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revision 69 by nigel, Sat Feb 24 21:40:18 2007 UTC revision 153 by ph10, Wed Apr 18 09:12:14 2007 UTC
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1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
# Line 5  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
15    
16    
17  DESCRIPTION  INTRODUCTION
18    
19       The PCRE library is a set of functions that implement  regu-         The  PCRE  library is a set of functions that implement regular expres-
20       lar  expression  pattern  matching using the same syntax and         sion pattern matching using the same syntax and semantics as Perl, with
21       semantics as Perl, with just a few differences. The  current         just  a  few differences. (Certain features that appeared in Python and
22       implementation  of  PCRE  (release 4.x) corresponds approxi-         PCRE before they appeared in Perl are also available using  the  Python
23       mately with Perl 5.8, including support  for  UTF-8  encoded         syntax.)
24       strings.    However,  this  support  has  to  be  explicitly  
25       enabled; it is not the default.         The  current  implementation of PCRE (release 7.x) corresponds approxi-
26           mately with Perl 5.10, including support for UTF-8 encoded strings  and
27       PCRE is written in C and released as a C library. However, a         Unicode general category properties. However, UTF-8 and Unicode support
28       number  of  people  have  written wrappers and interfaces of         has to be explicitly enabled; it is not the default. The Unicode tables
29       various kinds. A C++ class is included  in  these  contribu-         correspond to Unicode release 5.0.0.
30       tions,  which  can  be found in the Contrib directory at the  
31       primary FTP site, which is:         In  addition to the Perl-compatible matching function, PCRE contains an
32           alternative matching function that matches the same  compiled  patterns
33       ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         in  a different way. In certain circumstances, the alternative function
34           has some advantages. For a discussion of the two  matching  algorithms,
35       Details of exactly which Perl  regular  expression  features         see the pcrematching page.
36       are  and  are  not  supported  by PCRE are given in separate  
37       documents. See the pcrepattern and pcrecompat pages.         PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39       Some features of PCRE can be included, excluded, or  changed         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40       when  the library is built. The pcre_config() function makes         included as part of the PCRE distribution. The pcrecpp page has details
41       it possible for a client  to  discover  which  features  are         of  this  interface.  Other  people's contributions can be found in the
42       available.  Documentation  about  building  PCRE for various         Contrib directory at the primary FTP site, which is:
43       operating systems can be found in the  README  file  in  the  
44       source distribution.         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46           Details of exactly which Perl regular expression features are  and  are
47           not supported by PCRE are given in separate documents. See the pcrepat-
48           tern and pcrecompat pages.
49    
50           Some features of PCRE can be included, excluded, or  changed  when  the
51           library  is  built.  The pcre_config() function makes it possible for a
52           client to discover which features are  available.  The  features  them-
53           selves  are described in the pcrebuild page. Documentation about build-
54           ing PCRE for various operating systems can be found in the README  file
55           in the source distribution.
56    
57           The  library  contains  a number of undocumented internal functions and
58           data tables that are used by more than one  of  the  exported  external
59           functions,  but  which  are  not  intended for use by external callers.
60           Their names all begin with "_pcre_", which hopefully will  not  provoke
61           any name clashes. In some environments, it is possible to control which
62           external symbols are exported when a shared library is  built,  and  in
63           these cases the undocumented symbols are not exported.
64    
65    
66  USER DOCUMENTATION  USER DOCUMENTATION
67    
68       The user documentation for PCRE has been  split  up  into  a         The  user  documentation  for PCRE comprises a number of different sec-
69       number  of  different sections. In the "man" format, each of         tions. In the "man" format, each of these is a separate "man page".  In
70       these is a separate "man page". In the HTML format, each  is         the  HTML  format, each is a separate page, linked from the index page.
71       a  separate  page,  linked from the index page. In the plain         In the plain text format, all the sections are concatenated,  for  ease
72       text format, all the sections are concatenated, for ease  of         of searching. The sections are as follows:
73       searching. The sections are as follows:  
74             pcre              this document
75         pcre              this document           pcre-config       show PCRE installation configuration information
76         pcreapi           details of PCRE's native API           pcreapi           details of PCRE's native C API
77         pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
78         pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
79         pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
80         pcregrep          description of the pcregrep command           pcrecpp           details of the C++ wrapper
81         pcrepattern       syntax and semantics of supported           pcregrep          description of the pcregrep command
82                             regular expressions           pcrematching      discussion of the two matching algorithms
83         pcreperform       discussion of performance issues           pcrepartial       details of the partial matching facility
84         pcreposix         the POSIX-compatible API           pcrepattern       syntax and semantics of supported
85         pcresample        discussion of the sample program                               regular expressions
86         pcretest          the pcretest testing command           pcreperform       discussion of performance issues
87             pcreposix         the POSIX-compatible C API
88       In addition, in the "man" and HTML formats, there is a short           pcreprecompile    details of saving and re-using precompiled patterns
89       page  for  each  library function, listing its arguments and           pcresample        discussion of the sample program
90       results.           pcrestack         discussion of stack usage
91             pcretest          description of the pcretest testing command
92    
93           In addition, in the "man" and HTML formats, there is a short  page  for
94           each C library function, listing its arguments and results.
95    
96    
97  LIMITATIONS  LIMITATIONS
98    
99       There are some size limitations in PCRE but it is hoped that         There  are some size limitations in PCRE but it is hoped that they will
100       they will never in practice be relevant.         never in practice be relevant.
101    
102       The maximum length of a  compiled  pattern  is  65539  (sic)         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
103       bytes  if PCRE is compiled with the default internal linkage         is compiled with the default internal linkage size of 2. If you want to
104       size of 2. If you want to process regular  expressions  that         process regular expressions that are truly enormous,  you  can  compile
105       are  truly  enormous,  you can compile PCRE with an internal         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
106       linkage size of 3 or 4 (see the README file  in  the  source         the source distribution and the pcrebuild documentation  for  details).
107       distribution  and  the pcrebuild documentation for details).         In  these  cases the limit is substantially larger.  However, the speed
108       If these cases the limit is substantially larger.   However,         of execution is slower.
109       the speed of execution will be slower.  
110           All values in repeating quantifiers must be less than 65536. The  maxi-
111       All values in repeating quantifiers must be less than 65536.         mum  compiled  length  of  subpattern  with an explicit repeat count is
112       The maximum number of capturing subpatterns is 65535.         30000 bytes. The maximum number of capturing subpatterns is 65535.
113    
114       There is no limit to the  number  of  non-capturing  subpat-         There is no limit to the number of parenthesized subpatterns, but there
115       terns,  but  the  maximum  depth  of nesting of all kinds of         can be no more than 65535 capturing subpatterns.
116       parenthesized subpattern, including  capturing  subpatterns,  
117       assertions, and other types of subpattern, is 200.         The maximum length of name for a named subpattern is 32 characters, and
118           the maximum number of named subpatterns is 10000.
119       The maximum length of a subject string is the largest  posi-  
120       tive number that an integer variable can hold. However, PCRE         The maximum length of a subject string is the largest  positive  number
121       uses recursion to handle subpatterns and indefinite  repeti-         that  an integer variable can hold. However, when using the traditional
122       tion.  This  means  that the available stack space may limit         matching function, PCRE uses recursion to handle subpatterns and indef-
123       the size of a subject string that can be processed  by  cer-         inite  repetition.  This means that the available stack space may limit
124       tain patterns.         the size of a subject string that can be processed by certain patterns.
125           For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128    UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130           From  release  3.3,  PCRE  has  had  some support for character strings
131           encoded in the UTF-8 format. For release 4.0 this was greatly  extended
132           to  cover  most common requirements, and in release 5.0 additional sup-
133           port for Unicode general category properties was added.
134    
135           In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
136           support  in  the  code,  and, in addition, you must call pcre_compile()
137           with the PCRE_UTF8 option flag. When you do this, both the pattern  and
138           any  subject  strings  that are matched against it are treated as UTF-8
139           strings instead of just strings of bytes.
140    
141           If you compile PCRE with UTF-8 support, but do not use it at run  time,
142           the  library will be a bit bigger, but the additional run time overhead
143           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144           very big.
145    
146           If PCRE is built with Unicode character property support (which implies
147           UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
148           ported.  The available properties that can be tested are limited to the
149           general category properties such as Lu for an upper case letter  or  Nd
150           for  a  decimal number, the Unicode script names such as Arabic or Han,
151           and the derived properties Any and L&. A full  list  is  given  in  the
152           pcrepattern documentation. Only the short names for properties are sup-
153           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
154           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
155           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
156           does not support this.
157    
158           The following comments apply when PCRE is running in UTF-8 mode:
159    
160           1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and
161           subjects are checked for validity on entry to the  relevant  functions.
162           If an invalid UTF-8 string is passed, an error return is given. In some
163           situations, you may already know  that  your  strings  are  valid,  and
164           therefore want to skip these checks in order to improve performance. If
165           you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,
166           PCRE  assumes  that  the  pattern or subject it is given (respectively)
167           contains only valid UTF-8 codes. In this case, it does not diagnose  an
168           invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
169           PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
170           crash.
171    
172           2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
173           two-byte UTF-8 character if the value is greater than 127.
174    
175           3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
176           characters for values greater than \177.
177    
178           4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
179           vidual bytes, for example: \x{100}{3}.
180    
181           5. The dot metacharacter matches one UTF-8 character instead of a  sin-
182           gle byte.
183    
184           6.  The  escape sequence \C can be used to match a single byte in UTF-8
185           mode, but its use can lead to some strange effects.  This  facility  is
186           not available in the alternative matching function, pcre_dfa_exec().
187    
188           7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
189           test characters of any code value, but the characters that PCRE  recog-
190           nizes  as  digits,  spaces,  or  word characters remain the same set as
191           before, all with values less than 256. This remains true even when PCRE
192           includes  Unicode  property support, because to do otherwise would slow
193           down PCRE in many common cases. If you really want to test for a  wider
194           sense  of,  say,  "digit",  you must use Unicode property tests such as
195           \p{Nd}.
196    
197           8. Similarly, characters that match the POSIX named  character  classes
198           are all low-valued characters.
199    
200           9.  Case-insensitive  matching  applies only to characters whose values
201           are less than 128, unless PCRE is built with Unicode property  support.
202           Even  when  Unicode  property support is available, PCRE still uses its
203           own character tables when checking the case of  low-valued  characters,
204           so  as not to degrade performance.  The Unicode property information is
205           used only for characters with higher values. Even when Unicode property
206           support is available, PCRE supports case-insensitive matching only when
207           there is a one-to-one mapping between a letter's  cases.  There  are  a
208           small  number  of  many-to-one  mappings in Unicode; these are not sup-
209           ported by PCRE.
210    
211    
212  UTF-8 SUPPORT  AUTHOR
213    
214       Starting at release 3.3, PCRE has had some support for char-         Philip Hazel
215       acter  strings  encoded in the UTF-8 format. For release 4.0         University Computing Service
216       this has been greatly extended to cover most common require-         Cambridge CB2 3QH, England.
      ments.  
   
      In order process UTF-8  strings,  you  must  build  PCRE  to  
      include  UTF-8  support  in  the code, and, in addition, you  
      must call pcre_compile() with  the  PCRE_UTF8  option  flag.  
      When  you  do this, both the pattern and any subject strings  
      that are matched against it are  treated  as  UTF-8  strings  
      instead of just strings of bytes.  
   
      If you compile PCRE with UTF-8 support, but do not use it at  
      run  time,  the  library will be a bit bigger, but the addi-  
      tional run time overhead is limited to testing the PCRE_UTF8  
      flag in several places, so should not be very large.  
   
      The following comments apply when PCRE is running  in  UTF-8  
      mode:  
   
      1. PCRE assumes that the strings it is given  contain  valid  
      UTF-8  codes. It does not diagnose invalid UTF-8 strings. If  
      you pass invalid UTF-8 strings  to  PCRE,  the  results  are  
      undefined.  
   
      2. In a pattern, the escape sequence \x{...}, where the con-  
      tents  of  the  braces is a string of hexadecimal digits, is  
      interpreted as a UTF-8 character whose code  number  is  the  
      given  hexadecimal  number, for example: \x{1234}. If a non-  
      hexadecimal digit appears between the braces,  the  item  is  
      not  recognized.  This escape sequence can be used either as  
      a literal, or within a character class.  
   
      3. The original hexadecimal escape sequence, \xhh, matches a  
      two-byte UTF-8 character if the value is greater than 127.  
   
      4. Repeat quantifiers apply to  complete  UTF-8  characters,  
      not to individual bytes, for example: \x{100}{3}.  
   
      5. The dot metacharacter matches one UTF-8 character instead  
      of a single byte.  
   
      6. The escape sequence \C can be used to match a single byte  
      in UTF-8 mode, but its use can lead to some strange effects.  
   
      7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  
      correctly test characters of any code value, but the charac-  
      ters that PCRE recognizes as digits, spaces, or word charac-  
      ters  remain  the  same  set as before, all with values less  
      than 256.  
   
