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1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
# Line 5  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  DESCRIPTION  
17    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.  The current implementation of PCRE (release
22         4.x) corresponds approximately with Perl  5.8,  including  support  for         6.x) corresponds approximately with Perl  5.8,  including  support  for
23         UTF-8  encoded  strings.   However,  this  support has to be explicitly         UTF-8 encoded strings and Unicode general category properties. However,
24         enabled; it is not the default.         this support has to be explicitly enabled; it is not the default.
25    
26         PCRE is written in C and released as a C library. However, a number  of         In addition to the Perl-compatible matching function,  PCRE  also  con-
27         people  have  written  wrappers  and interfaces of various kinds. A C++         tains  an  alternative matching function that matches the same compiled
28         class is included in these contributions, which can  be  found  in  the         patterns in a different way. In certain circumstances, the  alternative
29           function  has  some  advantages.  For  a discussion of the two matching
30           algorithms, see the pcrematching page.
31    
32           PCRE is written in C and released as a C library. A  number  of  people
33           have  written  wrappers and interfaces of various kinds. In particular,
34           Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now
35           included as part of the PCRE distribution. The pcrecpp page has details
36           of this interface. Other people's contributions can  be  found  in  the
37         Contrib directory at the primary FTP site, which is:         Contrib directory at the primary FTP site, which is:
38    
39         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
# Line 34  DESCRIPTION Line 44  DESCRIPTION
44    
45         Some  features  of  PCRE can be included, excluded, or changed when the         Some  features  of  PCRE can be included, excluded, or changed when the
46         library is built. The pcre_config() function makes it  possible  for  a         library is built. The pcre_config() function makes it  possible  for  a
47         client  to  discover  which features are available. Documentation about         client  to  discover  which  features are available. The features them-
48         building PCRE for various operating systems can be found in the  README         selves are described in the pcrebuild page. Documentation about  build-
49         file in the source distribution.         ing  PCRE for various operating systems can be found in the README file
50           in the source distribution.
51    
52           The library contains a number of undocumented  internal  functions  and
53           data  tables  that  are  used by more than one of the exported external
54           functions, but which are not intended  for  use  by  external  callers.
55           Their  names  all begin with "_pcre_", which hopefully will not provoke
56           any name clashes.
57    
58    
59  USER DOCUMENTATION  USER DOCUMENTATION
60    
61         The user documentation for PCRE has been split up into a number of dif-         The user documentation for PCRE comprises a number  of  different  sec-
62         ferent sections. In the "man" format, each of these is a separate  "man         tions.  In the "man" format, each of these is a separate "man page". In
63         page".  In  the  HTML  format, each is a separate page, linked from the         the HTML format, each is a separate page, linked from the  index  page.
64         index page. In the plain text format, all  the  sections  are  concate-         In  the  plain text format, all the sections are concatenated, for ease
65         nated, for ease of searching. The sections are as follows:         of searching. The sections are as follows:
66    
67           pcre              this document           pcre              this document
68           pcreapi           details of PCRE's native API           pcreapi           details of PCRE's native C API
69           pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
70           pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
71           pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
72             pcrecpp           details of the C++ wrapper
73           pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
74             pcrematching      discussion of the two matching algorithms
75             pcrepartial       details of the partial matching facility
76           pcrepattern       syntax and semantics of supported           pcrepattern       syntax and semantics of supported
77                               regular expressions                               regular expressions
78           pcreperform       discussion of performance issues           pcreperform       discussion of performance issues
79           pcreposix         the POSIX-compatible API           pcreposix         the POSIX-compatible C API
80             pcreprecompile    details of saving and re-using precompiled patterns
81           pcresample        discussion of the sample program           pcresample        discussion of the sample program
82           pcretest          the pcretest testing command           pcretest          description of the pcretest testing command
83    
84         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
85         each library function, listing its arguments and results.         each C library function, listing its arguments and results.
86    
87    
88  LIMITATIONS  LIMITATIONS
# Line 74  LIMITATIONS Line 95  LIMITATIONS
95         process  regular  expressions  that are truly enormous, you can compile         process  regular  expressions  that are truly enormous, you can compile
96         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
97         the  source  distribution and the pcrebuild documentation for details).         the  source  distribution and the pcrebuild documentation for details).
98         If these cases the limit is substantially larger.  However,  the  speed         In these cases the limit is substantially larger.  However,  the  speed
99         of execution will be slower.         of execution will be slower.
100    
101         All values in repeating quantifiers must be less than 65536.  The maxi-         All values in repeating quantifiers must be less than 65536.  The maxi-
# Line 86  LIMITATIONS Line 107  LIMITATIONS
107         tern, is 200.         tern, is 200.
108    
109         The  maximum  length of a subject string is the largest positive number         The  maximum  length of a subject string is the largest positive number
110         that an integer variable can hold. However, PCRE uses recursion to han-         that an integer variable can hold. However, when using the  traditional
111         dle  subpatterns  and indefinite repetition. This means that the avail-         matching function, PCRE uses recursion to handle subpatterns and indef-
112         able stack space may limit the size of a subject  string  that  can  be         inite repetition.  This means that the available stack space may  limit
113         processed by certain patterns.         the size of a subject string that can be processed by certain patterns.
114    
115    
116  UTF-8 SUPPORT  UTF-8 AND UNICODE PROPERTY SUPPORT
117    
118         Starting  at  release  3.3,  PCRE  has  had  some support for character         From release 3.3, PCRE has  had  some  support  for  character  strings
119         strings encoded in the UTF-8 format. For  release  4.0  this  has  been         encoded  in the UTF-8 format. For release 4.0 this was greatly extended
120         greatly extended to cover most common requirements.         to cover most common requirements, and in release 5.0  additional  sup-
121           port for Unicode general category properties was added.
122    
123         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8         In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
124         support in the code, and, in addition,  you  must  call  pcre_compile()         support in the code, and, in addition,  you  must  call  pcre_compile()
# Line 109  UTF-8 SUPPORT Line 131  UTF-8 SUPPORT
131         is  limited  to testing the PCRE_UTF8 flag in several places, so should         is  limited  to testing the PCRE_UTF8 flag in several places, so should
132         not be very large.         not be very large.
133    
134           If PCRE is built with Unicode character property support (which implies
135           UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
136           ported.  The available properties that can be tested are limited to the
137           general  category  properties such as Lu for an upper case letter or Nd
138           for a decimal number. A full list is given in the pcrepattern  documen-
139           tation. The PCRE library is increased in size by about 90K when Unicode
140           property support is included.
141    
142         The following comments apply when PCRE is running in UTF-8 mode:         The following comments apply when PCRE is running in UTF-8 mode:
143    
144         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and         1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and
# Line 136  UTF-8 SUPPORT Line 166  UTF-8 SUPPORT
166         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-         4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
167         vidual bytes, for example: \x{100}{3}.         vidual bytes, for example: \x{100}{3}.
168    
169         5.  The  dot  metacharacter  matches  one  UTF-8 character instead of a         5.  The dot metacharacter matches one UTF-8 character instead of a sin-
170         single byte.         gle byte.
171    
172         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
173         mode, but its use can lead to some strange effects.         mode,  but  its  use can lead to some strange effects. This facility is
174           not available in the alternative matching function, pcre_dfa_exec().
        7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly  
        test characters of any code value, but the characters that PCRE  recog-  
        nizes  as  digits,  spaces,  or  word characters remain the same set as  
        before, all with values less than 256.  
   
        8. Case-insensitive matching applies only to  characters  whose  values  
        are  less  than  256.  PCRE  does  not support the notion of "case" for  
        higher-valued characters.  
175    
176         9. PCRE does not support the use of Unicode tables  and  properties  or         7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
177         the Perl escapes \p, \P, and \X.         test  characters of any code value, but the characters that PCRE recog-
178           nizes as digits, spaces, or word characters  remain  the  same  set  as
179           before, all with values less than 256. This remains true even when PCRE
180           includes Unicode property support, because to do otherwise  would  slow
181           down  PCRE in many common cases. If you really want to test for a wider
182           sense of, say, "digit", you must use Unicode  property  tests  such  as
183           \p{Nd}.
184    
185           8.  Similarly,  characters that match the POSIX named character classes
186           are all low-valued characters.
187    
188           9. Case-insensitive matching applies only to  characters  whose  values
189           are  less than 128, unless PCRE is built with Unicode property support.
190           Even when Unicode property support is available, PCRE  still  uses  its
191           own  character  tables when checking the case of low-valued characters,
192           so as not to degrade performance.  The Unicode property information  is
193           used only for characters with higher values.
194    
195    
196  AUTHOR  AUTHOR
197    
198         Philip Hazel <ph10@cam.ac.uk>         Philip Hazel
199         University Computing Service,         University Computing Service,
200         Cambridge CB2 3QG, England.         Cambridge CB2 3QG, England.
        Phone: +44 1223 334714  
201    
202  Last updated: 20 August 2003         Putting  an actual email address here seems to have been a spam magnet,
203  Copyright (c) 1997-2003 University of Cambridge.         so I've taken it away. If you want to email me, use my initial and sur-
204  -----------------------------------------------------------------------------         name, separated by a dot, at the domain ucs.cam.ac.uk.
205    
206  PCRE(3)                                                                PCRE(3)  Last updated: 07 March 2005
207    Copyright (c) 1997-2005 University of Cambridge.
208    ------------------------------------------------------------------------------
209    
210    
211    PCREBUILD(3)                                                      PCREBUILD(3)
212    
213    
214  NAME  NAME
215         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
216    
217    
218  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
219    
220         This  document  describes  the  optional  features  of PCRE that can be         This  document  describes  the  optional  features  of PCRE that can be
221         selected when the library is compiled. They are all selected, or  dese-         selected when the library is compiled. They are all selected, or  dese-
222         lected,  by  providing  options  to  the  configure script which is run         lected, by providing options to the configure script that is run before
223         before the make command. The complete list  of  options  for  configure         the make command. The complete list of  options  for  configure  (which
224         (which  includes the standard ones such as the selection of the instal-         includes  the  standard  ones such as the selection of the installation
225         lation directory) can be obtained by running         directory) can be obtained by running
226    
227           ./configure --help           ./configure --help
228    
# Line 204  UTF-8 SUPPORT Line 246  UTF-8 SUPPORT
246         function.         function.
247    
248    
249    UNICODE CHARACTER PROPERTY SUPPORT
250    
251           UTF-8 support allows PCRE to process character values greater than  255
252           in  the  strings that it handles. On its own, however, it does not pro-
253           vide any facilities for accessing the properties of such characters. If
254           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
255           refer to Unicode character properties, you must add
256    
257             --enable-unicode-properties
258    
259           to the configure command. This implies UTF-8 support, even if you  have
260           not explicitly requested it.
261    
262           Including  Unicode  property  support  adds around 90K of tables to the
263           PCRE library, approximately doubling its size. Only the  general  cate-
264           gory  properties  such as Lu and Nd are supported. Details are given in
265           the pcrepattern documentation.
266    
267    
268  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
269    
270         By default, PCRE treats character 10 (linefeed) as the newline  charac-         By default, PCRE treats character 10 (linefeed) as the newline  charac-
# Line 231  BUILDING SHARED AND STATIC LIBRARIES Line 292  BUILDING SHARED AND STATIC LIBRARIES
292    
293  POSIX MALLOC USAGE  POSIX MALLOC USAGE
294    
295         When PCRE is called through the  POSIX  interface  (see  the  pcreposix         When PCRE is called through the POSIX interface (see the pcreposix doc-
296         documentation),  additional working storage is required for holding the         umentation),  additional  working  storage  is required for holding the
297         pointers to capturing substrings because PCRE requires  three  integers         pointers to capturing substrings, because PCRE requires three  integers
298         per  substring,  whereas  the POSIX interface provides only two. If the         per  substring,  whereas  the POSIX interface provides only two. If the
299         number of expected substrings is small, the wrapper function uses space         number of expected substrings is small, the wrapper function uses space
300         on the stack, because this is faster than using malloc() for each call.         on the stack, because this is faster than using malloc() for each call.
# Line 247  POSIX MALLOC USAGE Line 308  POSIX MALLOC USAGE
308    
309  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
310    
311         Internally,  PCRE  has a function called match() which it calls repeat-         Internally,  PCRE has a function called match(), which it calls repeat-
312         edly (possibly recursively) when performing a  matching  operation.  By         edly  (possibly  recursively)  when  matching  a   pattern   with   the
313         limiting  the  number of times this function may be called, a limit can         pcre_exec()  function.  By controlling the maximum number of times this
314         be placed on the resources used by a single call  to  pcre_exec().  The         function may be called during a single matching operation, a limit  can
315         limit  can be changed at run time, as described in the pcreapi documen-         be  placed  on  the resources used by a single call to pcre_exec(). The
316         tation. The default is 10 million, but this can be changed by adding  a         limit can be changed at run time, as described in the pcreapi  documen-
317           tation.  The default is 10 million, but this can be changed by adding a
318         setting such as         setting such as
319    
320           --with-match-limit=500000           --with-match-limit=500000
321    
322         to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
323           pcre_dfa_exec() matching function.
324    
325    
326  HANDLING VERY LARGE PATTERNS  HANDLING VERY LARGE PATTERNS
327    
328         Within  a  compiled  pattern,  offset values are used to point from one         Within  a  compiled  pattern,  offset values are used to point from one
329         part to another (for example, from an opening parenthesis to an  alter-         part to another (for example, from an opening parenthesis to an  alter-
330         nation  metacharacter).  By  default two-byte values are used for these         nation  metacharacter).  By default, two-byte values are used for these
331         offsets, leading to a maximum size for a  compiled  pattern  of  around         offsets, leading to a maximum size for a  compiled  pattern  of  around
332         64K.  This  is sufficient to handle all but the most gigantic patterns.         64K.  This  is sufficient to handle all but the most gigantic patterns.
333         Nevertheless, some people do want to process enormous patterns,  so  it         Nevertheless, some people do want to process enormous patterns,  so  it
# Line 285  HANDLING VERY LARGE PATTERNS Line 348  HANDLING VERY LARGE PATTERNS
348    
349  AVOIDING EXCESSIVE STACK USAGE  AVOIDING EXCESSIVE STACK USAGE
350    
351         PCRE  implements  backtracking while matching by making recursive calls         When matching with the pcre_exec() function, PCRE implements backtrack-
352         to an internal function called match(). In environments where the  size         ing by making recursive calls to an internal function  called  match().
353         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-
354         Unix environment does not usually suffer from this problem.) An  alter-         verely limit PCRE's operation. (The Unix environment does  not  usually
355         native  approach  that  uses  memory  from  the  heap to remember data,         suffer  from  this  problem.)  An alternative approach that uses memory
356         instead of using recursive function calls, has been implemented to work         from the heap to remember data, instead  of  using  recursive  function
357         round  this  problem. If you want to build a version of PCRE that works         calls,  has been implemented to work round this problem. If you want to
358         this way, add         build a version of PCRE that works this way, add
359    
360           --disable-stack-for-recursion           --disable-stack-for-recursion
361    
362         to the configure command. With this configuration, PCRE  will  use  the         to the configure command. With this configuration, PCRE  will  use  the
363         pcre_stack_malloc   and   pcre_stack_free   variables  to  call  memory         pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
364         management functions. Separate functions are provided because the usage         ment functions. Separate functions are provided because  the  usage  is
365         is very predictable: the block sizes requested are always the same, and         very  predictable:  the  block sizes requested are always the same, and
366         the blocks are always freed in reverse order. A calling  program  might         the blocks are always freed in reverse order. A calling  program  might
367         be  able  to implement optimized functions that perform better than the         be  able  to implement optimized functions that perform better than the
368         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more         standard malloc() and  free()  functions.  PCRE  runs  noticeably  more
369         slowly when built in this way.         slowly when built in this way. This option affects only the pcre_exec()
370           function; it is not relevant for the the pcre_dfa_exec() function.
371    
372    
373  USING EBCDIC CODE  USING EBCDIC CODE
374    
375         PCRE  assumes  by  default that it will run in an environment where the         PCRE assumes by default that it will run in an  environment  where  the
376         character code is ASCII (or UTF-8, which is a superset of ASCII).  PCRE         character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
377         can, however, be compiled to run in an EBCDIC environment by adding         PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by
378           adding
379    
380           --enable-ebcdic           --enable-ebcdic
381    
382         to the configure command.         to the configure command.
383    
384  Last updated: 09 December 2003  Last updated: 28 February 2005
385  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2005 University of Cambridge.
386  -----------------------------------------------------------------------------  ------------------------------------------------------------------------------
387    
 PCRE(3)                                                                PCRE(3)  
388    
389    PCREMATCHING(3)                                                PCREMATCHING(3)
390    
391    
392    NAME
393           PCRE - Perl-compatible regular expressions
394    
395    
396    PCRE MATCHING ALGORITHMS
397    
398           This document describes the two different algorithms that are available
399           in PCRE for matching a compiled regular expression against a given sub-
400           ject  string.  The  "standard"  algorithm  is  the  one provided by the
401           pcre_exec() function.  This works in the same was  as  Perl's  matching
402           function, and provides a Perl-compatible matching operation.
403    
404           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
405           this operates in a different way, and is not  Perl-compatible.  It  has
406           advantages  and disadvantages compared with the standard algorithm, and
407           these are described below.
408    
409           When there is only one possible way in which a given subject string can
410           match  a pattern, the two algorithms give the same answer. A difference
411           arises, however, when there are multiple possibilities. For example, if
412           the pattern
413    
414             ^<.*>
415    
416           is matched against the string
417    
418             <something> <something else> <something further>
419    
420           there are three possible answers. The standard algorithm finds only one
421           of them, whereas the DFA algorithm finds all three.
422    
423    
424    REGULAR EXPRESSIONS AS TREES
425    
426           The set of strings that are matched by a regular expression can be rep-
427           resented  as  a  tree structure. An unlimited repetition in the pattern
428           makes the tree of infinite size, but it is still a tree.  Matching  the
429           pattern  to a given subject string (from a given starting point) can be
430           thought of as a search of the tree.  There are  two  standard  ways  to
431           search  a  tree: depth-first and breadth-first, and these correspond to
432           the two matching algorithms provided by PCRE.
433    
434    
435    THE STANDARD MATCHING ALGORITHM
436    
437           In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
438           sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
439           depth-first search of the pattern tree. That is, it  proceeds  along  a
440           single path through the tree, checking that the subject matches what is
441           required. When there is a mismatch, the algorithm  tries  any  alterna-
442           tives  at  the  current point, and if they all fail, it backs up to the
443           previous branch point in the  tree,  and  tries  the  next  alternative
444           branch  at  that  level.  This often involves backing up (moving to the
445           left) in the subject string as well.  The  order  in  which  repetition
446           branches  are  tried  is controlled by the greedy or ungreedy nature of
447           the quantifier.
448    
449           If a leaf node is reached, a matching string has  been  found,  and  at
450           that  point the algorithm stops. Thus, if there is more than one possi-
451           ble match, this algorithm returns the first one that it finds.  Whether
452           this  is the shortest, the longest, or some intermediate length depends
453           on the way the greedy and ungreedy repetition quantifiers are specified
454           in the pattern.
455    
456           Because  it  ends  up  with a single path through the tree, it is rela-
457           tively straightforward for this algorithm to keep  track  of  the  sub-
458           strings  that  are  matched  by portions of the pattern in parentheses.
459           This provides support for capturing parentheses and back references.
460    
461    
462    THE DFA MATCHING ALGORITHM
463    
464           DFA stands for "deterministic finite automaton", but you do not need to
465           understand the origins of that name. This algorithm conducts a breadth-
466           first search of the tree. Starting from the first matching point in the
467           subject,  it scans the subject string from left to right, once, charac-
468           ter by character, and as it does  this,  it  remembers  all  the  paths
469           through the tree that represent valid matches.
470    
471           The  scan  continues until either the end of the subject is reached, or
472           there are no more unterminated paths. At this point,  terminated  paths
473           represent  the different matching possibilities (if there are none, the
474           match has failed).  Thus, if there is more  than  one  possible  match,
475           this algorithm finds all of them, and in particular, it finds the long-
476           est. In PCRE, there is an option to stop the algorithm after the  first
477           match (which is necessarily the shortest) has been found.
478    
479           Note that all the matches that are found start at the same point in the
480           subject. If the pattern
481    
482             cat(er(pillar)?)
483    
484           is matched against the string "the caterpillar catchment",  the  result
485           will  be the three strings "cat", "cater", and "caterpillar" that start
486           at the fourth character of the subject. The algorithm does not automat-
487           ically move on to find matches that start at later positions.
488    
489           There are a number of features of PCRE regular expressions that are not
490           supported by the DFA matching algorithm. They are as follows:
491    
492           1. Because the algorithm finds all  possible  matches,  the  greedy  or
493           ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
494           ungreedy quantifiers are treated in exactly the same way.
