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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. Neither has
6    the pcredemo program. There are separate text files for the pcregrep and
7    pcretest commands.
8    -----------------------------------------------------------------------------
9    
10    
11    PCRE(3)                                                                PCRE(3)
12    
13    
14    NAME
15           PCRE - Perl-compatible regular expressions
16    
17    
18    INTRODUCTION
19    
20           The  PCRE  library is a set of functions that implement regular expres-
21           sion pattern matching using the same syntax and semantics as Perl, with
22           just  a few differences. Some features that appeared in Python and PCRE
23           before they appeared in Perl are also available using the  Python  syn-
24           tax,  there  is  some  support for one or two .NET and Oniguruma syntax
25           items, and there is an option for requesting some  minor  changes  that
26           give better JavaScript compatibility.
27    
28           The  current implementation of PCRE corresponds approximately with Perl
29           5.12, including support for UTF-8 encoded strings and  Unicode  general
30           category  properties.  However,  UTF-8  and  Unicode  support has to be
31           explicitly enabled; it is not the default. The  Unicode  tables  corre-
32           spond to Unicode release 6.0.0.
33    
34           In  addition to the Perl-compatible matching function, PCRE contains an
35           alternative function that matches the same compiled patterns in a  dif-
36           ferent way. In certain circumstances, the alternative function has some
37           advantages.  For a discussion of the two matching algorithms,  see  the
38           pcrematching page.
39    
40           PCRE  is  written  in C and released as a C library. A number of people
41           have written wrappers and interfaces of various kinds.  In  particular,
42           Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
43           included as part of the PCRE distribution. The pcrecpp page has details
44           of  this  interface.  Other  people's contributions can be found in the
45           Contrib directory at the primary FTP site, which is:
46    
47           ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
48    
49           Details of exactly which Perl regular expression features are  and  are
50           not supported by PCRE are given in separate documents. See the pcrepat-
51           tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
52           page.
53    
54           Some  features  of  PCRE can be included, excluded, or changed when the
55           library is built. The pcre_config() function makes it  possible  for  a
56           client  to  discover  which  features are available. The features them-
57           selves are described in the pcrebuild page. Documentation about  build-
58           ing  PCRE  for various operating systems can be found in the README and
59           NON-UNIX-USE files in the source distribution.
60    
61           The library contains a number of undocumented  internal  functions  and
62           data  tables  that  are  used by more than one of the exported external
63           functions, but which are not intended  for  use  by  external  callers.
64           Their  names  all begin with "_pcre_", which hopefully will not provoke
65           any name clashes. In some environments, it is possible to control which
66           external  symbols  are  exported when a shared library is built, and in
67           these cases the undocumented symbols are not exported.
68    
69    
70    USER DOCUMENTATION
71    
72           The user documentation for PCRE comprises a number  of  different  sec-
73           tions.  In the "man" format, each of these is a separate "man page". In
74           the HTML format, each is a separate page, linked from the  index  page.
75           In  the  plain  text format, all the sections, except the pcredemo sec-
76           tion, are concatenated, for ease of searching. The sections are as fol-
77           lows:
78    
79             pcre              this document
80             pcre-config       show PCRE installation configuration information
81             pcreapi           details of PCRE's native C API
82             pcrebuild         options for building PCRE
83             pcrecallout       details of the callout feature
84             pcrecompat        discussion of Perl compatibility
85             pcrecpp           details of the C++ wrapper
86             pcredemo          a demonstration C program that uses PCRE
87             pcregrep          description of the pcregrep command
88             pcrematching      discussion of the two matching algorithms
89             pcrepartial       details of the partial matching facility
90             pcrepattern       syntax and semantics of supported
91                                 regular expressions
92             pcreperform       discussion of performance issues
93             pcreposix         the POSIX-compatible C API
94             pcreprecompile    details of saving and re-using precompiled patterns
95             pcresample        discussion of the pcredemo program
96             pcrestack         discussion of stack usage
97             pcresyntax        quick syntax reference
98             pcretest          description of the pcretest testing command
99    
100           In  addition,  in the "man" and HTML formats, there is a short page for
101           each C library function, listing its arguments and results.
102    
103    
104    LIMITATIONS
105    
106           There are some size limitations in PCRE but it is hoped that they  will
107           never in practice be relevant.
108    
109           The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
110           is compiled with the default internal linkage size of 2. If you want to
111           process  regular  expressions  that are truly enormous, you can compile
112           PCRE with an internal linkage size of 3 or 4 (see the  README  file  in
113           the  source  distribution and the pcrebuild documentation for details).
114           In these cases the limit is substantially larger.  However,  the  speed
115           of execution is slower.
116    
117           All values in repeating quantifiers must be less than 65536.
118    
119           There is no limit to the number of parenthesized subpatterns, but there
120           can be no more than 65535 capturing subpatterns.
121    
122           The maximum length of name for a named subpattern is 32 characters, and
123           the maximum number of named subpatterns is 10000.
124    
125           The  maximum  length of a subject string is the largest positive number
126           that an integer variable can hold. However, when using the  traditional
127           matching function, PCRE uses recursion to handle subpatterns and indef-
128           inite repetition.  This means that the available stack space may  limit
129           the size of a subject string that can be processed by certain patterns.
130           For a discussion of stack issues, see the pcrestack documentation.
131    
132    
133    UTF-8 AND UNICODE PROPERTY SUPPORT
134    
135           From release 3.3, PCRE has  had  some  support  for  character  strings
136           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
137           to cover most common requirements, and in release 5.0  additional  sup-
138           port for Unicode general category properties was added.
139    
140           In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
141           support in the code, and, in addition,  you  must  call  pcre_compile()
142           with  the  PCRE_UTF8  option  flag,  or the pattern must start with the
143           sequence (*UTF8). When either of these is the case,  both  the  pattern
144           and  any  subject  strings  that  are matched against it are treated as
145           UTF-8 strings instead of strings of 1-byte characters.
146    
147           If you compile PCRE with UTF-8 support, but do not use it at run  time,
148           the  library will be a bit bigger, but the additional run time overhead
149           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
150           very big.
151    
152           If PCRE is built with Unicode character property support (which implies
153           UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
154           ported.  The available properties that can be tested are limited to the
155           general category properties such as Lu for an upper case letter  or  Nd
156           for  a  decimal number, the Unicode script names such as Arabic or Han,
157           and the derived properties Any and L&. A full  list  is  given  in  the
158           pcrepattern documentation. Only the short names for properties are sup-
159           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
160           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
161           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
162           does not support this.
163    
164       Validity of UTF-8 strings
165    
166           When  you  set  the  PCRE_UTF8 flag, the strings passed as patterns and
167           subjects are (by default) checked for validity on entry to the relevant
168           functions.  From  release 7.3 of PCRE, the check is according the rules
169           of RFC 3629, which are themselves derived from the  Unicode  specifica-
170           tion.  Earlier  releases  of PCRE followed the rules of RFC 2279, which
171           allows the full range of 31-bit values (0 to 0x7FFFFFFF).  The  current
172           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
173           to U+DFFF.
174    
175           The excluded code points are the "Low Surrogate Area"  of  Unicode,  of
176           which  the Unicode Standard says this: "The Low Surrogate Area does not
177           contain any  character  assignments,  consequently  no  character  code
178           charts or namelists are provided for this area. Surrogates are reserved
179           for use with UTF-16 and then must be used in pairs."  The  code  points
180           that  are  encoded  by  UTF-16  pairs are available as independent code
181           points in the UTF-8 encoding. (In  other  words,  the  whole  surrogate
182           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
183    
184           If an invalid UTF-8 string is passed to PCRE, an error return is given.
185           At compile time, the only additional information is the offset  to  the
186           first byte of the failing character. The runtime functions (pcre_exec()
187           and pcre_dfa_exec()), pass back this information  as  well  as  a  more
188           detailed  reason  code if the caller has provided memory in which to do
189           this.
190    
191           In some situations, you may already know that your strings  are  valid,
192           and  therefore  want  to  skip these checks in order to improve perfor-
193           mance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run
194           time,  PCRE  assumes  that  the pattern or subject it is given (respec-
195           tively) contains only valid UTF-8 codes. In  this  case,  it  does  not
196           diagnose an invalid UTF-8 string.
197    
198           If  you  pass  an  invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set,
199           what happens depends on why the string is invalid. If the  string  con-
200           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
201           string of characters in the range 0  to  0x7FFFFFFF.  In  other  words,
202           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
203           strings according to the more liberal rules of RFC  2279.  However,  if
204           the  string does not even conform to RFC 2279, the result is undefined.
205           Your program may crash.
206    
207           If you want to process strings  of  values  in  the  full  range  0  to
208           0x7FFFFFFF,  encoded in a UTF-8-like manner as per the old RFC, you can
209           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
210           this situation, you will have to apply your own validity check.
211    
212       General comments about UTF-8 mode
213    
214           1.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
215           two-byte UTF-8 character if the value is greater than 127.
216    
217           2. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
218           characters for values greater than \177.
219    
220           3.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
221           vidual bytes, for example: \x{100}{3}.
222    
223           4. The dot metacharacter matches one UTF-8 character instead of a  sin-
224           gle byte.
225    
226           5.  The  escape sequence \C can be used to match a single byte in UTF-8
227           mode, but its use can lead to some strange effects.  This  facility  is
228           not available in the alternative matching function, pcre_dfa_exec().
229    
230           6.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
231           test characters of any code value, but, by default, the characters that
232           PCRE  recognizes  as digits, spaces, or word characters remain the same
233           set as before, all with values less than 256. This  remains  true  even
234           when  PCRE  is built to include Unicode property support, because to do
235           otherwise would slow down PCRE in many common cases. Note in particular
236           that this applies to \b and \B, because they are defined in terms of \w
237           and \W. If you really want to test for a wider sense of, say,  "digit",
238           you  can  use  explicit Unicode property tests such as \p{Nd}. Alterna-
239           tively, if you set the PCRE_UCP option,  the  way  that  the  character
240           escapes  work  is changed so that Unicode properties are used to deter-
241           mine which characters match. There are more details in the  section  on
242           generic character types in the pcrepattern documentation.
243    
244           7.  Similarly,  characters that match the POSIX named character classes
245           are all low-valued characters, unless the PCRE_UCP option is set.
246    
247           8. However, the horizontal and  vertical  whitespace  matching  escapes
248           (\h,  \H,  \v, and \V) do match all the appropriate Unicode characters,
249           whether or not PCRE_UCP is set.
250    
251           9. Case-insensitive matching applies only to  characters  whose  values
252           are  less than 128, unless PCRE is built with Unicode property support.
253           Even when Unicode property support is available, PCRE  still  uses  its
254           own  character  tables when checking the case of low-valued characters,
255           so as not to degrade performance.  The Unicode property information  is
256           used only for characters with higher values. Furthermore, PCRE supports
257           case-insensitive matching only  when  there  is  a  one-to-one  mapping
258           between  a letter's cases. There are a small number of many-to-one map-
259           pings in Unicode; these are not supported by PCRE.
260    
261    
262    AUTHOR
263    
264           Philip Hazel
265           University Computing Service
266           Cambridge CB2 3QH, England.
267    
268           Putting an actual email address here seems to have been a spam  magnet,
269           so  I've  taken  it away. If you want to email me, use my two initials,
270           followed by the two digits 10, at the domain cam.ac.uk.
271    
272    
273    REVISION
274    
275           Last updated: 07 May 2011
276           Copyright (c) 1997-2011 University of Cambridge.
277    ------------------------------------------------------------------------------
278    
279    
280    PCREBUILD(3)                                                      PCREBUILD(3)
281    
282    
283    NAME
284           PCRE - Perl-compatible regular expressions
285    
286    
287    PCRE BUILD-TIME OPTIONS
288    
289           This  document  describes  the  optional  features  of PCRE that can be
290           selected when the library is compiled. It assumes use of the  configure
291           script,  where the optional features are selected or deselected by pro-
292           viding options to configure before running the make  command.  However,
293           the  same  options  can be selected in both Unix-like and non-Unix-like
294           environments using the GUI facility of cmake-gui if you are using CMake
295           instead of configure to build PCRE.
296    
297           There  is  a  lot more information about building PCRE in non-Unix-like
298           environments in the file called NON_UNIX_USE, which is part of the PCRE
299           distribution.  You  should consult this file as well as the README file
300           if you are building in a non-Unix-like environment.
301    
302           The complete list of options for configure (which includes the standard
303           ones  such  as  the  selection  of  the  installation directory) can be
304           obtained by running
305    
306             ./configure --help
307    
308           The following sections include  descriptions  of  options  whose  names
309           begin with --enable or --disable. These settings specify changes to the
310           defaults for the configure command. Because of the way  that  configure
311           works,  --enable  and --disable always come in pairs, so the complemen-
312           tary option always exists as well, but as it specifies the default,  it
313           is not described.
314    
315    
316    BUILDING SHARED AND STATIC LIBRARIES
317    
318           The  PCRE building process uses libtool to build both shared and static
319           Unix libraries by default. You can suppress one of these by adding  one
320           of
321    
322             --disable-shared
323             --disable-static
324    
325           to the configure command, as required.
326    
327    
328    C++ SUPPORT
329    
330           By default, the configure script will search for a C++ compiler and C++
331           header files. If it finds them, it automatically builds the C++ wrapper
332           library for PCRE. You can disable this by adding
333    
334             --disable-cpp
335    
336           to the configure command.
337    
338    
339    UTF-8 SUPPORT
340    
341           To build PCRE with support for UTF-8 Unicode character strings, add
342    
343             --enable-utf8
344    
345           to  the  configure  command.  Of  itself, this does not make PCRE treat
346           strings as UTF-8. As well as compiling PCRE with this option, you  also
347           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
348           or pcre_compile2() functions.
349    
350           If you set --enable-utf8 when compiling in an EBCDIC environment,  PCRE
351           expects its input to be either ASCII or UTF-8 (depending on the runtime
352           option). It is not possible to support both EBCDIC and UTF-8  codes  in
353           the  same  version  of  the  library.  Consequently,  --enable-utf8 and
354           --enable-ebcdic are mutually exclusive.
355    
356    
357    UNICODE CHARACTER PROPERTY SUPPORT
358    
359           UTF-8 support allows PCRE to process character values greater than  255
360           in  the  strings that it handles. On its own, however, it does not pro-
361           vide any facilities for accessing the properties of such characters. If
362           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
363           refer to Unicode character properties, you must add
364    
365             --enable-unicode-properties
366    
367           to the configure command. This implies UTF-8 support, even if you  have
368           not explicitly requested it.
369    
370           Including  Unicode  property  support  adds around 30K of tables to the
371           PCRE library. Only the general category properties such as  Lu  and  Nd
372           are supported. Details are given in the pcrepattern documentation.
373    
374    
375    CODE VALUE OF NEWLINE
376    
377           By  default,  PCRE interprets the linefeed (LF) character as indicating
378           the end of a line. This is the normal newline  character  on  Unix-like
379           systems.  You  can compile PCRE to use carriage return (CR) instead, by
380           adding
381    
382             --enable-newline-is-cr
383    
384           to the  configure  command.  There  is  also  a  --enable-newline-is-lf
385           option, which explicitly specifies linefeed as the newline character.
386    
387           Alternatively, you can specify that line endings are to be indicated by
388           the two character sequence CRLF. If you want this, add
389    
390             --enable-newline-is-crlf
391    
392           to the configure command. There is a fourth option, specified by
393    
394             --enable-newline-is-anycrlf
395    
396           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
397           CRLF as indicating a line ending. Finally, a fifth option, specified by
398    
399             --enable-newline-is-any
400    
401           causes PCRE to recognize any Unicode newline sequence.
402    
403           Whatever  line  ending convention is selected when PCRE is built can be
404           overridden when the library functions are called. At build time  it  is
405           conventional to use the standard for your operating system.
406    
407    
408    WHAT \R MATCHES
409    
410           By  default,  the  sequence \R in a pattern matches any Unicode newline
411           sequence, whatever has been selected as the line  ending  sequence.  If
412           you specify
413    
414             --enable-bsr-anycrlf
415    
416           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
417           ever is selected when PCRE is built can be overridden when the  library
418           functions are called.
419    
420    
421    POSIX MALLOC USAGE
422    
423           When PCRE is called through the POSIX interface (see the pcreposix doc-
424           umentation), additional working storage is  required  for  holding  the
425           pointers  to capturing substrings, because PCRE requires three integers
426           per substring, whereas the POSIX interface provides only  two.  If  the
427           number of expected substrings is small, the wrapper function uses space
428           on the stack, because this is faster than using malloc() for each call.
429           The default threshold above which the stack is no longer used is 10; it
430           can be changed by adding a setting such as
431    
432             --with-posix-malloc-threshold=20
433    
434           to the configure command.
435    
436    
437    HANDLING VERY LARGE PATTERNS
438    
439           Within a compiled pattern, offset values are used  to  point  from  one
440           part  to another (for example, from an opening parenthesis to an alter-
441           nation metacharacter). By default, two-byte values are used  for  these
442           offsets,  leading  to  a  maximum size for a compiled pattern of around
443           64K. This is sufficient to handle all but the most  gigantic  patterns.
444           Nevertheless,  some  people do want to process truyl enormous patterns,
445           so it is possible to compile PCRE to use three-byte or  four-byte  off-
446           sets by adding a setting such as
447    
448             --with-link-size=3
449    
450           to  the  configure  command.  The value given must be 2, 3, or 4. Using
451           longer offsets slows down the operation of PCRE because it has to  load
452           additional bytes when handling them.
