line 1606  INFORMATION ABOUT A PATTERN
1606         first two bytes of each entry are the number of the capturing parenthe-         first two bytes of each entry are the number of the capturing parenthe-
1607         sis, most significant byte first. The rest of the entry is  the  corre-         sis, most significant byte first. The rest of the entry is  the  corre-
1608         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1609         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1610         set, so white space - including newlines - is ignored):         theses  numbers.  For  example,  consider the following pattern (assume
1611           PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1612           ignored):
1613    
1614           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1615           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1616    
1617         There  are  four  named subpatterns, so the table has four entries, and         There  are  four  named subpatterns, so the table has four entries, and
1618         each entry in the table is eight bytes long. The table is  as  follows,         each entry in the table is eight bytes long. The table is  as  follows,
# Line 1307  INFORMATION ABOUT A PATTERN Line 1625  INFORMATION ABOUT A PATTERN
1625           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1626    
1627         When writing code to extract data  from  named  subpatterns  using  the         When writing code to extract data  from  named  subpatterns  using  the
1628         name-to-number map, remember that the length of each entry is likely to         name-to-number  map,  remember that the length of the entries is likely
1629         be different for each compiled pattern.         to be different for each compiled pattern.
1630    
1631             PCRE_INFO_OKPARTIAL
1632    
1633           Return 1 if the pattern can be used for partial matching, otherwise  0.
1634           The  fourth  argument  should point to an int variable. The pcrepartial
1635           documentation lists the restrictions that apply to patterns  when  par-
1636           tial matching is used.
1637    
1638           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1639    
1640         Return a copy of the options with which the pattern was  compiled.  The         Return  a  copy of the options with which the pattern was compiled. The
1641         fourth  argument  should  point to an unsigned long int variable. These         fourth argument should point to an unsigned long  int  variable.  These
1642         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1643         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1644           other  words,  they are the options that will be in force when matching
1645           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1646           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1647           and PCRE_EXTENDED.
1648    
1649         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1650         alternatives begin with one of the following:         alternatives begin with one of the following:
1651    
1652           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 1331  INFORMATION ABOUT A PATTERN Line 1660  INFORMATION ABOUT A PATTERN
1660    
1661           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1662    
1663         Return  the  size  of the compiled pattern, that is, the value that was         Return the size of the compiled pattern, that is, the  value  that  was
1664         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1665         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1666         size_t variable.         size_t variable.
# Line 1339  INFORMATION ABOUT A PATTERN Line 1668  INFORMATION ABOUT A PATTERN
1668           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1669    
1670         Return the size of the data block pointed to by the study_data field in         Return the size of the data block pointed to by the study_data field in
1671         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1672         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1673         created  by  pcre_study(). The fourth argument should point to a size_t         created by pcre_study(). The fourth argument should point to  a  size_t
1674         variable.         variable.
1675    
1676    
# Line 1349  OBSOLETE INFO FUNCTION Line 1678  OBSOLETE INFO FUNCTION
1678    
1679         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1680    
1681         The pcre_info() function is now obsolete because its interface  is  too         The  pcre_info()  function is now obsolete because its interface is too
1682         restrictive  to return all the available data about a compiled pattern.         restrictive to return all the available data about a compiled  pattern.
1683         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1684         pcre_info()  is the number of capturing subpatterns, or one of the fol-         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1685         lowing negative numbers:         lowing negative numbers:
1686    
1687           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1688           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1689    
1690         If the optptr argument is not NULL, a copy of the  options  with  which         If  the  optptr  argument is not NULL, a copy of the options with which
1691         the  pattern  was  compiled  is placed in the integer it points to (see         the pattern was compiled is placed in the integer  it  points  to  (see
1692         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1693    
1694         If the pattern is not anchored and the  firstcharptr  argument  is  not         If  the  pattern  is  not anchored and the firstcharptr argument is not
1695         NULL,  it is used to pass back information about the first character of         NULL, it is used to pass back information about the first character  of
1696         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1697    
1698    
# Line 1371  REFERENCE COUNTS Line 1700  REFERENCE COUNTS
1700    
1701         int pcre_refcount(pcre *code, int adjust);         int pcre_refcount(pcre *code, int adjust);
1702    
1703         The pcre_refcount() function is used to maintain a reference  count  in         The  pcre_refcount()  function is used to maintain a reference count in
1704         the data block that contains a compiled pattern. It is provided for the         the data block that contains a compiled pattern. It is provided for the
1705         benefit of applications that  operate  in  an  object-oriented  manner,         benefit  of  applications  that  operate  in an object-oriented manner,
1706         where different parts of the application may be using the same compiled         where different parts of the application may be using the same compiled
1707         pattern, but you want to free the block when they are all done.         pattern, but you want to free the block when they are all done.
1708    
1709         When a pattern is compiled, the reference count field is initialized to         When a pattern is compiled, the reference count field is initialized to
1710         zero.   It is changed only by calling this function, whose action is to         zero.  It is changed only by calling this function, whose action is  to
1711         add the adjust value (which may be positive or  negative)  to  it.  The         add  the  adjust  value  (which may be positive or negative) to it. The
1712         yield of the function is the new value. However, the value of the count         yield of the function is the new value. However, the value of the count
1713         is constrained to lie between 0 and 65535, inclusive. If the new  value         is  constrained to lie between 0 and 65535, inclusive. If the new value
1714         is outside these limits, it is forced to the appropriate limit value.         is outside these limits, it is forced to the appropriate limit value.
1715    
1716         Except  when it is zero, the reference count is not correctly preserved         Except when it is zero, the reference count is not correctly  preserved
1717         if a pattern is compiled on one host and then  transferred  to  a  host         if  a  pattern  is  compiled on one host and then transferred to a host
1718         whose byte-order is different. (This seems a highly unlikely scenario.)         whose byte-order is different. (This seems a highly unlikely scenario.)
1719    
1720    
# Line 1395  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1724  MATCHING A PATTERN: THE TRADITIONAL FUNC
1724              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1725              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1726    
1727         The function pcre_exec() is called to match a subject string against  a         The  function pcre_exec() is called to match a subject string against a
1728         compiled  pattern, which is passed in the code argument. If the pattern         compiled pattern, which is passed in the code argument. If the  pattern
1729         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1730         argument.  This  function is the main matching facility of the library,         argument. This function is the main matching facility of  the  library,
1731         and it operates in a Perl-like manner. For specialist use there is also         and it operates in a Perl-like manner. For specialist use there is also
1732         an  alternative matching function, which is described below in the sec-         an alternative matching function, which is described below in the  sec-
1733         tion about the pcre_dfa_exec() function.         tion about the pcre_dfa_exec() function.
1734    
1735         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1736         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1737         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1738         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1739         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1740    
1741         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1425  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1754  MATCHING A PATTERN: THE TRADITIONAL FUNC
1754    
1755     Extra data for pcre_exec()     Extra data for pcre_exec()
1756    
1757         If the extra argument is not NULL, it must point to a  pcre_extra  data         If  the  extra argument is not NULL, it must point to a pcre_extra data
1758         block.  The pcre_study() function returns such a block (when it doesn't         block. The pcre_study() function returns such a block (when it  doesn't
1759         return NULL), but you can also create one for yourself, and pass  addi-         return  NULL), but you can also create one for yourself, and pass addi-
1760         tional  information in it. The fields in a pcre_extra block are as fol-         tional information in it. The pcre_extra block contains  the  following
1761         lows:         fields (not necessarily in this order):
1762    
1763           unsigned long int flags;           unsigned long int flags;
1764           void *study_data;           void *study_data;
1765           unsigned long int match_limit;           unsigned long int match_limit;
1766             unsigned long int match_limit_recursion;
1767           void *callout_data;           void *callout_data;
1768           const unsigned char *tables;           const unsigned char *tables;
1769    
1770         The flags field is a bitmap that specifies which of  the  other  fields         The  flags  field  is a bitmap that specifies which of the other fields
1771         are set. The flag bits are:         are set. The flag bits are:
1772    
1773           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1774           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1775             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1776           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1777           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1778    
1779         Other  flag  bits should be set to zero. The study_data field is set in         Other flag bits should be set to zero. The study_data field is  set  in
1780         the pcre_extra block that is returned by  pcre_study(),  together  with         the  pcre_extra  block  that is returned by pcre_study(), together with
1781         the appropriate flag bit. You should not set this yourself, but you may         the appropriate flag bit. You should not set this yourself, but you may
1782         add to the block by setting the other fields  and  their  corresponding         add  to  the  block by setting the other fields and their corresponding
1783         flag bits.         flag bits.
1784    
1785         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1786         a vast amount of resources when running patterns that are not going  to         a  vast amount of resources when running patterns that are not going to
1787         match,  but  which  have  a very large number of possibilities in their         match, but which have a very large number  of  possibilities  in  their
1788         search trees. The classic  example  is  the  use  of  nested  unlimited         search  trees.  The  classic  example  is  the  use of nested unlimited
1789         repeats.         repeats.