495    
496           2. When dealing with multiple paths through the tree simultaneously, it
497           is  not  straightforward  to  keep track of captured substrings for the
498           different matching possibilities, and  PCRE's  implementation  of  this
499           algorithm does not attempt to do this. This means that no captured sub-
500           strings are available.
501    
502           3. Because no substrings are captured, back references within the  pat-
503           tern are not supported, and cause errors if encountered.
504    
505           4.  For  the same reason, conditional expressions that use a backrefer-
506           ence as the condition are not supported.
507    
508           5. Callouts are supported, but the value of the  capture_top  field  is
509           always 1, and the value of the capture_last field is always -1.
510    
511           6.  The \C escape sequence, which (in the standard algorithm) matches a
512           single byte, even in UTF-8 mode, is not supported because the DFA algo-
513           rithm moves through the subject string one character at a time, for all
514           active paths through the tree.
515    
516    
517    ADVANTAGES OF THE DFA ALGORITHM
518    
519           Using the DFA matching algorithm provides the following advantages:
520    
521           1. All possible matches (at a single point in the subject) are automat-
522           ically  found,  and  in particular, the longest match is found. To find
523           more than one match using the standard algorithm, you have to do kludgy
524           things with callouts.
525    
526           2.  There is much better support for partial matching. The restrictions
527           on the content of the pattern that apply when using the standard  algo-
528           rithm  for partial matching do not apply to the DFA algorithm. For non-
529           anchored patterns, the starting position of a partial match  is  avail-
530           able.
531    
532           3.  Because  the  DFA algorithm scans the subject string just once, and
533           never needs to backtrack, it is possible  to  pass  very  long  subject
534           strings  to  the matching function in several pieces, checking for par-
535           tial matching each time.
536    
537    
538    DISADVANTAGES OF THE DFA ALGORITHM
539    
540           The DFA algorithm suffers from a number of disadvantages:
541    
542           1. It is substantially slower than  the  standard  algorithm.  This  is
543           partly  because  it has to search for all possible matches, but is also
544           because it is less susceptible to optimization.
545    
546           2. Capturing parentheses and back references are not supported.
547    
548           3. The "atomic group" feature of PCRE regular expressions is supported,
549           but  does not provide the advantage that it does for the standard algo-
550           rithm.
551    
552    Last updated: 28 February 2005
553    Copyright (c) 1997-2005 University of Cambridge.
554    ------------------------------------------------------------------------------
555    
556    
557    PCREAPI(3)                                                          PCREAPI(3)
558    
559    
560  NAME  NAME
561         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
562    
563  SYNOPSIS OF PCRE API  
564    PCRE NATIVE API
565    
566         #include <pcre.h>         #include <pcre.h>
567    
# Line 335  SYNOPSIS OF PCRE API Line 569  SYNOPSIS OF PCRE API
569              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
570              const unsigned char *tableptr);              const unsigned char *tableptr);
571    
572           pcre *pcre_compile2(const char *pattern, int options,
573                int *errorcodeptr,
574                const char **errptr, int *erroffset,
575                const unsigned char *tableptr);
576    
577         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options,
578              const char **errptr);              const char **errptr);
579    
# Line 342  SYNOPSIS OF PCRE API Line 581  SYNOPSIS OF PCRE API
581              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
582              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
583    
584           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
585                const char *subject, int length, int startoffset,
586                int options, int *ovector, int ovecsize,
587                int *workspace, int wscount);
588    
589         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
590              const char *subject, int *ovector,              const char *subject, int *ovector,
591              int stringcount, const char *stringname,              int stringcount, const char *stringname,
# Line 377  SYNOPSIS OF PCRE API Line 621  SYNOPSIS OF PCRE API
621    
622         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
623    
624           int pcre_refcount(pcre *code, int adjust);
625    
626         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
627    
628         char *pcre_version(void);         char *pcre_version(void);
# Line 392  SYNOPSIS OF PCRE API Line 638  SYNOPSIS OF PCRE API
638         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
639    
640    
641  PCRE API  PCRE API OVERVIEW
642    
643         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
644         is also a set of wrapper functions that correspond to the POSIX regular         is also a set of wrapper functions that correspond to the POSIX regular
645         expression API.  These are described in the pcreposix documentation.         expression  API.  These  are  described in the pcreposix documentation.
646           Both of these APIs define a set of C function calls. A C++  wrapper  is
647         The  native  API  function  prototypes  are  defined in the header file         distributed with PCRE. It is documented in the pcrecpp page.
648         pcre.h, and on Unix systems the library itself is called libpcre.a,  so  
649         can be accessed by adding -lpcre to the command for linking an applica-         The  native  API  C  function prototypes are defined in the header file
650         tion which calls it. The header file defines the macros PCRE_MAJOR  and         pcre.h, and on Unix systems the library itself is called  libpcre.   It
651         PCRE_MINOR  to  contain  the  major  and  minor release numbers for the         can normally be accessed by adding -lpcre to the command for linking an
652         library. Applications can use these to include  support  for  different         application  that  uses  PCRE.  The  header  file  defines  the  macros
653         releases.         PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
654           bers for the library.  Applications can use these  to  include  support
655         The  functions  pcre_compile(),  pcre_study(), and pcre_exec() are used         for different releases of PCRE.
656         for compiling and matching regular expressions. A sample  program  that  
657         demonstrates  the simplest way of using them is given in the file pcre-         The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
658         demo.c. The pcresample documentation describes how to run it.         pcre_exec() are used for compiling and matching regular expressions  in
659           a  Perl-compatible  manner. A sample program that demonstrates the sim-
660         There are convenience functions for extracting captured substrings from         plest way of using them is provided in the file  called  pcredemo.c  in
661         a matched subject string. They are:         the  source distribution. The pcresample documentation describes how to
662           run it.
663    
664           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
665           ble,  is  also provided. This uses a different algorithm for the match-
666           ing. This allows it to find all possible matches (at a given  point  in
667           the  subject),  not  just  one. However, this algorithm does not return
668           captured substrings. A description of the two matching  algorithms  and
669           their  advantages  and disadvantages is given in the pcrematching docu-
670           mentation.
671    
672           In addition to the main compiling and  matching  functions,  there  are
673           convenience functions for extracting captured substrings from a subject
674           string that is matched by pcre_exec(). They are:
675    
676           pcre_copy_substring()           pcre_copy_substring()
677           pcre_copy_named_substring()           pcre_copy_named_substring()
678           pcre_get_substring()           pcre_get_substring()
679           pcre_get_named_substring()           pcre_get_named_substring()
680           pcre_get_substring_list()           pcre_get_substring_list()
681             pcre_get_stringnumber()
682    
683         pcre_free_substring() and pcre_free_substring_list() are also provided,         pcre_free_substring() and pcre_free_substring_list() are also provided,
684         to free the memory used for extracted strings.         to free the memory used for extracted strings.
685    
686         The function pcre_maketables() is used (optionally) to build a  set  of         The  function  pcre_maketables()  is  used  to build a set of character
687         character tables in the current locale for passing to pcre_compile().         tables  in  the  current  locale   for   passing   to   pcre_compile(),
688           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
689         The  function  pcre_fullinfo()  is used to find out information about a         provided for specialist use.  Most  commonly,  no  special  tables  are
690         compiled pattern; pcre_info() is an obsolete version which returns only         passed,  in  which case internal tables that are generated when PCRE is
691         some  of  the available information, but is retained for backwards com-         built are used.
692         patibility.  The function pcre_version() returns a pointer to a  string  
693           The function pcre_fullinfo() is used to find out  information  about  a
694           compiled  pattern; pcre_info() is an obsolete version that returns only
695           some of the available information, but is retained for  backwards  com-
696           patibility.   The function pcre_version() returns a pointer to a string
697         containing the version of PCRE and its date of release.         containing the version of PCRE and its date of release.
698    
699         The  global  variables  pcre_malloc and pcre_free initially contain the         The function pcre_refcount() maintains a  reference  count  in  a  data
700         entry points of the standard  malloc()  and  free()  functions  respec-         block  containing  a compiled pattern. This is provided for the benefit
701           of object-oriented applications.
702    
703           The global variables pcre_malloc and pcre_free  initially  contain  the
704           entry  points  of  the  standard malloc() and free() functions, respec-
705         tively. PCRE calls the memory management functions via these variables,         tively. PCRE calls the memory management functions via these variables,
706         so a calling program can replace them if it  wishes  to  intercept  the         so  a  calling  program  can replace them if it wishes to intercept the
707         calls. This should be done before calling any PCRE functions.         calls. This should be done before calling any PCRE functions.
708    
709         The  global  variables  pcre_stack_malloc  and pcre_stack_free are also         The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
710         indirections to memory management functions.  These  special  functions         indirections  to  memory  management functions. These special functions
711         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
712         data, instead of recursive function calls. This is a  non-standard  way         data, instead of recursive function calls, when running the pcre_exec()
713         of  building  PCRE,  for  use in environments that have limited stacks.         function. This is a non-standard way of building PCRE, for use in envi-
714         Because of the greater use of memory management, it runs  more  slowly.         ronments that have limited stacks. Because of the greater use of memory
715         Separate  functions  are provided so that special-purpose external code         management, it runs more slowly.  Separate functions  are  provided  so
716         can be used for this case. When used, these functions are always called         that  special-purpose  external  code  can  be used for this case. When
717         in  a  stack-like  manner  (last obtained, first freed), and always for         used, these functions are always called in a  stack-like  manner  (last
718         memory blocks of the same size.         obtained,  first freed), and always for memory blocks of the same size.
719    
720         The global variable pcre_callout initially contains NULL. It can be set         The global variable pcre_callout initially contains NULL. It can be set
721         by  the  caller  to  a "callout" function, which PCRE will then call at         by  the  caller  to  a "callout" function, which PCRE will then call at
# Line 467  MULTITHREADING Line 735  MULTITHREADING
735         at once.         at once.
736    
737    
738    SAVING PRECOMPILED PATTERNS FOR LATER USE
739    
740           The compiled form of a regular expression can be saved and re-used at a
741           later time, possibly by a different program, and even on a  host  other
742           than  the  one  on  which  it  was  compiled.  Details are given in the
743           pcreprecompile documentation.
744    
745    
746  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
747    
748         int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
749    
750         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-
751         cover which optional features have been compiled into the PCRE library.         cover which optional features have been compiled into the PCRE library.
752         The  pcrebuild documentation has more details about these optional fea-         The pcrebuild documentation has more details about these optional  fea-
753         tures.         tures.
754    
755         The first argument for pcre_config() is an  integer,  specifying  which         The  first  argument  for pcre_config() is an integer, specifying which
756         information is required; the second argument is a pointer to a variable         information is required; the second argument is a pointer to a variable
757         into which the information is  placed.  The  following  information  is         into  which  the  information  is  placed. The following information is
758         available:         available:
759    
760           PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
761    
762         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-
763         able; otherwise it is set to zero.         able; otherwise it is set to zero.
764    
765             PCRE_CONFIG_UNICODE_PROPERTIES
766    
767           The  output  is  an  integer  that is set to one if support for Unicode
768           character properties is available; otherwise it is set to zero.
769    
770           PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
771    
772         The output is an integer that is set to the value of the code  that  is         The output is an integer that is set to the value of the code  that  is
# Line 516  CHECKING BUILD-TIME OPTIONS Line 797  CHECKING BUILD-TIME OPTIONS
797    
798           PCRE_CONFIG_STACKRECURSE           PCRE_CONFIG_STACKRECURSE
799    
800         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
801         implemented  by recursive function calls that use the stack to remember         running pcre_exec() is implemented by recursive function calls that use
802         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
803         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
804         recursive  function  calls.  In  this   case,   pcre_stack_malloc   and         on the  heap  instead  of  recursive  function  calls.  In  this  case,
805         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
806         avoiding the use of the stack.         blocks on the heap, thus avoiding the use of the stack.
807    
808    
809  COMPILING A PATTERN  COMPILING A PATTERN
# Line 531  COMPILING A PATTERN Line 812  COMPILING A PATTERN
812              const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
813              const unsigned char *tableptr);              const unsigned char *tableptr);
814    
815           pcre *pcre_compile2(const char *pattern, int options,
816                int *errorcodeptr,
817                const char **errptr, int *erroffset,
818                const unsigned char *tableptr);
819    
820         The function pcre_compile() is called to  compile  a  pattern  into  an         Either of the functions pcre_compile() or pcre_compile2() can be called
821         internal  form.  The pattern is a C string terminated by a binary zero,         to compile a pattern into an internal form. The only difference between
822         and is passed in the argument pattern. A pointer to a single  block  of         the two interfaces is that pcre_compile2() has an additional  argument,
823         memory  that is obtained via pcre_malloc is returned. This contains the         errorcodeptr, via which a numerical error code can be returned.
824         compiled code and related data.  The  pcre  type  is  defined  for  the  
825         returned  block;  this  is a typedef for a structure whose contents are         The pattern is a C string terminated by a binary zero, and is passed in
826         not externally defined. It is up to the caller to free the memory  when         the pattern argument. A pointer to a single block  of  memory  that  is
827         it is no longer required.         obtained  via  pcre_malloc is returned. This contains the compiled code
828           and related data. The pcre type is defined for the returned block; this
829           is a typedef for a structure whose contents are not externally defined.
830           It is up to the caller  to  free  the  memory  when  it  is  no  longer
831           required.
832    
833         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
834         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
835         fully relocatable, because it contains a copy of the tableptr argument,         fully  relocatable, because it may contain a copy of the tableptr argu-
836         which is an address (see below).         ment, which is an address (see below).
837    
838         The options argument contains independent bits that affect the compila-         The options argument contains independent bits that affect the compila-
839         tion.  It  should  be  zero  if  no  options  are required. Some of the         tion.  It  should  be  zero  if  no options are required. The available
840         options, in particular, those that are compatible with Perl,  can  also         options are described below. Some of them, in  particular,  those  that
841         be  set and unset from within the pattern (see the detailed description         are  compatible  with  Perl,  can also be set and unset from within the
842         of regular expressions in the  pcrepattern  documentation).  For  these         pattern (see the detailed description  in  the  pcrepattern  documenta-
843         options,  the  contents of the options argument specifies their initial         tion).  For  these options, the contents of the options argument speci-
844         settings at the start of compilation and execution.  The  PCRE_ANCHORED         fies their initial settings at the start of compilation and  execution.
845         option can be set at the time of matching as well as at compile time.         The  PCRE_ANCHORED option can be set at the time of matching as well as
846           at compile time.
847    
848         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
849         if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and         if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
850         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-
851         sage. The offset from the start of the pattern to the  character  where         sage.  The  offset from the start of the pattern to the character where
852         the  error  was  discovered  is  placed  in  the variable pointed to by         the error was discovered is  placed  in  the  variable  pointed  to  by
853         erroffset, which must not be NULL. If it  is,  an  immediate  error  is         erroffset,  which  must  not  be  NULL. If it is, an immediate error is
854         given.         given.
855    
856           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
857           codeptr  argument is not NULL, a non-zero error code number is returned
858           via this argument in the event of an error. This is in addition to  the
859           textual error message. Error codes and messages are listed below.
860    
861         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
862         character tables which are built when it is compiled, using the default         character tables that are  built  when  PCRE  is  compiled,  using  the
863         C  locale.  Otherwise,  tableptr  must  be  the  result  of  a  call to         default  C  locale.  Otherwise, tableptr must be an address that is the
864         pcre_maketables(). See the section on locale support below.         result of a call to pcre_maketables(). This value is  stored  with  the
865           compiled  pattern,  and used again by pcre_exec(), unless another table
866           pointer is passed to it. For more discussion, see the section on locale
867           support below.
868    
869         This code fragment shows a typical straightforward  call  to  pcre_com-         This  code  fragment  shows a typical straightforward call to pcre_com-
870         pile():         pile():
871    
872           pcre *re;           pcre *re;
# Line 581  COMPILING A PATTERN Line 879  COMPILING A PATTERN
879             &erroffset,       /* for error offset */             &erroffset,       /* for error offset */
880             NULL);            /* use default character tables */             NULL);            /* use default character tables */
881    
882         The following option bits are defined:         The following names for option bits are defined in  the  pcre.h  header
883           file:
884    
885           PCRE_ANCHORED           PCRE_ANCHORED
886    
887         If this bit is set, the pattern is forced to be "anchored", that is, it         If this bit is set, the pattern is forced to be "anchored", that is, it
888         is constrained to match only at the first matching point in the  string         is constrained to match only at the first matching point in the  string
889         which is being searched (the "subject string"). This effect can also be         that  is being searched (the "subject string"). This effect can also be
890         achieved by appropriate constructs in the pattern itself, which is  the         achieved by appropriate constructs in the pattern itself, which is  the
891         only way to do it in Perl.         only way to do it in Perl.
892    
893             PCRE_AUTO_CALLOUT
894    
895           If this bit is set, pcre_compile() automatically inserts callout items,
896           all with number 255, before each pattern item. For  discussion  of  the
897           callout facility, see the pcrecallout documentation.
898    
899           PCRE_CASELESS           PCRE_CASELESS
900    
901         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
902         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
903         changed within a pattern by a (?i) option setting.         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
904           always understands the concept of case for characters whose values  are
905           less  than 128, so caseless matching is always possible. For characters
906           with higher values, the concept of case is supported if  PCRE  is  com-
907           piled  with Unicode property support, but not otherwise. If you want to
908           use caseless matching for characters 128 and  above,  you  must  ensure
909           that  PCRE  is  compiled  with Unicode property support as well as with
910           UTF-8 support.
911    
912           PCRE_DOLLAR_ENDONLY           PCRE_DOLLAR_ENDONLY
913    
914         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
915         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
916         matches  immediately before the final character if it is a newline (but         matches immediately before the final character if it is a newline  (but
917         not before any  other  newlines).  The  PCRE_DOLLAR_ENDONLY  option  is         not  before  any  other  newlines).  The  PCRE_DOLLAR_ENDONLY option is
918         ignored if PCRE_MULTILINE is set. There is no equivalent to this option         ignored if PCRE_MULTILINE is set. There is no equivalent to this option
919         in Perl, and no way to set it within a pattern.         in Perl, and no way to set it within a pattern.
920    
921           PCRE_DOTALL           PCRE_DOTALL
922    
923         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-
924         acters,  including  newlines.  Without  it, newlines are excluded. This         acters, including newlines. Without it,  newlines  are  excluded.  This
925         option is equivalent to Perl's /s option, and it can be changed  within         option  is equivalent to Perl's /s option, and it can be changed within
926         a  pattern  by  a  (?s)  option  setting. A negative class such as [^a]         a pattern by a (?s) option setting.  A  negative  class  such  as  [^a]
927         always matches a newline character, independent of the setting of  this         always  matches a newline character, independent of the setting of this
928         option.         option.
929    
930           PCRE_EXTENDED           PCRE_EXTENDED
931    
932         If  this  bit  is  set,  whitespace  data characters in the pattern are         If this bit is set, whitespace  data  characters  in  the  pattern  are
933         totally ignored except  when  escaped  or  inside  a  character  class.         totally ignored except when escaped or inside a character class. White-
934         Whitespace  does  not  include the VT character (code 11). In addition,         space does not include the VT character (code 11). In addition, charac-
935         characters between an unescaped # outside a  character  class  and  the         ters between an unescaped # outside a character class and the next new-
936         next newline character, inclusive, are also ignored. This is equivalent         line character, inclusive, are also  ignored.  This  is  equivalent  to
937         to Perl's /x option, and it can be changed within a pattern by  a  (?x)         Perl's  /x  option,  and  it  can be changed within a pattern by a (?x)
938         option setting.         option setting.
939    
940         This  option  makes  it possible to include comments inside complicated         This option makes it possible to include  comments  inside  complicated
941         patterns.  Note, however, that this applies only  to  data  characters.         patterns.   Note,  however,  that this applies only to data characters.
942         Whitespace   characters  may  never  appear  within  special  character         Whitespace  characters  may  never  appear  within  special   character
943         sequences in a pattern, for  example  within  the  sequence  (?(  which         sequences  in  a  pattern,  for  example  within the sequence (?( which
944         introduces a conditional subpattern.         introduces a conditional subpattern.
945    
946           PCRE_EXTRA           PCRE_EXTRA
947    
948         This  option  was invented in order to turn on additional functionality         This option was invented in order to turn on  additional  functionality
949         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
950         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
951         letter that has no special meaning  causes  an  error,  thus  reserving         letter  that  has  no  special  meaning causes an error, thus reserving
952         these  combinations  for  future  expansion.  By default, as in Perl, a         these combinations for future expansion. By  default,  as  in  Perl,  a
953         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
954         literal.  There  are  at  present  no other features controlled by this         literal. There are at present no  other  features  controlled  by  this
955         option. It can also be set by a (?X) option setting within a pattern.         option. It can also be set by a (?X) option setting within a pattern.