453    
454    
455    AVOIDING EXCESSIVE STACK USAGE
456    
457           When matching with the pcre_exec() function, PCRE implements backtrack-
458           ing by making recursive calls to an internal function  called  match().
459           In  environments  where  the size of the stack is limited, this can se-
460           verely limit PCRE's operation. (The Unix environment does  not  usually
461           suffer from this problem, but it may sometimes be necessary to increase
462           the maximum stack size.  There is a discussion in the  pcrestack  docu-
463           mentation.)  An alternative approach to recursion that uses memory from
464           the heap to remember data, instead of using recursive  function  calls,
465           has  been  implemented to work round the problem of limited stack size.
466           If you want to build a version of PCRE that works this way, add
467    
468             --disable-stack-for-recursion
469    
470           to the configure command. With this configuration, PCRE  will  use  the
471           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
472           ment functions. By default these point to malloc() and free(), but  you
473           can replace the pointers so that your own functions are used instead.
474    
475           Separate  functions  are  provided  rather  than  using pcre_malloc and
476           pcre_free because the  usage  is  very  predictable:  the  block  sizes
477           requested  are  always  the  same,  and  the blocks are always freed in
478           reverse order. A calling program might be able to  implement  optimized
479           functions  that  perform  better  than  malloc()  and free(). PCRE runs
480           noticeably more slowly when built in this way. This option affects only
481           the pcre_exec() function; it is not relevant for pcre_dfa_exec().
482    
483    
484    LIMITING PCRE RESOURCE USAGE
485    
486           Internally,  PCRE has a function called match(), which it calls repeat-
487           edly  (sometimes  recursively)  when  matching  a  pattern   with   the
488           pcre_exec()  function.  By controlling the maximum number of times this
489           function may be called during a single matching operation, a limit  can
490           be  placed  on  the resources used by a single call to pcre_exec(). The
491           limit can be changed at run time, as described in the pcreapi  documen-
492           tation.  The default is 10 million, but this can be changed by adding a
493           setting such as
494    
495             --with-match-limit=500000
496    
497           to  the  configure  command.  This  setting  has  no  effect   on   the
498           pcre_dfa_exec() matching function.
499    
500           In  some  environments  it is desirable to limit the depth of recursive
501           calls of match() more strictly than the total number of calls, in order
502           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
503           for-recursion is specified) that is used. A second limit controls this;
504           it  defaults  to  the  value  that is set for --with-match-limit, which
505           imposes no additional constraints. However, you can set a  lower  limit
506           by adding, for example,
507    
508             --with-match-limit-recursion=10000
509    
510           to  the  configure  command.  This  value can also be overridden at run
511           time.
512    
513    
514    CREATING CHARACTER TABLES AT BUILD TIME
515    
516           PCRE uses fixed tables for processing characters whose code values  are
517           less  than 256. By default, PCRE is built with a set of tables that are
518           distributed in the file pcre_chartables.c.dist. These  tables  are  for
519           ASCII codes only. If you add
520    
521             --enable-rebuild-chartables
522    
523           to  the  configure  command, the distributed tables are no longer used.
524           Instead, a program called dftables is compiled and  run.  This  outputs
525           the source for new set of tables, created in the default locale of your
526           C runtime system. (This method of replacing the tables does not work if
527           you  are cross compiling, because dftables is run on the local host. If
528           you need to create alternative tables when cross  compiling,  you  will
529           have to do so "by hand".)
530    
531    
532    USING EBCDIC CODE
533    
534           PCRE  assumes  by  default that it will run in an environment where the
535           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
536           This  is  the  case for most computer operating systems. PCRE can, how-
537           ever, be compiled to run in an EBCDIC environment by adding
538    
539             --enable-ebcdic
540    
541           to the configure command. This setting implies --enable-rebuild-charta-
542           bles.  You  should  only  use  it if you know that you are in an EBCDIC
543           environment (for example,  an  IBM  mainframe  operating  system).  The
544           --enable-ebcdic option is incompatible with --enable-utf8.
545    
546    
547    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
548    
549           By default, pcregrep reads all files as plain text. You can build it so
550           that it recognizes files whose names end in .gz or .bz2, and reads them
551           with libz or libbz2, respectively, by adding one or both of
552    
553             --enable-pcregrep-libz
554             --enable-pcregrep-libbz2
555    
556           to the configure command. These options naturally require that the rel-
557           evant libraries are installed on your system. Configuration  will  fail
558           if they are not.
559    
560    
561    PCREGREP BUFFER SIZE
562    
563           pcregrep  uses  an internal buffer to hold a "window" on the file it is
564           scanning, in order to be able to output "before" and "after" lines when
565           it  finds  a match. The size of the buffer is controlled by a parameter
566           whose default value is 20K. The buffer itself is three times this size,
567           but because of the way it is used for holding "before" lines, the long-
568           est line that is guaranteed to be processable is  the  parameter  size.
569           You can change the default parameter value by adding, for example,
570    
571             --with-pcregrep-bufsize=50K
572    
573           to the configure command. The caller of pcregrep can, however, override
574           this value by specifying a run-time option.
575    
576    
577    PCRETEST OPTION FOR LIBREADLINE SUPPORT
578    
579           If you add
580    
581             --enable-pcretest-libreadline
582    
583           to the configure command,  pcretest  is  linked  with  the  libreadline
584           library,  and  when its input is from a terminal, it reads it using the
585           readline() function. This provides line-editing and history facilities.
586           Note that libreadline is GPL-licensed, so if you distribute a binary of
587           pcretest linked in this way, there may be licensing issues.
588    
589           Setting this option causes the -lreadline option to  be  added  to  the
590           pcretest  build.  In many operating environments with a sytem-installed
591           libreadline this is sufficient. However, in some environments (e.g.  if
592           an  unmodified  distribution version of readline is in use), some extra
593           configuration may be necessary. The INSTALL file for  libreadline  says
594           this:
595    
596             "Readline uses the termcap functions, but does not link with the
597             termcap or curses library itself, allowing applications which link
598             with readline the to choose an appropriate library."
599    
600           If  your environment has not been set up so that an appropriate library
601           is automatically included, you may need to add something like
602    
603             LIBS="-ncurses"
604    
605           immediately before the configure command.
606    
607    
608    SEE ALSO
609    
610           pcreapi(3), pcre_config(3).
611    
612    
613    AUTHOR
614    
615           Philip Hazel
616           University Computing Service
617           Cambridge CB2 3QH, England.
618    
619    
620    REVISION
621    
622           Last updated: 02 August 2011
623           Copyright (c) 1997-2011 University of Cambridge.
624    ------------------------------------------------------------------------------
625    
626    
627    PCREMATCHING(3)                                                PCREMATCHING(3)
628    
629    
630    NAME
631           PCRE - Perl-compatible regular expressions
632    
633    
634    PCRE MATCHING ALGORITHMS
635    
636           This document describes the two different algorithms that are available
637           in PCRE for matching a compiled regular expression against a given sub-
638           ject  string.  The  "standard"  algorithm  is  the  one provided by the
639           pcre_exec() function.  This works in the same was  as  Perl's  matching
640           function, and provides a Perl-compatible matching operation.
641    
642           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
643           this operates in a different way, and is not  Perl-compatible.  It  has
644           advantages  and disadvantages compared with the standard algorithm, and
645           these are described below.
646    
647           When there is only one possible way in which a given subject string can
648           match  a pattern, the two algorithms give the same answer. A difference
649           arises, however, when there are multiple possibilities. For example, if
650           the pattern
651    
652             ^<.*>
653    
654           is matched against the string
655    
656             <something> <something else> <something further>
657    
658           there are three possible answers. The standard algorithm finds only one
659           of them, whereas the alternative algorithm finds all three.
660    
661    
662    REGULAR EXPRESSIONS AS TREES
663    
664           The set of strings that are matched by a regular expression can be rep-
665           resented  as  a  tree structure. An unlimited repetition in the pattern
666           makes the tree of infinite size, but it is still a tree.  Matching  the
667           pattern  to a given subject string (from a given starting point) can be
668           thought of as a search of the tree.  There are two  ways  to  search  a
669           tree:  depth-first  and  breadth-first, and these correspond to the two
670           matching algorithms provided by PCRE.
671    
672    
673    THE STANDARD MATCHING ALGORITHM
674    
675           In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
676           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
677           depth-first search of the pattern tree. That is, it  proceeds  along  a
678           single path through the tree, checking that the subject matches what is
679           required. When there is a mismatch, the algorithm  tries  any  alterna-
680           tives  at  the  current point, and if they all fail, it backs up to the
681           previous branch point in the  tree,  and  tries  the  next  alternative
682           branch  at  that  level.  This often involves backing up (moving to the
683           left) in the subject string as well.  The  order  in  which  repetition
684           branches  are  tried  is controlled by the greedy or ungreedy nature of
685           the quantifier.
686    
687           If a leaf node is reached, a matching string has  been  found,  and  at
688           that  point the algorithm stops. Thus, if there is more than one possi-
689           ble match, this algorithm returns the first one that it finds.  Whether
690           this  is the shortest, the longest, or some intermediate length depends
691           on the way the greedy and ungreedy repetition quantifiers are specified
692           in the pattern.
693    
694           Because  it  ends  up  with a single path through the tree, it is rela-
695           tively straightforward for this algorithm to keep  track  of  the  sub-
696           strings  that  are  matched  by portions of the pattern in parentheses.
697           This provides support for capturing parentheses and back references.
698    
699    
700    THE ALTERNATIVE MATCHING ALGORITHM
701    
702           This algorithm conducts a breadth-first search of  the  tree.  Starting
703           from  the  first  matching  point  in the subject, it scans the subject
704           string from left to right, once, character by character, and as it does
705           this,  it remembers all the paths through the tree that represent valid
706           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
707           though  it is not implemented as a traditional finite state machine (it
708           keeps multiple states active simultaneously).
709    
710           Although the general principle of this matching algorithm  is  that  it
711           scans  the subject string only once, without backtracking, there is one
712           exception: when a lookaround assertion is encountered,  the  characters
713           following  or  preceding  the  current  point  have to be independently
714           inspected.
715    
716           The scan continues until either the end of the subject is  reached,  or
717           there  are  no more unterminated paths. At this point, terminated paths
718           represent the different matching possibilities (if there are none,  the
719           match  has  failed).   Thus,  if there is more than one possible match,
720           this algorithm finds all of them, and in particular, it finds the long-
721           est.  The  matches are returned in decreasing order of length. There is
722           an option to stop the algorithm after the first match (which is  neces-
723           sarily the shortest) is found.
724    
725           Note that all the matches that are found start at the same point in the
726           subject. If the pattern
727    
728             cat(er(pillar)?)?
729    
730           is matched against the string "the caterpillar catchment",  the  result
731           will  be the three strings "caterpillar", "cater", and "cat" that start
732           at the fifth character of the subject. The algorithm does not automati-
733           cally move on to find matches that start at later positions.
734    
735           There are a number of features of PCRE regular expressions that are not
736           supported by the alternative matching algorithm. They are as follows:
737    
738           1. Because the algorithm finds all  possible  matches,  the  greedy  or
739           ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
740           ungreedy quantifiers are treated in exactly the same way. However, pos-
741           sessive  quantifiers can make a difference when what follows could also
742           match what is quantified, for example in a pattern like this:
743    
744             ^a++\w!
745    
746           This pattern matches "aaab!" but not "aaa!", which would be matched  by
747           a  non-possessive quantifier. Similarly, if an atomic group is present,
748           it is matched as if it were a standalone pattern at the current  point,
749           and  the  longest match is then "locked in" for the rest of the overall
750           pattern.
751    
752           2. When dealing with multiple paths through the tree simultaneously, it
753           is  not  straightforward  to  keep track of captured substrings for the
754           different matching possibilities, and  PCRE's  implementation  of  this
755           algorithm does not attempt to do this. This means that no captured sub-
756           strings are available.
757    
758           3. Because no substrings are captured, back references within the  pat-
759           tern are not supported, and cause errors if encountered.
760    
761           4.  For  the same reason, conditional expressions that use a backrefer-
762           ence as the condition or test for a specific group  recursion  are  not
763           supported.
764    
765           5.  Because  many  paths  through the tree may be active, the \K escape
766           sequence, which resets the start of the match when encountered (but may
767           be  on  some  paths  and not on others), is not supported. It causes an
768           error if encountered.
769    
770           6. Callouts are supported, but the value of the  capture_top  field  is
771           always 1, and the value of the capture_last field is always -1.
772    
773           7.  The \C escape sequence, which (in the standard algorithm) matches a
774           single byte, even in UTF-8 mode, is not supported because the  alterna-
775           tive  algorithm  moves  through  the  subject string one character at a
776           time, for all active paths through the tree.
777    
778           8. Except for (*FAIL), the backtracking control verbs such as  (*PRUNE)
779           are  not  supported.  (*FAIL)  is supported, and behaves like a failing
780           negative assertion.
781    
782    
783    ADVANTAGES OF THE ALTERNATIVE ALGORITHM
784    
785           Using the alternative matching algorithm provides the following  advan-
786           tages:
787    
788           1. All possible matches (at a single point in the subject) are automat-
789           ically found, and in particular, the longest match is  found.  To  find
790           more than one match using the standard algorithm, you have to do kludgy
791           things with callouts.
792    
793           2. Because the alternative algorithm  scans  the  subject  string  just
794           once,  and  never  needs to backtrack, it is possible to pass very long
795           subject strings to the matching function in  several  pieces,  checking
796           for  partial  matching  each time. Although it is possible to do multi-
797           segment matching using the standard algorithm (pcre_exec()), by retain-
798           ing  partially matched substrings, it is more complicated. The pcrepar-
799           tial documentation gives details  of  partial  matching  and  discusses
800           multi-segment matching.
801    
802    
803    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
804    
805           The alternative algorithm suffers from a number of disadvantages:
806    
807           1.  It  is  substantially  slower  than the standard algorithm. This is
808           partly because it has to search for all possible matches, but  is  also
809           because it is less susceptible to optimization.
810    
811           2. Capturing parentheses and back references are not supported.
812    
813           3. Although atomic groups are supported, their use does not provide the
814           performance advantage that it does for the standard algorithm.
815    
816    
817    AUTHOR
818    
819           Philip Hazel
820           University Computing Service
821           Cambridge CB2 3QH, England.
822    
823    
824    REVISION
825    
826           Last updated: 17 November 2010
827           Copyright (c) 1997-2010 University of Cambridge.
828    ------------------------------------------------------------------------------
829    
830    
831    PCREAPI(3)                                                          PCREAPI(3)
832    
833    
834    NAME
835           PCRE - Perl-compatible regular expressions
836    
837    
838    PCRE NATIVE API
839    
840           #include <pcre.h>
841    
842           pcre *pcre_compile(const char *pattern, int options,
843                const char **errptr, int *erroffset,
844                const unsigned char *tableptr);
845    
846           pcre *pcre_compile2(const char *pattern, int options,
847                int *errorcodeptr,
848                const char **errptr, int *erroffset,
849                const unsigned char *tableptr);
850    
851           pcre_extra *pcre_study(const pcre *code, int options,
852                const char **errptr);
853    
854           int pcre_exec(const pcre *code, const pcre_extra *extra,
855                const char *subject, int length, int startoffset,
856                int options, int *ovector, int ovecsize);
857    
858           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
859                const char *subject, int length, int startoffset,
860                int options, int *ovector, int ovecsize,
861                int *workspace, int wscount);
862    
863           int pcre_copy_named_substring(const pcre *code,
864                const char *subject, int *ovector,
865                int stringcount, const char *stringname,
866                char *buffer, int buffersize);
867    
868           int pcre_copy_substring(const char *subject, int *ovector,
869                int stringcount, int stringnumber, char *buffer,
870                int buffersize);
871    
872           int pcre_get_named_substring(const pcre *code,
873                const char *subject, int *ovector,
874                int stringcount, const char *stringname,
875                const char **stringptr);
876    
877           int pcre_get_stringnumber(const pcre *code,
878                const char *name);
879    
880           int pcre_get_stringtable_entries(const pcre *code,
881                const char *name, char **first, char **last);
882    
883           int pcre_get_substring(const char *subject, int *ovector,
884                int stringcount, int stringnumber,
885                const char **stringptr);
886    
887           int pcre_get_substring_list(const char *subject,
888                int *ovector, int stringcount, const char ***listptr);
889    
890           void pcre_free_substring(const char *stringptr);
891    
892           void pcre_free_substring_list(const char **stringptr);
893    
894           const unsigned char *pcre_maketables(void);
895    
896           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
897                int what, void *where);
898    
899           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
900    
901           int pcre_refcount(pcre *code, int adjust);
902    
903           int pcre_config(int what, void *where);
904    
905           char *pcre_version(void);
906    
907           void *(*pcre_malloc)(size_t);
908    
909           void (*pcre_free)(void *);
910    
911           void *(*pcre_stack_malloc)(size_t);
912    
913           void (*pcre_stack_free)(void *);
914    
915           int (*pcre_callout)(pcre_callout_block *);
916    
917    
918    PCRE API OVERVIEW
919    
920           PCRE has its own native API, which is described in this document. There
921           are also some wrapper functions that correspond to  the  POSIX  regular
922           expression  API.  These  are  described in the pcreposix documentation.
923           Both of these APIs define a set of C function calls. A C++  wrapper  is
924           distributed with PCRE. It is documented in the pcrecpp page.