      8. Case-insensitive  matching  applies  only  to  characters  
      whose  values  are  less than 256. PCRE does not support the  
      notion of "case" for higher-valued characters.  
217    
218       9. PCRE does not support the use of Unicode tables and  pro-         Putting an actual email address here seems to have been a spam  magnet,
219       perties or the Perl escapes \p, \P, and \X.         so  I've  taken  it away. If you want to email me, use my two initials,
220           followed by the two digits 10, at the domain cam.ac.uk.
221    
222    
223  AUTHOR  REVISION
224    
225       Philip Hazel <ph10@cam.ac.uk>         Last updated: 18 April 2007
226       University Computing Service,         Copyright (c) 1997-2007 University of Cambridge.
227       Cambridge CB2 3QG, England.  ------------------------------------------------------------------------------
228       Phone: +44 1223 334714  
229    
230    PCREBUILD(3)                                                      PCREBUILD(3)
231    
 Last updated: 04 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
232    
233  NAME  NAME
234       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
235    
236    
237  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
238    
239       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
240       can  be  selected when the library is compiled. They are all         selected when the library is compiled. They are all selected, or  dese-
241       selected, or deselected, by providing options to the config-         lected, by providing options to the configure script that is run before
242       ure  script  which  is run before the make command. The com-         the make command. The complete list of  options  for  configure  (which
243       plete list of options  for  configure  (which  includes  the         includes  the  standard  ones such as the selection of the installation
244       standard  ones  such  as  the  selection of the installation         directory) can be obtained by running
245       directory) can be obtained by running  
246             ./configure --help
247         ./configure --help  
248           The following sections include  descriptions  of  options  whose  names
249       The following sections describe certain options whose  names         begin with --enable or --disable. These settings specify changes to the
250       begin  with  --enable  or  --disable. These settings specify         defaults for the configure command. Because of the way  that  configure
251       changes to the defaults for the configure  command.  Because         works,  --enable  and --disable always come in pairs, so the complemen-
252       of  the  way  that  configure  works, --enable and --disable         tary option always exists as well, but as it specifies the default,  it
253       always come in pairs, so  the  complementary  option  always         is not described.
254       exists  as  well, but as it specifies the default, it is not  
255       described.  
256    C++ SUPPORT
257    
258           By default, the configure script will search for a C++ compiler and C++
259           header files. If it finds them, it automatically builds the C++ wrapper
260           library for PCRE. You can disable this by adding
261    
262             --disable-cpp
263    
264           to the configure command.
265    
266    
267  UTF-8 SUPPORT  UTF-8 SUPPORT
268    
269       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
270    
271             --enable-utf8
272    
273           to  the  configure  command.  Of  itself, this does not make PCRE treat
274           strings as UTF-8. As well as compiling PCRE with this option, you  also
275           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
276           function.
277    
278    
279    UNICODE CHARACTER PROPERTY SUPPORT
280    
281           UTF-8 support allows PCRE to process character values greater than  255
282           in  the  strings that it handles. On its own, however, it does not pro-
283           vide any facilities for accessing the properties of such characters. If
284           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
285           refer to Unicode character properties, you must add
286    
287         --enable-utf8           --enable-unicode-properties
288    
289       to the configure command. Of itself, this does not make PCRE         to the configure command. This implies UTF-8 support, even if you  have
290       treat  strings as UTF-8. As well as compiling PCRE with this         not explicitly requested it.
291       option, you also have have to set the PCRE_UTF8 option  when  
292       you call the pcre_compile() function.         Including  Unicode  property  support  adds around 30K of tables to the
293           PCRE library. Only the general category properties such as  Lu  and  Nd
294           are supported. Details are given in the pcrepattern documentation.
295    
296    
297  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
298    
299       By default, PCRE treats character 10 (linefeed) as the  new-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
300       line  character.  This  is  the  normal newline character on         the end of a line. This is the normal newline  character  on  Unix-like
301       Unix-like systems. You can compile PCRE to use character  13         systems. You can compile PCRE to use character 13 (carriage return, CR)
302       (carriage return) instead by adding         instead, by adding
303    
304         --enable-newline-is-cr           --enable-newline-is-cr
305    
306       to the configure command. For completeness there is  also  a         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
307       --enable-newline-is-lf  option,  which  explicitly specifies         option, which explicitly specifies linefeed as the newline character.
308       linefeed as the newline character.  
309           Alternatively, you can specify that line endings are to be indicated by
310           the two character sequence CRLF. If you want this, add
311    
312             --enable-newline-is-crlf
313    
314           to the configure command. There is a fourth option, specified by
315    
316             --enable-newline-is-anycrlf
317    
318           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
319           CRLF as indicating a line ending. Finally, a fifth option, specified by
320    
321             --enable-newline-is-any
322    
323           causes PCRE to recognize any Unicode newline sequence.
324    
325           Whatever line ending convention is selected when PCRE is built  can  be
326           overridden  when  the library functions are called. At build time it is
327           conventional to use the standard for your operating system.
328    
329    
330  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
331    
332       The PCRE building process uses libtool to build both  shared         The PCRE building process uses libtool to build both shared and  static
333       and  static  Unix libraries by default. You can suppress one         Unix  libraries by default. You can suppress one of these by adding one
334       of these by adding one of         of
335    
336         --disable-shared           --disable-shared
337         --disable-static           --disable-static
338    
339       to the configure command, as required.         to the configure command, as required.
340    
341    
342  POSIX MALLOC USAGE  POSIX MALLOC USAGE
343    
344       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
345       pcreposix  documentation),  additional  working  storage  is         umentation),  additional  working  storage  is required for holding the
346       required for holding the pointers  to  capturing  substrings         pointers to capturing substrings, because PCRE requires three  integers
347       because  PCRE requires three integers per substring, whereas         per  substring,  whereas  the POSIX interface provides only two. If the
348       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
349       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
350       space on the stack, because this is faster than  using  mal-         The default threshold above which the stack is no longer used is 10; it
351       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
352       stack is no longer used is 10; it can be changed by adding a  
353       setting such as           --with-posix-malloc-threshold=20
354    
355         --with-posix-malloc-threshold=20         to the configure command.
356    
357       to the configure command.  
358    HANDLING VERY LARGE PATTERNS
359    
360           Within  a  compiled  pattern,  offset values are used to point from one
361           part to another (for example, from an opening parenthesis to an  alter-
362           nation  metacharacter).  By default, two-byte values are used for these
363           offsets, leading to a maximum size for a  compiled  pattern  of  around
364           64K.  This  is sufficient to handle all but the most gigantic patterns.
365           Nevertheless, some people do want to process enormous patterns,  so  it
366           is  possible  to compile PCRE to use three-byte or four-byte offsets by
367           adding a setting such as
368    
369             --with-link-size=3
370    
371           to the configure command. The value given must be 2,  3,  or  4.  Using
372           longer  offsets slows down the operation of PCRE because it has to load
373           additional bytes when handling them.
374    
375    
376    AVOIDING EXCESSIVE STACK USAGE
377    
378           When matching with the pcre_exec() function, PCRE implements backtrack-
379           ing  by  making recursive calls to an internal function called match().
380           In environments where the size of the stack is limited,  this  can  se-
381           verely  limit  PCRE's operation. (The Unix environment does not usually
382           suffer from this problem, but it may sometimes be necessary to increase
383           the  maximum  stack size.  There is a discussion in the pcrestack docu-
384           mentation.) An alternative approach to recursion that uses memory  from
385           the  heap  to remember data, instead of using recursive function calls,
386           has been implemented to work round the problem of limited  stack  size.
387           If you want to build a version of PCRE that works this way, add
388    
389             --disable-stack-for-recursion
390    
391           to  the  configure  command. With this configuration, PCRE will use the
392           pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
393           ment  functions.  Separate  functions are provided because the usage is
394           very predictable: the block sizes requested are always  the  same,  and
395           the  blocks  are always freed in reverse order. A calling program might
396           be able to implement optimized functions that perform better  than  the
397           standard  malloc()  and  free()  functions.  PCRE  runs noticeably more
398           slowly when built in this way. This option affects only the pcre_exec()
399           function; it is not relevant for the the pcre_dfa_exec() function.
400    
401    
402  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
403    
404       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
405       calls  repeatedly  (possibly  recursively) when performing a         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
406       matching operation. By limiting the  number  of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
407       function  may  be  called,  a  limit  can  be  placed on the         function may be called during a single matching operation, a limit  can
408       resources used by a single call to  pcre_exec().  The  limit         be  placed  on  the resources used by a single call to pcre_exec(). The
409       can  be  changed  at  run  time, as described in the pcreapi         limit can be changed at run time, as described in the pcreapi  documen-
410       documentation. The default is 10 million, but  this  can  be         tation.  The default is 10 million, but this can be changed by adding a
411       changed by adding a setting such as         setting such as
412    
413         --with-match-limit=500000           --with-match-limit=500000
414    
415       to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
416           pcre_dfa_exec() matching function.
417    
418           In  some  environments  it is desirable to limit the depth of recursive
419           calls of match() more strictly than the total number of calls, in order
420           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
421           for-recursion is specified) that is used. A second limit controls this;
422           it  defaults  to  the  value  that is set for --with-match-limit, which
423           imposes no additional constraints. However, you can set a  lower  limit
424           by adding, for example,
425    
426  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
427    
428       Within a compiled pattern, offset values are used  to  point         to  the  configure  command.  This  value can also be overridden at run
429       from  one  part  to  another  (for  example, from an opening         time.
430       parenthesis to an  alternation  metacharacter).  By  default  
431       two-byte  values  are  used  for these offsets, leading to a  
432       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
433       sufficient  to  handle  all  but the most gigantic patterns.  
434       Nevertheless, some people do want to process  enormous  pat-         PCRE uses fixed tables for processing characters whose code values  are
435       terns,  so  it is possible to compile PCRE to use three-byte         less  than 256. By default, PCRE is built with a set of tables that are
436       or four-byte offsets by adding a setting such as         distributed in the file pcre_chartables.c.dist. These  tables  are  for
437           ASCII codes only. If you add
438         --with-link-size=3  
439             --enable-rebuild-chartables
440       to the configure command. The value given must be 2,  3,  or  
441       4.  Using  longer  offsets  slows down the operation of PCRE         to  the  configure  command, the distributed tables are no longer used.
442       because it has to load additional bytes when handling them.         Instead, a program called dftables is compiled and  run.  This  outputs
443           the source for new set of tables, created in the default locale of your
444       If you build PCRE with an increased link size, test  2  (and         C runtime system. (This method of replacing the tables does not work if
445       test 5 if you are using UTF-8) will fail. Part of the output         you  are cross compiling, because dftables is run on the local host. If
446       of these tests is a representation of the compiled  pattern,         you need to create alternative tables when cross  compiling,  you  will
447       and this changes with the link size.         have to do so "by hand".)
448    
449    
450    USING EBCDIC CODE
451    
452           PCRE  assumes  by  default that it will run in an environment where the
453           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
454           PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
455           adding
456    
457             --enable-ebcdic
458    
459           to the configure command. This setting implies --enable-rebuild-charta-
460           bles.
461    
462    
463    SEE ALSO
464    
465           pcreapi(3), pcre_config(3).
466    
467    
468    AUTHOR
469    
470           Philip Hazel
471           University Computing Service
472           Cambridge CB2 3QH, England.
473    
474    
475    REVISION
476    
477           Last updated: 16 April 2007
478           Copyright (c) 1997-2007 University of Cambridge.
479    ------------------------------------------------------------------------------
480    
481    
482    PCREMATCHING(3)                                                PCREMATCHING(3)
483    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
484    
485  NAME  NAME
486       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
487    
488    
489    PCRE MATCHING ALGORITHMS
490    
491           This document describes the two different algorithms that are available
492           in PCRE for matching a compiled regular expression against a given sub-
493           ject  string.  The  "standard"  algorithm  is  the  one provided by the
494           pcre_exec() function.  This works in the same was  as  Perl's  matching
495           function, and provides a Perl-compatible matching operation.
496    
497           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
498           this operates in a different way, and is not  Perl-compatible.  It  has
499           advantages  and disadvantages compared with the standard algorithm, and
500           these are described below.
501    
502           When there is only one possible way in which a given subject string can
503           match  a pattern, the two algorithms give the same answer. A difference
504           arises, however, when there are multiple possibilities. For example, if
505           the pattern
506    
507             ^<.*>
508    
509           is matched against the string
510    
511             <something> <something else> <something further>
512    
513           there are three possible answers. The standard algorithm finds only one
514           of them, whereas the alternative algorithm finds all three.
515    
516    
517  SYNOPSIS OF PCRE API  REGULAR EXPRESSIONS AS TREES
518    
519       #include <pcre.h>         The set of strings that are matched by a regular expression can be rep-
520           resented  as  a  tree structure. An unlimited repetition in the pattern
521           makes the tree of infinite size, but it is still a tree.  Matching  the
522           pattern  to a given subject string (from a given starting point) can be
523           thought of as a search of the tree.  There are two  ways  to  search  a
524           tree:  depth-first  and  breadth-first, and these correspond to the two
525           matching algorithms provided by PCRE.
526    
      pcre *pcre_compile(const char *pattern, int options,  
           const char **errptr, int *erroffset,  
           const unsigned char *tableptr);  
527    
528       pcre_extra *pcre_study(const pcre *code, int options,  THE STANDARD MATCHING ALGORITHM
           const char **errptr);  
529    
530       int pcre_exec(const pcre *code, const pcre_extra *extra,         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
531            const char *subject, int length, int startoffset,         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
532            int options, int *ovector, int ovecsize);         depth-first search of the pattern tree. That is, it  proceeds  along  a
533           single path through the tree, checking that the subject matches what is
534           required. When there is a mismatch, the algorithm  tries  any  alterna-
535           tives  at  the  current point, and if they all fail, it backs up to the
536           previous branch point in the  tree,  and  tries  the  next  alternative
537           branch  at  that  level.  This often involves backing up (moving to the
538           left) in the subject string as well.  The  order  in  which  repetition
539           branches  are  tried  is controlled by the greedy or ungreedy nature of
540           the quantifier.
541    
542       int pcre_copy_named_substring(const pcre *code,         If a leaf node is reached, a matching string has  been  found,  and  at
543            const char *subject, int *ovector,         that  point the algorithm stops. Thus, if there is more than one possi-
544            int stringcount, const char *stringname,         ble match, this algorithm returns the first one that it finds.  Whether
545            char *buffer, int buffersize);         this  is the shortest, the longest, or some intermediate length depends
546           on the way the greedy and ungreedy repetition quantifiers are specified
547           in the pattern.
548    
549       int pcre_copy_substring(const char *subject, int *ovector,         Because  it  ends  up  with a single path through the tree, it is rela-
550            int stringcount, int stringnumber, char *buffer,         tively straightforward for this algorithm to keep  track  of  the  sub-