956    
957             PCRE_FIRSTLINE
958    
959           If  this  option  is  set,  an  unanchored pattern is required to match
960           before or at the first newline character in the subject string,  though
961           the matched text may continue over the newline.
962    
963           PCRE_MULTILINE           PCRE_MULTILINE
964    
965         By default, PCRE treats the subject string as consisting  of  a  single         By  default,  PCRE  treats the subject string as consisting of a single
966         "line"  of  characters (even if it actually contains several newlines).         line of characters (even if it actually contains newlines). The  "start
967         The "start of line" metacharacter (^) matches only at the start of  the         of  line"  metacharacter  (^)  matches only at the start of the string,
968         string,  while  the "end of line" metacharacter ($) matches only at the         while the "end of line" metacharacter ($) matches only at  the  end  of
969         end of the string, or before a terminating  newline  (unless  PCRE_DOL-         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
970         LAR_ENDONLY is set). This is the same as Perl.         is set). This is the same as Perl.
971    
972         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"
973         constructs match immediately following or immediately before  any  new-         constructs  match  immediately following or immediately before any new-
974         line  in the subject string, respectively, as well as at the very start         line in the subject string, respectively, as well as at the very  start
975         and end. This is equivalent to Perl's /m option, and it can be  changed         and  end. This is equivalent to Perl's /m option, and it can be changed
976         within a pattern by a (?m) option setting. If there are no "\n" charac-         within a pattern by a (?m) option setting. If there are no "\n" charac-
977         ters in a subject string, or no occurrences of ^ or  $  in  a  pattern,         ters  in  a  subject  string, or no occurrences of ^ or $ in a pattern,
978         setting PCRE_MULTILINE has no effect.         setting PCRE_MULTILINE has no effect.
979    
980           PCRE_NO_AUTO_CAPTURE           PCRE_NO_AUTO_CAPTURE
981    
982         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-
983         theses in the pattern. Any opening parenthesis that is not followed  by         theses  in the pattern. Any opening parenthesis that is not followed by
984         ?  behaves as if it were followed by ?: but named parentheses can still         ? behaves as if it were followed by ?: but named parentheses can  still
985         be used for capturing (and they acquire  numbers  in  the  usual  way).         be  used  for  capturing  (and  they acquire numbers in the usual way).
986         There is no equivalent of this option in Perl.         There is no equivalent of this option in Perl.
987    
988           PCRE_UNGREEDY           PCRE_UNGREEDY
989    
990         This  option  inverts  the "greediness" of the quantifiers so that they         This option inverts the "greediness" of the quantifiers  so  that  they
991         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
992         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
993         within the pattern.         within the pattern.
994    
995           PCRE_UTF8           PCRE_UTF8
996    
997         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
998         strings  of  UTF-8 characters instead of single-byte character strings.         strings of UTF-8 characters instead of single-byte  character  strings.
999         However, it is available only if PCRE has been built to  include  UTF-8         However,  it is available only when PCRE is built to include UTF-8 sup-
1000         support.  If  not, the use of this option provokes an error. Details of         port. If not, the use of this option provokes an error. Details of  how
1001         how this option changes the behaviour of PCRE are given in the  section         this  option  changes the behaviour of PCRE are given in the section on
1002         on UTF-8 support in the main pcre page.         UTF-8 support in the main pcre page.
1003    
1004           PCRE_NO_UTF8_CHECK           PCRE_NO_UTF8_CHECK
1005    
1006         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
1007         automatically checked. If an invalid UTF-8 sequence of bytes is  found,         automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1008         pcre_compile()  returns an error. If you already know that your pattern         pcre_compile() returns an error. If you already know that your  pattern
1009         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
1010         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
1011         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
1012         your  program  to  crash.  Note that there is a similar option for sup-         your program to crash.  Note that this option can  also  be  passed  to
1013         pressing the checking of subject strings passed to pcre_exec().         pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1014           ing of subject strings.
1015    
1016    
1017    COMPILATION ERROR CODES
1018    
1019           The following table lists the error  codes  than  may  be  returned  by
1020           pcre_compile2(),  along with the error messages that may be returned by
1021           both compiling functions.
1022    
1023              0  no error
1024              1  \ at end of pattern
1025              2  \c at end of pattern
1026              3  unrecognized character follows \
1027              4  numbers out of order in {} quantifier
1028              5  number too big in {} quantifier
1029              6  missing terminating ] for character class
1030              7  invalid escape sequence in character class
1031              8  range out of order in character class
1032              9  nothing to repeat
1033             10  operand of unlimited repeat could match the empty string
1034             11  internal error: unexpected repeat
1035             12  unrecognized character after (?
1036             13  POSIX named classes are supported only within a class
1037             14  missing )
1038             15  reference to non-existent subpattern
1039             16  erroffset passed as NULL
1040             17  unknown option bit(s) set
1041             18  missing ) after comment
1042             19  parentheses nested too deeply
1043             20  regular expression too large
1044             21  failed to get memory
1045             22  unmatched parentheses
1046             23  internal error: code overflow
1047             24  unrecognized character after (?<
1048             25  lookbehind assertion is not fixed length
1049             26  malformed number after (?(
1050             27  conditional group contains more than two branches
1051             28  assertion expected after (?(
1052             29  (?R or (?digits must be followed by )
1053             30  unknown POSIX class name
1054             31  POSIX collating elements are not supported
1055             32  this version of PCRE is not compiled with PCRE_UTF8 support
1056             33  spare error
1057             34  character value in \x{...} sequence is too large
1058             35  invalid condition (?(0)
1059             36  \C not allowed in lookbehind assertion
1060             37  PCRE does not support \L, \l, \N, \U, or \u
1061             38  number after (?C is > 255
1062             39  closing ) for (?C expected
1063             40  recursive call could loop indefinitely
1064             41  unrecognized character after (?P
1065             42  syntax error after (?P
1066             43  two named groups have the same name
1067             44  invalid UTF-8 string
1068             45  support for \P, \p, and \X has not been compiled
1069             46  malformed \P or \p sequence
1070             47  unknown property name after \P or \p
1071    
1072    
1073  STUDYING A PATTERN  STUDYING A PATTERN
1074    
1075         pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1076              const char **errptr);              const char **errptr);
1077    
1078         When a pattern is going to be used several times, it is worth  spending         If a compiled pattern is going to be used several times,  it  is  worth
1079         more  time  analyzing it in order to speed up the time taken for match-         spending more time analyzing it in order to speed up the time taken for
1080         ing. The function pcre_study() takes a pointer to a compiled pattern as         matching. The function pcre_study() takes a pointer to a compiled  pat-
1081         its first argument. If studing the pattern produces additional informa-         tern as its first argument. If studying the pattern produces additional
1082         tion that will help speed up matching, pcre_study() returns  a  pointer         information that will help speed up matching,  pcre_study()  returns  a
1083         to  a  pcre_extra  block,  in  which the study_data field points to the         pointer  to a pcre_extra block, in which the study_data field points to
1084         results of the study.         the results of the study.
1085    
1086         The returned value from  a  pcre_study()  can  be  passed  directly  to         The  returned  value  from  pcre_study()  can  be  passed  directly  to
1087         pcre_exec().  However,  the pcre_extra block also contains other fields         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1088         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
1089         described  below.  If  studying  the pattern does not produce any addi-         described below in the section on matching a pattern.
        tional information, pcre_study() returns NULL. In that circumstance, if  
        the  calling  program  wants  to  pass  some  of  the  other  fields to  
        pcre_exec(), it must set up its own pcre_extra block.  
1090    
1091         The second argument contains option bits. At present,  no  options  are         If  studying  the  pattern  does not produce any additional information
1092         defined for pcre_study(), and this argument should always be zero.         pcre_study() returns NULL. In that circumstance, if the calling program
1093           wants  to  pass  any of the other fields to pcre_exec(), it must set up
1094           its own pcre_extra block.
1095    
1096           The second argument of pcre_study() contains option bits.  At  present,
1097           no options are defined, and this argument should always be zero.
1098    
1099         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.
1100         If studying succeeds (even if no data is  returned),  the  variable  it         If studying succeeds (even if no data is  returned),  the  variable  it
# Line 736  STUDYING A PATTERN Line 1112  STUDYING A PATTERN
1112    
1113         At present, studying a pattern is useful only for non-anchored patterns         At present, studying a pattern is useful only for non-anchored patterns
1114         that do not have a single fixed starting character. A bitmap of  possi-         that do not have a single fixed starting character. A bitmap of  possi-
1115         ble starting characters is created.         ble starting bytes is created.
1116    
1117    
1118  LOCALE SUPPORT  LOCALE SUPPORT
1119    
1120         PCRE  handles  caseless matching, and determines whether characters are         PCRE  handles  caseless matching, and determines whether characters are
1121         letters, digits, or whatever, by reference to a  set  of  tables.  When         letters digits, or whatever, by reference to a set of  tables,  indexed
1122         running  in UTF-8 mode, this applies only to characters with codes less         by  character  value.  When running in UTF-8 mode, this applies only to
1123         than 256. The library contains a default set of tables that is  created         characters with codes less than 128. Higher-valued  codes  never  match
1124         in  the  default  C locale when PCRE is compiled. This is used when the         escapes  such  as  \w or \d, but can be tested with \p if PCRE is built
1125         final argument of pcre_compile() is NULL, and is  sufficient  for  many         with Unicode character property support.
1126         applications.  
1127           An internal set of tables is created in the default C locale when  PCRE
1128         An alternative set of tables can, however, be supplied. Such tables are         is  built.  This  is  used when the final argument of pcre_compile() is
1129         built by calling the pcre_maketables() function,  which  has  no  argu-         NULL, and is sufficient for many applications. An  alternative  set  of
1130         ments,  in  the  relevant  locale.  The  result  can  then be passed to         tables  can,  however, be supplied. These may be created in a different
1131         pcre_compile() as often as necessary. For example,  to  build  and  use         locale from the default. As more and more applications change to  using
1132         tables that are appropriate for the French locale (where accented char-         Unicode, the need for this locale support is expected to die away.
1133         acters with codes greater than 128 are treated as letters), the follow-  
1134         ing code could be used:         External  tables  are  built by calling the pcre_maketables() function,
1135           which has no arguments, in the relevant locale. The result can then  be
1136           passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1137           example, to build and use tables that are appropriate  for  the  French
1138           locale  (where  accented  characters  with  values greater than 128 are
1139           treated as letters), the following code could be used:
1140    
1141           setlocale(LC_CTYPE, "fr");           setlocale(LC_CTYPE, "fr_FR");
1142           tables = pcre_maketables();           tables = pcre_maketables();
1143           re = pcre_compile(..., tables);           re = pcre_compile(..., tables);
1144    
1145         The  tables  are  built in memory that is obtained via pcre_malloc. The         When pcre_maketables() runs, the tables are built  in  memory  that  is
1146         pointer that is passed to pcre_compile is saved with the compiled  pat-         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1147         tern, and the same tables are used via this pointer by pcre_study() and         that the memory containing the tables remains available for as long  as
1148         pcre_exec(). Thus, for any single pattern,  compilation,  studying  and         it is needed.
1149         matching  all  happen in the same locale, but different patterns can be  
1150         compiled in different locales. It is  the  caller's  responsibility  to         The pointer that is passed to pcre_compile() is saved with the compiled
1151         ensure  that  the memory containing the tables remains available for as         pattern, and the same tables are used via this pointer by  pcre_study()
1152         long as it is needed.         and normally also by pcre_exec(). Thus, by default, for any single pat-
1153           tern, compilation, studying and matching all happen in the same locale,
1154           but different patterns can be compiled in different locales.
1155    
1156           It  is  possible to pass a table pointer or NULL (indicating the use of
1157           the internal tables) to pcre_exec(). Although  not  intended  for  this
1158           purpose,  this facility could be used to match a pattern in a different
1159           locale from the one in which it was compiled. Passing table pointers at
1160           run time is discussed below in the section on matching a pattern.
1161    
1162    
1163  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
# Line 776  INFORMATION ABOUT A PATTERN Line 1165  INFORMATION ABOUT A PATTERN
1165         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1166              int what, void *where);              int what, void *where);
1167    
1168         The pcre_fullinfo() function returns information about a compiled  pat-         The  pcre_fullinfo() function returns information about a compiled pat-
1169         tern. It replaces the obsolete pcre_info() function, which is neverthe-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1170         less retained for backwards compability (and is documented below).         less retained for backwards compability (and is documented below).
1171    
1172         The first argument for pcre_fullinfo() is a  pointer  to  the  compiled         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1173         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
1174         the pattern was not studied. The third argument specifies  which  piece         the  pattern  was not studied. The third argument specifies which piece
1175         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
1176         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
1177         success, or one of the following negative numbers:         success, or one of the following negative numbers:
1178    
1179           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
# Line 792  INFORMATION ABOUT A PATTERN Line 1181  INFORMATION ABOUT A PATTERN
1181           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1182           PCRE_ERROR_BADOPTION  the value of what was invalid           PCRE_ERROR_BADOPTION  the value of what was invalid
1183    
1184         Here  is a typical call of pcre_fullinfo(), to obtain the length of the         The "magic number" is placed at the start of each compiled  pattern  as
1185         compiled pattern:         an  simple check against passing an arbitrary memory pointer. Here is a
1186           typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1187           pattern:
1188    
1189           int rc;           int rc;
1190           unsigned long int length;           unsigned long int length;
# Line 803  INFORMATION ABOUT A PATTERN Line 1194  INFORMATION ABOUT A PATTERN
1194             PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1195             &length);         /* where to put the data */             &length);         /* where to put the data */
1196    
1197         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
1198         are as follows:         are as follows:
1199    
1200           PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1201    
1202         Return  the  number  of  the highest back reference in the pattern. The         Return the number of the highest back reference  in  the  pattern.  The
1203         fourth argument should point to an int variable. Zero  is  returned  if         fourth  argument  should  point to an int variable. Zero is returned if
1204         there are no back references.         there are no back references.
1205    
1206           PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1207    
1208         Return  the  number of capturing subpatterns in the pattern. The fourth         Return the number of capturing subpatterns in the pattern.  The  fourth
1209         argument should point to an int variable.         argument should point to an int variable.
1210    
1211             PCRE_INFO_DEFAULT_TABLES
1212    
1213           Return  a pointer to the internal default character tables within PCRE.
1214           The fourth argument should point to an unsigned char *  variable.  This
1215           information call is provided for internal use by the pcre_study() func-
1216           tion. External callers can cause PCRE to use  its  internal  tables  by
1217           passing a NULL table pointer.
1218    
1219           PCRE_INFO_FIRSTBYTE           PCRE_INFO_FIRSTBYTE
1220    
1221         Return information about the first byte of any matched  string,  for  a         Return  information  about  the first byte of any matched string, for a
1222         non-anchored    pattern.    (This    option    used    to   be   called         non-anchored   pattern.   (This    option    used    to    be    called
1223         PCRE_INFO_FIRSTCHAR; the old name is  still  recognized  for  backwards         PCRE_INFO_FIRSTCHAR;  the  old  name  is still recognized for backwards
1224         compatibility.)         compatibility.)
1225    
1226         If  there  is  a  fixed  first  byte,  e.g.  from  a  pattern  such  as         If there is a fixed first byte, for example, from  a  pattern  such  as
1227         (cat|cow|coyote), it is returned in the integer pointed  to  by  where.         (cat|cow|coyote),  it  is  returned in the integer pointed to by where.
1228         Otherwise, if either         Otherwise, if either
1229    
1230         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1231         branch starts with "^", or         branch starts with "^", or
1232    
1233         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1234         set (if it were set, the pattern would be anchored),         set (if it were set, the pattern would be anchored),
1235    
1236         -1  is  returned, indicating that the pattern matches only at the start         -1 is returned, indicating that the pattern matches only at  the  start
1237         of a subject string or after any newline within the  string.  Otherwise         of  a  subject string or after any newline within the string. Otherwise
1238         -2 is returned. For anchored patterns, -2 is returned.         -2 is returned. For anchored patterns, -2 is returned.
1239    
1240           PCRE_INFO_FIRSTTABLE           PCRE_INFO_FIRSTTABLE
1241    
1242         If  the pattern was studied, and this resulted in the construction of a         If the pattern was studied, and this resulted in the construction of  a
1243         256-bit table indicating a fixed set of bytes for the first byte in any         256-bit table indicating a fixed set of bytes for the first byte in any
1244         matching  string, a pointer to the table is returned. Otherwise NULL is         matching string, a pointer to the table is returned. Otherwise NULL  is
1245         returned. The fourth argument should point to an unsigned char *  vari-         returned.  The fourth argument should point to an unsigned char * vari-
1246         able.         able.
1247    
1248           PCRE_INFO_LASTLITERAL           PCRE_INFO_LASTLITERAL
1249    
1250         Return  the  value of the rightmost literal byte that must exist in any         Return the value of the rightmost literal byte that must exist  in  any
1251         matched string, other than at its  start,  if  such  a  byte  has  been         matched  string,  other  than  at  its  start,  if such a byte has been
1252         recorded. The fourth argument should point to an int variable. If there         recorded. The fourth argument should point to an int variable. If there
1253         is no such byte, -1 is returned. For anchored patterns, a last  literal         is  no such byte, -1 is returned. For anchored patterns, a last literal
1254         byte  is  recorded only if it follows something of variable length. For         byte is recorded only if it follows something of variable  length.  For
1255         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1256         /^a\dz\d/ the returned value is -1.         /^a\dz\d/ the returned value is -1.
1257    
# Line 860  INFORMATION ABOUT A PATTERN Line 1259  INFORMATION ABOUT A PATTERN
1259           PCRE_INFO_NAMEENTRYSIZE           PCRE_INFO_NAMEENTRYSIZE
1260           PCRE_INFO_NAMETABLE           PCRE_INFO_NAMETABLE
1261    
1262         PCRE  supports the use of named as well as numbered capturing parenthe-         PCRE supports the use of named as well as numbered capturing  parenthe-
1263         ses. The names are just an additional way of identifying the  parenthe-         ses.  The names are just an additional way of identifying the parenthe-
1264         ses,  which still acquire a number. A caller that wants to extract data         ses,  which  still  acquire  numbers.  A  convenience  function  called
1265         from a named subpattern must convert the name to a number in  order  to         pcre_get_named_substring()  is  provided  for  extracting an individual
1266         access  the  correct  pointers  in  the  output  vector (described with         captured substring by name. It is also possible  to  extract  the  data
1267         pcre_exec() below). In order to do this, it must first use these  three         directly,  by  first converting the name to a number in order to access
1268         values to obtain the name-to-number mapping table for the pattern.         the correct pointers in the output vector (described  with  pcre_exec()
1269           below).  To  do the conversion, you need to use the name-to-number map,
1270           which is described by these three values.
1271    
1272         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
1273         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1274         of  each  entry;  both  of  these  return  an int value. The entry size         of each entry; both of these  return  an  int  value.  The  entry  size
1275         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1276         a  pointer  to  the  first  entry of the table (a pointer to char). The         a pointer to the first entry of the table  (a  pointer  to  char).  The
1277         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-
1278         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-
1279         sponding name, zero terminated. The names are  in  alphabetical  order.         sponding  name,  zero  terminated. The names are in alphabetical order.
1280         For  example,  consider  the following pattern (assume PCRE_EXTENDED is         For example, consider the following pattern  (assume  PCRE_EXTENDED  is
1281         set, so white space - including newlines - is ignored):         set, so white space - including newlines - is ignored):
1282    
1283           (?P<date> (?P<year>(\d\d)?\d\d) -           (?P<date> (?P<year>(\d\d)?\d\d) -
1284           (?P<month>\d\d) - (?P<day>\d\d) )           (?P<month>\d\d) - (?P<day>\d\d) )
1285    
1286         There are four named subpatterns, so the table has  four  entries,  and         There  are  four  named subpatterns, so the table has four entries, and
1287         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,
1288         with non-printing bytes shows in hex, and undefined bytes shown as ??:         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1289           as ??:
1290    
1291           00 01 d  a  t  e  00 ??           00 01 d  a  t  e  00 ??
1292           00 05 d  a  y  00 ?? ??           00 05 d  a  y  00 ?? ??
1293           00 04 m  o  n  t  h  00           00 04 m  o  n  t  h  00
1294           00 02 y  e  a  r  00 ??           00 02 y  e  a  r  00 ??
1295    
1296         When writing code to extract data from named subpatterns, remember that         When writing code to extract data  from  named  subpatterns  using  the
1297         the length of each entry may be different for each compiled pattern.         name-to-number map, remember that the length of each entry is likely to
1298           be different for each compiled pattern.