925    
926           The  native  API  C  function prototypes are defined in the header file
927           pcre.h, and on Unix systems the library itself is called  libpcre.   It
928           can normally be accessed by adding -lpcre to the command for linking an
929           application  that  uses  PCRE.  The  header  file  defines  the  macros
930           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
931           bers for the library.  Applications can use these  to  include  support
932           for different releases of PCRE.
933    
934           In a Windows environment, if you want to statically link an application
935           program against a non-dll pcre.a  file,  you  must  define  PCRE_STATIC
936           before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal-
937           loc()   and   pcre_free()   exported   functions   will   be   declared
938           __declspec(dllimport), with unwanted results.
939    
940           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
941           pcre_exec() are used for compiling and matching regular expressions  in
942           a  Perl-compatible  manner. A sample program that demonstrates the sim-
943           plest way of using them is provided in the file  called  pcredemo.c  in
944           the PCRE source distribution. A listing of this program is given in the
945           pcredemo documentation, and the pcresample documentation describes  how
946           to compile and run it.
947    
948           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
949           ble, is also provided. This uses a different algorithm for  the  match-
950           ing.  The  alternative algorithm finds all possible matches (at a given
951           point in the subject), and scans the subject just  once  (unless  there
952           are  lookbehind  assertions).  However,  this algorithm does not return
953           captured substrings. A description of the two matching  algorithms  and
954           their  advantages  and disadvantages is given in the pcrematching docu-
955           mentation.
956    
957           In addition to the main compiling and  matching  functions,  there  are
958           convenience functions for extracting captured substrings from a subject
959           string that is matched by pcre_exec(). They are:
960    
961             pcre_copy_substring()
962             pcre_copy_named_substring()
963             pcre_get_substring()
964             pcre_get_named_substring()
965             pcre_get_substring_list()
966             pcre_get_stringnumber()
967             pcre_get_stringtable_entries()
968    
969           pcre_free_substring() and pcre_free_substring_list() are also provided,
970           to free the memory used for extracted strings.
971    
972           The  function  pcre_maketables()  is  used  to build a set of character
973           tables  in  the  current  locale   for   passing   to   pcre_compile(),
974           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
975           provided for specialist use.  Most  commonly,  no  special  tables  are
976           passed,  in  which case internal tables that are generated when PCRE is
977           built are used.
978    
979           The function pcre_fullinfo() is used to find out  information  about  a
980           compiled  pattern; pcre_info() is an obsolete version that returns only
981           some of the available information, but is retained for  backwards  com-
982           patibility.   The function pcre_version() returns a pointer to a string
983           containing the version of PCRE and its date of release.
984    
985           The function pcre_refcount() maintains a  reference  count  in  a  data
986           block  containing  a compiled pattern. This is provided for the benefit
987           of object-oriented applications.
988    
989           The global variables pcre_malloc and pcre_free  initially  contain  the
990           entry  points  of  the  standard malloc() and free() functions, respec-
991           tively. PCRE calls the memory management functions via these variables,
992           so  a  calling  program  can replace them if it wishes to intercept the
993           calls. This should be done before calling any PCRE functions.
994    
995           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
996           indirections  to  memory  management functions. These special functions
997           are used only when PCRE is compiled to use  the  heap  for  remembering
998           data, instead of recursive function calls, when running the pcre_exec()
999           function. See the pcrebuild documentation for  details  of  how  to  do
1000           this.  It  is  a non-standard way of building PCRE, for use in environ-
1001           ments that have limited stacks. Because of the greater  use  of  memory
1002           management,  it  runs  more  slowly. Separate functions are provided so
1003           that special-purpose external code can be  used  for  this  case.  When
1004           used,  these  functions  are always called in a stack-like manner (last
1005           obtained, first freed), and always for memory blocks of the same  size.
1006           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
1007           mentation.
1008    
1009           The global variable pcre_callout initially contains NULL. It can be set
1010           by  the  caller  to  a "callout" function, which PCRE will then call at
1011           specified points during a matching operation. Details are given in  the
1012           pcrecallout documentation.
1013    
1014    
1015    NEWLINES
1016    
1017           PCRE  supports five different conventions for indicating line breaks in
1018           strings: a single CR (carriage return) character, a  single  LF  (line-
1019           feed) character, the two-character sequence CRLF, any of the three pre-
1020           ceding, or any Unicode newline sequence. The Unicode newline  sequences
1021           are  the  three just mentioned, plus the single characters VT (vertical
1022           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
1023           separator, U+2028), and PS (paragraph separator, U+2029).
1024    
1025           Each  of  the first three conventions is used by at least one operating
1026           system as its standard newline sequence. When PCRE is built, a  default
1027           can  be  specified.  The default default is LF, which is the Unix stan-
1028           dard. When PCRE is run, the default can be overridden,  either  when  a
1029           pattern is compiled, or when it is matched.
1030    
1031           At compile time, the newline convention can be specified by the options
1032           argument of pcre_compile(), or it can be specified by special  text  at
1033           the start of the pattern itself; this overrides any other settings. See
1034           the pcrepattern page for details of the special character sequences.
1035    
1036           In the PCRE documentation the word "newline" is used to mean "the char-
1037           acter  or pair of characters that indicate a line break". The choice of
1038           newline convention affects the handling of  the  dot,  circumflex,  and
1039           dollar metacharacters, the handling of #-comments in /x mode, and, when
1040           CRLF is a recognized line ending sequence, the match position  advance-
1041           ment for a non-anchored pattern. There is more detail about this in the
1042           section on pcre_exec() options below.
1043    
1044           The choice of newline convention does not affect the interpretation  of
1045           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
1046           which is controlled in a similar way, but by separate options.
1047    
1048    
1049    MULTITHREADING
1050    
1051           The PCRE functions can be used in  multi-threading  applications,  with
1052           the  proviso  that  the  memory  management  functions  pointed  to  by
1053           pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1054           callout function pointed to by pcre_callout, are shared by all threads.
1055    
1056           The  compiled form of a regular expression is not altered during match-
1057           ing, so the same compiled pattern can safely be used by several threads
1058           at once.
1059    
1060    
1061    SAVING PRECOMPILED PATTERNS FOR LATER USE
1062    
1063           The compiled form of a regular expression can be saved and re-used at a
1064           later time, possibly by a different program, and even on a  host  other
1065           than  the  one  on  which  it  was  compiled.  Details are given in the
1066           pcreprecompile documentation. However, compiling a  regular  expression
1067           with  one version of PCRE for use with a different version is not guar-
1068           anteed to work and may cause crashes.
1069    
1070    
1071    CHECKING BUILD-TIME OPTIONS
1072    
1073           int pcre_config(int what, void *where);
1074    
1075           The function pcre_config() makes it possible for a PCRE client to  dis-
1076           cover which optional features have been compiled into the PCRE library.
1077           The pcrebuild documentation has more details about these optional  fea-
1078           tures.
1079    
1080           The  first  argument  for pcre_config() is an integer, specifying which
1081           information is required; the second argument is a pointer to a variable
1082           into  which  the  information  is  placed. The following information is
1083           available:
1084    
1085             PCRE_CONFIG_UTF8
1086    
1087           The output is an integer that is set to one if UTF-8 support is  avail-
1088           able; otherwise it is set to zero.
1089    
1090             PCRE_CONFIG_UNICODE_PROPERTIES
1091    
1092           The  output  is  an  integer  that is set to one if support for Unicode
1093           character properties is available; otherwise it is set to zero.
1094    
1095             PCRE_CONFIG_NEWLINE
1096    
1097           The output is an integer whose value specifies  the  default  character
1098           sequence  that is recognized as meaning "newline". The four values that
1099           are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1100           and  -1  for  ANY.  Though they are derived from ASCII, the same values
1101           are returned in EBCDIC environments. The default should normally corre-
1102           spond to the standard sequence for your operating system.
1103    
1104             PCRE_CONFIG_BSR
1105    
1106           The output is an integer whose value indicates what character sequences
1107           the \R escape sequence matches by default. A value of 0 means  that  \R
1108           matches  any  Unicode  line ending sequence; a value of 1 means that \R
1109           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1110           tern is compiled or matched.
1111    
1112             PCRE_CONFIG_LINK_SIZE
1113    
1114           The  output  is  an  integer that contains the number of bytes used for
1115           internal linkage in compiled regular expressions. The value is 2, 3, or
1116           4.  Larger  values  allow larger regular expressions to be compiled, at
1117           the expense of slower matching. The default value of  2  is  sufficient
1118           for  all  but  the  most massive patterns, since it allows the compiled
1119           pattern to be up to 64K in size.
1120    
1121             PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1122    
1123           The output is an integer that contains the threshold  above  which  the
1124           POSIX  interface  uses malloc() for output vectors. Further details are
1125           given in the pcreposix documentation.
1126    
1127             PCRE_CONFIG_MATCH_LIMIT
1128    
1129           The output is a long integer that gives the default limit for the  num-
1130           ber  of  internal  matching  function calls in a pcre_exec() execution.
1131           Further details are given with pcre_exec() below.
1132    
1133             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1134    
1135           The output is a long integer that gives the default limit for the depth
1136           of   recursion  when  calling  the  internal  matching  function  in  a
1137           pcre_exec() execution.  Further  details  are  given  with  pcre_exec()
1138           below.
1139    
1140             PCRE_CONFIG_STACKRECURSE
1141    
1142           The  output is an integer that is set to one if internal recursion when
1143           running pcre_exec() is implemented by recursive function calls that use
1144           the  stack  to remember their state. This is the usual way that PCRE is
1145           compiled. The output is zero if PCRE was compiled to use blocks of data
1146           on  the  heap  instead  of  recursive  function  calls.  In  this case,
1147           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1148           blocks on the heap, thus avoiding the use of the stack.
1149    
1150    
1151    COMPILING A PATTERN
1152    
1153           pcre *pcre_compile(const char *pattern, int options,
1154                const char **errptr, int *erroffset,
1155                const unsigned char *tableptr);
1156    
1157           pcre *pcre_compile2(const char *pattern, int options,
1158                int *errorcodeptr,
1159                const char **errptr, int *erroffset,
1160                const unsigned char *tableptr);
1161    
1162           Either of the functions pcre_compile() or pcre_compile2() can be called
1163           to compile a pattern into an internal form. The only difference between
1164           the  two interfaces is that pcre_compile2() has an additional argument,
1165           errorcodeptr, via which a numerical error  code  can  be  returned.  To
1166           avoid  too  much repetition, we refer just to pcre_compile() below, but
1167           the information applies equally to pcre_compile2().
1168    
1169           The pattern is a C string terminated by a binary zero, and is passed in
1170           the  pattern  argument.  A  pointer to a single block of memory that is
1171           obtained via pcre_malloc is returned. This contains the  compiled  code
1172           and related data. The pcre type is defined for the returned block; this
1173           is a typedef for a structure whose contents are not externally defined.
1174           It is up to the caller to free the memory (via pcre_free) when it is no
1175           longer required.
1176    
1177           Although the compiled code of a PCRE regex is relocatable, that is,  it
1178           does not depend on memory location, the complete pcre data block is not
1179           fully relocatable, because it may contain a copy of the tableptr  argu-
1180           ment, which is an address (see below).
1181    
1182           The options argument contains various bit settings that affect the com-
1183           pilation. It should be zero if no options are required.  The  available
1184           options  are  described  below. Some of them (in particular, those that
1185           are compatible with Perl, but some others as well) can also be set  and
1186           unset  from  within  the  pattern  (see the detailed description in the
1187           pcrepattern documentation). For those options that can be different  in
1188           different  parts  of  the pattern, the contents of the options argument
1189           specifies their settings at the start of compilation and execution. The
1190           PCRE_ANCHORED,  PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
1191           PCRE_NO_START_OPT options can be set at the time of matching as well as
1192           at compile time.
1193    
1194           If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1195           if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1196           sets the variable pointed to by errptr to point to a textual error mes-
1197           sage. This is a static string that is part of the library. You must not
1198           try  to  free it. Normally, the offset from the start of the pattern to
1199           the byte that was being processed when  the  error  was  discovered  is
1200           placed  in the variable pointed to by erroffset, which must not be NULL
1201           (if it is, an immediate error is given). However, for an invalid  UTF-8
1202           string,  the offset is that of the first byte of the failing character.
1203           Also, some errors are not detected until checks are  carried  out  when
1204           the  whole  pattern  has been scanned; in these cases the offset passed
1205           back is the length of the pattern.
1206    
1207           Note that the offset is in bytes, not characters, even in  UTF-8  mode.
1208           It may sometimes point into the middle of a UTF-8 character.
1209    
1210           If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1211           codeptr argument is not NULL, a non-zero error code number is  returned
1212           via  this argument in the event of an error. This is in addition to the
1213           textual error message. Error codes and messages are listed below.
1214    
1215           If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1216           character  tables  that  are  built  when  PCRE  is compiled, using the
1217           default C locale. Otherwise, tableptr must be an address  that  is  the
1218           result  of  a  call to pcre_maketables(). This value is stored with the
1219           compiled pattern, and used again by pcre_exec(), unless  another  table
1220           pointer is passed to it. For more discussion, see the section on locale
1221           support below.
1222    
1223           This code fragment shows a typical straightforward  call  to  pcre_com-
1224           pile():
1225    
1226             pcre *re;
1227             const char *error;
1228             int erroffset;
1229             re = pcre_compile(
1230               "^A.*Z",          /* the pattern */
1231               0,                /* default options */
1232               &error,           /* for error message */
1233               &erroffset,       /* for error offset */
1234               NULL);            /* use default character tables */
1235    
1236           The  following  names  for option bits are defined in the pcre.h header
1237           file:
1238    
1239             PCRE_ANCHORED
1240    
1241           If this bit is set, the pattern is forced to be "anchored", that is, it
1242           is  constrained to match only at the first matching point in the string
1243           that is being searched (the "subject string"). This effect can also  be
1244           achieved  by appropriate constructs in the pattern itself, which is the
1245           only way to do it in Perl.
1246    
1247             PCRE_AUTO_CALLOUT
1248    
1249           If this bit is set, pcre_compile() automatically inserts callout items,
1250           all  with  number  255, before each pattern item. For discussion of the
1251           callout facility, see the pcrecallout documentation.
1252    
1253             PCRE_BSR_ANYCRLF
1254             PCRE_BSR_UNICODE
1255    
1256           These options (which are mutually exclusive) control what the \R escape
1257           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1258           or to match any Unicode newline sequence. The default is specified when
1259           PCRE is built. It can be overridden from within the pattern, or by set-
1260           ting an option when a compiled pattern is matched.
1261    
1262             PCRE_CASELESS
1263    
1264           If this bit is set, letters in the pattern match both upper  and  lower
1265           case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1266           changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1267           always  understands the concept of case for characters whose values are
1268           less than 128, so caseless matching is always possible. For  characters
1269           with  higher  values,  the concept of case is supported if PCRE is com-
1270           piled with Unicode property support, but not otherwise. If you want  to
1271           use  caseless  matching  for  characters 128 and above, you must ensure
1272           that PCRE is compiled with Unicode property support  as  well  as  with
1273           UTF-8 support.
1274    
1275             PCRE_DOLLAR_ENDONLY
1276    
1277           If  this bit is set, a dollar metacharacter in the pattern matches only
1278           at the end of the subject string. Without this option,  a  dollar  also
1279           matches  immediately before a newline at the end of the string (but not
1280           before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1281           if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1282           Perl, and no way to set it within a pattern.
1283    
1284             PCRE_DOTALL
1285    
1286           If this bit is set, a dot metacharacter in the pattern matches a  char-
1287           acter of any value, including one that indicates a newline. However, it
1288           only ever matches one character, even if newlines are  coded  as  CRLF.
1289           Without  this option, a dot does not match when the current position is
1290           at a newline. This option is equivalent to Perl's /s option, and it can
1291           be  changed within a pattern by a (?s) option setting. A negative class
1292           such as [^a] always matches newline characters, independent of the set-
1293           ting of this option.
1294    
1295             PCRE_DUPNAMES
1296    
1297           If  this  bit is set, names used to identify capturing subpatterns need
1298           not be unique. This can be helpful for certain types of pattern when it
1299           is  known  that  only  one instance of the named subpattern can ever be
1300           matched. There are more details of named subpatterns  below;  see  also
1301           the pcrepattern documentation.
1302    
1303             PCRE_EXTENDED
1304    
1305           If  this  bit  is  set,  whitespace  data characters in the pattern are
1306           totally ignored except when escaped or inside a character class. White-
1307           space does not include the VT character (code 11). In addition, charac-
1308           ters between an unescaped # outside a character class and the next new-
1309           line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1310           option, and it can be changed within a pattern by a  (?x)  option  set-
1311           ting.
1312    
1313           Which  characters  are  interpreted  as  newlines  is controlled by the
1314           options passed to pcre_compile() or by a special sequence at the  start
1315           of  the  pattern, as described in the section entitled "Newline conven-
1316           tions" in the pcrepattern documentation. Note that the end of this type
1317           of  comment  is  a  literal  newline  sequence  in  the pattern; escape
1318           sequences that happen to represent a newline do not count.
1319    
1320           This option makes it possible to include  comments  inside  complicated
1321           patterns.   Note,  however,  that this applies only to data characters.
1322           Whitespace  characters  may  never  appear  within  special   character
1323           sequences in a pattern, for example within the sequence (?( that intro-
1324           duces a conditional subpattern.
