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revision 75 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 142 by ph10, Fri Mar 30 15:55:18 2007 UTC
# Line 6  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
 PCRE(3)                                                                PCRE(3)  
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
15    
16    
17  INTRODUCTION  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         5.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         PCRE is written in C and released as a C library. A  number  of  people         mately with Perl 5.10, including support for UTF-8 encoded strings  and
27         have  written  wrappers and interfaces of various kinds. A C++ class is         Unicode general category properties. However, UTF-8 and Unicode support
28         included in these contributions, which can  be  found  in  the  Contrib         has to be explicitly enabled; it is not the default. The Unicode tables
29         directory at the primary FTP site, which is:         correspond to Unicode release 5.0.0.
30    
31           In  addition to the Perl-compatible matching function, PCRE contains an
32           alternative matching function that matches the same  compiled  patterns
33           in  a different way. In certain circumstances, the alternative function
34           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
41           of  this  interface.  Other  people's contributions can be found in the
42           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.
49    
50         Some  features  of  PCRE can be included, excluded, or changed when the         Some features of PCRE can be included, excluded, or  changed  when  the
51         library is built. The pcre_config() function makes it  possible  for  a         library  is  built.  The pcre_config() function makes it possible for a
52         client  to  discover  which  features are available. The features them-         client to discover which features are  available.  The  features  them-
53         selves are described in the pcrebuild page. Documentation about  build-         selves  are described in the pcrebuild page. Documentation about build-
54         ing  PCRE for various operating systems can be found in the README file         ing PCRE for various operating systems can be found in the README  file
55         in the source distribution.         in the source distribution.
56    
57           The  library  contains  a number of undocumented internal functions and
58           data tables that are used by more than one  of  the  exported  external
59           functions,  but  which  are  not  intended for use by external callers.
60           Their names all begin with "_pcre_", which hopefully will  not  provoke
61           any name clashes. In some environments, it is possible to control which
62           external symbols are exported when a shared library is  built,  and  in
63           these cases the undocumented symbols are not exported.
64    
65    
66  USER DOCUMENTATION  USER DOCUMENTATION
67    
68         The user documentation for PCRE comprises a number  of  different  sec-         The  user  documentation  for PCRE comprises a number of different sec-
69         tions.  In the "man" format, each of these is a separate "man page". In         tions. In the "man" format, each of these is a separate "man page".  In
70         the HTML format, each is a separate page, linked from the  index  page.         the  HTML  format, each is a separate page, linked from the index page.
71         In  the  plain text format, all the sections are concatenated, for ease         In the plain text format, all the sections are concatenated,  for  ease
72         of searching. The sections are as follows:         of searching. The sections are as follows:
73    
74           pcre              this document           pcre              this document
75           pcreapi           details of PCRE's native API           pcreapi           details of PCRE's native C API
76           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
77           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
78           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
79             pcrecpp           details of the C++ wrapper
80           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
81             pcrematching      discussion of the two matching algorithms
82           pcrepartial       details of the partial matching facility           pcrepartial       details of the partial matching facility
83           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
84                               regular expressions                               regular expressions
85           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
86           pcreposix         the POSIX-compatible API           pcreposix         the POSIX-compatible C API
87           pcreprecompile    details of saving and re-using precompiled patterns           pcreprecompile    details of saving and re-using precompiled patterns
88           pcresample        discussion of the sample program           pcresample        discussion of the sample program
89             pcrestack         discussion of stack usage
90           pcretest          description of the pcretest testing command           pcretest          description of the pcretest testing command
91    
92         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
93         each library function, listing its arguments and results.         each C library function, listing its arguments and results.
94    
95    
96  LIMITATIONS  LIMITATIONS
97    
98         There are some size limitations in PCRE but it is hoped that they  will         There  are some size limitations in PCRE but it is hoped that they will
99         never in practice be relevant.         never in practice be relevant.
100    
101         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
102         is compiled with the default internal linkage size of 2. If you want to         is compiled with the default internal linkage size of 2. If you want to
103         process  regular  expressions  that are truly enormous, you can compile         process regular expressions that are truly enormous,  you  can  compile
104         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
105         the  source  distribution and the pcrebuild documentation for details).         the source distribution and the pcrebuild documentation  for  details).
106         In these cases the limit is substantially larger.  However,  the  speed         In  these  cases the limit is substantially larger.  However, the speed
107         of execution will be slower.         of execution is slower.
108    
109         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536. The  maxi-
110         mum number of capturing subpatterns is 65535.         mum  compiled  length  of  subpattern  with an explicit repeat count is
111           30000 bytes. The maximum number of capturing subpatterns is 65535.
112         There is no limit to the number of non-capturing subpatterns,  but  the  
113         maximum  depth  of  nesting  of  all kinds of parenthesized subpattern,         There is no limit to the number of parenthesized subpatterns, but there
114         including capturing subpatterns, assertions, and other types of subpat-         can be no more than 65535 capturing subpatterns.
115         tern, is 200.  
116           The maximum length of name for a named subpattern is 32 characters, and
117         The  maximum  length of a subject string is the largest positive number         the maximum number of named subpatterns is 10000.
118         that an integer variable can hold. However, PCRE uses recursion to han-  
119         dle  subpatterns  and indefinite repetition. This means that the avail-         The maximum length of a subject string is the largest  positive  number
120         able stack space may limit the size of a subject  string  that  can  be         that  an integer variable can hold. However, when using the traditional
121         processed by certain patterns.         matching function, PCRE uses recursion to handle subpatterns and indef-
122           inite  repetition.  This means that the available stack space may limit
123           the size of a subject string that can be processed by certain patterns.
124           For a discussion of stack issues, see the pcrestack documentation.
125    
126    
127  UTF-8 AND UNICODE PROPERTY SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
# Line 111  UTF-8 AND UNICODE PROPERTY SUPPORT Line 139  UTF-8 AND UNICODE PROPERTY SUPPORT
139    
140         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,
141         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
142         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
143         not be very large.         very big.
144    
145         If PCRE is built with Unicode character property support (which implies         If PCRE is built with Unicode character property support (which implies
146         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-         UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
147         ported.  The available properties that can be tested are limited to the         ported.  The available properties that can be tested are limited to the
148         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
149         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,
150         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
151         property support is included.         pcrepattern documentation. Only the short names for properties are sup-
152           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
153           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
154           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
155           does not support this.
156    
157         The following comments apply when PCRE is running in UTF-8 mode:         The following comments apply when PCRE is running in UTF-8 mode:
158    
# Line 136  UTF-8 AND UNICODE PROPERTY SUPPORT Line 168  UTF-8 AND UNICODE PROPERTY SUPPORT
168         PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may         PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
169         crash.         crash.
170    
171         2. In a pattern, the escape sequence \x{...}, where the contents of the         2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
172         braces is a string of hexadecimal digits, is  interpreted  as  a  UTF-8         two-byte UTF-8 character if the value is greater than 127.
        character  whose code number is the given hexadecimal number, for exam-  
        ple: \x{1234}. If a non-hexadecimal digit appears between  the  braces,  
        the item is not recognized.  This escape sequence can be used either as  
        a literal, or within a character class.  
173    
174         3. The original hexadecimal escape sequence, \xhh, matches  a  two-byte         3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
175         UTF-8 character if the value is greater than 127.         characters for values greater than \177.
176    
177         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-         4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
178         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
# Line 153  UTF-8 AND UNICODE PROPERTY SUPPORT Line 181  UTF-8 AND UNICODE PROPERTY SUPPORT
181         gle byte.         gle byte.
182    
183         6.  The  escape sequence \C can be used to match a single byte in UTF-8         6.  The  escape sequence \C can be used to match a single byte in UTF-8
184         mode, but its use can lead to some strange effects.         mode, but its use can lead to some strange effects.  This  facility  is
185           not available in the alternative matching function, pcre_dfa_exec().
186    
187         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly         7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
188         test  characters of any code value, but the characters that PCRE recog-         test characters of any code value, but the characters that PCRE  recog-
189         nizes as digits, spaces, or word characters  remain  the  same  set  as         nizes  as  digits,  spaces,  or  word characters remain the same set as
190         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
191         includes Unicode property support, because to do otherwise  would  slow         includes  Unicode  property support, because to do otherwise would slow
192         down  PCRE in many common cases. If you really want to test for a wider         down PCRE in many common cases. If you really want to test for a  wider
193         sense of, say, "digit", you must use Unicode  property  tests  such  as         sense  of,  say,  "digit",  you must use Unicode property tests such as
194         \p{Nd}.         \p{Nd}.
195    
196         8.  Similarly,  characters that match the POSIX named character classes         8. Similarly, characters that match the POSIX named  character  classes
197         are all low-valued characters.         are all low-valued characters.
198    
199         9. Case-insensitive matching applies only to  characters  whose  values         9.  Case-insensitive  matching  applies only to characters whose values
200         are  less than 128, unless PCRE is built with Unicode property support.         are less than 128, unless PCRE is built with Unicode property  support.
201         Even when Unicode property support is available, PCRE  still  uses  its         Even  when  Unicode  property support is available, PCRE still uses its
202         own  character  tables when checking the case of low-valued characters,         own character tables when checking the case of  low-valued  characters,
203         so as not to degrade performance.  The Unicode property information  is         so  as not to degrade performance.  The Unicode property information is
204         used only for characters with higher values.         used only for characters with higher values. Even when Unicode property
205           support is available, PCRE supports case-insensitive matching only when
206           there is a one-to-one mapping between a letter's  cases.  There  are  a
207           small  number  of  many-to-one  mappings in Unicode; these are not sup-
208           ported by PCRE.
209    
210    
211  AUTHOR  AUTHOR
212    
213         Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
214         University Computing Service,         University Computing Service
215         Cambridge CB2 3QG, England.         Cambridge CB2 3QH, England.
        Phone: +44 1223 334714  
216    
217  Last updated: 09 September 2004         Putting an actual email address here seems to have been a spam  magnet,
218  Copyright (c) 1997-2004 University of Cambridge.         so I've taken it away. If you want to email me, use my initial and sur-
219  -----------------------------------------------------------------------------         name, separated by a dot, at the domain ucs.cam.ac.uk.
220    
 PCRE(3)                                                                PCRE(3)  
221    
222    REVISION
223    
224           Last updated: 06 March 2007
225           Copyright (c) 1997-2007 University of Cambridge.
226    ------------------------------------------------------------------------------
227    
228    
229    PCREBUILD(3)                                                      PCREBUILD(3)
230    
231    
232  NAME  NAME
233         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
234    
235    
236  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
237    
238         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
# Line 204  PCRE BUILD-TIME OPTIONS Line 244  PCRE BUILD-TIME OPTIONS
244    
245           ./configure --help           ./configure --help
246    
247         The following sections describe certain options whose names begin  with         The following sections include  descriptions  of  options  whose  names
248         --enable  or  --disable. These settings specify changes to the defaults         begin with --enable or --disable. These settings specify changes to the
249         for the configure command. Because of the  way  that  configure  works,         defaults for the configure command. Because of the way  that  configure
250         --enable  and  --disable  always  come  in  pairs, so the complementary         works,  --enable  and --disable always come in pairs, so the complemen-
251         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
252         not described.         is not described.
253    
254    
255    C++ SUPPORT
256    
257           By default, the configure script will search for a C++ compiler and C++
258           header files. If it finds them, it automatically builds the C++ wrapper
259           library for PCRE. You can disable this by adding
260    
261             --disable-cpp
262    
263           to the configure command.
264    
265    
266  UTF-8 SUPPORT  UTF-8 SUPPORT
# Line 237  UNICODE CHARACTER PROPERTY SUPPORT Line 288  UNICODE CHARACTER PROPERTY SUPPORT
288         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
289         not explicitly requested it.         not explicitly requested it.
290    
291         Including  Unicode  property  support  adds around 90K of tables to the         Including  Unicode  property  support  adds around 30K of tables to the
292         PCRE library, approximately doubling its size. Only the  general  cate-         PCRE library. Only the general category properties such as  Lu  and  Nd
293         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.  
294    
295    
296  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
297    
298         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
299         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
300         compile PCRE to use character 13 (carriage return) instead by adding         systems. You can compile PCRE to use character 13 (carriage return, CR)
301           instead, by adding
302    
303           --enable-newline-is-cr           --enable-newline-is-cr
304    
305         to the configure command. For completeness there is  also  a  --enable-         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
306         newline-is-lf  option,  which explicitly specifies linefeed as the new-         option, which explicitly specifies linefeed as the newline character.
307         line character.  
308           Alternatively, you can specify that line endings are to be indicated by
309           the two character sequence CRLF. If you want this, add
310    
311             --enable-newline-is-crlf
312    
313           to the configure command. There is a fourth option, specified by
314    
315             --enable-newline-is-any
316    
317           which causes PCRE to recognize any Unicode newline sequence.
318    
319           Whatever line ending convention is selected when PCRE is built  can  be
320           overridden  when  the library functions are called. At build time it is
321           conventional to use the standard for your operating system.
322    
323    
324  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
# Line 284  POSIX MALLOC USAGE Line 349  POSIX MALLOC USAGE
349         to the configure command.         to the configure command.
350    
351    
 LIMITING PCRE RESOURCE USAGE  
   
        Internally,  PCRE has a function called match(), which it calls repeat-  
        edly (possibly recursively) when matching a pattern. 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 documentation. The default is 10 million,  but  
        this can be changed by adding a setting such as  
   
          --with-match-limit=500000  
   
        to the configure command.  
   
   
352  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
353    
354         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 316  HANDLING VERY LARGE PATTERNS Line 366  HANDLING VERY LARGE PATTERNS
366         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
367         additional bytes when handling them.         additional bytes when handling them.
368    
        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.  
   
369    
370  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
371    
372         PCRE  implements  backtracking while matching by making recursive calls         When matching with the pcre_exec() function, PCRE implements backtrack-
373         to an internal function called match(). In environments where the  size         ing  by  making recursive calls to an internal function called match().
374         of the stack is limited, this can severely limit PCRE's operation. (The         In environments where the size of the stack is limited,  this  can  se-
375         Unix environment does not usually suffer from this problem.) An  alter-         verely  limit  PCRE's operation. (The Unix environment does not usually
376         native  approach  that  uses  memory  from  the  heap to remember data,         suffer from this problem, but it may sometimes be necessary to increase
377         instead of using recursive function calls, has been implemented to work         the  maximum  stack size.  There is a discussion in the pcrestack docu-
378         round  this  problem. If you want to build a version of PCRE that works         mentation.) An alternative approach to recursion that uses memory  from
379         this way, add         the  heap  to remember data, instead of using recursive function calls,
380           has been implemented to work round the problem of limited  stack  size.
381           If you want to build a version of PCRE that works this way, add
382    
383           --disable-stack-for-recursion           --disable-stack-for-recursion
384    
385         to the configure command. With this configuration, PCRE  will  use  the         to  the  configure  command. With this configuration, PCRE will use the
386         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-         pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
387         ment functions. Separate functions are provided because  the  usage  is         ment  functions.  Separate  functions are provided because the usage is
388         very  predictable:  the  block sizes requested are always the same, and         very predictable: the block sizes requested are always  the  same,  and
389         the blocks are always freed in reverse order. A calling  program  might         the  blocks  are always freed in reverse order. A calling program might
390         be  able  to implement optimized functions that perform better than the         be able to implement optimized functions that perform better  than  the
391         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
392         slowly when built in this way.         slowly when built in this way. This option affects only the pcre_exec()
393           function; it is not relevant for the the pcre_dfa_exec() function.
394    
395    
396    LIMITING PCRE RESOURCE USAGE
397    
398           Internally,  PCRE has a function called match(), which it calls repeat-
399           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
400           pcre_exec()  function.  By controlling the maximum number of times this
401           function may be called during a single matching operation, a limit  can
402           be  placed  on  the resources used by a single call to pcre_exec(). The
403           limit can be changed at run time, as described in the pcreapi  documen-
404           tation.  The default is 10 million, but this can be changed by adding a
405           setting such as
406    
407             --with-match-limit=500000
408    
409           to  the  configure  command.  This  setting  has  no  effect   on   the
410           pcre_dfa_exec() matching function.
411    
412           In  some  environments  it is desirable to limit the depth of recursive
413           calls of match() more strictly than the total number of calls, in order
414           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
415           for-recursion is specified) that is used. A second limit controls this;
416           it  defaults  to  the  value  that is set for --with-match-limit, which
417           imposes no additional constraints. However, you can set a  lower  limit
418           by adding, for example,
419    
420             --with-match-limit-recursion=10000
421    
422           to  the  configure  command.  This  value can also be overridden at run
423           time.
424    
425    
426    CREATING CHARACTER TABLES AT BUILD TIME
427    
428           PCRE uses fixed tables for processing characters whose code values  are
429           less  than 256. By default, PCRE is built with a set of tables that are
430           distributed in the file pcre_chartables.c.dist. These  tables  are  for
431           ASCII codes only. If you add
432    
433             --enable-rebuild-chartables
434    
435           to  the  configure  command, the distributed tables are no longer used.
436           Instead, a program called dftables is compiled and  run.  This  outputs
437           the source for new set of tables, created in the default locale of your
438           C runtime system. (This method of replacing the tables does not work if
439           you  are cross compiling, because dftables is run on the local host. If
440           you need to create alternative tables when cross  compiling,  you  will
441           have to do so "by hand".)
442    
443    
444  USING EBCDIC CODE  USING EBCDIC CODE
# Line 354  USING EBCDIC CODE Line 450  USING EBCDIC CODE
450    
451           --enable-ebcdic           --enable-ebcdic
452    
453         to the configure command.         to the configure command. This setting implies --enable-rebuild-charta-
454           bles.