1299    
1300           PCRE_INFO_OPTIONS           PCRE_INFO_OPTIONS
1301    
1302         Return  a  copy of the options with which the pattern was compiled. The         Return a copy of the options with which the pattern was  compiled.  The
1303         fourth argument should point to an unsigned long  int  variable.  These         fourth  argument  should  point to an unsigned long int variable. These
1304         option bits are those specified in the call to pcre_compile(), modified         option bits are those specified in the call to pcre_compile(), modified
1305         by any top-level option settings within the pattern itself.         by any top-level option settings within the pattern itself.
1306    
1307         A pattern is automatically anchored by PCRE if  all  of  its  top-level         A  pattern  is  automatically  anchored by PCRE if all of its top-level
1308         alternatives begin with one of the following:         alternatives begin with one of the following:
1309    
1310           ^     unless PCRE_MULTILINE is set           ^     unless PCRE_MULTILINE is set
# Line 915  INFORMATION ABOUT A PATTERN Line 1318  INFORMATION ABOUT A PATTERN
1318    
1319           PCRE_INFO_SIZE           PCRE_INFO_SIZE
1320    
1321         Return the size of the compiled pattern, that is, the  value  that  was         Return  the  size  of the compiled pattern, that is, the value that was
1322         passed as the argument to pcre_malloc() when PCRE was getting memory in         passed as the argument to pcre_malloc() when PCRE was getting memory in
1323         which to place the compiled data. The fourth argument should point to a         which to place the compiled data. The fourth argument should point to a
1324         size_t variable.         size_t variable.
1325    
1326           PCRE_INFO_STUDYSIZE           PCRE_INFO_STUDYSIZE
1327    
1328         Returns  the  size of the data block pointed to by the study_data field         Return the size of the data block pointed to by the study_data field in
1329         in a pcre_extra block. That is, it is the  value  that  was  passed  to         a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
1330         pcre_malloc() when PCRE was getting memory into which to place the data         pcre_malloc() when PCRE was getting memory into which to place the data
1331         created by pcre_study(). The fourth argument should point to  a  size_t         created  by  pcre_study(). The fourth argument should point to a size_t
1332         variable.         variable.
1333    
1334    
# Line 933  OBSOLETE INFO FUNCTION Line 1336  OBSOLETE INFO FUNCTION
1336    
1337         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1338    
1339         The  pcre_info()  function is now obsolete because its interface is too         The pcre_info() function is now obsolete because its interface  is  too
1340         restrictive to return all the available data about a compiled  pattern.         restrictive  to return all the available data about a compiled pattern.
1341         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1342         pcre_info() is the number of capturing subpatterns, or one of the  fol-         pcre_info()  is the number of capturing subpatterns, or one of the fol-
1343         lowing negative numbers:         lowing negative numbers:
1344    
1345           PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_NULL       the argument code was NULL
1346           PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1347    
1348         If  the  optptr  argument is not NULL, a copy of the options with which         If the optptr argument is not NULL, a copy of the  options  with  which
1349         the pattern was compiled is placed in the integer  it  points  to  (see         the  pattern  was  compiled  is placed in the integer it points to (see
1350         PCRE_INFO_OPTIONS above).         PCRE_INFO_OPTIONS above).
1351    
1352         If  the  pattern  is  not anchored and the firstcharptr argument is not         If the pattern is not anchored and the  firstcharptr  argument  is  not
1353         NULL, it is used to pass back information about the first character  of         NULL,  it is used to pass back information about the first character of
1354         any matched string (see PCRE_INFO_FIRSTBYTE above).         any matched string (see PCRE_INFO_FIRSTBYTE above).
1355    
1356    
1357  MATCHING A PATTERN  REFERENCE COUNTS
1358    
1359           int pcre_refcount(pcre *code, int adjust);
1360    
1361           The pcre_refcount() function is used to maintain a reference  count  in
1362           the data block that contains a compiled pattern. It is provided for the
1363           benefit of applications that  operate  in  an  object-oriented  manner,
1364           where different parts of the application may be using the same compiled
1365           pattern, but you want to free the block when they are all done.
1366    
1367           When a pattern is compiled, the reference count field is initialized to
1368           zero.   It is changed only by calling this function, whose action is to
1369           add the adjust value (which may be positive or  negative)  to  it.  The
1370           yield of the function is the new value. However, the value of the count
1371           is constrained to lie between 0 and 65535, inclusive. If the new  value
1372           is outside these limits, it is forced to the appropriate limit value.
1373    
1374           Except  when it is zero, the reference count is not correctly preserved
1375           if a pattern is compiled on one host and then  transferred  to  a  host
1376           whose byte-order is different. (This seems a highly unlikely scenario.)
1377    
1378    
1379    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1380    
1381         int pcre_exec(const pcre *code, const pcre_extra *extra,         int pcre_exec(const pcre *code, const pcre_extra *extra,
1382              const char *subject, int length, int startoffset,              const char *subject, int length, int startoffset,
1383              int options, int *ovector, int ovecsize);              int options, int *ovector, int ovecsize);
1384    
1385         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
1386         pre-compiled pattern, which is passed in the code argument. If the pat-         compiled  pattern, which is passed in the code argument. If the pattern
1387         tern  has been studied, the result of the study should be passed in the         has been studied, the result of the study should be passed in the extra
1388         extra argument.         argument.  This  function is the main matching facility of the library,
1389           and it operates in a Perl-like manner. For specialist use there is also
1390           an  alternative matching function, which is described below in the sec-
1391           tion about the pcre_dfa_exec() function.
1392    
1393           In most applications, the pattern will have been compiled (and  option-
1394           ally  studied)  in the same process that calls pcre_exec(). However, it
1395           is possible to save compiled patterns and study data, and then use them
1396           later  in  different processes, possibly even on different hosts. For a
1397           discussion about this, see the pcreprecompile documentation.
1398    
1399         Here is an example of a simple call to pcre_exec():         Here is an example of a simple call to pcre_exec():
1400    
# Line 973  MATCHING A PATTERN Line 1407  MATCHING A PATTERN
1407             11,             /* the length of the subject string */             11,             /* the length of the subject string */
1408             0,              /* start at offset 0 in the subject */             0,              /* start at offset 0 in the subject */
1409             0,              /* default options */             0,              /* default options */
1410             ovector,        /* vector for substring information */             ovector,        /* vector of integers for substring information */
1411             30);            /* number of elements in the vector */             30);            /* number of elements (NOT size in bytes) */
1412    
1413       Extra data for pcre_exec()
1414    
1415         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
1416         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
1417         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-
1418         tional information in it. The fields in the block are as follows:         tional  information in it. The fields in a pcre_extra block are as fol-
1419           lows:
1420    
1421           unsigned long int flags;           unsigned long int flags;
1422           void *study_data;           void *study_data;
1423           unsigned long int match_limit;           unsigned long int match_limit;
1424           void *callout_data;           void *callout_data;
1425             const unsigned char *tables;
1426    
1427         The  flags  field  is a bitmap that specifies which of the other fields         The flags field is a bitmap that specifies which of  the  other  fields
1428         are set. The flag bits are:         are set. The flag bits are:
1429    
1430           PCRE_EXTRA_STUDY_DATA           PCRE_EXTRA_STUDY_DATA
1431           PCRE_EXTRA_MATCH_LIMIT           PCRE_EXTRA_MATCH_LIMIT
1432           PCRE_EXTRA_CALLOUT_DATA           PCRE_EXTRA_CALLOUT_DATA
1433             PCRE_EXTRA_TABLES
1434    
1435         Other flag bits should be set to zero. The study_data field is  set  in         Other  flag  bits should be set to zero. The study_data field is set in
1436         the  pcre_extra  block  that is returned by pcre_study(), together with         the pcre_extra block that is returned by  pcre_study(),  together  with
1437         the appropriate flag bit. You should not set this yourself, but you can         the appropriate flag bit. You should not set this yourself, but you may
1438         add to the block by setting the other fields.         add to the block by setting the other fields  and  their  corresponding
1439           flag bits.
1440    
1441         The match_limit field provides a means of preventing PCRE from using up         The match_limit field provides a means of preventing PCRE from using up
1442         a vast amount of resources when running patterns that are not going  to         a vast amount of resources when running patterns that are not going  to
1443         match,  but  which  have  a very large number of possibilities in their         match,  but  which  have  a very large number of possibilities in their
1444         search trees. The classic  example  is  the  use  of  nested  unlimited         search trees. The classic  example  is  the  use  of  nested  unlimited
1445         repeats. Internally, PCRE uses a function called match() which it calls         repeats.
1446         repeatedly (sometimes recursively). The limit is imposed on the  number  
1447         of  times  this function is called during a match, which has the effect         Internally,  PCRE uses a function called match() which it calls repeat-
1448         of limiting the amount of recursion  and  backtracking  that  can  take         edly (sometimes recursively). The limit is imposed  on  the  number  of
1449         place.  For  patterns that are not anchored, the count starts from zero         times  this  function is called during a match, which has the effect of
1450         for each position in the subject string.         limiting the amount of recursion and backtracking that can take  place.
1451           For patterns that are not anchored, the count starts from zero for each
1452           position in the subject string.
1453    
1454         The default limit for the library can be set when PCRE  is  built;  the         The default limit for the library can be set when PCRE  is  built;  the
1455         default  default  is 10 million, which handles all but the most extreme         default  default  is 10 million, which handles all but the most extreme
# Line 1019  MATCHING A PATTERN Line 1461  MATCHING A PATTERN
1461         The  pcre_callout  field is used in conjunction with the "callout" fea-         The  pcre_callout  field is used in conjunction with the "callout" fea-
1462         ture, which is described in the pcrecallout documentation.         ture, which is described in the pcrecallout documentation.
1463    
1464         The PCRE_ANCHORED option can be passed in the options  argument,  whose         The tables field  is  used  to  pass  a  character  tables  pointer  to
1465         unused  bits  must  be zero. This limits pcre_exec() to matching at the         pcre_exec();  this overrides the value that is stored with the compiled
1466         first matching position.  However,  if  a  pattern  was  compiled  with         pattern. A non-NULL value is stored with the compiled pattern  only  if
1467         PCRE_ANCHORED,  or turned out to be anchored by virtue of its contents,         custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1468         it cannot be made unachored at matching time.         ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1469           PCRE's  internal  tables  to be used. This facility is helpful when re-
1470         When PCRE_UTF8 was set at compile time, the validity of the subject  as         using patterns that have been saved after compiling  with  an  external
1471         a  UTF-8  string is automatically checked, and the value of startoffset         set  of  tables,  because  the  external tables might be at a different
1472         is also checked to ensure that it points to the start of a UTF-8  char-         address when pcre_exec() is called. See the  pcreprecompile  documenta-
1473         acter.  If  an  invalid  UTF-8  sequence of bytes is found, pcre_exec()         tion for a discussion of saving compiled patterns for later use.
1474         returns  the  error  PCRE_ERROR_BADUTF8.  If  startoffset  contains  an  
1475         invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.     Option bits for pcre_exec()
1476    
1477         If  you  already  know that your subject is valid, and you want to skip         The  unused  bits of the options argument for pcre_exec() must be zero.
1478         these   checks   for   performance   reasons,   you   can    set    the         The  only  bits  that  may  be  set  are  PCRE_ANCHORED,   PCRE_NOTBOL,
1479         PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to         PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
        do this for the second and subsequent calls to pcre_exec() if  you  are  
        making  repeated  calls  to  find  all  the matches in a single subject  
        string. However, you should be  sure  that  the  value  of  startoffset  
        points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is  
        set, the effect of passing an invalid UTF-8 string as a subject,  or  a  
        value  of startoffset that does not point to the start of a UTF-8 char-  
        acter, is undefined. Your program may crash.  
1480    
1481         There are also three further options that can be set only  at  matching           PCRE_ANCHORED
1482         time:  
1483           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1484           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1485           turned  out to be anchored by virtue of its contents, it cannot be made
1486           unachored at matching time.
1487    
1488           PCRE_NOTBOL           PCRE_NOTBOL
1489    
1490         The  first  character  of the string is not the beginning of a line, so         This option specifies that first character of the subject string is not
1491         the circumflex metacharacter should not match before it.  Setting  this         the  beginning  of  a  line, so the circumflex metacharacter should not
1492         without  PCRE_MULTILINE  (at  compile  time) causes circumflex never to         match before it. Setting this without PCRE_MULTILINE (at compile  time)
1493         match.         causes  circumflex  never to match. This option affects only the behav-
1494           iour of the circumflex metacharacter. It does not affect \A.
1495    
1496           PCRE_NOTEOL           PCRE_NOTEOL
1497    
1498         The end of the string is not the end of a line, so the dollar metachar-         This option specifies that the end of the subject string is not the end
1499         acter  should  not  match  it  nor (except in multiline mode) a newline         of  a line, so the dollar metacharacter should not match it nor (except
1500         immediately before it. Setting this without PCRE_MULTILINE (at  compile         in multiline mode) a newline immediately before it. Setting this  with-
1501         time) causes dollar never to match.         out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1502           option affects only the behaviour of the dollar metacharacter. It  does
1503           not affect \Z or \z.
1504    
1505           PCRE_NOTEMPTY           PCRE_NOTEMPTY
1506    
# Line 1078  MATCHING A PATTERN Line 1520  MATCHING A PATTERN
1520         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()
1521         function,  and  when  using  the /g modifier. It is possible to emulate         function,  and  when  using  the /g modifier. It is possible to emulate
1522         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
1523         again at the same offset with PCRE_NOTEMPTY set, and then if that fails         again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1524         by advancing the starting offset (see below)  and  trying  an  ordinary         if that fails by advancing the starting offset (see below)  and  trying
1525         match again.         an ordinary match again. There is some code that demonstrates how to do
1526           this in the pcredemo.c sample program.
1527         The  subject string is passed to pcre_exec() as a pointer in subject, a  
1528         length in length, and a starting byte offset in startoffset. Unlike the           PCRE_NO_UTF8_CHECK
1529         pattern  string,  the  subject  may contain binary zero bytes. When the  
1530         starting offset is zero, the search for a match starts at the beginning         When PCRE_UTF8 is set at compile time, the validity of the subject as a
1531         of the subject, and this is by far the most common case.         UTF-8  string is automatically checked when pcre_exec() is subsequently
1532           called.  The value of startoffset is also checked  to  ensure  that  it
1533         If the pattern was compiled with the PCRE_UTF8 option, the subject must         points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
1534         be a sequence of bytes that is a valid UTF-8 string, and  the  starting         of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1535         offset  must point to the beginning of a UTF-8 character. If an invalid         startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1536         UTF-8 string or offset is passed, an error  (either  PCRE_ERROR_BADUTF8         returned.
1537         or   PCRE_ERROR_BADUTF8_OFFSET)   is   returned,   unless   the  option  
1538         PCRE_NO_UTF8_CHECK is set,  in  which  case  PCRE's  behaviour  is  not         If you already know that your subject is valid, and you  want  to  skip
1539         defined.         these    checks    for   performance   reasons,   you   can   set   the
1540           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1541           do  this  for the second and subsequent calls to pcre_exec() if you are
1542           making repeated calls to find all  the  matches  in  a  single  subject
1543           string.  However,  you  should  be  sure  that the value of startoffset
1544           points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1545           set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1546           value of startoffset that does not point to the start of a UTF-8  char-
1547           acter, is undefined. Your program may crash.
1548    
1549             PCRE_PARTIAL
1550    
1551           This  option  turns  on  the  partial  matching feature. If the subject
1552           string fails to match the pattern, but at some point during the  match-
1553           ing  process  the  end of the subject was reached (that is, the subject
1554           partially matches the pattern and the failure to  match  occurred  only
1555           because  there were not enough subject characters), pcre_exec() returns
1556           PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1557           used,  there  are restrictions on what may appear in the pattern. These
1558           are discussed in the pcrepartial documentation.
1559    
1560       The string to be matched by pcre_exec()
1561    
1562           The subject string is passed to pcre_exec() as a pointer in subject,  a
1563           length  in  length, and a starting byte offset in startoffset. In UTF-8
1564           mode, the byte offset must point to the start  of  a  UTF-8  character.
1565           Unlike  the  pattern string, the subject may contain binary zero bytes.
1566           When the starting offset is zero, the search for a match starts at  the
1567           beginning of the subject, and this is by far the most common case.
1568    
1569         A  non-zero  starting offset is useful when searching for another match         A  non-zero  starting offset is useful when searching for another match
1570         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-
# Line 1111  MATCHING A PATTERN Line 1581  MATCHING A PATTERN
1581         the  remainder  of  the  subject,  namely  "issipi", it does not match,         the  remainder  of  the  subject,  namely  "issipi", it does not match,
1582         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
1583         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
1584         string again, but with startoffset  set  to  4,  it  finds  the  second         string again, but with startoffset set to 4, it finds the second occur-
1585         occurrence  of  "iss"  because  it  is able to look behind the starting         rence  of "iss" because it is able to look behind the starting point to
1586         point to discover that it is preceded by a letter.         discover that it is preceded by a letter.
1587    
1588         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,
1589         one  attempt  to match at the given offset is tried. This can only suc-         one attempt to match at the given offset is made. This can only succeed
1590         ceed if the pattern does not require the match to be at  the  start  of         if the pattern does not require the match to be at  the  start  of  the
1591         the subject.         subject.
1592    
1593       How pcre_exec() returns captured substrings
1594    
1595         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
1596         addition, further substrings from the subject  may  be  picked  out  by         addition, further substrings from the subject  may  be  picked  out  by
# Line 1130  MATCHING A PATTERN Line 1602  MATCHING A PATTERN
1602    
1603         Captured  substrings are returned to the caller via a vector of integer         Captured  substrings are returned to the caller via a vector of integer
1604         offsets whose address is passed in ovector. The number of  elements  in         offsets whose address is passed in ovector. The number of  elements  in
1605         the vector is passed in ovecsize. The first two-thirds of the vector is         the  vector is passed in ovecsize, which must be a non-negative number.
1606         used to pass back captured substrings, each substring using a  pair  of         Note: this argument is NOT the size of ovector in bytes.
1607         integers.  The  remaining  third  of the vector is used as workspace by  
1608         pcre_exec() while matching capturing subpatterns, and is not  available         The first two-thirds of the vector is used to pass back  captured  sub-
1609         for  passing  back  information.  The  length passed in ovecsize should         strings,  each  substring using a pair of integers. The remaining third
1610         always be a multiple of three. If it is not, it is rounded down.         of the vector is used as workspace by pcre_exec() while  matching  cap-
1611           turing  subpatterns, and is not available for passing back information.
1612         When a match has been successful, information about captured substrings         The length passed in ovecsize should always be a multiple of three.  If
1613         is returned in pairs of integers, starting at the beginning of ovector,         it is not, it is rounded down.
1614         and continuing up to two-thirds of its length at the  most.  The  first  
1615           When  a  match  is successful, information about captured substrings is
1616           returned in pairs of integers, starting at the  beginning  of  ovector,
1617           and  continuing  up  to two-thirds of its length at the most. The first
1618         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-
1619         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
1620         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-
1621         tor[1], identify the portion of  the  subject  string  matched  by  the         tor[1],  identify  the  portion  of  the  subject string matched by the
1622         entire  pattern.  The next pair is used for the first capturing subpat-         entire pattern. The next pair is used for the first  capturing  subpat-
1623         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 the number of
1624         pairs  that  have  been set. If there are no capturing subpatterns, the         pairs that have been set. If there are no  capturing  subpatterns,  the
1625         return value from a successful match is 1,  indicating  that  just  the         return  value  from  a  successful match is 1, indicating that just the
1626         first pair of offsets has been set.         first pair of offsets has been set.
1627    
1628         Some  convenience  functions  are  provided for extracting the captured         Some convenience functions are provided  for  extracting  the  captured
1629         substrings as separate strings. These are described  in  the  following         substrings  as  separate  strings. These are described in the following
1630         section.         section.
1631    
1632         It  is  possible  for  an capturing subpattern number n+1 to match some         It is possible for an capturing subpattern number  n+1  to  match  some
1633         part of the subject when subpattern n has not been  used  at  all.  For         part  of  the  subject  when subpattern n has not been used at all. For
1634         example, if the string "abc" is matched against the pattern (a|(z))(bc)         example, if the string "abc" is matched against the pattern (a|(z))(bc)
1635         subpatterns 1 and 3 are matched, but 2 is not. When this happens,  both         subpatterns  1 and 3 are matched, but 2 is not. When this happens, both
1636         offset values corresponding to the unused subpattern are set to -1.         offset values corresponding to the unused subpattern are set to -1.
1637    
1638         If a capturing subpattern is matched repeatedly, it is the last portion         If a capturing subpattern is matched repeatedly, it is the last portion
1639         of the string that it matched that gets returned.         of the string that it matched that is returned.