551            int buffersize);         strings  that  are  matched  by portions of the pattern in parentheses.
552           This provides support for capturing parentheses and back references.
553    
      int pcre_get_named_substring(const pcre *code,  
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           const char **stringptr);  
554    
555       int pcre_get_stringnumber(const pcre *code,  THE ALTERNATIVE MATCHING ALGORITHM
           const char *name);  
556    
557       int pcre_get_substring(const char *subject, int *ovector,         This algorithm conducts a breadth-first search of  the  tree.  Starting
558            int stringcount, int stringnumber,         from  the  first  matching  point  in the subject, it scans the subject
559            const char **stringptr);         string from left to right, once, character by character, and as it does
560           this,  it remembers all the paths through the tree that represent valid
561           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
562           though  it is not implemented as a traditional finite state machine (it
563           keeps multiple states active simultaneously).
564    
565       int pcre_get_substring_list(const char *subject,         The scan continues until either the end of the subject is  reached,  or
566            int *ovector, int stringcount, const char ***listptr);         there  are  no more unterminated paths. At this point, terminated paths
567           represent the different matching possibilities (if there are none,  the
568           match  has  failed).   Thus,  if there is more than one possible match,
569           this algorithm finds all of them, and in particular, it finds the long-
570           est.  In PCRE, there is an option to stop the algorithm after the first
571           match (which is necessarily the shortest) has been found.
572    
573       void pcre_free_substring(const char *stringptr);         Note that all the matches that are found start at the same point in the
574           subject. If the pattern
575    
576       void pcre_free_substring_list(const char **stringptr);           cat(er(pillar)?)
577    
578       const unsigned char *pcre_maketables(void);         is  matched  against the string "the caterpillar catchment", the result
579           will be the three strings "cat", "cater", and "caterpillar" that  start
580           at the fourth character of the subject. The algorithm does not automat-
581           ically move on to find matches that start at later positions.
582    
583       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         There are a number of features of PCRE regular expressions that are not
584            int what, void *where);         supported by the alternative matching algorithm. They are as follows:
585    
586           1.  Because  the  algorithm  finds  all possible matches, the greedy or
587           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
588           ungreedy quantifiers are treated in exactly the same way. However, pos-
589           sessive quantifiers can make a difference when what follows could  also
590           match what is quantified, for example in a pattern like this:
591    
592       int pcre_info(const pcre *code, int *optptr, *firstcharptr);           ^a++\w!
593    
594       int pcre_config(int what, void *where);         This  pattern matches "aaab!" but not "aaa!", which would be matched by
595           a non-possessive quantifier. Similarly, if an atomic group is  present,
596           it  is matched as if it were a standalone pattern at the current point,
597           and the longest match is then "locked in" for the rest of  the  overall
598           pattern.
599    
600       char *pcre_version(void);         2. When dealing with multiple paths through the tree simultaneously, it
601           is not straightforward to keep track of  captured  substrings  for  the
602           different  matching  possibilities,  and  PCRE's implementation of this
603           algorithm does not attempt to do this. This means that no captured sub-
604           strings are available.
605    
606       void *(*pcre_malloc)(size_t);         3.  Because no substrings are captured, back references within the pat-
607           tern are not supported, and cause errors if encountered.
608    
609       void (*pcre_free)(void *);         4. For the same reason, conditional expressions that use  a  backrefer-
610           ence  as  the  condition or test for a specific group recursion are not
611           supported.
612    
613       int (*pcre_callout)(pcre_callout_block *);         5. Callouts are supported, but the value of the  capture_top  field  is
614           always 1, and the value of the capture_last field is always -1.
615    
616           6.  The \C escape sequence, which (in the standard algorithm) matches a
617           single byte, even in UTF-8 mode, is not supported because the  alterna-
618           tive  algorithm  moves  through  the  subject string one character at a
619           time, for all active paths through the tree.
620    
 PCRE API  
621    
622       PCRE has its own native API,  which  is  described  in  this  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
      document.  There  is  also  a  set of wrapper functions that  
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
623    
624       The native API function prototypes are defined in the header         Using the alternative matching algorithm provides the following  advan-
625       file  pcre.h,  and  on  Unix  systems  the library itself is         tages:
      called libpcre.a, so can be accessed by adding -lpcre to the  
      command  for  linking  an  application  which  calls it. The  
      header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
626    
627       The functions pcre_compile(), pcre_study(), and  pcre_exec()         1. All possible matches (at a single point in the subject) are automat-
628       are  used  for compiling and matching regular expressions. A         ically found, and in particular, the longest match is  found.  To  find
629       sample program that demonstrates the simplest way  of  using         more than one match using the standard algorithm, you have to do kludgy
630       them  is  given in the file pcredemo.c. The pcresample docu-         things with callouts.
      mentation describes how to run it.  
631    
632       There are convenience functions for extracting captured sub-         2. There is much better support for partial matching. The  restrictions
633       strings from a matched subject string. They are:         on  the content of the pattern that apply when using the standard algo-
634           rithm for partial matching do not apply to the  alternative  algorithm.
635           For  non-anchored patterns, the starting position of a partial match is
636           available.
637    
638         pcre_copy_substring()         3. Because the alternative algorithm  scans  the  subject  string  just
639         pcre_copy_named_substring()         once,  and  never  needs to backtrack, it is possible to pass very long
640         pcre_get_substring()         subject strings to the matching function in  several  pieces,  checking
641         pcre_get_named_substring()         for partial matching each time.
        pcre_get_substring_list()  
642    
      pcre_free_substring()  and  pcre_free_substring_list()   are  
      also  provided,  to  free  the  memory  used  for  extracted  
      strings.  
643    
644       The function pcre_maketables() is used (optionally) to build  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
645    
646       The function pcre_fullinfo() is used to find out information         The alternative algorithm suffers from a number of disadvantages:
      about a compiled pattern; pcre_info() is an obsolete version  
      which returns only some of the available information, but is  
      retained   for   backwards   compatibility.    The  function  
      pcre_version() returns a pointer to a string containing  the  
      version of PCRE and its date of release.  
647    
648       The global variables  pcre_malloc  and  pcre_free  initially         1.  It  is  substantially  slower  than the standard algorithm. This is
649       contain the entry points of the standard malloc() and free()         partly because it has to search for all possible matches, but  is  also
650       functions respectively. PCRE  calls  the  memory  management         because it is less susceptible to optimization.
      functions  via  these  variables,  so  a calling program can  
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
651    
652       The global variable pcre_callout initially contains NULL. It         2. Capturing parentheses and back references are not supported.
653       can be set by the caller to a "callout" function, which PCRE  
654       will then call at specified points during a matching  opera-         3. Although atomic groups are supported, their use does not provide the
655       tion. Details are given in the pcrecallout documentation.         performance advantage that it does for the standard algorithm.
656    
657    
658    AUTHOR
659    
660           Philip Hazel
661           University Computing Service
662           Cambridge CB2 3QH, England.
663    
664    
665    REVISION
666    
667           Last updated: 06 March 2007
668           Copyright (c) 1997-2007 University of Cambridge.
669    ------------------------------------------------------------------------------
670    
671    
672    PCREAPI(3)                                                          PCREAPI(3)
673    
674    
675    NAME
676           PCRE - Perl-compatible regular expressions
677    
678    
679    PCRE NATIVE API
680    
681           #include <pcre.h>
682    
683           pcre *pcre_compile(const char *pattern, int options,
684                const char **errptr, int *erroffset,
685                const unsigned char *tableptr);
686    
687           pcre *pcre_compile2(const char *pattern, int options,
688                int *errorcodeptr,
689                const char **errptr, int *erroffset,
690                const unsigned char *tableptr);
691    
692           pcre_extra *pcre_study(const pcre *code, int options,
693                const char **errptr);
694    
695           int pcre_exec(const pcre *code, const pcre_extra *extra,
696                const char *subject, int length, int startoffset,
697                int options, int *ovector, int ovecsize);
698    
699           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
700                const char *subject, int length, int startoffset,
701                int options, int *ovector, int ovecsize,
702                int *workspace, int wscount);
703    
704           int pcre_copy_named_substring(const pcre *code,
705                const char *subject, int *ovector,
706                int stringcount, const char *stringname,
707                char *buffer, int buffersize);
708    
709           int pcre_copy_substring(const char *subject, int *ovector,
710                int stringcount, int stringnumber, char *buffer,
711                int buffersize);
712    
713           int pcre_get_named_substring(const pcre *code,
714                const char *subject, int *ovector,
715                int stringcount, const char *stringname,
716                const char **stringptr);
717    
718           int pcre_get_stringnumber(const pcre *code,
719                const char *name);
720    
721           int pcre_get_stringtable_entries(const pcre *code,
722                const char *name, char **first, char **last);
723    
724           int pcre_get_substring(const char *subject, int *ovector,
725                int stringcount, int stringnumber,
726                const char **stringptr);
727    
728           int pcre_get_substring_list(const char *subject,
729                int *ovector, int stringcount, const char ***listptr);
730    
731           void pcre_free_substring(const char *stringptr);
732    
733           void pcre_free_substring_list(const char **stringptr);
734    
735           const unsigned char *pcre_maketables(void);
736    
737           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
738                int what, void *where);
739    
740           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
741    
742           int pcre_refcount(pcre *code, int adjust);
743    
744           int pcre_config(int what, void *where);
745    
746           char *pcre_version(void);
747    
748           void *(*pcre_malloc)(size_t);
749    
750           void (*pcre_free)(void *);
751    
752           void *(*pcre_stack_malloc)(size_t);
753    
754           void (*pcre_stack_free)(void *);
755    
756           int (*pcre_callout)(pcre_callout_block *);
757    
758    
759    PCRE API OVERVIEW
760    
761           PCRE has its own native API, which is described in this document. There
762           are also some wrapper functions that correspond to  the  POSIX  regular
763           expression  API.  These  are  described in the pcreposix documentation.
764           Both of these APIs define a set of C function calls. A C++  wrapper  is
765           distributed with PCRE. It is documented in the pcrecpp page.
766    
767           The  native  API  C  function prototypes are defined in the header file
768           pcre.h, and on Unix systems the library itself is called  libpcre.   It
769           can normally be accessed by adding -lpcre to the command for linking an
770           application  that  uses  PCRE.  The  header  file  defines  the  macros
771           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
772           bers for the library.  Applications can use these  to  include  support
773           for different releases of PCRE.
774    
775           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
776           pcre_exec() are used for compiling and matching regular expressions  in
777           a  Perl-compatible  manner. A sample program that demonstrates the sim-
778           plest way of using them is provided in the file  called  pcredemo.c  in
779           the  source distribution. The pcresample documentation describes how to
780           run it.
781    
782           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
783           ble,  is  also provided. This uses a different algorithm for the match-
784           ing. The alternative algorithm finds all possible matches (at  a  given
785           point  in  the subject), and scans the subject just once. However, this
786           algorithm does not return captured substrings. A description of the two
787           matching  algorithms and their advantages and disadvantages is given in
788           the pcrematching documentation.
789    
790           In addition to the main compiling and  matching  functions,  there  are
791           convenience functions for extracting captured substrings from a subject
792           string that is matched by pcre_exec(). They are:
793    
794             pcre_copy_substring()
795             pcre_copy_named_substring()
796             pcre_get_substring()
797             pcre_get_named_substring()
798             pcre_get_substring_list()
799             pcre_get_stringnumber()
800             pcre_get_stringtable_entries()
801    
802           pcre_free_substring() and pcre_free_substring_list() are also provided,
803           to free the memory used for extracted strings.
804    
805           The  function  pcre_maketables()  is  used  to build a set of character
806           tables  in  the  current  locale   for   passing   to   pcre_compile(),
807           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
808           provided for specialist use.  Most  commonly,  no  special  tables  are
809           passed,  in  which case internal tables that are generated when PCRE is
810           built are used.
811    
812           The function pcre_fullinfo() is used to find out  information  about  a
813           compiled  pattern; pcre_info() is an obsolete version that returns only
814           some of the available information, but is retained for  backwards  com-
815           patibility.   The function pcre_version() returns a pointer to a string
816           containing the version of PCRE and its date of release.
817    
818           The function pcre_refcount() maintains a  reference  count  in  a  data
819           block  containing  a compiled pattern. This is provided for the benefit
820           of object-oriented applications.
821    
822           The global variables pcre_malloc and pcre_free  initially  contain  the
823           entry  points  of  the  standard malloc() and free() functions, respec-
824           tively. PCRE calls the memory management functions via these variables,
825           so  a  calling  program  can replace them if it wishes to intercept the
826           calls. This should be done before calling any PCRE functions.
827    
828           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
829           indirections  to  memory  management functions. These special functions
830           are used only when PCRE is compiled to use  the  heap  for  remembering
831           data, instead of recursive function calls, when running the pcre_exec()
832           function. See the pcrebuild documentation for  details  of  how  to  do
833           this.  It  is  a non-standard way of building PCRE, for use in environ-
834           ments that have limited stacks. Because of the greater  use  of  memory
835           management,  it  runs  more  slowly. Separate functions are provided so
836           that special-purpose external code can be  used  for  this  case.  When
837           used,  these  functions  are always called in a stack-like manner (last
838           obtained, first freed), and always for memory blocks of the same  size.
839           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
840           mentation.
841    
842           The global variable pcre_callout initially contains NULL. It can be set
843           by  the  caller  to  a "callout" function, which PCRE will then call at
844           specified points during a matching operation. Details are given in  the
845           pcrecallout documentation.
846    
847    
848    NEWLINES
849    
850           PCRE  supports five different conventions for indicating line breaks in
851           strings: a single CR (carriage return) character, a  single  LF  (line-
852           feed) character, the two-character sequence CRLF, any of the three pre-
853           ceding, or any Unicode newline sequence. The Unicode newline  sequences
854           are  the  three just mentioned, plus the single characters VT (vertical
855           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
856           separator, U+2028), and PS (paragraph separator, U+2029).
857    
858           Each  of  the first three conventions is used by at least one operating
859           system as its standard newline sequence. When PCRE is built, a  default
860           can  be  specified.  The default default is LF, which is the Unix stan-
861           dard. When PCRE is run, the default can be overridden,  either  when  a
862           pattern is compiled, or when it is matched.
863    
864           In the PCRE documentation the word "newline" is used to mean "the char-
865           acter or pair of characters that indicate a line break". The choice  of
866           newline  convention  affects  the  handling of the dot, circumflex, and
867           dollar metacharacters, the handling of #-comments in /x mode, and, when
868           CRLF  is a recognized line ending sequence, the match position advance-
869           ment for a non-anchored pattern. The choice of newline convention  does
870           not affect the interpretation of the \n or \r escape sequences.
871    
872    
873  MULTITHREADING  MULTITHREADING
874    
875       The PCRE functions can be used in  multi-threading  applica-         The  PCRE  functions  can be used in multi-threading applications, with
876       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
877       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
878       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
879       threads.  
880           The  compiled form of a regular expression is not altered during match-
881       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
882       during  matching, so the same compiled pattern can safely be         at once.