455    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
456    
457  PCRE(3)                                                                PCRE(3)  SEE ALSO
458    
459           pcreapi(3), pcre_config(3).
460    
461    
462    AUTHOR
463    
464           Philip Hazel
465           University Computing Service
466           Cambridge CB2 3QH, England.
467    
468    
469    REVISION
470    
471           Last updated: 20 March 2007
472           Copyright (c) 1997-2007 University of Cambridge.
473    ------------------------------------------------------------------------------
474    
475    
476    PCREMATCHING(3)                                                PCREMATCHING(3)
477    
478    
479  NAME  NAME
480         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
481    
482    
483    PCRE MATCHING ALGORITHMS
484    
485           This document describes the two different algorithms that are available
486           in PCRE for matching a compiled regular expression against a given sub-
487           ject  string.  The  "standard"  algorithm  is  the  one provided by the
488           pcre_exec() function.  This works in the same was  as  Perl's  matching
489           function, and provides a Perl-compatible matching operation.
490    
491           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
492           this operates in a different way, and is not  Perl-compatible.  It  has
493           advantages  and disadvantages compared with the standard algorithm, and
494           these are described below.
495    
496           When there is only one possible way in which a given subject string can
497           match  a pattern, the two algorithms give the same answer. A difference
498           arises, however, when there are multiple possibilities. For example, if
499           the pattern
500    
501             ^<.*>
502    
503           is matched against the string
504    
505             <something> <something else> <something further>
506    
507           there are three possible answers. The standard algorithm finds only one
508           of them, whereas the alternative algorithm finds all three.
509    
510    
511    REGULAR EXPRESSIONS AS TREES
512    
513           The set of strings that are matched by a regular expression can be rep-
514           resented  as  a  tree structure. An unlimited repetition in the pattern
515           makes the tree of infinite size, but it is still a tree.  Matching  the
516           pattern  to a given subject string (from a given starting point) can be
517           thought of as a search of the tree.  There are two  ways  to  search  a
518           tree:  depth-first  and  breadth-first, and these correspond to the two
519           matching algorithms provided by PCRE.
520    
521    
522    THE STANDARD MATCHING ALGORITHM
523    
524           In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
525           sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
526           depth-first search of the pattern tree. That is, it  proceeds  along  a
527           single path through the tree, checking that the subject matches what is
528           required. When there is a mismatch, the algorithm  tries  any  alterna-
529           tives  at  the  current point, and if they all fail, it backs up to the
530           previous branch point in the  tree,  and  tries  the  next  alternative
531           branch  at  that  level.  This often involves backing up (moving to the
532           left) in the subject string as well.  The  order  in  which  repetition
533           branches  are  tried  is controlled by the greedy or ungreedy nature of
534           the quantifier.
535    
536           If a leaf node is reached, a matching string has  been  found,  and  at
537           that  point the algorithm stops. Thus, if there is more than one possi-
538           ble match, this algorithm returns the first one that it finds.  Whether
539           this  is the shortest, the longest, or some intermediate length depends
540           on the way the greedy and ungreedy repetition quantifiers are specified
541           in the pattern.
542    
543           Because  it  ends  up  with a single path through the tree, it is rela-
544           tively straightforward for this algorithm to keep  track  of  the  sub-
545           strings  that  are  matched  by portions of the pattern in parentheses.
546           This provides support for capturing parentheses and back references.
547    
548    
549    THE ALTERNATIVE MATCHING ALGORITHM
550    
551           This algorithm conducts a breadth-first search of  the  tree.  Starting
552           from  the  first  matching  point  in the subject, it scans the subject
553           string from left to right, once, character by character, and as it does
554           this,  it remembers all the paths through the tree that represent valid
555           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
556           though  it is not implemented as a traditional finite state machine (it
557           keeps multiple states active simultaneously).
558    
559           The scan continues until either the end of the subject is  reached,  or
560           there  are  no more unterminated paths. At this point, terminated paths
561           represent the different matching possibilities (if there are none,  the
562           match  has  failed).   Thus,  if there is more than one possible match,
563           this algorithm finds all of them, and in particular, it finds the long-
564           est.  In PCRE, there is an option to stop the algorithm after the first
565           match (which is necessarily the shortest) has been found.
566    
567           Note that all the matches that are found start at the same point in the
568           subject. If the pattern
569    
570             cat(er(pillar)?)
571    
572           is  matched  against the string "the caterpillar catchment", the result
573           will be the three strings "cat", "cater", and "caterpillar" that  start
574           at the fourth character of the subject. The algorithm does not automat-
575           ically move on to find matches that start at later positions.
576    
577           There are a number of features of PCRE regular expressions that are not
578           supported by the alternative matching algorithm. They are as follows:
579    
580           1.  Because  the  algorithm  finds  all possible matches, the greedy or
581           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
582           ungreedy quantifiers are treated in exactly the same way. However, pos-
583           sessive quantifiers can make a difference when what follows could  also
584           match what is quantified, for example in a pattern like this:
585    
586             ^a++\w!
587    
588           This  pattern matches "aaab!" but not "aaa!", which would be matched by
589           a non-possessive quantifier. Similarly, if an atomic group is  present,
590           it  is matched as if it were a standalone pattern at the current point,
591           and the longest match is then "locked in" for the rest of  the  overall
592           pattern.
593    
594           2. When dealing with multiple paths through the tree simultaneously, it
595           is not straightforward to keep track of  captured  substrings  for  the
596           different  matching  possibilities,  and  PCRE's implementation of this
597           algorithm does not attempt to do this. This means that no captured sub-
598           strings are available.
599    
600           3.  Because no substrings are captured, back references within the pat-
601           tern are not supported, and cause errors if encountered.
602    
603           4. For the same reason, conditional expressions that use  a  backrefer-
604           ence  as  the  condition or test for a specific group recursion are not
605           supported.
606    
607           5. Callouts are supported, but the value of the  capture_top  field  is
608           always 1, and the value of the capture_last field is always -1.
609    
610           6.  The \C escape sequence, which (in the standard algorithm) matches a
611           single byte, even in UTF-8 mode, is not supported because the  alterna-
612           tive  algorithm  moves  through  the  subject string one character at a
613           time, for all active paths through the tree.
614    
615    
616    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
617    
618           Using the alternative matching algorithm provides the following  advan-
619           tages:
620    
621           1. All possible matches (at a single point in the subject) are automat-
622           ically found, and in particular, the longest match is  found.  To  find
623           more than one match using the standard algorithm, you have to do kludgy
624           things with callouts.
625    
626           2. There is much better support for partial matching. The  restrictions
627           on  the content of the pattern that apply when using the standard algo-
628           rithm for partial matching do not apply to the  alternative  algorithm.
629           For  non-anchored patterns, the starting position of a partial match is
630           available.
631    
632           3. Because the alternative algorithm  scans  the  subject  string  just
633           once,  and  never  needs to backtrack, it is possible to pass very long
634           subject strings to the matching function in  several  pieces,  checking
635           for partial matching each time.
636    
637    
638    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
639    
640           The alternative algorithm suffers from a number of disadvantages:
641    
642           1.  It  is  substantially  slower  than the standard algorithm. This is
643           partly because it has to search for all possible matches, but  is  also
644           because it is less susceptible to optimization.
645    
646           2. Capturing parentheses and back references are not supported.
647    
648           3. Although atomic groups are supported, their use does not provide the
649           performance advantage that it does for the standard algorithm.
650    
651    
652    AUTHOR
653    
654           Philip Hazel
655           University Computing Service
656           Cambridge CB2 3QH, England.
657    
658    
659    REVISION
660    
661           Last updated: 06 March 2007
662           Copyright (c) 1997-2007 University of Cambridge.
663    ------------------------------------------------------------------------------
664    
665    
666    PCREAPI(3)                                                          PCREAPI(3)
667    
668    
669    NAME
670           PCRE - Perl-compatible regular expressions
671    
672    
673  PCRE NATIVE API  PCRE NATIVE API
674    
675         #include <pcre.h>         #include <pcre.h>
# Line 375  PCRE NATIVE API Line 678  PCRE NATIVE API
678              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
679              const unsigned char *tableptr);              const unsigned char *tableptr);
680    
681           pcre *pcre_compile2(const char *pattern, int options,
682                int *errorcodeptr,
683                const char **errptr, int *erroffset,
684                const unsigned char *tableptr);
685    
686         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
687              const char **errptr);              const char **errptr);
688    
# Line 382  PCRE NATIVE API Line 690  PCRE NATIVE API
690              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
691              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
692    
693           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
694                const char *subject, int length, int startoffset,
695                int options, int *ovector, int ovecsize,
696                int *workspace, int wscount);
697    
698         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
699              const char *subject, int *ovector,              const char *subject, int *ovector,
700              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 399  PCRE NATIVE API Line 712  PCRE NATIVE API
712         int pcre_get_stringnumber(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
713              const char *name);              const char *name);
714    
715           int pcre_get_stringtable_entries(const pcre *code,
716                const char *name, char **first, char **last);
717    
718         int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
719              int stringcount, int stringnumber,              int stringcount, int stringnumber,
720              const char **stringptr);              const char **stringptr);
# Line 417  PCRE NATIVE API Line 733  PCRE NATIVE API
733    
734         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
735    
736           int pcre_refcount(pcre *code, int adjust);
737    
738         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
739    
740         char *pcre_version(void);         char *pcre_version(void);
# Line 435  PCRE NATIVE API Line 753  PCRE NATIVE API
753  PCRE API OVERVIEW  PCRE API OVERVIEW
754    
755         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
756         is also a set of wrapper functions that correspond to the POSIX regular         are also some wrapper functions that correspond to  the  POSIX  regular
757         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
758           Both of these APIs define a set of C function calls. A C++  wrapper  is
759           distributed with PCRE. It is documented in the pcrecpp page.
760    
761         The  native  API  function  prototypes  are  defined in the header file         The  native  API  C  function prototypes are defined in the header file
762         pcre.h, and on Unix systems the library itself is  called  libpcre.  It         pcre.h, and on Unix systems the library itself is called  libpcre.   It
763         can normally be accessed by adding -lpcre to the command for linking an         can normally be accessed by adding -lpcre to the command for linking an
764         application  that  uses  PCRE.  The  header  file  defines  the  macros         application  that  uses  PCRE.  The  header  file  defines  the  macros
765         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
766         bers for the library.  Applications can use these  to  include  support         bers for the library.  Applications can use these  to  include  support
767         for different releases of PCRE.         for different releases of PCRE.
768    
769         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
770         for compiling and matching regular expressions. A sample  program  that         pcre_exec() are used for compiling and matching regular expressions  in
771         demonstrates  the  simplest  way  of using them is provided in the file         a  Perl-compatible  manner. A sample program that demonstrates the sim-
772         called pcredemo.c in the source distribution. The pcresample documenta-         plest way of using them is provided in the file  called  pcredemo.c  in
773         tion describes how to run it.         the  source distribution. The pcresample documentation describes how to
774           run it.
775         In  addition  to  the  main compiling and matching functions, there are  
776         convenience functions for extracting captured substrings from a matched         A second matching function, pcre_dfa_exec(), which is not Perl-compati-
777         subject string.  They are:         ble,  is  also provided. This uses a different algorithm for the match-
778           ing. The alternative algorithm finds all possible matches (at  a  given
779           point  in  the subject), and scans the subject just once. However, this
780           algorithm does not return captured substrings. A description of the two
781           matching  algorithms and their advantages and disadvantages is given in
782           the pcrematching documentation.
783    
784           In addition to the main compiling and  matching  functions,  there  are
785           convenience functions for extracting captured substrings from a subject
786           string that is matched by pcre_exec(). They are:
787    
788           pcre_copy_substring()           pcre_copy_substring()
789           pcre_copy_named_substring()           pcre_copy_named_substring()
# Line 462  PCRE API OVERVIEW Line 791  PCRE API OVERVIEW
791           pcre_get_named_substring()           pcre_get_named_substring()
792           pcre_get_substring_list()           pcre_get_substring_list()
793           pcre_get_stringnumber()           pcre_get_stringnumber()
794             pcre_get_stringtable_entries()
795    
796         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
797         to free the memory used for extracted strings.         to free the memory used for extracted strings.
798    
799         The function pcre_maketables() is used to  build  a  set  of  character         The  function  pcre_maketables()  is  used  to build a set of character
800         tables   in  the  current  locale  for  passing  to  pcre_compile()  or         tables  in  the  current  locale   for   passing   to   pcre_compile(),
801         pcre_exec().  This is an optional facility that is  provided  for  spe-         pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
802         cialist use. Most commonly, no special tables are passed, in which case         provided for specialist use.  Most  commonly,  no  special  tables  are
803         internal tables that are generated when PCRE is built are used.         passed,  in  which case internal tables that are generated when PCRE is
804           built are used.
805    
806         The function pcre_fullinfo() is used to find out  information  about  a         The function pcre_fullinfo() is used to find out  information  about  a
807         compiled  pattern; pcre_info() is an obsolete version that returns only         compiled  pattern; pcre_info() is an obsolete version that returns only
# Line 478  PCRE API OVERVIEW Line 809  PCRE API OVERVIEW
809         patibility.   The function pcre_version() returns a pointer to a string         patibility.   The function pcre_version() returns a pointer to a string
810         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
811    
812           The function pcre_refcount() maintains a  reference  count  in  a  data
813           block  containing  a compiled pattern. This is provided for the benefit
814           of object-oriented applications.
815    
816         The global variables pcre_malloc and pcre_free  initially  contain  the         The global variables pcre_malloc and pcre_free  initially  contain  the
817         entry  points  of  the  standard malloc() and free() functions, respec-         entry  points  of  the  standard malloc() and free() functions, respec-
818         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
# Line 487  PCRE API OVERVIEW Line 822  PCRE API OVERVIEW
822         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
823         indirections  to  memory  management functions. These special functions         indirections  to  memory  management functions. These special functions
824         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
825         data,  instead  of recursive function calls. This is a non-standard way         data, instead of recursive function calls, when running the pcre_exec()
826         of building PCRE, for use in environments  that  have  limited  stacks.         function. See the pcrebuild documentation for  details  of  how  to  do
827         Because  of  the greater use of memory management, it runs more slowly.         this.  It  is  a non-standard way of building PCRE, for use in environ-
828         Separate functions are provided so that special-purpose  external  code         ments that have limited stacks. Because of the greater  use  of  memory
829         can be used for this case. When used, these functions are always called         management,  it  runs  more  slowly. Separate functions are provided so
830         in a stack-like manner (last obtained, first  freed),  and  always  for         that special-purpose external code can be  used  for  this  case.  When
831         memory blocks of the same size.         used,  these  functions  are always called in a stack-like manner (last
832           obtained, first freed), and always for memory blocks of the same  size.
833           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
834           mentation.
835    
836         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
837         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
838         specified  points during a matching operation. Details are given in the         specified points during a matching operation. Details are given in  the
839         pcrecallout documentation.         pcrecallout documentation.
840    
841    
842    NEWLINES
843    
844           PCRE  supports four different conventions for indicating line breaks in
845           strings: a single CR (carriage return) character, a  single  LF  (line-
846           feed)  character,  the two-character sequence CRLF, or any Unicode new-
847           line sequence.  The Unicode newline sequences are the three  just  men-
848           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
849           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
850           and PS (paragraph separator, U+2029).
851    
852           Each  of  the first three conventions is used by at least one operating
853           system as its standard newline sequence. When PCRE is built, a  default
854           can  be  specified.  The default default is LF, which is the Unix stan-
855           dard. When PCRE is run, the default can be overridden,  either  when  a
856           pattern is compiled, or when it is matched.
857    
858           In the PCRE documentation the word "newline" is used to mean "the char-
859           acter or pair of characters that indicate a line break". The choice  of
860           newline  convention  affects  the  handling of the dot, circumflex, and
861           dollar metacharacters, the handling of #-comments in /x mode, and, when
862           CRLF  is a recognized line ending sequence, the match position advance-
863           ment for a non-anchored pattern. The choice of newline convention  does
864           not affect the interpretation of the \n or \r escape sequences.
865    
866    
867  MULTITHREADING  MULTITHREADING
868    
869         The PCRE functions can be used in  multi-threading  applications,  with         The  PCRE  functions  can be used in multi-threading applications, with
870         the  proviso  that  the  memory  management  functions  pointed  to  by         the  proviso  that  the  memory  management  functions  pointed  to  by
871         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
872         callout function pointed to by pcre_callout, are shared by all threads.         callout function pointed to by pcre_callout, are shared by all threads.
873    
874         The compiled form of a regular expression is not altered during  match-         The  compiled form of a regular expression is not altered during match-
875         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
876         at once.         at once.
877    
# Line 516  MULTITHREADING Line 879  MULTITHREADING
879  SAVING PRECOMPILED PATTERNS FOR LATER USE  SAVING PRECOMPILED PATTERNS FOR LATER USE
880    
881         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
882         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
883         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
884         pcreprecompile documentation.         pcreprecompile documentation.
885    
886    
# Line 525  CHECKING BUILD-TIME OPTIONS Line 888  CHECKING BUILD-TIME OPTIONS
888    
889         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
890    
891         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-
892         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
893         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
894         tures.         tures.
895    
896         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
897         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
898         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
899         available:         available:
900    
901           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
902    
903         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-
904         able; otherwise it is set to zero.         able; otherwise it is set to zero.
905    
906           PCRE_CONFIG_UNICODE_PROPERTIES           PCRE_CONFIG_UNICODE_PROPERTIES
907    
908         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
909         character properties is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
910    
911           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
912    
913         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
914         used for the newline character. It is either linefeed (10) or  carriage         sequence  that is recognized as meaning "newline". The four values that
915         return  (13),  and  should  normally be the standard character for your         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY.