1790    
1791         Internally,  PCRE uses a function called match() which it calls repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1792         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1793         times  this  function is called during a match, which has the effect of         on the number of times this function is called during  a  match,  which
1794         limiting the amount of recursion and backtracking that can take  place.         has  the  effect  of  limiting the amount of backtracking that can take
1795         For patterns that are not anchored, the count starts from zero for each         place. For patterns that are not anchored, the count restarts from zero
1796         position in the subject string.         for each position in the subject string.
1797    
1798         The default limit for the library can be set when PCRE  is  built;  the         The  default  value  for  the  limit can be set when PCRE is built; the
1799         default  default  is 10 million, which handles all but the most extreme         default default is 10 million, which handles all but the  most  extreme
1800         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1801         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra    block    in    which    match_limit    is    set,     and
1802         PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is         PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1803         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1804    
1805         The  pcre_callout  field is used in conjunction with the "callout" fea-         The match_limit_recursion field is similar to match_limit, but  instead
1806           of limiting the total number of times that match() is called, it limits
1807           the depth of recursion. The recursion depth is a  smaller  number  than
1808           the  total number of calls, because not all calls to match() are recur-
1809           sive.  This limit is of use only if it is set smaller than match_limit.
1810    
1811           Limiting  the  recursion  depth  limits the amount of stack that can be
1812           used, or, when PCRE has been compiled to use memory on the heap instead
1813           of the stack, the amount of heap memory that can be used.
1814    
1815           The  default  value  for  match_limit_recursion can be set when PCRE is
1816           built; the default default  is  the  same  value  as  the  default  for
1817           match_limit.  You can override the default by suppling pcre_exec() with
1818           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1819           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1820           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1821    
1822           The pcre_callout field is used in conjunction with the  "callout"  fea-
1823         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1824    
1825         The tables field  is  used  to  pass  a  character  tables  pointer  to         The  tables  field  is  used  to  pass  a  character  tables pointer to
1826         pcre_exec();  this overrides the value that is stored with the compiled         pcre_exec(); this overrides the value that is stored with the  compiled
1827         pattern. A non-NULL value is stored with the compiled pattern  only  if         pattern.  A  non-NULL value is stored with the compiled pattern only if
1828         custom  tables  were  supplied to pcre_compile() via its tableptr argu-         custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1829         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1830         PCRE's  internal  tables  to be used. This facility is helpful when re-         PCRE's internal tables to be used. This facility is  helpful  when  re-
1831         using patterns that have been saved after compiling  with  an  external         using  patterns  that  have been saved after compiling with an external
1832         set  of  tables,  because  the  external tables might be at a different         set of tables, because the external tables  might  be  at  a  different
1833         address when pcre_exec() is called. See the  pcreprecompile  documenta-         address  when  pcre_exec() is called. See the pcreprecompile documenta-
1834         tion for a discussion of saving compiled patterns for later use.         tion for a discussion of saving compiled patterns for later use.
1835    
1836     Option bits for pcre_exec()     Option bits for pcre_exec()
1837    
1838         The  unused  bits of the options argument for pcre_exec() must be zero.         The unused bits of the options argument for pcre_exec() must  be  zero.
1839         The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,         The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1840         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1841           PCRE_PARTIAL.
1842    
1843           PCRE_ANCHORED           PCRE_ANCHORED
1844    
# Line 1498  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1847  MATCHING A PATTERN: THE TRADITIONAL FUNC
1847         turned  out to be anchored by virtue of its contents, it cannot be made         turned  out to be anchored by virtue of its contents, it cannot be made
1848         unachored at matching time.         unachored at matching time.
1849    
1850             PCRE_BSR_ANYCRLF
1851             PCRE_BSR_UNICODE
1852    
1853           These options (which are mutually exclusive) control what the \R escape
1854           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1855           or to match any Unicode newline sequence. These  options  override  the
1856           choice that was made or defaulted when the pattern was compiled.
1857    
1858             PCRE_NEWLINE_CR
1859             PCRE_NEWLINE_LF
1860             PCRE_NEWLINE_CRLF
1861             PCRE_NEWLINE_ANYCRLF
1862             PCRE_NEWLINE_ANY
1863    
1864           These  options  override  the  newline  definition  that  was chosen or
1865           defaulted when the pattern was compiled. For details, see the  descrip-
1866           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1867           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1868           ters.  It may also alter the way the match position is advanced after a
1869           match failure for an unanchored pattern.
1870    
1871           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1872           set,  and a match attempt for an unanchored pattern fails when the cur-
1873           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1874           explicit  matches  for  CR  or  LF  characters,  the  match position is
1875           advanced by two characters instead of one, in other words, to after the
1876           CRLF.
1877    
1878           The above rule is a compromise that makes the most common cases work as
1879           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1880           option is not set), it does not match the string "\r\nA" because, after
1881           failing at the start, it skips both the CR and the LF before  retrying.
1882           However,  the  pattern  [\r\n]A does match that string, because it con-
1883           tains an explicit CR or LF reference, and so advances only by one char-
1884           acter after the first failure.
1885    
1886           An explicit match for CR of LF is either a literal appearance of one of
1887           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1888           matches  such  as [^X] do not count, nor does \s (which includes CR and
1889           LF in the characters that it matches).
1890    
1891           Notwithstanding the above, anomalous effects may still occur when  CRLF
1892           is a valid newline sequence and explicit \r or \n escapes appear in the
1893           pattern.
1894    
1895           PCRE_NOTBOL           PCRE_NOTBOL
1896    
1897         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
# Line 1543  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1937  MATCHING A PATTERN: THE TRADITIONAL FUNC
1937         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1938         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1939         called.  The value of startoffset is also checked  to  ensure  that  it         called.  The value of startoffset is also checked  to  ensure  that  it
1940         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points  to  the start of a UTF-8 character. There is a discussion about
1941         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the validity of UTF-8 strings in the section on UTF-8  support  in  the
1942         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
1943         returned.         pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
1944           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1945         If you already know that your subject is valid, and you  want  to  skip  
1946         these    checks    for   performance   reasons,   you   can   set   the         If  you  already  know that your subject is valid, and you want to skip
1947         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to         these   checks   for   performance   reasons,   you   can    set    the
1948         do  this  for the second and subsequent calls to pcre_exec() if you are         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1949         making repeated calls to find all  the  matches  in  a  single  subject         do this for the second and subsequent calls to pcre_exec() if  you  are
1950         string.  However,  you  should  be  sure  that the value of startoffset         making  repeated  calls  to  find  all  the matches in a single subject
1951         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is         string. However, you should be  sure  that  the  value  of  startoffset
1952         set,  the  effect of passing an invalid UTF-8 string as a subject, or a         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1953         value of startoffset that does not point to the start of a UTF-8  char-         set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1954           value  of startoffset that does not point to the start of a UTF-8 char-
1955         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1956    
1957           PCRE_PARTIAL           PCRE_PARTIAL
1958    
1959         This  option  turns  on  the  partial  matching feature. If the subject         This option turns on the  partial  matching  feature.  If  the  subject
1960         string fails to match the pattern, but at some point during the  match-         string  fails to match the pattern, but at some point during the match-
1961         ing  process  the  end of the subject was reached (that is, the subject         ing process the end of the subject was reached (that  is,  the  subject
1962         partially matches the pattern and the failure to  match  occurred  only         partially  matches  the  pattern and the failure to match occurred only
1963         because  there were not enough subject characters), pcre_exec() returns         because there were not enough subject characters), pcre_exec()  returns
1964         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1965         used,  there  are restrictions on what may appear in the pattern. These         used, there are restrictions on what may appear in the  pattern.  These
1966         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1967    
1968     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1969    
1970         The subject string is passed to pcre_exec() as a pointer in subject,  a         The  subject string is passed to pcre_exec() as a pointer in subject, a
1971         length  in  length, and a starting byte offset in startoffset. In UTF-8         length in length, and a starting byte offset in startoffset.  In  UTF-8
1972         mode, the byte offset must point to the start  of  a  UTF-8  character.         mode,  the  byte  offset  must point to the start of a UTF-8 character.
1973         Unlike  the  pattern string, the subject may contain binary zero bytes.         Unlike the pattern string, the subject may contain binary  zero  bytes.
1974         When the starting offset is zero, the search for a match starts at  the         When  the starting offset is zero, the search for a match starts at the
1975         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1976    
1977         A  non-zero  starting offset is useful when searching for another match         A non-zero starting offset is useful when searching for  another  match
1978         in the same subject by calling pcre_exec() again after a previous  suc-         in  the same subject by calling pcre_exec() again after a previous suc-
1979         cess.   Setting  startoffset differs from just passing over a shortened         cess.  Setting startoffset differs from just passing over  a  shortened
1980         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1981         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1982    
1983           \Biss\B           \Biss\B
1984    
1985         which  finds  occurrences  of "iss" in the middle of words. (\B matches         which finds occurrences of "iss" in the middle of  words.  (\B  matches
1986         only if the current position in the subject is not  a  word  boundary.)         only  if  the  current position in the subject is not a word boundary.)