883       used by several threads at once.  
884    
885    SAVING PRECOMPILED PATTERNS FOR LATER USE
886    
887           The compiled form of a regular expression can be saved and re-used at a
888           later time, possibly by a different program, and even on a  host  other
889           than  the  one  on  which  it  was  compiled.  Details are given in the
890           pcreprecompile documentation.
891    
892    
893  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
894    
895       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
896    
897           The function pcre_config() makes it possible for a PCRE client to  dis-
898           cover which optional features have been compiled into the PCRE library.
899           The pcrebuild documentation has more details about these optional  fea-
900           tures.
901    
902           The  first  argument  for pcre_config() is an integer, specifying which
903           information is required; the second argument is a pointer to a variable
904           into  which  the  information  is  placed. The following information is
905           available:
906    
907             PCRE_CONFIG_UTF8
908    
909           The output is an integer that is set to one if UTF-8 support is  avail-
910           able; otherwise it is set to zero.
911    
912             PCRE_CONFIG_UNICODE_PROPERTIES
913    
914           The  output  is  an  integer  that is set to one if support for Unicode
915           character properties is available; otherwise it is set to zero.
916    
917       The function pcre_config() makes  it  possible  for  a  PCRE           PCRE_CONFIG_NEWLINE
      client  to  discover  which optional features have been com-  
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
918    
919       The first argument for pcre_config() is an integer, specify-         The output is an integer whose value specifies  the  default  character
920       ing  which information is required; the second argument is a         sequence  that is recognized as meaning "newline". The four values that
921       pointer to a variable into which the information is  placed.         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
922       The following information is available:         and  -1  for  ANY. The default should normally be the standard sequence
923           for your operating system.
924    
925         PCRE_CONFIG_UTF8           PCRE_CONFIG_LINK_SIZE
926    
927       The output is an integer that is set to one if UTF-8 support         The output is an integer that contains the number  of  bytes  used  for
928       is available; otherwise it is set to zero.         internal linkage in compiled regular expressions. The value is 2, 3, or
929           4. Larger values allow larger regular expressions to  be  compiled,  at
930           the  expense  of  slower matching. The default value of 2 is sufficient
931           for all but the most massive patterns, since  it  allows  the  compiled
932           pattern to be up to 64K in size.
933    
934         PCRE_CONFIG_NEWLINE           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
935    
936       The output is an integer that is set to  the  value  of  the         The  output  is  an integer that contains the threshold above which the
937       code  that  is  used for the newline character. It is either         POSIX interface uses malloc() for output vectors. Further  details  are
938       linefeed (10) or carriage return (13), and  should  normally         given in the pcreposix documentation.
      be the standard character for your operating system.  
939    
940         PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_MATCH_LIMIT
941    
942       The output is an integer that contains the number  of  bytes         The output is an integer that gives the default limit for the number of
943       used  for  internal linkage in compiled regular expressions.         internal matching function calls in a  pcre_exec()  execution.  Further
944       The value is 2, 3, or 4. Larger values allow larger  regular         details are given with pcre_exec() below.
      expressions  to be compiled, at the expense of slower match-  
      ing. The default value of 2 is sufficient for  all  but  the  
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
945    
946         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_MATCH_LIMIT_RECURSION
947    
948       The output is an integer that contains the  threshold  above         The  output is an integer that gives the default limit for the depth of
949       which  the POSIX interface uses malloc() for output vectors.         recursion when calling the internal matching function in a  pcre_exec()
950       Further details are given in the pcreposix documentation.         execution. Further details are given with pcre_exec() below.
951    
952         PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_STACKRECURSE
953    
954       The output is an integer that gives the  default  limit  for         The  output is an integer that is set to one if internal recursion when
955       the   number  of  internal  matching  function  calls  in  a         running pcre_exec() is implemented by recursive function calls that use
956       pcre_exec()  execution.  Further  details  are  given   with         the  stack  to remember their state. This is the usual way that PCRE is
957       pcre_exec() below.         compiled. The output is zero if PCRE was compiled to use blocks of data
958           on  the  heap  instead  of  recursive  function  calls.  In  this case,
959           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
960           blocks on the heap, thus avoiding the use of the stack.
961    
962    
963  COMPILING A PATTERN  COMPILING A PATTERN
964    
965       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
966            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
967            const unsigned char *tableptr);              const unsigned char *tableptr);
968    
969       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
970       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
971       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
972       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
973       pcre_malloc is returned. This contains the compiled code and  
974       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
975       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
976       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
977       memory when it is no longer required.         errorcodeptr, via which a numerical error code can be returned.
978    
979       Although the compiled code of a PCRE regex  is  relocatable,         The pattern is a C string terminated by a binary zero, and is passed in
980       that is, it does not depend on memory location, the complete         the  pattern  argument.  A  pointer to a single block of memory that is
981       pcre data block is not fully relocatable,  because  it  con-         obtained via pcre_malloc is returned. This contains the  compiled  code
982       tains  a  copy of the tableptr argument, which is an address         and related data. The pcre type is defined for the returned block; this
983       (see below).         is a typedef for a structure whose contents are not externally defined.
984       The options argument contains independent bits  that  affect         It is up to the caller to free the memory (via pcre_free) when it is no
985       the  compilation.  It  should  be  zero  if  no  options are         longer required.
986       required. Some of the options, in particular, those that are  
987       compatible  with Perl, can also be set and unset from within         Although the compiled code of a PCRE regex is relocatable, that is,  it
988       the pattern (see the detailed description of regular expres-         does not depend on memory location, the complete pcre data block is not
989       sions  in the pcrepattern documentation). For these options,         fully relocatable, because it may contain a copy of the tableptr  argu-
990       the contents of the options argument specifies their initial         ment, which is an address (see below).
991       settings  at  the  start  of  compilation and execution. The  
992       PCRE_ANCHORED option can be set at the time of  matching  as         The options argument contains various bit settings that affect the com-
993       well as at compile time.         pilation. It should be zero if no options are required.  The  available
994           options  are  described  below. Some of them, in particular, those that
995       If errptr is NULL, pcre_compile() returns NULL  immediately.         are compatible with Perl, can also be set and  unset  from  within  the
996       Otherwise, if compilation of a pattern fails, pcre_compile()         pattern  (see  the  detailed  description in the pcrepattern documenta-
997       returns NULL, and sets the variable pointed to by errptr  to         tion). For these options, the contents of the options  argument  speci-
998       point  to a textual error message. The offset from the start         fies  their initial settings at the start of compilation and execution.
999       of  the  pattern  to  the  character  where  the  error  was         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
1000       discovered   is   placed  in  the  variable  pointed  to  by         of matching as well as at compile time.
1001       erroffset, which must not be NULL. If it  is,  an  immediate  
1002       error is given.         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1003           if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1004       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         sets the variable pointed to by errptr to point to a textual error mes-
1005       default  set  of character tables which are built when it is         sage. This is a static string that is part of the library. You must not
1006       compiled, using the default C  locale.  Otherwise,  tableptr         try to free it. The offset from the start of the pattern to the charac-
1007       must  be  the result of a call to pcre_maketables(). See the         ter where the error was discovered is placed in the variable pointed to
1008       section on locale support below.         by  erroffset,  which must not be NULL. If it is, an immediate error is
1009           given.
1010       This code fragment shows a typical straightforward  call  to  
1011       pcre_compile():         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
1012           codeptr  argument is not NULL, a non-zero error code number is returned
1013         pcre *re;         via this argument in the event of an error. This is in addition to  the
1014         const char *error;         textual error message. Error codes and messages are listed below.
1015         int erroffset;  
1016         re = pcre_compile(         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
1017           "^A.*Z",          /* the pattern */         character tables that are  built  when  PCRE  is  compiled,  using  the
1018           0,                /* default options */         default  C  locale.  Otherwise, tableptr must be an address that is the
1019           &error,           /* for error message */         result of a call to pcre_maketables(). This value is  stored  with  the
1020           &erroffset,       /* for error offset */         compiled  pattern,  and used again by pcre_exec(), unless another table
1021           NULL);            /* use default character tables */         pointer is passed to it. For more discussion, see the section on locale
1022           support below.
1023       The following option bits are defined:  
1024           This  code  fragment  shows a typical straightforward call to pcre_com-
1025         PCRE_ANCHORED         pile():
1026    
1027       If this bit is set, the pattern is forced to be  "anchored",           pcre *re;
1028       that is, it is constrained to match only at the first match-           const char *error;
1029       ing point in the string which is being searched  (the  "sub-           int erroffset;
1030       ject string"). This effect can also be achieved by appropri-           re = pcre_compile(
1031       ate constructs in the pattern itself, which is the only  way             "^A.*Z",          /* the pattern */
1032       to do it in Perl.             0,                /* default options */
1033               &error,           /* for error message */
1034         PCRE_CASELESS             &erroffset,       /* for error offset */
1035               NULL);            /* use default character tables */
1036       If this bit is set, letters in the pattern match both  upper  
1037       and  lower  case  letters.  It  is  equivalent  to Perl's /i         The following names for option bits are defined in  the  pcre.h  header
1038       option, and it can be changed within a  pattern  by  a  (?i)         file:
1039       option setting.  
1040             PCRE_ANCHORED
1041         PCRE_DOLLAR_ENDONLY  
1042           If this bit is set, the pattern is forced to be "anchored", that is, it
1043       If this bit is set, a dollar metacharacter  in  the  pattern         is constrained to match only at the first matching point in the  string
1044       matches  only at the end of the subject string. Without this         that  is being searched (the "subject string"). This effect can also be
1045       option, a dollar also matches immediately before  the  final         achieved by appropriate constructs in the pattern itself, which is  the
1046       character  if it is a newline (but not before any other new-         only way to do it in Perl.
1047       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
1048       PCRE_MULTILINE is set. There is no equivalent to this option           PCRE_AUTO_CALLOUT
1049       in Perl, and no way to set it within a pattern.  
1050           If this bit is set, pcre_compile() automatically inserts callout items,
1051         PCRE_DOTALL         all with number 255, before each pattern item. For  discussion  of  the
1052           callout facility, see the pcrecallout documentation.
1053       If this bit is  set,  a  dot  metacharater  in  the  pattern  
1054       matches all characters, including newlines. Without it, new-           PCRE_CASELESS
1055       lines are excluded. This option is equivalent to  Perl's  /s  
1056       option,  and  it  can  be changed within a pattern by a (?s)         If  this  bit is set, letters in the pattern match both upper and lower
1057       option setting. A negative class such as [^a] always matches         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
1058       a  newline  character,  independent  of  the setting of this         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1059       option.         always understands the concept of case for characters whose values  are
1060           less  than 128, so caseless matching is always possible. For characters
1061         PCRE_EXTENDED         with higher values, the concept of case is supported if  PCRE  is  com-
1062           piled  with Unicode property support, but not otherwise. If you want to
1063       If this bit is set, whitespace data characters in  the  pat-         use caseless matching for characters 128 and  above,  you  must  ensure
1064       tern  are  totally  ignored  except when escaped or inside a         that  PCRE  is  compiled  with Unicode property support as well as with
1065       character class. Whitespace does not include the VT  charac-         UTF-8 support.
1066       ter  (code 11). In addition, characters between an unescaped  
1067       # outside a character class and the next newline  character,           PCRE_DOLLAR_ENDONLY
1068       inclusive, are also ignored. This is equivalent to Perl's /x  
1069       option, and it can be changed within a  pattern  by  a  (?x)         If this bit is set, a dollar metacharacter in the pattern matches  only
1070       option setting.         at  the  end  of the subject string. Without this option, a dollar also
1071           matches immediately before a newline at the end of the string (but  not
1072       This option makes it possible  to  include  comments  inside         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1073       complicated patterns.  Note, however, that this applies only         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
1074       to data characters. Whitespace characters may  never  appear         Perl, and no way to set it within a pattern.
1075       within special character sequences in a pattern, for example  
1076       within the sequence (?( which introduces a conditional  sub-           PCRE_DOTALL
1077       pattern.  
1078           If this bit is set, a dot metacharater in the pattern matches all char-
1079         PCRE_EXTRA         acters, including those that indicate newline. Without it, a  dot  does
1080           not  match  when  the  current position is at a newline. This option is
1081       This option was invented in  order  to  turn  on  additional         equivalent to Perl's /s option, and it can be changed within a  pattern
1082       functionality of PCRE that is incompatible with Perl, but it         by  a (?s) option setting. A negative class such as [^a] always matches
1083       is currently of very little use. When set, any backslash  in         newline characters, independent of the setting of this option.
1084       a  pattern  that is followed by a letter that has no special  
1085       meaning causes an error, thus reserving  these  combinations           PCRE_DUPNAMES
1086       for  future  expansion.  By default, as in Perl, a backslash  
1087       followed by a letter with no special meaning is treated as a         If this bit is set, names used to identify capturing  subpatterns  need
1088       literal.  There  are at present no other features controlled         not be unique. This can be helpful for certain types of pattern when it
1089       by this option. It can also be set by a (?X) option  setting         is known that only one instance of the named  subpattern  can  ever  be
1090       within a pattern.         matched.  There  are  more details of named subpatterns below; see also
1091           the pcrepattern documentation.
1092         PCRE_MULTILINE  
1093             PCRE_EXTENDED
1094       By default, PCRE treats the subject string as consisting  of  
1095       a  single "line" of characters (even if it actually contains         If this bit is set, whitespace  data  characters  in  the  pattern  are
1096       several newlines). The "start  of  line"  metacharacter  (^)         totally ignored except when escaped or inside a character class. White-
1097       matches  only  at the start of the string, while the "end of         space does not include the VT character (code 11). In addition, charac-
1098       line" metacharacter ($) matches  only  at  the  end  of  the         ters between an unescaped # outside a character class and the next new-
1099       string,    or   before   a   terminating   newline   (unless         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1100       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.         option,  and  it  can be changed within a pattern by a (?x) option set-
1101           ting.
1102       When PCRE_MULTILINE it is set, the "start of line" and  "end  
1103       of  line"  constructs match immediately following or immedi-         This option makes it possible to include  comments  inside  complicated
1104       ately before any newline  in  the  subject  string,  respec-         patterns.   Note,  however,  that this applies only to data characters.
1105       tively,  as  well  as  at  the  very  start and end. This is         Whitespace  characters  may  never  appear  within  special   character
1106       equivalent to Perl's /m option, and it can be changed within         sequences  in  a  pattern,  for  example  within the sequence (?( which
1107       a  pattern  by  a  (?m) option setting. If there are no "\n"         introduces a conditional subpattern.
1108       characters in a subject string, or no occurrences of ^ or  $  
1109       in a pattern, setting PCRE_MULTILINE has no effect.           PCRE_EXTRA
1110    
1111         PCRE_NO_AUTO_CAPTURE         This option was invented in order to turn on  additional  functionality
1112           of  PCRE  that  is  incompatible with Perl, but it is currently of very
