/[pcre]/code/trunk/doc/pcre.txt
ViewVC logotype

Diff of /code/trunk/doc/pcre.txt

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 83 by nigel, Sat Feb 24 21:41:06 2007 UTC revision 231 by ph10, Tue Sep 11 11:15:33 2007 UTC
# 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    REVISION
258    
259  Last updated: 07 March 2005         Last updated: 09 August 2007
260  Copyright (c) 1997-2005 University of Cambridge.         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  Last updated: 15 August 2005  
515  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
516    
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. 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         5. Callouts are supported, but the value of the  capture_top  field  is         6.  Callouts  are  supported, but the value of the capture_top field is
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.
716         rithm.  
717    
718    AUTHOR
719    
720           Philip Hazel
721           University Computing Service
722           Cambridge CB2 3QH, England.
723    
724    
725  Last updated: 28 February 2005  REVISION
726  Copyright (c) 1997-2005 University of Cambridge.  
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.
1569    
1570             PCRE_INFO_JCHANGED
1571    
1572           Return  1  if the (?J) option setting is used in the pattern, otherwise
1573           0. The fourth argument should point to an int variable. The (?J) inter-
1574           nal option setting changes the local PCRE_DUPNAMES option.
1575    
1576           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1577    
1578         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
1579         matched  string,  other  than  at  its  start,  if such a byte has been         matched string, other than at its  start,  if  such  a  byte  has  been
1580         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1581         is  no such byte, -1 is returned. For anchored patterns, a last literal         is no such byte, -1 is returned. For anchored patterns, a last  literal
1582         byte is recorded only if it follows something of variable  length.  For         byte  is  recorded only if it follows something of variable length. For
1583         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1584         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1585    
# Line 1272  INFORMATION ABOUT A PATTERN Line 1587  INFORMATION ABOUT A PATTERN
1587           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1588           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1589    
1590         PCRE supports the use of named as well as numbered capturing  parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1591         ses.  The names are just an additional way of identifying the parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1592         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1593         pcre_get_named_substring()  is  provided  for  extracting an individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1594         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
1595         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
1596         the correct pointers in the output vector (described  with  pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1597         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
1598         which is described by these three values.         described by these three values.
1599    
1600         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
1601         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1602         of each entry; both of these  return  an  int  value.  The  entry  size         of  each  entry;  both  of  these  return  an int value. The entry size
1603         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1604         a pointer to the first entry of the table  (a  pointer  to  char).  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1605         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-
1606         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-
1607         sponding  name,  zero  terminated. The names are in alphabetical order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1608         For example, consider the following pattern  (assume  PCRE_EXTENDED  is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1609         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1610           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1611           ignored):
1612    
1613           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1614           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1615    
1616         There  are  four  named subpatterns, so the table has four entries, and         There are four named subpatterns, so the table has  four  entries,  and
1617         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,
1618         with non-printing bytes shows in hexadecimal, and undefined bytes shown         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1619         as ??:         as ??:
1620    
# Line 1306  INFORMATION ABOUT A PATTERN Line 1623  INFORMATION ABOUT A PATTERN
1623           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1624           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1625    
1626         When writing code to extract data  from  named  subpatterns  using  the         When  writing  code  to  extract  data from named subpatterns using the
1627         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
1628         be different for each compiled pattern.         to be different for each compiled pattern.
1629    
1630             PCRE_INFO_OKPARTIAL
1631    
1632           Return  1 if the pattern can be used for partial matching, otherwise 0.
1633           The fourth argument should point to an int  variable.  The  pcrepartial
1634           documentation  lists  the restrictions that apply to patterns when par-
1635           tial matching is used.
1636    
1637           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1638    
1639         Return a copy of the options with which the pattern was  compiled.  The         Return a copy of the options with which the pattern was  compiled.  The
1640         fourth  argument  should  point to an unsigned long int variable. These         fourth  argument  should  point to an unsigned long int variable. These
1641         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1642         by any top-level option settings within the pattern itself.         by any top-level option settings at the start of the pattern itself. In
1643           other words, they are the options that will be in force  when  matching
1644           starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1645           the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1646           and PCRE_EXTENDED.
1647    
1648         A  pattern  is  automatically  anchored by PCRE if all of its top-level         A  pattern  is  automatically  anchored by PCRE if all of its top-level
1649         alternatives begin with one of the following:         alternatives begin with one of the following:
# Line 1428  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1756  MATCHING A PATTERN: THE TRADITIONAL FUNC
1756         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
1757         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
1758         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-
1759         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
1760         lows:         fields (not necessarily in this order):
1761    
1762           unsigned long int flags;           unsigned long int flags;
1763           void *study_data;           void *study_data;
1764           unsigned long int match_limit;           unsigned long int match_limit;
1765             unsigned long int match_limit_recursion;
1766           void *callout_data;           void *callout_data;
1767           const unsigned char *tables;           const unsigned char *tables;
1768    
# Line 1442  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1771  MATCHING A PATTERN: THE TRADITIONAL FUNC
1771    
1772           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1773           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1774             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1775           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1776           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1777    
# Line 1458  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1788  MATCHING A PATTERN: THE TRADITIONAL FUNC
1788         repeats.         repeats.
1789    
1790         Internally,  PCRE uses a function called match() which it calls repeat-         Internally,  PCRE uses a function called match() which it calls repeat-
1791         edly (sometimes recursively). The limit is imposed  on  the  number  of         edly (sometimes recursively). The limit set by match_limit  is  imposed
1792         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
1793         limiting the amount of recursion and backtracking that can take  place.         has the effect of limiting the amount of  backtracking  that  can  take
1794         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
1795         position in the subject string.         for each position in the subject string.
1796    
1797         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
1798         default  default  is 10 million, which handles all but the most extreme         default  default  is 10 million, which handles all but the most extreme
1799         cases. You can reduce  the  default  by  suppling  pcre_exec()  with  a         cases. You can override the default  by  suppling  pcre_exec()  with  a
1800         pcre_extra  block  in  which match_limit is set to a smaller value, and         pcre_extra     block    in    which    match_limit    is    set,    and
1801         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
1802         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1803    
1804           The  match_limit_recursion field is similar to match_limit, but instead
1805           of limiting the total number of times that match() is called, it limits
1806           the  depth  of  recursion. The recursion depth is a smaller number than
1807           the total number of calls, because not all calls to match() are  recur-
1808           sive.  This limit is of use only if it is set smaller than match_limit.
1809    
1810           Limiting the recursion depth limits the amount of  stack  that  can  be
1811           used, or, when PCRE has been compiled to use memory on the heap instead
1812           of the stack, the amount of heap memory that can be used.
1813    
1814           The default value for match_limit_recursion can be  set  when  PCRE  is
1815           built;  the  default  default  is  the  same  value  as the default for
1816           match_limit. You can override the default by suppling pcre_exec()  with
1817           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1818           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1819           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1820    
1821         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  pcre_callout  field is used in conjunction with the "callout" fea-
1822         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1823    
# Line 1488  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 1835  MATCHING A PATTERN: THE TRADITIONAL FUNC
1835     Option bits for pcre_exec()     Option bits for pcre_exec()
1836    
1837         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.
1838         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,
1839         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1840           PCRE_PARTIAL.
1841    
1842           PCRE_ANCHORED           PCRE_ANCHORED
1843    
1844         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1845         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1846         turned  out to be anchored by virtue of its contents, it cannot be made         turned out to be anchored by virtue of its contents, it cannot be  made
1847         unachored at matching time.         unachored at matching time.
1848    
1849             PCRE_BSR_ANYCRLF
1850             PCRE_BSR_UNICODE
1851    
1852           These options (which are mutually exclusive) control what the \R escape
1853           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1854           or  to  match  any Unicode newline sequence. These options override the
1855           choice that was made or defaulted when the pattern was compiled.
1856    
1857             PCRE_NEWLINE_CR
1858             PCRE_NEWLINE_LF
1859             PCRE_NEWLINE_CRLF
1860             PCRE_NEWLINE_ANYCRLF
1861             PCRE_NEWLINE_ANY
1862    
1863           These options override  the  newline  definition  that  was  chosen  or
1864           defaulted  when the pattern was compiled. For details, see the descrip-
1865           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1866           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1867           ters. It may also alter the way the match position is advanced after  a
1868           match failure for an unanchored pattern.
1869    
1870           When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
1871           set, and a match attempt for an unanchored pattern fails when the  cur-
1872           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
1873           explicit matches for  CR  or  LF  characters,  the  match  position  is
1874           advanced by two characters instead of one, in other words, to after the
1875           CRLF.
1876    
1877           The above rule is a compromise that makes the most common cases work as
1878           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
1879           option is not set), it does not match the string "\r\nA" because, after
1880           failing  at the start, it skips both the CR and the LF before retrying.
1881           However, the pattern [\r\n]A does match that string,  because  it  con-
1882           tains an explicit CR or LF reference, and so advances only by one char-
1883           acter after the first failure.
1884    
1885           An explicit match for CR of LF is either a literal appearance of one of
1886           those  characters,  or  one  of the \r or \n escape sequences. Implicit
1887           matches such as [^X] do not count, nor does \s (which includes  CR  and
1888           LF in the characters that it matches).
1889    
1890           Notwithstanding  the above, anomalous effects may still occur when CRLF
1891           is a valid newline sequence and explicit \r or \n escapes appear in the
1892           pattern.