916         operating system.         The default should normally be the standard sequence for your operating
917           system.
918    
919           PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
920    
# Line 573  CHECKING BUILD-TIME OPTIONS Line 937  CHECKING BUILD-TIME OPTIONS
937         internal matching function calls in a  pcre_exec()  execution.  Further         internal matching function calls in a  pcre_exec()  execution.  Further
938         details are given with pcre_exec() below.         details are given with pcre_exec() below.
939    
940             PCRE_CONFIG_MATCH_LIMIT_RECURSION
941    
942           The  output is an integer that gives the default limit for the depth of
943           recursion when calling the internal matching function in a  pcre_exec()
944           execution. Further details are given with pcre_exec() below.
945    
946           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
947    
948         The  output  is  an integer that is set to one if internal recursion is         The  output is an integer that is set to one if internal recursion when
949         implemented by recursive function calls that use the stack to  remember         running pcre_exec() is implemented by recursive function calls that use
950         their state. This is the usual way that PCRE is compiled. The output is         the  stack  to remember their state. This is the usual way that PCRE is
951         zero if PCRE was compiled to use blocks of data on the heap instead  of         compiled. The output is zero if PCRE was compiled to use blocks of data
952         recursive   function   calls.   In  this  case,  pcre_stack_malloc  and         on  the  heap  instead  of  recursive  function  calls.  In  this case,
953         pcre_stack_free are called to manage memory blocks on  the  heap,  thus         pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
954         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
955    
956    
957  COMPILING A PATTERN  COMPILING A PATTERN
# Line 590  COMPILING A PATTERN Line 960  COMPILING A PATTERN
960              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
961              const unsigned char *tableptr);              const unsigned char *tableptr);
962    
963         The  function  pcre_compile()  is  called  to compile a pattern into an         pcre *pcre_compile2(const char *pattern, int options,
964         internal form. The pattern is a C string terminated by a  binary  zero,              int *errorcodeptr,
965         and  is  passed in the pattern argument. A pointer to a single block of              const char **errptr, int *erroffset,
966         memory that is obtained via pcre_malloc is returned. This contains  the              const unsigned char *tableptr);
967         compiled  code  and  related  data.  The  pcre  type is defined for the  
968         returned block; this is a typedef for a structure  whose  contents  are         Either of the functions pcre_compile() or pcre_compile2() can be called
969         not  externally defined. It is up to the caller to free the memory when         to compile a pattern into an internal form. The only difference between
970         it is no longer required.         the  two interfaces is that pcre_compile2() has an additional argument,
971           errorcodeptr, via which a numerical error code can be returned.
972    
973           The pattern is a C string terminated by a binary zero, and is passed in
974           the  pattern  argument.  A  pointer to a single block of memory that is
975           obtained via pcre_malloc is returned. This contains the  compiled  code
976           and related data. The pcre type is defined for the returned block; this
977           is a typedef for a structure whose contents are not externally defined.
978           It is up to the caller to free the memory (via pcre_free) when it is no
979           longer required.
980    
981         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
982         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
983         fully relocatable, because it may contain a copy of the tableptr  argu-         fully relocatable, because it may contain a copy of the tableptr  argu-
984         ment, which is an address (see below).         ment, which is an address (see below).
985    
986         The options argument contains independent bits that affect the compila-         The options argument contains various bit settings that affect the com-
987         tion. It should be zero if  no  options  are  required.  The  available         pilation. It should be zero if no options are required.  The  available
988         options  are  described  below. Some of them, in particular, those that         options  are  described  below. Some of them, in particular, those that
989         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
990         pattern  (see  the  detailed  description in the pcrepattern documenta-         pattern  (see  the  detailed  description in the pcrepattern documenta-
991         tion). For these options, the contents of the options  argument  speci-         tion). For these options, the contents of the options  argument  speci-
992         fies  their initial settings at the start of compilation and execution.         fies  their initial settings at the start of compilation and execution.
993         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
994         at compile time.         of matching as well as at compile time.
995    
996         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
997         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
998         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-
999         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
1000         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-
1001         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
1002           by  erroffset,  which must not be NULL. If it is, an immediate error is
1003         given.         given.
1004    
1005           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
1006           codeptr  argument is not NULL, a non-zero error code number is returned
1007           via this argument in the event of an error. This is in addition to  the
1008           textual error message. Error codes and messages are listed below.
1009    
1010         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
1011         character tables that are  built  when  PCRE  is  compiled,  using  the         character tables that are  built  when  PCRE  is  compiled,  using  the
1012         default  C  locale.  Otherwise, tableptr must be an address that is the         default  C  locale.  Otherwise, tableptr must be an address that is the
# Line 664  COMPILING A PATTERN Line 1049  COMPILING A PATTERN
1049    
1050         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
1051         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
1052         changed  within  a  pattern  by  a (?i) option setting. When running in         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1053         UTF-8 mode, case support for high-valued characters is  available  only         always understands the concept of case for characters whose values  are
1054         when PCRE is built with Unicode character property support.         less  than 128, so caseless matching is always possible. For characters
1055           with higher values, the concept of case is supported if  PCRE  is  com-
1056           piled  with Unicode property support, but not otherwise. If you want to
1057           use caseless matching for characters 128 and  above,  you  must  ensure
1058           that  PCRE  is  compiled  with Unicode property support as well as with
1059           UTF-8 support.
1060    
1061           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
1062    
1063         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
1064         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
1065         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
1066         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1067         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
1068         in Perl, and no way to set it within a pattern.         Perl, and no way to set it within a pattern.
1069    
1070           PCRE_DOTALL           PCRE_DOTALL
1071    
1072         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-
1073         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including those that indicate newline. Without it, a  dot  does
1074         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
1075         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
1076         always matches a newline character, independent of the setting of  this         by  a (?s) option setting. A negative class such as [^a] always matches
1077         option.         newline characters, independent of the setting of this option.
1078    
1079             PCRE_DUPNAMES
1080    
1081           If this bit is set, names used to identify capturing  subpatterns  need
1082           not be unique. This can be helpful for certain types of pattern when it
1083           is known that only one instance of the named  subpattern  can  ever  be
1084           matched.  There  are  more details of named subpatterns below; see also
1085           the pcrepattern documentation.
1086    
1087           PCRE_EXTENDED           PCRE_EXTENDED
1088    
1089         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
1090         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
1091         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
1092         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
1093         next newline character, inclusive, are also ignored. This is equivalent         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1094         to 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-
1095         option setting.         ting.
1096    
1097         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
1098         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
1099         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
1100         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
1101         introduces a conditional subpattern.         introduces a conditional subpattern.
1102    
1103           PCRE_EXTRA           PCRE_EXTRA
1104    
1105         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
1106         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
1107         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
1108         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
1109         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
1110         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
1111         literal.  There  are  at  present  no other features controlled by this         literal. (Perl can, however, be persuaded to give a warning for  this.)
1112         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
1113           can also be set by a (?X) option setting within a pattern.
1114    
1115             PCRE_FIRSTLINE
1116    
1117           If this option is set, an  unanchored  pattern  is  required  to  match
1118           before  or  at  the  first  newline  in  the subject string, though the
1119           matched text may continue over the newline.
1120    
1121           PCRE_MULTILINE           PCRE_MULTILINE
1122    
# Line 723  COMPILING A PATTERN Line 1128  COMPILING A PATTERN
1128         is set). This is the same as Perl.         is set). This is the same as Perl.
1129    
1130         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"
1131         constructs match immediately following or immediately before  any  new-         constructs match immediately following or immediately  before  internal
1132         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
1133         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
1134         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-
1135         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,
1136         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
1137    
1138             PCRE_NEWLINE_CR
1139             PCRE_NEWLINE_LF
1140             PCRE_NEWLINE_CRLF
1141             PCRE_NEWLINE_ANY
1142    
1143           These  options  override the default newline definition that was chosen
1144           when PCRE was built. Setting the first or the second specifies  that  a
1145           newline  is  indicated  by a single character (CR or LF, respectively).
1146           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1147           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1148           any Unicode newline sequence should be recognized. The Unicode  newline
1149           sequences  are  the three just mentioned, plus the single characters VT
1150           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1151           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1152           last two are recognized only in UTF-8 mode.
1153    
1154           The newline setting in the  options  word  uses  three  bits  that  are
1155           treated  as  a  number, giving eight possibilities. Currently only five
1156           are used (default plus the four values above). This means that  if  you
1157           set  more  than  one  newline option, the combination may or may not be
1158           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1159           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1160           and cause an error.
1161    
1162           The only time that a line break is specially recognized when  compiling
1163           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1164           character class is encountered. This indicates  a  comment  that  lasts
1165           until  after the next line break sequence. In other circumstances, line
1166           break  sequences  are  treated  as  literal  data,   except   that   in
1167           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1168           and are therefore ignored.
1169    
1170           The newline option that is set at compile time becomes the default that
1171           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1172    
1173           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
1174    
1175         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-
1176         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
1177         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
1178         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
1179         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
1180    
1181           PCRE_UNGREEDY           PCRE_UNGREEDY
1182    
1183         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
1184         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
1185         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
1186         within the pattern.         within the pattern.
1187    
1188           PCRE_UTF8           PCRE_UTF8
1189    
1190         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
1191         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
1192         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-
1193         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
1194         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
1195         UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1196    
1197           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1198    
1199         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
1200         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1201         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1202         is valid, and you want to skip this check for performance reasons,  you         is  valid, and you want to skip this check for performance reasons, you
1203         can  set  the  PCRE_NO_UTF8_CHECK option. When it is set, the effect of         can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1204         passing an invalid UTF-8 string as a pattern is undefined. It may cause         passing an invalid UTF-8 string as a pattern is undefined. It may cause
1205         your  program  to  crash.   Note that this option can also be passed to         your program to crash.  Note that this option can  also  be  passed  to
1206         pcre_exec(),  to  suppress  the  UTF-8  validity  checking  of  subject         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1207         strings.         ing of subject strings.
1208    
1209    
1210    COMPILATION ERROR CODES
1211    
1212           The following table lists the error  codes  than  may  be  returned  by
1213           pcre_compile2(),  along with the error messages that may be returned by
1214           both compiling functions. As PCRE has developed, some error codes  have
1215           fallen out of use. To avoid confusion, they have not been re-used.
1216    
1217              0  no error
1218              1  \ at end of pattern
1219              2  \c at end of pattern
1220              3  unrecognized character follows \
1221              4  numbers out of order in {} quantifier
1222              5  number too big in {} quantifier
1223              6  missing terminating ] for character class
1224              7  invalid escape sequence in character class
1225              8  range out of order in character class
1226              9  nothing to repeat
1227             10  [this code is not in use]
1228             11  internal error: unexpected repeat
1229             12  unrecognized character after (?
1230             13  POSIX named classes are supported only within a class
1231             14  missing )
1232             15  reference to non-existent subpattern
1233             16  erroffset passed as NULL
1234             17  unknown option bit(s) set
1235             18  missing ) after comment
1236             19  [this code is not in use]
1237             20  regular expression too large
1238             21  failed to get memory
1239             22  unmatched parentheses
1240             23  internal error: code overflow
1241             24  unrecognized character after (?<
1242             25  lookbehind assertion is not fixed length
1243             26  malformed number or name after (?(
1244             27  conditional group contains more than two branches
1245             28  assertion expected after (?(
1246             29  (?R or (?digits must be followed by )
1247             30  unknown POSIX class name
1248             31  POSIX collating elements are not supported
1249             32  this version of PCRE is not compiled with PCRE_UTF8 support
1250             33  [this code is not in use]
1251             34  character value in \x{...} sequence is too large
1252             35  invalid condition (?(0)
1253             36  \C not allowed in lookbehind assertion
1254             37  PCRE does not support \L, \l, \N, \U, or \u
1255             38  number after (?C is > 255
1256             39  closing ) for (?C expected
1257             40  recursive call could loop indefinitely
1258             41  unrecognized character after (?P
1259             42  syntax error in subpattern name (missing terminator)
1260             43  two named subpatterns have the same name
1261             44  invalid UTF-8 string
1262             45  support for \P, \p, and \X has not been compiled
1263             46  malformed \P or \p sequence
1264             47  unknown property name after \P or \p
1265             48  subpattern name is too long (maximum 32 characters)
1266             49  too many named subpatterns (maximum 10,000)
1267             50  repeated subpattern is too long
1268             51  octal value is greater than \377 (not in UTF-8 mode)
1269             52  internal error: overran compiling workspace
1270             53   internal  error:  previously-checked  referenced  subpattern not
1271           found
1272             54  DEFINE group contains more than one branch
1273             55  repeating a DEFINE group is not allowed
1274             56  inconsistent NEWLINE options"
1275    
1276    
1277  STUDYING A PATTERN  STUDYING A PATTERN
1278    
1279         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1280              const char **errptr);              const char **errptr);
1281    
1282         If  a  compiled  pattern is going to be used several times, it is worth         If a compiled pattern is going to be used several times,  it  is  worth
1283         spending more time analyzing it in order to speed up the time taken for         spending more time analyzing it in order to speed up the time taken for
1284         matching.  The function pcre_study() takes a pointer to a compiled pat-         matching. The function pcre_study() takes a pointer to a compiled  pat-
1285         tern as its first argument. If studying the pattern produces additional         tern as its first argument. If studying the pattern produces additional
1286         information  that  will  help speed up matching, pcre_study() returns a         information that will help speed up matching,  pcre_study()  returns  a
1287         pointer to a pcre_extra block, in which the study_data field points  to         pointer  to a pcre_extra block, in which the study_data field points to
1288         the results of the study.         the results of the study.
1289    
1290         The  returned  value  from  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1291         pcre_exec(). However, a pcre_extra block  also  contains  other  fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1292         that  can  be  set  by the caller before the block is passed; these are         that can be set by the caller before the block  is  passed;  these  are
1293         described below in the section on matching a pattern.         described below in the section on matching a pattern.
1294    
1295         If studying the pattern does not produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1296         pcre_study() returns NULL. In that circumstance, if the calling program         pcre_study() returns NULL. In that circumstance, if the calling program
1297         wants to pass any of the other fields to pcre_exec(), it  must  set  up         wants  to  pass  any of the other fields to pcre_exec(), it must set up
1298         its own pcre_extra block.         its own pcre_extra block.
1299    
1300         The  second  argument of pcre_study() contains option bits. At present,         The second argument of pcre_study() contains option bits.  At  present,
1301         no options are defined, and this argument should always be zero.         no options are defined, and this argument should always be zero.
1302    
1303         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.
1304         If  studying  succeeds  (even  if no data is returned), the variable it         If studying succeeds (even if no data is  returned),  the  variable  it
1305         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
1306         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
1307         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
1308           after calling pcre_study(), to be sure that it has run successfully.
1309    
1310         This is a typical call to pcre_study():         This is a typical call to pcre_study():
1311    
# Line 816  LOCALE SUPPORT Line 1324  LOCALE SUPPORT
1324    
1325         PCRE handles caseless matching, and determines whether  characters  are         PCRE handles caseless matching, and determines whether  characters  are
1326         letters,  digits, or whatever, by reference to a set of tables, indexed         letters,  digits, or whatever, by reference to a set of tables, indexed
1327         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
1328         characters  with  codes  less than 128. Higher-valued codes never match         characters  with  codes  less than 128. Higher-valued codes never match
1329         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
1330         with Unicode character property support.)         with  Unicode  character property support. The use of locales with Uni-
1331           code is discouraged. If you are handling characters with codes  greater
1332         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
1333         is built. This is used when the final  argument  of  pcre_compile()  is         not try to mix the two.
1334         NULL,  and  is  sufficient for many applications. An alternative set of  
1335         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
1336         locale  from the default. As more and more applications change to using         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1337         Unicode, the need for this locale support is expected to die away.         applications.  Normally, the internal tables recognize only ASCII char-
1338           acters. However, when PCRE is built, it is possible to cause the inter-
1339           nal tables to be rebuilt in the default "C" locale of the local system,
1340           which may cause them to be different.
1341    
1342           The  internal tables can always be overridden by tables supplied by the
1343           application that calls PCRE. These may be created in a different locale
1344           from  the  default.  As more and more applications change to using Uni-
1345           code, the need for this locale support is expected to die away.
1346    
1347         External tables are built by calling  the  pcre_maketables()  function,         External tables are built by calling  the  pcre_maketables()  function,
1348         which  has no arguments, in the relevant locale. The result can then be         which  has no arguments, in the relevant locale. The result can then be
# Line 839  LOCALE SUPPORT Line 1355  LOCALE SUPPORT
1355           tables = pcre_maketables();           tables = pcre_maketables();
1356           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1357    
1358         When  pcre_maketables()  runs,  the  tables are built in memory that is         The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1359         obtained via pcre_malloc. It is the caller's responsibility  to  ensure         if you are using Windows, the name for the French locale is "french".
1360         that  the memory containing the tables remains available for as long as  
1361           When pcre_maketables() runs, the tables are built  in  memory  that  is
1362           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1363           that the memory containing the tables remains available for as long  as
1364         it is needed.         it is needed.
1365    
1366         The pointer that is passed to pcre_compile() is saved with the compiled         The pointer that is passed to pcre_compile() is saved with the compiled
1367         pattern,  and the same tables are used via this pointer by pcre_study()         pattern, and the same tables are used via this pointer by  pcre_study()
1368         and normally also by pcre_exec(). Thus, by default, for any single pat-         and normally also by pcre_exec(). Thus, by default, for any single pat-
1369         tern, compilation, studying and matching all happen in the same locale,         tern, compilation, studying and matching all happen in the same locale,
1370         but different patterns can be compiled in different locales.         but different patterns can be compiled in different locales.
