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1    -----------------------------------------------------------------------------
2    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
4    that do not have a man page processor. The small individual files that give
5    synopses of each function in the library have not been included. There are
6    separate text files for the pcregrep and pcretest commands.
7    -----------------------------------------------------------------------------
8    
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14       pcre - Perl-compatible regular expressions.         PCRE - Perl-compatible regular expressions
15    
16    
17    INTRODUCTION
18    
19  SYNOPSIS         The  PCRE  library is a set of functions that implement regular expres-
20       #include <pcre.h>         sion pattern matching using the same syntax and semantics as Perl, with
21           just  a  few differences. (Certain features that appeared in Python and
22           PCRE before they appeared in Perl are also available using  the  Python
23           syntax.)
24    
25           The  current  implementation of PCRE (release 7.x) corresponds approxi-
26           mately with Perl 5.10, including support for UTF-8 encoded strings  and
27           Unicode general category properties. However, UTF-8 and Unicode support
28           has to be explicitly enabled; it is not the default. The Unicode tables
29           correspond to Unicode release 5.0.0.
30    
31           In  addition to the Perl-compatible matching function, PCRE contains an
32           alternative matching function that matches the same  compiled  patterns
33           in  a different way. In certain circumstances, the alternative function
34           has some advantages. For a discussion of the two  matching  algorithms,
35           see the pcrematching page.
36    
37           PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40           included as part of the PCRE distribution. The pcrecpp page has details
41           of  this  interface.  Other  people's contributions can be found in the
42           Contrib directory at the primary FTP site, which is:
43    
44           ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46           Details of exactly which Perl regular expression features are  and  are
47           not supported by PCRE are given in separate documents. See the pcrepat-
48           tern and pcrecompat pages.
49    
50           Some features of PCRE can be included, excluded, or  changed  when  the
51           library  is  built.  The pcre_config() function makes it possible for a
52           client to discover which features are  available.  The  features  them-
53           selves  are described in the pcrebuild page. Documentation about build-
54           ing PCRE for various operating systems can be found in the README  file
55           in the source distribution.
56    
57           The  library  contains  a number of undocumented internal functions and
58           data tables that are used by more than one  of  the  exported  external
59           functions,  but  which  are  not  intended for use by external callers.
60           Their names all begin with "_pcre_", which hopefully will  not  provoke
61           any name clashes. In some environments, it is possible to control which
62           external symbols are exported when a shared library is  built,  and  in
63           these cases the undocumented symbols are not exported.
64    
65    
66    USER DOCUMENTATION
67    
68           The  user  documentation  for PCRE comprises a number of different sec-
69           tions. In the "man" format, each of these is a separate "man page".  In
70           the  HTML  format, each is a separate page, linked from the index page.
71           In the plain text format, all the sections are concatenated,  for  ease
72           of searching. The sections are as follows:
73    
74             pcre              this document
75             pcreapi           details of PCRE's native C API
76             pcrebuild         options for building PCRE
77             pcrecallout       details of the callout feature
78             pcrecompat        discussion of Perl compatibility
79             pcrecpp           details of the C++ wrapper
80             pcregrep          description of the pcregrep command
81             pcrematching      discussion of the two matching algorithms
82             pcrepartial       details of the partial matching facility
83             pcrepattern       syntax and semantics of supported
84                                 regular expressions
85             pcreperform       discussion of performance issues
86             pcreposix         the POSIX-compatible C API
87             pcreprecompile    details of saving and re-using precompiled patterns
88             pcresample        discussion of the sample program
89             pcrestack         discussion of stack usage
90             pcretest          description of the pcretest testing command
91    
92       pcre *pcre_compile(const char *pattern, int options,         In addition, in the "man" and HTML formats, there is a short  page  for
93            const char **errptr, int *erroffset,         each C library function, listing its arguments and results.
           const unsigned char *tableptr);  
94    
      pcre_extra *pcre_study(const pcre *code, int options,  
           const char **errptr);  
95    
96       int pcre_exec(const pcre *code, const pcre_extra *extra,  LIMITATIONS
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
97    
98       int pcre_copy_substring(const char *subject, int *ovector,         There  are some size limitations in PCRE but it is hoped that they will
99            int stringcount, int stringnumber, char *buffer,         never in practice be relevant.
           int buffersize);  
100    
101       int pcre_get_substring(const char *subject, int *ovector,         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
102            int stringcount, int stringnumber,         is compiled with the default internal linkage size of 2. If you want to
103            const char **stringptr);         process regular expressions that are truly enormous,  you  can  compile
104           PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
105           the source distribution and the pcrebuild documentation  for  details).
106           In  these  cases the limit is substantially larger.  However, the speed
107           of execution is slower.
108    
109           All values in repeating quantifiers must be less than 65536. The  maxi-
110           mum  compiled  length  of  subpattern  with an explicit repeat count is
111           30000 bytes. The maximum number of capturing subpatterns is 65535.
112    
113           There is no limit to the number of parenthesized subpatterns, but there
114           can be no more than 65535 capturing subpatterns.
115    
116           The maximum length of name for a named subpattern is 32 characters, and
117           the maximum number of named subpatterns is 10000.
118    
119           The maximum length of a subject string is the largest  positive  number
120           that  an integer variable can hold. However, when using the traditional
121           matching function, PCRE uses recursion to handle subpatterns and indef-
122           inite  repetition.  This means that the available stack space may limit
123           the size of a subject string that can be processed by certain patterns.
124           For a discussion of stack issues, see the pcrestack documentation.
125    
126    
127    UTF-8 AND UNICODE PROPERTY SUPPORT
128    
129           From  release  3.3,  PCRE  has  had  some support for character strings
130           encoded in the UTF-8 format. For release 4.0 this was greatly  extended
131           to  cover  most common requirements, and in release 5.0 additional sup-
132           port for Unicode general category properties was added.
133    
134           In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
135           support  in  the  code,  and, in addition, you must call pcre_compile()
136           with the PCRE_UTF8 option flag. When you do this, both the pattern  and
137           any  subject  strings  that are matched against it are treated as UTF-8
138           strings instead of just strings of bytes.
139    
140           If you compile PCRE with UTF-8 support, but do not use it at run  time,
141           the  library will be a bit bigger, but the additional run time overhead
142           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
143           very big.
144    
145           If PCRE is built with Unicode character property support (which implies
146           UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
147           ported.  The available properties that can be tested are limited to the
148           general category properties such as Lu for an upper case letter  or  Nd
149           for  a  decimal number, the Unicode script names such as Arabic or Han,
150           and the derived properties Any and L&. A full  list  is  given  in  the
151           pcrepattern documentation. Only the short names for properties are sup-
152           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
153           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
154           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
155           does not support this.
156    
157           The following comments apply when PCRE is running in UTF-8 mode:
158    
159           1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and
160           subjects are checked for validity on entry to the  relevant  functions.
161           If an invalid UTF-8 string is passed, an error return is given. In some
162           situations, you may already know  that  your  strings  are  valid,  and
163           therefore want to skip these checks in order to improve performance. If
164           you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,
165           PCRE  assumes  that  the  pattern or subject it is given (respectively)
166           contains only valid UTF-8 codes. In this case, it does not diagnose  an
167           invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
168           PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
169           crash.
170    
171           2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
172           two-byte UTF-8 character if the value is greater than 127.
173    
174           3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
175           characters for values greater than \177.
176    
177           4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
178           vidual bytes, for example: \x{100}{3}.
179    
180           5. The dot metacharacter matches one UTF-8 character instead of a  sin-
181           gle byte.
182    
183           6.  The  escape sequence \C can be used to match a single byte in UTF-8
184           mode, but its use can lead to some strange effects.  This  facility  is
185           not available in the alternative matching function, pcre_dfa_exec().
186    
187           7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
188           test characters of any code value, but the characters that PCRE  recog-
189           nizes  as  digits,  spaces,  or  word characters remain the same set as
190           before, all with values less than 256. This remains true even when PCRE
191           includes  Unicode  property support, because to do otherwise would slow
192           down PCRE in many common cases. If you really want to test for a  wider
193           sense  of,  say,  "digit",  you must use Unicode property tests such as
194           \p{Nd}.
195    
196           8. Similarly, characters that match the POSIX named  character  classes
197           are all low-valued characters.
198    
199           9.  Case-insensitive  matching  applies only to characters whose values
200           are less than 128, unless PCRE is built with Unicode property  support.
201           Even  when  Unicode  property support is available, PCRE still uses its
202           own character tables when checking the case of  low-valued  characters,
203           so  as not to degrade performance.  The Unicode property information is
204           used only for characters with higher values. Even when Unicode property
205           support is available, PCRE supports case-insensitive matching only when
206           there is a one-to-one mapping between a letter's  cases.  There  are  a
207           small  number  of  many-to-one  mappings in Unicode; these are not sup-
208           ported by PCRE.
209    
      int pcre_get_substring_list(const char *subject,  
           int *ovector, int stringcount, const char ***listptr);  
210    
211       void pcre_free_substring(const char *stringptr);  AUTHOR
212    
213       void pcre_free_substring_list(const char **stringptr);         Philip Hazel
214           University Computing Service
215           Cambridge CB2 3QH, England.
216    
217       const unsigned char *pcre_maketables(void);         Putting an actual email address here seems to have been a spam  magnet,
218           so I've taken it away. If you want to email me, use my initial and sur-
219           name, separated by a dot, at the domain ucs.cam.ac.uk.
220    
      int pcre_fullinfo(const pcre *code, const pcre_extra *extra,  
           int what, void *where);  
221    
222       int pcre_info(const pcre *code, int *optptr, *firstcharptr);  REVISION
223    
224       char *pcre_version(void);         Last updated: 06 March 2007
225           Copyright (c) 1997-2007 University of Cambridge.
226    ------------------------------------------------------------------------------
227    
      void *(*pcre_malloc)(size_t);  
228    
229       void (*pcre_free)(void *);  PCREBUILD(3)                                                      PCREBUILD(3)
230    
231    
232    NAME
233           PCRE - Perl-compatible regular expressions
234    
235    
236  DESCRIPTION  PCRE BUILD-TIME OPTIONS
237       The PCRE library is a set of functions that implement  regu-  
238       lar  expression  pattern  matching using the same syntax and         This  document  describes  the  optional  features  of PCRE that can be
239       semantics as Perl  5,  with  just  a  few  differences  (see         selected when the library is compiled. They are all selected, or  dese-
240           lected, by providing options to the configure script that is run before
241           the make command. The complete list of  options  for  configure  (which
242           includes  the  standard  ones such as the selection of the installation
243           directory) can be obtained by running
244    
245             ./configure --help
246    
247           The following sections describe certain options whose names begin  with
248           --enable  or  --disable. These settings specify changes to the defaults
249           for the configure command. Because of the  way  that  configure  works,
250           --enable  and  --disable  always  come  in  pairs, so the complementary
251           option always exists as well, but as it specifies the  default,  it  is
252           not described.
253    
254    
255    C++ SUPPORT
256    
257           By default, the configure script will search for a C++ compiler and C++
258           header files. If it finds them, it automatically builds the C++ wrapper
259           library for PCRE. You can disable this by adding
260    
261             --disable-cpp
262    
263           to the configure command.
264    
265    
266    UTF-8 SUPPORT
267    
268           To build PCRE with support for UTF-8 character strings, add
269    
270             --enable-utf8
271    
272           to  the  configure  command.  Of  itself, this does not make PCRE treat
273           strings as UTF-8. As well as compiling PCRE with this option, you  also
274           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
275           function.
276    
277    
278    UNICODE CHARACTER PROPERTY SUPPORT
279    
280           UTF-8 support allows PCRE to process character values greater than  255
281           in  the  strings that it handles. On its own, however, it does not pro-
282           vide any facilities for accessing the properties of such characters. If
283           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
284           refer to Unicode character properties, you must add
285    
286             --enable-unicode-properties
287    
288           to the configure command. This implies UTF-8 support, even if you  have
289           not explicitly requested it.
290    
291           Including  Unicode  property  support  adds around 90K of tables to the
292           PCRE library, approximately doubling its size. Only the  general  cate-
293           gory  properties  such as Lu and Nd are supported. Details are given in
294           the pcrepattern documentation.
295    
296    
297    CODE VALUE OF NEWLINE
298    
299           By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
300           the  end  of  a line. This is the normal newline character on Unix-like
301           systems. You can compile PCRE to use character 13 (carriage return, CR)
302           instead, by adding
303    
304             --enable-newline-is-cr
305    
306           to  the  configure  command.  There  is  also  a --enable-newline-is-lf
307           option, which explicitly specifies linefeed as the newline character.
308    
309           Alternatively, you can specify that line endings are to be indicated by
310           the two character sequence CRLF. If you want this, add
311    
312             --enable-newline-is-crlf
313    
314           to the configure command. There is a fourth option, specified by
315    
316             --enable-newline-is-any
317    
318           which causes PCRE to recognize any Unicode newline sequence.
319    
320           Whatever  line  ending convention is selected when PCRE is built can be
321           overridden when the library functions are called. At build time  it  is
322           conventional to use the standard for your operating system.
323    
324    
325    BUILDING SHARED AND STATIC LIBRARIES
326    
327           The  PCRE building process uses libtool to build both shared and static
328           Unix libraries by default. You can suppress one of these by adding  one
329           of
330    
331             --disable-shared
332             --disable-static
333    
334           to the configure command, as required.
335    
336    
337    POSIX MALLOC USAGE
338    
339           When PCRE is called through the POSIX interface (see the pcreposix doc-
340           umentation), additional working storage is  required  for  holding  the
341           pointers  to capturing substrings, because PCRE requires three integers
342           per substring, whereas the POSIX interface provides only  two.  If  the
343           number of expected substrings is small, the wrapper function uses space
344           on the stack, because this is faster than using malloc() for each call.
345           The default threshold above which the stack is no longer used is 10; it
346           can be changed by adding a setting such as
347    
348             --with-posix-malloc-threshold=20
349    
350           to the configure command.
351    
352    
353    HANDLING VERY LARGE PATTERNS
354    
355           Within a compiled pattern, offset values are used  to  point  from  one
356           part  to another (for example, from an opening parenthesis to an alter-
357           nation metacharacter). By default, two-byte values are used  for  these
358           offsets,  leading  to  a  maximum size for a compiled pattern of around
359           64K. This is sufficient to handle all but the most  gigantic  patterns.
360           Nevertheless,  some  people do want to process enormous patterns, so it
361           is possible to compile PCRE to use three-byte or four-byte  offsets  by
362           adding a setting such as
363    
364             --with-link-size=3
365    
366           to  the  configure  command.  The value given must be 2, 3, or 4. Using
367           longer offsets slows down the operation of PCRE because it has to  load
368           additional bytes when handling them.
369    
370           If  you  build  PCRE with an increased link size, test 2 (and test 5 if
371           you are using UTF-8) will fail. Part of the output of these tests is  a
372           representation  of the compiled pattern, and this changes with the link
373           size.
374    
375    
376    AVOIDING EXCESSIVE STACK USAGE
377    
378           When matching with the pcre_exec() function, PCRE implements backtrack-
379           ing  by  making recursive calls to an internal function called match().
380           In environments where the size of the stack is limited,  this  can  se-
381           verely  limit  PCRE's operation. (The Unix environment does not usually
382           suffer from this problem, but it may sometimes be necessary to increase
383           the  maximum  stack size.  There is a discussion in the pcrestack docu-
384           mentation.) An alternative approach to recursion that uses memory  from
385           the  heap  to remember data, instead of using recursive function calls,
386           has been implemented to work round the problem of limited  stack  size.
387           If you want to build a version of PCRE that works this way, add
388    
389             --disable-stack-for-recursion
390    
391           to  the  configure  command. With this configuration, PCRE will use the
392           pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
393           ment  functions.  Separate  functions are provided because the usage is
394           very predictable: the block sizes requested are always  the  same,  and
395           the  blocks  are always freed in reverse order. A calling program might
396           be able to implement optimized functions that perform better  than  the
397           standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
398           slowly when built in this way. This option affects only the pcre_exec()
399           function; it is not relevant for the the pcre_dfa_exec() function.
400    
401    
402    LIMITING PCRE RESOURCE USAGE
403    
404           Internally,  PCRE has a function called match(), which it calls repeat-
405           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
406           pcre_exec()  function.  By controlling the maximum number of times this
407           function may be called during a single matching operation, a limit  can
408           be  placed  on  the resources used by a single call to pcre_exec(). The
409           limit can be changed at run time, as described in the pcreapi  documen-
410           tation.  The default is 10 million, but this can be changed by adding a
411           setting such as
412    
413             --with-match-limit=500000
414    
415           to  the  configure  command.  This  setting  has  no  effect   on   the
416           pcre_dfa_exec() matching function.
417    
418           In  some  environments  it is desirable to limit the depth of recursive
419           calls of match() more strictly than the total number of calls, in order
420           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
421           for-recursion is specified) that is used. A second limit controls this;
422           it  defaults  to  the  value  that is set for --with-match-limit, which
423           imposes no additional constraints. However, you can set a  lower  limit
424           by adding, for example,
425    
426             --with-match-limit-recursion=10000
427    
428           to  the  configure  command.  This  value can also be overridden at run
429           time.
430    
431    
432    USING EBCDIC CODE
433    
434           PCRE assumes by default that it will run in an  environment  where  the
435           character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
436           PCRE can, however, be compiled to  run  in  an  EBCDIC  environment  by
437           adding
438    
439             --enable-ebcdic
440    
441           to the configure command.
442    
443    
444    SEE ALSO
445    
446           pcreapi(3), pcre_config(3).
447    
448    
449    AUTHOR
450    
451           Philip Hazel
452           University Computing Service
453           Cambridge CB2 3QH, England.
454    
455    
456    REVISION
457    
458           Last updated: 06 March 2007
459           Copyright (c) 1997-2007 University of Cambridge.
460    ------------------------------------------------------------------------------
461    
462    
463    PCREMATCHING(3)                                                PCREMATCHING(3)
464    
465    
466    NAME
467           PCRE - Perl-compatible regular expressions
468    
469    
470    PCRE MATCHING ALGORITHMS
471    
472           This document describes the two different algorithms that are available
473           in PCRE for matching a compiled regular expression against a given sub-
474           ject  string.  The  "standard"  algorithm  is  the  one provided by the
475           pcre_exec() function.  This works in the same was  as  Perl's  matching
476           function, and provides a Perl-compatible matching operation.
477    
478           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
479           this operates in a different way, and is not  Perl-compatible.  It  has
480           advantages  and disadvantages compared with the standard algorithm, and
481           these are described below.
482    
483           When there is only one possible way in which a given subject string can
484           match  a pattern, the two algorithms give the same answer. A difference
485           arises, however, when there are multiple possibilities. For example, if
486           the pattern
487    
488             ^<.*>
489    
490           is matched against the string
491    
492             <something> <something else> <something further>
493    
494           there are three possible answers. The standard algorithm finds only one
495           of them, whereas the alternative algorithm finds all three.
496    
497    
498    REGULAR EXPRESSIONS AS TREES
499    
500           The set of strings that are matched by a regular expression can be rep-
501           resented  as  a  tree structure. An unlimited repetition in the pattern
502           makes the tree of infinite size, but it is still a tree.  Matching  the
503           pattern  to a given subject string (from a given starting point) can be
504           thought of as a search of the tree.  There are two  ways  to  search  a
505           tree:  depth-first  and  breadth-first, and these correspond to the two
506           matching algorithms provided by PCRE.
507    
508    
509    THE STANDARD MATCHING ALGORITHM
510    
511           In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
512           sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
513           depth-first search of the pattern tree. That is, it  proceeds  along  a
514           single path through the tree, checking that the subject matches what is
515           required. When there is a mismatch, the algorithm  tries  any  alterna-
516           tives  at  the  current point, and if they all fail, it backs up to the
517           previous branch point in the  tree,  and  tries  the  next  alternative
518           branch  at  that  level.  This often involves backing up (moving to the
519           left) in the subject string as well.  The  order  in  which  repetition
520           branches  are  tried  is controlled by the greedy or ungreedy nature of
521           the quantifier.
522    
523           If a leaf node is reached, a matching string has  been  found,  and  at
524           that  point the algorithm stops. Thus, if there is more than one possi-
525           ble match, this algorithm returns the first one that it finds.  Whether
526           this  is the shortest, the longest, or some intermediate length depends
527           on the way the greedy and ungreedy repetition quantifiers are specified
528           in the pattern.
529    
530           Because  it  ends  up  with a single path through the tree, it is rela-
531           tively straightforward for this algorithm to keep  track  of  the  sub-
532           strings  that  are  matched  by portions of the pattern in parentheses.
533           This provides support for capturing parentheses and back references.
534    
535    
536    THE ALTERNATIVE MATCHING ALGORITHM
537    
538           This algorithm conducts a breadth-first search of  the  tree.  Starting
539           from  the  first  matching  point  in the subject, it scans the subject
540           string from left to right, once, character by character, and as it does
541           this,  it remembers all the paths through the tree that represent valid
542           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
543           though  it is not implemented as a traditional finite state machine (it
544           keeps multiple states active simultaneously).
545    
546           The scan continues until either the end of the subject is  reached,  or
547           there  are  no more unterminated paths. At this point, terminated paths
548           represent the different matching possibilities (if there are none,  the
549           match  has  failed).   Thus,  if there is more than one possible match,
550           this algorithm finds all of them, and in particular, it finds the long-
551           est.  In PCRE, there is an option to stop the algorithm after the first
552           match (which is necessarily the shortest) has been found.
553    
554           Note that all the matches that are found start at the same point in the
555           subject. If the pattern
556    
557             cat(er(pillar)?)
558    
559           is  matched  against the string "the caterpillar catchment", the result
560           will be the three strings "cat", "cater", and "caterpillar" that  start
561           at the fourth character of the subject. The algorithm does not automat-
562           ically move on to find matches that start at later positions.
563    
564           There are a number of features of PCRE regular expressions that are not
565           supported by the alternative matching algorithm. They are as follows:
566    
567           1.  Because  the  algorithm  finds  all possible matches, the greedy or
568           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
569           ungreedy quantifiers are treated in exactly the same way. However, pos-
570           sessive quantifiers can make a difference when what follows could  also
571           match what is quantified, for example in a pattern like this:
572    
573             ^a++\w!
574    
575           This  pattern matches "aaab!" but not "aaa!", which would be matched by
576           a non-possessive quantifier. Similarly, if an atomic group is  present,
577           it  is matched as if it were a standalone pattern at the current point,
578           and the longest match is then "locked in" for the rest of  the  overall
579           pattern.
580    
581           2. When dealing with multiple paths through the tree simultaneously, it
582           is not straightforward to keep track of  captured  substrings  for  the
583           different  matching  possibilities,  and  PCRE's implementation of this
584           algorithm does not attempt to do this. This means that no captured sub-
585           strings are available.
586    
587           3.  Because no substrings are captured, back references within the pat-
588           tern are not supported, and cause errors if encountered.
589    
590           4. For the same reason, conditional expressions that use  a  backrefer-
591           ence  as  the  condition or test for a specific group recursion are not
592           supported.
593    
594           5. Callouts are supported, but the value of the  capture_top  field  is
595           always 1, and the value of the capture_last field is always -1.
596    
597           6.  The \C escape sequence, which (in the standard algorithm) matches a
598           single byte, even in UTF-8 mode, is not supported because the  alterna-
599           tive  algorithm  moves  through  the  subject string one character at a
600           time, for all active paths through the tree.
601    
602    
603    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
604    
605           Using the alternative matching algorithm provides the following  advan-
606           tages:
607    
608           1. All possible matches (at a single point in the subject) are automat-
609           ically found, and in particular, the longest match is  found.  To  find
610           more than one match using the standard algorithm, you have to do kludgy
611           things with callouts.
612    
613           2. There is much better support for partial matching. The  restrictions
614           on  the content of the pattern that apply when using the standard algo-
615           rithm for partial matching do not apply to the  alternative  algorithm.
616           For  non-anchored patterns, the starting position of a partial match is
617           available.
618    
619           3. Because the alternative algorithm  scans  the  subject  string  just
620           once,  and  never  needs to backtrack, it is possible to pass very long
621           subject strings to the matching function in  several  pieces,  checking
622           for partial matching each time.
623    
624    
625       below).  The  current  implementation  corresponds  to  Perl  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      5.005, with some additional features  from  later  versions.  
      This  includes  some  experimental,  incomplete  support for  
      UTF-8 encoded strings. Details of exactly what is  and  what  
      is not supported are given below.  
626    
627       PCRE has its own native API,  which  is  described  in  this         The alternative algorithm suffers from a number of disadvantages:
      document.  There  is  also  a  set of wrapper functions that  
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
628    
629       The native API function prototypes are defined in the header         1.  It  is  substantially  slower  than the standard algorithm. This is
630       file  pcre.h,  and  on  Unix  systems  the library itself is         partly because it has to search for all possible matches, but  is  also
631       called libpcre.a, so can be accessed by adding -lpcre to the         because it is less susceptible to optimization.
      command  for  linking  an  application  which  calls it. The  
      header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
632    
633       The functions pcre_compile(), pcre_study(), and  pcre_exec()         2. Capturing parentheses and back references are not supported.
      are used for compiling and matching regular expressions.  
634    
635       The functions  pcre_copy_substring(),  pcre_get_substring(),         3. Although atomic groups are supported, their use does not provide the
636       and  pcre_get_substring_list() are convenience functions for         performance advantage that it does for the standard algorithm.
      extracting  captured  substrings  from  a  matched   subject  
      string; pcre_free_substring() and pcre_free_substring_list()  
      are also provided, to free the  memory  used  for  extracted  
      strings.  
637    
      The function pcre_maketables() is used (optionally) to build  
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
638    
639       The function pcre_fullinfo() is used to find out information  AUTHOR
640       about a compiled pattern; pcre_info() is an obsolete version  
641       which returns only some of the available information, but is         Philip Hazel
642       retained   for   backwards   compatibility.    The  function         University Computing Service
643       pcre_version() returns a pointer to a string containing  the         Cambridge CB2 3QH, England.
644       version of PCRE and its date of release.  
645    
646    REVISION
647    
648           Last updated: 06 March 2007
649           Copyright (c) 1997-2007 University of Cambridge.
650    ------------------------------------------------------------------------------
651    
652    
653    PCREAPI(3)                                                          PCREAPI(3)
654    
655    
656    NAME
657           PCRE - Perl-compatible regular expressions
658    
659    
660    PCRE NATIVE API
661    
662           #include <pcre.h>
663    
664           pcre *pcre_compile(const char *pattern, int options,
665                const char **errptr, int *erroffset,
666                const unsigned char *tableptr);
667    
668           pcre *pcre_compile2(const char *pattern, int options,
669                int *errorcodeptr,
670                const char **errptr, int *erroffset,
671                const unsigned char *tableptr);
672    
673           pcre_extra *pcre_study(const pcre *code, int options,
674                const char **errptr);
675    
676           int pcre_exec(const pcre *code, const pcre_extra *extra,
677                const char *subject, int length, int startoffset,
678                int options, int *ovector, int ovecsize);
679    
680           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
681                const char *subject, int length, int startoffset,
682                int options, int *ovector, int ovecsize,
683                int *workspace, int wscount);
684    
685           int pcre_copy_named_substring(const pcre *code,
686                const char *subject, int *ovector,
687                int stringcount, const char *stringname,
688                char *buffer, int buffersize);
689    
690           int pcre_copy_substring(const char *subject, int *ovector,
691                int stringcount, int stringnumber, char *buffer,
692                int buffersize);
693    
694           int pcre_get_named_substring(const pcre *code,
695                const char *subject, int *ovector,
696                int stringcount, const char *stringname,
697                const char **stringptr);
698    
699           int pcre_get_stringnumber(const pcre *code,
700                const char *name);
701    
702           int pcre_get_stringtable_entries(const pcre *code,
703                const char *name, char **first, char **last);
704    
705           int pcre_get_substring(const char *subject, int *ovector,
706                int stringcount, int stringnumber,
707                const char **stringptr);
708    
709           int pcre_get_substring_list(const char *subject,
710                int *ovector, int stringcount, const char ***listptr);
711    
712           void pcre_free_substring(const char *stringptr);
713    
714           void pcre_free_substring_list(const char **stringptr);
715    
716           const unsigned char *pcre_maketables(void);
717    
718           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
719                int what, void *where);
720    
721           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
722    
723           int pcre_refcount(pcre *code, int adjust);
724    
725           int pcre_config(int what, void *where);
726    
727           char *pcre_version(void);
728    
729           void *(*pcre_malloc)(size_t);
730    
731           void (*pcre_free)(void *);
732    
733           void *(*pcre_stack_malloc)(size_t);
734    
735           void (*pcre_stack_free)(void *);
736    
737           int (*pcre_callout)(pcre_callout_block *);
738    
739    
740    PCRE API OVERVIEW
741    
742           PCRE has its own native API, which is described in this document. There
743           are also some wrapper functions that correspond to  the  POSIX  regular
744           expression  API.  These  are  described in the pcreposix documentation.
745           Both of these APIs define a set of C function calls. A C++  wrapper  is
746           distributed with PCRE. It is documented in the pcrecpp page.
747    
748           The  native  API  C  function prototypes are defined in the header file
749           pcre.h, and on Unix systems the library itself is called  libpcre.   It
750           can normally be accessed by adding -lpcre to the command for linking an
751           application  that  uses  PCRE.  The  header  file  defines  the  macros
752           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
753           bers for the library.  Applications can use these  to  include  support
754           for different releases of PCRE.
755    
756           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
757           pcre_exec() are used for compiling and matching regular expressions  in
758           a  Perl-compatible  manner. A sample program that demonstrates the sim-
759           plest way of using them is provided in the file  called  pcredemo.c  in
760           the  source distribution. The pcresample documentation describes how to
761           run it.
762    
763           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
764           ble,  is  also provided. This uses a different algorithm for the match-
765           ing. The alternative algorithm finds all possible matches (at  a  given
766           point  in  the subject), and scans the subject just once. However, this
767           algorithm does not return captured substrings. A description of the two
768           matching  algorithms and their advantages and disadvantages is given in
769           the pcrematching documentation.
770    
771           In addition to the main compiling and  matching  functions,  there  are
772           convenience functions for extracting captured substrings from a subject
773           string that is matched by pcre_exec(). They are:
774    
775             pcre_copy_substring()
776             pcre_copy_named_substring()
777             pcre_get_substring()
778             pcre_get_named_substring()
779             pcre_get_substring_list()
780             pcre_get_stringnumber()
781             pcre_get_stringtable_entries()
782    
783           pcre_free_substring() and pcre_free_substring_list() are also provided,
784           to free the memory used for extracted strings.
785    
786           The  function  pcre_maketables()  is  used  to build a set of character
787           tables  in  the  current  locale   for   passing   to   pcre_compile(),
788           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
789           provided for specialist use.  Most  commonly,  no  special  tables  are
790           passed,  in  which case internal tables that are generated when PCRE is
791           built are used.
792    
793           The function pcre_fullinfo() is used to find out  information  about  a
794           compiled  pattern; pcre_info() is an obsolete version that returns only
795           some of the available information, but is retained for  backwards  com-
796           patibility.   The function pcre_version() returns a pointer to a string
797           containing the version of PCRE and its date of release.
798    
799           The function pcre_refcount() maintains a  reference  count  in  a  data
800           block  containing  a compiled pattern. This is provided for the benefit
801           of object-oriented applications.
802    
803           The global variables pcre_malloc and pcre_free  initially  contain  the
804           entry  points  of  the  standard malloc() and free() functions, respec-
805           tively. PCRE calls the memory management functions via these variables,
806           so  a  calling  program  can replace them if it wishes to intercept the
807           calls. This should be done before calling any PCRE functions.
808    
809           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
810           indirections  to  memory  management functions. These special functions
811           are used only when PCRE is compiled to use  the  heap  for  remembering
812           data, instead of recursive function calls, when running the pcre_exec()
813           function. See the pcrebuild documentation for  details  of  how  to  do
814           this.  It  is  a non-standard way of building PCRE, for use in environ-
815           ments that have limited stacks. Because of the greater  use  of  memory
816           management,  it  runs  more  slowly. Separate functions are provided so
817           that special-purpose external code can be  used  for  this  case.  When
818           used,  these  functions  are always called in a stack-like manner (last
819           obtained, first freed), and always for memory blocks of the same  size.
820           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
821           mentation.
822    
823           The global variable pcre_callout initially contains NULL. It can be set
824           by  the  caller  to  a "callout" function, which PCRE will then call at
825           specified points during a matching operation. Details are given in  the
826           pcrecallout documentation.
827    
828    
829    NEWLINES
830    
831           PCRE  supports four different conventions for indicating line breaks in
832           strings: a single CR (carriage return) character, a  single  LF  (line-
833           feed)  character,  the two-character sequence CRLF, or any Unicode new-
834           line sequence.  The Unicode newline sequences are the three  just  men-
835           tioned, plus the single characters VT (vertical tab, U+000B), FF (form-
836           feed, U+000C), NEL (next line, U+0085), LS  (line  separator,  U+2028),
837           and PS (paragraph separator, U+2029).
838    
839           Each  of  the first three conventions is used by at least one operating
840           system as its standard newline sequence. When PCRE is built, a  default
841           can  be  specified.  The default default is LF, which is the Unix stan-
842           dard. When PCRE is run, the default can be overridden,  either  when  a
843           pattern is compiled, or when it is matched.
844    
845           In the PCRE documentation the word "newline" is used to mean "the char-
846           acter or pair of characters that indicate a line break". The choice  of
847           newline  convention  affects  the  handling of the dot, circumflex, and
848           dollar metacharacters, the handling of #-comments in /x mode, and, when
849           CRLF  is a recognized line ending sequence, the match position advance-
850           ment for a non-anchored pattern. The choice of newline convention  does
851           not affect the interpretation of the \n or \r escape sequences.
852    
853    
854    MULTITHREADING
855    
856           The  PCRE  functions  can be used in multi-threading applications, with
857           the  proviso  that  the  memory  management  functions  pointed  to  by
858           pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
859           callout function pointed to by pcre_callout, are shared by all threads.
860    
861           The  compiled form of a regular expression is not altered during match-
862           ing, so the same compiled pattern can safely be used by several threads
863           at once.
864    
865    
866    SAVING PRECOMPILED PATTERNS FOR LATER USE
867    
868       The global variables  pcre_malloc  and  pcre_free  initially         The compiled form of a regular expression can be saved and re-used at a
869       contain the entry points of the standard malloc() and free()         later time, possibly by a different program, and even on a  host  other
870       functions respectively. PCRE  calls  the  memory  management         than  the  one  on  which  it  was  compiled.  Details are given in the
871       functions  via  these  variables,  so  a calling program can         pcreprecompile documentation.
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
872    
873    
874    CHECKING BUILD-TIME OPTIONS
875    
876  MULTI-THREADING         int pcre_config(int what, void *where);
      The  PCRE  functions  can   be   used   in   multi-threading  
877    
878           The function pcre_config() makes it possible for a PCRE client to  dis-
879           cover which optional features have been compiled into the PCRE library.
880           The pcrebuild documentation has more details about these optional  fea-
881           tures.
882    
883           The  first  argument  for pcre_config() is an integer, specifying which
884           information is required; the second argument is a pointer to a variable
885           into  which  the  information  is  placed. The following information is
886           available:
887    
888             PCRE_CONFIG_UTF8
889    
890           The output is an integer that is set to one if UTF-8 support is  avail-
891           able; otherwise it is set to zero.
892    
893  SunOS 5.8                 Last change:                          2           PCRE_CONFIG_UNICODE_PROPERTIES
894    
895           The  output  is  an  integer  that is set to one if support for Unicode
896           character properties is available; otherwise it is set to zero.
897    
898             PCRE_CONFIG_NEWLINE
899    
900       applications,  with  the  proviso that the memory management         The output is an integer whose value specifies  the  default  character
901       functions pointed to by pcre_malloc and pcre_free are shared         sequence  that is recognized as meaning "newline". The four values that
902       by all threads.         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, and -1 for ANY.
903           The default should normally be the standard sequence for your operating
904           system.
905    
906       The compiled form of a regular  expression  is  not  altered           PCRE_CONFIG_LINK_SIZE
      during  matching, so the same compiled pattern can safely be  
      used by several threads at once.  
907    
908           The output is an integer that contains the number  of  bytes  used  for
909           internal linkage in compiled regular expressions. The value is 2, 3, or
910           4. Larger values allow larger regular expressions to  be  compiled,  at
911           the  expense  of  slower matching. The default value of 2 is sufficient
912           for all but the most massive patterns, since  it  allows  the  compiled
913           pattern to be up to 64K in size.
914    
915             PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
916    
917           The  output  is  an integer that contains the threshold above which the
918           POSIX interface uses malloc() for output vectors. Further  details  are
919           given in the pcreposix documentation.
920    
921             PCRE_CONFIG_MATCH_LIMIT
922    
923           The output is an integer that gives the default limit for the number of
924           internal matching function calls in a  pcre_exec()  execution.  Further
925           details are given with pcre_exec() below.
926    
927             PCRE_CONFIG_MATCH_LIMIT_RECURSION
928    
929           The  output is an integer that gives the default limit for the depth of
930           recursion when calling the internal matching function in a  pcre_exec()
931           execution. Further details are given with pcre_exec() below.
932    
933             PCRE_CONFIG_STACKRECURSE
934    
935           The  output is an integer that is set to one if internal recursion when
936           running pcre_exec() is implemented by recursive function calls that use
937           the  stack  to remember their state. This is the usual way that PCRE is
938           compiled. The output is zero if PCRE was compiled to use blocks of data
939           on  the  heap  instead  of  recursive  function  calls.  In  this case,
940           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
941           blocks on the heap, thus avoiding the use of the stack.
942    
943    
944  COMPILING A PATTERN  COMPILING A PATTERN
      The function pcre_compile() is called to compile  a  pattern  
      into  an internal form. The pattern is a C string terminated  
      by a binary zero, and is passed in the argument  pattern.  A  
      pointer  to  a  single  block of memory that is obtained via  
      pcre_malloc is returned. This contains the compiled code and  
      related data. The pcre type is defined for this for conveni-  
      ence, but in fact pcre is just a typedef for void, since the  
      contents  of  the block are not externally defined. It is up  
      to the caller to free  the  memory  when  it  is  no  longer  
      required.  
   