1893    
1894           PCRE_NOTBOL           PCRE_NOTBOL
1895    
1896         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1897         the  beginning  of  a  line, so the circumflex metacharacter should not         the beginning of a line, so the  circumflex  metacharacter  should  not
1898         match before it. Setting this without PCRE_MULTILINE (at compile  time)         match  before it. Setting this without PCRE_MULTILINE (at compile time)
1899         causes  circumflex  never to match. This option affects only the behav-         causes circumflex never to match. This option affects only  the  behav-
1900         iour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1901    
1902           PCRE_NOTEOL           PCRE_NOTEOL
1903    
1904         This option specifies that the end of the subject string is not the end         This option specifies that the end of the subject string is not the end
1905         of  a line, so the dollar metacharacter should not match it nor (except         of a line, so the dollar metacharacter should not match it nor  (except
1906         in multiline mode) a newline immediately before it. Setting this  with-         in  multiline mode) a newline immediately before it. Setting this with-
1907         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1908         option affects only the behaviour of the dollar metacharacter. It  does         option  affects only the behaviour of the dollar metacharacter. It does
1909         not affect \Z or \z.         not affect \Z or \z.
1910    
1911           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1912    
1913         An empty string is not considered to be a valid match if this option is         An empty string is not considered to be a valid match if this option is
1914         set. If there are alternatives in the pattern, they are tried.  If  all         set.  If  there are alternatives in the pattern, they are tried. If all
1915         the  alternatives  match  the empty string, the entire match fails. For         the alternatives match the empty string, the entire  match  fails.  For
1916         example, if the pattern         example, if the pattern
1917    
1918           a?b?           a?b?
1919    
1920         is applied to a string not beginning with "a" or "b",  it  matches  the         is  applied  to  a string not beginning with "a" or "b", it matches the
1921         empty  string at the start of the subject. With PCRE_NOTEMPTY set, this         empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1922         match is not valid, so PCRE searches further into the string for occur-         match is not valid, so PCRE searches further into the string for occur-
1923         rences of "a" or "b".         rences of "a" or "b".
1924    
1925         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-         Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1926         cial case of a pattern match of the empty  string  within  its  split()         cial  case  of  a  pattern match of the empty string within its split()
1927         function,  and  when  using  the /g modifier. It is possible to emulate         function, and when using the /g modifier. It  is  possible  to  emulate
1928         Perl's behaviour after matching a null string by first trying the match         Perl's behaviour after matching a null string by first trying the match
1929         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1930         if that fails by advancing the starting offset (see below)  and  trying         if  that  fails by advancing the starting offset (see below) and trying
1931         an ordinary match again. There is some code that demonstrates how to do         an ordinary match again. There is some code that demonstrates how to do
1932         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1933    
1934           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1935    
1936         When PCRE_UTF8 is set at compile time, the validity of the subject as a         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1937         UTF-8  string is automatically checked when pcre_exec() is subsequently         UTF-8 string is automatically checked when pcre_exec() is  subsequently
1938         called.  The value of startoffset is also checked  to  ensure  that  it         called.   The  value  of  startoffset is also checked to ensure that it
1939         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence         points to the start of a UTF-8 character. There is a  discussion  about
1940         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         the  validity  of  UTF-8 strings in the section on UTF-8 support in the
1941         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is         main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
1942         returned.         pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
1943           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1944    
1945         If you already know that your subject is valid, and you  want  to  skip         If you already know that your subject is valid, and you  want  to  skip
1946         these    checks    for   performance   reasons,   you   can   set   the         these    checks    for   performance   reasons,   you   can   set   the
# Line 1633  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2027  MATCHING A PATTERN: THE TRADITIONAL FUNC
2027         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-
2028         tor[1],  identify  the  portion  of  the  subject string matched by the         tor[1],  identify  the  portion  of  the  subject string matched by the
2029         entire pattern. The next pair is used for the first  capturing  subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
2030         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
2031         pairs that have been set. If there are no  capturing  subpatterns,  the         highest numbered pair that has been set. For example, if two substrings
2032         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
2033         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
2034           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.  
2035    
2036         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
2037         of the string that it matched that is returned.         of the string that it matched that is returned.
2038    
2039         If  the vector is too small to hold all the captured substring offsets,         If the vector is too small to hold all the captured substring  offsets,
2040         it is used as far as possible (up to two-thirds of its length), and the         it is used as far as possible (up to two-thirds of its length), and the
2041         function  returns a value of zero. In particular, if the substring off-         function returns a value of zero. In particular, if the substring  off-
2042         sets are not of interest, pcre_exec() may be called with ovector passed         sets are not of interest, pcre_exec() may be called with ovector passed
2043         as  NULL  and  ovecsize  as zero. However, if the pattern contains back         as NULL and ovecsize as zero. However, if  the  pattern  contains  back
2044         references and the ovector is not big enough to  remember  the  related         references  and  the  ovector is not big enough to remember the related
2045         substrings,  PCRE has to get additional memory for use during matching.         substrings, PCRE has to get additional memory for use during  matching.
2046         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
2047    
2048         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
2049         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
2050         that will allow for n captured substrings, in addition to  the  offsets         ovector  that  will allow for n captured substrings, in addition to the
2051         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.
2052    
2053           It is possible for capturing subpattern number n+1 to match  some  part
2054           of the subject when subpattern n has not been used at all. For example,
2055           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2056           return from the function is 4, and subpatterns 1 and 3 are matched, but
2057           2 is not. When this happens, both values in  the  offset  pairs  corre-
2058           sponding to unused subpatterns are set to -1.
2059    
2060           Offset  values  that correspond to unused subpatterns at the end of the
2061           expression are also set to -1. For example,  if  the  string  "abc"  is
2062           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2063           matched. The return from the function is 2, because  the  highest  used
2064           capturing subpattern number is 1. However, you can refer to the offsets
2065           for the second and third capturing subpatterns if  you  wish  (assuming
2066           the vector is large enough, of course).
2067    
2068           Some  convenience  functions  are  provided for extracting the captured
2069           substrings as separate strings. These are described below.
2070    
2071     Return values from pcre_exec()     Error return values from pcre_exec()
2072    
2073         If  pcre_exec()  fails, it returns a negative number. The following are         If pcre_exec() fails, it returns a negative number. The  following  are
2074         defined in the header file:         defined in the header file:
2075    
2076           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1676  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2079  MATCHING A PATTERN: THE TRADITIONAL FUNC
2079    
2080           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
2081    
2082         Either code or subject was passed as NULL,  or  ovector  was  NULL  and         Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2083         ovecsize was not zero.         ovecsize was not zero.
2084    
2085           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1685  MATCHING A PATTERN: THE TRADITIONAL FUNC Line 2088  MATCHING A PATTERN: THE TRADITIONAL FUNC
2088    
2089           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
2090    
2091         PCRE  stores a 4-byte "magic number" at the start of the compiled code,         PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2092         to catch the case when it is passed a junk pointer and to detect when a         to catch the case when it is passed a junk pointer and to detect when a
2093         pattern that was compiled in an environment of one endianness is run in         pattern that was compiled in an environment of one endianness is run in
2094         an environment with the other endianness. This is the error  that  PCRE         an  environment  with the other endianness. This is the error that PCRE
2095         gives when the magic number is not present.         gives when the magic number is not present.
2096    
2097           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
2098    
2099         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
2100         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
2101         overwriting of the compiled pattern.         overwriting of the compiled pattern.
2102    
2103           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2104    
2105         If  a  pattern contains back references, but the ovector that is passed         If a pattern contains back references, but the ovector that  is  passed
2106         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
2107         PCRE  gets  a  block of memory at the start of matching to use for this         PCRE gets a block of memory at the start of matching to  use  for  this
2108         purpose. If the call via pcre_malloc() fails, this error is given.  The         purpose.  If the call via pcre_malloc() fails, this error is given. The
2109         memory is automatically freed at the end of matching.         memory is automatically freed at the end of matching.
2110    
2111           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2112    
2113         This  error is used by the pcre_copy_substring(), pcre_get_substring(),         This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2114         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2115         returned by pcre_exec().         returned by pcre_exec().
2116    
2117           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
2118    
2119         The  recursion  and backtracking limit, as specified by the match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
2120         field in a pcre_extra structure (or defaulted)  was  reached.  See  the         pcre_extra  structure  (or  defaulted) was reached. See the description
2121         description above.         above.
2122    
2123           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
2124    
2125         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
2126         use by callout functions that want to yield a distinctive  error  code.         use  by  callout functions that want to yield a distinctive error code.
2127         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
2128    
2129           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
2130    
2131         A  string  that contains an invalid UTF-8 byte sequence was passed as a         A string that contains an invalid UTF-8 byte sequence was passed  as  a
2132         subject.         subject.
2133    
2134           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
2135    
2136         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
2137         value  of startoffset did not point to the beginning of a UTF-8 charac-         value of startoffset did not point to the beginning of a UTF-8  charac-
2138         ter.         ter.
2139    
2140           PCRE_ERROR_PARTIAL        (-12)           PCRE_ERROR_PARTIAL        (-12)
2141    
2142         The subject string did not match, but it did match partially.  See  the         The  subject  string did not match, but it did match partially. See the
2143         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
2144    
2145           PCRE_ERROR_BADPARTIAL     (-13)           PCRE_ERROR_BADPARTIAL     (-13)
2146    
2147         The  PCRE_PARTIAL  option  was  used with a compiled pattern containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2148         items that are not supported for partial matching. See the  pcrepartial         items  that are not supported for partial matching. See the pcrepartial
2149         documentation for details of partial matching.         documentation for details of partial matching.