1325    
1326             PCRE_EXTRA
1327    
1328           This option was invented in order to turn on  additional  functionality
1329           of  PCRE  that  is  incompatible with Perl, but it is currently of very
1330           little use. When set, any backslash in a pattern that is followed by  a
1331           letter  that  has  no  special  meaning causes an error, thus reserving
1332           these combinations for future expansion. By  default,  as  in  Perl,  a
1333           backslash  followed by a letter with no special meaning is treated as a
1334           literal. (Perl can, however, be persuaded to give an error for this, by
1335           running  it with the -w option.) There are at present no other features
1336           controlled by this option. It can also be set by a (?X) option  setting
1337           within a pattern.
1338    
1339             PCRE_FIRSTLINE
1340    
1341           If  this  option  is  set,  an  unanchored pattern is required to match
1342           before or at the first  newline  in  the  subject  string,  though  the
1343           matched text may continue over the newline.
1344    
1345             PCRE_JAVASCRIPT_COMPAT
1346    
1347           If this option is set, PCRE's behaviour is changed in some ways so that
1348           it is compatible with JavaScript rather than Perl. The changes  are  as
1349           follows:
1350    
1351           (1)  A  lone  closing square bracket in a pattern causes a compile-time
1352           error, because this is illegal in JavaScript (by default it is  treated
1353           as a data character). Thus, the pattern AB]CD becomes illegal when this
1354           option is set.
1355    
1356           (2) At run time, a back reference to an unset subpattern group  matches
1357           an  empty  string (by default this causes the current matching alterna-
1358           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1359           set  (assuming  it can find an "a" in the subject), whereas it fails by
1360           default, for Perl compatibility.
1361    
1362             PCRE_MULTILINE
1363    
1364           By default, PCRE treats the subject string as consisting  of  a  single
1365           line  of characters (even if it actually contains newlines). The "start
1366           of line" metacharacter (^) matches only at the  start  of  the  string,
1367           while  the  "end  of line" metacharacter ($) matches only at the end of
1368           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1369           is set). This is the same as Perl.
1370    
1371           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1372           constructs match immediately following or immediately  before  internal
1373           newlines  in  the  subject string, respectively, as well as at the very
1374           start and end. This is equivalent to Perl's /m option, and  it  can  be
1375           changed within a pattern by a (?m) option setting. If there are no new-
1376           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1377           setting PCRE_MULTILINE has no effect.
1378    
1379             PCRE_NEWLINE_CR
1380             PCRE_NEWLINE_LF
1381             PCRE_NEWLINE_CRLF
1382             PCRE_NEWLINE_ANYCRLF
1383             PCRE_NEWLINE_ANY
1384    
1385           These  options  override the default newline definition that was chosen
1386           when PCRE was built. Setting the first or the second specifies  that  a
1387           newline  is  indicated  by a single character (CR or LF, respectively).
1388           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1389           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1390           that any of the three preceding sequences should be recognized. Setting
1391           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1392           recognized. The Unicode newline sequences are the three just mentioned,
1393           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1394           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1395           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1396           UTF-8 mode.
1397    
1398           The newline setting in the  options  word  uses  three  bits  that  are
1399           treated as a number, giving eight possibilities. Currently only six are
1400           used (default plus the five values above). This means that if  you  set
1401           more  than one newline option, the combination may or may not be sensi-
1402           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1403           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1404           cause an error.
1405    
1406           The only time that a line break in a pattern  is  specially  recognized
1407           when  compiling  is when PCRE_EXTENDED is set. CR and LF are whitespace
1408           characters, and so are ignored in this mode. Also, an unescaped #  out-
1409           side  a  character class indicates a comment that lasts until after the
1410           next line break sequence. In other circumstances, line break  sequences
1411           in patterns are treated as literal data.
1412    
1413           The newline option that is set at compile time becomes the default that
1414           is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1415    
1416             PCRE_NO_AUTO_CAPTURE
1417    
1418           If this option is set, it disables the use of numbered capturing paren-
1419           theses  in the pattern. Any opening parenthesis that is not followed by
1420           ? behaves as if it were followed by ?: but named parentheses can  still
1421           be  used  for  capturing  (and  they acquire numbers in the usual way).
1422           There is no equivalent of this option in Perl.
1423    
1424             NO_START_OPTIMIZE
1425    
1426           This is an option that acts at matching time; that is, it is really  an
1427           option  for  pcre_exec()  or  pcre_dfa_exec().  If it is set at compile
1428           time, it is remembered with the compiled pattern and assumed at  match-
1429           ing  time.  For  details  see  the discussion of PCRE_NO_START_OPTIMIZE
1430           below.
1431    
1432             PCRE_UCP
1433    
1434           This option changes the way PCRE processes \B, \b, \D, \d, \S, \s,  \W,
1435           \w,  and  some  of  the POSIX character classes. By default, only ASCII
1436           characters are recognized, but if PCRE_UCP is set,  Unicode  properties
1437           are  used instead to classify characters. More details are given in the
1438           section on generic character types in the pcrepattern page. If you  set
1439           PCRE_UCP,  matching  one of the items it affects takes much longer. The
1440           option is available only if PCRE has been compiled with  Unicode  prop-
1441           erty support.
1442    
1443             PCRE_UNGREEDY
1444    
1445           This  option  inverts  the "greediness" of the quantifiers so that they
1446           are not greedy by default, but become greedy if followed by "?". It  is
1447           not  compatible  with Perl. It can also be set by a (?U) option setting
1448           within the pattern.
1449    
1450             PCRE_UTF8
1451    
1452           This option causes PCRE to regard both the pattern and the  subject  as
1453           strings  of  UTF-8 characters instead of single-byte character strings.
1454           However, it is available only when PCRE is built to include UTF-8  sup-
1455           port.  If not, the use of this option provokes an error. Details of how
1456           this option changes the behaviour of PCRE are given in the  section  on
1457           UTF-8 support in the main pcre page.
1458    
1459             PCRE_NO_UTF8_CHECK
1460    
1461           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1462           automatically checked. There is a  discussion  about  the  validity  of
1463           UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1464           bytes is found, pcre_compile() returns an error. If  you  already  know
1465           that your pattern is valid, and you want to skip this check for perfor-
1466           mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1467           set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1468           undefined. It may cause your program to crash. Note  that  this  option
1469           can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1470           UTF-8 validity checking of subject strings.
1471    
1472    
1473    COMPILATION ERROR CODES
1474    
1475           The following table lists the error  codes  than  may  be  returned  by
1476           pcre_compile2(),  along with the error messages that may be returned by
1477           both compiling functions. As PCRE has developed, some error codes  have
1478           fallen out of use. To avoid confusion, they have not been re-used.
1479    
1480              0  no error
1481              1  \ at end of pattern
1482              2  \c at end of pattern
1483              3  unrecognized character follows \
1484              4  numbers out of order in {} quantifier
1485              5  number too big in {} quantifier
1486              6  missing terminating ] for character class
1487              7  invalid escape sequence in character class
1488              8  range out of order in character class
1489              9  nothing to repeat
1490             10  [this code is not in use]
1491             11  internal error: unexpected repeat
1492             12  unrecognized character after (? or (?-
1493             13  POSIX named classes are supported only within a class
1494             14  missing )
1495             15  reference to non-existent subpattern
1496             16  erroffset passed as NULL
1497             17  unknown option bit(s) set
1498             18  missing ) after comment
1499             19  [this code is not in use]
1500             20  regular expression is too large
1501             21  failed to get memory
1502             22  unmatched parentheses
1503             23  internal error: code overflow
1504             24  unrecognized character after (?<
1505             25  lookbehind assertion is not fixed length
1506             26  malformed number or name after (?(
1507             27  conditional group contains more than two branches
1508             28  assertion expected after (?(
1509             29  (?R or (?[+-]digits must be followed by )
1510             30  unknown POSIX class name
1511             31  POSIX collating elements are not supported
1512             32  this version of PCRE is not compiled with PCRE_UTF8 support
1513             33  [this code is not in use]
1514             34  character value in \x{...} sequence is too large
1515             35  invalid condition (?(0)
1516             36  \C not allowed in lookbehind assertion
1517             37  PCRE does not support \L, \l, \N, \U, or \u
1518             38  number after (?C is > 255
1519             39  closing ) for (?C expected
1520             40  recursive call could loop indefinitely
1521             41  unrecognized character after (?P
1522             42  syntax error in subpattern name (missing terminator)
1523             43  two named subpatterns have the same name
1524             44  invalid UTF-8 string
1525             45  support for \P, \p, and \X has not been compiled
1526             46  malformed \P or \p sequence
1527             47  unknown property name after \P or \p
1528             48  subpattern name is too long (maximum 32 characters)
1529             49  too many named subpatterns (maximum 10000)
1530             50  [this code is not in use]
1531             51  octal value is greater than \377 (not in UTF-8 mode)
1532             52  internal error: overran compiling workspace
1533             53  internal error: previously-checked referenced subpattern
1534                   not found
1535             54  DEFINE group contains more than one branch
1536             55  repeating a DEFINE group is not allowed
1537             56  inconsistent NEWLINE options
1538             57  \g is not followed by a braced, angle-bracketed, or quoted
1539                   name/number or by a plain number
1540             58  a numbered reference must not be zero
1541             59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
1542             60  (*VERB) not recognized
1543             61  number is too big
1544             62  subpattern name expected
1545             63  digit expected after (?+
1546             64  ] is an invalid data character in JavaScript compatibility mode
1547             65  different names for subpatterns of the same number are
1548                   not allowed
1549             66  (*MARK) must have an argument
1550             67  this version of PCRE is not compiled with PCRE_UCP support
1551    
1552           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1553           values may be used if the limits were changed when PCRE was built.
1554    
1555    
1556    STUDYING A PATTERN
1557    
1558           pcre_extra *pcre_study(const pcre *code, int options
1559                const char **errptr);
1560    
1561           If a compiled pattern is going to be used several times,  it  is  worth
1562           spending more time analyzing it in order to speed up the time taken for
1563           matching. The function pcre_study() takes a pointer to a compiled  pat-
1564           tern as its first argument. If studying the pattern produces additional
1565           information that will help speed up matching,  pcre_study()  returns  a
1566           pointer  to a pcre_extra block, in which the study_data field points to
1567           the results of the study.
1568    
1569           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1570           pcre_exec()  or  pcre_dfa_exec(). However, a pcre_extra block also con-
1571           tains other fields that can be set by the caller before  the  block  is
1572           passed; these are described below in the section on matching a pattern.
1573    
1574           If  studying  the  pattern  does  not  produce  any useful information,
1575           pcre_study() returns NULL. In that circumstance, if the calling program
1576           wants   to   pass   any   of   the   other  fields  to  pcre_exec()  or
1577           pcre_dfa_exec(), it must set up its own pcre_extra block.
1578    
1579           The second argument of pcre_study() contains option bits.  At  present,
1580           no options are defined, and this argument should always be zero.
1581    
1582           The  third argument for pcre_study() is a pointer for an error message.
1583           If studying succeeds (even if no data is  returned),  the  variable  it
1584           points  to  is  set  to NULL. Otherwise it is set to point to a textual
1585           error message. This is a static string that is part of the library. You
1586           must  not  try  to  free it. You should test the error pointer for NULL
1587           after calling pcre_study(), to be sure that it has run successfully.
1588    
1589           This is a typical call to pcre_study():
1590    
1591             pcre_extra *pe;
1592             pe = pcre_study(
1593               re,             /* result of pcre_compile() */
1594               0,              /* no options exist */
1595               &error);        /* set to NULL or points to a message */
1596    
1597           Studying a pattern does two things: first, a lower bound for the length
1598           of subject string that is needed to match the pattern is computed. This
1599           does not mean that there are any strings of that length that match, but
1600           it  does  guarantee that no shorter strings match. The value is used by
1601           pcre_exec() and pcre_dfa_exec() to avoid  wasting  time  by  trying  to
1602           match  strings  that are shorter than the lower bound. You can find out
1603           the value in a calling program via the pcre_fullinfo() function.
1604    
1605           Studying a pattern is also useful for non-anchored patterns that do not
1606           have  a  single fixed starting character. A bitmap of possible starting
1607           bytes is created. This speeds up finding a position in the  subject  at
1608           which to start matching.
1609    
1610           The  two  optimizations  just  described can be disabled by setting the
1611           PCRE_NO_START_OPTIMIZE   option    when    calling    pcre_exec()    or
1612           pcre_dfa_exec().  You  might  want  to do this if your pattern contains
1613           callouts or (*MARK), and you want to make use of  these  facilities  in
1614           cases  where  matching fails. See the discussion of PCRE_NO_START_OPTI-
1615           MIZE below.
1616    
1617    
1618    LOCALE SUPPORT
1619    
1620           PCRE handles caseless matching, and determines whether  characters  are
1621           letters,  digits, or whatever, by reference to a set of tables, indexed
1622           by character value. When running in UTF-8 mode, this  applies  only  to
1623           characters  with  codes  less than 128. By default, higher-valued codes
1624           never match escapes such as \w or \d, but they can be tested with \p if
1625           PCRE  is  built with Unicode character property support. Alternatively,
1626           the PCRE_UCP option can be set at compile  time;  this  causes  \w  and
1627           friends to use Unicode property support instead of built-in tables. The
1628           use of locales with Unicode is discouraged. If you are handling charac-
1629           ters  with codes greater than 128, you should either use UTF-8 and Uni-
1630           code, or use locales, but not try to mix the two.
1631    
1632           PCRE contains an internal set of tables that are used  when  the  final
1633           argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1634           applications.  Normally, the internal tables recognize only ASCII char-
1635           acters. However, when PCRE is built, it is possible to cause the inter-
1636           nal tables to be rebuilt in the default "C" locale of the local system,
1637           which may cause them to be different.
1638    
1639           The  internal tables can always be overridden by tables supplied by the
1640           application that calls PCRE. These may be created in a different locale
1641           from  the  default.  As more and more applications change to using Uni-
1642           code, the need for this locale support is expected to die away.
1643    
1644           External tables are built by calling  the  pcre_maketables()  function,
1645           which  has no arguments, in the relevant locale. The result can then be
1646           passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1647           example,  to  build  and use tables that are appropriate for the French
1648           locale (where accented characters with  values  greater  than  128  are
1649           treated as letters), the following code could be used:
1650    
1651             setlocale(LC_CTYPE, "fr_FR");
1652             tables = pcre_maketables();
1653             re = pcre_compile(..., tables);
1654    
1655           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1656           if you are using Windows, the name for the French locale is "french".
1657    
1658           When pcre_maketables() runs, the tables are built  in  memory  that  is
1659           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1660           that the memory containing the tables remains available for as long  as
1661           it is needed.
1662    
1663           The pointer that is passed to pcre_compile() is saved with the compiled
1664           pattern, and the same tables are used via this pointer by  pcre_study()
1665           and normally also by pcre_exec(). Thus, by default, for any single pat-
1666           tern, compilation, studying and matching all happen in the same locale,
1667           but different patterns can be compiled in different locales.
1668    
1669           It  is  possible to pass a table pointer or NULL (indicating the use of
1670           the internal tables) to pcre_exec(). Although  not  intended  for  this
1671           purpose,  this facility could be used to match a pattern in a different
1672           locale from the one in which it was compiled. Passing table pointers at
1673           run time is discussed below in the section on matching a pattern.
1674    
1675    
1676    INFORMATION ABOUT A PATTERN
1677    
1678           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1679                int what, void *where);
1680    
1681           The  pcre_fullinfo() function returns information about a compiled pat-
1682           tern. It replaces the obsolete pcre_info() function, which is neverthe-
1683           less retained for backwards compability (and is documented below).
1684    
1685           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1686           pattern. The second argument is the result of pcre_study(), or NULL  if
1687           the  pattern  was not studied. The third argument specifies which piece
1688           of information is required, and the fourth argument is a pointer  to  a
1689           variable  to  receive  the  data. The yield of the function is zero for
1690           success, or one of the following negative numbers:
1691    
1692             PCRE_ERROR_NULL       the argument code was NULL
1693                                   the argument where was NULL
1694             PCRE_ERROR_BADMAGIC   the "magic number" was not found
1695             PCRE_ERROR_BADOPTION  the value of what was invalid
1696    
1697           The "magic number" is placed at the start of each compiled  pattern  as
1698           an  simple check against passing an arbitrary memory pointer. Here is a
1699           typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1700           pattern:
1701    
1702             int rc;
1703             size_t length;
1704             rc = pcre_fullinfo(
1705               re,               /* result of pcre_compile() */
1706               pe,               /* result of pcre_study(), or NULL */
1707               PCRE_INFO_SIZE,   /* what is required */
1708               &length);         /* where to put the data */
1709    
1710           The  possible  values for the third argument are defined in pcre.h, and
1711           are as follows:
1712    
1713             PCRE_INFO_BACKREFMAX
1714    
1715           Return the number of the highest back reference  in  the  pattern.  The
1716           fourth  argument  should  point to an int variable. Zero is returned if
1717           there are no back references.
1718    
1719             PCRE_INFO_CAPTURECOUNT
1720    
1721           Return the number of capturing subpatterns in the pattern.  The  fourth
1722           argument should point to an int variable.
1723    
1724             PCRE_INFO_DEFAULT_TABLES
1725    
1726           Return  a pointer to the internal default character tables within PCRE.
1727           The fourth argument should point to an unsigned char *  variable.  This
1728           information call is provided for internal use by the pcre_study() func-
1729           tion. External callers can cause PCRE to use  its  internal  tables  by
1730           passing a NULL table pointer.
1731    
1732             PCRE_INFO_FIRSTBYTE
1733    
1734           Return  information  about  the first byte of any matched string, for a
1735           non-anchored pattern. The fourth argument should point to an int  vari-
1736           able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1737           is still recognized for backwards compatibility.)