      The size of a compiled pattern is  roughly  proportional  to  
      the length of the pattern string, except that each character  
      class (other than those containing just a single  character,  
      negated  or  not)  requires 33 bytes, and repeat quantifiers  
      with a minimum greater than one or a bounded  maximum  cause  
      the  relevant  portions of the compiled pattern to be repli-  
      cated.  
   
      The options argument contains independent bits  that  affect  
      the  compilation.  It  should  be  zero  if  no  options are  
      required. Some of the options, in particular, those that are  
      compatible  with Perl, can also be set and unset from within  
      the pattern (see the detailed description of regular expres-  
      sions below). For these options, the contents of the options  
      argument specifies their initial settings at  the  start  of  
      compilation  and  execution. The PCRE_ANCHORED option can be  
      set at the time of matching as well as at compile time.  
   
      If errptr is NULL, pcre_compile() returns NULL  immediately.  
      Otherwise, if compilation of a pattern fails, pcre_compile()  
      returns NULL, and sets the variable pointed to by errptr  to  
      point  to a textual error message. The offset from the start  
      of  the  pattern  to  the  character  where  the  error  was  
      discovered   is   placed  in  the  variable  pointed  to  by  
      erroffset, which must not be NULL. If it  is,  an  immediate  
      error is given.  
   
      If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a  
      default  set  of character tables which are built when it is  
      compiled, using the default C  locale.  Otherwise,  tableptr  
      must  be  the result of a call to pcre_maketables(). See the  
      section on locale support below.  
   
      The following option bits are defined in the header file:  
   
        PCRE_ANCHORED  
   
      If this bit is set, the pattern is forced to be  "anchored",  
      that is, it is constrained to match only at the start of the  
      string which is being searched (the "subject string").  This  
      effect can also be achieved by appropriate constructs in the  
      pattern itself, which is the only way to do it in Perl.  
   
        PCRE_CASELESS  
   
      If this bit is set, letters in the pattern match both  upper  
      and  lower  case  letters.  It  is  equivalent  to Perl's /i  
      option.  
   
        PCRE_DOLLAR_ENDONLY  
   
      If this bit is set, a dollar metacharacter  in  the  pattern  
      matches  only at the end of the subject string. Without this  
      option, a dollar also matches immediately before  the  final  
      character  if it is a newline (but not before any other new-  
      lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
      PCRE_MULTILINE is set. There is no equivalent to this option  
      in Perl.  
   
        PCRE_DOTALL  
   
      If this bit is  set,  a  dot  metacharater  in  the  pattern  
      matches all characters, including newlines. Without it, new-  
      lines are excluded. This option is equivalent to  Perl's  /s  
      option.  A negative class such as [^a] always matches a new-  
      line character, independent of the setting of this option.  
   
        PCRE_EXTENDED  
   
      If this bit is set, whitespace data characters in  the  pat-  
      tern  are  totally  ignored  except when escaped or inside a  
      character class, and characters between an unescaped #  out-  
      side  a  character  class  and  the  next newline character,  
      inclusive, are also ignored. This is equivalent to Perl's /x  
      option,  and  makes  it  possible to include comments inside  
      complicated patterns. Note, however, that this applies  only  
      to  data  characters. Whitespace characters may never appear  
      within special character sequences in a pattern, for example  
      within  the sequence (?( which introduces a conditional sub-  
      pattern.  
   
        PCRE_EXTRA  
   
      This option was invented in  order  to  turn  on  additional  
      functionality of PCRE that is incompatible with Perl, but it  
      is currently of very little use. When set, any backslash  in  
      a  pattern  that is followed by a letter that has no special  
      meaning causes an error, thus reserving  these  combinations  
      for  future  expansion.  By default, as in Perl, a backslash  
      followed by a letter with no special meaning is treated as a  
      literal.  There  are at present no other features controlled  
      by this option. It can also be set by a (?X) option  setting  
      within a pattern.  
   
        PCRE_MULTILINE  
   
      By default, PCRE treats the subject string as consisting  of  
      a  single "line" of characters (even if it actually contains  
      several newlines). The "start  of  line"  metacharacter  (^)  
      matches  only  at the start of the string, while the "end of  
      line" metacharacter ($) matches  only  at  the  end  of  the  
      string,    or   before   a   terminating   newline   (unless  
      PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.  
   
      When PCRE_MULTILINE it is set, the "start of line" and  "end  
      of  line"  constructs match immediately following or immedi-  
      ately before any newline  in  the  subject  string,  respec-  
      tively,  as  well  as  at  the  very  start and end. This is  
      equivalent to Perl's /m option. If there are no "\n" charac-  
      ters  in  a subject string, or no occurrences of ^ or $ in a  
      pattern, setting PCRE_MULTILINE has no effect.  
   
        PCRE_UNGREEDY  
   
      This option inverts the "greediness" of the  quantifiers  so  
      that  they  are  not greedy by default, but become greedy if  
      followed by "?". It is not compatible with Perl. It can also  
      be set by a (?U) option setting within the pattern.  
   
        PCRE_UTF8  
   
      This option causes PCRE to regard both the pattern  and  the  
      subject  as strings of UTF-8 characters instead of just byte  
      strings. However, it is available  only  if  PCRE  has  been  
      built  to  include  UTF-8  support.  If not, the use of this  
      option provokes an error. Support for UTF-8 is new,  experi-  
      mental,  and incomplete.  Details of exactly what it entails  
      are given below.  
945    
946           pcre *pcre_compile(const char *pattern, int options,
947                const char **errptr, int *erroffset,
948                const unsigned char *tableptr);
949    
950           pcre *pcre_compile2(const char *pattern, int options,
951                int *errorcodeptr,
952                const char **errptr, int *erroffset,
953                const unsigned char *tableptr);
954    
955           Either of the functions pcre_compile() or pcre_compile2() can be called
956           to compile a pattern into an internal form. The only difference between
957           the  two interfaces is that pcre_compile2() has an additional argument,
958           errorcodeptr, via which a numerical error code can be returned.
959    
960           The pattern is a C string terminated by a binary zero, and is passed in
961           the  pattern  argument.  A  pointer to a single block of memory that is
962           obtained via pcre_malloc is returned. This contains the  compiled  code
963           and related data. The pcre type is defined for the returned block; this
964           is a typedef for a structure whose contents are not externally defined.
965           It is up to the caller to free the memory (via pcre_free) when it is no
966           longer required.
967    
968           Although the compiled code of a PCRE regex is relocatable, that is,  it
969           does not depend on memory location, the complete pcre data block is not
970           fully relocatable, because it may contain a copy of the tableptr  argu-
971           ment, which is an address (see below).
972    
973           The options argument contains various bit settings that affect the com-
974           pilation. It should be zero if no options are required.  The  available
975           options  are  described  below. Some of them, in particular, those that
976           are compatible with Perl, can also be set and  unset  from  within  the
977           pattern  (see  the  detailed  description in the pcrepattern documenta-
978           tion). For these options, the contents of the options  argument  speci-
979           fies  their initial settings at the start of compilation and execution.
980           The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
981           of matching as well as at compile time.
982    
983           If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
984           if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
985           sets the variable pointed to by errptr to point to a textual error mes-
986           sage. This is a static string that is part of the library. You must not
987           try to free it. The offset from the start of the pattern to the charac-
988           ter where the error was discovered is placed in the variable pointed to
989           by  erroffset,  which must not be NULL. If it is, an immediate error is
990           given.
991    
992           If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
993           codeptr  argument is not NULL, a non-zero error code number is returned
994           via this argument in the event of an error. This is in addition to  the
995           textual error message. Error codes and messages are listed below.
996    
997           If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
998           character tables that are  built  when  PCRE  is  compiled,  using  the
999           default  C  locale.  Otherwise, tableptr must be an address that is the
1000           result of a call to pcre_maketables(). This value is  stored  with  the
1001           compiled  pattern,  and used again by pcre_exec(), unless another table
1002           pointer is passed to it. For more discussion, see the section on locale
1003           support below.
1004    
1005           This  code  fragment  shows a typical straightforward call to pcre_com-
1006           pile():
1007    
1008             pcre *re;
1009             const char *error;
1010             int erroffset;
1011             re = pcre_compile(
1012               "^A.*Z",          /* the pattern */
1013               0,                /* default options */
1014               &error,           /* for error message */
1015               &erroffset,       /* for error offset */
1016               NULL);            /* use default character tables */
1017    
1018           The following names for option bits are defined in  the  pcre.h  header
1019           file:
1020    
1021             PCRE_ANCHORED
1022    
1023           If this bit is set, the pattern is forced to be "anchored", that is, it
1024           is constrained to match only at the first matching point in the  string
1025           that  is being searched (the "subject string"). This effect can also be
1026           achieved by appropriate constructs in the pattern itself, which is  the
1027           only way to do it in Perl.
1028    
1029             PCRE_AUTO_CALLOUT
1030    
1031           If this bit is set, pcre_compile() automatically inserts callout items,
1032           all with number 255, before each pattern item. For  discussion  of  the
1033           callout facility, see the pcrecallout documentation.
1034    
1035             PCRE_CASELESS
1036    
1037           If  this  bit is set, letters in the pattern match both upper and lower
1038           case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
1039           changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1040           always understands the concept of case for characters whose values  are
1041           less  than 128, so caseless matching is always possible. For characters
1042           with higher values, the concept of case is supported if  PCRE  is  com-
1043           piled  with Unicode property support, but not otherwise. If you want to
1044           use caseless matching for characters 128 and  above,  you  must  ensure
1045           that  PCRE  is  compiled  with Unicode property support as well as with
1046           UTF-8 support.
1047    
1048             PCRE_DOLLAR_ENDONLY
1049    
1050           If this bit is set, a dollar metacharacter in the pattern matches  only
1051           at  the  end  of the subject string. Without this option, a dollar also
1052           matches immediately before a newline at the end of the string (but  not
1053           before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1054           if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
1055           Perl, and no way to set it within a pattern.
1056    
1057             PCRE_DOTALL
1058    
1059           If this bit is set, a dot metacharater in the pattern matches all char-
1060           acters, including those that indicate newline. Without it, a  dot  does
1061           not  match  when  the  current position is at a newline. This option is
1062           equivalent to Perl's /s option, and it can be changed within a  pattern
1063           by  a (?s) option setting. A negative class such as [^a] always matches
1064           newline characters, independent of the setting of this option.
1065    
1066             PCRE_DUPNAMES
1067    
1068           If this bit is set, names used to identify capturing  subpatterns  need
1069           not be unique. This can be helpful for certain types of pattern when it
1070           is known that only one instance of the named  subpattern  can  ever  be
1071           matched.  There  are  more details of named subpatterns below; see also
1072           the pcrepattern documentation.
1073    
1074             PCRE_EXTENDED
1075    
1076           If this bit is set, whitespace  data  characters  in  the  pattern  are
1077           totally ignored except when escaped or inside a character class. White-
1078           space does not include the VT character (code 11). In addition, charac-
1079           ters between an unescaped # outside a character class and the next new-
1080           line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1081           option,  and  it  can be changed within a pattern by a (?x) option set-
1082           ting.
1083    
1084           This option makes it possible to include  comments  inside  complicated
1085           patterns.   Note,  however,  that this applies only to data characters.
1086           Whitespace  characters  may  never  appear  within  special   character
1087           sequences  in  a  pattern,  for  example  within the sequence (?( which
1088           introduces a conditional subpattern.
1089    
1090             PCRE_EXTRA
1091    
1092           This option was invented in order to turn on  additional  functionality
1093           of  PCRE  that  is  incompatible with Perl, but it is currently of very
1094           little use. When set, any backslash in a pattern that is followed by  a
1095           letter  that  has  no  special  meaning causes an error, thus reserving
1096           these combinations for future expansion. By  default,  as  in  Perl,  a
1097           backslash  followed by a letter with no special meaning is treated as a
1098           literal. (Perl can, however, be persuaded to give a warning for  this.)
1099           There  are  at  present no other features controlled by this option. It
1100           can also be set by a (?X) option setting within a pattern.
1101    
1102             PCRE_FIRSTLINE
1103    
1104           If this option is set, an  unanchored  pattern  is  required  to  match
1105           before  or  at  the  first  newline  in  the subject string, though the
1106           matched text may continue over the newline.
1107    
1108             PCRE_MULTILINE
1109    
1110           By default, PCRE treats the subject string as consisting  of  a  single
1111           line  of characters (even if it actually contains newlines). The "start
1112           of line" metacharacter (^) matches only at the  start  of  the  string,
1113           while  the  "end  of line" metacharacter ($) matches only at the end of
1114           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1115           is set). This is the same as Perl.
1116    
1117           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1118           constructs match immediately following or immediately  before  internal
1119           newlines  in  the  subject string, respectively, as well as at the very
1120           start and end. This is equivalent to Perl's /m option, and  it  can  be
1121           changed within a pattern by a (?m) option setting. If there are no new-
1122           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1123           setting PCRE_MULTILINE has no effect.
1124    
1125             PCRE_NEWLINE_CR
1126             PCRE_NEWLINE_LF
1127             PCRE_NEWLINE_CRLF
1128             PCRE_NEWLINE_ANY
1129    
1130           These  options  override the default newline definition that was chosen
1131           when PCRE was built. Setting the first or the second specifies  that  a
1132           newline  is  indicated  by a single character (CR or LF, respectively).
1133           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1134           two-character  CRLF  sequence.  Setting PCRE_NEWLINE_ANY specifies that
1135           any Unicode newline sequence should be recognized. The Unicode  newline
1136           sequences  are  the three just mentioned, plus the single characters VT
1137           (vertical tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085),
1138           LS  (line separator, U+2028), and PS (paragraph separator, U+2029). The
1139           last two are recognized only in UTF-8 mode.
1140    
1141           The newline setting in the  options  word  uses  three  bits  that  are
1142           treated  as  a  number, giving eight possibilities. Currently only five
1143           are used (default plus the four values above). This means that  if  you
1144           set  more  than  one  newline option, the combination may or may not be
1145           sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is  equiva-
1146           lent  to PCRE_NEWLINE_CRLF, but other combinations yield unused numbers
1147           and cause an error.
1148    
1149           The only time that a line break is specially recognized when  compiling
1150           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1151           character class is encountered. This indicates  a  comment  that  lasts
1152           until  after the next line break sequence. In other circumstances, line
1153           break  sequences  are  treated  as  literal  data,   except   that   in
1154           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1155           and are therefore ignored.
1156    
1157           The newline option that is set at compile time becomes the default that
1158           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1159    
1160             PCRE_NO_AUTO_CAPTURE
1161    
1162           If this option is set, it disables the use of numbered capturing paren-
1163           theses  in the pattern. Any opening parenthesis that is not followed by
1164           ? behaves as if it were followed by ?: but named parentheses can  still
1165           be  used  for  capturing  (and  they acquire numbers in the usual way).
1166           There is no equivalent of this option in Perl.
1167    
1168             PCRE_UNGREEDY
1169    
1170           This option inverts the "greediness" of the quantifiers  so  that  they
1171           are  not greedy by default, but become greedy if followed by "?". It is
1172           not compatible with Perl. It can also be set by a (?U)  option  setting
1173           within the pattern.
1174    
1175             PCRE_UTF8
1176    
1177           This  option  causes PCRE to regard both the pattern and the subject as
1178           strings of UTF-8 characters instead of single-byte  character  strings.
1179           However,  it is available only when PCRE is built to include UTF-8 sup-
1180           port. If not, the use of this option provokes an error. Details of  how
1181           this  option  changes the behaviour of PCRE are given in the section on
1182           UTF-8 support in the main pcre page.
1183    
1184             PCRE_NO_UTF8_CHECK
1185    
1186           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1187           automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1188           pcre_compile() returns an error. If you already know that your  pattern
1189           is  valid, and you want to skip this check for performance reasons, you
1190           can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1191           passing an invalid UTF-8 string as a pattern is undefined. It may cause
1192           your program to crash.  Note that this option can  also  be  passed  to
1193           pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1194           ing of subject strings.
1195    
1196    
1197    COMPILATION ERROR CODES
1198    
1199           The following table lists the error  codes  than  may  be  returned  by
1200           pcre_compile2(),  along with the error messages that may be returned by
1201           both compiling functions. As PCRE has developed, some error codes  have
1202           fallen out of use. To avoid confusion, they have not been re-used.
1203    
1204              0  no error
1205              1  \ at end of pattern
1206              2  \c at end of pattern
1207              3  unrecognized character follows \
1208              4  numbers out of order in {} quantifier
1209              5  number too big in {} quantifier
1210              6  missing terminating ] for character class
1211              7  invalid escape sequence in character class
1212              8  range out of order in character class
1213              9  nothing to repeat
1214             10  [this code is not in use]
1215             11  internal error: unexpected repeat
1216             12  unrecognized character after (?
1217             13  POSIX named classes are supported only within a class
1218             14  missing )
1219             15  reference to non-existent subpattern
1220             16  erroffset passed as NULL
1221             17  unknown option bit(s) set
1222             18  missing ) after comment
1223             19  [this code is not in use]
1224             20  regular expression too large
1225             21  failed to get memory
1226             22  unmatched parentheses
1227             23  internal error: code overflow
1228             24  unrecognized character after (?<
1229             25  lookbehind assertion is not fixed length
1230             26  malformed number or name after (?(
1231             27  conditional group contains more than two branches
1232             28  assertion expected after (?(
1233             29  (?R or (?digits must be followed by )
1234             30  unknown POSIX class name
1235             31  POSIX collating elements are not supported
1236             32  this version of PCRE is not compiled with PCRE_UTF8 support
1237             33  [this code is not in use]
1238             34  character value in \x{...} sequence is too large
1239             35  invalid condition (?(0)
1240             36  \C not allowed in lookbehind assertion
1241             37  PCRE does not support \L, \l, \N, \U, or \u
1242             38  number after (?C is > 255
1243             39  closing ) for (?C expected
1244             40  recursive call could loop indefinitely
1245             41  unrecognized character after (?P
1246             42  syntax error in subpattern name (missing terminator)
1247             43  two named subpatterns have the same name
1248             44  invalid UTF-8 string
1249             45  support for \P, \p, and \X has not been compiled
1250             46  malformed \P or \p sequence
1251             47  unknown property name after \P or \p
1252             48  subpattern name is too long (maximum 32 characters)
1253             49  too many named subpatterns (maximum 10,000)
1254             50  repeated subpattern is too long
1255             51  octal value is greater than \377 (not in UTF-8 mode)
1256             52  internal error: overran compiling workspace
1257             53   internal  error:  previously-checked  referenced  subpattern not
1258           found
1259             54  DEFINE group contains more than one branch
1260             55  repeating a DEFINE group is not allowed
1261             56  inconsistent NEWLINE options"
1262    
1263    
1264  STUDYING A PATTERN  STUDYING A PATTERN
      When a pattern is going to be  used  several  times,  it  is  
      worth  spending  more time analyzing it in order to speed up  
      the time taken for matching. The function pcre_study() takes  
   
      a  pointer  to a compiled pattern as its first argument, and  
      returns a  pointer  to  a  pcre_extra  block  (another  void  
      typedef)  containing  additional  information about the pat-  
      tern; this can be passed to pcre_exec().  If  no  additional  
      information is available, NULL is returned.  
   