1113       If this option is set, it disables the use of numbered  cap-         little use. When set, any backslash in a pattern that is followed by  a
1114       turing  parentheses  in the pattern. Any opening parenthesis         letter  that  has  no  special  meaning causes an error, thus reserving
1115       that is not followed by ? behaves as if it were followed  by         these combinations for future expansion. By  default,  as  in  Perl,  a
1116       ?:  but  named  parentheses  can still be used for capturing         backslash  followed by a letter with no special meaning is treated as a
1117       (and they acquire numbers in the usual  way).  There  is  no         literal. (Perl can, however, be persuaded to give a warning for  this.)
1118       equivalent of this option in Perl.         There  are  at  present no other features controlled by this option. It
1119           can also be set by a (?X) option setting within a pattern.
1120         PCRE_UNGREEDY  
1121             PCRE_FIRSTLINE
1122       This option inverts the "greediness" of the  quantifiers  so  
1123       that  they  are  not greedy by default, but become greedy if         If this option is set, an  unanchored  pattern  is  required  to  match
1124       followed by "?". It is not compatible with Perl. It can also         before  or  at  the  first  newline  in  the subject string, though the
1125       be set by a (?U) option setting within the pattern.         matched text may continue over the newline.
1126    
1127         PCRE_UTF8           PCRE_MULTILINE
1128    
1129       This option causes PCRE to regard both the pattern  and  the         By default, PCRE treats the subject string as consisting  of  a  single
1130       subject  as  strings  of UTF-8 characters instead of single-         line  of characters (even if it actually contains newlines). The "start
1131       byte character strings. However, it  is  available  only  if         of line" metacharacter (^) matches only at the  start  of  the  string,
1132       PCRE  has  been  built to include UTF-8 support. If not, the         while  the  "end  of line" metacharacter ($) matches only at the end of
1133       use of this option provokes an error. Details  of  how  this         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1134       option  changes  the behaviour of PCRE are given in the sec-         is set). This is the same as Perl.
1135       tion on UTF-8 support in the main pcre page.  
1136           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1137           constructs match immediately following or immediately  before  internal
1138           newlines  in  the  subject string, respectively, as well as at the very
1139           start and end. This is equivalent to Perl's /m option, and  it  can  be
1140           changed within a pattern by a (?m) option setting. If there are no new-
1141           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1142           setting PCRE_MULTILINE has no effect.
1143    
1144             PCRE_NEWLINE_CR
1145             PCRE_NEWLINE_LF
1146             PCRE_NEWLINE_CRLF
1147             PCRE_NEWLINE_ANYCRLF
1148             PCRE_NEWLINE_ANY
1149    
1150           These  options  override the default newline definition that was chosen
1151           when PCRE was built. Setting the first or the second specifies  that  a
1152           newline  is  indicated  by a single character (CR or LF, respectively).
1153           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1154           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1155           that any of the three preceding sequences should be recognized. Setting
1156           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1157           recognized. The Unicode newline sequences are the three just mentioned,
1158           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1159           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1160           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1161           UTF-8 mode.
1162    
1163           The newline setting in the  options  word  uses  three  bits  that  are
1164           treated as a number, giving eight possibilities. Currently only six are
1165           used (default plus the five values above). This means that if  you  set
1166           more  than one newline option, the combination may or may not be sensi-
1167           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1168           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1169           cause an error.
1170    
1171           The only time that a line break is specially recognized when  compiling
1172           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1173           character class is encountered. This indicates  a  comment  that  lasts
1174           until  after the next line break sequence. In other circumstances, line
1175           break  sequences  are  treated  as  literal  data,   except   that   in
1176           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1177           and are therefore ignored.
1178    
1179           The newline option that is set at compile time becomes the default that
1180           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1181    
1182             PCRE_NO_AUTO_CAPTURE
1183    
1184           If this option is set, it disables the use of numbered capturing paren-
1185           theses  in the pattern. Any opening parenthesis that is not followed by
1186           ? behaves as if it were followed by ?: but named parentheses can  still
1187           be  used  for  capturing  (and  they acquire numbers in the usual way).
1188           There is no equivalent of this option in Perl.
1189    
1190             PCRE_UNGREEDY
1191    
1192           This option inverts the "greediness" of the quantifiers  so  that  they
1193           are  not greedy by default, but become greedy if followed by "?". It is
1194           not compatible with Perl. It can also be set by a (?U)  option  setting
1195           within the pattern.
1196    
1197             PCRE_UTF8
1198    
1199           This  option  causes PCRE to regard both the pattern and the subject as
1200           strings of UTF-8 characters instead of single-byte  character  strings.
1201           However,  it is available only when PCRE is built to include UTF-8 sup-
1202           port. If not, the use of this option provokes an error. Details of  how
1203           this  option  changes the behaviour of PCRE are given in the section on
1204           UTF-8 support in the main pcre page.
1205    
1206             PCRE_NO_UTF8_CHECK
1207    
1208           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1209           automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1210           pcre_compile() returns an error. If you already know that your  pattern
1211           is  valid, and you want to skip this check for performance reasons, you
1212           can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1213           passing an invalid UTF-8 string as a pattern is undefined. It may cause
1214           your program to crash.  Note that this option can  also  be  passed  to
1215           pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1216           ing of subject strings.
1217    
1218    
1219    COMPILATION ERROR CODES
1220    
1221           The following table lists the error  codes  than  may  be  returned  by
1222           pcre_compile2(),  along with the error messages that may be returned by
1223           both compiling functions. As PCRE has developed, some error codes  have
1224           fallen out of use. To avoid confusion, they have not been re-used.
1225    
1226              0  no error
1227              1  \ at end of pattern
1228              2  \c at end of pattern
1229              3  unrecognized character follows \
1230              4  numbers out of order in {} quantifier
1231              5  number too big in {} quantifier
1232              6  missing terminating ] for character class
1233              7  invalid escape sequence in character class
1234              8  range out of order in character class
1235              9  nothing to repeat
1236             10  [this code is not in use]
1237             11  internal error: unexpected repeat
1238             12  unrecognized character after (?
1239             13  POSIX named classes are supported only within a class
1240             14  missing )
1241             15  reference to non-existent subpattern
1242             16  erroffset passed as NULL
1243             17  unknown option bit(s) set
1244             18  missing ) after comment
1245             19  [this code is not in use]
1246             20  regular expression too large
1247             21  failed to get memory
1248             22  unmatched parentheses
1249             23  internal error: code overflow
1250             24  unrecognized character after (?<
1251             25  lookbehind assertion is not fixed length
1252             26  malformed number or name after (?(
1253             27  conditional group contains more than two branches
1254             28  assertion expected after (?(
1255             29  (?R or (?digits must be followed by )
1256             30  unknown POSIX class name
1257             31  POSIX collating elements are not supported
1258             32  this version of PCRE is not compiled with PCRE_UTF8 support
1259             33  [this code is not in use]
1260             34  character value in \x{...} sequence is too large
1261             35  invalid condition (?(0)
1262             36  \C not allowed in lookbehind assertion
1263             37  PCRE does not support \L, \l, \N, \U, or \u
1264             38  number after (?C is > 255
1265             39  closing ) for (?C expected
1266             40  recursive call could loop indefinitely
1267             41  unrecognized character after (?P
1268             42  syntax error in subpattern name (missing terminator)
1269             43  two named subpatterns have the same name
1270             44  invalid UTF-8 string
1271             45  support for \P, \p, and \X has not been compiled
1272             46  malformed \P or \p sequence
1273             47  unknown property name after \P or \p
1274             48  subpattern name is too long (maximum 32 characters)
1275             49  too many named subpatterns (maximum 10,000)
1276             50  repeated subpattern is too long
1277             51  octal value is greater than \377 (not in UTF-8 mode)
1278             52  internal error: overran compiling workspace
1279             53   internal  error:  previously-checked  referenced  subpattern not
1280           found
1281             54  DEFINE group contains more than one branch
1282             55  repeating a DEFINE group is not allowed
1283             56  inconsistent NEWLINE options"
1284    
1285    
1286  STUDYING A PATTERN  STUDYING A PATTERN
1287    
1288       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1289            const char **errptr);              const char **errptr);
1290    
1291       When a pattern is going to be  used  several  times,  it  is         If a compiled pattern is going to be used several times,  it  is  worth
1292       worth  spending  more time analyzing it in order to speed up         spending more time analyzing it in order to speed up the time taken for
1293       the time taken for matching. The function pcre_study() takes         matching. The function pcre_study() takes a pointer to a compiled  pat-
1294       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1295       studing the pattern  produces  additional  information  that         information that will help speed up matching,  pcre_study()  returns  a
1296       will  help speed up matching, pcre_study() returns a pointer         pointer  to a pcre_extra block, in which the study_data field points to
1297       to a pcre_extra block, in which the study_data field  points         the results of the study.
1298       to the results of the study.  
1299           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1300       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1301       directly  to pcre_exec(). However, the pcre_extra block also         that can be set by the caller before the block  is  passed;  these  are
1302       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
1303       the  block is passed; these are described below. If studying  
1304       the pattern does not  produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1305       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1306       ling program wants to pass  some  of  the  other  fields  to         wants  to  pass  any of the other fields to pcre_exec(), it must set up
1307       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
1308    
1309       The second argument contains option  bits.  At  present,  no         The second argument of pcre_study() contains option bits.  At  present,
1310       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1311       should always be zero.  
1312           The  third argument for pcre_study() is a pointer for an error message.
1313       The third argument for pcre_study()  is  a  pointer  for  an         If studying succeeds (even if no data is  returned),  the  variable  it
1314       error  message.  If  studying  succeeds  (even if no data is         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1315       returned), the variable it points to is set to NULL.  Other-         error message. This is a static string that is part of the library. You
1316       wise it points to a textual error message. You should there-         must  not  try  to  free it. You should test the error pointer for NULL
1317       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1318       pcre_study(), to be sure that it has run successfully.  
1319           This is a typical call to pcre_study():
1320       This is a typical call to pcre_study():  
1321             pcre_extra *pe;
1322         pcre_extra *pe;           pe = pcre_study(
1323         pe = pcre_study(             re,             /* result of pcre_compile() */
1324           re,             /* result of pcre_compile() */             0,              /* no options exist */
1325           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1326           &error);        /* set to NULL or points to a message */  
1327           At present, studying a pattern is useful only for non-anchored patterns
1328       At present, studying a  pattern  is  useful  only  for  non-         that  do not have a single fixed starting character. A bitmap of possi-
1329       anchored  patterns  that do not have a single fixed starting         ble starting bytes is created.
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1330    
1331    
1332  LOCALE SUPPORT  LOCALE SUPPORT
1333    
1334       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1335       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
1336       set of tables. When running in UTF-8 mode, this applies only         by character value. When running in UTF-8 mode, this  applies  only  to
1337       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
1338       a default set of tables that is created  in  the  default  C         escapes such as \w or \d, but can be tested with \p if  PCRE  is  built
1339       locale  when  PCRE  is compiled. This is used when the final         with  Unicode  character property support. The use of locales with Uni-
1340       argument of pcre_compile() is NULL, and  is  sufficient  for         code is discouraged. If you are handling characters with codes  greater
1341       many applications.         than  128, you should either use UTF-8 and Unicode, or use locales, but
1342           not try to mix the two.
1343       An alternative set of tables can, however, be supplied. Such  
1344       tables  are built by calling the pcre_maketables() function,         PCRE contains an internal set of tables that are used  when  the  final
1345       which has no arguments, in the relevant locale.  The  result         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1346       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1347       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1348       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1349       greater than 128 are treated as letters), the following code         which may cause them to be different.
1350       could be used:  
1351           The  internal tables can always be overridden by tables supplied by the
1352         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1353         tables = pcre_maketables();         from  the  default.  As more and more applications change to using Uni-
1354         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1355    
1356       The  tables  are  built  in  memory  that  is  obtained  via         External tables are built by calling  the  pcre_maketables()  function,
1357       pcre_malloc.  The  pointer that is passed to pcre_compile is         which  has no arguments, in the relevant locale. The result can then be
1358       saved with the compiled pattern, and  the  same  tables  are         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1359       used via this pointer by pcre_study() and pcre_exec(). Thus,         example,  to  build  and use tables that are appropriate for the French
1360       for any single pattern, compilation, studying  and  matching         locale (where accented characters with  values  greater  than  128  are
1361       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1362       compiled in different locales. It is the caller's  responsi-  
1363       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1364       remains available for as long as it is needed.           tables = pcre_maketables();
1365             re = pcre_compile(..., tables);
1366    
1367           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1368           if you are using Windows, the name for the French locale is "french".
1369    
1370           When pcre_maketables() runs, the tables are built  in  memory  that  is
1371           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1372           that the memory containing the tables remains available for as long  as
1373           it is needed.
1374    
1375           The pointer that is passed to pcre_compile() is saved with the compiled
1376           pattern, and the same tables are used via this pointer by  pcre_study()
1377           and normally also by pcre_exec(). Thus, by default, for any single pat-
1378           tern, compilation, studying and matching all happen in the same locale,
1379           but different patterns can be compiled in different locales.
1380    
1381           It  is  possible to pass a table pointer or NULL (indicating the use of
1382           the internal tables) to pcre_exec(). Although  not  intended  for  this
1383           purpose,  this facility could be used to match a pattern in a different
1384           locale from the one in which it was compiled. Passing table pointers at
1385           run time is discussed below in the section on matching a pattern.
1386    
1387    
1388  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1389    
1390       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1391            int what, void *where);              int what, void *where);
1392    
1393       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1394       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1395       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1396       ity (and is documented below).  
1397           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1398       The first argument for pcre_fullinfo() is a pointer  to  the         pattern. The second argument is the result of pcre_study(), or NULL  if
1399       compiled  pattern.  The  second  argument  is  the result of         the  pattern  was not studied. The third argument specifies which piece
1400       pcre_study(), or NULL if the pattern was  not  studied.  The         of information is required, and the fourth argument is a pointer  to  a
1401       third  argument  specifies  which  piece  of  information is         variable  to  receive  the  data. The yield of the function is zero for
1402       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1403       to  receive  the data. The yield of the function is zero for  
1404       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1405                                   the argument where was NULL