1640    
1641         If the vector is too small to hold all the captured substrings,  it  is         If  the vector is too small to hold all the captured substring offsets,
1642         used as far as possible (up to two-thirds of its length), and the func-         it is used as far as possible (up to two-thirds of its length), and the
1643         tion returns a value of zero. In particular, if the  substring  offsets         function  returns a value of zero. In particular, if the substring off-
1644         are  not  of interest, pcre_exec() may be called with ovector passed as         sets are not of interest, pcre_exec() may be called with ovector passed
1645         NULL and ovecsize as zero. However, if the pattern contains back refer-         as  NULL  and  ovecsize  as zero. However, if the pattern contains back
1646         ences  and  the  ovector  isn't big enough to remember the related sub-         references and the ovector is not big enough to  remember  the  related
1647         strings, PCRE has to get additional memory  for  use  during  matching.         substrings,  PCRE has to get additional memory for use during matching.
1648         Thus it is usually advisable to supply an ovector.         Thus it is usually advisable to supply an ovector.
1649    
1650         Note  that  pcre_info() can be used to find out how many capturing sub-         Note that pcre_info() can be used to find out how many  capturing  sub-
1651         patterns there are in a compiled pattern. The smallest size for ovector         patterns there are in a compiled pattern. The smallest size for ovector
1652         that  will  allow for n captured substrings, in addition to the offsets         that will allow for n captured substrings, in addition to  the  offsets
1653         of the substring matched by the whole pattern, is (n+1)*3.         of the substring matched by the whole pattern, is (n+1)*3.
1654    
1655         If pcre_exec() fails, it returns a negative number. The  following  are     Return values from pcre_exec()
1656    
1657           If  pcre_exec()  fails, it returns a negative number. The following are
1658         defined in the header file:         defined in the header file:
1659    
1660           PCRE_ERROR_NOMATCH        (-1)           PCRE_ERROR_NOMATCH        (-1)
# Line 1186  MATCHING A PATTERN Line 1663  MATCHING A PATTERN
1663    
1664           PCRE_ERROR_NULL           (-2)           PCRE_ERROR_NULL           (-2)
1665    
1666         Either  code  or  subject  was  passed as NULL, or ovector was NULL and         Either code or subject was passed as NULL,  or  ovector  was  NULL  and
1667         ovecsize was not zero.         ovecsize was not zero.
1668    
1669           PCRE_ERROR_BADOPTION      (-3)           PCRE_ERROR_BADOPTION      (-3)
# Line 1195  MATCHING A PATTERN Line 1672  MATCHING A PATTERN
1672    
1673           PCRE_ERROR_BADMAGIC       (-4)           PCRE_ERROR_BADMAGIC       (-4)
1674    
1675         PCRE stores a 4-byte "magic number" at the start of the compiled  code,         PCRE  stores a 4-byte "magic number" at the start of the compiled code,
1676         to  catch  the case when it is passed a junk pointer. This is the error         to catch the case when it is passed a junk pointer and to detect when a
1677         it gives when the magic number isn't present.         pattern that was compiled in an environment of one endianness is run in
1678           an environment with the other endianness. This is the error  that  PCRE
1679           gives when the magic number is not present.
1680    
1681           PCRE_ERROR_UNKNOWN_NODE   (-5)           PCRE_ERROR_UNKNOWN_NODE   (-5)
1682    
1683         While running the pattern match, an unknown item was encountered in the         While running the pattern match, an unknown item was encountered in the
1684         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
1685         overwriting of the compiled pattern.         overwriting of the compiled pattern.
1686    
1687           PCRE_ERROR_NOMEMORY       (-6)           PCRE_ERROR_NOMEMORY       (-6)
1688    
1689         If a pattern contains back references, but the ovector that  is  passed         If  a  pattern contains back references, but the ovector that is passed
1690         to pcre_exec() is not big enough to remember the referenced substrings,         to pcre_exec() is not big enough to remember the referenced substrings,
1691         PCRE gets a block of memory at the start of matching to  use  for  this         PCRE  gets  a  block of memory at the start of matching to use for this
1692         purpose.  If the call via pcre_malloc() fails, this error is given. The         purpose. If the call via pcre_malloc() fails, this error is given.  The
1693         memory is freed at the end of matching.         memory is automatically freed at the end of matching.
1694    
1695           PCRE_ERROR_NOSUBSTRING    (-7)           PCRE_ERROR_NOSUBSTRING    (-7)
1696    
1697         This error is used by the pcre_copy_substring(),  pcre_get_substring(),         This  error is used by the pcre_copy_substring(), pcre_get_substring(),
1698         and  pcre_get_substring_list()  functions  (see  below).  It  is  never         and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1699         returned by pcre_exec().         returned by pcre_exec().
1700    
1701           PCRE_ERROR_MATCHLIMIT     (-8)           PCRE_ERROR_MATCHLIMIT     (-8)
1702    
1703         The recursion and backtracking limit, as specified by  the  match_limit         The  recursion  and backtracking limit, as specified by the match_limit
1704         field  in  a  pcre_extra  structure (or defaulted) was reached. See the         field in a pcre_extra structure (or defaulted)  was  reached.  See  the
1705         description above.         description above.
1706    
1707           PCRE_ERROR_CALLOUT        (-9)           PCRE_ERROR_CALLOUT        (-9)
1708    
1709         This error is never generated by pcre_exec() itself. It is provided for         This error is never generated by pcre_exec() itself. It is provided for
1710         use  by  callout functions that want to yield a distinctive error code.         use by callout functions that want to yield a distinctive  error  code.
1711         See the pcrecallout documentation for details.         See the pcrecallout documentation for details.
1712    
1713           PCRE_ERROR_BADUTF8        (-10)           PCRE_ERROR_BADUTF8        (-10)
1714    
1715         A string that contains an invalid UTF-8 byte sequence was passed  as  a         A  string  that contains an invalid UTF-8 byte sequence was passed as a
1716         subject.         subject.
1717    
1718           PCRE_ERROR_BADUTF8_OFFSET (-11)           PCRE_ERROR_BADUTF8_OFFSET (-11)
1719    
1720         The UTF-8 byte sequence that was passed as a subject was valid, but the         The UTF-8 byte sequence that was passed as a subject was valid, but the
1721         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-
1722         ter.         ter.
1723    
1724             PCRE_ERROR_PARTIAL        (-12)
1725    
1726           The subject string did not match, but it did match partially.  See  the
1727           pcrepartial documentation for details of partial matching.
1728    
1729             PCRE_ERROR_BADPARTIAL     (-13)
1730    
1731           The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
1732           items that are not supported for partial matching. See the  pcrepartial
1733           documentation for details of partial matching.
1734    
1735             PCRE_ERROR_INTERNAL       (-14)
1736    
1737           An  unexpected  internal error has occurred. This error could be caused
1738           by a bug in PCRE or by overwriting of the compiled pattern.
1739    
1740             PCRE_ERROR_BADCOUNT       (-15)
1741    
1742           This error is given if the value of the ovecsize argument is  negative.
1743    
1744    
1745  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1746    
# Line 1267  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 1766  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1766         not, of course, a C string.         not, of course, a C string.
1767    
1768         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-
1769         tions: subject is the subject string which has just  been  successfully         tions: subject is the subject string that has  just  been  successfully
1770         matched, ovector is a pointer to the vector of integer offsets that was         matched, ovector is a pointer to the vector of integer offsets that was
1771         passed to pcre_exec(), and stringcount is the number of substrings that         passed to pcre_exec(), and stringcount is the number of substrings that
1772         were  captured  by  the match, including the substring that matched the         were  captured  by  the match, including the substring that matched the
1773         entire regular expression. This is the value returned by  pcre_exec  if         entire regular expression. This is the value returned by pcre_exec() if
1774         it  is greater than zero. If pcre_exec() returned zero, indicating that         it  is greater than zero. If pcre_exec() returned zero, indicating that
1775         it ran out of space in ovector, the value passed as stringcount  should         it ran out of space in ovector, the value passed as stringcount  should
1776         be the size of the vector divided by three.         be the number of elements in the vector divided by three.
1777    
1778         The  functions pcre_copy_substring() and pcre_get_substring() extract a         The  functions pcre_copy_substring() and pcre_get_substring() extract a
1779         single substring, whose number is given as  stringnumber.  A  value  of         single substring, whose number is given as  stringnumber.  A  value  of
1780         zero  extracts  the  substring  that  matched the entire pattern, while         zero  extracts  the  substring that matched the entire pattern, whereas
1781         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
1782         string(),  the  string  is  placed  in buffer, whose length is given by         string(),  the  string  is  placed  in buffer, whose length is given by
1783         buffersize, while for pcre_get_substring() a new  block  of  memory  is         buffersize, while for pcre_get_substring() a new  block  of  memory  is
# Line 1297  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 1796  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1796    
1797         The pcre_get_substring_list()  function  extracts  all  available  sub-         The pcre_get_substring_list()  function  extracts  all  available  sub-
1798         strings  and  builds  a list of pointers to them. All this is done in a         strings  and  builds  a list of pointers to them. All this is done in a
1799         single block of memory which is obtained via pcre_malloc.  The  address         single block of memory that is obtained via pcre_malloc. The address of
1800         of 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
1801         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
1802         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
1803    
# Line 1313  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 1812  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1812         string  by inspecting the appropriate offset in ovector, which is nega-         string  by inspecting the appropriate offset in ovector, which is nega-
1813         tive for unset substrings.         tive for unset substrings.
1814    
1815         The    two    convenience    functions    pcre_free_substring()     and         The two convenience functions pcre_free_substring() and  pcre_free_sub-
1816         pcre_free_substring_list() can be used to free the memory returned by a         string_list()  can  be  used  to free the memory returned by a previous
1817         previous call  of  pcre_get_substring()  or  pcre_get_substring_list(),         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
1818         respectively. They do nothing more than call the function pointed to by         tively.  They  do  nothing  more  than  call the function pointed to by
1819         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.
1820         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-
1821         cial  interface  to  another  programming  language  which  cannot  use         cial  interface  to  another  programming  language  which  cannot  use
# Line 1326  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER Line 1825  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1825    
1826  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
1827    
1828           int pcre_get_stringnumber(const pcre *code,
1829                const char *name);
1830    
1831         int pcre_copy_named_substring(const pcre *code,         int pcre_copy_named_substring(const pcre *code,
1832              const char *subject, int *ovector,              const char *subject, int *ovector,
1833              int stringcount, const char *stringname,              int stringcount, const char *stringname,
1834              char *buffer, int buffersize);              char *buffer, int buffersize);
1835    
        int pcre_get_stringnumber(const pcre *code,  
             const char *name);  
   
1836         int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
1837              const char *subject, int *ovector,              const char *subject, int *ovector,
1838              int stringcount, const char *stringname,              int stringcount, const char *stringname,
1839              const char **stringptr);              const char **stringptr);
1840    
1841         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-
1842         ber.  This  can  be  done by calling pcre_get_stringnumber(). The first         ber.  For example, for this pattern
1843         argument is the compiled pattern, and the second is the name. For exam-  
1844         ple, for this pattern           (a+)b(?P<xxx>\d+)...
1845    
1846           ab(?<xxx>\d+)...         the number of the subpattern called "xxx" is 2. You can find the number
1847           from the name by calling pcre_get_stringnumber(). The first argument is
1848         the  number  of the subpattern called "xxx" is 1. Given the number, you         the  compiled  pattern,  and  the  second is the name. The yield of the
1849         can then extract the substring directly, or use one  of  the  functions         function is the subpattern number, or  PCRE_ERROR_NOSUBSTRING  (-7)  if
1850         described  in the previous section. For convenience, there are also two         there is no subpattern of that name.
1851         functions that do the whole job.  
1852           Given the number, you can extract the substring directly, or use one of
1853         Most   of   the   arguments    of    pcre_copy_named_substring()    and         the functions described in the previous section. For convenience, there
1854         pcre_get_named_substring() are the same as those for the functions that         are also two functions that do the whole job.
1855         extract by number, and so are not re-described here. There are just two  
1856         differences.         Most    of    the    arguments   of   pcre_copy_named_substring()   and
1857           pcre_get_named_substring() are the same  as  those  for  the  similarly
1858           named  functions  that extract by number. As these are described in the
1859           previous section, they are not re-described here. There  are  just  two
1860           differences:
1861    
1862         First,  instead  of a substring number, a substring name is given. Sec-         First,  instead  of a substring number, a substring name is given. Sec-
1863         ond, there is an extra argument, given at the start, which is a pointer         ond, there is an extra argument, given at the start, which is a pointer
# Line 1365  EXTRACTING CAPTURED SUBSTRINGS BY NAME Line 1868  EXTRACTING CAPTURED SUBSTRINGS BY NAME
1868         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-         then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
1869         ate.         ate.
1870    
 Last updated: 09 December 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
1871    
1872  PCRE(3)                                                                PCRE(3)  FINDING ALL POSSIBLE MATCHES
1873    
1874           The traditional matching function uses a  similar  algorithm  to  Perl,
1875           which stops when it finds the first match, starting at a given point in
1876           the subject. If you want to find all possible matches, or  the  longest
1877           possible  match,  consider using the alternative matching function (see
1878           below) instead. If you cannot use the alternative function,  but  still
1879           need  to  find all possible matches, you can kludge it up by making use
1880           of the callout facility, which is described in the pcrecallout documen-
1881           tation.
1882    
1883           What you have to do is to insert a callout right at the end of the pat-
1884           tern.  When your callout function is called, extract and save the  cur-
1885           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
1886           backtrack and try other alternatives. Ultimately, when it runs  out  of
1887           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
1888    
1889    
1890    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
1891    
1892           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
1893                const char *subject, int length, int startoffset,
1894                int options, int *ovector, int ovecsize,
1895                int *workspace, int wscount);
1896    
1897           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
1898           against a compiled pattern, using a "DFA" matching algorithm. This  has
1899           different  characteristics to the normal algorithm, and is not compati-
1900           ble with Perl. Some of the features of PCRE patterns are not supported.
1901           Nevertheless, there are times when this kind of matching can be useful.
1902           For a discussion of the two matching algorithms, see  the  pcrematching
1903           documentation.
1904    
1905           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
1906           pcre_exec(), plus two extras. The ovector argument is used in a differ-
1907           ent  way,  and  this is described below. The other common arguments are
1908           used in the same way as for pcre_exec(), so their  description  is  not
1909           repeated here.
1910    
1911           The  two  additional  arguments provide workspace for the function. The
1912           workspace vector should contain at least 20 elements. It  is  used  for
1913           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
1914           workspace will be needed for patterns and subjects where  there  are  a
1915           lot of possible matches.
1916    
1917           Here is an example of a simple call to pcre_exec():
1918    
1919             int rc;
1920             int ovector[10];
1921             int wspace[20];
1922             rc = pcre_exec(
1923               re,             /* result of pcre_compile() */
1924               NULL,           /* we didn't study the pattern */
1925               "some string",  /* the subject string */
1926               11,             /* the length of the subject string */
1927               0,              /* start at offset 0 in the subject */
1928               0,              /* default options */
1929               ovector,        /* vector of integers for substring information */
1930               10,             /* number of elements (NOT size in bytes) */
1931               wspace,         /* working space vector */
1932               20);            /* number of elements (NOT size in bytes) */
1933    
1934       Option bits for pcre_dfa_exec()
1935    
1936           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
1937           zero. The only bits that may be  set  are  PCRE_ANCHORED,  PCRE_NOTBOL,
1938           PCRE_NOTEOL,     PCRE_NOTEMPTY,    PCRE_NO_UTF8_CHECK,    PCRE_PARTIAL,
1939           PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All  but  the  last  three  of
1940           these  are  the  same  as  for pcre_exec(), so their description is not
1941           repeated here.
1942    
1943             PCRE_PARTIAL
1944    
1945           This has the same general effect as it does for  pcre_exec(),  but  the
1946           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
1947           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
1948           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
1949           been no complete matches, but there is still at least one matching pos-
1950           sibility.  The portion of the string that provided the partial match is
1951           set as the first matching string.
1952    
1953             PCRE_DFA_SHORTEST
1954    
1955           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
1956           stop  as  soon  as  it  has found one match. Because of the way the DFA
1957           algorithm works, this is necessarily the shortest possible match at the
1958           first possible matching point in the subject string.
1959    
1960             PCRE_DFA_RESTART
1961    
1962           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
1963           returns a partial match, it is possible to call it  again,  with  addi-
1964           tional  subject  characters,  and have it continue with the same match.
1965           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
1966           workspace  and wscount options must reference the same vector as before
1967           because data about the match so far is left in  them  after  a  partial
1968           match.  There  is  more  discussion of this facility in the pcrepartial
1969           documentation.
1970    
1971       Successful returns from pcre_dfa_exec()
1972    
1973           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
1974           string in the subject. Note, however, that all the matches from one run
1975           of the function start at the same point in  the  subject.  The  shorter
1976           matches  are all initial substrings of the longer matches. For example,
1977           if the pattern
1978    
1979             <.*>
1980    
1981           is matched against the string
1982    
1983             This is <something> <something else> <something further> no more
1984    
1985           the three matched strings are
1986    
1987             <something>
1988             <something> <something else>
1989             <something> <something else> <something further>
1990    
1991           On success, the yield of the function is a number  greater  than  zero,
1992           which  is  the  number of matched substrings. The substrings themselves
1993           are returned in ovector. Each string uses two elements;  the  first  is
1994           the  offset  to the start, and the second is the offset to the end. All
1995           the strings have the same start offset. (Space could have been saved by
1996           giving  this only once, but it was decided to retain some compatibility
1997           with the way pcre_exec() returns data, even though the meaning  of  the
1998           strings is different.)
1999    
2000           The strings are returned in reverse order of length; that is, the long-
2001           est matching string is given first. If there were too many  matches  to
2002           fit  into ovector, the yield of the function is zero, and the vector is
2003           filled with the longest matches.
2004    
2005       Error returns from pcre_dfa_exec()
2006    
2007           The pcre_dfa_exec() function returns a negative number when  it  fails.
2008           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2009           described above.  There are in addition the following errors  that  are
2010           specific to pcre_dfa_exec():
2011    
2012             PCRE_ERROR_DFA_UITEM      (-16)
2013    
2014           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2015           tern that it does not support, for instance, the use of \C  or  a  back
2016           reference.
2017    
2018             PCRE_ERROR_DFA_UCOND      (-17)
2019    
2020           This  return is given if pcre_dfa_exec() encounters a condition item in
2021           a pattern that uses a back reference for the  condition.  This  is  not
2022           supported.
2023    
2024             PCRE_ERROR_DFA_UMLIMIT    (-18)
2025    
2026           This  return  is given if pcre_dfa_exec() is called with an extra block
2027           that contains a setting of the match_limit field. This is not supported
2028           (it is meaningless).
2029    
2030             PCRE_ERROR_DFA_WSSIZE     (-19)
2031    
2032           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2033           workspace vector.
2034    
2035             PCRE_ERROR_DFA_RECURSE    (-20)
2036    
2037           When a recursive subpattern is processed, the matching  function  calls
2038           itself  recursively,  using  private vectors for ovector and workspace.
2039           This error is given if the output vector  is  not  large  enough.  This
2040           should be extremely rare, as a vector of size 1000 is used.
2041    
2042    Last updated: 16 May 2005
2043    Copyright (c) 1997-2005 University of Cambridge.
2044    ------------------------------------------------------------------------------
2045    
2046    
2047    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2048    
2049    
2050  NAME  NAME
2051         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2052    
2053    
2054  PCRE CALLOUTS  PCRE CALLOUTS
2055    
2056         int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
# Line 1392  PCRE CALLOUTS Line 2067  PCRE CALLOUTS
2067         default value is zero.  For  example,  this  pattern  has  two  callout         default value is zero.  For  example,  this  pattern  has  two  callout
2068         points:         points:
2069    
2070           (?C1)abc(?C2)def           (?C1)eabc(?C2)def
2071    
2072         During matching, when PCRE reaches a callout point (and pcre_callout is         If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2073         set), the external function is called. Its only argument is  a  pointer         called, PCRE automatically  inserts  callouts,  all  with  number  255,
2074         to a pcre_callout block. This contains the following variables:         before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2075           used with the pattern
2076    
2077             A(\d{2}|--)
2078    
2079           it is processed as if it were
2080    
2081           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2082    
2083           Notice that there is a callout before and after  each  parenthesis  and
2084           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2085           progress of pattern matching. The pcretest command has an  option  that
2086           sets  automatic callouts; when it is used, the output indicates how the
2087           pattern is matched. This is useful information when you are  trying  to
2088           optimize the performance of a particular pattern.
2089    
2090    
2091    MISSING CALLOUTS
2092    
2093           You  should  be  aware  that,  because of optimizations in the way PCRE
2094           matches patterns, callouts sometimes do not happen. For example, if the
2095           pattern is
2096    
2097             ab(?C4)cd
2098    
2099           PCRE knows that any matching string must contain the letter "d". If the
2100           subject string is "abyz", the lack of "d" means that  matching  doesn't
2101           ever  start,  and  the  callout is never reached. However, with "abyd",
2102           though the result is still no match, the callout is obeyed.