      The second argument contains option  bits.  At  present,  no  
      options  are  defined  for  pcre_study(),  and this argument  
      should always be zero.  
   
      The third argument for pcre_study() is a pointer to an error  
      message. If studying succeeds (even if no data is returned),  
      the variable it points to  is  set  to  NULL.  Otherwise  it  
      points to a textual error message.  
   
      At present, studying a  pattern  is  useful  only  for  non-  
      anchored  patterns  that do not have a single fixed starting  
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1265    
1266           pcre_extra *pcre_study(const pcre *code, int options
1267                const char **errptr);
1268    
1269           If a compiled pattern is going to be used several times,  it  is  worth
1270           spending more time analyzing it in order to speed up the time taken for
1271           matching. The function pcre_study() takes a pointer to a compiled  pat-
1272           tern as its first argument. If studying the pattern produces additional
1273           information that will help speed up matching,  pcre_study()  returns  a
1274           pointer  to a pcre_extra block, in which the study_data field points to
1275           the results of the study.
1276    
1277           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1278           pcre_exec().  However,  a  pcre_extra  block also contains other fields
1279           that can be set by the caller before the block  is  passed;  these  are
1280           described below in the section on matching a pattern.
1281    
1282           If  studying  the  pattern  does not produce any additional information
1283           pcre_study() returns NULL. In that circumstance, if the calling program
1284           wants  to  pass  any of the other fields to pcre_exec(), it must set up
1285           its own pcre_extra block.
1286    
1287           The second argument of pcre_study() contains option bits.  At  present,
1288           no options are defined, and this argument should always be zero.
1289    
1290           The  third argument for pcre_study() is a pointer for an error message.
1291           If studying succeeds (even if no data is  returned),  the  variable  it
1292           points  to  is  set  to NULL. Otherwise it is set to point to a textual
1293           error message. This is a static string that is part of the library. You
1294           must  not  try  to  free it. You should test the error pointer for NULL
1295           after calling pcre_study(), to be sure that it has run successfully.
1296    
1297           This is a typical call to pcre_study():
1298    
1299             pcre_extra *pe;
1300             pe = pcre_study(
1301               re,             /* result of pcre_compile() */
1302               0,              /* no options exist */
1303               &error);        /* set to NULL or points to a message */
1304    
1305           At present, studying a pattern is useful only for non-anchored patterns
1306           that  do not have a single fixed starting character. A bitmap of possi-
1307           ble starting bytes is created.
1308    
1309    
1310  LOCALE SUPPORT  LOCALE SUPPORT
      PCRE handles caseless matching, and determines whether char-  
      acters  are  letters, digits, or whatever, by reference to a  
      set of tables. The library contains a default set of  tables  
      which  is  created in the default C locale when PCRE is com-  
      piled.  This  is   used   when   the   final   argument   of  
      pcre_compile()  is NULL, and is sufficient for many applica-  
      tions.  
   
      An alternative set of tables can, however, be supplied. Such  
      tables  are built by calling the pcre_maketables() function,  
      which has no arguments, in the relevant locale.  The  result  
      can  then be passed to pcre_compile() as often as necessary.  
      For example, to build and use tables  that  are  appropriate  
      for  the French locale (where accented characters with codes  
      greater than 128 are treated as letters), the following code  
      could be used:  
   
        setlocale(LC_CTYPE, "fr");  
        tables = pcre_maketables();  
        re = pcre_compile(..., tables);  
   
      The  tables  are  built  in  memory  that  is  obtained  via  
      pcre_malloc.  The  pointer that is passed to pcre_compile is  
      saved with the compiled pattern, and  the  same  tables  are  
      used  via this pointer by pcre_study() and pcre_exec(). Thus  
      for any single pattern, compilation, studying  and  matching  
      all happen in the same locale, but different patterns can be  
      compiled in different locales. It is the caller's  responsi-  
      bility  to  ensure  that  the  memory  containing the tables  
      remains available for as long as it is needed.  
1311    
1312           PCRE handles caseless matching, and determines whether  characters  are
1313           letters  digits,  or whatever, by reference to a set of tables, indexed
1314           by character value. When running in UTF-8 mode, this  applies  only  to
1315           characters  with  codes  less than 128. Higher-valued codes never match
1316           escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1317           with  Unicode  character property support. The use of locales with Uni-
1318           code is discouraged.
1319    
1320           An internal set of tables is created in the default C locale when  PCRE
1321           is  built.  This  is  used when the final argument of pcre_compile() is
1322           NULL, and is sufficient for many applications. An  alternative  set  of
1323           tables  can,  however, be supplied. These may be created in a different
1324           locale from the default. As more and more applications change to  using
1325           Unicode, the need for this locale support is expected to die away.
1326    
1327           External  tables  are  built by calling the pcre_maketables() function,
1328           which has no arguments, in the relevant locale. The result can then  be
1329           passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1330           example, to build and use tables that are appropriate  for  the  French
1331           locale  (where  accented  characters  with  values greater than 128 are
1332           treated as letters), the following code could be used:
1333    
1334             setlocale(LC_CTYPE, "fr_FR");
1335             tables = pcre_maketables();
1336             re = pcre_compile(..., tables);
1337    
1338           When pcre_maketables() runs, the tables are built  in  memory  that  is
1339           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1340           that the memory containing the tables remains available for as long  as
1341           it is needed.
1342    
1343           The pointer that is passed to pcre_compile() is saved with the compiled
1344           pattern, and the same tables are used via this pointer by  pcre_study()
1345           and normally also by pcre_exec(). Thus, by default, for any single pat-
1346           tern, compilation, studying and matching all happen in the same locale,
1347           but different patterns can be compiled in different locales.
1348    
1349           It  is  possible to pass a table pointer or NULL (indicating the use of
1350           the internal tables) to pcre_exec(). Although  not  intended  for  this
1351           purpose,  this facility could be used to match a pattern in a different
1352           locale from the one in which it was compiled. Passing table pointers at
1353           run time is discussed below in the section on matching a pattern.
1354    
1355    
1356  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
      The pcre_fullinfo() function  returns  information  about  a  
      compiled pattern. It replaces the obsolete pcre_info() func-  
      tion, which is nevertheless retained for backwards compabil-  
      ity (and is documented below).  
   
      The first argument for pcre_fullinfo() is a pointer  to  the  
      compiled  pattern.  The  second  argument  is  the result of  
      pcre_study(), or NULL if the pattern was  not  studied.  The  
      third  argument  specifies  which  piece  of  information is  
      required, while the fourth argument is a pointer to a  vari-  
      able  to receive the data. The yield of the function is zero  
      for success, or one of the following negative numbers:  
   
        PCRE_ERROR_NULL       the argument code was NULL  
                              the argument where was NULL  
        PCRE_ERROR_BADMAGIC   the "magic number" was not found  
        PCRE_ERROR_BADOPTION  the value of what was invalid  
   
      The possible values for the third argument  are  defined  in  
      pcre.h, and are as follows:  
   
        PCRE_INFO_OPTIONS  
   
      Return a copy of the options with which the pattern was com-  
      piled.  The fourth argument should point to au unsigned long  
      int variable. These option bits are those specified  in  the  
      call  to  pcre_compile(),  modified  by any top-level option  
      settings  within  the   pattern   itself,   and   with   the  
      PCRE_ANCHORED  bit  forcibly  set if the form of the pattern  
      implies that it can match only at the  start  of  a  subject  
      string.  
   
        PCRE_INFO_SIZE  
   
      Return the size of the compiled pattern, that is, the  value  
      that  was  passed as the argument to pcre_malloc() when PCRE  
      was getting memory in which to place the compiled data.  The  
      fourth argument should point to a size_t variable.  
   
        PCRE_INFO_CAPTURECOUNT  
   
      Return the number of capturing subpatterns in  the  pattern.  
      The fourth argument should point to an int variable.  
   
        PCRE_INFO_BACKREFMAX  
   
      Return the number of  the  highest  back  reference  in  the  
      pattern.  The  fourth  argument should point to an int vari-  
      able. Zero is returned if there are no back references.  
   
        PCRE_INFO_FIRSTCHAR  
   
      Return information about the first character of any  matched  
      string,  for  a  non-anchored  pattern.  If there is a fixed  
      first   character,   e.g.   from   a   pattern    such    as  
      (cat|cow|coyote),  it  is returned in the integer pointed to  
      by where. Otherwise, if either  
   
      (a) the pattern was compiled with the PCRE_MULTILINE option,  
      and every branch starts with "^", or  
   
      (b) every  branch  of  the  pattern  starts  with  ".*"  and  
      PCRE_DOTALL is not set (if it were set, the pattern would be  
      anchored),  
   
      -1 is returned, indicating that the pattern matches only  at  
      the  start  of a subject string or after any "\n" within the  
      string. Otherwise -2 is returned.  For anchored patterns, -2  
      is returned.  
   
        PCRE_INFO_FIRSTTABLE  
   
      If the pattern was studied, and this resulted  in  the  con-  
      struction of a 256-bit table indicating a fixed set of char-  
      acters for the first character in  any  matching  string,  a  
      pointer   to  the  table  is  returned.  Otherwise  NULL  is  
      returned. The fourth argument should point  to  an  unsigned  
      char * variable.  
   
        PCRE_INFO_LASTLITERAL  
   
      For a non-anchored pattern, return the value of  the  right-  
      most  literal  character  which  must  exist  in any matched  
      string, other than at its start. The fourth argument  should  
      point  to an int variable. If there is no such character, or  
      if the pattern is anchored, -1 is returned. For example, for  
      the pattern /a\d+z\d+/ the returned value is 'z'.  
   
      The pcre_info() function is now obsolete because its  inter-  
      face  is  too  restrictive  to return all the available data  
      about  a  compiled  pattern.   New   programs   should   use  
      pcre_fullinfo()  instead.  The  yield  of pcre_info() is the  
      number of capturing subpatterns, or  one  of  the  following  
      negative numbers:  
   
        PCRE_ERROR_NULL       the argument code was NULL  
        PCRE_ERROR_BADMAGIC   the "magic number" was not found  
   
      If the optptr argument is not NULL, a copy  of  the  options  
      with which the pattern was compiled is placed in the integer  
      it points to (see PCRE_INFO_OPTIONS above).  
   