2150    
2151           PCRE_ERROR_INTERNAL       (-14)           PCRE_ERROR_INTERNAL       (-14)
2152    
2153         An  unexpected  internal error has occurred. This error could be caused         An unexpected internal error has occurred. This error could  be  caused
2154         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2155    
2156           PCRE_ERROR_BADCOUNT       (-15)           PCRE_ERROR_BADCOUNT       (-15)
2157    
2158         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.
2159    
2160             PCRE_ERROR_RECURSIONLIMIT (-21)
2161    
2162           The internal recursion limit, as specified by the match_limit_recursion
2163           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2164           description above.
2165    
2166             PCRE_ERROR_BADNEWLINE     (-23)
2167    
2168           An invalid combination of PCRE_NEWLINE_xxx options was given.
2169    
2170           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2171    
2172    
2173  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
# Line 1768  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2183  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2183         int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2184              int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2185    
2186         Captured  substrings  can  be  accessed  directly  by using the offsets         Captured substrings can be  accessed  directly  by  using  the  offsets
2187         returned by pcre_exec() in  ovector.  For  convenience,  the  functions         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2188         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2189         string_list() are provided for extracting captured substrings  as  new,         string_list()  are  provided for extracting captured substrings as new,
2190         separate,  zero-terminated strings. These functions identify substrings         separate, zero-terminated strings. These functions identify  substrings
2191         by number. The next section describes functions  for  extracting  named         by  number.  The  next section describes functions for extracting named
2192         substrings.  A  substring  that  contains  a  binary  zero is correctly         substrings.
2193         extracted and has a further zero added on the end, but  the  result  is  
2194         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2195           a  further zero added on the end, but the result is not, of course, a C
2196           string.  However, you can process such a string  by  referring  to  the
2197           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2198           string().  Unfortunately, the interface to pcre_get_substring_list() is
2199           not  adequate for handling strings containing binary zeros, because the
2200           end of the final string is not independently indicated.
2201    
2202         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-
2203         tions: subject is the subject string that has  just  been  successfully         tions:  subject  is  the subject string that has just been successfully
2204         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
2205         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
2206         were  captured  by  the match, including the substring that matched the         were captured by the match, including the substring  that  matched  the
2207         entire regular expression. This is the value returned by pcre_exec() if         entire regular expression. This is the value returned by pcre_exec() if
2208         it  is greater than zero. If pcre_exec() returned zero, indicating that         it is greater than zero. If pcre_exec() returned zero, indicating  that
2209         it ran out of space in ovector, the value passed as stringcount  should         it  ran out of space in ovector, the value passed as stringcount should
2210         be the number of elements in the vector divided by three.         be the number of elements in the vector divided by three.
2211    
2212         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2213         single substring, whose number is given as  stringnumber.  A  value  of         single  substring,  whose  number  is given as stringnumber. A value of
2214         zero  extracts  the  substring that matched the entire pattern, whereas         zero extracts the substring that matched the  entire  pattern,  whereas
2215         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2216         string(),  the  string  is  placed  in buffer, whose length is given by         string(), the string is placed in buffer,  whose  length  is  given  by
2217         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2218         obtained  via  pcre_malloc,  and its address is returned via stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2219         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
2220         the terminating zero, or one of         the terminating zero, or one of these error codes:
2221    
2222           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2223    
2224         The  buffer  was too small for pcre_copy_substring(), or the attempt to         The buffer was too small for pcre_copy_substring(), or the  attempt  to
2225         get memory failed for pcre_get_substring().         get memory failed for pcre_get_substring().
2226    
2227           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
2228    
2229         There is no substring whose number is stringnumber.         There is no substring whose number is stringnumber.
2230    
2231         The pcre_get_substring_list()  function  extracts  all  available  sub-         The  pcre_get_substring_list()  function  extracts  all  available sub-
2232         strings  and  builds  a list of pointers to them. All this is done in a         strings and builds a list of pointers to them. All this is  done  in  a
2233         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
2234         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
2235         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
2236         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
2237           error code
2238    
2239           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2240    
# Line 1831  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2253  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2253         tively.  They  do  nothing  more  than  call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
2254         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.
2255         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-
2256         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2257         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-
2258         vided.         vided.
2259    
# Line 1854  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2276  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2276         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-
2277         ber.  For example, for this pattern         ber.  For example, for this pattern
2278    
2279           (a+)b(?P<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2280    
2281         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
2282         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
2283         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-
2284         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
2285         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2286           subpattern of that name.
2287    
2288         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
2289         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
2290         are also two functions that do the whole job.         are also two functions that do the whole job.
2291    
2292         Most    of    the    arguments   of   pcre_copy_named_substring()   and         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2293         pcre_get_named_substring() are the same  as  those  for  the  similarly         pcre_get_named_substring()  are  the  same  as  those for the similarly
2294         named  functions  that extract by number. As these are described in the         named functions that extract by number. As these are described  in  the
2295         previous section, they are not re-described here. There  are  just  two         previous  section,  they  are not re-described here. There are just two
2296         differences:         differences:
2297    
2298         First,  instead  of a substring number, a substring name is given. Sec-         First, instead of a substring number, a substring name is  given.  Sec-
2299         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
2300         to  the compiled pattern. This is needed in order to gain access to the         to the compiled pattern. This is needed in order to gain access to  the
2301         name-to-number translation table.         name-to-number translation table.
2302    
2303         These functions call pcre_get_stringnumber(), and if it succeeds,  they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2304         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2305         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2306           behaviour may not be what you want (see the next section).
2307    
2308    
2309    DUPLICATE SUBPATTERN NAMES
2310    
2311           int pcre_get_stringtable_entries(const pcre *code,
2312                const char *name, char **first, char **last);
2313    
2314           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2315           subpatterns  are  not  required  to  be unique. Normally, patterns with
2316           duplicate names are such that in any one match, only one of  the  named
2317           subpatterns  participates. An example is shown in the pcrepattern docu-
2318           mentation.
2319    
2320           When   duplicates   are   present,   pcre_copy_named_substring()    and
2321           pcre_get_named_substring()  return the first substring corresponding to
2322           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2323           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2324           function returns one of the numbers that are associated with the  name,
2325           but it is not defined which it is.
2326    
2327           If  you want to get full details of all captured substrings for a given
2328           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2329           first argument is the compiled pattern, and the second is the name. The
2330           third and fourth are pointers to variables which  are  updated  by  the
2331           function. After it has run, they point to the first and last entries in
2332           the name-to-number table  for  the  given  name.  The  function  itself
2333           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2334           there are none. The format of the table is described above in the  sec-
2335           tion  entitled  Information  about  a  pattern.  Given all the relevant
2336           entries for the name, you can extract each of their numbers, and  hence
2337           the captured data, if any.
2338    
2339    
2340  FINDING ALL POSSIBLE MATCHES  FINDING ALL POSSIBLE MATCHES
2341    
2342         The traditional matching function uses a  similar  algorithm  to  Perl,         The  traditional  matching  function  uses a similar algorithm to Perl,
2343         which stops when it finds the first match, starting at a given point in         which stops when it finds the first match, starting at a given point in
2344         the subject. If you want to find all possible matches, or  the  longest         the  subject.  If you want to find all possible matches, or the longest
2345         possible  match,  consider using the alternative matching function (see         possible match, consider using the alternative matching  function  (see
2346         below) instead. If you cannot use the alternative function,  but  still         below)  instead.  If you cannot use the alternative function, but still
2347         need  to  find all possible matches, you can kludge it up by making use         need to find all possible matches, you can kludge it up by  making  use
2348         of the callout facility, which is described in the pcrecallout documen-         of the callout facility, which is described in the pcrecallout documen-
2349         tation.         tation.
2350    
2351         What you have to do is to insert a callout right at the end of the pat-         What you have to do is to insert a callout right at the end of the pat-
2352         tern.  When your callout function is called, extract and save the  cur-         tern.   When your callout function is called, extract and save the cur-
2353         rent  matched  substring.  Then  return  1, which forces pcre_exec() to         rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2354         backtrack and try other alternatives. Ultimately, when it runs  out  of         backtrack  and  try other alternatives. Ultimately, when it runs out of
2355         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.         matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2356    
2357    
# Line 1907  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2362  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2362              int options, int *ovector, int ovecsize,              int options, int *ovector, int ovecsize,
2363              int *workspace, int wscount);              int *workspace, int wscount);
2364    
2365         The  function  pcre_dfa_exec()  is  called  to  match  a subject string         The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2366         against a compiled pattern, using a "DFA" matching algorithm. This  has         against  a  compiled pattern, using a matching algorithm that scans the
2367         different  characteristics to the normal algorithm, and is not compati-         subject string just once, and does not backtrack.  This  has  different
2368         ble with Perl. Some of the features of PCRE patterns are not supported.         characteristics  to  the  normal  algorithm, and is not compatible with
2369         Nevertheless, there are times when this kind of matching can be useful.         Perl. Some of the features of PCRE patterns are not  supported.  Never-
2370         For a discussion of the two matching algorithms, see  the  pcrematching         theless,  there are times when this kind of matching can be useful. For
2371         documentation.         a discussion of the two matching algorithms, see the pcrematching docu-
2372           mentation.
2373    
2374         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
2375         pcre_exec(), plus two extras. The ovector argument is used in a differ-         pcre_exec(), plus two extras. The ovector argument is used in a differ-
# Line 1925  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2381  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2381         workspace vector should contain at least 20 elements. It  is  used  for         workspace vector should contain at least 20 elements. It  is  used  for
2382         keeping  track  of  multiple  paths  through  the  pattern  tree.  More         keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2383         workspace will be needed for patterns and subjects where  there  are  a         workspace will be needed for patterns and subjects where  there  are  a
2384         lot of possible matches.         lot of potential matches.