1738    
1739           If there is a fixed first byte, for example, from  a  pattern  such  as
1740           (cat|cow|coyote), its value is returned. Otherwise, if either
1741    
1742           (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1743           branch starts with "^", or
1744    
1745           (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1746           set (if it were set, the pattern would be anchored),
1747    
1748           -1  is  returned, indicating that the pattern matches only at the start
1749           of a subject string or after any newline within the  string.  Otherwise
1750           -2 is returned. For anchored patterns, -2 is returned.
1751    
1752             PCRE_INFO_FIRSTTABLE
1753    
1754           If  the pattern was studied, and this resulted in the construction of a
1755           256-bit table indicating a fixed set of bytes for the first byte in any
1756           matching  string, a pointer to the table is returned. Otherwise NULL is
1757           returned. The fourth argument should point to an unsigned char *  vari-
1758           able.
1759    
1760             PCRE_INFO_HASCRORLF
1761    
1762           Return  1  if  the  pattern  contains any explicit matches for CR or LF
1763           characters, otherwise 0. The fourth argument should  point  to  an  int
1764           variable.  An explicit match is either a literal CR or LF character, or
1765           \r or \n.
1766    
1767             PCRE_INFO_JCHANGED
1768    
1769           Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1770           otherwise  0. The fourth argument should point to an int variable. (?J)
1771           and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1772    
1773             PCRE_INFO_LASTLITERAL
1774    
1775           Return the value of the rightmost literal byte that must exist  in  any
1776           matched  string,  other  than  at  its  start,  if such a byte has been
1777           recorded. The fourth argument should point to an int variable. If there
1778           is  no such byte, -1 is returned. For anchored patterns, a last literal
1779           byte is recorded only if it follows something of variable  length.  For
1780           example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1781           /^a\dz\d/ the returned value is -1.
1782    
1783             PCRE_INFO_MINLENGTH
1784    
1785           If the pattern was studied and a minimum length  for  matching  subject
1786           strings  was  computed,  its  value is returned. Otherwise the returned
1787           value is -1. The value is a number of characters, not bytes  (this  may
1788           be  relevant in UTF-8 mode). The fourth argument should point to an int
1789           variable. A non-negative value is a lower bound to the  length  of  any
1790           matching  string.  There  may not be any strings of that length that do
1791           actually match, but every string that does match is at least that long.
1792    
1793             PCRE_INFO_NAMECOUNT
1794             PCRE_INFO_NAMEENTRYSIZE
1795             PCRE_INFO_NAMETABLE
1796    
1797           PCRE supports the use of named as well as numbered capturing  parenthe-
1798           ses.  The names are just an additional way of identifying the parenthe-
1799           ses, which still acquire numbers. Several convenience functions such as
1800           pcre_get_named_substring()  are  provided  for extracting captured sub-
1801           strings by name. It is also possible to extract the data  directly,  by
1802           first  converting  the  name to a number in order to access the correct
1803           pointers in the output vector (described with pcre_exec() below). To do
1804           the  conversion,  you  need  to  use  the  name-to-number map, which is
1805           described by these three values.
1806    
1807           The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1808           gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1809           of each entry; both of these  return  an  int  value.  The  entry  size
1810           depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1811           a pointer to the first entry of the table  (a  pointer  to  char).  The
1812           first two bytes of each entry are the number of the capturing parenthe-
1813           sis, most significant byte first. The rest of the entry is  the  corre-
1814           sponding name, zero terminated.
1815    
1816           The  names are in alphabetical order. Duplicate names may appear if (?|
1817           is used to create multiple groups with the same number, as described in
1818           the  section  on  duplicate subpattern numbers in the pcrepattern page.
1819           Duplicate names for subpatterns with different  numbers  are  permitted
1820           only  if  PCRE_DUPNAMES  is  set. In all cases of duplicate names, they
1821           appear in the table in the order in which they were found in  the  pat-
1822           tern.  In  the  absence  of (?| this is the order of increasing number;
1823           when (?| is used this is not necessarily the case because later subpat-
1824           terns may have lower numbers.
1825    
1826           As  a  simple  example of the name/number table, consider the following
1827           pattern (assume PCRE_EXTENDED is set, so white space -  including  new-
1828           lines - is ignored):
1829    
1830             (?<date> (?<year>(\d\d)?\d\d) -
1831             (?<month>\d\d) - (?<day>\d\d) )
1832    
1833           There  are  four  named subpatterns, so the table has four entries, and
1834           each entry in the table is eight bytes long. The table is  as  follows,
1835           with non-printing bytes shows in hexadecimal, and undefined bytes shown
1836           as ??:
1837    
1838             00 01 d  a  t  e  00 ??
1839             00 05 d  a  y  00 ?? ??
1840             00 04 m  o  n  t  h  00
1841             00 02 y  e  a  r  00 ??
1842    
1843           When writing code to extract data  from  named  subpatterns  using  the
1844           name-to-number  map,  remember that the length of the entries is likely
1845           to be different for each compiled pattern.
1846    
1847             PCRE_INFO_OKPARTIAL
1848    
1849           Return 1  if  the  pattern  can  be  used  for  partial  matching  with
1850           pcre_exec(),  otherwise  0.  The fourth argument should point to an int
1851           variable. From  release  8.00,  this  always  returns  1,  because  the
1852           restrictions  that  previously  applied  to  partial matching have been
1853           lifted. The pcrepartial documentation gives details of  partial  match-
1854           ing.
1855    
1856             PCRE_INFO_OPTIONS
1857    
1858           Return  a  copy of the options with which the pattern was compiled. The
1859           fourth argument should point to an unsigned long  int  variable.  These
1860           option bits are those specified in the call to pcre_compile(), modified
1861           by any top-level option settings at the start of the pattern itself. In
1862           other  words,  they are the options that will be in force when matching
1863           starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1864           the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1865           and PCRE_EXTENDED.
1866    
1867           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1868           alternatives begin with one of the following:
1869    
1870             ^     unless PCRE_MULTILINE is set
1871             \A    always
1872             \G    always
1873             .*    if PCRE_DOTALL is set and there are no back
1874                     references to the subpattern in which .* appears
1875    
1876           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1877           by pcre_fullinfo().
1878    
1879             PCRE_INFO_SIZE
1880    
1881           Return the size of the compiled pattern, that is, the  value  that  was
1882           passed as the argument to pcre_malloc() when PCRE was getting memory in
1883           which to place the compiled data. The fourth argument should point to a
1884           size_t variable.
1885    
1886             PCRE_INFO_STUDYSIZE
1887    
1888           Return the size of the data block pointed to by the study_data field in
1889           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1890           pcre_malloc() when PCRE was getting memory into which to place the data
1891           created by pcre_study(). If pcre_extra is NULL, or there  is  no  study
1892           data,  zero  is  returned. The fourth argument should point to a size_t
1893           variable.
1894    
1895    
1896    OBSOLETE INFO FUNCTION
1897    
1898           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1899    
1900           The pcre_info() function is now obsolete because its interface  is  too
1901           restrictive  to return all the available data about a compiled pattern.
1902           New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1903           pcre_info()  is the number of capturing subpatterns, or one of the fol-
1904           lowing negative numbers:
1905    
1906             PCRE_ERROR_NULL       the argument code was NULL
1907             PCRE_ERROR_BADMAGIC   the "magic number" was not found
1908    
1909           If the optptr argument is not NULL, a copy of the  options  with  which
1910           the  pattern  was  compiled  is placed in the integer it points to (see
1911           PCRE_INFO_OPTIONS above).
1912    
1913           If the pattern is not anchored and the  firstcharptr  argument  is  not
1914           NULL,  it is used to pass back information about the first character of
1915           any matched string (see PCRE_INFO_FIRSTBYTE above).
1916    
1917    
1918    REFERENCE COUNTS
1919    
1920           int pcre_refcount(pcre *code, int adjust);
1921    
1922           The pcre_refcount() function is used to maintain a reference  count  in
1923           the data block that contains a compiled pattern. It is provided for the
1924           benefit of applications that  operate  in  an  object-oriented  manner,
1925           where different parts of the application may be using the same compiled
1926           pattern, but you want to free the block when they are all done.
1927    
1928           When a pattern is compiled, the reference count field is initialized to
1929           zero.   It is changed only by calling this function, whose action is to
1930           add the adjust value (which may be positive or  negative)  to  it.  The
1931           yield of the function is the new value. However, the value of the count
1932           is constrained to lie between 0 and 65535, inclusive. If the new  value
1933           is outside these limits, it is forced to the appropriate limit value.
1934    
1935           Except  when it is zero, the reference count is not correctly preserved
1936           if a pattern is compiled on one host and then  transferred  to  a  host
1937           whose byte-order is different. (This seems a highly unlikely scenario.)
1938    
1939    
1940    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1941    
1942           int pcre_exec(const pcre *code, const pcre_extra *extra,
1943                const char *subject, int length, int startoffset,
1944                int options, int *ovector, int ovecsize);
1945    
1946           The  function pcre_exec() is called to match a subject string against a
1947           compiled pattern, which is passed in the code argument. If the  pattern
1948           was  studied,  the  result  of  the study should be passed in the extra
1949           argument. This function is the main matching facility of  the  library,
1950           and it operates in a Perl-like manner. For specialist use there is also
1951           an alternative matching function, which is described below in the  sec-
1952           tion about the pcre_dfa_exec() function.
1953    
1954           In  most applications, the pattern will have been compiled (and option-
1955           ally studied) in the same process that calls pcre_exec().  However,  it
1956           is possible to save compiled patterns and study data, and then use them
1957           later in different processes, possibly even on different hosts.  For  a
1958           discussion about this, see the pcreprecompile documentation.
1959    
1960           Here is an example of a simple call to pcre_exec():
1961    
1962             int rc;
1963             int ovector[30];
1964             rc = pcre_exec(
1965               re,             /* result of pcre_compile() */
1966               NULL,           /* we didn't study the pattern */
1967               "some string",  /* the subject string */
1968               11,             /* the length of the subject string */
1969               0,              /* start at offset 0 in the subject */
1970               0,              /* default options */
1971               ovector,        /* vector of integers for substring information */
1972               30);            /* number of elements (NOT size in bytes) */
1973    
1974       Extra data for pcre_exec()
1975    
1976           If  the  extra argument is not NULL, it must point to a pcre_extra data
1977           block. The pcre_study() function returns such a block (when it  doesn't
1978           return  NULL), but you can also create one for yourself, and pass addi-
1979           tional information in it. The pcre_extra block contains  the  following
1980           fields (not necessarily in this order):
1981    
1982             unsigned long int flags;
1983             void *study_data;
1984             unsigned long int match_limit;
1985             unsigned long int match_limit_recursion;
1986             void *callout_data;
1987             const unsigned char *tables;
1988             unsigned char **mark;
1989    
1990           The  flags  field  is a bitmap that specifies which of the other fields
1991           are set. The flag bits are:
1992    
1993             PCRE_EXTRA_STUDY_DATA
1994             PCRE_EXTRA_MATCH_LIMIT
1995             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1996             PCRE_EXTRA_CALLOUT_DATA
1997             PCRE_EXTRA_TABLES
1998             PCRE_EXTRA_MARK
1999    
2000           Other flag bits should be set to zero. The study_data field is  set  in
2001           the  pcre_extra  block  that is returned by pcre_study(), together with
2002           the appropriate flag bit. You should not set this yourself, but you may
2003           add  to  the  block by setting the other fields and their corresponding
2004           flag bits.
2005    
2006           The match_limit field provides a means of preventing PCRE from using up
2007           a  vast amount of resources when running patterns that are not going to
2008           match, but which have a very large number  of  possibilities  in  their
2009           search  trees. The classic example is a pattern that uses nested unlim-
2010           ited repeats.
2011    
2012           Internally, PCRE uses a function called match() which it calls  repeat-
2013           edly  (sometimes  recursively). The limit set by match_limit is imposed
2014           on the number of times this function is called during  a  match,  which
2015           has  the  effect  of  limiting the amount of backtracking that can take
2016           place. For patterns that are not anchored, the count restarts from zero
2017           for each position in the subject string.
2018    
2019           The  default  value  for  the  limit can be set when PCRE is built; the
2020           default default is 10 million, which handles all but the  most  extreme
2021           cases.  You  can  override  the  default by suppling pcre_exec() with a
2022           pcre_extra    block    in    which    match_limit    is    set,     and
2023           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
2024           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
2025    
2026           The match_limit_recursion field is similar to match_limit, but  instead
2027           of limiting the total number of times that match() is called, it limits
2028           the depth of recursion. The recursion depth is a  smaller  number  than
2029           the  total number of calls, because not all calls to match() are recur-
2030           sive.  This limit is of use only if it is set smaller than match_limit.
2031    
2032           Limiting the recursion depth limits the amount of  stack  that  can  be
2033           used, or, when PCRE has been compiled to use memory on the heap instead
2034           of the stack, the amount of heap memory that can be used.
2035    
2036           The default value for match_limit_recursion can be  set  when  PCRE  is
2037           built;  the  default  default  is  the  same  value  as the default for
2038           match_limit. You can override the default by suppling pcre_exec()  with
2039           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
2040           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
2041           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
2042    
2043           The  callout_data  field is used in conjunction with the "callout" fea-
2044           ture, and is described in the pcrecallout documentation.
2045    
2046           The tables field  is  used  to  pass  a  character  tables  pointer  to
2047           pcre_exec();  this overrides the value that is stored with the compiled
2048           pattern. A non-NULL value is stored with the compiled pattern  only  if
2049           custom  tables  were  supplied to pcre_compile() via its tableptr argu-
2050           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
2051           PCRE's  internal  tables  to be used. This facility is helpful when re-
2052           using patterns that have been saved after compiling  with  an  external
2053           set  of  tables,  because  the  external tables might be at a different
2054           address when pcre_exec() is called. See the  pcreprecompile  documenta-
2055           tion for a discussion of saving compiled patterns for later use.
2056    
2057           If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
2058           set to point to a char * variable. If the pattern  contains  any  back-
2059           tracking  control verbs such as (*MARK:NAME), and the execution ends up
2060           with a name to pass back, a pointer to the  name  string  (zero  termi-
2061           nated)  is  placed  in  the  variable pointed to by the mark field. The
2062           names are within the compiled pattern; if you wish  to  retain  such  a
2063           name  you must copy it before freeing the memory of a compiled pattern.
2064           If there is no name to pass back, the variable pointed to by  the  mark
2065           field  set  to NULL. For details of the backtracking control verbs, see
2066           the section entitled "Backtracking control" in the pcrepattern documen-
2067           tation.
2068    
2069       Option bits for pcre_exec()
2070    
2071           The  unused  bits of the options argument for pcre_exec() must be zero.
2072           The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
2073           PCRE_NOTBOL,    PCRE_NOTEOL,    PCRE_NOTEMPTY,   PCRE_NOTEMPTY_ATSTART,
2074           PCRE_NO_START_OPTIMIZE,  PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,   and
2075           PCRE_PARTIAL_HARD.
2076    
2077             PCRE_ANCHORED
2078    
2079           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
2080           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
2081           turned  out to be anchored by virtue of its contents, it cannot be made
2082           unachored at matching time.
2083    
2084             PCRE_BSR_ANYCRLF
2085             PCRE_BSR_UNICODE
2086    
2087           These options (which are mutually exclusive) control what the \R escape
2088           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
2089           or to match any Unicode newline sequence. These  options  override  the
2090           choice that was made or defaulted when the pattern was compiled.
2091    
2092             PCRE_NEWLINE_CR
2093             PCRE_NEWLINE_LF
2094             PCRE_NEWLINE_CRLF
2095             PCRE_NEWLINE_ANYCRLF
2096             PCRE_NEWLINE_ANY
2097    
2098           These  options  override  the  newline  definition  that  was chosen or
2099           defaulted when the pattern was compiled. For details, see the  descrip-
2100           tion  of  pcre_compile()  above.  During  matching,  the newline choice
2101           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
2102           ters.  It may also alter the way the match position is advanced after a
2103           match failure for an unanchored pattern.
2104    
2105           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
2106           set,  and a match attempt for an unanchored pattern fails when the cur-
2107           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
2108           explicit  matches  for  CR  or  LF  characters,  the  match position is
2109           advanced by two characters instead of one, in other words, to after the
2110           CRLF.
2111    
2112           The above rule is a compromise that makes the most common cases work as
2113           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
2114           option is not set), it does not match the string "\r\nA" because, after
2115           failing at the start, it skips both the CR and the LF before  retrying.
2116           However,  the  pattern  [\r\n]A does match that string, because it con-
2117           tains an explicit CR or LF reference, and so advances only by one char-
2118           acter after the first failure.
2119    
2120           An explicit match for CR of LF is either a literal appearance of one of
2121           those characters, or one of the \r or  \n  escape  sequences.  Implicit
2122           matches  such  as [^X] do not count, nor does \s (which includes CR and
2123           LF in the characters that it matches).
2124    
2125           Notwithstanding the above, anomalous effects may still occur when  CRLF
2126           is a valid newline sequence and explicit \r or \n escapes appear in the
2127           pattern.
2128    
2129             PCRE_NOTBOL
2130    
2131           This option specifies that first character of the subject string is not
2132           the  beginning  of  a  line, so the circumflex metacharacter should not
2133           match before it. Setting this without PCRE_MULTILINE (at compile  time)
2134           causes  circumflex  never to match. This option affects only the behav-
2135           iour of the circumflex metacharacter. It does not affect \A.