      If the pattern is not anchored and the firstcharptr argument  
      is  not  NULL, it is used to pass back information about the  
      first    character    of    any    matched    string    (see  
      PCRE_INFO_FIRSTCHAR above).  
1357    
1358           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1359                int what, void *where);
1360    
1361           The  pcre_fullinfo() function returns information about a compiled pat-
1362           tern. It replaces the obsolete pcre_info() function, which is neverthe-
1363           less retained for backwards compability (and is documented below).
1364    
1365           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1366           pattern. The second argument is the result of pcre_study(), or NULL  if
1367           the  pattern  was not studied. The third argument specifies which piece
1368           of information is required, and the fourth argument is a pointer  to  a
1369           variable  to  receive  the  data. The yield of the function is zero for
1370           success, or one of the following negative numbers:
1371    
1372             PCRE_ERROR_NULL       the argument code was NULL
1373                                   the argument where was NULL
1374             PCRE_ERROR_BADMAGIC   the "magic number" was not found
1375             PCRE_ERROR_BADOPTION  the value of what was invalid
1376    
1377           The "magic number" is placed at the start of each compiled  pattern  as
1378           an  simple check against passing an arbitrary memory pointer. Here is a
1379           typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1380           pattern:
1381    
1382             int rc;
1383             size_t length;
1384             rc = pcre_fullinfo(
1385               re,               /* result of pcre_compile() */
1386               pe,               /* result of pcre_study(), or NULL */
1387               PCRE_INFO_SIZE,   /* what is required */
1388               &length);         /* where to put the data */
1389    
1390           The  possible  values for the third argument are defined in pcre.h, and
1391           are as follows:
1392    
1393             PCRE_INFO_BACKREFMAX
1394    
1395           Return the number of the highest back reference  in  the  pattern.  The
1396           fourth  argument  should  point to an int variable. Zero is returned if
1397           there are no back references.
1398    
1399             PCRE_INFO_CAPTURECOUNT
1400    
1401           Return the number of capturing subpatterns in the pattern.  The  fourth
1402           argument should point to an int variable.
1403    
1404             PCRE_INFO_DEFAULT_TABLES
1405    
1406           Return  a pointer to the internal default character tables within PCRE.
1407           The fourth argument should point to an unsigned char *  variable.  This
1408           information call is provided for internal use by the pcre_study() func-
1409           tion. External callers can cause PCRE to use  its  internal  tables  by
1410           passing a NULL table pointer.
1411    
1412             PCRE_INFO_FIRSTBYTE
1413    
1414           Return  information  about  the first byte of any matched string, for a
1415           non-anchored pattern. The fourth argument should point to an int  vari-
1416           able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1417           is still recognized for backwards compatibility.)
1418    
1419           If there is a fixed first byte, for example, from  a  pattern  such  as
1420           (cat|cow|coyote), its value is returned. Otherwise, if either
1421    
1422           (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1423           branch starts with "^", or
1424    
1425           (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1426           set (if it were set, the pattern would be anchored),
1427    
1428           -1  is  returned, indicating that the pattern matches only at the start
1429           of a subject string or after any newline within the  string.  Otherwise
1430           -2 is returned. For anchored patterns, -2 is returned.
1431    
1432             PCRE_INFO_FIRSTTABLE
1433    
1434           If  the pattern was studied, and this resulted in the construction of a
1435           256-bit table indicating a fixed set of bytes for the first byte in any
1436           matching  string, a pointer to the table is returned. Otherwise NULL is
1437           returned. The fourth argument should point to an unsigned char *  vari-
1438           able.
1439    
1440             PCRE_INFO_LASTLITERAL
1441    
1442           Return  the  value of the rightmost literal byte that must exist in any
1443           matched string, other than at its  start,  if  such  a  byte  has  been
1444           recorded. The fourth argument should point to an int variable. If there
1445           is no such byte, -1 is returned. For anchored patterns, a last  literal
1446           byte  is  recorded only if it follows something of variable length. For
1447           example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1448           /^a\dz\d/ the returned value is -1.
1449    
1450             PCRE_INFO_NAMECOUNT
1451             PCRE_INFO_NAMEENTRYSIZE
1452             PCRE_INFO_NAMETABLE
1453    
1454           PCRE  supports the use of named as well as numbered capturing parenthe-
1455           ses. The names are just an additional way of identifying the  parenthe-
1456           ses, which still acquire numbers. Several convenience functions such as
1457           pcre_get_named_substring() are provided for  extracting  captured  sub-
1458           strings  by  name. It is also possible to extract the data directly, by
1459           first converting the name to a number in order to  access  the  correct
1460           pointers in the output vector (described with pcre_exec() below). To do
1461           the conversion, you need  to  use  the  name-to-number  map,  which  is
1462           described by these three values.
1463    
1464           The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1465           gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1466           of  each  entry;  both  of  these  return  an int value. The entry size
1467           depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1468           a  pointer  to  the  first  entry of the table (a pointer to char). The
1469           first two bytes of each entry are the number of the capturing parenthe-
1470           sis,  most  significant byte first. The rest of the entry is the corre-
1471           sponding name, zero terminated. The names are  in  alphabetical  order.
1472           When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1473           theses numbers. For example, consider  the  following  pattern  (assume
1474           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1475           ignored):
1476    
1477             (?<date> (?<year>(\d\d)?\d\d) -
1478             (?<month>\d\d) - (?<day>\d\d) )
1479    
1480           There are four named subpatterns, so the table has  four  entries,  and
1481           each  entry  in the table is eight bytes long. The table is as follows,
1482           with non-printing bytes shows in hexadecimal, and undefined bytes shown
1483           as ??:
1484    
1485             00 01 d  a  t  e  00 ??
1486             00 05 d  a  y  00 ?? ??
1487             00 04 m  o  n  t  h  00
1488             00 02 y  e  a  r  00 ??
1489    
1490           When  writing  code  to  extract  data from named subpatterns using the
1491           name-to-number map, remember that the length of the entries  is  likely
1492           to be different for each compiled pattern.
1493    
1494             PCRE_INFO_OPTIONS
1495    
1496           Return  a  copy of the options with which the pattern was compiled. The
1497           fourth argument should point to an unsigned long  int  variable.  These
1498           option bits are those specified in the call to pcre_compile(), modified
1499           by any top-level option settings within the pattern itself.
1500    
1501           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1502           alternatives begin with one of the following:
1503    
1504             ^     unless PCRE_MULTILINE is set
1505             \A    always
1506             \G    always
1507             .*    if PCRE_DOTALL is set and there are no back
1508                     references to the subpattern in which .* appears
1509    
1510           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1511           by pcre_fullinfo().
1512    
1513             PCRE_INFO_SIZE
1514    
1515           Return the size of the compiled pattern, that is, the  value  that  was
1516           passed as the argument to pcre_malloc() when PCRE was getting memory in
1517           which to place the compiled data. The fourth argument should point to a
1518           size_t variable.
1519    
1520             PCRE_INFO_STUDYSIZE
1521    
1522           Return the size of the data block pointed to by the study_data field in
1523           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1524           pcre_malloc() when PCRE was getting memory into which to place the data
1525           created by pcre_study(). The fourth argument should point to  a  size_t
1526           variable.
1527    
1528    
1529    OBSOLETE INFO FUNCTION
1530    
1531           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1532    
1533           The  pcre_info()  function is now obsolete because its interface is too
1534           restrictive to return all the available data about a compiled  pattern.
1535           New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1536           pcre_info() is the number of capturing subpatterns, or one of the  fol-
1537           lowing negative numbers:
1538    
1539             PCRE_ERROR_NULL       the argument code was NULL
1540             PCRE_ERROR_BADMAGIC   the "magic number" was not found
1541    
1542           If  the  optptr  argument is not NULL, a copy of the options with which
1543           the pattern was compiled is placed in the integer  it  points  to  (see
1544           PCRE_INFO_OPTIONS above).
1545    
1546           If  the  pattern  is  not anchored and the firstcharptr argument is not
1547           NULL, it is used to pass back information about the first character  of
1548           any matched string (see PCRE_INFO_FIRSTBYTE above).
1549    
1550    
1551    REFERENCE COUNTS
1552    
1553           int pcre_refcount(pcre *code, int adjust);
1554    
1555           The  pcre_refcount()  function is used to maintain a reference count in
1556           the data block that contains a compiled pattern. It is provided for the
1557           benefit  of  applications  that  operate  in an object-oriented manner,
1558           where different parts of the application may be using the same compiled
1559           pattern, but you want to free the block when they are all done.
1560    
1561           When a pattern is compiled, the reference count field is initialized to
1562           zero.  It is changed only by calling this function, whose action is  to
1563           add  the  adjust  value  (which may be positive or negative) to it. The
1564           yield of the function is the new value. However, the value of the count
1565           is  constrained to lie between 0 and 65535, inclusive. If the new value
1566           is outside these limits, it is forced to the appropriate limit value.
1567    
1568           Except when it is zero, the reference count is not correctly  preserved
1569           if  a  pattern  is  compiled on one host and then transferred to a host
1570           whose byte-order is different. (This seems a highly unlikely scenario.)
1571    
1572    
1573    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1574    
1575           int pcre_exec(const pcre *code, const pcre_extra *extra,
1576                const char *subject, int length, int startoffset,
1577                int options, int *ovector, int ovecsize);
1578    
1579           The  function pcre_exec() is called to match a subject string against a
1580           compiled pattern, which is passed in the code argument. If the  pattern
1581           has been studied, the result of the study should be passed in the extra
1582           argument. This function is the main matching facility of  the  library,
1583           and it operates in a Perl-like manner. For specialist use there is also
1584           an alternative matching function, which is described below in the  sec-
1585           tion about the pcre_dfa_exec() function.
1586    
1587           In  most applications, the pattern will have been compiled (and option-
1588           ally studied) in the same process that calls pcre_exec().  However,  it
1589           is possible to save compiled patterns and study data, and then use them
1590           later in different processes, possibly even on different hosts.  For  a
1591           discussion about this, see the pcreprecompile documentation.
1592    
1593           Here is an example of a simple call to pcre_exec():
1594    
1595             int rc;
1596             int ovector[30];
1597             rc = pcre_exec(
1598               re,             /* result of pcre_compile() */
1599               NULL,           /* we didn't study the pattern */
1600               "some string",  /* the subject string */
1601               11,             /* the length of the subject string */
1602               0,              /* start at offset 0 in the subject */
1603               0,              /* default options */
1604               ovector,        /* vector of integers for substring information */
1605               30);            /* number of elements (NOT size in bytes) */
1606    
1607       Extra data for pcre_exec()
1608    
1609           If  the  extra argument is not NULL, it must point to a pcre_extra data
1610           block. The pcre_study() function returns such a block (when it  doesn't
1611           return  NULL), but you can also create one for yourself, and pass addi-
1612           tional information in it. The pcre_extra block contains  the  following
1613           fields (not necessarily in this order):
1614    
1615             unsigned long int flags;
1616             void *study_data;
1617             unsigned long int match_limit;
1618             unsigned long int match_limit_recursion;
1619             void *callout_data;
1620             const unsigned char *tables;
1621    
1622           The  flags  field  is a bitmap that specifies which of the other fields
1623           are set. The flag bits are:
1624    
1625             PCRE_EXTRA_STUDY_DATA
1626             PCRE_EXTRA_MATCH_LIMIT
1627             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1628             PCRE_EXTRA_CALLOUT_DATA
1629             PCRE_EXTRA_TABLES
1630    
1631           Other flag bits should be set to zero. The study_data field is  set  in
1632           the  pcre_extra  block  that is returned by pcre_study(), together with
1633           the appropriate flag bit. You should not set this yourself, but you may
1634           add  to  the  block by setting the other fields and their corresponding
1635           flag bits.
1636    
1637           The match_limit field provides a means of preventing PCRE from using up
1638           a  vast amount of resources when running patterns that are not going to
1639           match, but which have a very large number  of  possibilities  in  their
1640           search  trees.  The  classic  example  is  the  use of nested unlimited
1641           repeats.
1642    
1643           Internally, PCRE uses a function called match() which it calls  repeat-
1644           edly  (sometimes  recursively). The limit set by match_limit is imposed
1645           on the number of times this function is called during  a  match,  which
1646           has  the  effect  of  limiting the amount of backtracking that can take
1647           place. For patterns that are not anchored, the count restarts from zero
1648           for each position in the subject string.
1649    
1650           The  default  value  for  the  limit can be set when PCRE is built; the
1651           default default is 10 million, which handles all but the  most  extreme
1652           cases.  You  can  override  the  default by suppling pcre_exec() with a
1653           pcre_extra    block    in    which    match_limit    is    set,     and
1654           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1655           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1656    
1657           The match_limit_recursion field is similar to match_limit, but  instead
1658           of limiting the total number of times that match() is called, it limits
1659           the depth of recursion. The recursion depth is a  smaller  number  than
1660           the  total number of calls, because not all calls to match() are recur-
1661           sive.  This limit is of use only if it is set smaller than match_limit.
1662    
1663           Limiting  the  recursion  depth  limits the amount of stack that can be
1664           used, or, when PCRE has been compiled to use memory on the heap instead
1665           of the stack, the amount of heap memory that can be used.
1666    
1667           The  default  value  for  match_limit_recursion can be set when PCRE is
1668           built; the default default  is  the  same  value  as  the  default  for
1669           match_limit.  You can override the default by suppling pcre_exec() with
1670           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1671           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1672           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1673    
1674           The pcre_callout field is used in conjunction with the  "callout"  fea-
1675           ture, which is described in the pcrecallout documentation.
1676    
1677           The  tables  field  is  used  to  pass  a  character  tables pointer to
1678           pcre_exec(); this overrides the value that is stored with the  compiled
1679           pattern.  A  non-NULL value is stored with the compiled pattern only if
1680           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1681           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1682           PCRE's internal tables to be used. This facility is  helpful  when  re-
1683           using  patterns  that  have been saved after compiling with an external
1684           set of tables, because the external tables  might  be  at  a  different
1685           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1686           tion for a discussion of saving compiled patterns for later use.
1687    
1688       Option bits for pcre_exec()
1689    
1690           The unused bits of the options argument for pcre_exec() must  be  zero.
1691           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1692           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1693           PCRE_PARTIAL.
1694    
1695             PCRE_ANCHORED
1696    
1697           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1698           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1699           turned  out to be anchored by virtue of its contents, it cannot be made
1700           unachored at matching time.
1701    
1702             PCRE_NEWLINE_CR
1703             PCRE_NEWLINE_LF
1704             PCRE_NEWLINE_CRLF
1705             PCRE_NEWLINE_ANY
1706    
1707           These options override  the  newline  definition  that  was  chosen  or
1708           defaulted  when the pattern was compiled. For details, see the descrip-
1709           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1710           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1711           ters. It may also alter the way the match position is advanced after  a
1712           match  failure  for  an  unanchored  pattern. When PCRE_NEWLINE_CRLF or
1713           PCRE_NEWLINE_ANY is set, and a match attempt  fails  when  the  current
1714           position  is  at a CRLF sequence, the match position is advanced by two
1715           characters instead of one, in other words, to after the CRLF.
1716    
1717             PCRE_NOTBOL
1718    
1719           This option specifies that first character of the subject string is not
1720           the  beginning  of  a  line, so the circumflex metacharacter should not
1721           match before it. Setting this without PCRE_MULTILINE (at compile  time)
1722           causes  circumflex  never to match. This option affects only the behav-
1723           iour of the circumflex metacharacter. It does not affect \A.
1724    
1725             PCRE_NOTEOL
1726    
1727           This option specifies that the end of the subject string is not the end
1728           of  a line, so the dollar metacharacter should not match it nor (except
1729           in multiline mode) a newline immediately before it. Setting this  with-
1730           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1731           option affects only the behaviour of the dollar metacharacter. It  does
1732           not affect \Z or \z.
1733    
1734             PCRE_NOTEMPTY
1735    
1736           An empty string is not considered to be a valid match if this option is
1737           set. If there are alternatives in the pattern, they are tried.  If  all
1738           the  alternatives  match  the empty string, the entire match fails. For
1739           example, if the pattern
1740    
1741             a?b?
1742    
1743           is applied to a string not beginning with "a" or "b",  it  matches  the
1744           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
1745           match is not valid, so PCRE searches further into the string for occur-
1746           rences of "a" or "b".
1747    
1748           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1749           cial case of a pattern match of the empty  string  within  its  split()
1750           function,  and  when  using  the /g modifier. It is possible to emulate
1751           Perl's behaviour after matching a null string by first trying the match
1752           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1753           if that fails by advancing the starting offset (see below)  and  trying
1754           an ordinary match again. There is some code that demonstrates how to do
1755           this in the pcredemo.c sample program.
1756    
1757             PCRE_NO_UTF8_CHECK
1758    
1759           When PCRE_UTF8 is set at compile time, the validity of the subject as a
1760           UTF-8  string is automatically checked when pcre_exec() is subsequently
1761           called.  The value of startoffset is also checked  to  ensure  that  it
1762           points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
1763           of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1764           startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1765           returned.
1766    
1767           If you already know that your subject is valid, and you  want  to  skip
1768           these    checks    for   performance   reasons,   you   can   set   the
1769           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1770           do  this  for the second and subsequent calls to pcre_exec() if you are
1771           making repeated calls to find all  the  matches  in  a  single  subject
1772           string.  However,  you  should  be  sure  that the value of startoffset
1773           points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1774           set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1775           value of startoffset that does not point to the start of a UTF-8  char-
1776           acter, is undefined. Your program may crash.
1777    
1778             PCRE_PARTIAL
1779    
1780           This  option  turns  on  the  partial  matching feature. If the subject
1781           string fails to match the pattern, but at some point during the  match-
1782           ing  process  the  end of the subject was reached (that is, the subject
1783           partially matches the pattern and the failure to  match  occurred  only
1784           because  there were not enough subject characters), pcre_exec() returns
1785           PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1786           used,  there  are restrictions on what may appear in the pattern. These
1787           are discussed in the pcrepartial documentation.
1788    
1789       The string to be matched by pcre_exec()
1790    
1791           The subject string is passed to pcre_exec() as a pointer in subject,  a
1792           length  in  length, and a starting byte offset in startoffset. In UTF-8
1793           mode, the byte offset must point to the start  of  a  UTF-8  character.
1794           Unlike  the  pattern string, the subject may contain binary zero bytes.
1795           When the starting offset is zero, the search for a match starts at  the
1796           beginning of the subject, and this is by far the most common case.
1797    
1798           A  non-zero  starting offset is useful when searching for another match
1799           in the same subject by calling pcre_exec() again after a previous  suc-
1800           cess.   Setting  startoffset differs from just passing over a shortened
1801           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1802           with any kind of lookbehind. For example, consider the pattern
1803    
1804             \Biss\B
1805    
1806           which  finds  occurrences  of "iss" in the middle of words. (\B matches
1807           only if the current position in the subject is not  a  word  boundary.)
1808           When  applied  to the string "Mississipi" the first call to pcre_exec()
1809           finds the first occurrence. If pcre_exec() is called  again  with  just
1810           the  remainder  of  the  subject,  namely  "issipi", it does not match,
1811           because \B is always false at the start of the subject, which is deemed
1812           to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1813           string again, but with startoffset set to 4, it finds the second occur-
1814           rence  of "iss" because it is able to look behind the starting point to
1815           discover that it is preceded by a letter.
1816    
1817           If a non-zero starting offset is passed when the pattern  is  anchored,
1818           one attempt to match at the given offset is made. This can only succeed
1819           if the pattern does not require the match to be at  the  start  of  the
1820           subject.
1821    
1822       How pcre_exec() returns captured substrings
1823    
1824           In  general, a pattern matches a certain portion of the subject, and in
1825           addition, further substrings from the subject  may  be  picked  out  by
1826           parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1827           this is called "capturing" in what follows, and the  phrase  "capturing
1828           subpattern"  is  used for a fragment of a pattern that picks out a sub-
1829           string. PCRE supports several other kinds of  parenthesized  subpattern
1830           that do not cause substrings to be captured.
1831    
1832           Captured  substrings are returned to the caller via a vector of integer
1833           offsets whose address is passed in ovector. The number of  elements  in
1834           the  vector is passed in ovecsize, which must be a non-negative number.
1835           Note: this argument is NOT the size of ovector in bytes.
1836    
1837           The first two-thirds of the vector is used to pass back  captured  sub-
1838           strings,  each  substring using a pair of integers. The remaining third