2385    
2386         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_dfa_exec():
2387    
2388           int rc;           int rc;
2389           int ovector[10];           int ovector[10];
2390           int wspace[20];           int wspace[20];
2391           rc = pcre_exec(           rc = pcre_dfa_exec(
2392             re,             /* result of pcre_compile() */             re,             /* result of pcre_compile() */
2393             NULL,           /* we didn't study the pattern */             NULL,           /* we didn't study the pattern */
2394             "some string",  /* the subject string */             "some string",  /* the subject string */
# Line 1947  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2403  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2403     Option bits for pcre_dfa_exec()     Option bits for pcre_dfa_exec()
2404    
2405         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
2406         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-
2407         PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,         LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2408         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
2409         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
2410         repeated here.         not repeated here.
2411    
2412           PCRE_PARTIAL           PCRE_PARTIAL
2413    
# Line 1966  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2422  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2422           PCRE_DFA_SHORTEST           PCRE_DFA_SHORTEST
2423    
2424         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to         Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2425         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-
2426         algorithm works, this is necessarily the shortest possible match at the         tive algorithm works, this is necessarily the shortest  possible  match
2427         first possible matching point in the subject string.         at the first possible matching point in the subject string.
2428    
2429           PCRE_DFA_RESTART           PCRE_DFA_RESTART
2430    
# Line 2004  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2460  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2460         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,
2461         which  is  the  number of matched substrings. The substrings themselves         which  is  the  number of matched substrings. The substrings themselves
2462         are returned in ovector. Each string uses two elements;  the  first  is         are returned in ovector. Each string uses two elements;  the  first  is
2463         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
2464         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
2465         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
2466         with the way pcre_exec() returns data, even though the meaning  of  the         compatibility with the way pcre_exec() returns data,  even  though  the
2467         strings is different.)         meaning of the strings is different.)
2468    
2469         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-
2470         est matching string is given first. If there were too many  matches  to         est matching string is given first. If there were too many  matches  to
# Line 2030  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2486  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2486    
2487           PCRE_ERROR_DFA_UCOND      (-17)           PCRE_ERROR_DFA_UCOND      (-17)
2488    
2489         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
2490         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
2491         supported.         in a specific group. These are not supported.
2492    
2493           PCRE_ERROR_DFA_UMLIMIT    (-18)           PCRE_ERROR_DFA_UMLIMIT    (-18)
2494    
# Line 2052  MATCHING A PATTERN: THE ALTERNATIVE FUNC Line 2508  MATCHING A PATTERN: THE ALTERNATIVE FUNC
2508         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
2509         should be extremely rare, as a vector of size 1000 is used.         should be extremely rare, as a vector of size 1000 is used.
2510    
2511  Last updated: 16 May 2005  
2512  Copyright (c) 1997-2005 University of Cambridge.  SEE ALSO
2513    
2514           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2515           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2516    
2517    
2518    AUTHOR
2519    
2520           Philip Hazel
2521           University Computing Service
2522           Cambridge CB2 3QH, England.
2523    
2524    
2525    REVISION
2526    
2527           Last updated: 11 September 2007
2528           Copyright (c) 1997-2007 University of Cambridge.
2529  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2530    
2531    
# Line 2080  PCRE CALLOUTS Line 2552  PCRE CALLOUTS
2552         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2553         points:         points:
2554    
2555           (?C1)eabc(?C2)def           (?C1)abc(?C2)def
2556    
2557         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
2558         called, PCRE automatically  inserts  callouts,  all  with  number  255,         called, PCRE automatically  inserts  callouts,  all  with  number  255,
# Line 2155  THE CALLOUT INTERFACE Line 2627  THE CALLOUT INTERFACE
2627         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2628         were passed to pcre_exec().         were passed to pcre_exec().
2629    
2630         The start_match field contains the offset within the subject  at  which         The start_match field normally contains the offset within  the  subject
2631         the  current match attempt started. If the pattern is not anchored, the         at  which  the  current  match  attempt started. However, if the escape
2632         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
2633         pattern for different starting points in the subject.         modified  starting  point.  If the pattern is not anchored, the callout
2634           function may be called several times from the same point in the pattern
2635           for different starting points in the subject.
2636    
2637         The  current_position  field  contains the offset within the subject of         The  current_position  field  contains the offset within the subject of
2638         the current match pointer.         the current match pointer.
# Line 2211  RETURN VALUES Line 2685  RETURN VALUES
2685         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
2686         itself.         itself.
2687    
2688  Last updated: 28 February 2005  
2689  Copyright (c) 1997-2005 University of Cambridge.  AUTHOR
2690    
2691           Philip Hazel
2692           University Computing Service
2693           Cambridge CB2 3QH, England.
2694    
2695    
2696    REVISION
2697    
2698           Last updated: 29 May 2007
2699           Copyright (c) 1997-2007 University of Cambridge.
2700  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2701    
2702    
# Line 2226  NAME Line 2710  NAME
2710  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2711    
2712         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2713         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2714         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2715           some features that are expected to be in the forthcoming Perl 5.10.
2716         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2717         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
2718           of  what  it does have are given in the section on UTF-8 support in the
2719           main pcre page.
2720    
2721         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2722         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 2743  DIFFERENCES BETWEEN PCRE AND PERL
2743         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
2744         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2745         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-
2746         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2747           derived properties Any and L&.
2748    
2749         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2750         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2751         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2752         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2753         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2754    
2755             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 2272  DIFFERENCES BETWEEN PCRE AND PERL Line 2759  DIFFERENCES BETWEEN PCRE AND PERL
2759             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2760             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2761    
2762         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2763         classes.         classes.
2764    
2765         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2766         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2767         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
2768         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2769         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2770    
2771         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2772         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2773         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2774    
2775           10.  There are some differences that are concerned with the settings of
2776           captured strings when part of  a  pattern  is  repeated.  For  example,
2777           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2778         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2779    
2780         10. PCRE provides some extensions to the Perl regular expression facil-         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2781         ities:         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2782           the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2783           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2784           ture group; this is different to Perl.
2785    
2786           12. PCRE provides some extensions to the Perl regular expression facil-
2787           ities.   Perl  5.10  will  include new features that are not in earlier
2788           versions, some of which (such as named parentheses) have been  in  PCRE
2789           for some time. This list is with respect to Perl 5.10:
2790    
2791         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2792         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2793         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2794    
2795         (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 $
2796         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2797    
2798         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2799         cial meaning is faulted.         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2800           ignored.  (Perl can be made to issue a warning.)
2801    
2802         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2803         fiers is inverted, that is, by default they are not greedy, but if fol-         fiers is inverted, that is, by default they are not greedy, but if fol-
# Line 2309  DIFFERENCES BETWEEN PCRE AND PERL Line 2809  DIFFERENCES BETWEEN PCRE AND PERL
2809         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2810         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2811    
2812         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive         (g) The \R escape sequence can be restricted to match only CR,  LF,  or
2813         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,         CRLF by the PCRE_BSR_ANYCRLF option.
        which PCRE cannot support.)  
2814    
2815         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The callout facility is PCRE-specific.
2816    
2817         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) The partial matching facility is PCRE-specific.
        Sun's Java package.  
2818    
2819         (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,
2820           even on different hosts that have the other endianness.
2821    
2822         (k) The callout facility is PCRE-specific.         (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
2823           different way and is not Perl-compatible.
2824    
2825         (l) The partial matching facility is PCRE-specific.         (l)  PCRE  recognizes some special sequences such as (*CR) at the start
2826           of a pattern that set overall options that cannot be changed within the
2827           pattern.
2828    
        (m) Patterns compiled by PCRE can be saved and re-used at a later time,  
        even on different hosts that have the other endianness.  
2829    
2830         (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a  AUTHOR
2831         different way and is not Perl-compatible.  
2832           Philip Hazel
2833           University Computing Service
2834           Cambridge CB2 3QH, England.
2835    
2836    
2837  Last updated: 28 February 2005  REVISION
2838  Copyright (c) 1997-2005 University of Cambridge.  
2839           Last updated: 11 September 2007
2840           Copyright (c) 1997-2007 University of Cambridge.
2841  ------------------------------------------------------------------------------  ------------------------------------------------------------------------------
2842    
2843    
# Line 2344  NAME Line 2850  NAME
2850    
2851  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2852    
2853         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax and semantics of the regular expressions that are supported
2854         are described below. Regular expressions are also described in the Perl         by PCRE are described in detail below. There is a quick-reference  syn-
2855         documentation  and  in  a  number  of books, some of which have copious         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2856         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published         described in its own documentation, and regular expressions in  general
2857         by  O'Reilly, covers regular expressions in great detail. This descrip-         are  covered in a number of books, some of which have copious examples.
2858         tion of PCRE's regular expressions is intended as reference material.         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2859           O'Reilly,  covers regular expressions in great detail. This description
2860           of PCRE's regular expressions is intended as reference material.
2861    
2862         The original operation of PCRE was on strings of  one-byte  characters.         The original operation of PCRE was on strings of  one-byte  characters.