1987         When  applied  to the string "Mississipi" the first call to pcre_exec()         When applied to the string "Mississipi" the first call  to  pcre_exec()
1988         finds the first occurrence. If pcre_exec() is called  again  with  just         finds  the  first  occurrence. If pcre_exec() is called again with just
1989         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the remainder of the subject,  namely  "issipi",  it  does  not  match,
1990         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1991         to  be  a  word  boundary. However, if pcre_exec() is passed the entire         to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1992         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1993         rence  of "iss" because it is able to look behind the starting point to         rence of "iss" because it is able to look behind the starting point  to
1994         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1995    
1996         If a non-zero starting offset is passed when the pattern  is  anchored,         If  a  non-zero starting offset is passed when the pattern is anchored,
1997         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1998         if the pattern does not require the match to be at  the  start  of  the         if  the  pattern  does  not require the match to be at the start of the
1999         subject.         subject.
2000    
2001     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
2002    
2003         In  general, a pattern matches a certain portion of the subject, and in         In general, a pattern matches a certain portion of the subject, and  in
2004         addition, further substrings from the subject  may  be  picked  out  by         addition,  further  substrings  from  the  subject may be picked out by
2005         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2006         this is called "capturing" in what follows, and the  phrase  "capturing         this  is  called "capturing" in what follows, and the phrase "capturing
2007         subpattern"  is  used for a fragment of a pattern that picks out a sub-         subpattern" is used for a fragment of a pattern that picks out  a  sub-
2008         string. PCRE supports several other kinds of  parenthesized  subpattern         string.  PCRE  supports several other kinds of parenthesized subpattern
2009         that do not cause substrings to be captured.         that do not cause substrings to be captured.
2010    
2011         Captured  substrings are returned to the caller via a vector of integer         Captured substrings are returned to the caller via a vector of  integer
2012         offsets whose address is passed in ovector. The number of  elements  in         offsets  whose  address is passed in ovector. The number of elements in
2013         the  vector is passed in ovecsize, which must be a non-negative number.         the vector is passed in ovecsize, which must be a non-negative  number.
2014         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
2015    
2016         The first two-thirds of the vector is used to pass back  captured  sub-         The  first  two-thirds of the vector is used to pass back captured sub-
2017         strings,  each  substring using a pair of integers. The remaining third         strings, each substring using a pair of integers. The  remaining  third
2018         of the vector is used as workspace by pcre_exec() while  matching  cap-         of  the  vector is used as workspace by pcre_exec() while matching cap-
2019         turing  subpatterns, and is not available for passing back information.         turing subpatterns, and is not available for passing back  information.
2020         The length passed in ovecsize should always be a multiple of three.  If         The  length passed in ovecsize should always be a multiple of three. If
2021         it is not, it is rounded down.         it is not, it is rounded down.
2022    
2023         When  a  match  is successful, information about captured substrings is         When a match is successful, information about  captured  substrings  is
2024         returned in pairs of integers, starting at the  beginning  of  ovector,         returned  in  pairs  of integers, starting at the beginning of ovector,
2025         and  continuing  up  to two-thirds of its length at the most. The first         and continuing up to two-thirds of its length at the  most.  The  first
2026         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
2027         string,  and  the  second  is  set to the offset of the first character         string, and the second is set to the  offset  of  the  first  character
2028         after the end of a substring. The  first  pair,  ovector[0]  and  ovec-         after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2029         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1], identify the portion of  the  subject  string  matched  by  the
2030         entire pattern. The next pair is used for the first  capturing  subpat-         entire  pattern.  The next pair is used for the first capturing subpat-
2031         tern,  and  so  on.  The value returned by pcre_exec() is the number of         tern, and so on. The value returned by pcre_exec() is one more than the
2032         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
2033         return  value  from  a  successful match is 1, indicating that just the         have been captured, the returned value is 3. If there are no  capturing
2034         first pair of offsets has been set.         subpatterns,  the return value from a successful match is 1, indicating
2035           that just the first pair of offsets has been set.
        Some convenience functions are provided  for  extracting  the  captured  
        substrings  as  separate  strings. These are described in the following  
        section.  
   
        It is possible for an capturing subpattern number  n+1  to  match  some  
        part  of  the  subject  when subpattern n has not been used at all. For  
        example, if the string "abc" is matched against the pattern (a|(z))(bc)  
        subpatterns  1 and 3 are matched, but 2 is not. When this happens, both  
        offset values corresponding to the unused subpattern are set to -1.  
2036    
2037         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2038         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1660  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2046  MATCHING A PATTERN: THE TRADITIONAL FUNC
2046         substrings,  PCRE has to get additional memory for use during matching.         substrings,  PCRE has to get additional memory for use during matching.
2047         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2048    
2049         Note that pcre_info() can be used to find out how many  capturing  sub-         The pcre_info() function can be used to find  out  how  many  capturing
2050         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns  there  are  in  a  compiled pattern. The smallest size for
2051         that will allow for n captured substrings, in addition to  the  offsets         ovector that will allow for n captured substrings, in addition  to  the
2052         of the substring matched by the whole pattern, is (n+1)*3.         offsets of the substring matched by the whole pattern, is (n+1)*3.
2053    
2054           It  is  possible for capturing subpattern number n+1 to match some part
2055           of the subject when subpattern n has not been used at all. For example,
2056           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2057           return from the function is 4, and subpatterns 1 and 3 are matched, but
2058           2  is  not.  When  this happens, both values in the offset pairs corre-
2059           sponding to unused subpatterns are set to -1.
2060    
2061           Offset values that correspond to unused subpatterns at the end  of  the
2062           expression  are  also  set  to  -1. For example, if the string "abc" is
2063           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2064           matched.  The  return  from the function is 2, because the highest used
2065           capturing subpattern number is 1. However, you can refer to the offsets
2066           for  the  second  and third capturing subpatterns if you wish (assuming
2067           the vector is large enough, of course).
2068    
2069     Return values from pcre_exec()         Some convenience functions are provided  for  extracting  the  captured
2070           substrings as separate strings. These are described below.
2071    
2072       Error return values from pcre_exec()
2073    
2074         If  pcre_exec()  fails, it returns a negative number. The following are         If  pcre_exec()  fails, it returns a negative number. The following are
2075         defined in the header file:         defined in the header file:
# Line 1691  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2095  MATCHING A PATTERN: THE TRADITIONAL FUNC
2095         an environment with the other endianness. This is the error  that  PCRE         an environment with the other endianness. This is the error  that  PCRE
2096         gives when the magic number is not present.         gives when the magic number is not present.
2097    
2098           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2099    
2100         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2101         compiled pattern. This error could be caused by a bug  in  PCRE  or  by         compiled pattern. This error could be caused by a bug  in  PCRE  or  by
# Line 1713  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2117  MATCHING A PATTERN: THE TRADITIONAL FUNC
2117    
2118           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2119    
2120         The  recursion  and backtracking limit, as specified by the match_limit         The  backtracking  limit,  as  specified  by the match_limit field in a
2121         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra structure (or defaulted) was reached.  See  the  description
2122         description above.         above.
2123    
2124           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2125    
# Line 1754  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2158  MATCHING A PATTERN: THE TRADITIONAL FUNC
2158    
2159         This error is given if the value of the ovecsize argument is  negative.         This error is given if the value of the ovecsize argument is  negative.
2160    
2161             PCRE_ERROR_RECURSIONLIMIT (-21)
2162    
2163           The internal recursion limit, as specified by the match_limit_recursion
2164           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2165           description above.
2166    
2167             PCRE_ERROR_BADNEWLINE     (-23)
2168    
2169           An invalid combination of PCRE_NEWLINE_xxx options was given.
2170    
2171           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2172    
2173    
2174  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2175    
# Line 1774  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2190  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2190         string_list() are provided for extracting captured substrings  as  new,         string_list() are provided for extracting captured substrings  as  new,
2191         separate,  zero-terminated strings. These functions identify substrings         separate,  zero-terminated strings. These functions identify substrings
2192         by number. The next section describes functions  for  extracting  named         by number. The next section describes functions  for  extracting  named
2193         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2194         extracted and has a further zero added on the end, but  the  result  is  
2195         not, of course, a C string.         A  substring that contains a binary zero is correctly extracted and has
2196           a further zero added on the end, but the result is not, of course, a  C
2197           string.   However,  you  can  process such a string by referring to the
2198           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2199           string().  Unfortunately, the interface to pcre_get_substring_list() is
2200           not adequate for handling strings containing binary zeros, because  the
2201           end of the final string is not independently indicated.