1839           of the vector is used as workspace by pcre_exec() while  matching  cap-
1840           turing  subpatterns, and is not available for passing back information.
1841           The length passed in ovecsize should always be a multiple of three.  If
1842           it is not, it is rounded down.
1843    
1844           When  a  match  is successful, information about captured substrings is
1845           returned in pairs of integers, starting at the  beginning  of  ovector,
1846           and  continuing  up  to two-thirds of its length at the most. The first
1847           element of a pair is set to the offset of the first character in a sub-
1848           string,  and  the  second  is  set to the offset of the first character
1849           after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1850           tor[1],  identify  the  portion  of  the  subject string matched by the
1851           entire pattern. The next pair is used for the first  capturing  subpat-
1852           tern, and so on. The value returned by pcre_exec() is one more than the
1853           highest numbered pair that has been set. For example, if two substrings
1854           have  been captured, the returned value is 3. If there are no capturing
1855           subpatterns, the return value from a successful match is 1,  indicating
1856           that just the first pair of offsets has been set.
1857    
1858           If a capturing subpattern is matched repeatedly, it is the last portion
1859           of the string that it matched that is returned.
1860    
1861           If the vector is too small to hold all the captured substring  offsets,
1862           it is used as far as possible (up to two-thirds of its length), and the
1863           function returns a value of zero. In particular, if the substring  off-
1864           sets are not of interest, pcre_exec() may be called with ovector passed
1865           as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1866           references  and  the  ovector is not big enough to remember the related
1867           substrings, PCRE has to get additional memory for use during  matching.
1868           Thus it is usually advisable to supply an ovector.
1869    
1870           The  pcre_info()  function  can  be used to find out how many capturing
1871           subpatterns there are in a compiled  pattern.  The  smallest  size  for
1872           ovector  that  will allow for n captured substrings, in addition to the
1873           offsets of the substring matched by the whole pattern, is (n+1)*3.
1874    
1875           It is possible for capturing subpattern number n+1 to match  some  part
1876           of the subject when subpattern n has not been used at all. For example,
1877           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1878           return from the function is 4, and subpatterns 1 and 3 are matched, but
1879           2 is not. When this happens, both values in  the  offset  pairs  corre-
1880           sponding to unused subpatterns are set to -1.
1881    
1882           Offset  values  that correspond to unused subpatterns at the end of the
1883           expression are also set to -1. For example,  if  the  string  "abc"  is
1884           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1885           matched. The return from the function is 2, because  the  highest  used
1886           capturing subpattern number is 1. However, you can refer to the offsets
1887           for the second and third capturing subpatterns if  you  wish  (assuming
1888           the vector is large enough, of course).
1889    
1890           Some  convenience  functions  are  provided for extracting the captured
1891           substrings as separate strings. These are described below.
1892    
1893       Error return values from pcre_exec()
1894    
1895           If pcre_exec() fails, it returns a negative number. The  following  are
1896           defined in the header file:
1897    
1898             PCRE_ERROR_NOMATCH        (-1)
1899    
1900           The subject string did not match the pattern.
1901    
1902             PCRE_ERROR_NULL           (-2)
1903    
1904           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
1905           ovecsize was not zero.
1906    
1907             PCRE_ERROR_BADOPTION      (-3)
1908    
1909           An unrecognized bit was set in the options argument.
1910    
1911             PCRE_ERROR_BADMAGIC       (-4)
1912    
1913           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
1914           to catch the case when it is passed a junk pointer and to detect when a
1915           pattern that was compiled in an environment of one endianness is run in
1916           an  environment  with the other endianness. This is the error that PCRE
1917           gives when the magic number is not present.
1918    
1919             PCRE_ERROR_UNKNOWN_OPCODE (-5)
1920    
1921           While running the pattern match, an unknown item was encountered in the
1922           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
1923           overwriting of the compiled pattern.
1924    
1925             PCRE_ERROR_NOMEMORY       (-6)
1926    
1927           If a pattern contains back references, but the ovector that  is  passed
1928           to pcre_exec() is not big enough to remember the referenced substrings,
1929           PCRE gets a block of memory at the start of matching to  use  for  this
1930           purpose.  If the call via pcre_malloc() fails, this error is given. The
1931           memory is automatically freed at the end of matching.
1932    
1933             PCRE_ERROR_NOSUBSTRING    (-7)
1934    
1935           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
1936           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1937           returned by pcre_exec().
1938    
1939             PCRE_ERROR_MATCHLIMIT     (-8)
1940    
1941           The backtracking limit, as specified by  the  match_limit  field  in  a
1942           pcre_extra  structure  (or  defaulted) was reached. See the description
1943           above.
1944    
1945             PCRE_ERROR_CALLOUT        (-9)
1946    
1947           This error is never generated by pcre_exec() itself. It is provided for
1948           use  by  callout functions that want to yield a distinctive error code.
1949           See the pcrecallout documentation for details.
1950    
1951             PCRE_ERROR_BADUTF8        (-10)
1952    
1953           A string that contains an invalid UTF-8 byte sequence was passed  as  a
1954           subject.
1955    
1956             PCRE_ERROR_BADUTF8_OFFSET (-11)
1957    
1958           The UTF-8 byte sequence that was passed as a subject was valid, but the
1959           value of startoffset did not point to the beginning of a UTF-8  charac-
1960           ter.
1961    
1962             PCRE_ERROR_PARTIAL        (-12)
1963    
1964           The  subject  string did not match, but it did match partially. See the
1965           pcrepartial documentation for details of partial matching.
1966    
1967             PCRE_ERROR_BADPARTIAL     (-13)
1968    
1969           The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
1970           items  that are not supported for partial matching. See the pcrepartial
1971           documentation for details of partial matching.
1972    
1973             PCRE_ERROR_INTERNAL       (-14)
1974    
1975           An unexpected internal error has occurred. This error could  be  caused
1976           by a bug in PCRE or by overwriting of the compiled pattern.
1977    
1978             PCRE_ERROR_BADCOUNT       (-15)
1979    
1980           This  error is given if the value of the ovecsize argument is negative.
1981    
1982             PCRE_ERROR_RECURSIONLIMIT (-21)
1983    
1984           The internal recursion limit, as specified by the match_limit_recursion
1985           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
1986           description above.
1987    
1988             PCRE_ERROR_NULLWSLIMIT    (-22)
1989    
1990           When a group that can match an empty  substring  is  repeated  with  an
1991           unbounded  upper  limit, the subject position at the start of the group
1992           must be remembered, so that a test for an empty string can be made when
1993           the  end  of the group is reached. Some workspace is required for this;
1994           if it runs out, this error is given.
1995    
1996             PCRE_ERROR_BADNEWLINE     (-23)
1997    
1998           An invalid combination of PCRE_NEWLINE_xxx options was given.
1999    
2000           Error numbers -16 to -20 are not used by pcre_exec().
2001    
2002    
2003    EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2004    
2005           int pcre_copy_substring(const char *subject, int *ovector,
2006                int stringcount, int stringnumber, char *buffer,
2007                int buffersize);
2008    
2009           int pcre_get_substring(const char *subject, int *ovector,
2010                int stringcount, int stringnumber,
2011                const char **stringptr);
2012    
2013           int pcre_get_substring_list(const char *subject,
2014                int *ovector, int stringcount, const char ***listptr);
2015    
2016           Captured substrings can be  accessed  directly  by  using  the  offsets
2017           returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2018           pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2019           string_list()  are  provided for extracting captured substrings as new,
2020           separate, zero-terminated strings. These functions identify  substrings
2021           by  number.  The  next section describes functions for extracting named
2022           substrings.
2023    
2024           A substring that contains a binary zero is correctly extracted and  has
2025           a  further zero added on the end, but the result is not, of course, a C
2026           string.  However, you can process such a string  by  referring  to  the
2027           length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2028           string().  Unfortunately, the interface to pcre_get_substring_list() is
2029           not  adequate for handling strings containing binary zeros, because the
2030           end of the final string is not independently indicated.
2031    
2032           The first three arguments are the same for all  three  of  these  func-
2033           tions:  subject  is  the subject string that has just been successfully
2034           matched, ovector is a pointer to the vector of integer offsets that was
2035           passed to pcre_exec(), and stringcount is the number of substrings that
2036           were captured by the match, including the substring  that  matched  the
2037           entire regular expression. This is the value returned by pcre_exec() if
2038           it is greater than zero. If pcre_exec() returned zero, indicating  that
2039           it  ran out of space in ovector, the value passed as stringcount should
2040           be the number of elements in the vector divided by three.
2041    
2042           The functions pcre_copy_substring() and pcre_get_substring() extract  a
2043           single  substring,  whose  number  is given as stringnumber. A value of
2044           zero extracts the substring that matched the  entire  pattern,  whereas
2045           higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2046           string(), the string is placed in buffer,  whose  length  is  given  by
2047           buffersize,  while  for  pcre_get_substring()  a new block of memory is
2048           obtained via pcre_malloc, and its address is  returned  via  stringptr.
2049           The  yield  of  the function is the length of the string, not including
2050           the terminating zero, or one of these error codes:
2051    
2052             PCRE_ERROR_NOMEMORY       (-6)
2053    
2054           The buffer was too small for pcre_copy_substring(), or the  attempt  to
2055           get memory failed for pcre_get_substring().
2056    
2057             PCRE_ERROR_NOSUBSTRING    (-7)
2058    
2059           There is no substring whose number is stringnumber.
2060    
2061           The  pcre_get_substring_list()  function  extracts  all  available sub-
2062           strings and builds a list of pointers to them. All this is  done  in  a
2063           single block of memory that is obtained via pcre_malloc. The address of
2064           the memory block is returned via listptr, which is also  the  start  of
2065           the  list  of  string pointers. The end of the list is marked by a NULL
2066           pointer. The yield of the function is zero if all  went  well,  or  the
2067           error code
2068    
2069             PCRE_ERROR_NOMEMORY       (-6)
2070    
2071           if the attempt to get the memory block failed.
2072    
2073           When  any of these functions encounter a substring that is unset, which
2074           can happen when capturing subpattern number n+1 matches  some  part  of
2075           the  subject, but subpattern n has not been used at all, they return an
2076           empty string. This can be distinguished from a genuine zero-length sub-
2077           string  by inspecting the appropriate offset in ovector, which is nega-
2078           tive for unset substrings.
2079    
2080           The two convenience functions pcre_free_substring() and  pcre_free_sub-
2081           string_list()  can  be  used  to free the memory returned by a previous
2082           call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2083           tively.  They  do  nothing  more  than  call the function pointed to by
2084           pcre_free, which of course could be called directly from a  C  program.
2085           However,  PCRE is used in some situations where it is linked via a spe-
2086           cial  interface  to  another  programming  language  that  cannot   use
2087           pcre_free  directly;  it is for these cases that the functions are pro-
2088           vided.
2089    
2090    
2091    EXTRACTING CAPTURED SUBSTRINGS BY NAME
2092    
2093           int pcre_get_stringnumber(const pcre *code,
2094                const char *name);
2095    
2096           int pcre_copy_named_substring(const pcre *code,
2097                const char *subject, int *ovector,
2098                int stringcount, const char *stringname,
2099                char *buffer, int buffersize);
2100    
2101           int pcre_get_named_substring(const pcre *code,
2102                const char *subject, int *ovector,
2103                int stringcount, const char *stringname,
2104                const char **stringptr);
2105    
2106           To extract a substring by name, you first have to find associated  num-
2107           ber.  For example, for this pattern
2108    
2109             (a+)b(?<xxx>\d+)...
2110    
2111           the number of the subpattern called "xxx" is 2. If the name is known to
2112           be unique (PCRE_DUPNAMES was not set), you can find the number from the
2113           name by calling pcre_get_stringnumber(). The first argument is the com-
2114           piled pattern, and the second is the name. The yield of the function is
2115           the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2116           subpattern of that name.
2117    
2118           Given the number, you can extract the substring directly, or use one of
2119           the functions described in the previous section. For convenience, there
2120           are also two functions that do the whole job.
2121    
2122           Most   of   the   arguments    of    pcre_copy_named_substring()    and
2123           pcre_get_named_substring()  are  the  same  as  those for the similarly
2124           named functions that extract by number. As these are described  in  the
2125           previous  section,  they  are not re-described here. There are just two
2126           differences:
2127    
2128           First, instead of a substring number, a substring name is  given.  Sec-
2129           ond, there is an extra argument, given at the start, which is a pointer
2130           to the compiled pattern. This is needed in order to gain access to  the
2131           name-to-number translation table.
2132    
2133           These  functions call pcre_get_stringnumber(), and if it succeeds, they
2134           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2135           ate.
2136    
2137    
2138    DUPLICATE SUBPATTERN NAMES
2139    
2140           int pcre_get_stringtable_entries(const pcre *code,
2141                const char *name, char **first, char **last);
2142    
2143           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2144           subpatterns are not required to  be  unique.  Normally,  patterns  with
2145           duplicate  names  are such that in any one match, only one of the named
2146           subpatterns participates. An example is shown in the pcrepattern  docu-
2147           mentation. When duplicates are present, pcre_copy_named_substring() and
2148           pcre_get_named_substring() return the first substring corresponding  to
2149           the  given  name  that  is  set.  If  none  are set, an empty string is
2150           returned.  The pcre_get_stringnumber() function returns one of the num-
2151           bers  that are associated with the name, but it is not defined which it
2152           is.
2153    
2154           If you want to get full details of all captured substrings for a  given
2155           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2156           first argument is the compiled pattern, and the second is the name. The
2157           third  and  fourth  are  pointers to variables which are updated by the
2158           function. After it has run, they point to the first and last entries in
2159           the  name-to-number  table  for  the  given  name.  The function itself
2160           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2161           there  are none. The format of the table is described above in the sec-
2162           tion entitled Information about a  pattern.   Given  all  the  relevant
2163           entries  for the name, you can extract each of their numbers, and hence
2164           the captured data, if any.
2165    
2166    
2167    FINDING ALL POSSIBLE MATCHES
2168    
2169           The traditional matching function uses a  similar  algorithm  to  Perl,
2170           which stops when it finds the first match, starting at a given point in
2171           the subject. If you want to find all possible matches, or  the  longest
2172           possible  match,  consider using the alternative matching function (see
2173           below) instead. If you cannot use the alternative function,  but  still
2174           need  to  find all possible matches, you can kludge it up by making use
2175           of the callout facility, which is described in the pcrecallout documen-
2176           tation.
2177    
2178           What you have to do is to insert a callout right at the end of the pat-
2179           tern.  When your callout function is called, extract and save the  cur-
2180           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2181           backtrack and try other alternatives. Ultimately, when it runs  out  of
2182           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2183    
2184    
2185    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2186    
2187           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2188                const char *subject, int length, int startoffset,
2189                int options, int *ovector, int ovecsize,
2190                int *workspace, int wscount);
2191    
2192           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2193           against a compiled pattern, using a matching algorithm that  scans  the
2194           subject  string  just  once, and does not backtrack. This has different
2195           characteristics to the normal algorithm, and  is  not  compatible  with
2196           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2197           theless, there are times when this kind of matching can be useful.  For
2198           a discussion of the two matching algorithms, see the pcrematching docu-
2199           mentation.
2200    
2201           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2202           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2203           ent way, and this is described below. The other  common  arguments  are
2204           used  in  the  same way as for pcre_exec(), so their description is not
2205           repeated here.
2206    
2207           The two additional arguments provide workspace for  the  function.  The
2208           workspace  vector  should  contain at least 20 elements. It is used for
2209           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2210           workspace  will  be  needed for patterns and subjects where there are a
2211           lot of potential matches.
2212    
2213           Here is an example of a simple call to pcre_dfa_exec():
2214    
2215             int rc;
2216             int ovector[10];
2217             int wspace[20];
2218             rc = pcre_dfa_exec(
2219               re,             /* result of pcre_compile() */
2220               NULL,           /* we didn't study the pattern */
2221               "some string",  /* the subject string */
2222               11,             /* the length of the subject string */
2223               0,              /* start at offset 0 in the subject */
2224               0,              /* default options */
2225               ovector,        /* vector of integers for substring information */
2226               10,             /* number of elements (NOT size in bytes) */
2227               wspace,         /* working space vector */
2228               20);            /* number of elements (NOT size in bytes) */
2229    
2230       Option bits for pcre_dfa_exec()
2231    
2232           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2233           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2234           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2235           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2236           three of these are the same as for pcre_exec(), so their description is
2237           not repeated here.
2238    
2239             PCRE_PARTIAL
2240    
2241           This  has  the  same general effect as it does for pcre_exec(), but the
2242           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2243           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2244           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2245           been no complete matches, but there is still at least one matching pos-
2246           sibility. The portion of the string that provided the partial match  is
2247           set as the first matching string.
2248    
2249             PCRE_DFA_SHORTEST
2250    
2251           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2252           stop as soon as it has found one match. Because of the way the alterna-
2253           tive  algorithm  works, this is necessarily the shortest possible match
2254           at the first possible matching point in the subject string.
2255    
2256             PCRE_DFA_RESTART
2257    
2258           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2259           returns  a  partial  match, it is possible to call it again, with addi-
2260           tional subject characters, and have it continue with  the  same  match.
2261           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2262           workspace and wscount options must reference the same vector as  before
2263           because  data  about  the  match so far is left in them after a partial
2264           match. There is more discussion of this  facility  in  the  pcrepartial
2265           documentation.
2266    
2267       Successful returns from pcre_dfa_exec()
2268    
2269           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2270           string in the subject. Note, however, that all the matches from one run
2271           of  the  function  start  at the same point in the subject. The shorter
2272           matches are all initial substrings of the longer matches. For  example,
2273           if the pattern
2274    
2275             <.*>
2276    
2277           is matched against the string
2278    
2279             This is <something> <something else> <something further> no more
2280    
2281           the three matched strings are
2282    
2283             <something>
2284             <something> <something else>
2285             <something> <something else> <something further>
2286    
2287           On  success,  the  yield of the function is a number greater than zero,
2288           which is the number of matched substrings.  The  substrings  themselves
2289           are  returned  in  ovector. Each string uses two elements; the first is
2290           the offset to the start, and the second is the offset to  the  end.  In
2291           fact,  all  the  strings  have the same start offset. (Space could have
2292           been saved by giving this only once, but it was decided to retain  some
2293           compatibility  with  the  way pcre_exec() returns data, even though the
2294           meaning of the strings is different.)
2295    
2296           The strings are returned in reverse order of length; that is, the long-
2297           est  matching  string is given first. If there were too many matches to
2298           fit into ovector, the yield of the function is zero, and the vector  is
2299           filled with the longest matches.
2300    
2301       Error returns from pcre_dfa_exec()
2302    
2303           The  pcre_dfa_exec()  function returns a negative number when it fails.
2304           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2305           described  above.   There are in addition the following errors that are
2306           specific to pcre_dfa_exec():
2307    
2308             PCRE_ERROR_DFA_UITEM      (-16)
2309    
2310           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2311           tern  that  it  does not support, for instance, the use of \C or a back
2312           reference.
2313    
2314             PCRE_ERROR_DFA_UCOND      (-17)
2315    
2316           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2317           that  uses  a back reference for the condition, or a test for recursion
2318           in a specific group. These are not supported.
2319    
2320             PCRE_ERROR_DFA_UMLIMIT    (-18)
2321    
2322           This return is given if pcre_dfa_exec() is called with an  extra  block
2323           that contains a setting of the match_limit field. This is not supported
2324           (it is meaningless).
2325    
2326             PCRE_ERROR_DFA_WSSIZE     (-19)
2327    
2328           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2329           workspace vector.
2330    
2331             PCRE_ERROR_DFA_RECURSE    (-20)
2332    
2333           When  a  recursive subpattern is processed, the matching function calls
2334           itself recursively, using private vectors for  ovector  and  workspace.
2335           This  error  is  given  if  the output vector is not large enough. This
2336           should be extremely rare, as a vector of size 1000 is used.
2337    
 MATCHING A PATTERN  
      The function pcre_exec() is called to match a subject string  
      against  a pre-compiled pattern, which is passed in the code  
      argument. If the pattern has been studied, the result of the  
      study should be passed in the extra argument. Otherwise this  
      must be NULL.  
   