2863         However,  there is now also support for UTF-8 character strings. To use         However,  there is now also support for UTF-8 character strings. To use
# Line 2363  PCRE REGULAR EXPRESSION DETAILS Line 2871  PCRE REGULAR EXPRESSION DETAILS
2871         ported  by  PCRE when its main matching function, pcre_exec(), is used.         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2872         From  release  6.0,   PCRE   offers   a   second   matching   function,         From  release  6.0,   PCRE   offers   a   second   matching   function,
2873         pcre_dfa_exec(),  which matches using a different algorithm that is not         pcre_dfa_exec(),  which matches using a different algorithm that is not
2874         Perl-compatible. The advantages and disadvantages  of  the  alternative         Perl-compatible. Some of the features discussed below are not available
2875         function, and how it differs from the normal function, are discussed in         when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2876         the pcrematching page.         alternative function, and how it differs from the normal function,  are
2877           discussed in the pcrematching page.
2878    
2879    
2880    NEWLINE CONVENTIONS
2881    
2882           PCRE  supports five different conventions for indicating line breaks in
2883           strings: a single CR (carriage return) character, a  single  LF  (line-
2884           feed) character, the two-character sequence CRLF, any of the three pre-
2885           ceding, or any Unicode newline sequence. The pcreapi page  has  further
2886           discussion  about newlines, and shows how to set the newline convention
2887           in the options arguments for the compiling and matching functions.
2888    
2889           It is also possible to specify a newline convention by starting a  pat-
2890           tern string with one of the following five sequences:
2891    
2892             (*CR)        carriage return
2893             (*LF)        linefeed
2894             (*CRLF)      carriage return, followed by linefeed
2895             (*ANYCRLF)   any of the three above
2896             (*ANY)       all Unicode newline sequences
2897    
2898           These override the default and the options given to pcre_compile(). For
2899           example, on a Unix system where LF is the default newline sequence, the
2900           pattern
2901    
2902             (*CR)a.b
2903    
2904           changes the convention to CR. That pattern matches "a\nb" because LF is
2905           no longer a newline. Note that these special settings,  which  are  not
2906           Perl-compatible,  are  recognized  only at the very start of a pattern,
2907           and that they must be in upper case.  If  more  than  one  of  them  is
2908           present, the last one is used.
2909    
2910           The  newline  convention  does  not  affect what the \R escape sequence
2911           matches. By default, this is any Unicode  newline  sequence,  for  Perl
2912           compatibility.  However, this can be changed; see the description of \R
2913           in the section entitled "Newline sequences" below.
2914    
2915    
2916    CHARACTERS AND METACHARACTERS
2917    
2918         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2919         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
# Line 2391  PCRE REGULAR EXPRESSION DETAILS Line 2939  PCRE REGULAR EXPRESSION DETAILS
2939    
2940         There are two different sets of metacharacters: those that  are  recog-         There are two different sets of metacharacters: those that  are  recog-
2941         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2942         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized within square brackets.  Outside  square  brackets,
2943         metacharacters are as follows:         the metacharacters are as follows:
2944    
2945           \      general escape character with several uses           \      general escape character with several uses
2946           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 2439  BACKSLASH Line 2987  BACKSLASH
2987    
2988         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2989         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
2990         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2991         An escaping backslash can be used to include a whitespace or #  charac-         ing backslash can be used to include a whitespace  or  #  character  as
2992         ter as part of the pattern.         part of the pattern.
2993    
2994         If  you  want  to remove the special meaning from a sequence of charac-         If  you  want  to remove the special meaning from a sequence of charac-
2995         ters, you can do so by putting them between \Q and \E. This is  differ-         ters, you can do so by putting them between \Q and \E. This is  differ-
# Line 2472  BACKSLASH Line 3020  BACKSLASH
3020           \cx       "control-x", where x is any character           \cx       "control-x", where x is any character
3021           \e        escape (hex 1B)           \e        escape (hex 1B)
3022           \f        formfeed (hex 0C)           \f        formfeed (hex 0C)
3023           \n        newline (hex 0A)           \n        linefeed (hex 0A)
3024           \r        carriage return (hex 0D)           \r        carriage return (hex 0D)
3025           \t        tab (hex 09)           \t        tab (hex 09)
3026           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
3027           \xhh      character with hex code hh           \xhh      character with hex code hh
3028           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
3029    
3030         The  precise  effect of \cx is as follows: if x is a lower case letter,         The  precise  effect of \cx is as follows: if x is a lower case letter,
3031         it is converted to upper case. Then bit 6 of the character (hex 40)  is         it is converted to upper case. Then bit 6 of the character (hex 40)  is
# Line 2485  BACKSLASH Line 3033  BACKSLASH
3033         becomes hex 7B.         becomes hex 7B.
3034    
3035         After \x, from zero to two hexadecimal digits are read (letters can  be         After \x, from zero to two hexadecimal digits are read (letters can  be
3036         in  upper or lower case). In UTF-8 mode, any number of hexadecimal dig-         in  upper  or  lower case). Any number of hexadecimal digits may appear
3037         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
3038         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,
3039         7FFFFFFF). If characters other than hexadecimal digits  appear  between         the maximum value in hexadecimal is 7FFFFFFF. Note that this is  bigger
3040         \x{  and }, or if there is no terminating }, this form of escape is not         than the largest Unicode code point, which is 10FFFF.
3041         recognized. Instead, the initial \x will  be  interpreted  as  a  basic  
3042         hexadecimal  escape, with no following digits, giving a character whose         If  characters  other than hexadecimal digits appear between \x{ and },
3043         value is zero.         or if there is no terminating }, this form of escape is not recognized.
3044           Instead,  the  initial  \x  will  be interpreted as a basic hexadecimal
3045           escape, with no following digits, giving a  character  whose  value  is
3046           zero.
3047    
3048         Characters whose value is less than 256 can be defined by either of the         Characters whose value is less than 256 can be defined by either of the
3049         two  syntaxes for \x 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-
3050         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}.
3051         \x{dc}.  
3052           After  \0  up  to two further octal digits are read. If there are fewer
3053         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
3054         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
3055         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
3056         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.  
3057    
3058         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-
3059         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
3060         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
3061         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
3062         expression, the entire  sequence  is  taken  as  a  back  reference.  A         expression,  the  entire  sequence  is  taken  as  a  back reference. A
3063         description  of how this works is given later, following the discussion         description of how this works is given later, following the  discussion
3064         of parenthesized subpatterns.         of parenthesized subpatterns.
3065    
3066         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
3067         and  there have not been that many capturing subpatterns, PCRE re-reads         and there have not been that many capturing subpatterns, PCRE  re-reads
3068         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-
3069         gle byte from the least significant 8 bits of the value. Any subsequent         erate a data character. Any subsequent digits stand for themselves.  In
3070         digits stand for themselves.  For example:         non-UTF-8  mode,  the  value  of a character specified in octal must be
3071           less than \400. In UTF-8 mode, values up to  \777  are  permitted.  For
3072           example:
3073    
3074           \040   is another way of writing a space           \040   is another way of writing a space
3075           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 2535  BACKSLASH Line 3086  BACKSLASH
3086           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
3087                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
3088    
3089         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
3090         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
3091    
3092         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
3093         character (in UTF-8 mode) can be used both inside and outside character         inside  and  outside character classes. In addition, inside a character
3094         classes.  In  addition,  inside  a  character class, the sequence \b is         class, the sequence \b is interpreted as the backspace  character  (hex
3095         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"
3096         interpreted  as  the  character  "X".  Outside a character class, these         and "X", respectively. Outside a character class, these sequences  have
3097         sequences have different meanings (see below).         different meanings (see below).
3098    
3099       Absolute and relative back references
3100    
3101           The  sequence  \g followed by an unsigned or a negative number, option-
3102           ally enclosed in braces, is an absolute or relative back  reference.  A
3103           named back reference can be coded as \g{name}. Back references are dis-
3104           cussed later, following the discussion of parenthesized subpatterns.
3105    
3106     Generic character types     Generic character types
3107    
3108         The third use of backslash is for specifying generic  character  types.         Another use of backslash is for specifying generic character types. The
3109         The following are always recognized:         following are always recognized:
3110    
3111           \d     any decimal digit           \d     any decimal digit
3112           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
3113             \h     any horizontal whitespace character
3114             \H     any character that is not a horizontal whitespace character
3115           \s     any whitespace character           \s     any whitespace character
3116           \S     any character that is not a whitespace character           \S     any character that is not a whitespace character
3117             \v     any vertical whitespace character
3118             \V     any character that is not a vertical whitespace character
3119           \w     any "word" character           \w     any "word" character
3120           \W     any "non-word" character           \W     any "non-word" character
3121    
# Line 2568  BACKSLASH Line 3130  BACKSLASH
3130    
3131         For compatibility with Perl, \s does not match the VT  character  (code         For compatibility with Perl, \s does not match the VT  character  (code
3132         11).   This makes it different from the the POSIX "space" class. The \s         11).   This makes it different from the the POSIX "space" class. The \s
3133         characters are HT (9), LF (10), FF (12), CR (13), and space (32).         characters are HT (9), LF (10), FF (12), CR (13), and  space  (32).  If
3134           "use locale;" is included in a Perl script, \s may match the VT charac-
3135           ter. In PCRE, it never does.
3136    
3137           In UTF-8 mode, characters with values greater than 128 never match  \d,
3138           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
3139           code character property support is available.  These  sequences  retain
3140           their original meanings from before UTF-8 support was available, mainly
3141           for efficiency reasons.