2202    
2203         The  first  three  arguments  are the same for all three of these func-         The  first  three  arguments  are the same for all three of these func-
2204         tions: subject is the subject string that has  just  been  successfully         tions: subject is the subject string that has  just  been  successfully
# Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2218  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2218         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2219         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2220         The yield of the function is the length of the  string,  not  including         The yield of the function is the length of the  string,  not  including
2221         the terminating zero, or one of         the terminating zero, or one of these error codes:
2222    
2223           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2224    
# Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2234  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2234         single block of memory that is obtained via pcre_malloc. The address of         single block of memory that is obtained via pcre_malloc. The address of
2235         the  memory  block  is returned via listptr, which is also the start of         the  memory  block  is returned via listptr, which is also the start of
2236         the list of string pointers. The end of the list is marked  by  a  NULL         the list of string pointers. The end of the list is marked  by  a  NULL
2237         pointer. The yield of the function is zero if all went well, or         pointer.  The  yield  of  the function is zero if all went well, or the
2238           error code
2239    
2240           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2241    
2242         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2243    
2244         When  any of these functions encounter a substring that is unset, which         When any of these functions encounter a substring that is unset,  which
2245         can happen when capturing subpattern number n+1 matches  some  part  of         can  happen  when  capturing subpattern number n+1 matches some part of
2246         the  subject, but subpattern n has not been used at all, they return an         the subject, but subpattern n has not been used at all, they return  an
2247         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2248         string  by inspecting the appropriate offset in ovector, which is nega-         string by inspecting the appropriate offset in ovector, which is  nega-
2249         tive for unset substrings.         tive for unset substrings.
2250    
2251         The two convenience functions pcre_free_substring() and  pcre_free_sub-         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2252         string_list()  can  be  used  to free the memory returned by a previous         string_list() can be used to free the memory  returned  by  a  previous
2253         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2254         tively.  They  do  nothing  more  than  call the function pointed to by         tively. They do nothing more than  call  the  function  pointed  to  by
2255         pcre_free, which of course could be called directly from a  C  program.         pcre_free,  which  of course could be called directly from a C program.
2256         However,  PCRE is used in some situations where it is linked via a spe-         However, PCRE is used in some situations where it is linked via a  spe-
2257         cial  interface  to  another  programming  language  which  cannot  use         cial   interface  to  another  programming  language  that  cannot  use
2258         pcre_free  directly;  it is for these cases that the functions are pro-         pcre_free directly; it is for these cases that the functions  are  pro-
2259         vided.         vided.
2260    
2261    
# Line 1851  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2274  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2274              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2275              const char **stringptr);              const char **stringptr);
2276    
2277         To extract a substring by name, you first have to find associated  num-         To  extract a substring by name, you first have to find associated num-
2278         ber.  For example, for this pattern         ber.  For example, for this pattern
2279    
2280           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2281    
2282         the number of the subpattern called "xxx" is 2. You can find the number         the number of the subpattern called "xxx" is 2. If the name is known to
2283         from the name by calling pcre_get_stringnumber(). The first argument is         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2284         the  compiled  pattern,  and  the  second is the name. The yield of the         name by calling pcre_get_stringnumber(). The first argument is the com-
2285         function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if         piled pattern, and the second is the name. The yield of the function is
2286         there is no subpattern of that name.         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2287           subpattern of that name.
2288    
2289         Given the number, you can extract the substring directly, or use one of         Given the number, you can extract the substring directly, or use one of
2290         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1879  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2303  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2303    
2304         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2305         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2306         ate.         ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2307           behaviour may not be what you want (see the next section).
2308    
2309    
2310    DUPLICATE SUBPATTERN NAMES
2311    
2312           int pcre_get_stringtable_entries(const pcre *code,
2313                const char *name, char **first, char **last);
2314    
2315           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2316           subpatterns are not required to  be  unique.  Normally,  patterns  with
2317           duplicate  names  are such that in any one match, only one of the named
2318           subpatterns participates. An example is shown in the pcrepattern  docu-
2319           mentation.
2320    
2321           When    duplicates   are   present,   pcre_copy_named_substring()   and
2322           pcre_get_named_substring() return the first substring corresponding  to
2323           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2324           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2325           function  returns one of the numbers that are associated with the name,
2326           but it is not defined which it is.
2327    
2328           If you want to get full details of all captured substrings for a  given
2329           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2330           first argument is the compiled pattern, and the second is the name. The
2331           third  and  fourth  are  pointers to variables which are updated by the
2332           function. After it has run, they point to the first and last entries in
2333           the  name-to-number  table  for  the  given  name.  The function itself
2334           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2335           there  are none. The format of the table is described above in the sec-
2336           tion entitled Information about a  pattern.   Given  all  the  relevant
2337           entries  for the name, you can extract each of their numbers, and hence
2338           the captured data, if any.
2339    
2340    
2341  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
# Line 1908  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2364  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2364              int *workspace, int wscount);              int *workspace, int wscount);
2365    
2366         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2367         against a compiled pattern, using a "DFA" matching algorithm. This  has         against a compiled pattern, using a matching algorithm that  scans  the
2368         different  characteristics to the normal algorithm, and is not compati-         subject  string  just  once, and does not backtrack. This has different
2369         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics to the normal algorithm, and  is  not  compatible  with
2370         Nevertheless, there are times when this kind of matching can be useful.         Perl.  Some  of the features of PCRE patterns are not supported. Never-
2371         For a discussion of the two matching algorithms, see  the  pcrematching         theless, there are times when this kind of matching can be useful.  For
2372         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2373           mentation.
2374    
2375         The  arguments  for  the  pcre_dfa_exec()  function are the same as for         The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2376         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
2377         ent  way,  and  this is described below. The other common arguments are         ent way, and this is described below. The other  common  arguments  are
2378         used in the same way as for pcre_exec(), so their  description  is  not         used  in  the  same way as for pcre_exec(), so their description is not
2379         repeated here.         repeated here.
2380    
2381         The  two  additional  arguments provide workspace for the function. The         The two additional arguments provide workspace for  the  function.  The
2382         workspace vector should contain at least 20 elements. It  is  used  for         workspace  vector  should  contain at least 20 elements. It is used for
2383         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2384         workspace will be needed for patterns and subjects where  there  are  a         workspace  will  be  needed for patterns and subjects where there are a
2385         lot of possible matches.         lot of potential matches.
2386    
2387         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2388    
2389           int rc;           int rc;
2390           int ovector[10];           int ovector[10];
2391           int wspace[20];           int wspace[20];
2392           rc = pcre_exec(           rc = pcre_dfa_exec(
2393             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2394             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2395             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1946  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2403  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2403    
2404     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2405    
2406         The  unused  bits  of  the options argument for pcre_dfa_exec() must be         The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2407         zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,         zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2408         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2409         PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of         PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2410         these  are  the  same  as  for pcre_exec(), so their description is not         three of these are the same as for pcre_exec(), so their description is
2411         repeated here.         not repeated here.
2412    
2413           PCRE_PARTIAL           PCRE_PARTIAL
2414    
2415         This has the same general effect as it does for  pcre_exec(),  but  the         This  has  the  same general effect as it does for pcre_exec(), but the
2416         details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for         details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2417         pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into         pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2418         PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have         PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2419         been no complete matches, but there is still at least one matching pos-         been no complete matches, but there is still at least one matching pos-
2420         sibility.  The portion of the string that provided the partial match is         sibility. The portion of the string that provided the partial match  is
2421         set as the first matching string.         set as the first matching string.
2422    
2423           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2424    
2425         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2426         stop  as  soon  as  it  has found one match. Because of the way the DFA         stop as soon as it has found one match. Because of the way the alterna-
2427         algorithm works, this is necessarily the shortest possible match at the         tive  algorithm  works, this is necessarily the shortest possible match
2428         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2429    
2430           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2431    
2432         When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and         When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2433         returns a partial match, it is possible to call it  again,  with  addi-         returns  a  partial  match, it is possible to call it again, with addi-
2434         tional  subject  characters,  and have it continue with the same match.         tional subject characters, and have it continue with  the  same  match.
2435         The PCRE_DFA_RESTART option requests this action; when it is  set,  the         The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2436         workspace  and wscount options must reference the same vector as before         workspace and wscount options must reference the same vector as  before
2437         because data about the match so far is left in  them  after  a  partial         because  data  about  the  match so far is left in them after a partial
2438         match.  There  is  more  discussion of this facility in the pcrepartial         match. There is more discussion of this  facility  in  the  pcrepartial
2439         documentation.         documentation.
2440    
2441     Successful returns from pcre_dfa_exec()     Successful returns from pcre_dfa_exec()
2442    
2443         When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-         When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2444         string in the subject. Note, however, that all the matches from one run         string in the subject. Note, however, that all the matches from one run
2445         of the function start at the same point in  the  subject.  The  shorter         of  the  function  start  at the same point in the subject. The shorter
2446         matches  are all initial substrings of the longer matches. For example,         matches are all initial substrings of the longer matches. For  example,
2447         if the pattern         if the pattern
2448    
2449           <.*>           <.*>
# Line 2001  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2458  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2458           <something> <something else>           <something> <something else>
2459           <something> <something else> <something further>           <something> <something else> <something further>
2460    
2461         On success, the yield of the function is a number  greater  than  zero,         On  success,  the  yield of the function is a number greater than zero,
2462         which  is  the  number of matched substrings. The substrings themselves         which is the number of matched substrings.  The  substrings  themselves
2463         are returned in ovector. Each string uses two elements;  the  first  is         are  returned  in  ovector. Each string uses two elements; the first is
2464         the  offset  to the start, and the second is the offset to the end. All         the offset to the start, and the second is the offset to  the  end.  In
2465         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
2466         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
2467         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility  with  the  way pcre_exec() returns data, even though the
2468         strings is different.)         meaning of the strings is different.)