      The PCRE_ANCHORED option can be passed in the options  argu-  
      ment,  whose unused bits must be zero. However, if a pattern  
      was  compiled  with  PCRE_ANCHORED,  or  turned  out  to  be  
      anchored  by  virtue  of  its  contents,  it  cannot be made  
      unachored at matching time.  
   
      There are also three further options that can be set only at  
      matching time:  
   
        PCRE_NOTBOL  
   
      The first character of the string is not the beginning of  a  
      line,  so  the  circumflex  metacharacter  should  not match  
      before it. Setting this without PCRE_MULTILINE  (at  compile  
      time) causes circumflex never to match.  
   
        PCRE_NOTEOL  
   
      The end of the string is not the end of a line, so the  dol-  
      lar  metacharacter should not match it nor (except in multi-  
      line mode) a newline immediately  before  it.  Setting  this  
      without PCRE_MULTILINE (at compile time) causes dollar never  
      to match.  
   
        PCRE_NOTEMPTY  
   
      An empty string is not considered to be  a  valid  match  if  
      this  option  is  set. If there are alternatives in the pat-  
      tern, they are tried. If  all  the  alternatives  match  the  
      empty  string,  the  entire match fails. For example, if the  
      pattern  
   
        a?b?  
   
      is applied to a string not beginning with  "a"  or  "b",  it  
      matches  the  empty string at the start of the subject. With  
      PCRE_NOTEMPTY set, this match is not valid, so PCRE searches  
      further into the string for occurrences of "a" or "b".  
   
      Perl has no direct equivalent of PCRE_NOTEMPTY, but it  does  
      make  a  special case of a pattern match of the empty string  
      within its split() function, and when using the /g modifier.  
      It  is possible to emulate Perl's behaviour after matching a  
      null string by first trying the  match  again  at  the  same  
      offset  with  PCRE_NOTEMPTY  set,  and then if that fails by  
      advancing the starting offset  (see  below)  and  trying  an  
      ordinary match again.  
   
      The subject string is passed as  a  pointer  in  subject,  a  
      length  in  length,  and  a  starting offset in startoffset.  
      Unlike the pattern string, it may contain binary zero  char-  
      acters.  When  the starting offset is zero, the search for a  
      match starts at the beginning of the subject, and this is by  
      far the most common case.  
   
      A non-zero starting offset  is  useful  when  searching  for  
      another  match  in  the  same subject by calling pcre_exec()  
      again after a previous success.  Setting startoffset differs  
      from  just  passing  over  a  shortened  string  and setting  
      PCRE_NOTBOL in the case of a pattern that  begins  with  any  
      kind of lookbehind. For example, consider the pattern  
   
        \Biss\B  
   
      which finds occurrences of "iss" in the middle of words. (\B  
      matches only if the current position in the subject is not a  
      word boundary.) When applied to the string "Mississipi"  the  
      first  call  to  pcre_exec()  finds the first occurrence. If  
      pcre_exec() is called again with just the remainder  of  the  
      subject,  namely  "issipi", it does not match, because \B is  
      always false at the start of the subject, which is deemed to  
      be  a  word  boundary. However, if pcre_exec() is passed the  
      entire string again, but with startoffset set to 4, it finds  
      the  second  occurrence  of "iss" because it is able to look  
      behind the starting point to discover that it is preceded by  
      a letter.  
   
      If a non-zero starting offset is passed when the pattern  is  
      anchored, one attempt to match at the given offset is tried.  
      This can only succeed if the pattern does  not  require  the  
      match to be at the start of the subject.  
   
      In general, a pattern matches a certain portion of the  sub-  
      ject,  and  in addition, further substrings from the subject  
      may be picked out by parts of  the  pattern.  Following  the  
      usage  in  Jeffrey Friedl's book, this is called "capturing"  
      in what follows, and the phrase  "capturing  subpattern"  is  
      used for a fragment of a pattern that picks out a substring.  
      PCRE supports several other kinds of  parenthesized  subpat-  
      tern that do not cause substrings to be captured.  
   
      Captured substrings are returned to the caller via a  vector  
      of  integer  offsets whose address is passed in ovector. The  
      number of elements in the vector is passed in ovecsize.  The  
      first two-thirds of the vector is used to pass back captured  
      substrings, each substring using a  pair  of  integers.  The  
      remaining  third  of  the  vector  is  used  as workspace by  
      pcre_exec() while matching capturing subpatterns, and is not  
      available for passing back information. The length passed in  
      ovecsize should always be a multiple of three. If it is not,  
      it is rounded down.  
   
      When a match has been successful, information about captured  
      substrings is returned in pairs of integers, starting at the  
      beginning of ovector, and continuing up to two-thirds of its  
      length  at  the  most. The first element of a pair is set to  
      the offset of the first character in a  substring,  and  the  
      second is set to the offset of the first character after the  
      end of a substring. The first  pair,  ovector[0]  and  ovec-  
      tor[1],  identify  the portion of the subject string matched  
      by the entire pattern. The next pair is used for  the  first  
      capturing  subpattern,  and  so  on.  The  value returned by  
      pcre_exec() is the number of pairs that have  been  set.  If  
      there  are no capturing subpatterns, the return value from a  
      successful match is 1, indicating that just the  first  pair  
      of offsets has been set.  
   