3142    
3143           The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
3144           the  other  sequences, these do match certain high-valued codepoints in
3145           UTF-8 mode.  The horizontal space characters are:
3146    
3147             U+0009     Horizontal tab
3148             U+0020     Space
3149             U+00A0     Non-break space
3150             U+1680     Ogham space mark
3151             U+180E     Mongolian vowel separator
3152             U+2000     En quad
3153             U+2001     Em quad
3154             U+2002     En space
3155             U+2003     Em space
3156             U+2004     Three-per-em space
3157             U+2005     Four-per-em space
3158             U+2006     Six-per-em space
3159             U+2007     Figure space
3160             U+2008     Punctuation space
3161             U+2009     Thin space
3162             U+200A     Hair space
3163             U+202F     Narrow no-break space
3164             U+205F     Medium mathematical space
3165             U+3000     Ideographic space
3166    
3167           The vertical space characters are:
3168    
3169             U+000A     Linefeed
3170             U+000B     Vertical tab
3171             U+000C     Formfeed
3172             U+000D     Carriage return
3173             U+0085     Next line
3174             U+2028     Line separator
3175             U+2029     Paragraph separator
3176    
3177         A "word" character is an underscore or any character less than 256 that         A "word" character is an underscore or any character less than 256 that
3178         is  a  letter  or  digit.  The definition of letters and digits is con-         is  a  letter  or  digit.  The definition of letters and digits is con-
3179         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-
3180         specific  matching is taking place (see "Locale support" in the pcreapi         specific  matching is taking place (see "Locale support" in the pcreapi
3181         page). For example, in the  "fr_FR"  (French)  locale,  some  character         page). For example, in a French locale such  as  "fr_FR"  in  Unix-like
3182         codes  greater  than  128  are used for accented letters, and these are         systems,  or "french" in Windows, some character codes greater than 128
3183         matched by \w.         are used for accented letters, and these are matched by \w. The use  of
3184           locales with Unicode is discouraged.
3185    
3186       Newline sequences
3187    
3188           Outside  a  character class, by default, the escape sequence \R matches
3189           any Unicode newline sequence. This is a Perl 5.10 feature. In non-UTF-8
3190           mode \R is equivalent to the following:
3191    
3192             (?>\r\n|\n|\x0b|\f|\r|\x85)
3193    
3194           This  is  an  example  of an "atomic group", details of which are given
3195           below.  This particular group matches either the two-character sequence
3196           CR  followed  by  LF,  or  one  of  the single characters LF (linefeed,
3197           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
3198           return, U+000D), or NEL (next line, U+0085). The two-character sequence
3199           is treated as a single unit that cannot be split.
3200    
3201           In UTF-8 mode, two additional characters whose codepoints  are  greater
3202           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
3203           rator, U+2029).  Unicode character property support is not  needed  for
3204           these characters to be recognized.
3205    
3206           It is possible to restrict \R to match only CR, LF, or CRLF (instead of
3207           the complete set  of  Unicode  line  endings)  by  setting  the  option
3208           PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
3209           This can be made the default when PCRE is built; if this is  the  case,
3210           the  other  behaviour can be requested via the PCRE_BSR_UNICODE option.
3211           It is also possible to specify these settings  by  starting  a  pattern
3212           string with one of the following sequences:
3213    
3214             (*BSR_ANYCRLF)   CR, LF, or CRLF only
3215             (*BSR_UNICODE)   any Unicode newline sequence
3216    
3217           These override the default and the options given to pcre_compile(), but
3218           they can be overridden by options given to pcre_exec(). Note that these
3219           special settings, which are not Perl-compatible, are recognized only at
3220           the very start of a pattern, and that they must be in  upper  case.  If
3221           more than one of them is present, the last one is used.
3222    
3223         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.  
3224    
3225     Unicode character properties     Unicode character properties
3226    
3227         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
3228         tional  escape sequences to match generic character types are available         tional escape sequences that match characters with specific  properties
3229         when UTF-8 mode is selected. They are:         are  available.   When not in UTF-8 mode, these sequences are of course
3230           limited to testing characters whose codepoints are less than  256,  but
3231          \p{xx}   a character with the xx property         they do work in this mode.  The extra escape sequences are:
3232          \P{xx}   a character without the xx property  
3233          \X       an extended Unicode sequence           \p{xx}   a character with the xx property
3234             \P{xx}   a character without the xx property
3235         The property names represented by xx above are limited to  the  Unicode           \X       an extended Unicode sequence
3236         general  category properties. Each character has exactly one such prop-  
3237         erty, specified by a two-letter abbreviation.  For  compatibility  with         The  property  names represented by xx above are limited to the Unicode
3238         Perl,  negation  can be specified by including a circumflex between the         script names, the general category properties, and "Any", which matches
3239         opening brace and the property name. For example, \p{^Lu} is  the  same         any character (including newline). Other properties such as "InMusical-
3240         as \P{Lu}.         Symbols" are not currently supported by PCRE. Note  that  \P{Any}  does
3241           not match any characters, so always causes a match failure.
3242         If  only  one  letter  is  specified with \p or \P, it includes all the  
3243         properties that start with that letter. In this case, in the absence of         Sets of Unicode characters are defined as belonging to certain scripts.
3244         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.
3245         two examples have the same effect:         For example:
3246    
3247             \p{Greek}
3248             \P{Han}
3249    
3250           Those  that are not part of an identified script are lumped together as
3251           "Common". The current list of scripts is:
3252    
3253           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
3254           Buhid,   Canadian_Aboriginal,   Cherokee,  Common,  Coptic,  Cuneiform,
3255           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
3256           Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
3257           gana, Inherited, Kannada,  Katakana,  Kharoshthi,  Khmer,  Lao,  Latin,
3258           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
3259           Ogham, Old_Italic, Old_Persian, Oriya, Osmanya,  Phags_Pa,  Phoenician,
3260           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
3261           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
3262    
3263           Each character has exactly one general category property, specified  by
3264           a two-letter abbreviation. For compatibility with Perl, negation can be
3265           specified by including a circumflex between the opening brace  and  the
3266           property name. For example, \p{^Lu} is the same as \P{Lu}.
3267    
3268           If only one letter is specified with \p or \P, it includes all the gen-
3269           eral category properties that start with that letter. In this case,  in
3270           the  absence of negation, the curly brackets in the escape sequence are
3271           optional; these two examples have the same effect:
3272    
3273           \p{L}           \p{L}
3274           \pL           \pL
3275    
3276         The following property codes are supported:         The following general category property codes are supported:
3277    
3278           C     Other           C     Other
3279           Cc    Control           Cc    Control
# Line 2653  BACKSLASH Line 3319  BACKSLASH
3319           Zp    Paragraph separator           Zp    Paragraph separator
3320           Zs    Space separator           Zs    Space separator
3321    
3322         Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-         The special property L& is also supported: it matches a character  that
3323         ported by PCRE.         has  the  Lu,  Ll, or Lt property, in other words, a letter that is not
3324           classified as a modifier or "other".
3325    
3326           The Cs (Surrogate) property applies only to  characters  in  the  range
3327           U+D800  to  U+DFFF. Such characters are not valid in UTF-8 strings (see
3328           RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
3329           ing  has  been  turned off (see the discussion of PCRE_NO_UTF8_CHECK in
3330           the pcreapi page).
3331    
3332           The long synonyms for these properties  that  Perl  supports  (such  as
3333           \p{Letter})  are  not  supported by PCRE, nor is it permitted to prefix
3334           any of these properties with "Is".
3335    
3336           No character that is in the Unicode table has the Cn (unassigned) prop-
3337           erty.  Instead, this property is assumed for any code point that is not
3338           in the Unicode table.
3339    
3340         Specifying  caseless  matching  does not affect these escape sequences.         Specifying caseless matching does not affect  these  escape  sequences.
3341         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3342    
3343         The \X escape matches any number of Unicode  characters  that  form  an         The  \X  escape  matches  any number of Unicode characters that form an
3344         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3345    
3346           (?>\PM\pM*)           (?>\PM\pM*)
3347    
3348         That  is,  it matches a character without the "mark" property, followed         That is, it matches a character without the "mark"  property,  followed
3349         by zero or more characters with the "mark"  property,  and  treats  the         by  zero  or  more  characters with the "mark" property, and treats the
3350         sequence  as  an  atomic group (see below).  Characters with the "mark"         sequence as an atomic group (see below).  Characters  with  the  "mark"
3351         property are typically accents that affect the preceding character.         property  are  typically  accents  that affect the preceding character.
3352           None of them have codepoints less than 256, so  in  non-UTF-8  mode  \X
3353           matches any one character.
3354    
3355         Matching characters by Unicode property is not fast, because  PCRE  has         Matching  characters  by Unicode property is not fast, because PCRE has
3356         to  search  a  structure  that  contains data for over fifteen thousand         to search a structure that contains  data  for  over  fifteen  thousand
3357         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3358         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3359    
3360       Resetting the match start
3361    
3362           The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
3363           ously  matched  characters  not  to  be  included  in the final matched
3364           sequence. For example, the pattern:
3365    
3366             foo\Kbar
3367    
3368           matches "foobar", but reports that it has matched "bar".  This  feature
3369           is  similar  to  a lookbehind assertion (described below).  However, in
3370           this case, the part of the subject before the real match does not  have
3371           to  be of fixed length, as lookbehind assertions do. The use of \K does
3372           not interfere with the setting of captured  substrings.   For  example,
3373           when the pattern
3374    
3375             (foo)\Kbar
3376    
3377           matches "foobar", the first substring is still set to "foo".
3378    
3379     Simple assertions     Simple assertions
3380    
3381         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3382         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
3383         a  match, without consuming any characters from the subject string. The         a  match, without consuming any characters from the subject string. The
3384         use of subpatterns for more complicated assertions is described  below.         use of subpatterns for more complicated assertions is described  below.