1371    
1372         It is possible to pass a table pointer or NULL (indicating the  use  of         It  is  possible to pass a table pointer or NULL (indicating the use of
1373         the  internal  tables)  to  pcre_exec(). Although not intended for this         the internal tables) to pcre_exec(). Although  not  intended  for  this
1374         purpose, this facility could be used to match a pattern in a  different         purpose,  this facility could be used to match a pattern in a different
1375         locale from the one in which it was compiled. Passing table pointers at         locale from the one in which it was compiled. Passing table pointers at
1376         run time is discussed below in the section on matching a pattern.         run time is discussed below in the section on matching a pattern.
1377    
# Line 862  INFORMATION ABOUT A PATTERN Line 1381  INFORMATION ABOUT A PATTERN
1381         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1382              int what, void *where);              int what, void *where);
1383    
1384         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1385         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1386         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1387    
1388         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1389         pattern.  The second argument is the result of pcre_study(), or NULL if         pattern. The second argument is the result of pcre_study(), or NULL  if
1390         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1391         of  information  is required, and the fourth argument is a pointer to a         of information is required, and the fourth argument is a pointer  to  a
1392         variable to receive the data. The yield of the  function  is  zero  for         variable  to  receive  the  data. The yield of the function is zero for
1393         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1394    
1395           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 878  INFORMATION ABOUT A PATTERN Line 1397  INFORMATION ABOUT A PATTERN
1397           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1398           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1399    
1400         The  "magic  number" is placed at the start of each compiled pattern as         The "magic number" is placed at the start of each compiled  pattern  as
1401         an simple check against passing an arbitrary memory pointer. Here is  a         an  simple check against passing an arbitrary memory pointer. Here is a
1402         typical  call  of pcre_fullinfo(), to obtain the length of the compiled         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1403         pattern:         pattern:
1404    
1405           int rc;           int rc;
1406           unsigned long int length;           size_t length;
1407           rc = pcre_fullinfo(           rc = pcre_fullinfo(
1408             re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1409             pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1410             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1411             &length);         /* where to put the data */             &length);         /* where to put the data */
1412    
1413         The possible values for the third argument are defined in  pcre.h,  and         The  possible  values for the third argument are defined in pcre.h, and
1414         are as follows:         are as follows:
1415    
1416           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1417    
1418         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1419         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1420         there are no back references.         there are no back references.
1421    
1422           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1423    
1424         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1425         argument should point to an int variable.         argument should point to an int variable.
1426    
1427           PCRE_INFO_DEFAULTTABLES           PCRE_INFO_DEFAULT_TABLES
1428    
1429         Return a pointer to the internal default character tables within  PCRE.         Return  a pointer to the internal default character tables within PCRE.
1430         The  fourth  argument should point to an unsigned char * variable. This         The fourth argument should point to an unsigned char *  variable.  This
1431         information call is provided for internal use by the pcre_study() func-         information call is provided for internal use by the pcre_study() func-
1432         tion.  External  callers  can  cause PCRE to use its internal tables by         tion. External callers can cause PCRE to use  its  internal  tables  by
1433         passing a NULL table pointer.         passing a NULL table pointer.
1434    
1435           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1436    
1437         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1438         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored pattern. The fourth argument should point to an int  vari-
1439         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1440         compatibility.)         is still recognized for backwards compatibility.)
1441    
1442         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
1443         (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  
1444    
1445         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1446         branch starts with "^", or         branch starts with "^", or
# Line 958  INFORMATION ABOUT A PATTERN Line 1476  INFORMATION ABOUT A PATTERN
1476    
1477         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE  supports the use of named as well as numbered capturing parenthe-
1478         ses. The names are just an additional way of identifying the  parenthe-         ses. The names are just an additional way of identifying the  parenthe-
1479         ses,  which  still  acquire  numbers.  A  convenience  function  called         ses, which still acquire numbers. Several convenience functions such as
1480         pcre_get_named_substring() is provided  for  extracting  an  individual         pcre_get_named_substring() are provided for  extracting  captured  sub-
1481         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
1482         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
1483         the  correct  pointers in the output vector (described with pcre_exec()         pointers in the output vector (described with pcre_exec() below). To do
1484         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
1485         which is described by these three values.         described by these three values.
1486    
1487         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
1488         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
# Line 974  INFORMATION ABOUT A PATTERN Line 1492  INFORMATION ABOUT A PATTERN
1492         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-
1493         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-
1494         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding name, zero terminated. The names are  in  alphabetical  order.
1495         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1496         set, so white space - including newlines - is ignored):         theses numbers. For example, consider  the  following  pattern  (assume
1497           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1498           ignored):
1499    
1500           (?P<date> (?P<year>(\d\d)?\d\d) -           (?<date> (?<year>(\d\d)?\d\d) -
1501           (?P<month>\d\d) - (?P<day>\d\d) )           (?<month>\d\d) - (?<day>\d\d) )
1502    
1503         There are four named subpatterns, so the table has  four  entries,  and         There are four named subpatterns, so the table has  four  entries,  and
1504         each  entry  in the table is eight bytes long. The table is as follows,         each  entry  in the table is eight bytes long. The table is as follows,
# Line 991  INFORMATION ABOUT A PATTERN Line 1511  INFORMATION ABOUT A PATTERN
1511           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1512    
1513         When  writing  code  to  extract  data from named subpatterns using the         When  writing  code  to  extract  data from named subpatterns using the
1514         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
1515         be different for each compiled pattern.         to be different for each compiled pattern.
1516    
1517           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1518    
# Line 1051  OBSOLETE INFO FUNCTION Line 1571  OBSOLETE INFO FUNCTION
1571         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1572    
1573    
1574  MATCHING A PATTERN  REFERENCE COUNTS
1575    
1576           int pcre_refcount(pcre *code, int adjust);
1577    
1578           The  pcre_refcount()  function is used to maintain a reference count in
1579           the data block that contains a compiled pattern. It is provided for the
1580           benefit  of  applications  that  operate  in an object-oriented manner,
1581           where different parts of the application may be using the same compiled
1582           pattern, but you want to free the block when they are all done.
1583    
1584           When a pattern is compiled, the reference count field is initialized to
1585           zero.  It is changed only by calling this function, whose action is  to
1586           add  the  adjust  value  (which may be positive or negative) to it. The
1587           yield of the function is the new value. However, the value of the count
1588           is  constrained to lie between 0 and 65535, inclusive. If the new value
1589           is outside these limits, it is forced to the appropriate limit value.
1590    
1591           Except when it is zero, the reference count is not correctly  preserved
1592           if  a  pattern  is  compiled on one host and then transferred to a host
1593           whose byte-order is different. (This seems a highly unlikely scenario.)
1594    
1595    
1596    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1597    
1598         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1599              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
# Line 1060  MATCHING A PATTERN Line 1602  MATCHING A PATTERN
1602         The  function pcre_exec() is called to match a subject string against a         The  function pcre_exec() is called to match a subject string against a
1603         compiled pattern, which is passed in the code argument. If the  pattern         compiled pattern, which is passed in the code argument. If the  pattern
1604         has been studied, the result of the study should be passed in the extra         has been studied, the result of the study should be passed in the extra
1605         argument.         argument. This function is the main matching facility of  the  library,
1606           and it operates in a Perl-like manner. For specialist use there is also
1607           an alternative matching function, which is described below in the  sec-
1608           tion about the pcre_dfa_exec() function.
1609    
1610         In most applications, the pattern will have been compiled (and  option-         In  most applications, the pattern will have been compiled (and option-
1611         ally  studied)  in the same process that calls pcre_exec(). However, it         ally studied) in the same process that calls pcre_exec().  However,  it
1612         is possible to save compiled patterns and study data, and then use them         is possible to save compiled patterns and study data, and then use them
1613         later  in  different processes, possibly even on different hosts. For a         later in different processes, possibly even on different hosts.  For  a
1614         discussion about this, see the pcreprecompile documentation.         discussion about this, see the pcreprecompile documentation.
1615    
1616         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
# Line 1080  MATCHING A PATTERN Line 1625  MATCHING A PATTERN
1625             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1626             0,              /* default options */             0,              /* default options */
1627             ovector,        /* vector of integers for substring information */             ovector,        /* vector of integers for substring information */
1628             30);            /* number of elements in the vector  (NOT  size  in             30);            /* number of elements (NOT size in bytes) */
        bytes) */  
1629    
1630     Extra data for pcre_exec()     Extra data for pcre_exec()
1631    
1632         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
1633         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
1634         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-
1635         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
1636         lows:         fields (not necessarily in this order):
1637    
1638           unsigned long int flags;           unsigned long int flags;
1639           void *study_data;           void *study_data;
1640           unsigned long int match_limit;           unsigned long int match_limit;
1641             unsigned long int match_limit_recursion;
1642           void *callout_data;           void *callout_data;
1643           const unsigned char *tables;           const unsigned char *tables;
1644    
# Line 1102  MATCHING A PATTERN Line 1647  MATCHING A PATTERN
1647    
1648           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1649           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1650             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1651           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1652           PCRE_EXTRA_TABLES           PCRE_EXTRA_TABLES
1653    
# Line 1118  MATCHING A PATTERN Line 1664  MATCHING A PATTERN
1664         repeats.         repeats.
1665    
1666         Internally, PCRE uses a function called match() which it calls  repeat-         Internally, PCRE uses a function called match() which it calls  repeat-
1667         edly  (sometimes  recursively).  The  limit is imposed on the number of         edly  (sometimes  recursively). The limit set by match_limit is imposed
1668         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
1669         limiting  the amount of recursion and backtracking that can take place.         has  the  effect  of  limiting the amount of backtracking that can take
1670         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
1671         position in the subject string.         for each position in the subject string.
1672    
1673         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
1674         default default is 10 million, which handles all but the  most  extreme         default default is 10 million, which handles all but the  most  extreme
1675         cases.  You  can  reduce  the  default  by  suppling pcre_exec() with a         cases.  You  can  override  the  default by suppling pcre_exec() with a
1676         pcre_extra block in which match_limit is set to a  smaller  value,  and         pcre_extra    block    in    which    match_limit    is    set,     and
1677         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
1678         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.         exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1679    
1680           The match_limit_recursion field is similar to match_limit, but  instead
1681           of limiting the total number of times that match() is called, it limits
1682           the depth of recursion. The recursion depth is a  smaller  number  than
1683           the  total number of calls, because not all calls to match() are recur-
1684           sive.  This limit is of use only if it is set smaller than match_limit.
1685    
1686           Limiting  the  recursion  depth  limits the amount of stack that can be
1687           used, or, when PCRE has been compiled to use memory on the heap instead
1688           of the stack, the amount of heap memory that can be used.
1689    
1690           The  default  value  for  match_limit_recursion can be set when PCRE is
1691           built; the default default  is  the  same  value  as  the  default  for
1692           match_limit.  You can override the default by suppling pcre_exec() with
1693           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1694           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1695           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1696    
1697         The pcre_callout field is used in conjunction with the  "callout"  fea-         The pcre_callout field is used in conjunction with the  "callout"  fea-
1698         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1699    
# Line 1148  MATCHING A PATTERN Line 1711  MATCHING A PATTERN
1711     Option bits for pcre_exec()     Option bits for pcre_exec()
1712    
1713         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.
1714         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,
1715         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.         PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1716           PCRE_PARTIAL.
1717    
1718           PCRE_ANCHORED           PCRE_ANCHORED
1719    
1720         The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first         The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1721         matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or         matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1722         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
1723         unachored at matching time.         unachored at matching time.
1724    
1725             PCRE_NEWLINE_CR
1726             PCRE_NEWLINE_LF
1727             PCRE_NEWLINE_CRLF
1728             PCRE_NEWLINE_ANY
1729    
1730           These options override  the  newline  definition  that  was  chosen  or
1731           defaulted  when the pattern was compiled. For details, see the descrip-
1732           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1733           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1734           ters. It may also alter the way the match position is advanced after  a
1735           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1736           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1737           position  is  at a CRLF sequence, the match position is advanced by two
1738           characters instead of one, in other words, to after the CRLF.
1739    
1740           PCRE_NOTBOL           PCRE_NOTBOL
1741    
1742         This option specifies that first character of the subject string is not         This option specifies that first character of the subject string is not
1743         the beginning of a line, so the  circumflex  metacharacter  should  not         the  beginning  of  a  line, so the circumflex metacharacter should not
1744         match  before it. Setting this without PCRE_MULTILINE (at compile time)         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1745         causes  circumflex  never  to  match.  This  option  affects  only  the         causes  circumflex  never to match. This option affects only the behav-
1746         behaviour of the circumflex metacharacter. It does not affect \A.         iour of the circumflex metacharacter. It does not affect \A.
1747    
1748           PCRE_NOTEOL           PCRE_NOTEOL
1749    
1750         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
1751         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
1752         in  multiline mode) a newline immediately before it. Setting this with-         in multiline mode) a newline immediately before it. Setting this  with-
1753         out PCRE_MULTILINE (at compile time) causes dollar never to match. This         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1754         option  affects only the behaviour of the dollar metacharacter. It does         option affects only the behaviour of the dollar metacharacter. It  does
1755         not affect \Z or \z.         not affect \Z or \z.
1756    
1757           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1758    
1759         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
1760         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
1761         the alternatives match the empty string, the entire  match  fails.  For         the  alternatives  match  the empty string, the entire match fails. For
1762         example, if the pattern         example, if the pattern
1763    
1764           a?b?           a?b?
1765    
1766         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
1767         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
1768         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-
1769         rences of "a" or "b".         rences of "a" or "b".
1770    
1771         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-
1772         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()
1773         function, and when using the /g modifier. It  is  possible  to  emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1774         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
1775         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
1776         if  that  fails by advancing the starting offset (see below) and trying         if that fails by advancing the starting offset (see below)  and  trying
1777         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
1778         this in the pcredemo.c sample program.         this in the pcredemo.c sample program.
1779    
1780           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1781    
1782         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
1783         UTF-8 string is automatically checked when pcre_exec() is  subsequently         UTF-8  string is automatically checked when pcre_exec() is subsequently
1784         called.   The  value  of  startoffset is also checked to ensure that it         called.  The value of startoffset is also checked  to  ensure  that  it
1785         points to the start of a UTF-8 character. If an invalid UTF-8  sequence         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
1786         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1787         startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1788         returned.         returned.
1789    
1790         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
1791         these   checks   for   performance   reasons,   you   can    set    the         these    checks    for   performance   reasons,   you   can   set   the
1792         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1793         do this for the second and subsequent calls to pcre_exec() if  you  are         do  this  for the second and subsequent calls to pcre_exec() if you are
1794         making  repeated  calls  to  find  all  the matches in a single subject         making repeated calls to find all  the  matches  in  a  single  subject
1795         string. However, you should be  sure  that  the  value  of  startoffset         string.  However,  you  should  be  sure  that the value of startoffset
1796         points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is         points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1797         set, the effect of passing an invalid UTF-8 string as a subject,  or  a         set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1798         value  of startoffset that does not point to the start of a UTF-8 char-         value of startoffset that does not point to the start of a UTF-8  char-
1799         acter, is undefined. Your program may crash.         acter, is undefined. Your program may crash.
1800    
1801           PCRE_PARTIAL           PCRE_PARTIAL
1802    
1803         This option turns on the  partial  matching  feature.  If  the  subject         This  option  turns  on  the  partial  matching feature. If the subject
1804         string  fails to match the pattern, but at some point during the match-         string fails to match the pattern, but at some point during the  match-
1805         ing process the end of the subject was reached (that  is,  the  subject         ing  process  the  end of the subject was reached (that is, the subject
1806         partially  matches  the  pattern and the failure to match occurred only         partially matches the pattern and the failure to  match  occurred  only
1807         because there were not enough subject characters), pcre_exec()  returns         because  there were not enough subject characters), pcre_exec() returns
1808         PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is         PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1809         used, there are restrictions on what may appear in the  pattern.  These         used,  there  are restrictions on what may appear in the pattern. These
1810         are discussed in the pcrepartial documentation.         are discussed in the pcrepartial documentation.
1811    
1812     The string to be matched by pcre_exec()     The string to be matched by pcre_exec()
1813    
1814         The  subject string is passed to pcre_exec() as a pointer in subject, a         The subject string is passed to pcre_exec() as a pointer in subject,  a
1815         length in length, and a starting byte offset in startoffset.  In  UTF-8         length  in  length, and a starting byte offset in startoffset. In UTF-8
1816         mode,  the  byte  offset  must point to the start of a UTF-8 character.         mode, the byte offset must point to the start  of  a  UTF-8  character.
1817         Unlike the pattern string, the subject may contain binary  zero  bytes.         Unlike  the  pattern string, the subject may contain binary zero bytes.
1818         When  the starting offset is zero, the search for a match starts at the         When the starting offset is zero, the search for a match starts at  the
1819         beginning of the subject, and this is by far the most common case.         beginning of the subject, and this is by far the most common case.
1820    
1821         A non-zero starting offset is useful when searching for  another  match         A  non-zero  starting offset is useful when searching for another match
1822         in  the same subject by calling pcre_exec() again after a previous suc-         in the same subject by calling pcre_exec() again after a previous  suc-
1823         cess.  Setting startoffset differs from just passing over  a  shortened         cess.   Setting  startoffset differs from just passing over a shortened
1824         string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins         string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1825         with any kind of lookbehind. For example, consider the pattern         with any kind of lookbehind. For example, consider the pattern
1826    
1827           \Biss\B           \Biss\B
1828    
1829         which finds occurrences of "iss" in the middle of  words.  (\B  matches         which  finds  occurrences  of "iss" in the middle of words. (\B matches
1830         only  if  the  current position in the subject is not a word boundary.)         only if the current position in the subject is not  a  word  boundary.)