      Some convenience functions are provided for  extracting  the  
      captured substrings as separate strings. These are described  
      in the following section.  
   
      It is possible for an capturing  subpattern  number  n+1  to  
      match  some  part  of  the subject when subpattern n has not  
      been used at all.  For  example,  if  the  string  "abc"  is  
      matched  against the pattern (a|(z))(bc) subpatterns 1 and 3  
      are matched, but 2 is not. When this  happens,  both  offset  
      values corresponding to the unused subpattern are set to -1.  
   
      If a capturing subpattern is matched repeatedly, it  is  the  
      last  portion  of  the  string  that  it  matched  that gets  
      returned.  
   
      If the vector is too small to hold  all  the  captured  sub-  
      strings,  it is used as far as possible (up to two-thirds of  
      its length), and the function returns a value  of  zero.  In  
      particular,  if  the  substring offsets are not of interest,  
      pcre_exec() may be called with ovector passed  as  NULL  and  
      ovecsize  as  zero.  However,  if  the pattern contains back  
      references and the ovector isn't big enough to remember  the  
      related  substrings,  PCRE  has to get additional memory for  
      use during matching. Thus it is usually advisable to  supply  
      an ovector.  
   
      Note that pcre_info() can be used to find out how many  cap-  
      turing  subpatterns  there  are  in  a compiled pattern. The  
      smallest size for ovector that will  allow  for  n  captured  
      substrings  in  addition  to  the  offsets  of the substring  
      matched by the whole pattern is (n+1)*3.  
   
      If pcre_exec() fails, it returns a negative number. The fol-  
      lowing are defined in the header file:  
   
        PCRE_ERROR_NOMATCH        (-1)  
   
      The subject string did not match the pattern.  
   
        PCRE_ERROR_NULL           (-2)  
   
      Either code or subject was passed as NULL,  or  ovector  was  
      NULL and ovecsize was not zero.  
   
        PCRE_ERROR_BADOPTION      (-3)  
   
      An unrecognized bit was set in the options argument.  
   
        PCRE_ERROR_BADMAGIC       (-4)  
   
      PCRE stores a 4-byte "magic number" at the start of the com-  
      piled  code,  to  catch  the  case  when it is passed a junk  
      pointer. This is the error it gives when  the  magic  number  
      isn't present.  
   
        PCRE_ERROR_UNKNOWN_NODE   (-5)  
   
      While running the pattern match, an unknown item was encoun-  
      tered in the compiled pattern. This error could be caused by  
      a bug in PCRE or by overwriting of the compiled pattern.  
   
        PCRE_ERROR_NOMEMORY       (-6)  
   
      If a pattern contains back references, but the ovector  that  
      is  passed  to pcre_exec() is not big enough to remember the  
      referenced substrings, PCRE gets a block of  memory  at  the  
      start  of  matching to use for this purpose. If the call via  
      pcre_malloc() fails, this error  is  given.  The  memory  is  
      freed at the end of matching.  
   
   
   
 EXTRACTING CAPTURED SUBSTRINGS  
      Captured substrings can be accessed directly  by  using  the  
   
   
   
   
   
 SunOS 5.8                 Last change:                         12  
   
   
   
      offsets returned by pcre_exec() in ovector. For convenience,  
      the functions  pcre_copy_substring(),  pcre_get_substring(),  
      and  pcre_get_substring_list()  are  provided for extracting  
      captured  substrings  as  new,   separate,   zero-terminated  
      strings.   A  substring  that  contains  a  binary  zero  is  
      correctly extracted and has a further zero added on the end,  
      but the result does not, of course, function as a C string.  
   
      The first three arguments are the same for all  three  func-  
      tions:  subject  is  the  subject string which has just been  
      successfully matched, ovector is a pointer to the vector  of  
      integer   offsets   that  was  passed  to  pcre_exec(),  and  
      stringcount is the number of substrings that  were  captured  
      by  the  match,  including  the  substring  that matched the  
      entire regular expression. This is  the  value  returned  by  
      pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()  
      returned zero, indicating that it ran out of space in  ovec-  
      tor,  the  value passed as stringcount should be the size of  
      the vector divided by three.  
   
      The functions pcre_copy_substring() and pcre_get_substring()  
      extract a single substring, whose number is given as string-  
      number. A value of zero extracts the substring that  matched  
      the entire pattern, while higher values extract the captured  
      substrings. For pcre_copy_substring(), the string is  placed  
      in  buffer,  whose  length is given by buffersize, while for  
      pcre_get_substring() a new block of memory is  obtained  via  
      pcre_malloc,  and its address is returned via stringptr. The  
      yield of the function is  the  length  of  the  string,  not  
      including the terminating zero, or one of  
   
        PCRE_ERROR_NOMEMORY       (-6)  
   
      The buffer was too small for pcre_copy_substring(),  or  the  
      attempt to get memory failed for pcre_get_substring().  
   
        PCRE_ERROR_NOSUBSTRING    (-7)  
   
      There is no substring whose number is stringnumber.  
   
      The pcre_get_substring_list() function extracts  all  avail-  
      able  substrings  and builds a list of pointers to them. All  
      this is done in a single block of memory which  is  obtained  
      via pcre_malloc. The address of the memory block is returned  
      via listptr, which is also the start of the list  of  string  
      pointers.  The  end of the list is marked by a NULL pointer.  
      The yield of the function is zero if all went well, or  
   
        PCRE_ERROR_NOMEMORY       (-6)  
   
      if the attempt to get the memory block failed.  
   
      When any of these functions encounter a  substring  that  is  
      unset, which can happen when capturing subpattern number n+1  
      matches some part of the subject, but subpattern n  has  not  
      been  used  at all, they return an empty string. This can be  
      distinguished  from  a  genuine  zero-length  substring   by  
      inspecting the appropriate offset in ovector, which is nega-  
      tive for unset substrings.  
   
      The  two  convenience  functions  pcre_free_substring()  and  
      pcre_free_substring_list()  can  be  used to free the memory  
      returned by  a  previous  call  of  pcre_get_substring()  or  
      pcre_get_substring_list(),  respectively.  They  do  nothing  
      more than call the function pointed to by  pcre_free,  which  
      of  course  could  be called directly from a C program. How-  
      ever, PCRE is used in some situations where it is linked via  
      a  special  interface  to another programming language which  
      cannot use pcre_free directly; it is for  these  cases  that  
      the functions are provided.  
2338    
2339    SEE ALSO
2340    
2341           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2342           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2343    
 LIMITATIONS  
      There are some size limitations in PCRE but it is hoped that  
      they will never in practice be relevant.  The maximum length  
      of a compiled pattern is 65539 (sic) bytes.  All  values  in  
      repeating  quantifiers must be less than 65536.  The maximum  
      number of capturing subpatterns is 99.  The  maximum  number  
      of  all  parenthesized subpatterns, including capturing sub-  
      patterns, assertions, and other types of subpattern, is 200.  
   
      The maximum length of a subject string is the largest  posi-  
      tive number that an integer variable can hold. However, PCRE  
      uses recursion to handle subpatterns and indefinite  repeti-  
      tion.  This  means  that the available stack space may limit  
      the size of a subject string that can be processed  by  cer-  
      tain patterns.  
   
   
   
 DIFFERENCES FROM PERL  
      The differences described here  are  with  respect  to  Perl  
      5.005.  
   
      1. By default, a whitespace character is any character  that  
      the  C  library  function isspace() recognizes, though it is  
      possible to compile PCRE  with  alternative  character  type  
      tables. Normally isspace() matches space, formfeed, newline,  
      carriage return, horizontal tab, and vertical tab. Perl 5 no  
      longer  includes vertical tab in its set of whitespace char-  
      acters. The \v escape that was in the Perl documentation for  
      a long time was never in fact recognized. However, the char-  
      acter itself was treated as whitespace at least up to 5.002.  
      In 5.004 and 5.005 it does not match \s.  
   
      2. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
      assertions. Perl permits them, but they do not mean what you  
      might think. For example, (?!a){3} does not assert that  the  
      next  three characters are not "a". It just asserts that the  
      next character is not "a" three times.  
   
      3. Capturing subpatterns that occur inside  negative  looka-  
      head  assertions  are  counted,  but  their  entries  in the  
      offsets vector are never set. Perl sets its numerical  vari-  
      ables  from  any  such  patterns that are matched before the  
      assertion fails to match something (thereby succeeding), but  
      only  if  the negative lookahead assertion contains just one  
      branch.  
   
      4. Though binary zero characters are supported in  the  sub-  
      ject  string,  they  are  not  allowed  in  a pattern string  
      because it is passed as a normal  C  string,  terminated  by  
      zero. The escape sequence "\0" can be used in the pattern to  
      represent a binary zero.  
   
      5. The following Perl escape sequences  are  not  supported:  
      \l,  \u,  \L,  \U,  \E, \Q. In fact these are implemented by  
      Perl's general string-handling and are not part of its  pat-  
      tern matching engine.  
   
      6. The Perl \G assertion is  not  supported  as  it  is  not  
      relevant to single pattern matches.  
   
      7. Fairly obviously, PCRE does not support the (?{code}) and  
      (?p{code})  constructions. However, there is some experimen-  
      tal support for recursive patterns using the  non-Perl  item  
      (?R).  
   
      8. There are at the time of writing some  oddities  in  Perl  
      5.005_02  concerned  with  the  settings of captured strings  
      when part of a pattern is repeated.  For  example,  matching  
      "aba"  against the pattern /^(a(b)?)+$/ sets $2 to the value  
      "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves  $2  
      unset.    However,    if   the   pattern   is   changed   to  
      /^(aa(b(b))?)+$/ then $2 (and $3) are set.  
   
      In Perl 5.004 $2 is set in both cases, and that is also true  
      of PCRE. If in the future Perl changes to a consistent state  
      that is different, PCRE may change to follow.  
   
      9. Another as yet unresolved discrepancy  is  that  in  Perl  
      5.005_02  the  pattern /^(a)?(?(1)a|b)+$/ matches the string  
      "a", whereas in PCRE it does not.  However, in both Perl and  
      PCRE /^(a)?a/ matched against "a" leaves $1 unset.  
   
      10. PCRE  provides  some  extensions  to  the  Perl  regular  
      expression facilities:  
   
      (a) Although lookbehind assertions must match  fixed  length  
      strings,  each  alternative branch of a lookbehind assertion  
      can match a different length of string. Perl 5.005  requires  
      them all to have the same length.  
   
      (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not  
      set,  the  $ meta- character matches only at the very end of  
      the string.  
   
      (c) If PCRE_EXTRA is set, a backslash followed by  a  letter  
      with no special meaning is faulted.  
   
      (d) If PCRE_UNGREEDY is set, the greediness of  the  repeti-  
      tion  quantifiers  is inverted, that is, by default they are  
      not greedy, but if followed by a question mark they are.  
   
      (e) PCRE_ANCHORED can be used to force a pattern to be tried  
      only at the start of the subject.  
   
      (f) The PCRE_NOTBOL, PCRE_NOTEOL, and PCRE_NOTEMPTY  options  
      for pcre_exec() have no Perl equivalents.  
   
      (g) The (?R) construct allows for recursive pattern matching  
      (Perl  5.6 can do this using the (?p{code}) construct, which  
      PCRE cannot of course support.)  
   
   
   
 REGULAR EXPRESSION DETAILS  
      The syntax and semantics of  the  regular  expressions  sup-  
      ported  by PCRE are described below. Regular expressions are  
      also described in the Perl documentation and in a number  of  
      other  books,  some  of which have copious examples. Jeffrey  
      Friedl's  "Mastering  Regular  Expressions",  published   by  
      O'Reilly (ISBN 1-56592-257), covers them in great detail.  
   
      The description here is intended as reference documentation.  
      The basic operation of PCRE is on strings of bytes. However,  
      there is the beginnings of some support for UTF-8  character  
      strings.  To  use  this  support  you must configure PCRE to  
      include it, and then call pcre_compile() with the  PCRE_UTF8  
      option.  How  this affects the pattern matching is described  
      in the final section of this document.  
   
      A regular expression is a pattern that is matched against  a  
      subject string from left to right. Most characters stand for  
      themselves in a pattern, and match the corresponding charac-  
      ters in the subject. As a trivial example, the pattern  
   
        The quick brown fox  
   
      matches a portion of a subject string that is  identical  to  
      itself.  The  power  of  regular  expressions comes from the  
      ability to include alternatives and repetitions in the  pat-  
      tern.  These  are encoded in the pattern by the use of meta-  
      characters, which do not stand for  themselves  but  instead  
      are interpreted in some special way.  
   
      There are two different sets of meta-characters: those  that  
      are  recognized anywhere in the pattern except within square  
      brackets, and those that are recognized in square  brackets.  
      Outside square brackets, the meta-characters are as follows:  
   
        \      general escape character with several uses  
        ^      assert start of  subject  (or  line,  in  multiline  
      mode)  
        $      assert end of subject (or line, in multiline mode)  
        .      match any character except newline (by default)  
        [      start character class definition  
        |      start of alternative branch  
        (      start subpattern  
        )      end subpattern  
        ?      extends the meaning of (  
               also 0 or 1 quantifier  
               also quantifier minimizer  
        *      0 or more quantifier  
        +      1 or more quantifier  
        {      start min/max quantifier  
   
      Part of a pattern that is in square  brackets  is  called  a  
      "character  class".  In  a  character  class  the only meta-  
      characters are:  
   