# Line 2684  BACKSLASH Line 3386  BACKSLASH
3386    
3387           \b     matches at a word boundary           \b     matches at a word boundary
3388           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3389           \A     matches at start of subject           \A     matches at the start of the subject
3390           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3391           \z     matches at end of subject                   also matches before a newline at the end of the subject
3392           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3393             \G     matches at the first matching position in the subject
3394    
3395         These  assertions may not appear in character classes (but note that \b         These  assertions may not appear in character classes (but note that \b
3396         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 3410  BACKSLASH
3410         However, if the startoffset argument of pcre_exec() is non-zero,  indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3411         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
3412         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
3413         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
3414         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.
3415         the end.  
3416           The \G assertion is true only when the current matching position is  at
3417         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
3418         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
3419         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-  
3420         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-
3421         mentation where \G can be useful.         mentation where \G can be useful.
3422    
3423         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
3424         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
3425         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
3426         previously  matched  string was empty. Because PCRE does just one match         previously matched string was empty. Because PCRE does just  one  match
3427         at a time, it cannot reproduce this behaviour.         at a time, it cannot reproduce this behaviour.
3428    
3429         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
3430         anchored to the starting match position, and the "anchored" flag is set         anchored to the starting match position, and the "anchored" flag is set
3431         in the compiled regular expression.         in the compiled regular expression.
3432    
# Line 2732  BACKSLASH Line 3434  BACKSLASH
3434  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
3435    
3436         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
3437         character  is  an  assertion  that is true only if the current matching         character is an assertion that is true only  if  the  current  matching
3438         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-
3439         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
3440         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE  option  is  unset. Inside a character class, circumflex
3441         has an entirely different meaning (see below).         has an entirely different meaning (see below).
3442    
3443         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
3444         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
3445         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
3446         branch. If all possible alternatives start with a circumflex, that  is,         branch.  If all possible alternatives start with a circumflex, that is,
3447         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-
3448         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
3449         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
3450    
3451         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
3452         matching point is at the end of  the  subject  string,  or  immediately         matching  point  is  at  the  end of the subject string, or immediately
3453         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
3454         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
3455         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
3456         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.  
3457    
3458         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
3459         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
3460         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3461    
3462         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3463         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
3464         ately  after  and  immediately  before  an  internal newline character,         matches  immediately after internal newlines as well as at the start of
3465         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
3466         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         string.  A dollar matches before any newlines in the string, as well as
3467         string "def\nabc" (where \n represents a newline character)  in  multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3468         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3469         in single line mode because all branches start with ^ are not  anchored         not indicate newlines.
3470         in  multiline  mode,  and  a  match for circumflex is possible when the  
3471         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3472         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3473           Consequently, patterns that are anchored in single  line  mode  because
3474         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
3475         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
3476         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
3477         not.         PCRE_MULTILINE is set.
3478    
3479           Note that the sequences \A, \Z, and \z can be used to match  the  start
3480           and  end of the subject in both modes, and if all branches of a pattern
3481           start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3482           set.
3483    
3484    
3485  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3486    
3487         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-
3488         ter  in  the  subject,  including a non-printing character, but not (by         ter in the subject string except (by default) a character  that  signi-
3489         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
3490         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3491         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-  
3492         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
3493         dollar, the only relationship being  that  they  both  involve  newline         that  character; when the two-character sequence CRLF is used, dot does
3494         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3495           matches  all characters (including isolated CRs and LFs). When any Uni-
3496           code line endings are being recognized, dot does not match CR or LF  or
3497           any of the other line ending characters.
3498    
3499           The  behaviour  of  dot  with regard to newlines can be changed. If the
3500           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3501           exception. If the two-character sequence CRLF is present in the subject
3502           string, it takes two dots to match it.
3503    
3504           The handling of dot is entirely independent of the handling of  circum-
3505           flex  and  dollar,  the  only relationship being that they both involve
3506           newlines. Dot has no special meaning in a character class.
3507    
3508    
3509  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3510    
3511         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3512         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
3513         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
3514         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-
3515         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-
3516         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3517           avoided.
3518    
3519         PCRE does not allow \C to appear in  lookbehind  assertions  (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3520         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 3561  SQUARE BRACKETS AND CHARACTER CLASSES
3561         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
3562         support.         support.
3563    
3564         The newline character is never treated in any special way in  character         Characters that might indicate line breaks are  never  treated  in  any
3565         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         special  way  when  matching  character  classes,  whatever line-ending
3566         options is. A class such as [^a] will always match a newline.         sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3567           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3568           of these characters.
3569    
3570         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-
3571         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 3591  SQUARE BRACKETS AND CHARACTER CLASSES
3591         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,
3592         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
3593         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3594         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
3595         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
3596         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3597         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2945  VERTICAL BAR Line 3666  VERTICAL BAR
3666    
3667         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3668         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3669         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3670         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
3671         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3672         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.  
3673    
3674    
3675  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2977  INTERNAL OPTION SETTING Line 3697  INTERNAL OPTION SETTING
3697         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
3698         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3699    
3700         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
3701         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3702           it, so
3703    
3704           (a(?i)b)c           (a(?i)b)c
3705    
3706         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
3707         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3708         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3709         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3710         example,         example,
3711    
3712           (a(?i)b|c)           (a(?i)b|c)
3713    
3714         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3715         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3716         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3717         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3718    
3719         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3720         in the same way as the Perl-compatible options by using the  characters         can  be changed in the same way as the Perl-compatible options by using
3721         U  and X respectively. The (?X) flag setting is special in that it must         the characters J, U and X respectively.
        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.  
3722    
3723    
3724  SUBPATTERNS  SUBPATTERNS
# Line 3013  SUBPATTERNS Line 3731  SUBPATTERNS
3731           cat(aract|erpillar|)           cat(aract|erpillar|)
3732    
3733         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3734         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3735         string.         string.
3736    
3737         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 3760  SUBPATTERNS
3760           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3761    
3762         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3763         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.  
3764    
3765         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3766         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 3776  SUBPATTERNS
3776         "Saturday".         "Saturday".
3777    
3778    
3779    DUPLICATE SUBPATTERN NUMBERS
3780    
3781           Perl 5.10 introduced a feature whereby each alternative in a subpattern
3782           uses the same numbers for its capturing parentheses. Such a  subpattern
3783           starts  with (?| and is itself a non-capturing subpattern. For example,
3784           consider this pattern:
3785    
3786             (?|(Sat)ur|(Sun))day
3787    
3788           Because the two alternatives are inside a (?| group, both sets of  cap-
3789           turing  parentheses  are  numbered one. Thus, when the pattern matches,
3790           you can look at captured substring number  one,  whichever  alternative
3791           matched.  This  construct  is useful when you want to capture part, but
3792           not all, of one of a number of alternatives. Inside a (?| group, paren-
3793           theses  are  numbered as usual, but the number is reset at the start of
3794           each branch. The numbers of any capturing buffers that follow the  sub-
3795           pattern  start after the highest number used in any branch. The follow-
3796           ing example is taken from the Perl documentation.  The  numbers  under-
3797           neath show in which buffer the captured content will be stored.
3798    
3799             # before  ---------------branch-reset----------- after
3800             / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
3801             # 1            2         2  3        2     3     4
3802    
3803           A  backreference  or  a  recursive call to a numbered subpattern always
3804           refers to the first one in the pattern with the given number.
3805    
3806           An alternative approach to using this "branch reset" feature is to  use
3807           duplicate named subpatterns, as described in the next section.
3808    
3809    
3810  NAMED SUBPATTERNS  NAMED SUBPATTERNS
3811    
3812         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
3813         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3814         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3815         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3816         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3817         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3818         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3819           tax.
3820    
3821           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3822           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3823           to capturing parentheses from other parts of the pattern, such as back-
3824           references,  recursion,  and conditions, can be made by name as well as
3825           by number.
3826    
3827           Names consist of up to  32  alphanumeric  characters  and  underscores.
3828         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3829         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
3830         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3831         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3832         ther details see the pcreapi documentation.         a captured substring by name.
3833    
3834           By  default, a name must be unique within a pattern, but it is possible
3835           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3836           time.  This  can  be useful for patterns where only one instance of the
3837           named parentheses can match. Suppose you want to match the  name  of  a
3838           weekday,  either as a 3-letter abbreviation or as the full name, and in
3839           both cases you want to extract the abbreviation. This pattern (ignoring
3840           the line breaks) does the job:
3841    
3842             (?<DN>Mon|Fri|Sun)(?:day)?|
3843             (?<DN>Tue)(?:sday)?|
3844             (?<DN>Wed)(?:nesday)?|
3845             (?<DN>Thu)(?:rsday)?|
3846             (?<DN>Sat)(?:urday)?
3847    
3848           There  are  five capturing substrings, but only one is ever set after a
3849           match.  (An alternative way of solving this problem is to use a "branch
3850           reset" subpattern, as described in the previous section.)
3851    
3852           The  convenience  function  for extracting the data by name returns the
3853           substring for the first (and in this example, the only)  subpattern  of
3854           that  name  that  matched.  This saves searching to find which numbered
3855           subpattern it was. If you make a reference to a non-unique  named  sub-
3856           pattern  from elsewhere in the pattern, the one that corresponds to the
3857           lowest number is used. For further details of the interfaces  for  han-
3858           dling named subpatterns, see the pcreapi documentation.