2469    
2470         The strings are returned in reverse order of length; that is, the long-         The strings are returned in reverse order of length; that is, the long-
2471         est matching string is given first. If there were too many  matches  to         est  matching  string is given first. If there were too many matches to
2472         fit  into ovector, the yield of the function is zero, and the vector is         fit into ovector, the yield of the function is zero, and the vector  is
2473         filled with the longest matches.         filled with the longest matches.
2474    
2475     Error returns from pcre_dfa_exec()     Error returns from pcre_dfa_exec()
2476    
2477         The pcre_dfa_exec() function returns a negative number when  it  fails.         The  pcre_dfa_exec()  function returns a negative number when it fails.
2478         Many  of  the  errors  are  the  same as for pcre_exec(), and these are         Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2479         described above.  There are in addition the following errors  that  are         described  above.   There are in addition the following errors that are
2480         specific to pcre_dfa_exec():         specific to pcre_dfa_exec():
2481    
2482           PCRE_ERROR_DFA_UITEM      (-16)           PCRE_ERROR_DFA_UITEM      (-16)
2483    
2484         This  return is given if pcre_dfa_exec() encounters an item in the pat-         This return is given if pcre_dfa_exec() encounters an item in the  pat-
2485         tern that it does not support, for instance, the use of \C  or  a  back         tern  that  it  does not support, for instance, the use of \C or a back
2486         reference.         reference.
2487    
2488           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2489    
2490         This  return is given if pcre_dfa_exec() encounters a condition item in         This return is given if pcre_dfa_exec()  encounters  a  condition  item
2491         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
2492         supported.         in a specific group. These are not supported.
2493    
2494           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2495    
2496         This  return  is given if pcre_dfa_exec() is called with an extra block         This return is given if pcre_dfa_exec() is called with an  extra  block
2497         that contains a setting of the match_limit field. This is not supported         that contains a setting of the match_limit field. This is not supported
2498         (it is meaningless).         (it is meaningless).
2499    
2500           PCRE_ERROR_DFA_WSSIZE     (-19)           PCRE_ERROR_DFA_WSSIZE     (-19)
2501    
2502         This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the         This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2503         workspace vector.         workspace vector.
2504    
2505           PCRE_ERROR_DFA_RECURSE    (-20)           PCRE_ERROR_DFA_RECURSE    (-20)
2506    
2507         When a recursive subpattern is processed, the matching  function  calls         When  a  recursive subpattern is processed, the matching function calls
2508         itself  recursively,  using  private vectors for ovector and workspace.         itself recursively, using private vectors for  ovector  and  workspace.
2509         This error is given if the output vector  is  not  large  enough.  This         This  error  is  given  if  the output vector is not large enough. This
2510         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2511    
2512  Last updated: 16 May 2005  
2513  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2514    
2515           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2516           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2517    
2518    
2519    AUTHOR
2520    
2521           Philip Hazel
2522           University Computing Service
2523           Cambridge CB2 3QH, England.
2524    
2525    
2526    REVISION
2527    
2528           Last updated: 11 September 2007
2529           Copyright (c) 1997-2007 University of Cambridge.
2530  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2531    
2532    
# Line 2080  PCRE CALLOUTS Line 2553  PCRE CALLOUTS
2553         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2554         points:         points:
2555    
2556           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2557    
2558         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
2559         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2155  THE CALLOUT INTERFACE Line 2628  THE CALLOUT INTERFACE
2628         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2629         were passed to pcre_exec().         were passed to pcre_exec().
2630    
2631         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2632         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2633         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
2634         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2635           function may be called several times from the same point in the pattern
2636           for different starting points in the subject.
2637    
2638         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2639         the current match pointer.         the current match pointer.
# Line 2211  RETURN VALUES Line 2686  RETURN VALUES
2686         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
2687         itself.         itself.
2688    
2689  Last updated: 28 February 2005  
2690  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2691    
2692           Philip Hazel
2693           University Computing Service
2694           Cambridge CB2 3QH, England.
2695    
2696    
2697    REVISION
2698    
2699           Last updated: 29 May 2007
2700           Copyright (c) 1997-2007 University of Cambridge.
2701  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2702    
2703    
# Line 2226  NAME Line 2711  NAME
2711  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2712    
2713         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2714         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2715         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2716           some features that are expected to be in the forthcoming Perl 5.10.
2717         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2718         are given in the section on UTF-8 support in the main pcre page.         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2719           of  what  it does have are given in the section on UTF-8 support in the
2720           main pcre page.
2721    
2722         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2723         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,
# Line 2257  DIFFERENCES BETWEEN PCRE AND PERL Line 2744  DIFFERENCES BETWEEN PCRE AND PERL
2744         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
2745         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2746         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-
2747         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2748           derived properties Any and L&.
2749    
2750         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2751         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2752         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2753         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2754         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2755    
2756             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2760  DIFFERENCES BETWEEN PCRE AND PERL
2760             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2761             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2762    
2763         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2764         classes.         classes.
2765    
2766         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2767         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2768         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
2769         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2770         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2771    
2772         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2773         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2774         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2775    
2776           10.  There are some differences that are concerned with the settings of
2777           captured strings when part of  a  pattern  is  repeated.  For  example,
2778           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2779         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2780    
2781         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2782         ities:         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2783           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2784           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2785           ture group; this is different to Perl.
2786    
2787           12. PCRE provides some extensions to the Perl regular expression facil-
2788           ities.   Perl  5.10  will  include new features that are not in earlier
2789           versions, some of which (such as named parentheses) have been  in  PCRE
2790           for some time. This list is with respect to Perl 5.10:
2791    
2792         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2793         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2794         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2795    
2796         (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 $
2797         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2798    
2799         (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-
2800         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2801           ignored.  (Perl can be made to issue a warning.)
2802    
2803         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2804         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2309  DIFFERENCES BETWEEN PCRE AND PERL Line 2810  DIFFERENCES BETWEEN PCRE AND PERL
2810         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2811         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2812    
2813         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2814         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
2815    
2816         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The callout facility is PCRE-specific.
2817    
2818         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
2819    
2820         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j) Patterns compiled by PCRE can be saved and re-used at a later time,
2821           even on different hosts that have the other endianness.
2822    
2823         (k) The callout facility is PCRE-specific.         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2824           different way and is not Perl-compatible.
2825    
2826         (l) The partial matching facility is PCRE-specific.         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2827           of a pattern that set overall options that cannot be changed within the
2828           pattern.
2829    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
2830    
2831         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  AUTHOR
2832         different way and is not Perl-compatible.  
2833           Philip Hazel
2834           University Computing Service
2835           Cambridge CB2 3QH, England.
2836    
2837    
2838  Last updated: 28 February 2005  REVISION
2839  Copyright (c) 1997-2005 University of Cambridge.  
2840           Last updated: 11 September 2007
2841           Copyright (c) 1997-2007 University of Cambridge.
2842  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2843    
2844    
# Line 2344  NAME Line 2851  NAME
2851    
2852  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2853    
2854         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2855         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2856         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2857         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2858         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2859         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2860           O'Reilly,  covers regular expressions in great detail. This description
2861           of PCRE's regular expressions is intended as reference material.
2862    
2863         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2864         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
# Line 2363  PCRE REGULAR EXPRESSION DETAILS Line 2872  PCRE REGULAR EXPRESSION DETAILS
2872         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2873         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2874         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2875         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2876         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2877         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2878           discussed in the pcrematching page.
2879    
2880    
2881    NEWLINE CONVENTIONS
2882    
2883           PCRE  supports five different conventions for indicating line breaks in
2884           strings: a single CR (carriage return) character, a  single  LF  (line-
2885           feed) character, the two-character sequence CRLF, any of the three pre-
2886           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2887           discussion  about newlines, and shows how to set the newline convention
2888           in the options arguments for the compiling and matching functions.
2889    
2890           It is also possible to specify a newline convention by starting a  pat-
2891           tern string with one of the following five sequences:
2892    
2893             (*CR)        carriage return
2894             (*LF)        linefeed
2895             (*CRLF)      carriage return, followed by linefeed
2896             (*ANYCRLF)   any of the three above
2897             (*ANY)       all Unicode newline sequences
2898    
2899           These override the default and the options given to pcre_compile(). For
2900           example, on a Unix system where LF is the default newline sequence, the
2901           pattern
2902    
2903             (*CR)a.b
2904    
2905           changes the convention to CR. That pattern matches "a\nb" because LF is
2906           no longer a newline. Note that these special settings,  which  are  not
2907           Perl-compatible,  are  recognized  only at the very start of a pattern,
2908           and that they must be in upper case.  If  more  than  one  of  them  is
2909           present, the last one is used.