        \      general escape character  
        ^      negate the class, but only if the first character  
        -      indicates character range  
        ]      terminates the character class  
2344    
2345       The following sections describe  the  use  of  each  of  the  AUTHOR
2346       meta-characters.  
2347           Philip Hazel
2348           University Computing Service
2349           Cambridge CB2 3QH, England.
2350    
2351    
2352    REVISION
2353    
2354           Last updated: 06 March 2007
2355           Copyright (c) 1997-2007 University of Cambridge.
2356    ------------------------------------------------------------------------------
2357    
2358    
2359    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2360    
2361    
2362    NAME
2363           PCRE - Perl-compatible regular expressions
2364    
2365    
2366    PCRE CALLOUTS
2367    
2368           int (*pcre_callout)(pcre_callout_block *);
2369    
2370           PCRE provides a feature called "callout", which is a means of temporar-
2371           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2372           matching.  The  caller of PCRE provides an external function by putting
2373           its entry point in the global variable pcre_callout. By  default,  this
2374           variable contains NULL, which disables all calling out.
2375    
2376           Within  a  regular  expression,  (?C) indicates the points at which the
2377           external function is to be called.  Different  callout  points  can  be
2378           identified  by  putting  a number less than 256 after the letter C. The
2379           default value is zero.  For  example,  this  pattern  has  two  callout
2380           points:
2381    
2382             (?C1)eabc(?C2)def
2383    
2384           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2385           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2386           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2387           used with the pattern
2388    
2389             A(\d{2}|--)
2390    
2391           it is processed as if it were
2392    
2393           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2394    
2395           Notice that there is a callout before and after  each  parenthesis  and
2396           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2397           progress of pattern matching. The pcretest command has an  option  that
2398           sets  automatic callouts; when it is used, the output indicates how the
2399           pattern is matched. This is useful information when you are  trying  to
2400           optimize the performance of a particular pattern.
2401    
2402    
2403    MISSING CALLOUTS
2404    
2405           You  should  be  aware  that,  because of optimizations in the way PCRE
2406           matches patterns, callouts sometimes do not happen. For example, if the
2407           pattern is
2408    
2409             ab(?C4)cd
2410    
2411           PCRE knows that any matching string must contain the letter "d". If the
2412           subject string is "abyz", the lack of "d" means that  matching  doesn't
2413           ever  start,  and  the  callout is never reached. However, with "abyd",
2414           though the result is still no match, the callout is obeyed.
2415    
2416    
2417    THE CALLOUT INTERFACE
2418    
2419           During matching, when PCRE reaches a callout point, the external  func-
2420           tion  defined by pcre_callout is called (if it is set). This applies to
2421           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2422           only  argument  to  the callout function is a pointer to a pcre_callout
2423           block. This structure contains the following fields:
2424    
2425             int          version;
2426             int          callout_number;
2427             int         *offset_vector;
2428             const char  *subject;
2429             int          subject_length;
2430             int          start_match;
2431             int          current_position;
2432             int          capture_top;
2433             int          capture_last;
2434             void        *callout_data;
2435             int          pattern_position;
2436             int          next_item_length;
2437    
2438           The version field is an integer containing the version  number  of  the
2439           block  format. The initial version was 0; the current version is 1. The
2440           version number will change again in future  if  additional  fields  are
2441           added, but the intention is never to remove any of the existing fields.
2442    
2443           The callout_number field contains the number of the  callout,  as  com-
2444           piled  into  the pattern (that is, the number after ?C for manual call-
2445           outs, and 255 for automatically generated callouts).
2446    
2447           The offset_vector field is a pointer to the vector of offsets that  was
2448           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2449           pcre_exec() is used, the contents can be inspected in order to  extract
2450           substrings  that  have  been  matched  so  far,  in the same way as for
2451           extracting substrings after a match has completed. For  pcre_dfa_exec()
2452           this field is not useful.
2453    
2454           The subject and subject_length fields contain copies of the values that
2455           were passed to pcre_exec().
2456    
2457           The start_match field contains the offset within the subject  at  which
2458           the  current match attempt started. If the pattern is not anchored, the
2459           callout function may be called several times from the same point in the
2460           pattern for different starting points in the subject.
2461    
2462           The  current_position  field  contains the offset within the subject of
2463           the current match pointer.
2464    
2465           When the pcre_exec() function is used, the capture_top  field  contains
2466           one  more than the number of the highest numbered captured substring so
2467           far. If no substrings have been captured, the value of  capture_top  is
2468           one.  This  is always the case when pcre_dfa_exec() is used, because it
2469           does not support captured substrings.
2470    
2471           The capture_last field contains the number of the  most  recently  cap-
2472           tured  substring. If no substrings have been captured, its value is -1.
2473           This is always the case when pcre_dfa_exec() is used.
2474    
2475           The callout_data field contains a value that is passed  to  pcre_exec()
2476           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2477           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2478           structure.  If  no such data was passed, the value of callout_data in a
2479           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2480           structure in the pcreapi documentation.
2481    
2482           The  pattern_position field is present from version 1 of the pcre_call-
2483           out structure. It contains the offset to the next item to be matched in
2484           the pattern string.
2485    
2486           The  next_item_length field is present from version 1 of the pcre_call-
2487           out structure. It contains the length of the next item to be matched in
2488           the  pattern  string. When the callout immediately precedes an alterna-
2489           tion bar, a closing parenthesis, or the end of the pattern, the  length
2490           is  zero.  When the callout precedes an opening parenthesis, the length
2491           is that of the entire subpattern.
2492    
2493           The pattern_position and next_item_length fields are intended  to  help
2494           in  distinguishing between different automatic callouts, which all have
2495           the same callout number. However, they are set for all callouts.
2496    
2497    
2498    RETURN VALUES
2499    
2500           The external callout function returns an integer to PCRE. If the  value
2501           is  zero,  matching  proceeds  as  normal. If the value is greater than
2502           zero, matching fails at the current point, but  the  testing  of  other
2503           matching possibilities goes ahead, just as if a lookahead assertion had
2504           failed. If the value is less than zero, the  match  is  abandoned,  and
2505           pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2506    
2507           Negative   values   should   normally   be   chosen  from  the  set  of
2508           PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2509           dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2510           reserved for use by callout functions; it will never be  used  by  PCRE
2511           itself.
2512    
2513    
2514    AUTHOR
2515    
2516           Philip Hazel
2517           University Computing Service
2518           Cambridge CB2 3QH, England.
2519    
2520    
2521    REVISION
2522    
2523           Last updated: 06 March 2007
2524           Copyright (c) 1997-2007 University of Cambridge.
2525    ------------------------------------------------------------------------------
2526    
2527    
2528    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2529    
2530    
2531    NAME
2532           PCRE - Perl-compatible regular expressions
2533    
2534    
2535    DIFFERENCES BETWEEN PCRE AND PERL
2536    
2537           This  document describes the differences in the ways that PCRE and Perl
2538           handle regular expressions. The differences described here  are  mainly
2539           with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2540           tures that are expected to be in the forthcoming Perl 5.10.
2541    
2542           1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2543           of  what  it does have are given in the section on UTF-8 support in the
2544           main pcre page.
2545    
2546           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2547           permits  them,  but they do not mean what you might think. For example,
2548           (?!a){3} does not assert that the next three characters are not "a". It
2549           just asserts that the next character is not "a" three times.
2550    
2551           3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2552           tions are counted, but their entries in the offsets  vector  are  never
2553           set.  Perl sets its numerical variables from any such patterns that are
2554           matched before the assertion fails to match something (thereby succeed-
2555           ing),  but  only  if the negative lookahead assertion contains just one
2556           branch.
2557    
2558           4. Though binary zero characters are supported in the  subject  string,
2559           they are not allowed in a pattern string because it is passed as a nor-
2560           mal C string, terminated by zero. The escape sequence \0 can be used in
2561           the pattern to represent a binary zero.
2562    
2563           5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2564           \U, and \N. In fact these are implemented by Perl's general string-han-
2565           dling  and are not part of its pattern matching engine. If any of these
2566           are encountered by PCRE, an error is generated.
2567    
2568           6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2569           is  built  with Unicode character property support. The properties that
2570           can be tested with \p and \P are limited to the general category  prop-
2571           erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2572           derived properties Any and L&.
2573    
2574           7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2575           ters  in  between  are  treated as literals. This is slightly different
2576           from Perl in that $ and @ are  also  handled  as  literals  inside  the
2577           quotes.  In Perl, they cause variable interpolation (but of course PCRE
2578           does not have variables). Note the following examples:
2579    
2580               Pattern            PCRE matches      Perl matches
2581    
2582               \Qabc$xyz\E        abc$xyz           abc followed by the
2583                                                      contents of $xyz
2584               \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2585               \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2586    
2587           The \Q...\E sequence is recognized both inside  and  outside  character
2588           classes.
2589    
2590           8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2591           constructions. However, there is support for recursive  patterns.  This
2592           is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2593           "callout" feature allows an external function to be called during  pat-
2594           tern matching. See the pcrecallout documentation for details.
2595    
2596           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2597           always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2598           unlike Perl.
2599    
2600           10.  There are some differences that are concerned with the settings of
2601           captured strings when part of  a  pattern  is  repeated.  For  example,
2602           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2603           unset, but in PCRE it is set to "b".
2604    
2605           11. PCRE provides some extensions to the Perl regular expression facil-
2606           ities.   Perl  5.10  will  include new features that are not in earlier
2607           versions, some of which (such as named parentheses) have been  in  PCRE
2608           for some time. This list is with respect to Perl 5.10:
2609    
2610           (a)  Although  lookbehind  assertions  must match fixed length strings,
2611           each alternative branch of a lookbehind assertion can match a different
2612           length of string. Perl requires them all to have the same length.
2613    
2614           (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2615           meta-character matches only at the very end of the string.
2616    
2617           (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2618           cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2619           ignored. (Perl can be made to issue a warning.)
2620    
2621           (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2622           fiers is inverted, that is, by default they are not greedy, but if fol-
2623           lowed by a question mark they are.
2624    
2625           (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2626           tried only at the first matching position in the subject string.
2627    
2628           (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2629           TURE options for pcre_exec() have no Perl equivalents.
2630    
2631           (g) The callout facility is PCRE-specific.
2632    
2633           (h) The partial matching facility is PCRE-specific.
2634    
2635           (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2636           even on different hosts that have the other endianness.
2637    
2638           (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2639           different way and is not Perl-compatible.
2640    
2641    
2642    AUTHOR
2643    
2644           Philip Hazel
2645           University Computing Service
2646           Cambridge CB2 3QH, England.
2647    
2648    
2649    REVISION
2650    
2651           Last updated: 06 March 2007
2652           Copyright (c) 1997-2007 University of Cambridge.
2653    ------------------------------------------------------------------------------
2654    
2655    
2656    PCREPATTERN(3)                                                  PCREPATTERN(3)
2657    
2658    
2659    NAME
2660           PCRE - Perl-compatible regular expressions
2661    
2662    
2663    PCRE REGULAR EXPRESSION DETAILS
2664    
2665           The  syntax  and semantics of the regular expressions supported by PCRE
2666           are described below. Regular expressions are also described in the Perl
2667           documentation  and  in  a  number  of books, some of which have copious
2668           examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
2669           by  O'Reilly, covers regular expressions in great detail. This descrip-
2670           tion of PCRE's regular expressions is intended as reference material.
2671    
2672           The original operation of PCRE was on strings of  one-byte  characters.
2673           However,  there is now also support for UTF-8 character strings. To use
2674           this, you must build PCRE to  include  UTF-8  support,  and  then  call
2675           pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2676           matching is mentioned in several places below. There is also a  summary
2677           of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2678           page.
2679    
2680           The remainder of this document discusses the  patterns  that  are  sup-
2681           ported  by  PCRE when its main matching function, pcre_exec(), is used.
2682           From  release  6.0,   PCRE   offers   a   second   matching   function,
2683           pcre_dfa_exec(),  which matches using a different algorithm that is not
2684           Perl-compatible. The advantages and disadvantages  of  the  alternative
2685           function, and how it differs from the normal function, are discussed in
2686           the pcrematching page.
2687    
2688    
2689    CHARACTERS AND METACHARACTERS
2690    
2691           A regular expression is a pattern that is  matched  against  a  subject
2692           string  from  left  to right. Most characters stand for themselves in a
2693           pattern, and match the corresponding characters in the  subject.  As  a
2694           trivial example, the pattern
2695    
2696             The quick brown fox
2697    
2698           matches a portion of a subject string that is identical to itself. When
2699           caseless matching is specified (the PCRE_CASELESS option), letters  are
2700           matched  independently  of case. In UTF-8 mode, PCRE always understands
2701           the concept of case for characters whose values are less than  128,  so
2702           caseless  matching  is always possible. For characters with higher val-
2703           ues, the concept of case is supported if PCRE is compiled with  Unicode
2704           property  support,  but  not  otherwise.   If  you want to use caseless
2705           matching for characters 128 and above, you must  ensure  that  PCRE  is
2706           compiled with Unicode property support as well as with UTF-8 support.
2707    
2708           The  power  of  regular  expressions  comes from the ability to include
2709           alternatives and repetitions in the pattern. These are encoded  in  the
2710           pattern by the use of metacharacters, which do not stand for themselves
2711           but instead are interpreted in some special way.
2712    
2713           There are two different sets of metacharacters: those that  are  recog-
2714           nized  anywhere in the pattern except within square brackets, and those
2715           that are recognized within square brackets.  Outside  square  brackets,
2716           the metacharacters are as follows:
2717    
2718             \      general escape character with several uses
2719             ^      assert start of string (or line, in multiline mode)
2720             $      assert end of string (or line, in multiline mode)
2721             .      match any character except newline (by default)
2722             [      start character class definition
2723             |      start of alternative branch
2724             (      start subpattern
2725             )      end subpattern
2726             ?      extends the meaning of (
2727                    also 0 or 1 quantifier
2728                    also quantifier minimizer
2729             *      0 or more quantifier
2730             +      1 or more quantifier
2731                    also "possessive quantifier"
2732             {      start min/max quantifier
2733    
2734           Part  of  a  pattern  that is in square brackets is called a "character
2735           class". In a character class the only metacharacters are:
2736    
2737             \      general escape character
2738             ^      negate the class, but only if the first character
2739             -      indicates character range
2740             [      POSIX character class (only if followed by POSIX
2741                      syntax)
2742             ]      terminates the character class
2743    
2744           The following sections describe the use of each of the  metacharacters.
2745    
2746    
2747  BACKSLASH  BACKSLASH
      The backslash character has several uses. Firstly, if it  is  
      followed  by  a  non-alphameric character, it takes away any  
      special  meaning  that  character  may  have.  This  use  of  
      backslash  as  an  escape  character applies both inside and  
      outside character classes.  
   
      For example, if you want to match a "*" character, you write  
      "\*" in the pattern. This applies whether or not the follow-  
      ing character would otherwise  be  interpreted  as  a  meta-  
      character,  so it is always safe to precede a non-alphameric  
      with "\" to specify that it stands for itself.  In  particu-  
      lar, if you want to match a backslash, you write "\\".  
   
      If a pattern is compiled with the PCRE_EXTENDED option, whi-  
      tespace in the pattern (other than in a character class) and  
      characters between a "#" outside a character class  and  the  
      next  newline  character  are ignored. An escaping backslash  
      can be used to include a whitespace or "#" character as part  
      of the pattern.  
   
      A second use of backslash provides a way  of  encoding  non-  
      printing  characters  in patterns in a visible manner. There  
      is no restriction on the appearance of non-printing  charac-  
      ters,  apart from the binary zero that terminates a pattern,  
      but when a pattern is being prepared by text editing, it  is  
      usually  easier to use one of the following escape sequences  
      than the binary character it represents:  
   
        \a     alarm, that is, the BEL character (hex 07)  
        \cx    "control-x", where x is any character  
        \e     escape (hex 1B)  
        \f     formfeed (hex 0C)  
        \n     newline (hex 0A)  
        \r     carriage return (hex 0D)  
        \t     tab (hex 09)  
        \xhh   character with hex code hh  
        \ddd   character with octal code ddd, or backreference  
   
      The precise effect of "\cx" is as follows: if "x" is a lower  
      case  letter,  it  is converted to upper case. Then bit 6 of  
      the character (hex 40) is inverted.  Thus "\cz" becomes  hex  
      1A, but "\c{" becomes hex 3B, while "\c;" becomes hex 7B.  
   
      After "\x", up to two hexadecimal digits are  read  (letters  
      can be in upper or lower case).  
   
      After "\0" up to two further octal digits are read. In  both  
      cases,  if  there are fewer than two digits, just those that  
      are present are used. Thus the sequence "\0\x\07"  specifies  
      two binary zeros followed by a BEL character.  Make sure you  
      supply two digits after the initial zero  if  the  character  
      that follows is itself an octal digit.  
   
      The handling of a backslash followed by a digit other than 0  
      is  complicated.   Outside  a character class, PCRE reads it  
      and any following digits as a decimal number. If the  number  
      is  less  than  10, or if there have been at least that many  
      previous capturing left parentheses in the  expression,  the  
      entire  sequence is taken as a back reference. A description  
      of how this works is given later, following  the  discussion  
      of parenthesized subpatterns.  
   
      Inside a character  class,  or  if  the  decimal  number  is  
      greater  than  9 and there have not been that many capturing  
      subpatterns, PCRE re-reads up to three octal digits  follow-  
      ing  the  backslash,  and  generates  a single byte from the  
      least significant 8 bits of the value. Any subsequent digits  
      stand for themselves.  For example:  
   
        \040   is another way of writing a space  
        \40    is the same, provided there are fewer than 40  
                  previous capturing subpatterns  
        \7     is always a back reference  
        \11    might be a back reference, or another way of  
                  writing a tab  
        \011   is always a tab  
        \0113  is a tab followed by the character "3"  
        \113   is the character with octal code 113 (since there  
                  can be no more than 99 back references)  
        \377   is a byte consisting entirely of 1 bits  
        \81    is either a back reference, or a binary zero  
                  followed by the two characters "8" and "1"  
   
      Note that octal values of 100 or greater must not be  intro-  
      duced  by  a  leading zero, because no more than three octal  
      digits are ever read.  
   
      All the sequences that define a single  byte  value  can  be  
      used both inside and outside character classes. In addition,  
      inside a character class, the sequence "\b"  is  interpreted  
      as  the  backspace  character  (hex 08). Outside a character  
      class it has a different meaning (see below).  
   
      The third use of backslash is for specifying generic charac-  
      ter types:  
   
        \d     any decimal digit  
        \D     any character that is not a decimal digit  
        \s     any whitespace character  
        \S     any character that is not a whitespace character  
        \w     any "word" character  
        \W     any "non-word" character  
   
      Each pair of escape sequences partitions the complete set of  
      characters  into  two  disjoint  sets.  Any  given character  
      matches one, and only one, of each pair.  
   
      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 definition of letters and  digits  is  con-  
      trolled  by PCRE's character tables, and may vary if locale-  
      specific matching is  taking  place  (see  "Locale  support"  
      above). For example, in the "fr" (French) locale, some char-  
      acter codes greater than 128 are used for accented  letters,  
      and these are matched by \w.  
   
      These character type sequences can appear  both  inside  and  
      outside  character classes. They each match one character of  
      the appropriate type. If the current matching  point  is  at  
      the end of the subject string, all of them fail, since there  
      is no character to match.  
   
      The fourth use of backslash is  for  certain  simple  asser-  
      tions. An assertion specifies a condition that has to be met  
      at a particular point in  a  match,  without  consuming  any  
      characters  from  the subject string. The use of subpatterns  
      for more complicated  assertions  is  described  below.  The  
      backslashed assertions are  
   
        \b     word boundary  
        \B     not a word boundary  
        \A     start of subject (independent of multiline mode)  
        \Z     end of subject or newline at  end  (independent  of  
      multiline mode)  
        \z     end of subject (independent of multiline mode)  
   
      These assertions may not appear in  character  classes  (but  
      note that "\b" has a different meaning, namely the backspace  
      character, inside a character class).  
   
      A word boundary is a position in the  subject  string  where  
      the current character and the previous character do not both  
      match \w or \W (i.e. one matches \w and  the  other  matches  
      \W),  or the start or end of the string if the first or last  
      character matches \w, respectively.  
   
      The \A, \Z, and \z assertions differ  from  the  traditional  
      circumflex  and  dollar  (described below) in that they only  
      ever match at the very start and end of the subject  string,  
      whatever  options  are  set.  They  are  not affected by the  
      PCRE_NOTBOL or PCRE_NOTEOL options. If the startoffset argu-  
      ment  of  pcre_exec()  is  non-zero, \A can never match. The  
      difference between \Z and \z is that  \Z  matches  before  a  
      newline  that is the last character of the string as well as  
      at the end of the string, whereas \z  matches  only  at  the  
      end.  
2748    
2749           The backslash character has several uses. Firstly, if it is followed by
2750           a non-alphanumeric character, it takes away any  special  meaning  that
2751           character  may  have.  This  use  of  backslash  as an escape character
2752           applies both inside and outside character classes.
2753    
2754           For example, if you want to match a * character, you write  \*  in  the
2755           pattern.   This  escaping  action  applies whether or not the following
2756           character would otherwise be interpreted as a metacharacter, so  it  is
2757           always  safe  to  precede  a non-alphanumeric with backslash to specify
2758           that it stands for itself. In particular, if you want to match a  back-
2759           slash, you write \\.
2760    
2761           If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2762           the pattern (other than in a character class) and characters between  a
2763           # outside a character class and the next newline are ignored. An escap-
2764           ing backslash can be used to include a whitespace  or  #  character  as
2765           part of the pattern.
2766    
2767           If  you  want  to remove the special meaning from a sequence of charac-
2768           ters, you can do so by putting them between \Q and \E. This is  differ-
2769           ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
2770           sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
2771           tion. Note the following examples:
2772    
2773             Pattern            PCRE matches   Perl matches
2774    
2775             \Qabc$xyz\E        abc$xyz        abc followed by the
2776                                                 contents of $xyz
2777             \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2778             \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2779    
2780           The  \Q...\E  sequence  is recognized both inside and outside character
2781           classes.
2782    
2783       Non-printing characters
2784    
2785           A second use of backslash provides a way of encoding non-printing char-
2786           acters  in patterns in a visible manner. There is no restriction on the
2787           appearance of non-printing characters, apart from the binary zero  that
2788           terminates  a  pattern,  but  when  a pattern is being prepared by text
2789           editing, it is usually easier  to  use  one  of  the  following  escape
2790           sequences than the binary character it represents:
2791    
2792             \a        alarm, that is, the BEL character (hex 07)
2793             \cx       "control-x", where x is any character
2794             \e        escape (hex 1B)
2795             \f        formfeed (hex 0C)
2796             \n        newline (hex 0A)
2797             \r        carriage return (hex 0D)
2798             \t        tab (hex 09)
2799             \ddd      character with octal code ddd, or backreference
2800             \xhh      character with hex code hh
2801             \x{hhh..} character with hex code hhh..
2802    
2803           The  precise  effect of \cx is as follows: if x is a lower case letter,
2804           it is converted to upper case. Then bit 6 of the character (hex 40)  is
2805           inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
2806           becomes hex 7B.
2807    
2808           After \x, from zero to two hexadecimal digits are read (letters can  be
2809           in  upper  or  lower case). Any number of hexadecimal digits may appear
2810           between \x{ and }, but the value of the character  code  must  be  less
2811           than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,
2812           the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2813           hexadecimal  digits  appear between \x{ and }, or if there is no termi-
2814           nating }, this form of escape is not recognized.  Instead, the  initial
2815           \x will be interpreted as a basic hexadecimal escape, with no following
2816           digits, giving a character whose value is zero.
2817    
2818           Characters whose value is less than 256 can be defined by either of the
2819           two  syntaxes  for  \x. There is no difference in the way they are han-
2820           dled. For example, \xdc is exactly the same as \x{dc}.
2821    
2822           After \0 up to two further octal digits are read. If  there  are  fewer
2823           than  two  digits,  just  those  that  are  present  are used. Thus the
2824           sequence \0\x\07 specifies two binary zeros followed by a BEL character
2825           (code  value 7). Make sure you supply two digits after the initial zero
2826           if the pattern character that follows is itself an octal digit.
2827    
2828