1406         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1407                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1408         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1409         PCRE_ERROR_BADOPTION  the value of what was invalid         The "magic number" is placed at the start of each compiled  pattern  as
1410           an  simple check against passing an arbitrary memory pointer. Here is a
1411       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1412       length of the compiled pattern:         pattern:
1413    
1414         int rc;           int rc;
1415         unsigned long int length;           size_t length;
1416         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1417           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1418           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1419           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1420           &length);         /* where to put the data */             &length);         /* where to put the data */
1421    
1422       The possible values for the third argument  are  defined  in         The  possible  values for the third argument are defined in pcre.h, and
1423       pcre.h, and are as follows:         are as follows:
1424    
1425         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1426    
1427       Return the number of the highest back reference in the  pat-         Return the number of the highest back reference  in  the  pattern.  The
1428       tern.  The  fourth argument should point to an int variable.         fourth  argument  should  point to an int variable. Zero is returned if
1429       Zero is returned if there are no back references.         there are no back references.
1430    
1431         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1432    
1433       Return the number of capturing subpatterns in  the  pattern.         Return the number of capturing subpatterns in the pattern.  The  fourth
1434       The fourth argument should point to an int variable.         argument should point to an int variable.
1435    
1436         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1437    
1438       Return information about  the  first  byte  of  any  matched         Return  a pointer to the internal default character tables within PCRE.
1439       string,  for a non-anchored pattern. (This option used to be         The fourth argument should point to an unsigned char *  variable.  This
1440       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1441       for backwards compatibility.)         tion. External callers can cause PCRE to use  its  internal  tables  by
1442           passing a NULL table pointer.
1443       If there is a fixed first byte, e.g. from a pattern such  as  
1444       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1445       by where. Otherwise, if either  
1446           Return  information  about  the first byte of any matched string, for a
1447       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored pattern. The fourth argument should point to an int  vari-
1448       and every branch starts with "^", or         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1449           is still recognized for backwards compatibility.)
1450       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1451       PCRE_DOTALL is not set (if it were set, the pattern would be         If there is a fixed first byte, for example, from  a  pattern  such  as
1452       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1453    
1454       -1 is returned, indicating that the pattern matches only  at         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1455       the  start  of  a subject string or after any newline within         branch starts with "^", or
1456       the string. Otherwise -2 is returned. For anchored patterns,  
1457       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1458           set (if it were set, the pattern would be anchored),
1459         PCRE_INFO_FIRSTTABLE  
1460           -1  is  returned, indicating that the pattern matches only at the start
1461       If the pattern was studied, and this resulted  in  the  con-         of a subject string or after any newline within the  string.  Otherwise
1462       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1463       for the first byte in any matching string, a pointer to  the  
1464       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1465       argument should point to an unsigned char * variable.  
1466           If  the pattern was studied, and this resulted in the construction of a
1467         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1468           matching  string, a pointer to the table is returned. Otherwise NULL is
1469       Return the value of the rightmost  literal  byte  that  must         returned. The fourth argument should point to an unsigned char *  vari-
1470       exist  in  any  matched  string, other than at its start, if         able.
1471       such a byte has been recorded. The  fourth  argument  should  
1472       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_LASTLITERAL
1473       returned. For anchored patterns,  a  last  literal  byte  is  
1474       recorded  only  if  it follows something of variable length.         Return  the  value of the rightmost literal byte that must exist in any
1475       For example, for the pattern /^a\d+z\d+/ the returned  value         matched string, other than at its  start,  if  such  a  byte  has  been
1476       is "z", but for /^a\dz\d/ the returned value is -1.         recorded. The fourth argument should point to an int variable. If there
1477           is no such byte, -1 is returned. For anchored patterns, a last  literal
1478         PCRE_INFO_NAMECOUNT         byte  is  recorded only if it follows something of variable length. For
1479         PCRE_INFO_NAMEENTRYSIZE         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1480         PCRE_INFO_NAMETABLE         /^a\dz\d/ the returned value is -1.
1481    
1482       PCRE supports the use of named as well as numbered capturing           PCRE_INFO_NAMECOUNT
1483       parentheses. The names are just an additional way of identi-           PCRE_INFO_NAMEENTRYSIZE
1484       fying the parentheses,  which  still  acquire  a  number.  A           PCRE_INFO_NAMETABLE
1485       caller  that  wants  to extract data from a named subpattern  
1486       must convert the name to a number in  order  to  access  the         PCRE  supports the use of named as well as numbered capturing parenthe-
1487       correct  pointers  in  the  output  vector  (described  with         ses. The names are just an additional way of identifying the  parenthe-
1488       pcre_exec() below). In order to do this, it must  first  use         ses, which still acquire numbers. Several convenience functions such as
1489       these  three  values  to  obtain  the name-to-number mapping         pcre_get_named_substring() are provided for  extracting  captured  sub-
1490       table for the pattern.         strings  by  name. It is also possible to extract the data directly, by
1491           first converting the name to a number in order to  access  the  correct
1492       The  map  consists  of  a  number  of  fixed-size   entries.         pointers in the output vector (described with pcre_exec() below). To do
1493       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         the conversion, you need  to  use  the  name-to-number  map,  which  is
1494       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both         described by these three values.
1495       of  these return an int value. The entry size depends on the  
1496       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1497       pointer to the first entry of the table (a pointer to char).         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1498       The first two bytes of each entry are the number of the cap-         of  each  entry;  both  of  these  return  an int value. The entry size
1499       turing parenthesis, most significant byte first. The rest of         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1500       the entry is the corresponding name,  zero  terminated.  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1501       names  are  in alphabetical order. For example, consider the         first two bytes of each entry are the number of the capturing parenthe-
1502       following pattern (assume PCRE_EXTENDED  is  set,  so  white         sis,  most  significant byte first. The rest of the entry is the corre-
1503       space - including newlines - is ignored):         sponding name, zero terminated. The names are  in  alphabetical  order.
1504           When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1505         (?P<date> (?P<year>(\d\d)?\d\d) -         theses numbers. For example, consider  the  following  pattern  (assume
1506         (?P<month>\d\d) - (?P<day>\d\d) )         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1507           ignored):
1508       There are four named subpatterns,  so  the  table  has  four  
1509       entries,  and  each  entry in the table is eight bytes long.           (?<date> (?<year>(\d\d)?\d\d) -
1510       The table is as follows, with non-printing  bytes  shows  in           (?<month>\d\d) - (?<day>\d\d) )
1511       hex, and undefined bytes shown as ??:  
1512           There are four named subpatterns, so the table has  four  entries,  and
1513         00 01 d  a  t  e  00 ??         each  entry  in the table is eight bytes long. The table is as follows,
1514         00 05 d  a  y  00 ?? ??         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1515         00 04 m  o  n  t  h  00         as ??:
1516         00 02 y  e  a  r  00 ??  
1517             00 01 d  a  t  e  00 ??
1518       When writing code to extract data  from  named  subpatterns,           00 05 d  a  y  00 ?? ??
1519       remember  that the length of each entry may be different for           00 04 m  o  n  t  h  00
1520       each compiled pattern.           00 02 y  e  a  r  00 ??
1521    
1522         PCRE_INFO_OPTIONS         When  writing  code  to  extract  data from named subpatterns using the
1523           name-to-number map, remember that the length of the entries  is  likely
1524       Return a copy of the options with which the pattern was com-         to be different for each compiled pattern.
1525       piled.  The fourth argument should point to an unsigned long  
1526       int variable. These option bits are those specified  in  the           PCRE_INFO_OPTIONS
1527       call  to  pcre_compile(),  modified  by any top-level option  
1528       settings within the pattern itself.         Return  a  copy of the options with which the pattern was compiled. The
1529           fourth argument should point to an unsigned long  int  variable.  These
1530       A pattern is automatically anchored by PCRE if  all  of  its         option bits are those specified in the call to pcre_compile(), modified
1531       top-level alternatives begin with one of the following:         by any top-level option settings within the pattern itself.
1532    
1533         ^     unless PCRE_MULTILINE is set         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1534         \A    always         alternatives begin with one of the following:
1535         \G    always  
1536         .*    if PCRE_DOTALL is set and there are no back           ^     unless PCRE_MULTILINE is set
1537                 references to the subpattern in which .* appears           \A    always
1538             \G    always
1539       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the           .*    if PCRE_DOTALL is set and there are no back
1540       options returned by pcre_fullinfo().                   references to the subpattern in which .* appears
1541    
1542         PCRE_INFO_SIZE         For such patterns, the PCRE_ANCHORED bit is set in the options returned
1543           by pcre_fullinfo().
1544       Return the size of the compiled pattern, that is, the  value  
1545       that  was  passed as the argument to pcre_malloc() when PCRE           PCRE_INFO_SIZE
1546       was getting memory in which to place the compiled data.  The  
1547       fourth argument should point to a size_t variable.         Return the size of the compiled pattern, that is, the  value  that  was
1548           passed as the argument to pcre_malloc() when PCRE was getting memory in
1549         PCRE_INFO_STUDYSIZE         which to place the compiled data. The fourth argument should point to a
1550           size_t variable.
1551       Returns the size  of  the  data  block  pointed  to  by  the  
1552       study_data  field  in a pcre_extra block. That is, it is the           PCRE_INFO_STUDYSIZE
1553       value that was passed to pcre_malloc() when PCRE was getting  
1554       memory into which to place the data created by pcre_study().         Return the size of the data block pointed to by the study_data field in
1555       The fourth argument should point to a size_t variable.         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1556           pcre_malloc() when PCRE was getting memory into which to place the data
1557           created by pcre_study(). The fourth argument should point to  a  size_t
1558           variable.
1559    
1560    
1561  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1562    
1563       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1564    
1565       The pcre_info() function is now obsolete because its  inter-         The  pcre_info()  function is now obsolete because its interface is too
1566       face  is  too  restrictive  to return all the available data         restrictive to return all the available data about a compiled  pattern.
1567       about  a  compiled  pattern.   New   programs   should   use         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1568       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1569       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1570       negative numbers:  
1571             PCRE_ERROR_NULL       the argument code was NULL
1572         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1573         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1574           If  the  optptr  argument is not NULL, a copy of the options with which
1575       If the optptr argument is not NULL, a copy  of  the  options         the pattern was compiled is placed in the integer  it  points  to  (see
1576       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1577       it points to (see PCRE_INFO_OPTIONS above).  
1578           If  the  pattern  is  not anchored and the firstcharptr argument is not
1579       If the pattern is not anchored and the firstcharptr argument         NULL, it is used to pass back information about the first character  of
1580       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1581       first    character    of    any    matched    string    (see  
1582       PCRE_INFO_FIRSTBYTE above).  
1583    REFERENCE COUNTS
1584    
1585           int pcre_refcount(pcre *code, int adjust);
1586    
1587           The  pcre_refcount()  function is used to maintain a reference count in
1588           the data block that contains a compiled pattern. It is provided for the
1589           benefit  of  applications  that  operate  in an object-oriented manner,
1590           where different parts of the application may be using the same compiled
1591           pattern, but you want to free the block when they are all done.
1592    
1593           When a pattern is compiled, the reference count field is initialized to
1594           zero.  It is changed only by calling this function, whose action is  to
1595           add  the  adjust  value  (which may be positive or negative) to it. The
1596           yield of the function is the new value. However, the value of the count
1597           is  constrained to lie between 0 and 65535, inclusive. If the new value
1598           is outside these limits, it is forced to the appropriate limit value.
1599    
1600           Except when it is zero, the reference count is not correctly  preserved
1601           if  a  pattern  is  compiled on one host and then transferred to a host
1602           whose byte-order is different. (This seems a highly unlikely scenario.)
1603    
1604    
1605    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1606    
1607           int pcre_exec(const pcre *code, const pcre_extra *extra,
1608                const char *subject, int length, int startoffset,
1609                int options, int *ovector, int ovecsize);
1610    
1611           The  function pcre_exec() is called to match a subject string against a
1612           compiled pattern, which is passed in the code argument. If the  pattern
1613           has been studied, the result of the study should be passed in the extra
1614           argument. This function is the main matching facility of  the  library,
1615           and it operates in a Perl-like manner. For specialist use there is also
1616           an alternative matching function, which is described below in the  sec-
1617           tion about the pcre_dfa_exec() function.
1618    
1619           In  most applications, the pattern will have been compiled (and option-
1620           ally studied) in the same process that calls pcre_exec().  However,  it
1621           is possible to save compiled patterns and study data, and then use them
1622           later in different processes, possibly even on different hosts.  For  a
1623           discussion about this, see the pcreprecompile documentation.
1624    
1625           Here is an example of a simple call to pcre_exec():
1626    
1627             int rc;
1628             int ovector[30];
1629             rc = pcre_exec(
1630               re,             /* result of pcre_compile() */
1631               NULL,           /* we didn't study the pattern */
1632               "some string",  /* the subject string */
1633               11,             /* the length of the subject string */
1634               0,              /* start at offset 0 in the subject */
1635               0,              /* default options */
1636               ovector,        /* vector of integers for substring information */
1637               30);            /* number of elements (NOT size in bytes) */
1638    
1639       Extra data for pcre_exec()
1640    
1641           If  the  extra argument is not NULL, it must point to a pcre_extra data
1642           block. The pcre_study() function returns such a block (when it  doesn't
1643           return  NULL), but you can also create one for yourself, and pass addi-
1644           tional information in it. The pcre_extra block contains  the  following
1645           fields (not necessarily in this order):
1646    
1647             unsigned long int flags;
1648             void *study_data;
1649             unsigned long int match_limit;
1650             unsigned long int match_limit_recursion;
1651             void *callout_data;
1652             const unsigned char *tables;
1653    
1654           The  flags  field  is a bitmap that specifies which of the other fields
1655           are set. The flag bits are:
1656    
1657             PCRE_EXTRA_STUDY_DATA
1658             PCRE_EXTRA_MATCH_LIMIT
1659             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1660             PCRE_EXTRA_CALLOUT_DATA
1661             PCRE_EXTRA_TABLES
1662    
1663           Other flag bits should be set to zero. The study_data field is  set  in
1664           the  pcre_extra  block  that is returned by pcre_study(), together with
1665           the appropriate flag bit. You should not set this yourself, but you may
1666           add  to  the  block by setting the other fields and their corresponding
1667           flag bits.
1668    
1669           The match_limit field provides a means of preventing PCRE from using up
1670           a  vast amount of resources when running patterns that are not going to
1671           match, but which have a very large number  of  possibilities  in  their
1672           search  trees.  The  classic  example  is  the  use of nested unlimited
1673           repeats.
1674    
1675           Internally, PCRE uses a function called match() which it calls  repeat-
1676           edly  (sometimes  recursively). The limit set by match_limit is imposed
1677           on the number of times this function is called during  a  match,  which
1678           has  the  effect  of  limiting the amount of backtracking that can take
1679           place. For patterns that are not anchored, the count restarts from zero