1831         When applied to the string "Mississipi" the first call  to  pcre_exec()         When  applied  to the string "Mississipi" the first call to pcre_exec()
1832         finds  the  first  occurrence. If pcre_exec() is called again with just         finds the first occurrence. If pcre_exec() is called  again  with  just
1833         the remainder of the subject,  namely  "issipi",  it  does  not  match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1834         because \B is always false at the start of the subject, which is deemed         because \B is always false at the start of the subject, which is deemed
1835         to be a word boundary. However, if pcre_exec()  is  passed  the  entire         to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1836         string again, but with startoffset set to 4, it finds the second occur-         string again, but with startoffset set to 4, it finds the second occur-
1837         rence of "iss" because it is able to look behind the starting point  to         rence  of "iss" because it is able to look behind the starting point to
1838         discover that it is preceded by a letter.         discover that it is preceded by a letter.
1839    
1840         If  a  non-zero starting offset is passed when the pattern is anchored,         If a non-zero starting offset is passed when the pattern  is  anchored,
1841         one attempt to match at the given offset is made. This can only succeed         one attempt to match at the given offset is made. This can only succeed
1842         if  the  pattern  does  not require the match to be at the start of the         if the pattern does not require the match to be at  the  start  of  the
1843         subject.         subject.
1844    
1845     How pcre_exec() returns captured substrings     How pcre_exec() returns captured substrings
1846    
1847         In general, a pattern matches a certain portion of the subject, and  in         In  general, a pattern matches a certain portion of the subject, and in
1848         addition,  further  substrings  from  the  subject may be picked out by         addition, further substrings from the subject  may  be  picked  out  by
1849         parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,         parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1850         this  is  called "capturing" in what follows, and the phrase "capturing         this is called "capturing" in what follows, and the  phrase  "capturing
1851         subpattern" is used for a fragment of a pattern that picks out  a  sub-         subpattern"  is  used for a fragment of a pattern that picks out a sub-
1852         string.  PCRE  supports several other kinds of parenthesized subpattern         string. PCRE supports several other kinds of  parenthesized  subpattern
1853         that do not cause substrings to be captured.         that do not cause substrings to be captured.
1854    
1855         Captured substrings are returned to the caller via a vector of  integer         Captured  substrings are returned to the caller via a vector of integer
1856         offsets  whose  address is passed in ovector. The number of elements in         offsets whose address is passed in ovector. The number of  elements  in
1857         the vector is passed in ovecsize, which must be a non-negative  number.         the  vector is passed in ovecsize, which must be a non-negative number.
1858         Note: this argument is NOT the size of ovector in bytes.         Note: this argument is NOT the size of ovector in bytes.
1859    
1860         The  first  two-thirds of the vector is used to pass back captured sub-         The first two-thirds of the vector is used to pass back  captured  sub-
1861         strings, each substring using a pair of integers. The  remaining  third         strings,  each  substring using a pair of integers. The remaining third
1862         of  the  vector is used as workspace by pcre_exec() while matching cap-         of the vector is used as workspace by pcre_exec() while  matching  cap-
1863         turing subpatterns, and is not available for passing back  information.         turing  subpatterns, and is not available for passing back information.
1864         The  length passed in ovecsize should always be a multiple of three. If         The length passed in ovecsize should always be a multiple of three.  If
1865         it is not, it is rounded down.         it is not, it is rounded down.
1866    
1867         When a match is successful, information about  captured  substrings  is         When  a  match  is successful, information about captured substrings is
1868         returned  in  pairs  of integers, starting at the beginning of ovector,         returned in pairs of integers, starting at the  beginning  of  ovector,
1869         and continuing up to two-thirds of its length at the  most.  The  first         and  continuing  up  to two-thirds of its length at the most. The first
1870         element of a pair is set to the offset of the first character in a sub-         element of a pair is set to the offset of the first character in a sub-
1871         string, and the second is set to the  offset  of  the  first  character         string,  and  the  second  is  set to the offset of the first character
1872         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-
1873         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1],  identify  the  portion  of  the  subject string matched by the
1874         entire  pattern.  The next pair is used for the first capturing subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1875         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
1876         pairs  that  have  been set. If there are no capturing subpatterns, the         highest numbered pair that has been set. For example, if two substrings
1877         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
1878         first pair of offsets has been set.         subpatterns, the return value from a successful match is 1,  indicating
1879           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.  
1880    
1881         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1882         of the string that it matched that is returned.         of the string that it matched that is returned.
# Line 1320  MATCHING A PATTERN Line 1890  MATCHING A PATTERN
1890         substrings, PCRE has to get additional memory for use during  matching.         substrings, PCRE has to get additional memory for use during  matching.
1891         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1892    
1893         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
1894         patterns there are in a compiled pattern. The smallest size for ovector         subpatterns there are in a compiled  pattern.  The  smallest  size  for
1895         that  will  allow for n captured substrings, in addition to the offsets         ovector  that  will allow for n captured substrings, in addition to the
1896         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.
1897    
1898           It is possible for capturing subpattern number n+1 to match  some  part
1899           of the subject when subpattern n has not been used at all. For example,
1900           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1901           return from the function is 4, and subpatterns 1 and 3 are matched, but
1902           2 is not. When this happens, both values in  the  offset  pairs  corre-
1903           sponding to unused subpatterns are set to -1.
1904    
1905           Offset  values  that correspond to unused subpatterns at the end of the
1906           expression are also set to -1. For example,  if  the  string  "abc"  is
1907           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1908           matched. The return from the function is 2, because  the  highest  used
1909           capturing subpattern number is 1. However, you can refer to the offsets
1910           for the second and third capturing subpatterns if  you  wish  (assuming
1911           the vector is large enough, of course).
1912    
1913     Return values from pcre_exec()         Some  convenience  functions  are  provided for extracting the captured
1914           substrings as separate strings. These are described below.
1915    
1916       Error return values from pcre_exec()
1917    
1918         If pcre_exec() fails, it returns a negative number. The  following  are         If pcre_exec() fails, it returns a negative number. The  following  are
1919         defined in the header file:         defined in the header file:
# Line 1351  MATCHING A PATTERN Line 1939  MATCHING A PATTERN
1939         an  environment  with the other endianness. This is the error that PCRE         an  environment  with the other endianness. This is the error that PCRE
1940         gives when the magic number is not present.         gives when the magic number is not present.
1941    
1942           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_OPCODE (-5)
1943    
1944         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1945         compiled  pattern.  This  error  could be caused by a bug in PCRE or by         compiled  pattern.  This  error  could be caused by a bug in PCRE or by
# Line 1373  MATCHING A PATTERN Line 1961  MATCHING A PATTERN
1961    
1962           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1963    
1964         The recursion and backtracking limit, as specified by  the  match_limit         The backtracking limit, as specified by  the  match_limit  field  in  a
1965         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         pcre_extra  structure  (or  defaulted) was reached. See the description
1966         description above.         above.
1967    
1968           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1969    
# Line 1394  MATCHING A PATTERN Line 1982  MATCHING A PATTERN
1982         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-
1983         ter.         ter.
1984    
1985           PCRE_ERROR_PARTIAL (-12)           PCRE_ERROR_PARTIAL        (-12)
1986    
1987         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
1988         pcrepartial documentation for details of partial matching.         pcrepartial documentation for details of partial matching.
1989    
1990           PCRE_ERROR_BAD_PARTIAL (-13)           PCRE_ERROR_BADPARTIAL     (-13)
1991    
1992         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing         The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1993         items  that are not supported for partial matching. See the pcrepartial         items  that are not supported for partial matching. See the pcrepartial
1994         documentation for details of partial matching.         documentation for details of partial matching.
1995    
1996           PCRE_ERROR_INTERNAL (-14)           PCRE_ERROR_INTERNAL       (-14)
1997    
1998         An unexpected internal error has occurred. This error could  be  caused         An unexpected internal error has occurred. This error could  be  caused
1999         by a bug in PCRE or by overwriting of the compiled pattern.         by a bug in PCRE or by overwriting of the compiled pattern.
2000    
2001           PCRE_ERROR_BADCOUNT (-15)           PCRE_ERROR_BADCOUNT       (-15)
2002    
2003         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.
2004    
2005             PCRE_ERROR_RECURSIONLIMIT (-21)
2006    
2007           The internal recursion limit, as specified by the match_limit_recursion
2008           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2009           description above.
2010    
2011             PCRE_ERROR_NULLWSLIMIT    (-22)
2012    
2013           When a group that can match an empty  substring  is  repeated  with  an
2014           unbounded  upper  limit, the subject position at the start of the group
2015           must be remembered, so that a test for an empty string can be made when
2016           the  end  of the group is reached. Some workspace is required for this;
2017           if it runs out, this error is given.
2018    
2019             PCRE_ERROR_BADNEWLINE     (-23)
2020    
2021           An invalid combination of PCRE_NEWLINE_xxx options was given.
2022    
2023           Error numbers -16 to -20 are not used by pcre_exec().
2024    
2025    
2026  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2027    
# Line 1434  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2042  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2042         string_list()  are  provided for extracting captured substrings as new,         string_list()  are  provided for extracting captured substrings as new,
2043         separate, zero-terminated strings. These functions identify  substrings         separate, zero-terminated strings. These functions identify  substrings
2044         by  number.  The  next section describes functions for extracting named         by  number.  The  next section describes functions for extracting named
2045         substrings. A substring  that  contains  a  binary  zero  is  correctly         substrings.
2046         extracted  and  has  a further zero added on the end, but the result is  
2047         not, of course, a C string.         A substring that contains a binary zero is correctly extracted and  has
2048           a  further zero added on the end, but the result is not, of course, a C
2049           string.  However, you can process such a string  by  referring  to  the
2050           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2051           string().  Unfortunately, the interface to pcre_get_substring_list() is
2052           not  adequate for handling strings containing binary zeros, because the
2053           end of the final string is not independently indicated.
2054    
2055         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-
2056         tions:  subject  is  the subject string that has just been successfully         tions:  subject  is  the subject string that has just been successfully
# Line 1456  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2070  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2070         buffersize,  while  for  pcre_get_substring()  a new block of memory is         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2071         obtained via pcre_malloc, and its address is  returned  via  stringptr.         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2072         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
2073         the terminating zero, or one of         the terminating zero, or one of these error codes:
2074    
2075           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2076    
# Line 1472  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 2086  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2086         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
2087         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
2088         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
2089         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
2090           error code
2091    
2092           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
2093    
2094         if the attempt to get the memory block failed.         if the attempt to get the memory block failed.
2095    
2096         When any of these functions encounter a substring that is unset,  which         When  any of these functions encounter a substring that is unset, which
2097         can  happen  when  capturing subpattern number n+1 matches some part of         can happen when capturing subpattern number n+1 matches  some  part  of
2098         the subject, but subpattern n has not been used at all, they return  an         the  subject, but subpattern n has not been used at all, they return an
2099         empty string. This can be distinguished from a genuine zero-length sub-         empty string. This can be distinguished from a genuine zero-length sub-
2100         string by inspecting the appropriate offset in ovector, which is  nega-         string  by inspecting the appropriate offset in ovector, which is nega-
2101         tive for unset substrings.         tive for unset substrings.
2102    
2103         The  two convenience functions pcre_free_substring() and pcre_free_sub-         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2104         string_list() can be used to free the memory  returned  by  a  previous         string_list()  can  be  used  to free the memory returned by a previous
2105         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2106         tively. They do nothing more than  call  the  function  pointed  to  by         tively.  They  do  nothing  more  than  call the function pointed to by
2107         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.
2108         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-
2109         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  that  cannot   use
2110         pcre_free directly; it is  for  these  cases  that  the  functions  are         pcre_free  directly;  it is for these cases that the functions are pro-
2111         provided.         vided.
2112    
2113    
2114  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
# Line 1511  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2126  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2126              int stringcount, const char *stringname,              int stringcount, const char *stringname,
2127              const char **stringptr);              const char **stringptr);
2128    
2129         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-
2130         ber.  For example, for this pattern         ber.  For example, for this pattern
2131    
2132           (a+)b(?<xxx>\d+)...           (a+)b(?<xxx>\d+)...
2133    
2134         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
2135         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
2136         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-
2137         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
2138         there is no subpattern of that name.         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2139           subpattern of that name.
2140    
2141         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
2142         the functions described in the previous section. For convenience, there         the functions described in the previous section. For convenience, there
# Line 1539  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 2155  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2155    
2156         These  functions call pcre_get_stringnumber(), and if it succeeds, they         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2157         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-         then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2158         ate.         ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2159           behaviour may not be what you want (see the next section).
2160    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2161    
2162  PCRE(3)                                                                PCRE(3)  DUPLICATE SUBPATTERN NAMES
2163    
2164           int pcre_get_stringtable_entries(const pcre *code,
2165                const char *name, char **first, char **last);
2166    
2167           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2168           subpatterns  are  not  required  to  be unique. Normally, patterns with
2169           duplicate names are such that in any one match, only one of  the  named
2170           subpatterns  participates. An example is shown in the pcrepattern docu-
2171           mentation. When duplicates are present, pcre_copy_named_substring() and
2172           pcre_get_named_substring()  return the first substring corresponding to
2173           the given name that is set.  If  none  are  set,  an  empty  string  is
2174           returned.  The pcre_get_stringnumber() function returns one of the num-
2175           bers that are associated with the name, but it is not defined which  it
2176           is.
2177    
2178           If  you want to get full details of all captured substrings for a given
2179           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2180           first argument is the compiled pattern, and the second is the name. The
2181           third and fourth are pointers to variables which  are  updated  by  the
2182           function. After it has run, they point to the first and last entries in
2183           the name-to-number table  for  the  given  name.  The  function  itself
2184           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2185           there are none. The format of the table is described above in the  sec-
2186           tion  entitled  Information  about  a  pattern.  Given all the relevant
2187           entries for the name, you can extract each of their numbers, and  hence
2188           the captured data, if any.
2189    
2190    
2191    FINDING ALL POSSIBLE MATCHES
2192    
2193           The  traditional  matching  function  uses a similar algorithm to Perl,
2194           which stops when it finds the first match, starting at a given point in
2195           the  subject.  If you want to find all possible matches, or the longest
2196           possible match, consider using the alternative matching  function  (see
2197           below)  instead.  If you cannot use the alternative function, but still
2198           need to find all possible matches, you can kludge it up by  making  use
2199           of the callout facility, which is described in the pcrecallout documen-
2200           tation.
2201    
2202           What you have to do is to insert a callout right at the end of the pat-
2203           tern.   When your callout function is called, extract and save the cur-
2204           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2205           backtrack  and  try other alternatives. Ultimately, when it runs out of
2206           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2207    
2208    
2209    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2210    
2211           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2212                const char *subject, int length, int startoffset,
2213                int options, int *ovector, int ovecsize,
2214                int *workspace, int wscount);
2215    
2216           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2217           against  a  compiled pattern, using a matching algorithm that scans the
2218           subject string just once, and does not backtrack.  This  has  different
2219           characteristics  to  the  normal  algorithm, and is not compatible with
2220           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2221           theless,  there are times when this kind of matching can be useful. For
2222           a discussion of the two matching algorithms, see the pcrematching docu-
2223           mentation.
2224    
2225           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2226           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2227           ent  way,  and  this is described below. The other common arguments are
2228           used in the same way as for pcre_exec(), so their  description  is  not
2229           repeated here.
2230    
2231           The  two  additional  arguments provide workspace for the function. The
2232           workspace vector should contain at least 20 elements. It  is  used  for
2233           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2234           workspace will be needed for patterns and subjects where  there  are  a
2235           lot of potential matches.
2236    
2237           Here is an example of a simple call to pcre_dfa_exec():
2238    
2239             int rc;
2240             int ovector[10];
2241             int wspace[20];
2242             rc = pcre_dfa_exec(
2243               re,             /* result of pcre_compile() */
2244               NULL,           /* we didn't study the pattern */
2245               "some string",  /* the subject string */
2246               11,             /* the length of the subject string */
2247               0,              /* start at offset 0 in the subject */
2248               0,              /* default options */
2249               ovector,        /* vector of integers for substring information */
2250               10,             /* number of elements (NOT size in bytes) */
2251               wspace,         /* working space vector */
2252               20);            /* number of elements (NOT size in bytes) */
2253    
2254       Option bits for pcre_dfa_exec()
2255    
2256           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2257           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2258           LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2259           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2260           three of these are the same as for pcre_exec(), so their description is
2261           not repeated here.
2262    
2263             PCRE_PARTIAL
2264    
2265           This has the same general effect as it does for  pcre_exec(),  but  the
2266           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2267           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2268           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2269           been no complete matches, but there is still at least one matching pos-
2270           sibility.  The portion of the string that provided the partial match is
2271           set as the first matching string.
2272    
2273             PCRE_DFA_SHORTEST
2274    
2275           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2276           stop as soon as it has found one match. Because of the way the alterna-
2277           tive algorithm works, this is necessarily the shortest  possible  match
2278           at the first possible matching point in the subject string.
2279    
2280             PCRE_DFA_RESTART
2281    
2282           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2283           returns a partial match, it is possible to call it  again,  with  addi-
2284           tional  subject  characters,  and have it continue with the same match.
2285           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2286           workspace  and wscount options must reference the same vector as before
2287           because data about the match so far is left in  them  after  a  partial
2288           match.  There  is  more  discussion of this facility in the pcrepartial
2289           documentation.