2136    
2137             PCRE_NOTEOL
2138    
2139           This option specifies that the end of the subject string is not the end
2140           of  a line, so the dollar metacharacter should not match it nor (except
2141           in multiline mode) a newline immediately before it. Setting this  with-
2142           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
2143           option affects only the behaviour of the dollar metacharacter. It  does
2144           not affect \Z or \z.
2145    
2146             PCRE_NOTEMPTY
2147    
2148           An empty string is not considered to be a valid match if this option is
2149           set. If there are alternatives in the pattern, they are tried.  If  all
2150           the  alternatives  match  the empty string, the entire match fails. For
2151           example, if the pattern
2152    
2153             a?b?
2154    
2155           is applied to a string not beginning with "a" or  "b",  it  matches  an
2156           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2157           match is not valid, so PCRE searches further into the string for occur-
2158           rences of "a" or "b".
2159    
2160             PCRE_NOTEMPTY_ATSTART
2161    
2162           This  is  like PCRE_NOTEMPTY, except that an empty string match that is
2163           not at the start of  the  subject  is  permitted.  If  the  pattern  is
2164           anchored, such a match can occur only if the pattern contains \K.
2165    
2166           Perl     has    no    direct    equivalent    of    PCRE_NOTEMPTY    or
2167           PCRE_NOTEMPTY_ATSTART, but it does make a special  case  of  a  pattern
2168           match  of  the empty string within its split() function, and when using
2169           the /g modifier. It is  possible  to  emulate  Perl's  behaviour  after
2170           matching a null string by first trying the match again at the same off-
2171           set with PCRE_NOTEMPTY_ATSTART and  PCRE_ANCHORED,  and  then  if  that
2172           fails, by advancing the starting offset (see below) and trying an ordi-
2173           nary match again. There is some code that demonstrates how to  do  this
2174           in  the  pcredemo sample program. In the most general case, you have to
2175           check to see if the newline convention recognizes CRLF  as  a  newline,
2176           and  if so, and the current character is CR followed by LF, advance the
2177           starting offset by two characters instead of one.
2178    
2179             PCRE_NO_START_OPTIMIZE
2180    
2181           There are a number of optimizations that pcre_exec() uses at the  start
2182           of  a  match,  in  order to speed up the process. For example, if it is
2183           known that an unanchored match must start with a specific character, it
2184           searches  the  subject  for that character, and fails immediately if it
2185           cannot find it, without actually running the  main  matching  function.
2186           This means that a special item such as (*COMMIT) at the start of a pat-
2187           tern is not considered until after a suitable starting  point  for  the
2188           match  has been found. When callouts or (*MARK) items are in use, these
2189           "start-up" optimizations can cause them to be skipped if the pattern is
2190           never  actually  used.  The start-up optimizations are in effect a pre-
2191           scan of the subject that takes place before the pattern is run.
2192    
2193           The PCRE_NO_START_OPTIMIZE option disables the start-up  optimizations,
2194           possibly  causing  performance  to  suffer,  but ensuring that in cases
2195           where the result is "no match", the callouts do occur, and  that  items
2196           such as (*COMMIT) and (*MARK) are considered at every possible starting
2197           position in the subject string. If  PCRE_NO_START_OPTIMIZE  is  set  at
2198           compile time, it cannot be unset at matching time.
2199    
2200           Setting  PCRE_NO_START_OPTIMIZE  can  change  the outcome of a matching
2201           operation.  Consider the pattern
2202    
2203             (*COMMIT)ABC
2204    
2205           When this is compiled, PCRE records the fact that a  match  must  start
2206           with  the  character  "A".  Suppose the subject string is "DEFABC". The
2207           start-up optimization scans along the subject, finds "A" and  runs  the
2208           first  match attempt from there. The (*COMMIT) item means that the pat-
2209           tern must match the current starting position, which in this  case,  it
2210           does.  However,  if  the  same match is run with PCRE_NO_START_OPTIMIZE
2211           set, the initial scan along the subject string  does  not  happen.  The
2212           first  match  attempt  is  run  starting  from "D" and when this fails,
2213           (*COMMIT) prevents any further matches  being  tried,  so  the  overall
2214           result  is  "no  match". If the pattern is studied, more start-up opti-
2215           mizations may be used. For example, a minimum length  for  the  subject
2216           may be recorded. Consider the pattern
2217    
2218             (*MARK:A)(X|Y)
2219    
2220           The  minimum  length  for  a  match is one character. If the subject is
2221           "ABC", there will be attempts to  match  "ABC",  "BC",  "C",  and  then
2222           finally  an empty string.  If the pattern is studied, the final attempt
2223           does not take place, because PCRE knows that the subject is too  short,
2224           and  so  the  (*MARK) is never encountered.  In this case, studying the
2225           pattern does not affect the overall match result, which  is  still  "no
2226           match", but it does affect the auxiliary information that is returned.
2227    
2228             PCRE_NO_UTF8_CHECK
2229    
2230           When PCRE_UTF8 is set at compile time, the validity of the subject as a
2231           UTF-8 string is automatically checked when pcre_exec() is  subsequently
2232           called.   The  value  of  startoffset is also checked to ensure that it
2233           points to the start of a UTF-8 character. There is a  discussion  about
2234           the  validity  of  UTF-8 strings in the section on UTF-8 support in the
2235           main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
2236           pcre_exec()  returns  the  error  PCRE_ERROR_BADUTF8  or,  if PCRE_PAR-
2237           TIAL_HARD is set and the problem is a truncated UTF-8 character at  the
2238           end  of  the  subject, PCRE_ERROR_SHORTUTF8. In both cases, information
2239           about the precise nature of the error may also  be  returned  (see  the
2240           descriptions  of these errors in the section entitled Error return val-
2241           ues from pcre_exec() below).  If startoffset contains a value that does
2242           not  point to the start of a UTF-8 character (or to the end of the sub-
2243           ject), PCRE_ERROR_BADUTF8_OFFSET is returned.
2244    
2245           If you already know that your subject is valid, and you  want  to  skip
2246           these    checks    for   performance   reasons,   you   can   set   the
2247           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
2248           do  this  for the second and subsequent calls to pcre_exec() if you are
2249           making repeated calls to find all  the  matches  in  a  single  subject
2250           string.  However,  you  should  be  sure  that the value of startoffset
2251           points to the start of a UTF-8 character (or the end of  the  subject).
2252           When  PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8
2253           string as a subject or an invalid value of  startoffset  is  undefined.
2254           Your program may crash.
2255    
2256             PCRE_PARTIAL_HARD
2257             PCRE_PARTIAL_SOFT
2258    
2259           These  options turn on the partial matching feature. For backwards com-
2260           patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A  partial
2261           match  occurs if the end of the subject string is reached successfully,
2262           but there are not enough subject characters to complete the  match.  If
2263           this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
2264           matching continues by testing any remaining alternatives.  Only  if  no
2265           complete  match  can be found is PCRE_ERROR_PARTIAL returned instead of
2266           PCRE_ERROR_NOMATCH. In other words,  PCRE_PARTIAL_SOFT  says  that  the
2267           caller  is  prepared to handle a partial match, but only if no complete
2268           match can be found.
2269    
2270           If PCRE_PARTIAL_HARD is set, it overrides  PCRE_PARTIAL_SOFT.  In  this
2271           case,  if  a  partial  match  is found, pcre_exec() immediately returns
2272           PCRE_ERROR_PARTIAL, without  considering  any  other  alternatives.  In
2273           other  words, when PCRE_PARTIAL_HARD is set, a partial match is consid-
2274           ered to be more important that an alternative complete match.
2275    
2276           In both cases, the portion of the string that was  inspected  when  the
2277           partial match was found is set as the first matching string. There is a
2278           more detailed discussion of partial and  multi-segment  matching,  with
2279           examples, in the pcrepartial documentation.
2280    
2281       The string to be matched by pcre_exec()
2282    
2283           The  subject string is passed to pcre_exec() as a pointer in subject, a
2284           length (in bytes) in length, and a starting byte offset in startoffset.
2285           If  this  is  negative  or  greater  than  the  length  of the subject,
2286           pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting  offset  is
2287           zero,  the  search  for a match starts at the beginning of the subject,
2288           and this is by far the most common case. In UTF-8 mode, the byte offset
2289           must  point  to  the start of a UTF-8 character (or the end of the sub-
2290           ject). Unlike the pattern string, the subject may contain  binary  zero
2291           bytes.
2292    
2293           A  non-zero  starting offset is useful when searching for another match
2294           in the same subject by calling pcre_exec() again after a previous  suc-
2295           cess.   Setting  startoffset differs from just passing over a shortened
2296           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
2297           with any kind of lookbehind. For example, consider the pattern
2298    
2299             \Biss\B
2300    
2301           which  finds  occurrences  of "iss" in the middle of words. (\B matches
2302           only if the current position in the subject is not  a  word  boundary.)
2303           When  applied  to the string "Mississipi" the first call to pcre_exec()
2304           finds the first occurrence. If pcre_exec() is called  again  with  just
2305           the  remainder  of  the  subject,  namely  "issipi", it does not match,
2306           because \B is always false at the start of the subject, which is deemed
2307           to  be  a  word  boundary. However, if pcre_exec() is passed the entire
2308           string again, but with startoffset set to 4, it finds the second occur-
2309           rence  of "iss" because it is able to look behind the starting point to
2310           discover that it is preceded by a letter.
2311    
2312           Finding all the matches in a subject is tricky  when  the  pattern  can
2313           match an empty string. It is possible to emulate Perl's /g behaviour by
2314           first  trying  the  match  again  at  the   same   offset,   with   the
2315           PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED  options,  and  then  if that
2316           fails, advancing the starting  offset  and  trying  an  ordinary  match
2317           again. There is some code that demonstrates how to do this in the pcre-
2318           demo sample program. In the most general case, you have to check to see
2319           if  the newline convention recognizes CRLF as a newline, and if so, and
2320           the current character is CR followed by LF, advance the starting offset
2321           by two characters instead of one.
2322    
2323           If  a  non-zero starting offset is passed when the pattern is anchored,
2324           one attempt to match at the given offset is made. This can only succeed
2325           if  the  pattern  does  not require the match to be at the start of the
2326           subject.
2327    
2328       How pcre_exec() returns captured substrings
2329    
2330           In general, a pattern matches a certain portion of the subject, and  in
2331           addition,  further  substrings  from  the  subject may be picked out by
2332           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2333           this  is  called "capturing" in what follows, and the phrase "capturing
2334           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2335           string.  PCRE  supports several other kinds of parenthesized subpattern
2336           that do not cause substrings to be captured.
2337    
2338           Captured substrings are returned to the caller via a vector of integers
2339           whose  address is passed in ovector. The number of elements in the vec-
2340           tor is passed in ovecsize, which must be a non-negative  number.  Note:
2341           this argument is NOT the size of ovector in bytes.
2342    
2343           The  first  two-thirds of the vector is used to pass back captured sub-
2344           strings, each substring using a pair of integers. The  remaining  third
2345           of  the  vector is used as workspace by pcre_exec() while matching cap-
2346           turing subpatterns, and is not available for passing back  information.
2347           The  number passed in ovecsize should always be a multiple of three. If
2348           it is not, it is rounded down.
2349    
2350           When a match is successful, information about  captured  substrings  is
2351           returned  in  pairs  of integers, starting at the beginning of ovector,
2352           and continuing up to two-thirds of its length at the  most.  The  first
2353           element  of  each pair is set to the byte offset of the first character
2354           in a substring, and the second is set to the byte offset of  the  first
2355           character  after  the end of a substring. Note: these values are always
2356           byte offsets, even in UTF-8 mode. They are not character counts.
2357    
2358           The first pair of integers, ovector[0]  and  ovector[1],  identify  the
2359           portion  of  the subject string matched by the entire pattern. The next
2360           pair is used for the first capturing subpattern, and so on.  The  value
2361           returned by pcre_exec() is one more than the highest numbered pair that
2362           has been set.  For example, if two substrings have been  captured,  the
2363           returned  value is 3. If there are no capturing subpatterns, the return
2364           value from a successful match is 1, indicating that just the first pair
2365           of offsets has been set.
2366    
2367           If a capturing subpattern is matched repeatedly, it is the last portion
2368           of the string that it matched that is returned.
2369    
2370           If the vector is too small to hold all the captured substring  offsets,
2371           it is used as far as possible (up to two-thirds of its length), and the
2372           function returns a value of zero. If the substring offsets are  not  of
2373           interest,  pcre_exec()  may  be  called with ovector passed as NULL and
2374           ovecsize as zero. However, if the pattern contains back references  and
2375           the  ovector is not big enough to remember the related substrings, PCRE
2376           has to get additional memory for use during matching. Thus it  is  usu-
2377           ally advisable to supply an ovector.
2378    
2379           The pcre_fullinfo() function can be used to find out how many capturing
2380           subpatterns there are in a compiled  pattern.  The  smallest  size  for
2381           ovector  that  will allow for n captured substrings, in addition to the
2382           offsets of the substring matched by the whole pattern, is (n+1)*3.
2383    
2384           It is possible for capturing subpattern number n+1 to match  some  part
2385           of the subject when subpattern n has not been used at all. For example,
2386           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2387           return from the function is 4, and subpatterns 1 and 3 are matched, but
2388           2 is not. When this happens, both values in  the  offset  pairs  corre-
2389           sponding to unused subpatterns are set to -1.
2390    
2391           Offset  values  that correspond to unused subpatterns at the end of the
2392           expression are also set to -1. For example,  if  the  string  "abc"  is
2393           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2394           matched. The return from the function is 2, because  the  highest  used
2395           capturing  subpattern  number  is 1, and the offsets for for the second
2396           and third capturing subpatterns (assuming the vector is  large  enough,
2397           of course) are set to -1.
2398    
2399           Note: Elements of ovector that do not correspond to capturing parenthe-
2400           ses in the pattern are never changed. That is, if a pattern contains  n
2401           capturing parentheses, no more than ovector[0] to ovector[2n+1] are set
2402           by pcre_exec(). The other elements retain whatever values  they  previ-
2403           ously had.
2404    
2405           Some  convenience  functions  are  provided for extracting the captured
2406           substrings as separate strings. These are described below.
2407    
2408       Error return values from pcre_exec()
2409    
2410           If pcre_exec() fails, it returns a negative number. The  following  are
2411           defined in the header file:
2412    
2413             PCRE_ERROR_NOMATCH        (-1)
2414    
2415           The subject string did not match the pattern.
2416    
2417             PCRE_ERROR_NULL           (-2)
2418    
2419           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2420           ovecsize was not zero.
2421    
2422             PCRE_ERROR_BADOPTION      (-3)
2423    
2424           An unrecognized bit was set in the options argument.
2425    
2426             PCRE_ERROR_BADMAGIC       (-4)
2427    
2428           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2429           to catch the case when it is passed a junk pointer and to detect when a
2430           pattern that was compiled in an environment of one endianness is run in
2431           an  environment  with the other endianness. This is the error that PCRE
2432           gives when the magic number is not present.
2433    
2434             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2435    
2436           While running the pattern match, an unknown item was encountered in the
2437           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2438           overwriting of the compiled pattern.
2439    
2440             PCRE_ERROR_NOMEMORY       (-6)
2441    
2442           If a pattern contains back references, but the ovector that  is  passed
2443           to pcre_exec() is not big enough to remember the referenced substrings,
2444           PCRE gets a block of memory at the start of matching to  use  for  this
2445           purpose.  If the call via pcre_malloc() fails, this error is given. The
2446           memory is automatically freed at the end of matching.
2447    
2448           This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
2449           This  can happen only when PCRE has been compiled with --disable-stack-
2450           for-recursion.
2451    
2452             PCRE_ERROR_NOSUBSTRING    (-7)
2453    
2454           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2455           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2456           returned by pcre_exec().
2457    
2458             PCRE_ERROR_MATCHLIMIT     (-8)
2459    
2460           The backtracking limit, as specified by  the  match_limit  field  in  a
2461           pcre_extra  structure  (or  defaulted) was reached. See the description
2462           above.
2463    
2464             PCRE_ERROR_CALLOUT        (-9)
2465    
2466           This error is never generated by pcre_exec() itself. It is provided for
2467           use  by  callout functions that want to yield a distinctive error code.
2468           See the pcrecallout documentation for details.
2469    
2470             PCRE_ERROR_BADUTF8        (-10)
2471    
2472           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2473           subject,  and the PCRE_NO_UTF8_CHECK option was not set. If the size of
2474           the output vector (ovecsize) is at least 2,  the  byte  offset  to  the
2475           start  of  the  the invalid UTF-8 character is placed in the first ele-
2476           ment, and a reason code is placed in the  second  element.  The  reason
2477           codes are listed in the following section.  For backward compatibility,
2478           if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8  char-
2479           acter   at   the   end   of   the   subject  (reason  codes  1  to  5),
2480           PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
2481    
2482             PCRE_ERROR_BADUTF8_OFFSET (-11)
2483    
2484           The UTF-8 byte sequence that was passed as a subject  was  checked  and
2485           found  to be valid (the PCRE_NO_UTF8_CHECK option was not set), but the
2486           value of startoffset did not point to the beginning of a UTF-8  charac-
2487           ter or the end of the subject.
2488    
2489             PCRE_ERROR_PARTIAL        (-12)
2490    
2491           The  subject  string did not match, but it did match partially. See the
2492           pcrepartial documentation for details of partial matching.