2910    
2911           The  newline  convention  does  not  affect what the \R escape sequence
2912           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2913           compatibility.  However, this can be changed; see the description of \R
2914           in the section entitled "Newline sequences" below.
2915    
2916    
2917    CHARACTERS AND METACHARACTERS
2918    
2919         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2920         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
# Line 2391  PCRE REGULAR EXPRESSION DETAILS Line 2940  PCRE REGULAR EXPRESSION DETAILS
2940    
2941         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2942         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2943         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2944         metacharacters are as follows:         the metacharacters are as follows:
2945    
2946           \      general escape character with several uses           \      general escape character with several uses
2947           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2439  BACKSLASH Line 2988  BACKSLASH
2988    
2989         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2990         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2991         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2992         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2993         ter as part of the pattern.         part of the pattern.
2994    
2995         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-
2996         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-
# Line 2472  BACKSLASH Line 3021  BACKSLASH
3021           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3022           \e        escape (hex 1B)           \e        escape (hex 1B)
3023           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3024           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3025           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3026           \t        tab (hex 09)           \t        tab (hex 09)
3027           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3028           \xhh      character with hex code hh           \xhh      character with hex code hh
3029           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3030    
3031         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,
3032         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
# Line 2485  BACKSLASH Line 3034  BACKSLASH
3034         becomes hex 7B.         becomes hex 7B.
3035    
3036         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
3037         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         in  upper  or  lower case). Any number of hexadecimal digits may appear
3038         its may appear between \x{ and }, but the value of the  character  code         between \x{ and }, but the value of the character  code  must  be  less
3039         must  be  less  than  2**31  (that is, the maximum hexadecimal value is         than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is,
3040         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3041         \x{  and }, or if there is no terminating }, this form of escape is not         than the largest Unicode code point, which is 10FFFF.
3042         recognized. Instead, the initial \x will  be  interpreted  as  a  basic  
3043         hexadecimal  escape, with no following digits, giving a character whose         If  characters  other than hexadecimal digits appear between \x{ and },
3044         value is zero.         or if there is no terminating }, this form of escape is not recognized.
3045           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3046           escape, with no following digits, giving a  character  whose  value  is
3047           zero.
3048    
3049         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
3050         two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference         two syntaxes for \x. There is no difference in the way  they  are  han-
3051         in the way they are handled. For example, \xdc is exactly the  same  as         dled. For example, \xdc is exactly the same as \x{dc}.
3052         \x{dc}.  
3053           After  \0  up  to two further octal digits are read. If there are fewer
3054         After  \0  up  to  two further octal digits are read. In both cases, if         than two digits, just  those  that  are  present  are  used.  Thus  the
3055         there are fewer than two digits, just those that are present are  used.         sequence \0\x\07 specifies two binary zeros followed by a BEL character
3056         Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL         (code value 7). Make sure you supply two digits after the initial  zero
3057         character (code value 7). Make sure you supply  two  digits  after  the         if the pattern character that follows is itself an octal digit.
        initial  zero  if the pattern character that follows is itself an octal  
        digit.  
3058    
3059         The handling of a backslash followed by a digit other than 0 is compli-         The handling of a backslash followed by a digit other than 0 is compli-
3060         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3061         its as a decimal number. If the number is less than  10,  or  if  there         its  as  a  decimal  number. If the number is less than 10, or if there
3062         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3063         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3064         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3065         of parenthesized subpatterns.         of parenthesized subpatterns.
3066    
3067         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
3068         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3069         up to three octal digits following the backslash, and generates a  sin-         up to three octal digits following the backslash, and uses them to gen-
3070         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
3071         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
3072           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3073           example:
3074    
3075           \040   is another way of writing a space           \040   is another way of writing a space
3076           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2535  BACKSLASH Line 3087  BACKSLASH
3087           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3088                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3089    
3090         Note that octal values of 100 or greater must not be  introduced  by  a         Note  that  octal  values of 100 or greater must not be introduced by a
3091         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3092    
3093         All  the  sequences  that  define a single byte value or a single UTF-8         All the sequences that define a single character value can be used both
3094         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
3095         classes.  In  addition,  inside  a  character class, the sequence \b is         class, the sequence \b is interpreted as the backspace  character  (hex
3096         interpreted as the backspace character (hex 08), and the sequence \X is         08),  and the sequences \R and \X are interpreted as the characters "R"
3097         interpreted  as  the  character  "X".  Outside a character class, these         and "X", respectively. Outside a character class, these sequences  have
3098         sequences have different meanings (see below).         different meanings (see below).
3099    
3100       Absolute and relative back references
3101    
3102           The  sequence  \g followed by an unsigned or a negative number, option-
3103           ally enclosed in braces, is an absolute or relative back  reference.  A
3104           named back reference can be coded as \g{name}. Back references are dis-
3105           cussed later, following the discussion of parenthesized subpatterns.
3106    
3107     Generic character types     Generic character types
3108    
3109         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
3110         The following are always recognized:         following are always recognized:
3111    
3112           \d     any decimal digit           \d     any decimal digit
3113           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3114             \h     any horizontal whitespace character
3115             \H     any character that is not a horizontal whitespace character
3116           \s     any whitespace character           \s     any whitespace character
3117           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3118             \v     any vertical whitespace character
3119             \V     any character that is not a vertical whitespace character
3120           \w     any "word" character           \w     any "word" character
3121           \W     any "non-word" character           \W     any "non-word" character
3122    
# Line 2568  BACKSLASH Line 3131  BACKSLASH
3131    
3132         For compatibility with Perl, \s does not match the VT  character  (code         For compatibility with Perl, \s does not match the VT  character  (code
3133         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
3134         characters are HT (9), LF (10), FF (12), CR (13), and space (32).         characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If
3135           "use locale;" is included in a Perl script, \s may match the VT charac-
3136           ter. In PCRE, it never does.
3137    
3138           In UTF-8 mode, characters with values greater than 128 never match  \d,
3139           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3140           code character property support is available.  These  sequences  retain
3141           their original meanings from before UTF-8 support was available, mainly
3142           for efficiency reasons.
3143    
3144           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3145           the  other  sequences, these do match certain high-valued codepoints in
3146           UTF-8 mode.  The horizontal space characters are:
3147    
3148             U+0009     Horizontal tab
3149             U+0020     Space
3150             U+00A0     Non-break space
3151             U+1680     Ogham space mark
3152             U+180E     Mongolian vowel separator
3153             U+2000     En quad
3154             U+2001     Em quad
3155             U+2002     En space
3156             U+2003     Em space
3157             U+2004     Three-per-em space
3158             U+2005     Four-per-em space
3159             U+2006     Six-per-em space
3160             U+2007     Figure space
3161             U+2008     Punctuation space
3162             U+2009     Thin space
3163             U+200A     Hair space
3164             U+202F     Narrow no-break space
3165             U+205F     Medium mathematical space
3166             U+3000     Ideographic space
3167    
3168           The vertical space characters are:
3169    
3170             U+000A     Linefeed
3171             U+000B     Vertical tab
3172             U+000C     Formfeed
3173             U+000D     Carriage return
3174             U+0085     Next line
3175             U+2028     Line separator
3176             U+2029     Paragraph separator
3177    
3178         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
3179         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-
3180         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-
3181         specific  matching is taking place (see "Locale support" in the pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3182         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
3183         codes  greater  than  128  are used for accented letters, and these are         systems,  or "french" in Windows, some character codes greater than 128
3184         matched by \w.         are used for accented letters, and these are matched by \w. The use  of
3185           locales with Unicode is discouraged.
3186    
3187       Newline sequences
3188    
3189           Outside  a  character class, by default, the escape sequence \R matches
3190           any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3191           mode \R is equivalent to the following:
3192    
3193             (?>\r\n|\n|\x0b|\f|\r|\x85)
3194    
3195           This  is  an  example  of an "atomic group", details of which are given
3196           below.  This particular group matches either the two-character sequence
3197           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3198           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3199           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3200           is treated as a single unit that cannot be split.
3201    
3202           In UTF-8 mode, two additional characters whose codepoints  are  greater
3203           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3204           rator, U+2029).  Unicode character property support is not  needed  for
3205           these characters to be recognized.
3206    
3207           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3208           the complete set  of  Unicode  line  endings)  by  setting  the  option
3209           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3210           This can be made the default when PCRE is built; if this is  the  case,
3211           the  other  behaviour can be requested via the PCRE_BSR_UNICODE option.
3212           It is also possible to specify these settings  by  starting  a  pattern
3213           string with one of the following sequences:
3214    
3215             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3216             (*BSR_UNICODE)   any Unicode newline sequence
3217    
3218           These override the default and the options given to pcre_compile(), but
3219           they can be overridden by options given to pcre_exec(). Note that these
3220           special settings, which are not Perl-compatible, are recognized only at
3221           the very start of a pattern, and that they must be in  upper  case.  If
3222           more than one of them is present, the last one is used.