2290    
2291       Successful returns from pcre_dfa_exec()
2292    
2293           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2294           string in the subject. Note, however, that all the matches from one run
2295           of the function start at the same point in  the  subject.  The  shorter
2296           matches  are all initial substrings of the longer matches. For example,
2297           if the pattern
2298    
2299             <.*>
2300    
2301           is matched against the string
2302    
2303             This is <something> <something else> <something further> no more
2304    
2305           the three matched strings are
2306    
2307             <something>
2308             <something> <something else>
2309             <something> <something else> <something further>
2310    
2311           On success, the yield of the function is a number  greater  than  zero,
2312           which  is  the  number of matched substrings. The substrings themselves
2313           are returned in ovector. Each string uses two elements;  the  first  is
2314           the  offset  to  the start, and the second is the offset to the end. In
2315           fact, all the strings have the same start  offset.  (Space  could  have
2316           been  saved by giving this only once, but it was decided to retain some
2317           compatibility with the way pcre_exec() returns data,  even  though  the
2318           meaning of the strings is different.)
2319    
2320           The strings are returned in reverse order of length; that is, the long-
2321           est matching string is given first. If there were too many  matches  to
2322           fit  into ovector, the yield of the function is zero, and the vector is
2323           filled with the longest matches.
2324    
2325       Error returns from pcre_dfa_exec()
2326    
2327           The pcre_dfa_exec() function returns a negative number when  it  fails.
2328           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2329           described above.  There are in addition the following errors  that  are
2330           specific to pcre_dfa_exec():
2331    
2332             PCRE_ERROR_DFA_UITEM      (-16)
2333    
2334           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2335           tern that it does not support, for instance, the use of \C  or  a  back
2336           reference.
2337    
2338             PCRE_ERROR_DFA_UCOND      (-17)
2339    
2340           This  return  is  given  if pcre_dfa_exec() encounters a condition item
2341           that uses a back reference for the condition, or a test  for  recursion
2342           in a specific group. These are not supported.
2343    
2344             PCRE_ERROR_DFA_UMLIMIT    (-18)
2345    
2346           This  return  is given if pcre_dfa_exec() is called with an extra block
2347           that contains a setting of the match_limit field. This is not supported
2348           (it is meaningless).
2349    
2350             PCRE_ERROR_DFA_WSSIZE     (-19)
2351    
2352           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2353           workspace vector.
2354    
2355             PCRE_ERROR_DFA_RECURSE    (-20)
2356    
2357           When a recursive subpattern is processed, the matching  function  calls
2358           itself  recursively,  using  private vectors for ovector and workspace.
2359           This error is given if the output vector  is  not  large  enough.  This
2360           should be extremely rare, as a vector of size 1000 is used.
2361    
2362    
2363    SEE ALSO
2364    
2365           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2366           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2367    
2368    
2369    AUTHOR
2370    
2371           Philip Hazel
2372           University Computing Service
2373           Cambridge CB2 3QH, England.
2374    
2375    
2376    REVISION
2377    
2378           Last updated: 06 March 2007
2379           Copyright (c) 1997-2007 University of Cambridge.
2380    ------------------------------------------------------------------------------
2381    
2382    
2383    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2384    
2385    
2386  NAME  NAME
2387         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2388    
2389    
2390  PCRE CALLOUTS  PCRE CALLOUTS
2391    
2392         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
# Line 1606  MISSING CALLOUTS Line 2441  MISSING CALLOUTS
2441  THE CALLOUT INTERFACE  THE CALLOUT INTERFACE
2442    
2443         During matching, when PCRE reaches a callout point, the external  func-         During matching, when PCRE reaches a callout point, the external  func-
2444         tion  defined  by pcre_callout is called (if it is set). The only argu-         tion  defined by pcre_callout is called (if it is set). This applies to
2445         ment is a pointer to a pcre_callout block. This structure contains  the         both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2446         following fields:         only  argument  to  the callout function is a pointer to a pcre_callout
2447           block. This structure contains the following fields:
2448    
2449           int          version;           int          version;
2450           int          callout_number;           int          callout_number;
# Line 1623  THE CALLOUT INTERFACE Line 2459  THE CALLOUT INTERFACE
2459           int          pattern_position;           int          pattern_position;
2460           int          next_item_length;           int          next_item_length;
2461    
2462         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2463         block format. The initial version was 0; the current version is 1.  The         block  format. The initial version was 0; the current version is 1. The
2464         version  number  will  change  again in future if additional fields are         version number will change again in future  if  additional  fields  are
2465         added, but the intention is never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2466    
2467         The  callout_number  field  contains the number of the callout, as com-         The callout_number field contains the number of the  callout,  as  com-
2468         piled into the pattern (that is, the number after ?C for  manual  call-         piled  into  the pattern (that is, the number after ?C for manual call-
2469         outs, and 255 for automatically generated callouts).         outs, and 255 for automatically generated callouts).
2470    
2471         The  offset_vector field is a pointer to the vector of offsets that was         The offset_vector field is a pointer to the vector of offsets that  was
2472         passed by the caller to pcre_exec(). The contents can be  inspected  in         passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2473         order  to extract substrings that have been matched so far, in the same         pcre_exec() is used, the contents can be inspected in order to  extract
2474         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2475           extracting substrings after a match has completed. For  pcre_dfa_exec()
2476           this field is not useful.
2477    
2478         The subject and subject_length fields contain copies of the values that         The subject and subject_length fields contain copies of the values that
2479         were passed to pcre_exec().         were passed to pcre_exec().
2480    
2481         The  start_match  field contains the offset within the subject at which         The start_match field contains the offset within the subject  at  which
2482         the current match attempt started. If the pattern is not anchored,  the         the  current match attempt started. If the pattern is not anchored, the
2483         callout function may be called several times from the same point in the         callout function may be called several times from the same point in the
2484         pattern for different starting points in the subject.         pattern for different starting points in the subject.
2485    
2486         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2487         the current match pointer.         the current match pointer.
2488    
2489         The  capture_top field contains one more than the number of the highest         When the pcre_exec() function is used, the capture_top  field  contains
2490         numbered captured substring so far. If no  substrings  have  been  cap-         one  more than the number of the highest numbered captured substring so
2491         tured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2492           one.  This  is always the case when pcre_dfa_exec() is used, because it
2493         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2494         tured substring. If no substrings have been captured, its value is  -1.  
2495           The capture_last field contains the number of the  most  recently  cap-
2496         The  callout_data  field contains a value that is passed to pcre_exec()         tured  substring. If no substrings have been captured, its value is -1.
2497         by the caller specifically so that it can be passed back  in  callouts.         This is always the case when pcre_dfa_exec() is used.
2498         It  is  passed  in the pcre_callout field of the pcre_extra data struc-  
2499         ture. If no such data was  passed,  the  value  of  callout_data  in  a         The callout_data field contains a value that is passed  to  pcre_exec()
2500         pcre_callout  block  is  NULL. There is a description of the pcre_extra         or  pcre_dfa_exec() specifically so that it can be passed back in call-
2501           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2502           structure.  If  no such data was passed, the value of callout_data in a
2503           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2504         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2505    
2506         The pattern_position field is present from version 1 of the  pcre_call-         The  pattern_position field is present from version 1 of the pcre_call-
2507         out structure. It contains the offset to the next item to be matched in         out structure. It contains the offset to the next item to be matched in
2508         the pattern string.         the pattern string.
2509    
2510         The next_item_length field is present from version 1 of the  pcre_call-         The  next_item_length field is present from version 1 of the pcre_call-
2511         out structure. It contains the length of the next item to be matched in         out structure. It contains the length of the next item to be matched in
2512         the pattern string. When the callout immediately precedes  an  alterna-         the  pattern  string. When the callout immediately precedes an alterna-
2513         tion  bar, a closing parenthesis, or the end of the pattern, the length         tion bar, a closing parenthesis, or the end of the pattern, the  length
2514         is zero. When the callout precedes an opening parenthesis,  the  length         is  zero.  When the callout precedes an opening parenthesis, the length
2515         is that of the entire subpattern.         is that of the entire subpattern.
2516    
2517         The  pattern_position  and next_item_length fields are intended to help         The pattern_position and next_item_length fields are intended  to  help
2518         in distinguishing between different automatic callouts, which all  have         in  distinguishing between different automatic callouts, which all have
2519         the same callout number. However, they are set for all callouts.         the same callout number. However, they are set for all callouts.
2520    
2521    
2522  RETURN VALUES  RETURN VALUES
2523    
2524         The  external callout function returns an integer to PCRE. If the value         The external callout function returns an integer to PCRE. If the  value
2525         is zero, matching proceeds as normal. If  the  value  is  greater  than         is  zero,  matching  proceeds  as  normal. If the value is greater than
2526         zero,  matching  fails  at  the current point, but backtracking to test         zero, matching fails at the current point, but  the  testing  of  other
2527         other matching possibilities goes ahead, just as if a lookahead  asser-         matching possibilities goes ahead, just as if a lookahead assertion had
2528         tion  had  failed.  If  the value is less than zero, the match is aban-         failed. If the value is less than zero, the  match  is  abandoned,  and
2529         doned, and pcre_exec() returns the negative value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2530    
2531         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2532         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2533         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2534         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
2535         itself.         itself.
2536    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2537    
2538  PCRE(3)                                                                PCRE(3)  AUTHOR
2539    
2540           Philip Hazel
2541           University Computing Service
2542           Cambridge CB2 3QH, England.
2543    
2544    
2545    REVISION
2546    
2547           Last updated: 06 March 2007
2548           Copyright (c) 1997-2007 University of Cambridge.
2549    ------------------------------------------------------------------------------
2550    
2551    
2552    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2553    
2554    
2555  NAME  NAME
2556         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2557    
2558    
2559  DIFFERENCES BETWEEN PCRE AND PERL  DIFFERENCES BETWEEN PCRE AND PERL
2560    
2561         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2562         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences described here  are  mainly
2563         respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2564           tures that are expected to be in the forthcoming Perl 5.10.
2565         1.  PCRE does not have full UTF-8 support. Details of what it does have  
2566         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
2567           of  what  it does have are given in the section on UTF-8 support in the
2568           main pcre page.
2569    
2570         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2571         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 1738  DIFFERENCES BETWEEN PCRE AND PERL Line 2592  DIFFERENCES BETWEEN PCRE AND PERL
2592         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
2593         is  built  with Unicode character property support. The properties that         is  built  with Unicode character property support. The properties that
2594         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-
2595         erties such as Lu and Nd.         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2596           derived properties Any and L&.
2597    
2598         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2599         ters in between are treated as literals.  This  is  slightly  different         ters  in  between  are  treated as literals. This is slightly different
2600         from  Perl  in  that  $  and  @ are also handled as literals inside the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2601         quotes. In Perl, they cause variable interpolation (but of course  PCRE         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2602         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2603    
2604             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 1753  DIFFERENCES BETWEEN PCRE AND PERL Line 2608  DIFFERENCES BETWEEN PCRE AND PERL
2608             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2609             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2610    
2611         The  \Q...\E  sequence  is recognized both inside and outside character         The \Q...\E sequence is recognized both inside  and  outside  character
2612         classes.         classes.
2613    
2614         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2615         constructions.  However,  there is support for recursive patterns using         constructions. However, there is support for recursive  patterns.  This
2616         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
2617         "callout"  feature allows an external function to be called during pat-         "callout" feature allows an external function to be called during  pat-
2618         tern matching. See the pcrecallout documentation for details.         tern matching. See the pcrecallout documentation for details.
2619    
2620         9. There are some differences that are concerned with the  settings  of         9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2621         captured  strings  when  part  of  a  pattern is repeated. For example,         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2622         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2         unlike Perl.
2623    
2624           10.  There are some differences that are concerned with the settings of
2625           captured strings when part of  a  pattern  is  repeated.  For  example,
2626           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2627         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2628    
2629         10. PCRE provides some extensions to the Perl regular expression facil-         11. PCRE provides some extensions to the Perl regular expression facil-
2630         ities:         ities.   Perl  5.10  will  include new features that are not in earlier
2631           versions, some of which (such as named parentheses) have been  in  PCRE
2632           for some time. This list is with respect to Perl 5.10:
2633    
2634         (a) Although lookbehind assertions must  match  fixed  length  strings,         (a)  Although  lookbehind  assertions  must match fixed length strings,
2635         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2636         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2637    
2638         (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 $
2639         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2640    
2641         (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-
2642         cial meaning is faulted.         cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2643           ignored. (Perl can be made to issue a warning.)
2644    
2645         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2646         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 1790  DIFFERENCES BETWEEN PCRE AND PERL Line 2652  DIFFERENCES BETWEEN PCRE AND PERL
2652         (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-
2653         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2654    
2655         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive         (g) The callout facility is PCRE-specific.
        pattern  matching  (Perl  can  do  this using the (?p{code}) construct,  
        which PCRE cannot support.)  
2656    
2657         (h) PCRE supports named capturing substrings, using the Python  syntax.         (h) The partial matching facility is PCRE-specific.
2658    
2659         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2660         Sun's Java package.         even on different hosts that have the other endianness.
2661    
2662         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2663           different way and is not Perl-compatible.
2664    
        (k) The callout facility is PCRE-specific.  
2665    
2666         (l) The partial matching facility is PCRE-specific.  AUTHOR
2667    
2668         (m) Patterns compiled by PCRE can be saved and re-used at a later time,         Philip Hazel
2669         even on different hosts that have the other endianness.         University Computing Service
2670           Cambridge CB2 3QH, England.
2671    
 Last updated: 09 September 2004  
 Copyright (c) 1997-2004 University of Cambridge.  
 -----------------------------------------------------------------------------  
2672    
2673  PCRE(3)                                                                PCRE(3)  REVISION
2674    
2675           Last updated: 06 March 2007
2676           Copyright (c) 1997-2007 University of Cambridge.
2677    ------------------------------------------------------------------------------
2678    
2679    
2680    PCREPATTERN(3)                                                  PCREPATTERN(3)
2681    
2682    
2683  NAME  NAME
2684         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2685    
2686    
2687  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2688    
2689         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax  and semantics of the regular expressions supported by PCRE
# Line 1836  PCRE REGULAR EXPRESSION DETAILS Line 2701  PCRE REGULAR EXPRESSION DETAILS
2701         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2702         page.         page.
2703    
2704           The remainder of this document discusses the  patterns  that  are  sup-
2705           ported  by  PCRE when its main matching function, pcre_exec(), is used.
2706           From  release  6.0,   PCRE   offers   a   second   matching   function,
2707           pcre_dfa_exec(),  which matches using a different algorithm that is not
2708           Perl-compatible. The advantages and disadvantages  of  the  alternative
2709           function, and how it differs from the normal function, are discussed in
2710           the pcrematching page.
2711    
2712    
2713    CHARACTERS AND METACHARACTERS
2714    
2715         A regular expression is a pattern that is  matched  against  a  subject         A regular expression is a pattern that is  matched  against  a  subject
2716         string  from  left  to right. Most characters stand for themselves in a         string  from  left  to right. Most characters stand for themselves in a
2717         pattern, and match the corresponding characters in the  subject.  As  a         pattern, and match the corresponding characters in the  subject.  As  a
# Line 1843  PCRE REGULAR EXPRESSION DETAILS Line 2719  PCRE REGULAR EXPRESSION DETAILS
2719    
2720           The quick brown fox           The quick brown fox
2721    
2722         matches  a portion of a subject string that is identical to itself. The         matches a portion of a subject string that is identical to itself. When
2723         power of regular expressions comes from the ability to include alterna-         caseless matching is specified (the PCRE_CASELESS option), letters  are
2724         tives  and repetitions in the pattern. These are encoded in the pattern         matched  independently  of case. In UTF-8 mode, PCRE always understands
2725         by the use of metacharacters, which do not  stand  for  themselves  but         the concept of case for characters whose values are less than  128,  so
2726         instead are interpreted in some special way.         caseless  matching  is always possible. For characters with higher val-
2727           ues, the concept of case is supported if PCRE is compiled with  Unicode
2728         There  are  two different sets of metacharacters: those that are recog-         property  support,  but  not  otherwise.   If  you want to use caseless
2729         nized anywhere in the pattern except within square brackets, and  those         matching for characters 128 and above, you must  ensure  that  PCRE  is
2730         that  are  recognized  in square brackets. Outside square brackets, the         compiled with Unicode property support as well as with UTF-8 support.
2731         metacharacters are as follows:  
2732           The  power  of  regular  expressions  comes from the ability to include
2733           alternatives and repetitions in the pattern. These are encoded  in  the
2734           pattern by the use of metacharacters, which do not stand for themselves
2735           but instead are interpreted in some special way.
2736    
2737           There are two different sets of metacharacters: those that  are  recog-
2738           nized  anywhere in the pattern except within square brackets, and those
2739           that are recognized within square brackets.  Outside  square  brackets,
2740           the metacharacters are as follows:
2741    
2742           \      general escape character with several uses           \      general escape character with several uses
2743           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 1870  PCRE REGULAR EXPRESSION DETAILS Line 2755  PCRE REGULAR EXPRESSION DETAILS
2755                  also "possessive quantifier"                  also "possessive quantifier"
2756           {      start min/max quantifier           {      start min/max quantifier
2757    
2758         Part of a pattern that is in square brackets  is  called  a  "character         Part  of  a  pattern  that is in square brackets is called a "character
2759         class". In a character class the only metacharacters are:         class". In a character class the only metacharacters are:
2760    
2761           \      general escape character           \      general escape character
# Line 1880  PCRE REGULAR EXPRESSION DETAILS Line 2765  PCRE REGULAR EXPRESSION DETAILS
2765                    syntax)                    syntax)
2766           ]      terminates the character class           ]      terminates the character class
2767    
2768         The  following sections describe the use of each of the metacharacters.         The following sections describe the use of each of the  metacharacters.