2493    
2494             PCRE_ERROR_BADPARTIAL     (-13)
2495    
2496           This code is no longer in  use.  It  was  formerly  returned  when  the
2497           PCRE_PARTIAL  option  was used with a compiled pattern containing items
2498           that were  not  supported  for  partial  matching.  From  release  8.00
2499           onwards, there are no restrictions on partial matching.
2500    
2501             PCRE_ERROR_INTERNAL       (-14)
2502    
2503           An  unexpected  internal error has occurred. This error could be caused
2504           by a bug in PCRE or by overwriting of the compiled pattern.
2505    
2506             PCRE_ERROR_BADCOUNT       (-15)
2507    
2508           This error is given if the value of the ovecsize argument is negative.
2509    
2510             PCRE_ERROR_RECURSIONLIMIT (-21)
2511    
2512           The internal recursion limit, as specified by the match_limit_recursion
2513           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2514           description above.
2515    
2516             PCRE_ERROR_BADNEWLINE     (-23)
2517    
2518           An invalid combination of PCRE_NEWLINE_xxx options was given.
2519    
2520             PCRE_ERROR_BADOFFSET      (-24)
2521    
2522           The value of startoffset was negative or greater than the length of the
2523           subject, that is, the value in length.
2524    
2525             PCRE_ERROR_SHORTUTF8      (-25)
2526    
2527           This  error  is returned instead of PCRE_ERROR_BADUTF8 when the subject
2528           string ends with a truncated UTF-8 character and the  PCRE_PARTIAL_HARD
2529           option  is  set.   Information  about  the  failure  is returned as for
2530           PCRE_ERROR_BADUTF8. It is in fact sufficient to detect this  case,  but
2531           this  special error code for PCRE_PARTIAL_HARD precedes the implementa-
2532           tion of returned information; it is retained for backwards  compatibil-
2533           ity.
2534    
2535             PCRE_ERROR_RECURSELOOP    (-26)
2536    
2537           This error is returned when pcre_exec() detects a recursion loop within
2538           the pattern. Specifically, it means that either the whole pattern or  a
2539           subpattern  has been called recursively for the second time at the same
2540           position in the subject string. Some simple patterns that might do this
2541           are  detected  and faulted at compile time, but more complicated cases,
2542           in particular mutual recursions between two different subpatterns, can-
2543           not be detected until run time.
2544    
2545           Error numbers -16 to -20 and -22 are not used by pcre_exec().
2546    
2547       Reason codes for invalid UTF-8 strings
2548    
2549           When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
2550           UTF8, and the size of the output vector (ovecsize) is at least  2,  the
2551           offset  of  the  start  of the invalid UTF-8 character is placed in the
2552           first output vector element (ovector[0]) and a reason code is placed in
2553           the  second  element  (ovector[1]). The reason codes are given names in
2554           the pcre.h header file:
2555    
2556             PCRE_UTF8_ERR1
2557             PCRE_UTF8_ERR2
2558             PCRE_UTF8_ERR3
2559             PCRE_UTF8_ERR4
2560             PCRE_UTF8_ERR5
2561    
2562           The string ends with a truncated UTF-8 character;  the  code  specifies
2563           how  many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
2564           characters to be no longer than 4 bytes, the  encoding  scheme  (origi-
2565           nally  defined  by  RFC  2279)  allows  for  up to 6 bytes, and this is
2566           checked first; hence the possibility of 4 or 5 missing bytes.
2567    
2568             PCRE_UTF8_ERR6
2569             PCRE_UTF8_ERR7
2570             PCRE_UTF8_ERR8
2571             PCRE_UTF8_ERR9
2572             PCRE_UTF8_ERR10
2573    
2574           The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
2575           the  character  do  not have the binary value 0b10 (that is, either the
2576           most significant bit is 0, or the next bit is 1).
2577    
2578             PCRE_UTF8_ERR11
2579             PCRE_UTF8_ERR12
2580    
2581           A character that is valid by the RFC 2279 rules is either 5 or 6  bytes
2582           long; these code points are excluded by RFC 3629.
2583    
2584             PCRE_UTF8_ERR13
2585    
2586           A  4-byte character has a value greater than 0x10fff; these code points
2587           are excluded by RFC 3629.
2588    
2589             PCRE_UTF8_ERR14
2590    
2591           A 3-byte character has a value in the  range  0xd800  to  0xdfff;  this
2592           range  of code points are reserved by RFC 3629 for use with UTF-16, and
2593           so are excluded from UTF-8.
2594    
2595             PCRE_UTF8_ERR15
2596             PCRE_UTF8_ERR16
2597             PCRE_UTF8_ERR17
2598             PCRE_UTF8_ERR18
2599             PCRE_UTF8_ERR19
2600    
2601           A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it  codes
2602           for  a  value that can be represented by fewer bytes, which is invalid.
2603           For example, the two bytes 0xc0, 0xae give the value 0x2e,  whose  cor-
2604           rect coding uses just one byte.
2605    
2606             PCRE_UTF8_ERR20
2607    
2608           The two most significant bits of the first byte of a character have the
2609           binary value 0b10 (that is, the most significant bit is 1 and the  sec-
2610           ond  is  0). Such a byte can only validly occur as the second or subse-
2611           quent byte of a multi-byte character.
2612    
2613             PCRE_UTF8_ERR21
2614    
2615           The first byte of a character has the value 0xfe or 0xff. These  values
2616           can never occur in a valid UTF-8 string.
2617    
2618    
2619    EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2620    
2621           int pcre_copy_substring(const char *subject, int *ovector,
2622                int stringcount, int stringnumber, char *buffer,
2623                int buffersize);
2624    
2625           int pcre_get_substring(const char *subject, int *ovector,
2626                int stringcount, int stringnumber,
2627                const char **stringptr);
2628    
2629           int pcre_get_substring_list(const char *subject,
2630                int *ovector, int stringcount, const char ***listptr);
2631    
2632           Captured  substrings  can  be  accessed  directly  by using the offsets
2633           returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2634           pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2635           string_list() are provided for extracting captured substrings  as  new,
2636           separate,  zero-terminated strings. These functions identify substrings
2637           by number. The next section describes functions  for  extracting  named
2638           substrings.
2639    
2640           A  substring that contains a binary zero is correctly extracted and has
2641           a further zero added on the end, but the result is not, of course, a  C
2642           string.   However,  you  can  process such a string by referring to the
2643           length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2644           string().  Unfortunately, the interface to pcre_get_substring_list() is
2645           not adequate for handling strings containing binary zeros, because  the
2646           end of the final string is not independently indicated.
2647    
2648           The  first  three  arguments  are the same for all three of these func-
2649           tions: subject is the subject string that has  just  been  successfully
2650           matched, ovector is a pointer to the vector of integer offsets that was
2651           passed to pcre_exec(), and stringcount is the number of substrings that
2652           were  captured  by  the match, including the substring that matched the
2653           entire regular expression. This is the value returned by pcre_exec() if
2654           it  is greater than zero. If pcre_exec() returned zero, indicating that
2655           it ran out of space in ovector, the value passed as stringcount  should
2656           be the number of elements in the vector divided by three.
2657    
2658           The  functions pcre_copy_substring() and pcre_get_substring() extract a
2659           single substring, whose number is given as  stringnumber.  A  value  of
2660           zero  extracts  the  substring that matched the entire pattern, whereas
2661           higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2662           string(),  the  string  is  placed  in buffer, whose length is given by
2663           buffersize, while for pcre_get_substring() a new  block  of  memory  is
2664           obtained  via  pcre_malloc,  and its address is returned via stringptr.
2665           The yield of the function is the length of the  string,  not  including
2666           the terminating zero, or one of these error codes:
2667    
2668             PCRE_ERROR_NOMEMORY       (-6)
2669    
2670           The  buffer  was too small for pcre_copy_substring(), or the attempt to
2671           get memory failed for pcre_get_substring().
2672    
2673             PCRE_ERROR_NOSUBSTRING    (-7)
2674    
2675           There is no substring whose number is stringnumber.
2676    
2677           The pcre_get_substring_list()  function  extracts  all  available  sub-
2678           strings  and  builds  a list of pointers to them. All this is done in a
2679           single block of memory that is obtained via pcre_malloc. The address of
2680           the  memory  block  is returned via listptr, which is also the start of
2681           the list of string pointers. The end of the list is marked  by  a  NULL
2682           pointer.  The  yield  of  the function is zero if all went well, or the
2683           error code
2684    
2685             PCRE_ERROR_NOMEMORY       (-6)
2686    
2687           if the attempt to get the memory block failed.
2688    
2689           When any of these functions encounter a substring that is unset,  which
2690           can  happen  when  capturing subpattern number n+1 matches some part of
2691           the subject, but subpattern n has not been used at all, they return  an
2692           empty string. This can be distinguished from a genuine zero-length sub-
2693           string by inspecting the appropriate offset in ovector, which is  nega-
2694           tive for unset substrings.
2695    
2696           The  two convenience functions pcre_free_substring() and pcre_free_sub-
2697           string_list() can be used to free the memory  returned  by  a  previous
2698           call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2699           tively. They do nothing more than  call  the  function  pointed  to  by
2700           pcre_free,  which  of course could be called directly from a C program.
2701           However, PCRE is used in some situations where it is linked via a  spe-
2702           cial   interface  to  another  programming  language  that  cannot  use
2703           pcre_free directly; it is for these cases that the functions  are  pro-
2704           vided.
2705    
2706    
2707    EXTRACTING CAPTURED SUBSTRINGS BY NAME
2708    
2709           int pcre_get_stringnumber(const pcre *code,
2710                const char *name);
2711    
2712           int pcre_copy_named_substring(const pcre *code,
2713                const char *subject, int *ovector,
2714                int stringcount, const char *stringname,
2715                char *buffer, int buffersize);
2716    
2717           int pcre_get_named_substring(const pcre *code,
2718                const char *subject, int *ovector,
2719                int stringcount, const char *stringname,
2720                const char **stringptr);
2721    
2722           To  extract a substring by name, you first have to find associated num-
2723           ber.  For example, for this pattern
2724    
2725             (a+)b(?<xxx>\d+)...
2726    
2727           the number of the subpattern called "xxx" is 2. If the name is known to
2728           be unique (PCRE_DUPNAMES was not set), you can find the number from the
2729           name by calling pcre_get_stringnumber(). The first argument is the com-
2730           piled pattern, and the second is the name. The yield of the function is
2731           the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2732           subpattern of that name.
2733    
2734           Given the number, you can extract the substring directly, or use one of
2735           the functions described in the previous section. For convenience, there
2736           are also two functions that do the whole job.
2737    
2738           Most    of    the    arguments   of   pcre_copy_named_substring()   and
2739           pcre_get_named_substring() are the same  as  those  for  the  similarly
2740           named  functions  that extract by number. As these are described in the
2741           previous section, they are not re-described here. There  are  just  two
2742           differences:
2743    
2744           First,  instead  of a substring number, a substring name is given. Sec-
2745           ond, there is an extra argument, given at the start, which is a pointer
2746           to  the compiled pattern. This is needed in order to gain access to the
2747           name-to-number translation table.
2748    
2749           These functions call pcre_get_stringnumber(), and if it succeeds,  they
2750           then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2751           ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2752           behaviour may not be what you want (see the next section).
2753    
2754           Warning: If the pattern uses the (?| feature to set up multiple subpat-
2755           terns with the same number, as described in the  section  on  duplicate
2756           subpattern  numbers  in  the  pcrepattern page, you cannot use names to
2757           distinguish the different subpatterns, because names are  not  included
2758           in  the compiled code. The matching process uses only numbers. For this
2759           reason, the use of different names for subpatterns of the  same  number
2760           causes an error at compile time.
2761    
2762    
2763    DUPLICATE SUBPATTERN NAMES
2764    
2765           int pcre_get_stringtable_entries(const pcre *code,
2766                const char *name, char **first, char **last);
2767    
2768           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2769           subpatterns are not required to be unique. (Duplicate names are  always
2770           allowed  for subpatterns with the same number, created by using the (?|
2771           feature. Indeed, if such subpatterns are named, they  are  required  to
2772           use the same names.)
2773    
2774           Normally, patterns with duplicate names are such that in any one match,
2775           only one of the named subpatterns participates. An example is shown  in
2776           the pcrepattern documentation.
2777    
2778           When    duplicates   are   present,   pcre_copy_named_substring()   and
2779           pcre_get_named_substring() return the first substring corresponding  to
2780           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2781           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2782           function  returns one of the numbers that are associated with the name,
2783           but it is not defined which it is.
2784    
2785           If you want to get full details of all captured substrings for a  given
2786           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2787           first argument is the compiled pattern, and the second is the name. The
2788           third  and  fourth  are  pointers to variables which are updated by the
2789           function. After it has run, they point to the first and last entries in
2790           the  name-to-number  table  for  the  given  name.  The function itself
2791           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2792           there  are none. The format of the table is described above in the sec-
2793           tion entitled Information about a pattern above.  Given all  the  rele-
2794           vant  entries  for the name, you can extract each of their numbers, and
2795           hence the captured data, if any.
2796    
2797    
2798    FINDING ALL POSSIBLE MATCHES
2799    
2800           The traditional matching function uses a  similar  algorithm  to  Perl,
2801           which stops when it finds the first match, starting at a given point in
2802           the subject. If you want to find all possible matches, or  the  longest
2803           possible  match,  consider using the alternative matching function (see
2804           below) instead. If you cannot use the alternative function,  but  still
2805           need  to  find all possible matches, you can kludge it up by making use
2806           of the callout facility, which is described in the pcrecallout documen-
2807           tation.
2808    
2809           What you have to do is to insert a callout right at the end of the pat-
2810           tern.  When your callout function is called, extract and save the  cur-
2811           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2812           backtrack and try other alternatives. Ultimately, when it runs  out  of
2813           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2814    
2815    
2816    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2817    
2818           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2819                const char *subject, int length, int startoffset,
2820                int options, int *ovector, int ovecsize,
2821                int *workspace, int wscount);
2822    
2823           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2824           against a compiled pattern, using a matching algorithm that  scans  the
2825           subject  string  just  once, and does not backtrack. This has different
2826           characteristics to the normal algorithm, and  is  not  compatible  with
2827           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2828           theless, there are times when this kind of matching can be useful.  For
2829           a  discussion  of  the  two matching algorithms, and a list of features
2830           that pcre_dfa_exec() does not support, see the pcrematching  documenta-
2831           tion.
2832    
2833           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2834           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2835           ent  way,  and  this is described below. The other common arguments are
2836           used in the same way as for pcre_exec(), so their  description  is  not
2837           repeated here.
2838    
2839           The  two  additional  arguments provide workspace for the function. The
2840           workspace vector should contain at least 20 elements. It  is  used  for
2841           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2842           workspace will be needed for patterns and subjects where  there  are  a
2843           lot of potential matches.
2844    
2845           Here is an example of a simple call to pcre_dfa_exec():
2846    
2847             int rc;
2848             int ovector[10];
2849             int wspace[20];
2850             rc = pcre_dfa_exec(
2851               re,             /* result of pcre_compile() */
2852               NULL,           /* we didn't study the pattern */
2853               "some string",  /* the subject string */
2854               11,             /* the length of the subject string */
2855               0,              /* start at offset 0 in the subject */
2856               0,              /* default options */
2857               ovector,        /* vector of integers for substring information */
2858               10,             /* number of elements (NOT size in bytes) */
2859               wspace,         /* working space vector */
2860               20);            /* number of elements (NOT size in bytes) */
2861    
2862       Option bits for pcre_dfa_exec()
2863    
2864           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2865           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2866           LINE_xxx,        PCRE_NOTBOL,        PCRE_NOTEOL,        PCRE_NOTEMPTY,
2867           PCRE_NOTEMPTY_ATSTART,      PCRE_NO_UTF8_CHECK,       PCRE_BSR_ANYCRLF,
2868           PCRE_BSR_UNICODE,  PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR-
2869           TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.  All but  the  last
2870           four  of  these  are  exactly  the  same  as  for pcre_exec(), so their
2871           description is not repeated here.
2872    
2873             PCRE_PARTIAL_HARD
2874             PCRE_PARTIAL_SOFT
2875    
2876           These have the same general effect as they do for pcre_exec(), but  the
2877           details  are  slightly  different.  When  PCRE_PARTIAL_HARD  is set for
2878           pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub-
2879           ject  is  reached  and there is still at least one matching possibility
2880           that requires additional characters. This happens even if some complete
2881           matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
2882           code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
2883           of  the  subject  is  reached, there have been no complete matches, but
2884           there is still at least one matching possibility. The  portion  of  the
2885           string  that  was inspected when the longest partial match was found is
2886           set as the first matching string  in  both  cases.   There  is  a  more
2887           detailed  discussion  of partial and multi-segment matching, with exam-
2888           ples, in the pcrepartial documentation.
2889    
2890             PCRE_DFA_SHORTEST
2891    
2892           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2893           stop as soon as it has found one match. Because of the way the alterna-
2894           tive algorithm works, this is necessarily the shortest  possible  match
2895           at the first possible matching point in the subject string.
2896    
2897             PCRE_DFA_RESTART
2898    
2899           When pcre_dfa_exec() returns a partial match, it is possible to call it
2900           again, with additional subject characters, and have  it  continue  with
2901           the  same match. The PCRE_DFA_RESTART option requests this action; when
2902           it is set, the workspace and wscount options must  reference  the  same
2903           vector  as  before  because data about the match so far is left in them
2904           after a partial match. There is more discussion of this facility in the
2905           pcrepartial documentation.