2103    
2104    
2105    THE CALLOUT INTERFACE
2106    
2107           During matching, when PCRE reaches a callout point, the external  func-
2108           tion  defined by pcre_callout is called (if it is set). This applies to
2109           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2110           only  argument  to  the callout function is a pointer to a pcre_callout
2111           block. This structure contains the following fields:
2112    
2113           int          version;           int          version;
2114           int          callout_number;           int          callout_number;
# Line 1408  PCRE CALLOUTS Line 2120  PCRE CALLOUTS
2120           int          capture_top;           int          capture_top;
2121           int          capture_last;           int          capture_last;
2122           void        *callout_data;           void        *callout_data;
2123             int          pattern_position;
2124             int          next_item_length;
2125    
2126         The  version  field  is an integer containing the version number of the         The version field is an integer containing the version  number  of  the
2127         block format. The current version  is  zero.  The  version  number  may         block  format. The initial version was 0; the current version is 1. The
2128         change  in  future if additional fields are added, but the intention is         version number will change again in future  if  additional  fields  are
2129         never to remove any of the existing fields.         added, but the intention is never to remove any of the existing fields.
2130    
2131         The callout_number field contains the number of the  callout,  as  com-         The callout_number field contains the number of the  callout,  as  com-
2132         piled into the pattern (that is, the number after ?C).         piled  into  the pattern (that is, the number after ?C for manual call-
2133           outs, and 255 for automatically generated callouts).
2134    
2135         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
2136         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
2137         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
2138         way as for extracting substrings after a match has completed.         substrings  that  have  been  matched  so  far,  in the same way as for
2139           extracting substrings after a match has completed. For  pcre_dfa_exec()
2140           this field is not useful.
2141    
2142         The subject and subject_length fields contain copies  the  values  that         The subject and subject_length fields contain copies of the values that
2143         were passed to pcre_exec().         were passed to pcre_exec().
2144    
2145         The  start_match  field contains the offset within the subject at which         The start_match field contains the offset within the subject  at  which
2146         the current match attempt started. If the pattern is not anchored,  the         the  current match attempt started. If the pattern is not anchored, the
2147         callout  function  may  be  called several times for different starting         callout function may be called several times from the same point in the
2148         points.         pattern for different starting points in the subject.
2149    
2150         The current_position field contains the offset within  the  subject  of         The  current_position  field  contains the offset within the subject of
2151         the current match pointer.         the current match pointer.
2152    
2153         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
2154         numbered  captured  substring  so  far.  If  no  substrings  have  been         one  more than the number of the highest numbered captured substring so
2155         captured, the value of capture_top is one.         far. If no substrings have been captured, the value of  capture_top  is
2156           one.  This  is always the case when pcre_dfa_exec() is used, because it
2157         The  capture_last  field  contains the number of the most recently cap-         does not support captured substrings.
2158         tured substring.  
2159           The capture_last field contains the number of the  most  recently  cap-
2160           tured  substring. If no substrings have been captured, its value is -1.
2161           This is always the case when pcre_dfa_exec() is used.
2162    
2163         The callout_data field contains a value that is passed  to  pcre_exec()         The callout_data field contains a value that is passed  to  pcre_exec()
2164         by  the  caller specifically so that it can be passed back in callouts.         or  pcre_dfa_exec() specifically so that it can be passed back in call-
2165         It is passed in the pcre_callout field of the  pcre_extra  data  struc-         outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2166         ture.  If  no  such  data  was  passed,  the value of callout_data in a         structure.  If  no such data was passed, the value of callout_data in a
2167         pcre_callout block is NULL. There is a description  of  the  pcre_extra         pcre_callout block is NULL. There is a description  of  the  pcre_extra
2168         structure in the pcreapi documentation.         structure in the pcreapi documentation.
2169    
2170           The  pattern_position field is present from version 1 of the pcre_call-
2171           out structure. It contains the offset to the next item to be matched in
2172           the pattern string.
2173    
2174           The  next_item_length field is present from version 1 of the pcre_call-
2175           out structure. It contains the length of the next item to be matched in
2176           the  pattern  string. When the callout immediately precedes an alterna-
2177           tion bar, a closing parenthesis, or the end of the pattern, the  length
2178           is  zero.  When the callout precedes an opening parenthesis, the length
2179           is that of the entire subpattern.
2180    
2181           The pattern_position and next_item_length fields are intended  to  help
2182           in  distinguishing between different automatic callouts, which all have
2183           the same callout number. However, they are set for all callouts.
2184    
2185    
2186  RETURN VALUES  RETURN VALUES
2187    
2188         The callout function returns an integer. If the value is zero, matching         The external callout function returns an integer to PCRE. If the  value
2189         proceeds as normal. If the value is greater than zero,  matching  fails         is  zero,  matching  proceeds  as  normal. If the value is greater than
2190         at the current point, but backtracking to test other possibilities goes         zero, matching fails at the current point, but  the  testing  of  other
2191         ahead, just as if a lookahead assertion had failed.  If  the  value  is         matching possibilities goes ahead, just as if a lookahead assertion had
2192         less  than  zero,  the  match is abandoned, and pcre_exec() returns the         failed. If the value is less than zero, the  match  is  abandoned,  and
2193         value.         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2194    
2195         Negative  values  should  normally  be   chosen   from   the   set   of         Negative   values   should   normally   be   chosen  from  the  set  of
2196         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2197         dard "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT  is         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2198         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
2199         itself.         itself.
2200    
2201  Last updated: 21 January 2003  Last updated: 28 February 2005
2202  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2005 University of Cambridge.
2203  -----------------------------------------------------------------------------  ------------------------------------------------------------------------------
2204    
 PCRE(3)                                                                PCRE(3)  
2205    
2206    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2207    
2208    
2209  NAME  NAME
2210         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2211    
2212  DIFFERENCES FROM PERL  
2213    DIFFERENCES BETWEEN PCRE AND PERL
2214    
2215         This  document describes the differences in the ways that PCRE and Perl         This  document describes the differences in the ways that PCRE and Perl
2216         handle regular expressions. The differences  described  here  are  with         handle regular expressions. The differences  described  here  are  with
# Line 1498  DIFFERENCES FROM PERL Line 2233  DIFFERENCES FROM PERL
2233    
2234         4. Though binary zero characters are supported in the  subject  string,         4. Though binary zero characters are supported in the  subject  string,
2235         they are not allowed in a pattern string because it is passed as a nor-         they are not allowed in a pattern string because it is passed as a nor-
2236         mal C string, terminated by zero. The escape sequence "\0" can be  used         mal C string, terminated by zero. The escape sequence \0 can be used in
2237         in the pattern to represent a binary zero.         the pattern to represent a binary zero.
2238    
2239         5.  The  following Perl escape sequences are not supported: \l, \u, \L,         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2240         \U, \P, \p, \N, and \X. In fact these are implemented by Perl's general         \U, and \N. In fact these are implemented by Perl's general string-han-
2241         string-handling and are not part of its pattern matching engine. If any         dling  and are not part of its pattern matching engine. If any of these
2242         of these are encountered by PCRE, an error is generated.         are encountered by PCRE, an error is generated.
2243    
2244         6. PCRE does support the \Q...\E escape for quoting substrings. Charac-         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2245         ters  in  between  are  treated as literals. This is slightly different         is  built  with Unicode character property support. The properties that
2246         from Perl in that $ and @ are  also  handled  as  literals  inside  the         can be tested with \p and \P are limited to the general category  prop-
2247         quotes.  In Perl, they cause variable interpolation (but of course PCRE         erties such as Lu and Nd.
2248    
2249           7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2250           ters in between are treated as literals.  This  is  slightly  different
2251           from  Perl  in  that  $  and  @ are also handled as literals inside the
2252           quotes. In Perl, they cause variable interpolation (but of course  PCRE
2253         does not have variables). Note the following examples:         does not have variables). Note the following examples:
2254    
2255             Pattern            PCRE matches      Perl matches             Pattern            PCRE matches      Perl matches
# Line 1519  DIFFERENCES FROM PERL Line 2259  DIFFERENCES FROM PERL
2259             \Qabc\$xyz\E       abc\$xyz          abc\$xyz             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2260             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2261    
2262         The \Q...\E sequence is recognized both inside  and  outside  character         The  \Q...\E  sequence  is recognized both inside and outside character
2263         classes.         classes.
2264    
2265         7. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})         8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})
2266         constructions. However, there is some experimental support  for  recur-         constructions.  However,  there is support for recursive patterns using
2267         sive  patterns  using the non-Perl items (?R), (?number) and (?P>name).         the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE
2268         Also, the PCRE "callout" feature allows  an  external  function  to  be         "callout"  feature allows an external function to be called during pat-
2269         called during pattern matching.         tern matching. See the pcrecallout documentation for details.
2270    
2271         8.  There  are some differences that are concerned with the settings of         9. There are some differences that are concerned with the  settings  of
2272         captured strings when part of  a  pattern  is  repeated.  For  example,         captured  strings  when  part  of  a  pattern is repeated. For example,
2273         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2         matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
2274         unset, but in PCRE it is set to "b".         unset, but in PCRE it is set to "b".
2275    
2276         9. PCRE  provides  some  extensions  to  the  Perl  regular  expression         10. PCRE provides some extensions to the Perl regular expression facil-
2277         facilities:         ities:
2278    
2279         (a)  Although  lookbehind  assertions  must match fixed length strings,         (a) Although lookbehind assertions must  match  fixed  length  strings,
2280         each alternative branch of a lookbehind assertion can match a different         each alternative branch of a lookbehind assertion can match a different
2281         length of string. Perl requires them all to have the same length.         length of string. Perl requires them all to have the same length.
2282    
2283         (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  $
2284         meta-character matches only at the very end of the string.         meta-character matches only at the very end of the string.
2285    
2286         (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-
2287         cial meaning is faulted.         cial meaning is faulted.
2288    
2289         (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2290         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-
2291         lowed by a question mark they are.         lowed by a question mark they are.
2292    
2293         (e)  PCRE_ANCHORED  can  be used to force a pattern to be tried only at         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2294         the first matching position in the subject string.         tried only at the first matching position in the subject string.
2295    
2296         (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-
2297         TURE options for pcre_exec() have no Perl equivalents.         TURE options for pcre_exec() have no Perl equivalents.
2298    
2299         (g)  The (?R), (?number), and (?P>name) constructs allows for recursive         (g) The (?R), (?number), and (?P>name) constructs allows for  recursive
2300         pattern matching (Perl can do  this  using  the  (?p{code})  construct,         pattern  matching  (Perl  can  do  this using the (?p{code}) construct,
2301         which PCRE cannot support.)         which PCRE cannot support.)
2302    
2303         (h)  PCRE supports named capturing substrings, using the Python syntax.         (h) PCRE supports named capturing substrings, using the Python  syntax.
2304    
2305         (i) PCRE supports the possessive quantifier  "++"  syntax,  taken  from         (i)  PCRE  supports  the  possessive quantifier "++" syntax, taken from
2306         Sun's Java package.         Sun's Java package.
2307    
2308         (j) The (R) condition, for testing recursion, is a PCRE extension.         (j) The (R) condition, for testing recursion, is a PCRE extension.
2309    
2310         (k) The callout facility is PCRE-specific.         (k) The callout facility is PCRE-specific.
2311    
2312  Last updated: 09 December 2003         (l) The partial matching facility is PCRE-specific.
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2313    
2314  PCRE(3)                                                                PCRE(3)         (m) Patterns compiled by PCRE can be saved and re-used at a later time,
2315           even on different hosts that have the other endianness.
2316    
2317           (n)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2318           different way and is not Perl-compatible.
2319    
2320    Last updated: 28 February 2005
2321    Copyright (c) 1997-2005 University of Cambridge.
2322    ------------------------------------------------------------------------------
2323    
2324    
2325    PCREPATTERN(3)                                                  PCREPATTERN(3)
2326    
2327    
2328  NAME  NAME
2329         PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2330    
2331    
2332  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2333    
2334         The  syntax  and semantics of the regular expressions supported by PCRE         The  syntax  and semantics of the regular expressions supported by PCRE
2335         are described below. Regular expressions are also described in the Perl         are described below. Regular expressions are also described in the Perl
2336         documentation  and in a number of other books, some of which have copi-         documentation  and  in  a  number  of books, some of which have copious
2337         ous examples. Jeffrey Friedl's "Mastering  Regular  Expressions",  pub-         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
2338         lished  by  O'Reilly, covers them in great detail. The description here         by  O'Reilly, covers regular expressions in great detail. This descrip-
2339         is intended as reference documentation.         tion of PCRE's regular expressions is intended as reference material.
2340    
2341         The basic operation of PCRE is on strings of bytes. However,  there  is         The original operation of PCRE was on strings of  one-byte  characters.
2342         also  support for UTF-8 character strings. To use this support you must         However,  there is now also support for UTF-8 character strings. To use
2343         build PCRE to include UTF-8 support, and then call pcre_compile()  with         this, you must build PCRE to  include  UTF-8  support,  and  then  call
2344         the  PCRE_UTF8  option.  How  this affects the pattern matching is men-         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2345         tioned in several places below. There is also a summary of  UTF-8  fea-         matching is mentioned in several places below. There is also a  summary
2346         tures in the section on UTF-8 support in the main pcre page.         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2347           page.
2348         A  regular  expression  is  a pattern that is matched against a subject  
2349         string from left to right. Most characters stand for  themselves  in  a         The remainder of this document discusses the  patterns  that  are  sup-
2350         pattern,  and  match  the corresponding characters in the subject. As a         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2351           From  release  6.0,   PCRE   offers   a   second   matching   function,
2352           pcre_dfa_exec(),  which matches using a different algorithm that is not
2353           Perl-compatible. The advantages and disadvantages  of  the  alternative
2354           function, and how it differs from the normal function, are discussed in
2355           the pcrematching page.
2356    
2357           A regular expression is a pattern that is  matched  against  a  subject
2358           string  from  left  to right. Most characters stand for themselves in a
2359           pattern, and match the corresponding characters in the  subject.  As  a
2360         trivial example, the pattern         trivial example, the pattern
2361    
2362           The quick brown fox           The quick brown fox
2363    
2364         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
2365         power of regular expressions comes from the ability to include alterna-         caseless matching is specified (the PCRE_CASELESS option), letters  are
2366         tives and repetitions in the pattern. These are encoded in the  pattern         matched  independently  of case. In UTF-8 mode, PCRE always understands
2367         by  the  use  of meta-characters, which do not stand for themselves but         the concept of case for characters whose values are less than  128,  so
2368         instead are interpreted in some special way.         caseless  matching  is always possible. For characters with higher val-
2369           ues, the concept of case is supported if PCRE is compiled with  Unicode
2370           property  support,  but  not  otherwise.   If  you want to use caseless
2371           matching for characters 128 and above, you must  ensure  that  PCRE  is
2372           compiled with Unicode property support as well as with UTF-8 support.
2373    
2374           The  power  of  regular  expressions  comes from the ability to include
2375           alternatives and repetitions in the pattern. These are encoded  in  the
2376           pattern by the use of metacharacters, which do not stand for themselves
2377           but instead are interpreted in some special way.
2378    
2379         There are two different sets of meta-characters: those that are  recog-         There are two different sets of metacharacters: those that  are  recog-
2380         nized  anywhere in the pattern except within square brackets, and those         nized  anywhere in the pattern except within square brackets, and those
2381         that are recognized in square brackets. Outside  square  brackets,  the         that are recognized in square brackets. Outside  square  brackets,  the
2382         meta-characters are as follows:         metacharacters are as follows:
2383    
2384           \      general escape character with several uses           \      general escape character with several uses
2385           ^      assert start of string (or line, in multiline mode)           ^      assert start of string (or line, in multiline mode)
# Line 1631  PCRE REGULAR EXPRESSION DETAILS Line 2398  PCRE REGULAR EXPRESSION DETAILS
2398           {      start min/max quantifier           {      start min/max quantifier
2399    
2400         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
2401         class". In a character class the only meta-characters are:         class". In a character class the only metacharacters are:
2402    
2403           \      general escape character           \      general escape character
2404           ^      negate the class, but only if the first character           ^      negate the class, but only if the first character
# Line 1640  PCRE REGULAR EXPRESSION DETAILS Line 2407  PCRE REGULAR EXPRESSION DETAILS
2407                    syntax)                    syntax)
2408           ]      terminates the character class           ]      terminates the character class
2409    
2410         The following sections describe the use of each of the meta-characters.         The following sections describe the use of each of the  metacharacters.
2411    
2412    
2413  BACKSLASH  BACKSLASH
2414    
2415         The backslash character has several uses. Firstly, if it is followed by         The backslash character has several uses. Firstly, if it is followed by
2416         a non-alphameric character, it takes  away  any  special  meaning  that         a non-alphanumeric character, it takes away any  special  meaning  that
2417         character  may  have.  This  use  of  backslash  as an escape character         character  may  have.  This  use  of  backslash  as an escape character
2418         applies both inside and outside character classes.         applies both inside and outside character classes.
2419    
2420         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
2421         pattern.   This  escaping  action  applies whether or not the following         pattern.   This  escaping  action  applies whether or not the following
2422         character would otherwise be interpreted as a meta-character, so it  is         character would otherwise be interpreted as a metacharacter, so  it  is
2423         always  safe to precede a non-alphameric with backslash to specify that         always  safe  to  precede  a non-alphanumeric with backslash to specify
2424         it stands for itself. In particular, if you want to match a  backslash,         that it stands for itself. In particular, if you want to match a  back-
2425         you write \\.         slash, you write \\.
2426    
2427         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2428         the pattern (other than in a character class) and characters between  a         the pattern (other than in a character class) and characters between  a
# Line 1679  BACKSLASH Line 2446  BACKSLASH
2446         The  \Q...\E  sequence  is recognized both inside and outside character         The  \Q...\E  sequence  is recognized both inside and outside character
2447         classes.         classes.
2448    
2449       Non-printing characters
2450    
2451         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-
2452         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
2453         appearance of non-printing characters, apart from the binary zero  that         appearance of non-printing characters, apart from the binary zero  that
# Line 1708  BACKSLASH Line 2477  BACKSLASH
2477         must  be  less  than  2**31  (that is, the maximum hexadecimal value is         must  be  less  than  2**31  (that is, the maximum hexadecimal value is
2478         7FFFFFFF). If characters other than hexadecimal digits  appear  between         7FFFFFFF). If characters other than hexadecimal digits  appear  between
2479         \x{  and }, or if there is no terminating }, this form of escape is not         \x{  and }, or if there is no terminating }, this form of escape is not
2480         recognized. Instead, the initial \x will be interpreted as a basic hex-         recognized. Instead, the initial \x will  be  interpreted  as  a  basic
2481         adecimal escape, with no following digits, giving a byte whose value is         hexadecimal  escape, with no following digits, giving a character whose
2482         zero.         value is zero.
2483    
2484         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
2485         two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference         two  syntaxes for \x when PCRE is in UTF-8 mode. There is no difference
# Line 1721  BACKSLASH Line 2490  BACKSLASH
2490         there are fewer than two digits, just those that are present are  used.         there are fewer than two digits, just those that are present are  used.
2491         Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL         Thus  the sequence \0\x\07 specifies two binary zeros followed by a BEL
2492         character (code value 7). Make sure you supply  two  digits  after  the         character (code value 7). Make sure you supply  two  digits  after  the
2493         initial zero if the character that follows is itself an octal digit.         initial  zero  if the pattern character that follows is itself an octal
2494           digit.
2495    
2496         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-
2497         cated.  Outside a character class, PCRE reads it and any following dig-         cated.  Outside a character class, PCRE reads it and any following dig-
2498         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
2499         have been at least that many previous capturing left parentheses in the         have been at least that many previous capturing left parentheses in the
2500         expression,  the  entire  sequence  is  taken  as  a  back reference. A         expression, the entire  sequence  is  taken  as  a  back  reference.  A
2501         description of how this works is given later, following the  discussion         description  of how this works is given later, following the discussion
2502         of parenthesized subpatterns.         of parenthesized subpatterns.
2503    
2504         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
2505         and there have not been that many capturing subpatterns, PCRE  re-reads         and  there have not been that many capturing subpatterns, PCRE re-reads
2506         up  to three octal digits following the backslash, and generates a sin-         up to three octal digits following the backslash, and generates a  sin-
2507         gle byte from the least significant 8 bits of the value. Any subsequent         gle byte from the least significant 8 bits of the value. Any subsequent
2508         digits stand for themselves.  For example:         digits stand for themselves.  For example:
2509    
# Line 1752  BACKSLASH Line 2522  BACKSLASH
2522           \81    is either a back reference, or a binary zero           \81    is either a back reference, or a binary zero
2523                     followed by the two characters "8" and "1"                     followed by the two characters "8" and "1"
2524    
2525         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
2526         leading zero, because no more than three octal digits are ever read.         leading zero, because no more than three octal digits are ever read.