2769    
2770    
2771  BACKSLASH  BACKSLASH
2772    
2773         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2774         a  non-alphanumeric  character,  it takes away any special meaning that         a non-alphanumeric character, it takes away any  special  meaning  that
2775         character may have. This  use  of  backslash  as  an  escape  character         character  may  have.  This  use  of  backslash  as an escape character
2776         applies both inside and outside character classes.         applies both inside and outside character classes.
2777    
2778         For  example,  if  you want to match a * character, you write \* in the         For example, if you want to match a * character, you write  \*  in  the
2779         pattern.  This escaping action applies whether  or  not  the  following         pattern.   This  escaping  action  applies whether or not the following
2780         character  would  otherwise be interpreted as a metacharacter, so it is         character would otherwise be interpreted as a metacharacter, so  it  is
2781         always safe to precede a non-alphanumeric  with  backslash  to  specify         always  safe  to  precede  a non-alphanumeric with backslash to specify
2782         that  it stands for itself. In particular, if you want to match a back-         that it stands for itself. In particular, if you want to match a  back-
2783         slash, you write \\.         slash, you write \\.
2784    
2785         If a pattern is compiled with the PCRE_EXTENDED option,  whitespace  in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2786         the  pattern (other than in a character class) and characters between a         the pattern (other than in a character class) and characters between  a
2787         # outside a character class and the next newline character are ignored.         # outside a character class and the next newline are ignored. An escap-
2788         An  escaping backslash can be used to include a whitespace or # charac-         ing backslash can be used to include a whitespace  or  #  character  as
2789         ter as part of the pattern.         part of the pattern.
2790    
2791         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-
2792         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-
2793         ent from Perl in that $ and  @  are  handled  as  literals  in  \Q...\E         ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
2794         sequences  in  PCRE, whereas in Perl, $ and @ cause variable interpola-         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
2795         tion. Note the following examples:         tion. Note the following examples:
2796    
2797           Pattern            PCRE matches   Perl matches           Pattern            PCRE matches   Perl matches
# Line 1916  BACKSLASH Line 2801  BACKSLASH
2801           \Qabc\$xyz\E       abc\$xyz       abc\$xyz           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2802           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz           \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2803    
2804         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
2805         classes.         classes.
2806    
2807     Non-printing characters     Non-printing characters
2808    
2809         A second use of backslash provides a way of encoding non-printing char-         A second use of backslash provides a way of encoding non-printing char-
2810         acters in patterns in a visible manner. There is no restriction on  the         acters  in patterns in a visible manner. There is no restriction on the
2811         appearance  of non-printing characters, apart from the binary zero that         appearance of non-printing characters, apart from the binary zero  that
2812         terminates a pattern, but when a pattern  is  being  prepared  by  text         terminates  a  pattern,  but  when  a pattern is being prepared by text
2813         editing,  it  is  usually  easier  to  use  one of the following escape         editing, it is usually easier  to  use  one  of  the  following  escape
2814         sequences than the binary character it represents:         sequences than the binary character it represents:
2815    
2816           \a        alarm, that is, the BEL character (hex 07)           \a        alarm, that is, the BEL character (hex 07)
# Line 1937  BACKSLASH Line 2822  BACKSLASH
2822           \t        tab (hex 09)           \t        tab (hex 09)
2823           \ddd      character with octal code ddd, or backreference           \ddd      character with octal code ddd, or backreference
2824           \xhh      character with hex code hh           \xhh      character with hex code hh
2825           \x{hhh..} character with hex code hhh... (UTF-8 mode only)           \x{hhh..} character with hex code hhh..
2826    
2827         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,
2828         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
2829         inverted.  Thus \cz becomes hex 1A, but \c{ becomes hex 3B,  while  \c;         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
2830         becomes hex 7B.         becomes hex 7B.
2831    
2832         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
2833         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
2834         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
2835         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,
2836         7FFFFFFF).  If  characters other than hexadecimal digits appear between         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2837         \x{ and }, or if there is no terminating }, this form of escape is  not         hexadecimal  digits  appear between \x{ and }, or if there is no termi-
2838         recognized. Instead, the initial \x will be interpreted as a basic hex-         nating }, this form of escape is not recognized.  Instead, the  initial
2839         adecimal escape, with no following digits,  giving  a  character  whose         \x will be interpreted as a basic hexadecimal escape, with no following
2840         value is zero.         digits, giving a character whose value is zero.
2841    
2842         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
2843         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-
2844         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}.
2845         \x{dc}.  
2846           After \0 up to two further octal digits are read. If  there  are  fewer
2847         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
2848         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
2849         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
2850         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.  
2851    
2852         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-
2853         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
2854         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
2855         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
2856         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
2857         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
2858         of parenthesized subpatterns.         of parenthesized subpatterns.
2859    
2860         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
2861         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2862         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-
2863         gle byte from the least significant 8 bits of the value. Any subsequent         erate  a data character. Any subsequent digits stand for themselves. In
2864         digits stand for themselves.  For example:         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2865           less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2866           example:
2867    
2868           \040   is another way of writing a space           \040   is another way of writing a space
2869           \40    is the same, provided there are fewer than 40           \40    is the same, provided there are fewer than 40
# Line 1995  BACKSLASH Line 2880  BACKSLASH
2880           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
2881                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
2882    
2883         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
2884         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2885    
2886         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
2887         character (in UTF-8 mode) can be used both inside and outside character         inside and outside character classes. In addition, inside  a  character
2888         classes. In addition, inside a character  class,  the  sequence  \b  is         class,  the  sequence \b is interpreted as the backspace character (hex
2889         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"
2890         interpreted as the character "X".  Outside  a  character  class,  these         and  "X", respectively. Outside a character class, these sequences have
2891         sequences have different meanings (see below).         different meanings (see below).
2892    
2893       Absolute and relative back references
2894    
2895           The sequence \g followed by a positive or negative  number,  optionally
2896           enclosed  in  braces,  is  an absolute or relative back reference. Back
2897           references are discussed later, following the discussion  of  parenthe-
2898           sized subpatterns.
2899    
2900     Generic character types     Generic character types
2901    
2902         The  third  use of backslash is for specifying generic character types.         Another use of backslash is for specifying generic character types. The
2903         The following are always recognized:         following are always recognized:
2904    
2905           \d     any decimal digit           \d     any decimal digit
2906           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 2028  BACKSLASH Line 2920  BACKSLASH
2920    
2921         For  compatibility  with Perl, \s does not match the VT character (code         For  compatibility  with Perl, \s does not match the VT character (code
2922         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
2923         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
2924           "use locale;" is included in a Perl script, \s may match the VT charac-
2925           ter. In PCRE, it never does.)
2926    
2927         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
2928         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-
2929         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-
2930         specific matching is taking place (see "Locale support" in the  pcreapi         specific matching is taking place (see "Locale support" in the  pcreapi
2931         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
2932         codes greater than 128 are used for accented  letters,  and  these  are         systems, or "french" in Windows, some character codes greater than  128
2933         matched by \w.         are used for accented letters, and these are matched by \w.
2934    
2935         In  UTF-8 mode, characters with values greater than 128 never match \d,         In  UTF-8 mode, characters with values greater than 128 never match \d,
2936         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-         \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2937         code character property support is available.         code  character  property support is available. The use of locales with
2938           Unicode is discouraged.
2939    
2940       Newline sequences
2941    
2942           Outside a character class, the escape sequence \R matches  any  Unicode
2943           newline sequence. This is an extension to Perl. In non-UTF-8 mode \R is
2944           equivalent to the following:
2945    
2946             (?>\r\n|\n|\x0b|\f|\r|\x85)
2947    
2948           This is an example of an "atomic group", details  of  which  are  given
2949           below.  This particular group matches either the two-character sequence
2950           CR followed by LF, or  one  of  the  single  characters  LF  (linefeed,
2951           U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
2952           return, U+000D), or NEL (next line, U+0085). The two-character sequence
2953           is treated as a single unit that cannot be split.
2954    
2955           In  UTF-8  mode, two additional characters whose codepoints are greater
2956           than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
2957           rator,  U+2029).   Unicode character property support is not needed for
2958           these characters to be recognized.
2959    
2960           Inside a character class, \R matches the letter "R".
2961    
2962     Unicode character properties     Unicode character properties
2963    
2964         When PCRE is built with Unicode character property support, three addi-         When PCRE is built with Unicode character property support, three addi-
2965         tional escape sequences to match generic character types are  available         tional  escape  sequences  to  match character properties are available
2966         when UTF-8 mode is selected. They are:         when UTF-8 mode is selected. They are:
2967    
2968          \p{xx}   a character with the xx property           \p{xx}   a character with the xx property
2969          \P{xx}   a character without the xx property           \P{xx}   a character without the xx property
2970          \X       an extended Unicode sequence           \X       an extended Unicode sequence
2971    
2972         The  property  names represented by xx above are limited to the Unicode         The property names represented by xx above are limited to  the  Unicode
2973         general category properties. Each character has exactly one such  prop-         script names, the general category properties, and "Any", which matches
2974         erty,  specified  by  a two-letter abbreviation. For compatibility with         any character (including newline). Other properties such as "InMusical-
2975         Perl, negation can be specified by including a circumflex  between  the         Symbols"  are  not  currently supported by PCRE. Note that \P{Any} does
2976         opening  brace  and the property name. For example, \p{^Lu} is the same         not match any characters, so always causes a match failure.
2977         as \P{Lu}.  
2978           Sets of Unicode characters are defined as belonging to certain scripts.
2979         If only one letter is specified with \p or  \P,  it  includes  all  the         A  character from one of these sets can be matched using a script name.
2980         properties that start with that letter. In this case, in the absence of         For example:
2981         negation, the curly brackets in the escape sequence are optional; these  
2982         two examples have the same effect:           \p{Greek}
2983             \P{Han}
2984    
2985           Those that are not part of an identified script are lumped together  as
2986           "Common". The current list of scripts is:
2987    
2988           Arabic,  Armenian,  Balinese,  Bengali,  Bopomofo,  Braille,  Buginese,
2989           Buhid,  Canadian_Aboriginal,  Cherokee,  Common,   Coptic,   Cuneiform,
2990           Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
2991           Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,  Hira-
2992           gana,  Inherited,  Kannada,  Katakana,  Kharoshthi,  Khmer, Lao, Latin,
2993           Limbu,  Linear_B,  Malayalam,  Mongolian,  Myanmar,  New_Tai_Lue,  Nko,
2994           Ogham,  Old_Italic,  Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
2995           Runic,  Shavian,  Sinhala,  Syloti_Nagri,  Syriac,  Tagalog,  Tagbanwa,
2996           Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
2997    
2998           Each  character has exactly one general category property, specified by
2999           a two-letter abbreviation. For compatibility with Perl, negation can be
3000           specified  by  including a circumflex between the opening brace and the
3001           property name. For example, \p{^Lu} is the same as \P{Lu}.
3002    
3003           If only one letter is specified with \p or \P, it includes all the gen-
3004           eral  category properties that start with that letter. In this case, in
3005           the absence of negation, the curly brackets in the escape sequence  are
3006           optional; these two examples have the same effect:
3007    
3008           \p{L}           \p{L}
3009           \pL           \pL
3010    
3011         The following property codes are supported:         The following general category property codes are supported:
3012    
3013           C     Other           C     Other
3014           Cc    Control           Cc    Control
# Line 2113  BACKSLASH Line 3054  BACKSLASH
3054           Zp    Paragraph separator           Zp    Paragraph separator
3055           Zs    Space separator           Zs    Space separator
3056    
3057         Extended  properties such as "Greek" or "InMusicalSymbols" are not sup-         The  special property L& is also supported: it matches a character that
3058         ported by PCRE.         has the Lu, Ll, or Lt property, in other words, a letter  that  is  not
3059           classified as a modifier or "other".
3060    
3061           The  long  synonyms  for  these  properties that Perl supports (such as
3062           \p{Letter}) are not supported by PCRE, nor is it  permitted  to  prefix
3063           any of these properties with "Is".
3064    
3065           No character that is in the Unicode table has the Cn (unassigned) prop-
3066           erty.  Instead, this property is assumed for any code point that is not
3067           in the Unicode table.
3068    
3069         Specifying caseless matching does not affect  these  escape  sequences.         Specifying  caseless  matching  does not affect these escape sequences.
3070         For example, \p{Lu} always matches only upper case letters.         For example, \p{Lu} always matches only upper case letters.
3071    
3072         The  \X  escape  matches  any number of Unicode characters that form an         The \X escape matches any number of Unicode  characters  that  form  an
3073         extended Unicode sequence. \X is equivalent to         extended Unicode sequence. \X is equivalent to
3074    
3075           (?>\PM\pM*)           (?>\PM\pM*)
3076    
3077         That is, it matches a character without the "mark"  property,  followed         That  is,  it matches a character without the "mark" property, followed
3078         by  zero  or  more  characters with the "mark" property, and treats the         by zero or more characters with the "mark"  property,  and  treats  the
3079         sequence as an atomic group (see below).  Characters  with  the  "mark"         sequence  as  an  atomic group (see below).  Characters with the "mark"
3080         property are typically accents that affect the preceding character.         property are typically accents that affect the preceding character.
3081    
3082         Matching  characters  by Unicode property is not fast, because PCRE has         Matching characters by Unicode property is not fast, because  PCRE  has
3083         to search a structure that contains  data  for  over  fifteen  thousand         to  search  a  structure  that  contains data for over fifteen thousand
3084         characters. That is why the traditional escape sequences such as \d and         characters. That is why the traditional escape sequences such as \d and
3085         \w do not use Unicode properties in PCRE.         \w do not use Unicode properties in PCRE.
3086    
3087     Simple assertions     Simple assertions
3088    
3089         The fourth use of backslash is for certain simple assertions. An asser-         The  final use of backslash is for certain simple assertions. An asser-
3090         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
3091         a match, without consuming any characters from the subject string.  The         a  match, without consuming any characters from the subject string. The
3092         use  of subpatterns for more complicated assertions is described below.         use of subpatterns for more complicated assertions is described  below.
3093         The backslashed assertions are:         The backslashed assertions are:
3094    
3095           \b     matches at a word boundary           \b     matches at a word boundary
3096           \B     matches when not at a word boundary           \B     matches when not at a word boundary
3097           \A     matches at start of subject           \A     matches at the start of the subject
3098           \Z     matches at end of subject or before newline at end           \Z     matches at the end of the subject
3099           \z     matches at end of subject                   also matches before a newline at the end of the subject
3100           \G     matches at first matching position in subject           \z     matches only at the end of the subject
3101             \G     matches at the first matching position in the subject
3102    
3103         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
3104         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
3105         acter class).         acter class).
3106    
3107         A word boundary is a position in the subject string where  the  current         A  word  boundary is a position in the subject string where the current
3108         character  and  the previous character do not both match \w or \W (i.e.         character and the previous character do not both match \w or  \W  (i.e.
3109         one matches \w and the other matches \W), or the start or  end  of  the         one  matches  \w  and the other matches \W), or the start or end of the
3110         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
3111    
3112         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
3113         and dollar (described in the next section) in that they only ever match         and dollar (described in the next section) in that they only ever match
3114         at  the  very start and end of the subject string, whatever options are         at the very start and end of the subject string, whatever  options  are
3115         set. Thus, they are independent of multiline mode. These  three  asser-         set.  Thus,  they are independent of multiline mode. These three asser-
3116         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which         tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
3117         affect only the behaviour of the circumflex and dollar  metacharacters.         affect  only the behaviour of the circumflex and dollar metacharacters.
3118         However,  if the startoffset argument of pcre_exec() is non-zero, indi-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
3119         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
3120         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
3121         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
3122         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.
        the end.  
3123    
3124         The \G assertion is true only when the current matching position is  at         The \G assertion is true only when the current matching position is  at
3125         the  start point of the match, as specified by the startoffset argument         the  start point of the match, as specified by the startoffset argument
# Line 2208  CIRCUMFLEX AND DOLLAR Line 3158  CIRCUMFLEX AND DOLLAR
3158    
3159         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
3160         matching  point  is  at  the  end of the subject string, or immediately         matching  point  is  at  the  end of the subject string, or immediately
3161         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
3162         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
3163         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
3164         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.  
3165    
3166         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
3167         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
3168         compile time. This does not affect the \Z assertion.         compile time. This does not affect the \Z assertion.
3169    
3170         The meanings of the circumflex and dollar characters are changed if the         The meanings of the circumflex and dollar characters are changed if the
3171         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
3172         ately after and  immediately  before  an  internal  newline  character,         matches  immediately after internal newlines as well as at the start of
3173         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
3174         ject string. For example,  the  pattern  /^abc$/  matches  the  subject         string.  A dollar matches before any newlines in the string, as well as
3175         string  "def\nabc"  (where \n represents a newline character) in multi-         at the very end, when PCRE_MULTILINE is set. When newline is  specified
3176         line mode, but not otherwise.  Consequently, patterns that are anchored         as  the  two-character  sequence CRLF, isolated CR and LF characters do
3177         in  single line mode because all branches start with ^ are not anchored         not indicate newlines.
3178         in multiline mode, and a match for  circumflex  is  possible  when  the  
3179         startoffset   argument   of  pcre_exec()  is  non-zero.  The  PCRE_DOL-         For example, the pattern /^abc$/ matches the subject string  "def\nabc"
3180         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.         (where  \n  represents a newline) in multiline mode, but not otherwise.