2906    
2907       Successful returns from pcre_dfa_exec()
2908    
2909           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2910           string in the subject. Note, however, that all the matches from one run
2911           of  the  function  start  at the same point in the subject. The shorter
2912           matches are all initial substrings of the longer matches. For  example,
2913           if the pattern
2914    
2915             <.*>
2916    
2917           is matched against the string
2918    
2919             This is <something> <something else> <something further> no more
2920    
2921           the three matched strings are
2922    
2923             <something>
2924             <something> <something else>
2925             <something> <something else> <something further>
2926    
2927           On  success,  the  yield of the function is a number greater than zero,
2928           which is the number of matched substrings.  The  substrings  themselves
2929           are  returned  in  ovector. Each string uses two elements; the first is
2930           the offset to the start, and the second is the offset to  the  end.  In
2931           fact,  all  the  strings  have the same start offset. (Space could have
2932           been saved by giving this only once, but it was decided to retain  some
2933           compatibility  with  the  way pcre_exec() returns data, even though the
2934           meaning of the strings is different.)
2935    
2936           The strings are returned in reverse order of length; that is, the long-
2937           est  matching  string is given first. If there were too many matches to
2938           fit into ovector, the yield of the function is zero, and the vector  is
2939           filled with the longest matches.
2940    
2941       Error returns from pcre_dfa_exec()
2942    
2943           The  pcre_dfa_exec()  function returns a negative number when it fails.
2944           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2945           described  above.   There are in addition the following errors that are
2946           specific to pcre_dfa_exec():
2947    
2948             PCRE_ERROR_DFA_UITEM      (-16)
2949    
2950           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2951           tern  that  it  does not support, for instance, the use of \C or a back
2952           reference.
2953    
2954             PCRE_ERROR_DFA_UCOND      (-17)
2955    
2956           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2957           that  uses  a back reference for the condition, or a test for recursion
2958           in a specific group. These are not supported.
2959    
2960             PCRE_ERROR_DFA_UMLIMIT    (-18)
2961    
2962           This return is given if pcre_dfa_exec() is called with an  extra  block
2963           that contains a setting of the match_limit field. This is not supported
2964           (it is meaningless).
2965    
2966             PCRE_ERROR_DFA_WSSIZE     (-19)
2967    
2968           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2969           workspace vector.
2970    
2971             PCRE_ERROR_DFA_RECURSE    (-20)
2972    
2973           When  a  recursive subpattern is processed, the matching function calls
2974           itself recursively, using private vectors for  ovector  and  workspace.
2975           This  error  is  given  if  the output vector is not large enough. This
2976           should be extremely rare, as a vector of size 1000 is used.
2977    
2978    
2979    SEE ALSO
2980    
2981           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2982           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2983    
2984    
2985    AUTHOR
2986    
2987           Philip Hazel
2988           University Computing Service
2989           Cambridge CB2 3QH, England.
2990    
2991    
2992    REVISION
2993    
2994           Last updated: 28 July 2011
2995           Copyright (c) 1997-2011 University of Cambridge.
2996    ------------------------------------------------------------------------------
2997    
2998    
2999    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
3000    
3001    
3002    NAME
3003           PCRE - Perl-compatible regular expressions
3004    
3005    
3006    PCRE CALLOUTS
3007    
3008           int (*pcre_callout)(pcre_callout_block *);
3009    
3010           PCRE provides a feature called "callout", which is a means of temporar-
3011           ily passing control to the caller of PCRE  in  the  middle  of  pattern
3012           matching.  The  caller of PCRE provides an external function by putting
3013           its entry point in the global variable pcre_callout. By  default,  this
3014           variable contains NULL, which disables all calling out.
3015    
3016           Within  a  regular  expression,  (?C) indicates the points at which the
3017           external function is to be called.  Different  callout  points  can  be
3018           identified  by  putting  a number less than 256 after the letter C. The
3019           default value is zero.  For  example,  this  pattern  has  two  callout
3020           points:
3021    
3022             (?C1)abc(?C2)def
3023    
3024           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() or
3025           pcre_compile2() is called, PCRE  automatically  inserts  callouts,  all
3026           with  number  255,  before  each  item  in the pattern. For example, if
3027           PCRE_AUTO_CALLOUT is used with the pattern
3028    
3029             A(\d{2}|--)
3030    
3031           it is processed as if it were
3032    
3033           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
3034    
3035           Notice that there is a callout before and after  each  parenthesis  and
3036           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
3037           progress of pattern matching. The pcretest command has an  option  that
3038           sets  automatic callouts; when it is used, the output indicates how the
3039           pattern is matched. This is useful information when you are  trying  to
3040           optimize the performance of a particular pattern.
3041    
3042    
3043    MISSING CALLOUTS
3044    
3045           You  should  be  aware  that,  because of optimizations in the way PCRE
3046           matches patterns by default, callouts  sometimes  do  not  happen.  For
3047           example, if the pattern is
3048    
3049             ab(?C4)cd
3050    
3051           PCRE knows that any matching string must contain the letter "d". If the
3052           subject string is "abyz", the lack of "d" means that  matching  doesn't
3053           ever  start,  and  the  callout is never reached. However, with "abyd",
3054           though the result is still no match, the callout is obeyed.
3055    
3056           If the pattern is studied, PCRE knows the minimum length of a  matching
3057           string,  and will immediately give a "no match" return without actually
3058           running a match if the subject is not long enough, or,  for  unanchored
3059           patterns, if it has been scanned far enough.
3060    
3061           You  can disable these optimizations by passing the PCRE_NO_START_OPTI-
3062           MIZE option to pcre_compile(), pcre_exec(), or pcre_dfa_exec(),  or  by
3063           starting the pattern with (*NO_START_OPT). This slows down the matching
3064           process, but does ensure that callouts such as the  example  above  are
3065           obeyed.
3066    
3067    
3068    THE CALLOUT INTERFACE
3069    
3070           During  matching, when PCRE reaches a callout point, the external func-
3071           tion defined by pcre_callout is called (if it is set). This applies  to
3072           both  the  pcre_exec()  and the pcre_dfa_exec() matching functions. The
3073           only argument to the callout function is a pointer  to  a  pcre_callout
3074           block. This structure contains the following fields:
3075    
3076             int         version;
3077             int         callout_number;
3078             int        *offset_vector;
3079             const char *subject;
3080             int         subject_length;
3081             int         start_match;
3082             int         current_position;
3083             int         capture_top;
3084             int         capture_last;
3085             void       *callout_data;
3086             int         pattern_position;
3087             int         next_item_length;
3088             const unsigned char *mark;
3089    
3090           The  version  field  is an integer containing the version number of the
3091           block format. The initial version was 0; the current version is 2.  The
3092           version  number  will  change  again in future if additional fields are
3093           added, but the intention is never to remove any of the existing fields.
3094    
3095           The callout_number field contains the number of the  callout,  as  com-
3096           piled  into  the pattern (that is, the number after ?C for manual call-
3097           outs, and 255 for automatically generated callouts).
3098    
3099           The offset_vector field is a pointer to the vector of offsets that  was
3100           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
3101           pcre_exec() is used, the contents can be inspected in order to  extract
3102           substrings  that  have  been  matched  so  far,  in the same way as for
3103           extracting substrings after a match has completed. For  pcre_dfa_exec()
3104           this field is not useful.
3105    
3106           The subject and subject_length fields contain copies of the values that
3107           were passed to pcre_exec().
3108    
3109           The start_match field normally contains the offset within  the  subject
3110           at  which  the  current  match  attempt started. However, if the escape
3111           sequence \K has been encountered, this value is changed to reflect  the
3112           modified  starting  point.  If the pattern is not anchored, the callout
3113           function may be called several times from the same point in the pattern
3114           for different starting points in the subject.
3115    
3116           The  current_position  field  contains the offset within the subject of
3117           the current match pointer.
3118    
3119           When the pcre_exec() function is used, the capture_top  field  contains
3120           one  more than the number of the highest numbered captured substring so
3121           far. If no substrings have been captured, the value of  capture_top  is
3122           one.  This  is always the case when pcre_dfa_exec() is used, because it
3123           does not support captured substrings.
3124    
3125           The capture_last field contains the number of the  most  recently  cap-
3126           tured  substring. If no substrings have been captured, its value is -1.
3127           This is always the case when pcre_dfa_exec() is used.
3128    
3129           The callout_data field contains a value that is passed  to  pcre_exec()
3130           or  pcre_dfa_exec() specifically so that it can be passed back in call-
3131           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
3132           structure.  If  no such data was passed, the value of callout_data in a
3133           pcre_callout block is NULL. There is a description  of  the  pcre_extra
3134           structure in the pcreapi documentation.
3135    
3136           The  pattern_position field is present from version 1 of the pcre_call-
3137           out structure. It contains the offset to the next item to be matched in
3138           the pattern string.
3139    
3140           The  next_item_length field is present from version 1 of the pcre_call-
3141           out structure. It contains the length of the next item to be matched in
3142           the  pattern  string. When the callout immediately precedes an alterna-
3143           tion bar, a closing parenthesis, or the end of the pattern, the  length
3144           is  zero.  When the callout precedes an opening parenthesis, the length
3145           is that of the entire subpattern.
3146    
3147           The pattern_position and next_item_length fields are intended  to  help
3148           in  distinguishing between different automatic callouts, which all have
3149           the same callout number. However, they are set for all callouts.
3150    
3151           The mark field is present from version 2 of the pcre_callout structure.
3152           In  callouts  from pcre_exec() it contains a pointer to the zero-termi-
3153           nated name of the most recently passed (*MARK) item in  the  match,  or
3154           NULL if there are no (*MARK)s in the current matching path. In callouts
3155           from pcre_dfa_exec() this field always contains NULL.
3156    
3157    
3158    RETURN VALUES
3159    
3160           The external callout function returns an integer to PCRE. If the  value
3161           is  zero,  matching  proceeds  as  normal. If the value is greater than
3162           zero, matching fails at the current point, but  the  testing  of  other
3163           matching possibilities goes ahead, just as if a lookahead assertion had
3164           failed. If the value is less than zero, the  match  is  abandoned,  and
3165           pcre_exec() or pcre_dfa_exec() returns the negative value.
3166    
3167           Negative   values   should   normally   be   chosen  from  the  set  of
3168           PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
3169           dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
3170           reserved for use by callout functions; it will never be  used  by  PCRE
3171           itself.
3172    
3173    
3174    AUTHOR
3175    
3176           Philip Hazel
3177           University Computing Service
3178           Cambridge CB2 3QH, England.
3179    
3180    
3181    REVISION
3182    
3183           Last updated: 31 July 2011
3184           Copyright (c) 1997-2011 University of Cambridge.
3185    ------------------------------------------------------------------------------
3186    
3187    
3188    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
3189    
3190    
3191    NAME
3192           PCRE - Perl-compatible regular expressions
3193    
3194    
3195    DIFFERENCES BETWEEN PCRE AND PERL
3196    
3197           This  document describes the differences in the ways that PCRE and Perl
3198           handle regular expressions. The differences  described  here  are  with
3199           respect to Perl versions 5.10 and above.
3200    
3201           1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
3202           of what it does have are given in the section on UTF-8 support  in  the
3203           main pcre page.
3204    
3205           2. PCRE allows repeat quantifiers only on parenthesized assertions, but
3206           they do not mean what you might think. For example, (?!a){3}  does  not
3207           assert that the next three characters are not "a". It just asserts that
3208           the next character is not "a" three times (in principle: PCRE optimizes
3209           this to run the assertion just once). Perl allows repeat quantifiers on
3210           other assertions such as \b, but these do not seem to have any use.
3211    
3212           3. Capturing subpatterns that occur inside  negative  lookahead  asser-
3213           tions  are  counted,  but their entries in the offsets vector are never
3214           set. Perl sets its numerical variables from any such patterns that  are
3215           matched before the assertion fails to match something (thereby succeed-
3216           ing), but only if the negative lookahead assertion  contains  just  one
3217           branch.
3218    
3219           4.  Though  binary zero characters are supported in the subject string,
3220           they are not allowed in a pattern string because it is passed as a nor-
3221           mal C string, terminated by zero. The escape sequence \0 can be used in
3222           the pattern to represent a binary zero.
3223    
3224           5. The following Perl escape sequences are not supported: \l,  \u,  \L,
3225           \U,  and  \N when followed by a character name or Unicode value. (\N on
3226           its own, matching a non-newline character, is supported.) In fact these
3227           are  implemented  by Perl's general string-handling and are not part of
3228           its pattern matching engine. If any of these are encountered  by  PCRE,
3229           an error is generated.
3230    
3231           6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE
3232           is built with Unicode character property support. The  properties  that
3233           can  be tested with \p and \P are limited to the general category prop-
3234           erties such as Lu and Nd, script names such as Greek or  Han,  and  the
3235           derived  properties  Any  and  L&. PCRE does support the Cs (surrogate)
3236           property, which Perl does not; the  Perl  documentation  says  "Because
3237           Perl hides the need for the user to understand the internal representa-
3238           tion of Unicode characters, there is no need to implement the  somewhat
3239           messy concept of surrogates."
3240    
3241           7.  PCRE implements a simpler version of \X than Perl, which changed to
3242           make \X match what Unicode calls an "extended grapheme  cluster".  This
3243           is  more  complicated  than an extended Unicode sequence, which is what
3244           PCRE matches.
3245    
3246           8. PCRE does support the \Q...\E escape for quoting substrings. Charac-
3247           ters  in  between  are  treated as literals. This is slightly different
3248           from Perl in that $ and @ are  also  handled  as  literals  inside  the
3249           quotes.  In Perl, they cause variable interpolation (but of course PCRE
3250           does not have variables). Note the following examples:
3251    
3252               Pattern            PCRE matches      Perl matches
3253    
3254               \Qabc$xyz\E        abc$xyz           abc followed by the
3255                                                      contents of $xyz
3256               \Qabc\$xyz\E       abc\$xyz          abc\$xyz
3257               \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
3258    
3259           The \Q...\E sequence is recognized both inside  and  outside  character
3260           classes.
3261    
3262           9. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
3263           constructions. However, there is support for recursive  patterns.  This
3264           is  not  available  in Perl 5.8, but it is in Perl 5.10. Also, the PCRE
3265           "callout" feature allows an external function to be called during  pat-
3266           tern matching. See the pcrecallout documentation for details.
3267    
3268           10.  Subpatterns  that  are  called recursively or as "subroutines" are
3269           always treated as atomic groups in  PCRE.  This  is  like  Python,  but
3270           unlike  Perl. There is a discussion of an example that explains this in
3271           more detail in the section on recursion differences from  Perl  in  the
3272           pcrepattern page.
3273    
3274           11.  There are some differences that are concerned with the settings of
3275           captured strings when part of  a  pattern  is  repeated.  For  example,
3276           matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
3277           unset, but in PCRE it is set to "b".
3278    
3279           12. PCRE's handling of duplicate subpattern numbers and duplicate  sub-
3280           pattern names is not as general as Perl's. This is a consequence of the
3281           fact the PCRE works internally just with numbers, using an external ta-
3282           ble  to  translate  between numbers and names. In particular, a pattern
3283           such as (?|(?<a>A)|(?<b)B), where the two  capturing  parentheses  have
3284           the  same  number  but different names, is not supported, and causes an
3285           error at compile time. If it were allowed, it would not be possible  to
3286           distinguish  which  parentheses matched, because both names map to cap-
3287           turing subpattern number 1. To avoid this confusing situation, an error
3288           is given at compile time.
3289    
3290           13.  Perl  recognizes  comments  in some places that PCRE does not, for
3291           example, between the ( and ? at the start of a subpattern.  If  the  /x
3292           modifier  is set, Perl allows whitespace between ( and ? but PCRE never
3293           does, even if the PCRE_EXTENDED option is set.
3294    
3295           14. PCRE provides some extensions to the Perl regular expression facil-
3296           ities.   Perl  5.10  includes new features that are not in earlier ver-
3297           sions of Perl, some of which (such as named parentheses) have  been  in
3298           PCRE for some time. This list is with respect to Perl 5.10:
3299    
3300           (a)  Although  lookbehind  assertions  in  PCRE must match fixed length
3301           strings, each alternative branch of a lookbehind assertion can match  a
3302           different  length  of  string.  Perl requires them all to have the same
3303           length.
3304    
3305           (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
3306           meta-character matches only at the very end of the string.
3307    
3308           (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
3309           cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
3310           ignored.  (Perl can be made to issue a warning.)
3311    
3312           (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
3313           fiers is inverted, that is, by default they are not greedy, but if fol-
3314           lowed by a question mark they are.
3315    
3316           (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
3317           tried only at the first matching position in the subject string.
3318    
3319           (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
3320           and  PCRE_NO_AUTO_CAPTURE  options for pcre_exec() have no Perl equiva-
3321           lents.
3322    
3323           (g) The \R escape sequence can be restricted to match only CR,  LF,  or
3324           CRLF by the PCRE_BSR_ANYCRLF option.
3325    
3326           (h) The callout facility is PCRE-specific.
3327    
3328           (i) The partial matching facility is PCRE-specific.
3329    
3330           (j) Patterns compiled by PCRE can be saved and re-used at a later time,
3331           even on different hosts that have the other endianness.
3332    
3333           (k) The alternative matching function (pcre_dfa_exec())  matches  in  a
3334           different way and is not Perl-compatible.
3335    
3336           (l)  PCRE  recognizes some special sequences such as (*CR) at the start
3337           of a pattern that set overall options that cannot be changed within the
3338           pattern.
3339    
3340    
3341    AUTHOR
3342    
3343           Philip Hazel
3344         &n