1680           for each position in the subject string.
1681    
1682           The  default  value  for  the  limit can be set when PCRE is built; the
1683           default default is 10 million, which handles all but the  most  extreme
1684           cases.  You  can  override  the  default by suppling pcre_exec() with a
1685           pcre_extra    block    in    which    match_limit    is    set,     and
1686           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1687           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1688    
1689           The match_limit_recursion field is similar to match_limit, but  instead
1690           of limiting the total number of times that match() is called, it limits
1691           the depth of recursion. The recursion depth is a  smaller  number  than
1692           the  total number of calls, because not all calls to match() are recur-
1693           sive.  This limit is of use only if it is set smaller than match_limit.
1694    
1695           Limiting  the  recursion  depth  limits the amount of stack that can be
1696           used, or, when PCRE has been compiled to use memory on the heap instead
1697           of the stack, the amount of heap memory that can be used.
1698    
1699           The  default  value  for  match_limit_recursion can be set when PCRE is
1700           built; the default default  is  the  same  value  as  the  default  for
1701           match_limit.  You can override the default by suppling pcre_exec() with
1702           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1703           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1704           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1705    
1706           The pcre_callout field is used in conjunction with the  "callout"  fea-
1707           ture, which is described in the pcrecallout documentation.
1708    
1709           The  tables  field  is  used  to  pass  a  character  tables pointer to
1710           pcre_exec(); this overrides the value that is stored with the  compiled
1711           pattern.  A  non-NULL value is stored with the compiled pattern only if
1712           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1713           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1714           PCRE's internal tables to be used. This facility is  helpful  when  re-
1715           using  patterns  that  have been saved after compiling with an external
1716           set of tables, because the external tables  might  be  at  a  different
1717           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1718           tion for a discussion of saving compiled patterns for later use.
1719    
1720       Option bits for pcre_exec()
1721    
1722           The unused bits of the options argument for pcre_exec() must  be  zero.
1723           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1724           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1725           PCRE_PARTIAL.
1726    
1727             PCRE_ANCHORED
1728    
1729           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1730           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1731           turned  out to be anchored by virtue of its contents, it cannot be made
1732           unachored at matching time.
1733    
1734             PCRE_NEWLINE_CR
1735             PCRE_NEWLINE_LF
1736             PCRE_NEWLINE_CRLF
1737             PCRE_NEWLINE_ANYCRLF
1738             PCRE_NEWLINE_ANY
1739    
1740           These options override  the  newline  definition  that  was  chosen  or
1741           defaulted  when the pattern was compiled. For details, see the descrip-
1742           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1743           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1744           ters. It may also alter the way the match position is advanced after  a
1745           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1746           PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt
1747           fails  when the current position is at a CRLF sequence, the match posi-
1748           tion is advanced by two characters instead of one, in other  words,  to
1749           after the CRLF.
1750    
1751             PCRE_NOTBOL
1752    
1753           This option specifies that first character of the subject string is not
1754           the beginning of a line, so the  circumflex  metacharacter  should  not
1755           match  before it. Setting this without PCRE_MULTILINE (at compile time)
1756           causes circumflex never to match. This option affects only  the  behav-
1757           iour of the circumflex metacharacter. It does not affect \A.
1758    
1759             PCRE_NOTEOL
1760    
1761           This option specifies that the end of the subject string is not the end
1762           of a line, so the dollar metacharacter should not match it nor  (except
1763           in  multiline mode) a newline immediately before it. Setting this with-
1764           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1765           option  affects only the behaviour of the dollar metacharacter. It does
1766           not affect \Z or \z.
1767    
1768             PCRE_NOTEMPTY
1769    
1770           An empty string is not considered to be a valid match if this option is
1771           set.  If  there are alternatives in the pattern, they are tried. If all
1772           the alternatives match the empty string, the entire  match  fails.  For
1773           example, if the pattern
1774    
1775             a?b?
1776    
1777           is  applied  to  a string not beginning with "a" or "b", it matches the
1778           empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1779           match is not valid, so PCRE searches further into the string for occur-
1780           rences of "a" or "b".
1781    
1782           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1783           cial  case  of  a  pattern match of the empty string within its split()
1784           function, and when using the /g modifier. It  is  possible  to  emulate
1785           Perl's behaviour after matching a null string by first trying the match
1786           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1787           if  that  fails by advancing the starting offset (see below) and trying
1788           an ordinary match again. There is some code that demonstrates how to do
1789           this in the pcredemo.c sample program.
1790    
1791             PCRE_NO_UTF8_CHECK
1792    
1793           When PCRE_UTF8 is set at compile time, the validity of the subject as a
1794           UTF-8 string is automatically checked when pcre_exec() is  subsequently
1795           called.   The  value  of  startoffset is also checked to ensure that it
1796           points to the start of a UTF-8 character. If an invalid UTF-8  sequence
1797           of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1798           startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is
1799           returned.
1800    
1801           If  you  already  know that your subject is valid, and you want to skip
1802           these   checks   for   performance   reasons,   you   can    set    the
1803           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1804           do this for the second and subsequent calls to pcre_exec() if  you  are
1805           making  repeated  calls  to  find  all  the matches in a single subject
1806           string. However, you should be  sure  that  the  value  of  startoffset
1807           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1808           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1809           value  of startoffset that does not point to the start of a UTF-8 char-
1810           acter, is undefined. Your program may crash.
1811    
1812             PCRE_PARTIAL
1813    
1814           This option turns on the  partial  matching  feature.  If  the  subject
1815           string  fails to match the pattern, but at some point during the match-
1816           ing process the end of the subject was reached (that  is,  the  subject
1817           partially  matches  the  pattern and the failure to match occurred only
1818           because there were not enough subject characters), pcre_exec()  returns
1819           PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1820           used, there are restrictions on what may appear in the  pattern.  These
1821           are discussed in the pcrepartial documentation.
1822    
1823       The string to be matched by pcre_exec()
1824    
1825           The  subject string is passed to pcre_exec() as a pointer in subject, a
1826           length in length, and a starting byte offset in startoffset.  In  UTF-8
1827           mode,  the  byte  offset  must point to the start of a UTF-8 character.
1828           Unlike the pattern string, the subject may contain binary  zero  bytes.
1829           When  the starting offset is zero, the search for a match starts at the
1830           beginning of the subject, and this is by far the most common case.
1831    
1832           A non-zero starting offset is useful when searching for  another  match
1833           in  the same subject by calling pcre_exec() again after a previous suc-
1834           cess.  Setting startoffset differs from just passing over  a  shortened
1835           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1836           with any kind of lookbehind. For example, consider the pattern
1837    
1838             \Biss\B
1839    
1840           which finds occurrences of "iss" in the middle of  words.  (\B  matches
1841           only  if  the  current position in the subject is not a word boundary.)
1842           When applied to the string "Mississipi" the first call  to  pcre_exec()
1843           finds  the  first  occurrence. If pcre_exec() is called again with just
1844           the remainder of the subject,  namely  "issipi",  it  does  not  match,
1845           because \B is always false at the start of the subject, which is deemed
1846           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1847           string again, but with startoffset set to 4, it finds the second occur-
1848           rence of "iss" because it is able to look behind the starting point  to
1849           discover that it is preceded by a letter.
1850    
1851           If  a  non-zero starting offset is passed when the pattern is anchored,
1852           one attempt to match at the given offset is made. This can only succeed
1853           if  the  pattern  does  not require the match to be at the start of the
1854           subject.
1855    
1856       How pcre_exec() returns captured substrings
1857    
1858           In general, a pattern matches a certain portion of the subject, and  in
1859           addition,  further  substrings  from  the  subject may be picked out by
1860           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
1861           this  is  called "capturing" in what follows, and the phrase "capturing
1862           subpattern" is used for a fragment of a pattern that picks out  a  sub-
1863           string.  PCRE  supports several other kinds of parenthesized subpattern
1864           that do not cause substrings to be captured.
1865    
1866           Captured substrings are returned to the caller via a vector of  integer
1867           offsets  whose  address is passed in ovector. The number of elements in
1868           the vector is passed in ovecsize, which must be a non-negative  number.
1869           Note: this argument is NOT the size of ovector in bytes.
1870    
1871           The  first  two-thirds of the vector is used to pass back captured sub-
1872           strings, each substring using a pair of integers. The  remaining  third
1873           of  the  vector is used as workspace by pcre_exec() while matching cap-
1874           turing subpatterns, and is not available for passing back  information.
1875           The  length passed in ovecsize should always be a multiple of three. If
1876           it is not, it is rounded down.
1877    
1878           When a match is successful, information about  captured  substrings  is
1879           returned  in  pairs  of integers, starting at the beginning of ovector,
1880           and continuing up to two-thirds of its length at the  most.  The  first
1881           element of a pair is set to the offset of the first character in a sub-
1882           string, and the second is set to the  offset  of  the  first  character
1883           after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
1884           tor[1], identify the portion of  the  subject  string  matched  by  the
1885           entire  pattern.  The next pair is used for the first capturing subpat-
1886           tern, and so on. The value returned by pcre_exec() is one more than the
1887           highest numbered pair that has been set. For example, if two substrings
1888           have been captured, the returned value is 3. If there are no  capturing
1889           subpatterns,  the return value from a successful match is 1, indicating
1890           that just the first pair of offsets has been set.
1891    
1892           If a capturing subpattern is matched repeatedly, it is the last portion
1893           of the string that it matched that is returned.
1894    
1895           If  the vector is too small to hold all the captured substring offsets,
1896           it is used as far as possible (up to two-thirds of its length), and the
1897           function  returns a value of zero. In particular, if the substring off-
1898           sets are not of interest, pcre_exec() may be called with ovector passed
1899           as  NULL  and  ovecsize  as zero. However, if the pattern contains back
1900           references and the ovector is not big enough to  remember  the  related
1901           substrings,  PCRE has to get additional memory for use during matching.
1902           Thus it is usually advisable to supply an ovector.
1903    
1904           The pcre_info() function can be used to find  out  how  many  capturing
1905           subpatterns  there  are  in  a  compiled pattern. The smallest size for
1906           ovector that will allow for n captured substrings, in addition  to  the
1907           offsets of the substring matched by the whole pattern, is (n+1)*3.
1908    
1909           It  is  possible for capturing subpattern number n+1 to match some part
1910           of the subject when subpattern n has not been used at all. For example,
1911           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
1912           return from the function is 4, and subpatterns 1 and 3 are matched, but
1913           2  is  not.  When  this happens, both values in the offset pairs corre-
1914           sponding to unused subpatterns are set to -1.
1915    
1916           Offset values that correspond to unused subpatterns at the end  of  the
1917           expression  are  also  set  to  -1. For example, if the string "abc" is
1918           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
1919           matched.  The  return  from the function is 2, because the highest used
1920           capturing subpattern number is 1. However, you can refer to the offsets
1921           for  the  second  and third capturing subpatterns if you wish (assuming
1922           the vector is large enough, of course).
1923    
1924           Some convenience functions are provided  for  extracting  the  captured
1925           substrings as separate strings. These are described below.
1926    
1927       Error return values from pcre_exec()
1928    
1929           If  pcre_exec()  fails, it returns a negative number. The following are
1930           defined in the header file:
1931    
1932             PCRE_ERROR_NOMATCH        (-1)
1933    
1934           The subject string did not match the pattern.
1935    
1936             PCRE_ERROR_NULL           (-2)
1937    
1938           Either code or subject was passed as NULL,  or  ovector  was  NULL  and
1939           ovecsize was not zero.
1940    
1941             PCRE_ERROR_BADOPTION      (-3)
1942    
1943           An unrecognized bit was set in the options argument.
1944    
1945             PCRE_ERROR_BADMAGIC       (-4)
1946    
1947           PCRE  stores a 4-byte "magic number" at the start of the compiled code,
1948           to catch the case when it is passed a junk pointer and to detect when a
1949           pattern that was compiled in an environment of one endianness is run in
1950           an environment with the other endianness. This is the error  that  PCRE
1951           gives when the magic number is not present.
1952    
1953             PCRE_ERROR_UNKNOWN_OPCODE (-5)
1954    
1955           While running the pattern match, an unknown item was encountered in the
1956           compiled pattern. This error could be caused by a bug  in  PCRE  or  by
1957           overwriting of the compiled pattern.
1958    
1959             PCRE_ERROR_NOMEMORY       (-6)
1960    
1961           If  a  pattern contains back references, but the ovector that is passed
1962           to pcre_exec() is not big enough to remember the referenced substrings,
1963           PCRE  gets  a  block of memory at the start of matching to use for this
1964           purpose. If the call via pcre_malloc() fails, this error is given.  The
1965           memory is automatically freed at the end of matching.
1966    
1967             PCRE_ERROR_NOSUBSTRING    (-7)
1968    
1969           This  error is used by the pcre_copy_substring(), pcre_get_substring(),
1970           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1971           returned by pcre_exec().
1972    
1973             PCRE_ERROR_MATCHLIMIT     (-8)
1974    
1975           The  backtracking  limit,  as  specified  by the match_limit field in a
1976           pcre_extra structure (or defaulted) was reached.  See  the  description
1977           above.
1978    
1979             PCRE_ERROR_CALLOUT        (-9)
1980    
1981           This error is never generated by pcre_exec() itself. It is provided for
1982           use by callout functions that want to yield a distinctive  error  code.
1983           See the pcrecallout documentation for details.
1984    
1985             PCRE_ERROR_BADUTF8        (-10)
1986    
1987           A  string  that contains an invalid UTF-8 byte sequence was passed as a
1988           subject.
1989    
1990             PCRE_ERROR_BADUTF8_OFFSET (-11)
1991    
1992           The UTF-8 byte sequence that was passed as a subject was valid, but the
1993           value  of startoffset did not point to the beginning of a UTF-8 charac-
1994           ter.
1995    
1996             PCRE_ERROR_PARTIAL        (-12)
1997    
1998           The subject string did not match, but it did match partially.  See  the
1999           pcrepartial documentation for details of partial matching.
2000    
2001             PCRE_ERROR_BADPARTIAL     (-13)
2002    
2003           The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2004           items that are not supported for partial matching. See the  pcrepartial
2005           documentation for details of partial matching.
2006    
2007             PCRE_ERROR_INTERNAL       (-14)
2008    
2009           An  unexpected  internal error has occurred. This error could be caused
2010           by a bug in PCRE or by overwriting of the compiled pattern.
2011    
2012             PCRE_ERROR_BADCOUNT       (-15)
2013    
2014           This error is given if the value of the ovecsize argument is  negative.
2015    
2016             PCRE_ERROR_RECURSIONLIMIT (-21)
2017    
2018           The internal recursion limit, as specified by the match_limit_recursion
2019           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2020           description above.
2021    
2022             PCRE_ERROR_NULLWSLIMIT    (-22)
2023    
2024           When  a  group  that  can  match an empty substring is repeated with an
2025           unbounded upper limit, the subject position at the start of  the  group
2026           must be remembered, so that a test for an empty string can be made when
2027           the end of the group is reached. Some workspace is required  for  this;
2028           if it runs out, this error is given.
2029    
2030             PCRE_ERROR_BADNEWLINE     (-23)
2031    
2032  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2033    
2034       int pcre_exec(const pcre *code, const pcre_extra *extra,         Error numbers -16 to -20 are not used by pcre_exec().
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
   