3181           Consequently, patterns that are anchored in single  line  mode  because
3182           all  branches  start  with  ^ are not anchored in multiline mode, and a
3183           match for circumflex is  possible  when  the  startoffset  argument  of
3184           pcre_exec()  is  non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
3185           PCRE_MULTILINE is set.
3186    
3187         Note that the sequences \A, \Z, and \z can be used to match  the  start         Note that the sequences \A, \Z, and \z can be used to match  the  start
3188         and  end of the subject in both modes, and if all branches of a pattern         and  end of the subject in both modes, and if all branches of a pattern
3189         start with \A it is always anchored, whether PCRE_MULTILINE is  set  or         start with \A it is always anchored, whether or not  PCRE_MULTILINE  is
3190         not.         set.
3191    
3192    
3193  FULL STOP (PERIOD, DOT)  FULL STOP (PERIOD, DOT)
3194    
3195         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-
3196         ter in the subject, including a non-printing  character,  but  not  (by         ter in the subject string except (by default) a character  that  signi-
3197         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
3198         which might be more than one byte long, except (by default) newline. If         more than one byte long.
3199         the  PCRE_DOTALL  option  is set, dots match newlines as well. The han-  
3200         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
3201         dollar,  the  only  relationship  being  that they both involve newline         that  character; when the two-character sequence CRLF is used, dot does
3202         characters. Dot has no special meaning in a character class.         not match CR if it is immediately followed  by  LF,  but  otherwise  it
3203           matches  all characters (including isolated CRs and LFs). When any Uni-
3204           code line endings are being recognized, dot does not match CR or LF  or
3205           any of the other line ending characters.
3206    
3207           The  behaviour  of  dot  with regard to newlines can be changed. If the
3208           PCRE_DOTALL option is set, a dot matches  any  one  character,  without
3209           exception. If the two-character sequence CRLF is present in the subject
3210           string, it takes two dots to match it.
3211    
3212           The handling of dot is entirely independent of the handling of  circum-
3213           flex  and  dollar,  the  only relationship being that they both involve
3214           newlines. Dot has no special meaning in a character class.
3215    
3216    
3217  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
3218    
3219         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
3220         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
3221         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
3222         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-
3223         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-
3224         this reason, the \C escape sequence is best avoided.         formed  UTF-8  string.  For this reason, the \C escape sequence is best
3225           avoided.
3226    
3227         PCRE  does  not  allow \C to appear in lookbehind assertions (described         PCRE does not allow \C to appear in  lookbehind  assertions  (described
3228         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-
3229         late the length of the lookbehind.         late the length of the lookbehind.
3230    
3231    
# Line 2267  SQUARE BRACKETS AND CHARACTER CLASSES Line 3234  SQUARE BRACKETS AND CHARACTER CLASSES
3234         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
3235         closing square bracket. A closing square bracket on its own is not spe-         closing square bracket. A closing square bracket on its own is not spe-
3236         cial. If a closing square bracket is required as a member of the class,         cial. If a closing square bracket is required as a member of the class,
3237         it should be the first data character in the class  (after  an  initial         it  should  be  the first data character in the class (after an initial
3238         circumflex, if present) or escaped with a backslash.         circumflex, if present) or escaped with a backslash.
3239    
3240         A  character  class matches a single character in the subject. In UTF-8         A character class matches a single character in the subject.  In  UTF-8
3241         mode, the character may occupy more than one byte. A matched  character         mode,  the character may occupy more than one byte. A matched character
3242         must be in the set of characters defined by the class, unless the first         must be in the set of characters defined by the class, unless the first
3243         character in the class definition is a circumflex, in  which  case  the         character  in  the  class definition is a circumflex, in which case the
3244         subject  character  must  not  be in the set defined by the class. If a         subject character must not be in the set defined by  the  class.  If  a
3245         circumflex is actually required as a member of the class, ensure it  is         circumflex  is actually required as a member of the class, ensure it is
3246         not the first character, or escape it with a backslash.         not the first character, or escape it with a backslash.
3247    
3248         For  example, the character class [aeiou] matches any lower case vowel,         For example, the character class [aeiou] matches any lower case  vowel,
3249         while [^aeiou] matches any character that is not a  lower  case  vowel.         while  [^aeiou]  matches  any character that is not a lower case vowel.
3250         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
3251         characters that are in the class by enumerating those that are  not.  A         characters  that  are in the class by enumerating those that are not. A
3252         class  that starts with a circumflex is not an assertion: it still con-         class that starts with a circumflex is not an assertion: it still  con-
3253         sumes a character from the subject string, and therefore  it  fails  if         sumes  a  character  from the subject string, and therefore it fails if
3254         the current pointer is at the end of the string.         the current pointer is at the end of the string.
3255    
3256         In  UTF-8 mode, characters with values greater than 255 can be included         In UTF-8 mode, characters with values greater than 255 can be  included
3257         in a class as a literal string of bytes, or by using the  \x{  escaping         in  a  class as a literal string of bytes, or by using the \x{ escaping
3258         mechanism.         mechanism.
3259    
3260         When  caseless  matching  is set, any letters in a class represent both         When caseless matching is set, any letters in a  class  represent  both
3261         their upper case and lower case versions, so for  example,  a  caseless         their  upper  case  and lower case versions, so for example, a caseless
3262         [aeiou]  matches  "A"  as well as "a", and a caseless [^aeiou] does not         [aeiou] matches "A" as well as "a", and a caseless  [^aeiou]  does  not
3263         match "A", whereas a caseful version would. When running in UTF-8 mode,         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always
3264         PCRE  supports  the  concept of case for characters with values greater         understands the concept of case for characters whose  values  are  less
3265         than 128 only when it is compiled with Unicode property support.         than  128, so caseless matching is always possible. For characters with
3266           higher values, the concept of case is supported  if  PCRE  is  compiled
3267         The newline character is never treated in any special way in  character         with  Unicode  property support, but not otherwise.  If you want to use
3268         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE         caseless matching for characters 128 and above, you  must  ensure  that
3269         options is. A class such as [^a] will always match a newline.         PCRE  is  compiled  with Unicode property support as well as with UTF-8
3270           support.
3271    
3272           Characters that might indicate line breaks are  never  treated  in  any
3273           special  way  when  matching  character  classes,  whatever line-ending
3274           sequence is in  use,  and  whatever  setting  of  the  PCRE_DOTALL  and
3275           PCRE_MULTILINE options is used. A class such as [^a] always matches one
3276           of these characters.
3277    
3278         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-
3279         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 2325  SQUARE BRACKETS AND CHARACTER CLASSES Line 3299  SQUARE BRACKETS AND CHARACTER CLASSES
3299         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,
3300         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
3301         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
3302         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
3303         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
3304         concept of case for characters with values greater than 128  only  when         concept of case for characters with values greater than 128  only  when
3305         it is compiled with Unicode property support.         it is compiled with Unicode property support.
# Line 2400  VERTICAL BAR Line 3374  VERTICAL BAR
3374    
3375         matches  either "gilbert" or "sullivan". Any number of alternatives may         matches  either "gilbert" or "sullivan". Any number of alternatives may
3376         appear, and an empty  alternative  is  permitted  (matching  the  empty         appear, and an empty  alternative  is  permitted  (matching  the  empty
3377         string).   The  matching  process  tries each alternative in turn, from         string). The matching process tries each alternative in turn, from left
3378         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
3379         tives  are within a subpattern (defined below), "succeeds" means match-         are  within a subpattern (defined below), "succeeds" means matching the
3380         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.  
3381    
3382    
3383  INTERNAL OPTION SETTING  INTERNAL OPTION SETTING
# Line 2432  INTERNAL OPTION SETTING Line 3405  INTERNAL OPTION SETTING
3405         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
3406         in data extracted by the pcre_fullinfo() function).         in data extracted by the pcre_fullinfo() function).
3407    
3408         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
3409         rent pattern that follows it, so         subpatterns) affects only that part of the current pattern that follows
3410           it, so
3411    
3412           (a(?i)b)c           (a(?i)b)c
3413    
3414         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
3415         used).   By  this means, options can be made to have different settings         used).  By this means, options can be made to have  different  settings
3416         in different parts of the pattern. Any changes made in one  alternative         in  different parts of the pattern. Any changes made in one alternative
3417         do  carry  on  into subsequent branches within the same subpattern. For         do carry on into subsequent branches within the  same  subpattern.  For
3418         example,         example,
3419    
3420           (a(?i)b|c)           (a(?i)b|c)
3421    
3422         matches "ab", "aB", "c", and "C", even though  when  matching  "C"  the         matches  "ab",  "aB",  "c",  and "C", even though when matching "C" the
3423         first  branch  is  abandoned before the option setting. This is because         first branch is abandoned before the option setting.  This  is  because
3424         the effects of option settings happen at compile time. There  would  be         the  effects  of option settings happen at compile time. There would be
3425         some very weird behaviour otherwise.         some very weird behaviour otherwise.
3426    
3427         The  PCRE-specific  options PCRE_UNGREEDY and PCRE_EXTRA can be changed         The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and  PCRE_EXTRA
3428         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
3429         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.  
3430    
3431    
3432  SUBPATTERNS  SUBPATTERNS
# Line 2468  SUBPATTERNS Line 3439  SUBPATTERNS
3439           cat(aract|erpillar|)           cat(aract|erpillar|)
3440    
3441         matches  one  of the words "cat", "cataract", or "caterpillar". Without         matches  one  of the words "cat", "cataract", or "caterpillar". Without
3442         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match  "cataract",  "erpillar"  or  an  empty
3443         string.         string.
3444    
3445         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 2497  SUBPATTERNS Line 3468  SUBPATTERNS
3468           the ((?:red|white) (king|queen))           the ((?:red|white) (king|queen))
3469    
3470         the captured substrings are "white queen" and "queen", and are numbered         the captured substrings are "white queen" and "queen", and are numbered
3471         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.  
3472    
3473         As  a  convenient shorthand, if any option settings are required at the         As  a  convenient shorthand, if any option settings are required at the
3474         start of a non-capturing subpattern,  the  option  letters  may  appear         start of a non-capturing subpattern,  the  option  letters  may  appear
# Line 2521  NAMED SUBPATTERNS Line 3490  NAMED SUBPATTERNS
3490         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3491         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3492         change. To help with this difficulty, PCRE supports the naming of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3493         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns. This feature was not added to Perl until release 5.10. Python
3494         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         had the feature earlier, and PCRE introduced it at release  4.0,  using
3495         underscores, and must be unique within a pattern.         the  Python syntax. PCRE now supports both the Perl and the Python syn-
3496           tax.
3497    
3498           In PCRE, a subpattern can be named in one of three  ways:  (?<name>...)
3499           or  (?'name'...)  as in Perl, or (?P<name>...) as in Python. References
3500           to capturing parentheses from other parts of the pattern, such as back-
3501           references,  recursion,  and conditions, can be made by name as well as
3502           by number.
3503    
3504           Names consist of up to  32  alphanumeric  characters  and  underscores.
3505         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3506         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
3507         number  translation table from a compiled pattern. There is also a con-         function calls for extracting the name-to-number translation table from
3508         venience function for extracting a captured substring by name. For fur-         a compiled pattern. There is also a convenience function for extracting
3509         ther details see the pcreapi documentation.         a captured substring by name.
3510    
3511           By  default, a name must be unique within a pattern, but it is possible
3512           to relax this constraint by setting the PCRE_DUPNAMES option at compile
3513           time.  This  can  be useful for patterns where only one instance of the
3514           named parentheses can match. Suppose you want to match the  name  of  a
3515           weekday,  either as a 3-letter abbreviation or as the full name, and in
3516           both cases you want to extract the abbreviation. This pattern (ignoring
3517           the line breaks) does the job:
3518    
3519             (?<DN>Mon|Fri|Sun)(?:day)?|
3520             (?<DN>Tue)(?:sday)?|
3521             (?<DN>Wed)(?:nesday)?|
3522             (?<DN>Thu)(?:rsday)?|
3523             (?<DN>Sat)(?:urday)?
3524    
3525           There  are  five capturing substrings, but only one is ever set after a
3526           match.  The convenience  function  for  extracting  the  data  by  name
3527           returns  the  substring  for  the first (and in this example, the only)
3528           subpattern of that name that matched.  This  saves  searching  to  find
3529           which  numbered  subpattern  it  was. If you make a reference to a non-
3530           unique named subpattern from elsewhere in the  pattern,  the  one  that
3531           corresponds  to  the  lowest number is used. For further details of the
3532           interfaces for handling named subpatterns, see the  pcreapi  documenta-
3533           tion.
3534    
3535    
3536  REPETITION  REPETITION
# Line 2538  REPETITION Line 3539  REPETITION
3539         following items:         following items:
3540    
3541           a literal data character           a literal data character
3542           the . metacharacter           the dot metacharacter
3543           the \C escape sequence           the \C escape sequence
3544           the \X escape sequence (in UTF-8 mode with Unicode properties)           the \X escape sequence (in UTF-8 mode with Unicode properties)
3545             the \R escape sequence
3546           an escape such as \d that matches a single character           an escape such as \d that matches a single character
3547           a character class           a character class
3548           a back reference (see next section)           a back reference (see next section)
# Line 2580  REPETITION Line 3582  REPETITION
3582         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3583         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
3584    
3585         For  convenience  (and  historical compatibility) the three most common         For  convenience, the three most common quantifiers have single-charac-
3586         quantifiers have single-character abbreviations:         ter abbreviations:
3587    
3588           *    is equivalent to {0,}           *    is equivalent to {0,}
3589           +    is equivalent to {1,}           +    is equivalent to {1,}
# Line 2633  REPETITION Line 3635  REPETITION
3635         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
3636         only way the rest of the pattern matches.         only way the rest of the pattern matches.
3637    
3638         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
3639         Perl),  the  quantifiers are not greedy by default, but individual ones         Perl),  the  quantifiers are not greedy by default, but individual ones
3640         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
3641         words, it inverts the default behaviour.         words, it inverts the default behaviour.
# Line 2644  REPETITION Line 3646  REPETITION
3646         minimum or maximum.         minimum or maximum.
3647    
3648         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-
3649         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,
3650         pattern is implicitly anchored, because whatever follows will be  tried         the pattern is implicitly anchored, because whatever  follows  will  be
3651         against  every character position in the subject string, so there is no         tried  against every character position in the subject string, so there
3652         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
3653         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
3654           by \A.
3655    
3656         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-
3657         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-
3658         mization, or alternatively using ^ to indicate anchoring explicitly.         mization, or alternatively using ^ to indicate anchoring explicitly.
3659    
3660         However,  there is one situation where the optimization cannot be used.         However, there is one situation where the optimization cannot be  used.
3661         When .*  is inside capturing parentheses that  are  the  subject  of  a         When  .*   is  inside  capturing  parentheses that are the subject of a
3662         backreference  elsewhere in the pattern, a match at the start may fail,         backreference elsewhere in the pattern, a match at the start  may  fail
3663         and a later one succeed. Consider, for example:         where a later one succeeds. Consider, for example:
3664    
3665           (.*)abc\1           (.*)abc\1
3666    
3667         If the subject is "xyz123abc123" the match point is the fourth  charac-         If  the subject is "xyz123abc123" the match point is the fourth charac-
3668         ter. For this reason, such a pattern is not implicitly anchored.         ter. For this reason, such a pattern is not implicitly anchored.
3669    
3670         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 2670  REPETITION Line 3673  REPETITION
3673           (tweedle[dume]{3}\s*)+           (tweedle[dume]{3}\s*)+
3674    
3675         has matched "tweedledum tweedledee" the value of the captured substring         has matched "tweedledum tweedledee" the value of the captured substring
3676         is  "tweedledee".  However,  if there are nested capturing subpatterns,         is "tweedledee". However, if there are  nested  capturing  subpatterns,
3677         the corresponding captured values may have been set in previous  itera-         the  corresponding captured values may have been set in previous itera-
3678         tions. For example, after         tions. For example, after
3679    
3680           /(a|(b))+/           /(a|(b))+/
# Line 2681  REPETITION Line 3684  REPETITION
3684    
3685  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS  ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
3686    
3687         With both maximizing and minimizing repetition, failure of what follows         With both maximizing ("greedy") and minimizing ("ungreedy"  or  "lazy")
3688         normally causes the repeated item to be re-evaluated to see if  a  dif-         repetition,  failure  of what follows normally causes the repeated item
3689         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
3690         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,
3691         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
3692         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
3693           no point in carrying on.
3694    
3695         Consider, for example, the pattern \d+foo when applied to  the  subject         Consider, for example, the pattern \d+foo when applied to  the  subject
3696         line         line
# Line 2700  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3704  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3704         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
3705         to be re-evaluated in this way.         to be re-evaluated in this way.
3706    
3707         If we use atomic grouping for the previous example, the  matcher  would         If we use atomic grouping for the previous example, the  matcher  gives
3708         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
3709         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:  
3710    
3711           (?>\d+)foo           (?>\d+)foo
3712    
# Line 2735  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3738  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3738         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3739         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
3740         simpler forms of atomic group. However, there is no difference  in  the         simpler forms of atomic group. However, there is no difference  in  the
3741         meaning  or  processing  of  a possessive quantifier and the equivalent         meaning  of  a  possessive  quantifier and the equivalent atomic group,
3742         atomic group.         though there may be a performance  difference;  possessive  quantifiers
3743           should be slightly faster.
3744         The possessive quantifier syntax is an extension to the Perl syntax. It  
3745         originates in Sun's Java package.         The  possessive  quantifier syntax is an extension to the Perl 5.8 syn-
3746           tax.  Jeffrey Friedl originated the idea (and the name)  in  the  first
3747         When  a  pattern  contains an unlimited repeat inside a subpattern that         edition of his book. Mike McCloskey liked it, so implemented it when he
3748         can itself be repeated an unlimited number of  times,  the  use  of  an         built Sun's Java package, and PCRE copied it from there. It  ultimately
3749         atomic  group  is  the  only way to avoid some failing matches taking a         found its way into Perl at release 5.10.