2527    
2528         All the sequences that define a single byte value  or  a  single  UTF-8         All  the  sequences  that  define a single byte value or a single UTF-8
2529         character (in UTF-8 mode) can be used both inside and outside character         character (in UTF-8 mode) can be used both inside and outside character
2530         classes. In addition, inside a character  class,  the  sequence  \b  is         classes.  In  addition,  inside  a  character class, the sequence \b is
2531         interpreted  as  the  backspace character (hex 08). Outside a character         interpreted as the backspace character (hex 08), and the sequence \X is
2532         class it has a different meaning (see below).         interpreted  as  the  character  "X".  Outside a character class, these
2533           sequences have different meanings (see below).
2534    
2535       Generic character types
2536    
2537         The third use of backslash is for specifying generic character types:         The third use of backslash is for specifying generic  character  types.
2538           The following are always recognized:
2539    
2540           \d     any decimal digit           \d     any decimal digit
2541           \D     any character that is not a decimal digit           \D     any character that is not a decimal digit
# Line 1771  BACKSLASH Line 2545  BACKSLASH
2545           \W     any "non-word" character           \W     any "non-word" character
2546    
2547         Each pair of escape sequences partitions the complete set of characters         Each pair of escape sequences partitions the complete set of characters
2548         into  two disjoint sets. Any given character matches one, and only one,         into two disjoint sets. Any given character matches one, and only  one,
2549         of each pair.         of each pair.
2550    
        In UTF-8 mode, characters with values greater than 255 never match  \d,  
        \s, or \w, and always match \D, \S, and \W.  
   
        For  compatibility  with Perl, \s does not match the VT character (code  
        11).  This makes it different from the the POSIX "space" class. The  \s  
        characters are HT (9), LF (10), FF (12), CR (13), and space (32).  
   
        A  "word" character is any letter or digit or the underscore character,  
        that is, any character which can be part of a Perl "word". The  defini-  
        tion  of  letters  and digits is controlled by PCRE's character tables,  
        and may vary if locale- specific matching is taking place (see  "Locale  
        support"  in  the  pcreapi  page).  For  example,  in the "fr" (French)  
        locale, some character codes greater than 128  are  used  for  accented  
        letters, and these are matched by \w.  
   
2551         These character type sequences can appear both inside and outside char-         These character type sequences can appear both inside and outside char-
2552         acter classes. They each match one character of the  appropriate  type.         acter classes. They each match one character of the  appropriate  type.
2553         If  the current matching point is at the end of the subject string, all         If  the current matching point is at the end of the subject string, all
2554         of them fail, since there is no character to match.         of them fail, since there is no character to match.
2555    
2556           For compatibility with Perl, \s does not match the VT  character  (code
2557           11).   This makes it different from the the POSIX "space" class. The \s
2558           characters are HT (9), LF (10), FF (12), CR (13), and space (32).
2559    
2560           A "word" character is an underscore or any character less than 256 that
2561           is  a  letter  or  digit.  The definition of letters and digits is con-
2562           trolled by PCRE's low-valued character tables, and may vary if  locale-
2563           specific  matching is taking place (see "Locale support" in the pcreapi
2564           page). For example, in the  "fr_FR"  (French)  locale,  some  character
2565           codes  greater  than  128  are used for accented letters, and these are
2566           matched by \w.
2567    
2568           In UTF-8 mode, characters with values greater than 128 never match  \d,
2569           \s, or \w, and always match \D, \S, and \W. This is true even when Uni-
2570           code character property support is available.
2571    
2572       Unicode character properties
2573    
2574           When PCRE is built with Unicode character property support, three addi-
2575           tional  escape sequences to match generic character types are available
2576           when UTF-8 mode is selected. They are:
2577    
2578            \p{xx}   a character with the xx property
2579            \P{xx}   a character without the xx property
2580            \X       an extended Unicode sequence
2581    
2582           The property names represented by xx above are limited to  the  Unicode
2583           general  category properties. Each character has exactly one such prop-
2584           erty, specified by a two-letter abbreviation.  For  compatibility  with
2585           Perl,  negation  can be specified by including a circumflex between the
2586           opening brace and the property name. For example, \p{^Lu} is  the  same
2587           as \P{Lu}.
2588    
2589           If  only  one  letter  is  specified with \p or \P, it includes all the
2590           properties that start with that letter. In this case, in the absence of
2591           negation, the curly brackets in the escape sequence are optional; these
2592           two examples have the same effect:
2593    
2594             \p{L}
2595             \pL
2596    
2597           The following property codes are supported:
2598    
2599             C     Other
2600             Cc    Control
2601             Cf    Format
2602             Cn    Unassigned
2603             Co    Private use
2604             Cs    Surrogate
2605    
2606             L     Letter
2607             Ll    Lower case letter
2608             Lm    Modifier letter
2609             Lo    Other letter
2610             Lt    Title case letter
2611             Lu    Upper case letter
2612    
2613             M     Mark
2614             Mc    Spacing mark
2615             Me    Enclosing mark
2616             Mn    Non-spacing mark
2617    
2618             N     Number
2619             Nd    Decimal number
2620             Nl    Letter number
2621             No    Other number
2622    
2623             P     Punctuation
2624             Pc    Connector punctuation
2625             Pd    Dash punctuation
2626             Pe    Close punctuation
2627             Pf    Final punctuation
2628             Pi    Initial punctuation
2629             Po    Other punctuation
2630             Ps    Open punctuation
2631    
2632             S     Symbol
2633             Sc    Currency symbol
2634             Sk    Modifier symbol
2635             Sm    Mathematical symbol
2636             So    Other symbol
2637    
2638             Z     Separator
2639             Zl    Line separator
2640             Zp    Paragraph separator
2641             Zs    Space separator
2642    
2643           Extended properties such as "Greek" or "InMusicalSymbols" are not  sup-
2644           ported by PCRE.
2645    
2646           Specifying  caseless  matching  does not affect these escape sequences.
2647           For example, \p{Lu} always matches only upper case letters.
2648    
2649           The \X escape matches any number of Unicode  characters  that  form  an
2650           extended Unicode sequence. \X is equivalent to
2651    
2652             (?>\PM\pM*)
2653    
2654           That  is,  it matches a character without the "mark" property, followed
2655           by zero or more characters with the "mark"  property,  and  treats  the
2656           sequence  as  an  atomic group (see below).  Characters with the "mark"
2657           property are typically accents that affect the preceding character.
2658    
2659           Matching characters by Unicode property is not fast, because  PCRE  has
2660           to  search  a  structure  that  contains data for over fifteen thousand
2661           characters. That is why the traditional escape sequences such as \d and
2662           \w do not use Unicode properties in PCRE.
2663    
2664       Simple assertions
2665    
2666         The fourth use of backslash is for certain simple assertions. An asser-         The fourth use of backslash is for certain simple assertions. An asser-
2667         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
2668         a match, without consuming any characters from the subject string.  The         a  match, without consuming any characters from the subject string. The
2669         use  of subpatterns for more complicated assertions is described below.         use of subpatterns for more complicated assertions is described  below.
2670         The backslashed assertions are         The backslashed assertions are:
2671    
2672           \b     matches at a word boundary           \b     matches at a word boundary
2673           \B     matches when not at a word boundary           \B     matches when not at a word boundary
# Line 1807  BACKSLASH Line 2676  BACKSLASH
2676           \z     matches at end of subject           \z     matches at end of subject
2677           \G     matches at first matching position in subject           \G     matches at first matching position in subject
2678    
2679         These assertions may not appear in character classes (but note that  \b         These  assertions may not appear in character classes (but note that \b
2680         has a different meaning, namely the backspace character, inside a char-         has a different meaning, namely the backspace character, inside a char-
2681         acter class).         acter class).
2682    
2683         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
2684         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.
2685         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
2686         string if the first or last character matches \w, respectively.         string if the first or last character matches \w, respectively.
2687    
2688         The  \A,  \Z,  and \z assertions differ from the traditional circumflex         The \A, \Z, and \z assertions differ from  the  traditional  circumflex
2689         and dollar (described below) in that they only ever match at  the  very         and dollar (described in the next section) in that they only ever match
2690         start  and  end  of the subject string, whatever options are set. Thus,         at the very start and end of the subject string, whatever  options  are
2691         they are independent of multiline mode.         set.  Thus,  they are independent of multiline mode. These three asser-
2692           tions are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options, which
2693         They are not affected by the PCRE_NOTBOL or PCRE_NOTEOL options. If the         affect  only the behaviour of the circumflex and dollar metacharacters.
2694         startoffset argument of pcre_exec() is non-zero, indicating that match-         However, if the startoffset argument of pcre_exec() is non-zero,  indi-
2695         ing is to start at a point other than the beginning of the subject,  \A         cating that matching is to start at a point other than the beginning of
2696         can  never  match.  The difference between \Z and \z is that \Z matches         the subject, \A can never match. The difference between \Z  and  \z  is
2697         before a newline that is the last character of the string as well as at         that  \Z  matches  before  a  newline that is the last character of the
2698         the end of the string, whereas \z matches only at the end.         string as well as at the end of the string, whereas \z matches only  at
2699           the end.
2700    
2701         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
2702         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 1849  BACKSLASH Line 2719  BACKSLASH
2719  CIRCUMFLEX AND DOLLAR  CIRCUMFLEX AND DOLLAR
2720    
2721         Outside a character class, in the default matching mode, the circumflex         Outside a character class, in the default matching mode, the circumflex
2722         character  is  an  assertion which is true only if the current matching         character  is  an  assertion  that is true only if the current matching
2723         point is at the start of the subject string. If the  startoffset  argu-         point is at the start of the subject string. If the  startoffset  argu-
2724         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the         ment  of  pcre_exec()  is  non-zero,  circumflex can never match if the
2725         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex         PCRE_MULTILINE option is unset. Inside a  character  class,  circumflex
# Line 1863  CIRCUMFLEX AND DOLLAR Line 2733  CIRCUMFLEX AND DOLLAR
2733         ject, it is said to be an "anchored" pattern.  (There  are  also  other         ject, it is said to be an "anchored" pattern.  (There  are  also  other
2734         constructs that can cause a pattern to be anchored.)         constructs that can cause a pattern to be anchored.)
2735    
2736         A  dollar  character  is an assertion which is true only if the current         A  dollar  character  is  an assertion that is true only if the current
2737         matching point is at the end of  the  subject  string,  or  immediately         matching point is at the end of  the  subject  string,  or  immediately
2738         before a newline character that is the last character in the string (by         before a newline character that is the last character in the string (by
2739         default). Dollar need not be the last character of  the  pattern  if  a         default). Dollar need not be the last character of  the  pattern  if  a
# Line 1880  CIRCUMFLEX AND DOLLAR Line 2750  CIRCUMFLEX AND DOLLAR
2750         ately  after  and  immediately  before  an  internal newline character,         ately  after  and  immediately  before  an  internal newline character,
2751         respectively, in addition to matching at the start and end of the  sub-         respectively, in addition to matching at the start and end of the  sub-
2752         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject         ject  string.  For  example,  the  pattern  /^abc$/ matches the subject
2753         string "def\nabc" in multiline mode, but not  otherwise.  Consequently,         string "def\nabc" (where \n represents a newline character)  in  multi-
2754         patterns  that  are  anchored  in single line mode because all branches         line mode, but not otherwise.  Consequently, patterns that are anchored
2755         start with ^ are not anchored in multiline mode, and a match  for  cir-         in single line mode because all branches start with ^ are not  anchored
2756         cumflex  is  possible  when  the startoffset argument of pcre_exec() is         in  multiline  mode,  and  a  match for circumflex is possible when the
2757         non-zero. The PCRE_DOLLAR_ENDONLY option is ignored  if  PCRE_MULTILINE         startoffset  argument  of  pcre_exec()  is  non-zero.   The   PCRE_DOL-
2758         is set.         LAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
2759    
2760         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
2761         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
# Line 1898  FULL STOP (PERIOD, DOT) Line 2768  FULL STOP (PERIOD, DOT)
2768         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-
2769         ter  in  the  subject,  including a non-printing character, but not (by         ter  in  the  subject,  including a non-printing character, but not (by
2770         default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,         default) newline.  In UTF-8 mode, a dot matches  any  UTF-8  character,
2771         which  might  be  more than one byte long, except (by default) for new-         which might be more than one byte long, except (by default) newline. If
2772         line. If the PCRE_DOTALL option is set, dots match  newlines  as  well.         the PCRE_DOTALL option is set, dots match newlines as  well.  The  han-
2773         The  handling of dot is entirely independent of the handling of circum-         dling  of dot is entirely independent of the handling of circumflex and
2774         flex and dollar, the only relationship being  that  they  both  involve         dollar, the only relationship being  that  they  both  involve  newline
2775         newline characters. Dot has no special meaning in a character class.         characters. Dot has no special meaning in a character class.
2776    
2777    
2778  MATCHING A SINGLE BYTE  MATCHING A SINGLE BYTE
2779    
2780         Outside a character class, the escape sequence \C matches any one byte,         Outside a character class, the escape sequence \C matches any one byte,
2781         both in and out of UTF-8 mode. Unlike a dot, it always matches  a  new-         both in and out of UTF-8 mode. Unlike a dot, it can  match  a  newline.
2782         line.  The  feature  is  provided  in Perl in order to match individual         The  feature  is provided in Perl in order to match individual bytes in
2783         bytes in UTF-8 mode.  Because it breaks up UTF-8 characters into  indi-         UTF-8 mode. Because it  breaks  up  UTF-8  characters  into  individual
2784         vidual  bytes,  what  remains  in  the  string may be a malformed UTF-8         bytes,  what remains in the string may be a malformed UTF-8 string. For
2785         string. For this reason it is best avoided.         this reason, the \C escape sequence is best avoided.
2786    
2787         PCRE does not allow \C to appear in lookbehind assertions (see  below),         PCRE does not allow \C to appear in  lookbehind  assertions  (described
2788         because in UTF-8 mode it makes it impossible to calculate the length of         below),  because  in UTF-8 mode this would make it impossible to calcu-
2789         the lookbehind.         late the length of the lookbehind.
2790    
2791    
2792  SQUARE BRACKETS  SQUARE BRACKETS AND CHARACTER CLASSES
2793    
2794         An opening square bracket introduces a character class, terminated by a         An opening square bracket introduces a character class, terminated by a
2795         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-
# Line 1938  SQUARE BRACKETS Line 2808  SQUARE BRACKETS
2808         For example, the character class [aeiou] matches any lower case  vowel,         For example, the character class [aeiou] matches any lower case  vowel,
2809         while  [^aeiou]  matches  any character that is not a lower case vowel.         while  [^aeiou]  matches  any character that is not a lower case vowel.
2810         Note that a circumflex is just a convenient notation for specifying the         Note that a circumflex is just a convenient notation for specifying the
2811         characters which are in the class by enumerating those that are not. It         characters  that  are in the class by enumerating those that are not. A
2812         is not an assertion: it still consumes a  character  from  the  subject         class that starts with a circumflex is not an assertion: it still  con-
2813         string, and fails if the current pointer is at the end of the string.         sumes  a  character  from the subject string, and therefore it fails if
2814           the current pointer is at the end of the string.
2815    
2816         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
2817         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
2818         mechanism.         mechanism.
2819    
2820         When  caseless  matching  is set, any letters in a class represent both         When caseless matching is set, any letters in a  class  represent  both
2821         their upper case and lower case versions, so for  example,  a  caseless         their  upper  case  and lower case versions, so for example, a caseless
2822         [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
2823         match "A", whereas a caseful version would. PCRE does not  support  the         match  "A", whereas a caseful version would. In UTF-8 mode, PCRE always
2824         concept of case for characters with values greater than 255.         understands the concept of case for characters whose  values  are  less
2825           than  128, so caseless matching is always possible. For characters with
2826           higher values, the concept of case is supported  if  PCRE  is  compiled
2827           with  Unicode  property support, but not otherwise.  If you want to use
2828           caseless matching for characters 128 and above, you  must  ensure  that
2829           PCRE  is  compiled  with Unicode property support as well as with UTF-8
2830           support.
2831    
2832         The  newline character is never treated in any special way in character         The newline character is never treated in any special way in  character
2833         classes, whatever the setting  of  the  PCRE_DOTALL  or  PCRE_MULTILINE         classes,  whatever  the  setting  of  the PCRE_DOTALL or PCRE_MULTILINE
2834         options is. A class such as [^a] will always match a newline.         options is. A class such as [^a] will always match a newline.
2835    
2836         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-
2837         ters in a character  class.  For  example,  [d-m]  matches  any  letter         ters  in  a  character  class.  For  example,  [d-m] matches any letter
2838         between  d  and  m,  inclusive.  If  a minus character is required in a         between d and m, inclusive. If a  minus  character  is  required  in  a
2839         class, it must be escaped with a backslash  or  appear  in  a  position         class,  it  must  be  escaped  with a backslash or appear in a position
2840         where  it cannot be interpreted as indicating a range, typically as the         where it cannot be interpreted as indicating a range, typically as  the
2841         first or last character in the class.         first or last character in the class.
2842    
2843         It is not possible to have the literal character "]" as the end charac-         It is not possible to have the literal character "]" as the end charac-
2844         ter  of a range. A pattern such as [W-]46] is interpreted as a class of         ter of a range. A pattern such as [W-]46] is interpreted as a class  of
2845         two characters ("W" and "-") followed by a literal string "46]", so  it         two  characters ("W" and "-") followed by a literal string "46]", so it
2846         would  match  "W46]"  or  "-46]". However, if the "]" is escaped with a         would match "W46]" or "-46]". However, if the "]"  is  escaped  with  a
2847         backslash it is interpreted as the end of range, so [W-\]46] is  inter-         backslash  it is interpreted as the end of range, so [W-\]46] is inter-
2848         preted  as  a  single class containing a range followed by two separate         preted as a class containing a range followed by two other  characters.
2849         characters. The octal or hexadecimal representation of "]" can also  be         The  octal or hexadecimal representation of "]" can also be used to end
2850         used to end a range.         a range.
2851    
2852         Ranges  operate in the collating sequence of character values. They can         Ranges operate in the collating sequence of character values. They  can
2853         also  be  used  for  characters  specified  numerically,  for   example         also   be  used  for  characters  specified  numerically,  for  example
2854         [\000-\037].  In UTF-8 mode, ranges can include characters whose values         [\000-\037]. In UTF-8 mode, ranges can include characters whose  values
2855         are greater than 255, for example [\x{100}-\x{2ff}].         are greater than 255, for example [\x{100}-\x{2ff}].
2856    
2857         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,
2858         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
2859         to [][\^_`wxyzabc], matched caselessly, and if character tables for the         to  [][\\^_`wxyzabc],  matched  caselessly,  and  in non-UTF-8 mode, if
2860         "fr"  locale  are  in use, [\xc8-\xcb] matches accented E characters in         character tables for the "fr_FR" locale are in use, [\xc8-\xcb] matches
2861         both cases.         accented  E  characters in both cases. In UTF-8 mode, PCRE supports the
2862           concept of case for characters with values greater than 128  only  when
2863         The character types \d, \D, \s, \S, \w, and \W may  also  appear  in  a         it is compiled with Unicode property support.
2864         character  class,  and add the characters that they match to the class.  
2865         For example, [\dABCDEF] matches any hexadecimal digit. A circumflex can         The  character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
2866         conveniently  be  used with the upper case character types to specify a         in a character class, and add the characters that  they  match  to  the
2867         more restricted set of characters than the matching  lower  case  type.         class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
2868         For  example,  the  class  [^\W_]  matches any letter or digit, but not         flex can conveniently be used with the upper case  character  types  to
2869         underscore.         specify  a  more  restricted  set of characters than the matching lower
2870           case type. For example, the class [^\W_] matches any letter  or  digit,
2871         All non-alphameric characters other than \, -, ^ (at the start) and the         but not underscore.
2872         terminating ] are non-special in character classes, but it does no harm  
2873         if they are escaped.         The  only  metacharacters  that are recognized in character classes are
2874           backslash, hyphen (only where it can be  interpreted  as  specifying  a
2875           range),  circumflex  (only  at the start), opening square bracket (only
2876           when it can be interpreted as introducing a POSIX class name - see  the
2877           next  section),  and  the  terminating closing square bracket. However,
2878           escaping other non-alphanumeric characters does no harm.
2879    
2880    
2881  POSIX CHARACTER CLASSES  POSIX CHARACTER CLASSES
2882    
2883         Perl supports the POSIX notation  for  character  classes,  which  uses         Perl supports the POSIX notation for character classes. This uses names
2884         names  enclosed by [: and :] within the enclosing square brackets. PCRE         enclosed  by  [: and :] within the enclosing square brackets. PCRE also
2885         also supports this notation. For example,         supports this notation. For example,
2886    
2887           [01[:alpha:]%]           [01[:alpha:]%]
2888    
# Line 2037  POSIX CHARACTER CLASSES Line 2919  POSIX CHARACTER CLASSES
2919         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but         POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
2920         these are not supported, and an error is given if they are encountered.         these are not supported, and an error is given if they are encountered.