3223    
3224         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.  
3225    
3226     Unicode character properties     Unicode character properties
3227    
3228         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3229         tional  escape sequences to match generic character types are available         tional escape sequences that match characters with specific  properties
3230         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3231           limited to testing characters whose codepoints are less than  256,  but
3232          \p{xx}   a character with the xx property         they do work in this mode.  The extra escape sequences are:
3233          \P{xx}   a character without the xx property  
3234          \X       an extended Unicode sequence           \p{xx}   a character with the xx property
3235             \P{xx}   a character without the xx property
3236         The property names represented by xx above are limited to  the  Unicode           \X       an extended Unicode sequence
3237         general  category properties. Each character has exactly one such prop-  
3238         erty, specified by a two-letter abbreviation.  For  compatibility  with         The  property  names represented by xx above are limited to the Unicode
3239         Perl,  negation  can be specified by including a circumflex between the         script names, the general category properties, and "Any", which matches
3240         opening brace and the property name. For example, \p{^Lu} is  the  same         any character (including newline). Other properties such as "InMusical-
3241         as \P{Lu}.         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3242           not match any characters, so always causes a match failure.
3243         If  only  one  letter  is  specified with \p or \P, it includes all the  
3244         properties that start with that letter. In this case, in the absence of         Sets of Unicode characters are defined as belonging to certain scripts.
3245         negation, the curly brackets in the escape sequence are optional; these         A character from one of these sets can be matched using a script  name.
3246         two examples have the same effect:         For example:
3247    
3248             \p{Greek}
3249             \P{Han}
3250    
3251           Those  that are not part of an identified script are lumped together as
3252           "Common". The current list of scripts is:
3253    
3254           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3255           Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3256           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3257           Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3258           gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3259           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3260           Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3261           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3262           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3263    
3264           Each character has exactly one general category property, specified  by
3265           a two-letter abbreviation. For compatibility with Perl, negation can be
3266           specified by including a circumflex between the opening brace  and  the
3267           property name. For example, \p{^Lu} is the same as \P{Lu}.
3268    
3269           If only one letter is specified with \p or \P, it includes all the gen-
3270           eral category properties that start with that letter. In this case,  in
3271           the  absence of negation, the curly brackets in the escape sequence are
3272           optional; these two examples have the same effect:
3273    
3274           \p{L}           \p{L}
3275           \pL           \pL
3276    
3277         The following property codes are supported:         The following general category property codes are supported:
3278    
3279           C     Other           C     Other
3280           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3320  BACKSLASH
3320           Zp    Paragraph separator           Zp    Paragraph separator
3321           Zs    Space separator           Zs    Space separator
3322    
3323         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The special property L& is also supported: it matches a character  that
3324         ported by PCRE.         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3325           classified as a modifier or "other".
3326    
3327           The Cs (Surrogate) property applies only to  characters  in  the  range
3328           U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3329           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3330           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3331           the pcreapi page).
3332    
3333           The long synonyms for these properties  that  Perl  supports  (such  as
3334           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3335           any of these properties with "Is".
3336    
3337           No character that is in the Unicode table has the Cn (unassigned) prop-
3338           erty.  Instead, this property is assumed for any code point that is not
3339           in the Unicode table.
3340    
3341         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3342         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3343    
3344         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3345         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3346    
3347           (?>\PM\pM*)           (?>\PM\pM*)
3348    
3349         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3350         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3351         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3352         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3353           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3354           matches any one character.
3355    
3356         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3357         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3358         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3359         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3360    
3361       Resetting the match start
3362    
3363           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3364           ously  matched  characters  not  to  be  included  in the final matched
3365           sequence. For example, the pattern:
3366    
3367             foo\Kbar
3368    
3369           matches "foobar", but reports that it has matched "bar".  This  feature
3370           is  similar  to  a lookbehind assertion (described below).  However, in
3371           this case, the part of the subject before the real match does not  have
3372           to  be of fixed length, as lookbehind assertions do. The use of \K does
3373           not interfere with the setting of captured  substrings.   For  example,
3374           when the pattern
3375    
3376             (foo)\Kbar
3377    
3378           matches "foobar", the first substring is still set to "foo".
3379    
3380     Simple assertions     Simple assertions
3381    
3382         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3383         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
3384         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3385         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3387  BACKSLASH
3387    
3388           \b     matches at a word boundary           \b     matches at a word boundary
3389           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3390           \A     matches at start of subject           \A     matches at the start of the subject
3391           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3392           \z     matches at end of subject                   also matches before a newline at the end of the subject
3393           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3394             \G     matches at the first matching position in the subject
3395    
3396         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3397         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
# Line 2707  BACKSLASH Line 3411  BACKSLASH
3411         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3412         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
3413         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
3414         that  \Z  matches  before  a  newline that is the last character of the         that \Z matches before a newline at the end of the string as well as at
3415         string as well as at the end of the string, whereas \z matches only  at         the very end, whereas \z matches only at the end.
3416         the end.  
3417           The \G assertion is true only when the current matching position is  at
3418         The  \G assertion is true only when the current matching position is at         the  start point of the match, as specified by the startoffset argument
3419         the start point of the match, as specified by the startoffset  argument         of pcre_exec(). It differs from \A when the  value  of  startoffset  is
3420         of  pcre_exec().  It  differs  from \A when the value of startoffset is         non-zero.  By calling pcre_exec() multiple times with appropriate argu-
        non-zero. By calling pcre_exec() multiple times with appropriate  argu-  
3421         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-
3422         mentation where \G can be useful.         mentation where \G can be useful.
3423    
3424         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
3425         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
3426         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
3427         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3428         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3429    
3430         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
3431         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3432         in the compiled regular expression.         in the compiled regular expression.
3433    
# Line 2732  BACKSLASH Line 3435  BACKSLASH
3435  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3436    
3437         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3438         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3439         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-
3440         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
3441         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3442         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3443    
3444         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
3445         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
3446         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
3447         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3448         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-
3449         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
3450         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3451    
3452         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
3453         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3454         before a newline character that is the last character in the string (by         before a newline at the end of the string (by default). Dollar need not
3455         default). Dollar need not be the last character of  the  pattern  if  a         be  the  last  character of the pattern if a number of alternatives are
3456         number  of alternatives are involved, but it should be the last item in         involved, but it should be the last item in  any  branch  in  which  it
3457         any branch in which it appears.  Dollar has no  special  meaning  in  a         appears. Dollar has no special meaning in a character class.
        character class.  
3458    
3459         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
3460         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
3461         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3462    
3463         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3464         PCRE_MULTILINE option is set. When this is the case, they match immedi-         PCRE_MULTILINE option is set. When  this  is  the  case,  a  circumflex
3465         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3466         respectively, in addition to matching at the start and end of the  sub-         the subject string. It does not match after a  newline  that  ends  the
3467         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3468         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3469         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3470         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3471         in  multiline  mode,  and  a  match for circumflex is possible when the  
3472         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3473         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3474           Consequently, patterns that are anchored in single  line  mode  because
3475         Note  that  the sequences \A, \Z, and \z can be used to match the start         all  branches  start  with  ^ are not anchored in multiline mode, and a
3476         and end of the subject in both modes, and if all branches of a  pattern         match for circumflex is  possible  when  the  startoffset  argument  of
3477         start  with  \A it is always anchored, whether PCRE_MULTILINE is set or         pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3478         not.         PCRE_MULTILINE is set.
3479    
3480           Note that the sequences \A, \Z, and \z can be used to match  the  start
3481           and  end of the subject in both modes, and if all branches of a pattern
3482           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3483           set.
3484    
3485    
3486  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3487    
3488         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-
3489         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3490         default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,         fies  the  end  of  a line. In UTF-8 mode, the matched character may be
3491         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3492         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3493         dling  of dot is entirely independent of the handling of circumflex and         When a line ending is defined as a single character, dot never  matches
3494         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3495         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3496           matches  all characters (including isolated CRs and LFs). When any Uni-
3497           code line endings are being recognized, dot does not match CR or LF  or
3498           any of the other line ending characters.
3499    
3500           The  behaviour  of  dot  with regard to newlines can be changed. If the
3501           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3502           exception. If the two-character sequence CRLF is present in the subject
3503           string, it takes two dots to match it.
3504    
3505           The handling of dot is entirely independent of the handling of  circum-
3506           flex  and  dollar,  the  only relationship being that they both involve
3507           newlines. Dot has no special meaning in a character class.
3508    
3509    
3510  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3511    
3512         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3513         both in and out of UTF-8 mode. Unlike a dot, it can  match  a  newline.         both  in  and  out  of  UTF-8 mode. Unlike a dot, it always matches any
3514         The  feature  is provided in Perl in order to match individual bytes in         line-ending characters. The feature is provided in  Perl  in  order  to
3515         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-
3516         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-
3517         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3518           avoided.
3519    
3520         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3521         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-
# Line 2842  SQUARE BRACKETS AND CHARACTER CLASSES Line 3562  SQUARE BRACKETS AND CHARACTER CLASSES
3562         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
3563         support.         support.