3859    
3860    
3861  REPETITION  REPETITION
# Line 3083  REPETITION Line 3864  REPETITION
3864         following items:         following items:
3865    
3866           a literal data character           a literal data character
3867           the . metacharacter           the dot metacharacter
3868           the \C escape sequence           the \C escape sequence
3869           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3870             the \R escape sequence
3871           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3872           a character class           a character class
3873           a back reference (see next section)           a back reference (see next section)
# Line 3125  REPETITION Line 3907  REPETITION
3907         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3908         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3909    
3910         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3911         quantifiers have single-character abbreviations:         ter abbreviations:
3912    
3913           *    is equivalent to {0,}           *    is equivalent to {0,}
3914           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 3178  REPETITION Line 3960  REPETITION
3960         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
3961         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3962    
3963         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
3964         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3965         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
3966         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 3189  REPETITION Line 3971  REPETITION
3971         minimum or maximum.         minimum or maximum.
3972    
3973         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-
3974         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,
3975         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3976         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3977         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
3978         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
3979           by \A.
3980    
3981         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-
3982         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-
3983         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3984    
3985         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3986         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3987         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3988         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3989    
3990           (.*)abc\1           (.*)abc\1
3991    
3992         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3993         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3994    
3995         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 3998  REPETITION
3998           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3999    
4000         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
4001         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
4002         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
4003         tions. For example, after         tions. For example, after
4004    
4005           /(a|(b))+/           /(a|(b))+/
# Line 3226  REPETITION Line 4009  REPETITION
4009    
4010  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
4011    
4012         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
4013         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
4014         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
4015         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,
4016         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
4017         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
4018           no point in carrying on.
4019    
4020         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
4021         line         line
# Line 3245  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4029  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4029         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
4030         to be re-evaluated in this way.         to be re-evaluated in this way.
4031    
4032         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
4033         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
4034         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:  
4035    
4036           (?>\d+)foo           (?>\d+)foo
4037    
# Line 3277  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 4060  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
4060    
4061           \d++foo           \d++foo
4062    
4063         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Note that a possessive quantifier can be used with an entire group, for
4064         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.  
4065    
4066         The possessive quantifier syntax is an extension to the Perl syntax. It           (abc|xyz){2,3}+
4067         originates in Sun's Java package.  
4068           Possessive   quantifiers   are   always  greedy;  the  setting  of  the
4069           PCRE_UNGREEDY option is ignored. They are a convenient notation for the
4070           simpler  forms  of atomic group. However, there is no difference in the
4071           meaning of a possessive quantifier and  the  equivalent  atomic  group,
4072           though  there  may  be a performance difference; possessive quantifiers
4073           should be slightly faster.
4074    
4075           The possessive quantifier syntax is an extension to the Perl  5.8  syn-
4076           tax.   Jeffrey  Friedl  originated the idea (and the name) in the first
4077           edition of his book. Mike McCloskey liked it, so implemented it when he
4078           built  Sun's Java package, and PCRE copied it from there. It ultimately
4079           found its way into Perl at release 5.10.
4080    
4081           PCRE has an optimization that automatically "possessifies" certain sim-
4082           ple  pattern  constructs.  For  example, the sequence A+B is treated as
4083           A++B because there is no point in backtracking into a sequence  of  A's
4084           when B must follow.
4085    
4086         When  a  pattern  contains an unlimited repeat inside a subpattern that         When  a  pattern  contains an unlimited repeat inside a subpattern that
4087         can itself be repeated an unlimited number of  times,  the  use  of  an         can itself be repeated an unlimited number of  times,  the  use  of  an
# Line 3325  BACK REFERENCES Line 4122  BACK REFERENCES
4122         it  is  always  taken  as a back reference, and causes an error only if         it  is  always  taken  as a back reference, and causes an error only if
4123         there are not that many capturing left parentheses in the  entire  pat-         there are not that many capturing left parentheses in the  entire  pat-
4124         tern.  In  other words, the parentheses that are referenced need not be         tern.  In  other words, the parentheses that are referenced need not be
4125         to the left of the reference for numbers less than 10. See the  subsec-         to the left of the reference for numbers less than 10. A "forward  back
4126         tion  entitled  "Non-printing  characters" above for further details of         reference"  of  this  type can make sense when a repetition is involved
4127         the handling of digits following a backslash.         and the subpattern to the right has participated in an  earlier  itera-
4128           tion.
4129    
4130           It  is  not  possible to have a numerical "forward back reference" to a
4131           subpattern whose number is 10 or  more  using  this  syntax  because  a
4132           sequence  such  as  \50 is interpreted as a character defined in octal.
4133           See the subsection entitled "Non-printing characters" above for further
4134           details  of  the  handling of digits following a backslash. There is no
4135           such problem when named parentheses are used. A back reference  to  any
4136           subpattern is possible using named parentheses (see below).
4137    
4138           Another  way  of  avoiding  the ambiguity inherent in the use of digits
4139           following a backslash is to use the \g escape sequence, which is a fea-
4140           ture  introduced  in  Perl  5.10.  This  escape  must be followed by an
4141           unsigned number or a negative number, optionally  enclosed  in  braces.
4142           These examples are all identical:
4143    
4144             (ring), \1
4145             (ring), \g1
4146             (ring), \g{1}
4147    
4148           An  unsigned number specifies an absolute reference without the ambigu-
4149           ity that is present in the older syntax. It is also useful when literal
4150           digits follow the reference. A negative number is a relative reference.
4151           Consider this example:
4152    
4153             (abc(def)ghi)\g{-1}
4154    
4155           The sequence \g{-1} is a reference to the most recently started captur-
4156           ing  subpattern  before \g, that is, is it equivalent to \2. Similarly,
4157           \g{-2} would be equivalent to \1. The use of relative references can be
4158           helpful  in  long  patterns,  and  also in patterns that are created by
4159           joining together fragments that contain references within themselves.
4160    
4161         A back reference matches whatever actually matched the  capturing  sub-         A back reference matches whatever actually matched the  capturing  sub-
4162         pattern  in  the  current subject string, rather than anything matching         pattern  in  the  current subject string, rather than anything matching
# Line 3346  BACK REFERENCES Line 4175  BACK REFERENCES
4175         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the
4176         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
4177    
4178         Back  references  to named subpatterns use the Python syntax (?P=name).         There  are  several  different ways of writing back references to named
4179         We could rewrite the above example as follows:         subpatterns. The .NET syntax \k{name} and the Perl syntax  \k<name>  or
4180           \k'name'  are supported, as is the Python syntax (?P=name). Perl 5.10's
4181           unified back reference syntax, in which \g can be used for both numeric
4182           and  named  references,  is  also supported. We could rewrite the above
4183           example in any of the following ways:
4184    
4185             (?<p1>(?i)rah)\s+\k<p1>
4186             (?'p1'(?i)rah)\s+\k{p1}
4187             (?P<p1>(?i)rah)\s+(?P=p1)
4188             (?<p1>(?i)rah)\s+\g{p1}
4189    
4190           (?<p1>(?i)rah)\s+(?P=p1)         A subpattern that is referenced by  name  may  appear  in  the  pattern
4191           before or after the reference.
4192    
4193         There may be more than one back reference to the same subpattern. If  a         There  may be more than one back reference to the same subpattern. If a
4194         subpattern  has  not actually been used in a particular match, any back         subpattern has not actually been used in a particular match,  any  back
4195         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
4196    
4197           (a|(bc))\2           (a|(bc))\2
4198    
4199         always fails if it starts to match "a" rather than "bc". Because  there         always  fails if it starts to match "a" rather than "bc". Because there
4200         may  be  many  capturing parentheses in a pattern, all digits following         may be many capturing parentheses in a pattern,  all  digits  following
4201         the backslash are taken as part of a potential back  reference  number.         the  backslash  are taken as part of a potential back reference number.
4202         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
4203         used to terminate the back reference. If the  PCRE_EXTENDED  option  is         used  to  terminate  the back reference. If the PCRE_EXTENDED option is
4204         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-         set, this can be whitespace.  Otherwise an  empty  comment  (see  "Com-
4205         ments" below) can be used.         ments" below) can be used.
4206    
4207         A back reference that occurs inside the parentheses to which it  refers         A  back reference that occurs inside the parentheses to which it refers
4208         fails  when  the subpattern is first used, so, for example, (a\1) never         fails when the subpattern is first used, so, for example,  (a\1)  never
4209         matches.  However, such references can be useful inside  repeated  sub-         matches.   However,  such references can be useful inside repeated sub-
4210         patterns. For example, the pattern         patterns. For example, the pattern
4211    
4212           (a|b\1)+           (a|b\1)+
4213    
4214         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-         matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
4215         ation of the subpattern,  the  back  reference  matches  the  character         ation  of  the  subpattern,  the  back  reference matches the character
4216         string  corresponding  to  the previous iteration. In order for this to         string corresponding to the previous iteration. In order  for  this  to
4217         work, the pattern must be such that the first iteration does  not  need         work,  the  pattern must be such that the first iteration does not need
4218         to  match the back reference. This can be done using alternation, as in         to match the back reference. This can be done using alternation, as  in
4219         the example above, or by a quantifier with a minimum of zero.         the example above, or by a quantifier with a minimum of zero.
4220    
4221    
4222  ASSERTIONS  ASSERTIONS
4223    
4224         An assertion is a test on the characters  following  or  preceding  the         An  assertion  is  a  test on the characters following or preceding the
4225         current  matching  point that does not actually consume any characters.         current matching point that does not actually consume  any  characters.
4226         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are         The  simple  assertions  coded  as  \b, \B, \A, \G, \Z, \z, ^ and $ are
4227         described above.         described above.
4228    
4229         More  complicated  assertions  are  coded as subpatterns. There are two         More complicated assertions are coded as  subpatterns.  There  are  two