2921    
2922         In UTF-8 mode, characters with values greater than 255 do not match any         In UTF-8 mode, characters with values greater than 128 do not match any
2923         of the POSIX character classes.         of the POSIX character classes.
2924    
2925    
# Line 2104  INTERNAL OPTION SETTING Line 2986  INTERNAL OPTION SETTING
2986         in the same way as the Perl-compatible options by using the  characters         in the same way as the Perl-compatible options by using the  characters
2987         U  and X respectively. The (?X) flag setting is special in that it must         U  and X respectively. The (?X) flag setting is special in that it must
2988         always occur earlier in the pattern than any of the additional features         always occur earlier in the pattern than any of the additional features
2989         it turns on, even when it is at top level. It is best put at the start.         it  turns on, even when it is at top level. It is best to put it at the
2990           start.
2991    
2992    
2993  SUBPATTERNS  SUBPATTERNS
2994    
2995         Subpatterns are delimited by parentheses (round brackets), which can be         Subpatterns are delimited by parentheses (round brackets), which can be
2996         nested.  Marking part of a pattern as a subpattern does two things:         nested.  Turning part of a pattern into a subpattern does two things:
2997    
2998         1. It localizes a set of alternatives. For example, the pattern         1. It localizes a set of alternatives. For example, the pattern
2999    
# Line 2120  SUBPATTERNS Line 3003  SUBPATTERNS
3003         the parentheses, it would match "cataract",  "erpillar"  or  the  empty         the parentheses, it would match "cataract",  "erpillar"  or  the  empty
3004         string.         string.
3005    
3006         2.  It  sets  up  the  subpattern as a capturing subpattern (as defined         2.  It  sets  up  the  subpattern as a capturing subpattern. This means
3007         above).  When the whole pattern matches, that portion  of  the  subject         that, when the whole pattern  matches,  that  portion  of  the  subject
3008         string that matched the subpattern is passed back to the caller via the         string that matched the subpattern is passed back to the caller via the
3009         ovector argument of pcre_exec(). Opening parentheses are  counted  from         ovector argument of pcre_exec(). Opening parentheses are  counted  from
3010         left  to right (starting from 1) to obtain the numbers of the capturing         left  to  right  (starting  from 1) to obtain numbers for the capturing
3011         subpatterns.         subpatterns.
3012    
3013         For example, if the string "the red king" is matched against  the  pat-         For example, if the string "the red king" is matched against  the  pat-
# Line 2169  NAMED SUBPATTERNS Line 3052  NAMED SUBPATTERNS
3052         Identifying  capturing  parentheses  by number is simple, but it can be         Identifying  capturing  parentheses  by number is simple, but it can be
3053         very hard to keep track of the numbers in complicated  regular  expres-         very hard to keep track of the numbers in complicated  regular  expres-
3054         sions.  Furthermore,  if  an  expression  is  modified, the numbers may         sions.  Furthermore,  if  an  expression  is  modified, the numbers may
3055         change. To help with the difficulty, PCRE supports the naming  of  sub-         change. To help with this difficulty, PCRE supports the naming of  sub-
3056         patterns,  something  that  Perl  does  not  provide. The Python syntax         patterns,  something  that  Perl  does  not  provide. The Python syntax
3057         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and         (?P<name>...) is used. Names consist  of  alphanumeric  characters  and
3058         underscores, and must be unique within a pattern.         underscores, and must be unique within a pattern.
3059    
3060         Named  capturing  parentheses  are  still  allocated numbers as well as         Named  capturing  parentheses  are  still  allocated numbers as well as
3061         names. The PCRE API provides function calls for extracting the name-to-         names. The PCRE API provides function calls for extracting the name-to-
3062         number  translation  table from a compiled pattern. For further details         number  translation table from a compiled pattern. There is also a con-
3063         see the pcreapi documentation.         venience function for extracting a captured substring by name. For fur-
3064           ther details see the pcreapi documentation.
3065    
3066    
3067  REPETITION  REPETITION
3068    
3069         Repetition is specified by quantifiers, which can  follow  any  of  the         Repetition  is  specified  by  quantifiers, which can follow any of the
3070         following items:         following items:
3071    
3072           a literal data character           a literal data character
3073           the . metacharacter           the . metacharacter
3074           the \C escape sequence           the \C escape sequence
3075           escapes such as \d that match single characters           the \X escape sequence (in UTF-8 mode with Unicode properties)
3076             an escape such as \d that matches a single character
3077           a character class           a character class
3078           a back reference (see next section)           a back reference (see next section)
3079           a parenthesized subpattern (unless it is an assertion)           a parenthesized subpattern (unless it is an assertion)
3080    
3081         The  general repetition quantifier specifies a minimum and maximum num-         The general repetition quantifier specifies a minimum and maximum  num-
3082         ber of permitted matches, by giving the two numbers in  curly  brackets         ber  of  permitted matches, by giving the two numbers in curly brackets
3083         (braces),  separated  by  a comma. The numbers must be less than 65536,         (braces), separated by a comma. The numbers must be  less  than  65536,
3084         and the first must be less than or equal to the second. For example:         and the first must be less than or equal to the second. For example:
3085    
3086           z{2,4}           z{2,4}
3087    
3088         matches "zz", "zzz", or "zzzz". A closing brace on its  own  is  not  a         matches  "zz",  "zzz",  or  "zzzz". A closing brace on its own is not a
3089         special  character.  If  the second number is omitted, but the comma is         special character. If the second number is omitted, but  the  comma  is
3090         present, there is no upper limit; if the second number  and  the  comma         present,  there  is  no upper limit; if the second number and the comma
3091         are  both omitted, the quantifier specifies an exact number of required         are both omitted, the quantifier specifies an exact number of  required
3092         matches. Thus         matches. Thus
3093    
3094           [aeiou]{3,}           [aeiou]{3,}
# Line 2212  REPETITION Line 3097  REPETITION
3097    
3098           \d{8}           \d{8}
3099    
3100         matches exactly 8 digits. An opening curly bracket that  appears  in  a         matches  exactly  8  digits. An opening curly bracket that appears in a
3101         position  where a quantifier is not allowed, or one that does not match         position where a quantifier is not allowed, or one that does not  match
3102         the syntax of a quantifier, is taken as a literal character. For  exam-         the  syntax of a quantifier, is taken as a literal character. For exam-
3103         ple, {,6} is not a quantifier, but a literal string of four characters.         ple, {,6} is not a quantifier, but a literal string of four characters.
3104    
3105         In UTF-8 mode, quantifiers apply to UTF-8  characters  rather  than  to         In  UTF-8  mode,  quantifiers  apply to UTF-8 characters rather than to
3106         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-         individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
3107         acters, each of which is represented by a two-byte sequence.         acters, each of which is represented by a two-byte sequence. Similarly,
3108           when Unicode property support is available, \X{3} matches three Unicode
3109           extended  sequences,  each of which may be several bytes long (and they
3110           may be of different lengths).
3111    
3112         The quantifier {0} is permitted, causing the expression to behave as if         The quantifier {0} is permitted, causing the expression to behave as if
3113         the previous item and the quantifier were not present.         the previous item and the quantifier were not present.
# Line 2247  REPETITION Line 3135  REPETITION
3135         as  possible  (up  to  the  maximum number of permitted times), without         as  possible  (up  to  the  maximum number of permitted times), without
3136         causing the rest of the pattern to fail. The classic example  of  where         causing the rest of the pattern to fail. The classic example  of  where
3137         this gives problems is in trying to match comments in C programs. These         this gives problems is in trying to match comments in C programs. These
3138         appear between the sequences /* and */ and within the  sequence,  indi-         appear between /* and */ and within the comment,  individual  *  and  /
3139         vidual * and / characters may appear. An attempt to match C comments by         characters  may  appear. An attempt to match C comments by applying the
3140         applying the pattern         pattern
3141    
3142           /\*.*\*/           /\*.*\*/
3143    
3144         to the string         to the string
3145    
3146           /* first command */  not comment  /* second comment */           /* first comment */  not comment  /* second comment */
3147    
3148         fails, because it matches the entire string owing to the greediness  of         fails, because it matches the entire string owing to the greediness  of
3149         the .*  item.         the .*  item.
# Line 2283  REPETITION Line 3171  REPETITION
3171         words, it inverts the default behaviour.         words, it inverts the default behaviour.
3172    
3173         When  a  parenthesized  subpattern  is quantified with a minimum repeat         When  a  parenthesized  subpattern  is quantified with a minimum repeat
3174         count that is greater than 1 or with a limited maximum, more  store  is         count that is greater than 1 or with a limited maximum, more memory  is
3175         required  for  the  compiled  pattern, in proportion to the size of the         required  for  the  compiled  pattern, in proportion to the size of the
3176         minimum or maximum.         minimum or maximum.
3177    
# Line 2374  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3262  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3262         consists  of  an  additional  + character following a quantifier. Using         consists  of  an  additional  + character following a quantifier. Using
3263         this notation, the previous example can be rewritten as         this notation, the previous example can be rewritten as
3264    
3265           \d++bar           \d++foo
3266    
3267         Possessive  quantifiers  are  always  greedy;  the   setting   of   the         Possessive  quantifiers  are  always  greedy;  the   setting   of   the
3268         PCRE_UNGREEDY option is ignored. They are a convenient notation for the         PCRE_UNGREEDY option is ignored. They are a convenient notation for the
# Line 2399  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE Line 3287  ATOMIC GROUPING AND POSSESSIVE QUANTIFIE
3287           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa           aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
3288    
3289         it takes a long time before reporting  failure.  This  is  because  the         it takes a long time before reporting  failure.  This  is  because  the
3290         string  can  be  divided  between  the two repeats in a large number of         string  can be divided between the internal \D+ repeat and the external
3291         ways, and all have to be tried. (The example used [!?]  rather  than  a         * repeat in a large number of ways, and all  have  to  be  tried.  (The
3292         single  character  at the end, because both PCRE and Perl have an opti-         example  uses  [!?]  rather than a single character at the end, because
3293         mization that allows for fast failure when a single character is  used.         both PCRE and Perl have an optimization that allows  for  fast  failure
3294         They  remember  the last single character that is required for a match,         when  a single character is used. They remember the last single charac-
3295         and fail early if it is not present in the string.)  If the pattern  is         ter that is required for a match, and fail early if it is  not  present
3296         changed to         in  the  string.)  If  the pattern is changed so that it uses an atomic
3297           group, like this:
3298    
3299           ((?>\D+)|<\d+>)*[!?]           ((?>\D+)|<\d+>)*[!?]
3300    
3301         sequences  of non-digits cannot be broken, and failure happens quickly.         sequences of non-digits cannot be broken, and failure happens  quickly.
3302    
3303    
3304  BACK REFERENCES  BACK REFERENCES
3305    
3306         Outside a character class, a backslash followed by a digit greater than         Outside a character class, a backslash followed by a digit greater than
3307         0 (and possibly further digits) is a back reference to a capturing sub-         0 (and possibly further digits) is a back reference to a capturing sub-
3308         pattern earlier (that is, to its left) in the pattern,  provided  there         pattern  earlier  (that is, to its left) in the pattern, provided there
3309         have been that many previous capturing left parentheses.         have been that many previous capturing left parentheses.
3310    
3311         However, if the decimal number following the backslash is less than 10,         However, if the decimal number following the backslash is less than 10,
3312         it is always taken as a back reference, and causes  an  error  only  if         it  is  always  taken  as a back reference, and causes an error only if
3313         there  are  not that many capturing left parentheses in the entire pat-         there are not that many capturing left parentheses in the  entire  pat-
3314         tern. In other words, the parentheses that are referenced need  not  be         tern.  In  other words, the parentheses that are referenced need not be
3315         to  the left of the reference for numbers less than 10. See the section         to the left of the reference for numbers less than 10. See the  subsec-
3316         entitled "Backslash" above for further details of the handling of  dig-         tion  entitled  "Non-printing  characters" above for further details of
3317         its following a backslash.         the handling of digits following a backslash.
3318    
3319         A  back  reference matches whatever actually matched the capturing sub-         A back reference matches whatever actually matched the  capturing  sub-
3320         pattern in the current subject string, rather  than  anything  matching         pattern  in  the  current subject string, rather than anything matching
3321         the subpattern itself (see "Subpatterns as subroutines" below for a way         the subpattern itself (see "Subpatterns as subroutines" below for a way
3322         of doing that). So the pattern         of doing that). So the pattern
3323    
3324           (sens|respons)e and \1ibility           (sens|respons)e and \1ibility
3325    
3326         matches "sense and sensibility" and "response and responsibility",  but         matches  "sense and sensibility" and "response and responsibility", but
3327         not  "sense and responsibility". If caseful matching is in force at the         not "sense and responsibility". If caseful matching is in force at  the
3328         time of the back reference, the case of letters is relevant. For  exam-         time  of the back reference, the case of letters is relevant. For exam-
3329         ple,         ple,
3330    
3331           ((?i)rah)\s+\1           ((?i)rah)\s+\1
3332    
3333         matches  "rah  rah"  and  "RAH RAH", but not "RAH rah", even though the         matches "rah rah" and "RAH RAH", but not "RAH  rah",  even  though  the
3334         original capturing subpattern is matched caselessly.         original capturing subpattern is matched caselessly.
3335    
3336         Back references to named subpatterns use the Python  syntax  (?P=name).         Back  references  to named subpatterns use the Python syntax (?P=name).
3337         We could rewrite the above example as follows:         We could rewrite the above example as follows:
3338    
3339           (?<p1>(?i)rah)\s+(?P=p1)           (?<p1>(?i)rah)\s+(?P=p1)
3340    
3341         There  may be more than one back reference to the same subpattern. If a         There may be more than one back reference to the same subpattern. If  a
3342         subpattern has not actually been used in a particular match,  any  back         subpattern  has  not actually been used in a particular match, any back
3343         references to it always fail. For example, the pattern         references to it always fail. For example, the pattern
3344    
3345           (a|(bc))\2           (a|(bc))\2
3346    
3347         always  fails if it starts to match "a" rather than "bc". Because there         always fails if it starts to match "a" rather than "bc". Because  there
3348         may be many capturing parentheses in a pattern,  all  digits  following         may  be  many  capturing parentheses in a pattern, all digits following
3349         the  backslash  are taken as part of a potential back reference number.         the backslash are taken as part of a potential back  reference  number.
3350         If the pattern continues with a digit character, some delimiter must be         If the pattern continues with a digit character, some delimiter must be
3351         used  to  terminate  the back reference. If the PCRE_EXTENDED option is         used to terminate the back reference. If the  PCRE_EXTENDED  option  is
3352         set, this can be whitespace.  Otherwise an empty comment can be used.         set,  this  can  be  whitespace.  Otherwise an empty comment (see "Com-
3353           ments" below) can be used.
3354    
3355         A back reference that occurs inside the parentheses to which it  refers         A back reference that occurs inside the parentheses to which it  refers
3356         fails  when  the subpattern is first used, so, for example, (a\1) never         fails  when  the subpattern is first used, so, for example, (a\1) never
# Line 2482  ASSERTIONS Line 3372  ASSERTIONS
3372         An assertion is a test on the characters  following  or  preceding  the         An assertion is a test on the characters  following  or  preceding  the
3373         current  matching  point that does not actually consume any characters.         current  matching  point that does not actually consume any characters.
3374         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are         The simple assertions coded as \b, \B, \A, \G, \Z,  \z,  ^  and  $  are
3375         described above.  More complicated assertions are coded as subpatterns.         described above.
3376         There are two kinds: those that look ahead of the current  position  in  
3377         the subject string, and those that look behind it.         More  complicated  assertions  are  coded as subpatterns. There are two
3378           kinds: those that look ahead of the current  position  in  the  subject
3379         An  assertion  subpattern  is matched in the normal way, except that it         string,  and  those  that  look  behind  it. An assertion subpattern is
3380         does not cause the current matching position to be  changed.  Lookahead         matched in the normal way, except that it does not  cause  the  current
3381         assertions  start with (?= for positive assertions and (?! for negative         matching position to be changed.
3382         assertions. For example,  
3383           Assertion  subpatterns  are  not  capturing subpatterns, and may not be
3384           repeated, because it makes no sense to assert the  same  thing  several
3385           times.  If  any kind of assertion contains capturing subpatterns within
3386           it, these are counted for the purposes of numbering the capturing  sub-
3387           patterns in the whole pattern.  However, substring capturing is carried
3388           out only for positive assertions, because it does not  make  sense  for
3389           negative assertions.
3390    
3391       Lookahead assertions
3392    
3393           Lookahead assertions start with (?= for positive assertions and (?! for
3394           negative assertions. For example,
3395    
3396           \w+(?=;)           \w+(?=;)
3397    
# Line 2506  ASSERTIONS Line 3408  ASSERTIONS
3408         does not find an occurrence of "bar"  that  is  preceded  by  something         does not find an occurrence of "bar"  that  is  preceded  by  something
3409         other  than "foo"; it finds any occurrence of "bar" whatsoever, because         other  than "foo"; it finds any occurrence of "bar" whatsoever, because
3410         the assertion (?!foo) is always true when the next three characters are         the assertion (?!foo) is always true when the next three characters are
3411         "bar". A lookbehind assertion is needed to achieve this effect.         "bar". A lookbehind assertion is needed to achieve the other effect.
3412    
3413         If you want to force a matching failure at some point in a pattern, the         If you want to force a matching failure at some point in a pattern, the
3414         most convenient way to do it is  with  (?!)  because  an  empty  string         most convenient way to do it is  with  (?!)  because  an  empty  string
3415         always  matches, so an assertion that requires there not to be an empty         always  matches, so an assertion that requires there not to be an empty
3416         string must always fail.         string must always fail.
3417    
3418       Lookbehind assertions
3419    
3420         Lookbehind assertions start with (?<= for positive assertions and  (?<!         Lookbehind assertions start with (?<= for positive assertions and  (?<!
3421         for negative assertions. For example,         for negative assertions. For example,
3422    
# Line 2551  ASSERTIONS Line 3455  ASSERTIONS
3455    
3456         PCRE does not allow the \C escape (which matches a single byte in UTF-8         PCRE does not allow the \C escape (which matches a single byte in UTF-8
3457         mode)  to appear in lookbehind assertions, because it makes it impossi-         mode)  to appear in lookbehind assertions, because it makes it impossi-
3458         ble to calculate the length of the lookbehind.         ble to calculate the length of the lookbehind. The \X escape, which can
3459           match different numbers of bytes, is also not permitted.
3460    
3461         Atomic groups can be used in conjunction with lookbehind assertions  to         Atomic  groups can be used in conjunction with lookbehind assertions to
3462         specify efficient matching at the end of the subject string. Consider a         specify efficient matching at the end of the subject string. Consider a
3463         simple pattern such as         simple pattern such as
3464    
3465           abcd$           abcd$
3466    
3467         when applied to a long string that does  not  match.  Because  matching         when  applied  to  a  long string that does not match. Because matching
3468         proceeds from left to right, PCRE will look for each "a" in the subject         proceeds from left to right, PCRE will look for each "a" in the subject
3469         and then see if what follows matches the rest of the  pattern.  If  the         and  then  see  if what follows matches the rest of the pattern. If the
3470         pattern is specified as         pattern is specified as
3471    
3472           ^.*abcd$           ^.*abcd$
3473    
3474         the  initial .* matches the entire string at first, but when this fails         the initial .* matches the entire string at first, but when this  fails
3475         (because there is no following "a"), it backtracks to match all but the         (because there is no following "a"), it backtracks to match all but the
3476         last  character,  then all but the last two characters, and so on. Once         last character, then all but the last two characters, and so  on.  Once
3477         again the search for "a" covers the entire string, from right to  left,         again  the search for "a" covers the entire string, from right to left,
3478         so we are no better off. However, if the pattern is written as         so we are no better off. However, if the pattern is written as
3479    
3480           ^(?>.*)(?<=abcd)           ^(?>.*)(?<=abcd)
3481    
3482         or, equivalently,         or, equivalently, using the possessive quantifier syntax,
3483    
3484           ^.*+(?<=abcd)           ^.*+(?<=abcd)
3485    
3486         there  can  be  no  backtracking for the .* item; it can match only the         there can be no backtracking for the .* item; it  can  match  only  the
3487         entire string. The subsequent lookbehind assertion does a  single  test         entire  string.  The subsequent lookbehind assertion does a single test
3488         on  the last four characters. If it fails, the match fails immediately.         on the last four characters. If it fails, the match fails  immediately.
3489         For long strings, this approach makes a significant difference  to  the         For  long  strings, this approach makes a significant difference to the
3490         processing time.         processing time.
3491    
3492       Using multiple assertions
3493