3564    
3565         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3566         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3567         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3568           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3569           of these characters.
3570    
3571         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-
3572         ters  in  a  character  class.  For  example,  [d-m] matches any letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
# Line 2870  SQUARE BRACKETS AND CHARACTER CLASSES Line 3592  SQUARE BRACKETS AND CHARACTER CLASSES
3592         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,
3593         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
3594         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3595         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
3596         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
3597         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3598         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3667  VERTICAL BAR
3667    
3668         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3669         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3670         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3671         left to right, and the first one that succeeds is used. If the alterna-         to right, and the first one that succeeds is used. If the  alternatives
3672         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3673         ing the rest of the main pattern as well as the alternative in the sub-         rest of the main pattern as well as the alternative in the  subpattern.
        pattern.  
3674    
3675    
3676  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
3677    
3678         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and         The  settings  of  the  PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
3679         PCRE_EXTENDED options can be changed  from  within  the  pattern  by  a         PCRE_EXTENDED options (which are Perl-compatible) can be  changed  from
3680         sequence  of  Perl  option  letters  enclosed between "(?" and ")". The         within  the  pattern  by  a  sequence  of  Perl option letters enclosed
3681         option letters are         between "(?" and ")".  The option letters are
3682    
3683           i  for PCRE_CASELESS           i  for PCRE_CASELESS
3684           m  for PCRE_MULTILINE           m  for PCRE_MULTILINE
# Line 2971  INTERNAL OPTION SETTING Line 3692  INTERNAL OPTION SETTING
3692         is also permitted. If a  letter  appears  both  before  and  after  the         is also permitted. If a  letter  appears  both  before  and  after  the
3693         hyphen, the option is unset.         hyphen, the option is unset.
3694    
3695           The  PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
3696           can be changed in the same way as the Perl-compatible options by  using
3697           the characters J, U and X respectively.
3698    
3699         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-
3700         tern parentheses), the change applies to the remainder of  the  pattern         tern parentheses), the change applies to the remainder of  the  pattern
3701         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,
3702         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
3703         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3704    
3705         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
3706         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3707           it, so
3708    
3709           (a(?i)b)c           (a(?i)b)c
3710    
3711         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not         matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
3712         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3713         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3714         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3715         example,         example,
3716    
3717           (a(?i)b|c)           (a(?i)b|c)
3718    
3719         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3720         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3721         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3722         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3723    
        The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed  
        in the same way as the Perl-compatible options by using the  characters  
        U  and X respectively. The (?X) flag setting is special in that it must  
        always occur earlier in the pattern than any of the additional features  
        it  turns on, even when it is at top level. It is best to put it at the  
        start.  
   
3724    
3725  SUBPATTERNS  SUBPATTERNS
3726    
# Line 3013  SUBPATTERNS Line 3732  SUBPATTERNS
3732           cat(aract|erpillar|)           cat(aract|erpillar|)
3733    
3734         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3735         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3736         string.         string.
3737    
3738         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 3042  SUBPATTERNS Line 3761  SUBPATTERNS
3761           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3762    
3763         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3764         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.  
3765    
3766         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3767         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 3060  SUBPATTERNS Line 3777  SUBPATTERNS
3777         "Saturday".         "Saturday".
3778    
3779    
3780    DUPLICATE SUBPATTERN NUMBERS
3781    
3782           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3783           uses the same numbers for its capturing parentheses. Such a  subpattern
3784           starts  with (?| and is itself a non-capturing subpattern. For example,
3785           consider this pattern:
3786    
3787             (?|(Sat)ur|(Sun))day
3788    
3789           Because the two alternatives are inside a (?| group, both sets of  cap-
3790           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3791           you can look at captured substring number  one,  whichever  alternative
3792           matched.  This  construct  is useful when you want to capture part, but
3793           not all, of one of a number of alternatives. Inside a (?| group, paren-
3794           theses  are  numbered as usual, but the number is reset at the start of
3795           each branch. The numbers of any capturing buffers that follow the  sub-
3796           pattern  start after the highest number used in any branch. The follow-
3797           ing example is taken from the Perl documentation.  The  numbers  under-
3798           neath show in which buffer the captured content will be stored.
3799    
3800             # before  ---------------branch-reset----------- after
3801             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3802             # 1            2         2  3        2     3     4
3803    
3804           A  backreference  or  a  recursive call to a numbered subpattern always
3805           refers to the first one in the pattern with the given number.
3806    
3807           An alternative approach to using this "branch reset" feature is to  use
3808           duplicate named subpatterns, as described in the next section.
3809    
3810    
3811  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3812    
3813         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
3814         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3815         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3816         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3817         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3818         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3819         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3820           tax.
3821    
3822           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3823           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3824           to capturing parentheses from other parts of the pattern, such as back-
3825           references,  recursion,  and conditions, can be made by name as well as
3826           by number.
3827    
3828           Names consist of up to  32  alphanumeric  characters  and  underscores.
3829         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3830         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
3831         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3832         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3833         ther details see the pcreapi documentation.         a captured substring by name.
3834    
3835           By  default, a name must be unique within a pattern, but it is possible
3836           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3837           time.  This  can  be useful for patterns where only one instance of the
3838           named parentheses can match. Suppose you want to match the  name  of  a
3839           weekday,  either as a 3-letter abbreviation or as the full name, and in
3840           both cases you want to extract the abbreviation. This pattern (ignoring
3841           the line breaks) does the job:
3842    
3843             (?<DN>Mon|Fri|Sun)(?:day)?|
3844             (?<DN>Tue)(?:sday)?|
3845             (?<DN>Wed)(?:nesday)?|
3846             (?<DN>Thu)(?:rsday)?|
3847             (?<DN>Sat)(?:urday)?
3848    
3849           There  are  five capturing substrings, but only one is ever set after a
3850           match.  (An alternative way of solving this problem is to use a "branch
3851           reset" subpattern, as described in the previous section.)
3852    
3853           The  convenience  function  for extracting the data by name returns the
3854           substring for the first (and in this example, the only)  subpattern  of
3855           that  name  that  matched.  This saves searching to find which numbered
3856           subpattern it was. If you make a reference to a non-unique  named  sub-
3857           pattern  from elsewhere in the pattern, the one that corresponds to the
3858           lowest number is used. For further details of the interfaces  for  han-
3859           dling named subpatterns, see the pcreapi documentation.
3860    
3861    
3862  REPETITION  REPETITION
# Line 3083  REPETITION Line 3865  REPETITION
3865         following items:         following items:
3866    
3867           a literal data character           a literal data character
3868           the . metacharacter           the dot metacharacter
3869           the \C escape sequence           the \C escape sequence
3870           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3871             the \R escape sequence
3872           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3873           a character class           a character class
3874           a back reference (see next section)           a back reference (see next section)
# Line 3125  REPETITION Line 3908  REPETITION
3908         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3909         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3910    
3911         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3912         quantifiers have single-character abbreviations:         ter abbreviations:
3913    
3914           *    is equivalent to {0,}           *    is equivalent to {0,}
3915           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3178  REPETITION Line 3961  REPETITION
3961         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
3962         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3963    
3964         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
3965         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3966         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
3967         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3189  REPETITION Line 3972  REPETITION
3972         minimum or maximum.         minimum or maximum.
3973    
3974         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-
3975         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,
3976         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3977         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3978         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
3979         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
3980           by \A.
3981    
3982         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-
3983         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-
3984         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3985    
3986         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3987         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3988         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3989         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3990    
3991           (.*)abc\1           (.*)abc\1
3992    
3993         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3994         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3995    
3996         When a capturing subpattern is repeated, the value captured is the sub-         When a capturing subpattern is repeated, the value captured is the sub-
# Line 3215  REPETITION Line 3999  REPETITION
3999           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
4000    
4001         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4002         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
4003         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
4004         tions. For example, after         tions. For example, after
4005    
4006           /(a|(b))+/           /(a|(b))+/
# Line 3226  REPETITION Line 4010  REPETITION
4010    
4011  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4012    
4013         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
4014         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
4015         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
4016         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,
4017         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
4018         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
4019           no point in carrying on.
4020    
4021         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
4022         line         line
# Line 3245  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4030  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4030         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
4031         to be re-evaluated in this way.         to be re-evaluated in this way.
4032    
4033         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
4034         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
4035         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:  
4036    
4037           (?>\d+)foo           (?>\d+)foo
4038    
# Line 3277  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4061  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4061    
4062           \d++foo           \d++foo
4063    
4064         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4065         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         example:
        simpler forms of atomic group. However, there is no difference  in  the  
        meaning  or  processing  of  a possessive quantifier and the equivalent  
        atomic group.  
4066    
4067         The possessive quantifier syntax is an extension to the Perl syntax. It           (abc|xyz){2,3}+
4068         originates in Sun's Java package.  
4069           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4070           PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4071           simpler  forms  of atomic group. However, there is no difference in the
4072           meaning of a possessive quantifier and  the  equivalent  atomic  group,
4073           though  ther