      The function pcre_exec() is called to match a subject string  
      against  a pre-compiled pattern, which is passed in the code  
      argument. If the pattern has been studied, the result of the  
      study should be passed in the extra argument.  
   
      Here is an example of a simple call to pcre_exec():  
   
        int rc;  
        int ovector[30];  
        rc = pcre_exec(  
          re,             /* result of pcre_compile() */  
          NULL,           /* we didn't study the pattern */  
          "some string",  /* the subject string */  
          11,             /* the length of the subject string */  
          0,              /* start at offset 0 in the subject */  
          0,              /* default options */  
          ovector,        /* vector for substring information */  
          30);            /* number of elements in the vector */  
   
      If the extra argument is  not  NULL,  it  must  point  to  a  
      pcre_extra  data  block.  The  pcre_study() function returns  
      such a block (when it doesn't return NULL), but you can also  
      create  one for yourself, and pass additional information in  
      it. The fields in the block are as follows:  
   
        unsigned long int flags;  
        void *study_data;  
        unsigned long int match_limit;  
        void *callout_data;  
   
      The flags field is a bitmap  that  specifies  which  of  the  
      other fields are set. The flag bits are:  
   
        PCRE_EXTRA_STUDY_DATA  
        PCRE_EXTRA_MATCH_LIMIT  
        PCRE_EXTRA_CALLOUT_DATA  
   
      Other flag bits should be set to zero. The study_data  field  
      is   set  in  the  pcre_extra  block  that  is  returned  by  
      pcre_study(), together with the appropriate  flag  bit.  You  
      should  not  set this yourself, but you can add to the block  
      by setting the other fields.  
   
      The match_limit field provides a means  of  preventing  PCRE  
      from  using  up a vast amount of resources when running pat-  
      terns that are not going to match, but  which  have  a  very  
      large  number  of  possibilities  in their search trees. The  
      classic example is the  use  of  nested  unlimited  repeats.  
      Internally,  PCRE  uses  a  function called match() which it  
      calls  repeatedly  (sometimes  recursively).  The  limit  is  
      imposed  on the number of times this function is called dur-  
      ing a match, which has the effect of limiting the amount  of  
      recursion and backtracking that can take place. For patterns  
      that are not anchored, the count starts from zero  for  each  
      position in the subject string.  
   
      The default limit for the library can be set  when  PCRE  is  
      built;  the default default is 10 million, which handles all  
      but the most extreme cases. You can reduce  the  default  by  
      suppling  pcre_exec()  with  a  pcre_extra  block  in  which  
      match_limit   is   set   to    a    smaller    value,    and  
      PCRE_EXTRA_MATCH_LIMIT  is  set  in  the flags field. If the  
      limit      is      exceeded,       pcre_exec()       returns  
      PCRE_ERROR_MATCHLIMIT.  
   
      The pcre_callout field is used in conjunction with the "cal-  
      lout"  feature,  which is described in the pcrecallout docu-  
      mentation.  
   
      The PCRE_ANCHORED option can be passed in the options  argu-  
      ment,   whose   unused   bits  must  be  zero.  This  limits  
      pcre_exec() to matching at the first matching position. How-  
      ever,  if  a  pattern  was  compiled  with PCRE_ANCHORED, or  
      turned out to be anchored by virtue of its contents, it can-  
      not be made unachored at matching time.  
   
      There are also three further options that can be set only at  
      matching time:  
   
        PCRE_NOTBOL  
   
      The first character of the string is not the beginning of  a  
      line,  so  the  circumflex  metacharacter  should  not match  
      before it. Setting this without PCRE_MULTILINE  (at  compile  
      time) causes circumflex never to match.  
   
        PCRE_NOTEOL  
   
      The end of the string is not the end of a line, so the  dol-  
      lar  metacharacter should not match it nor (except in multi-  
      line mode) a newline immediately  before  it.  Setting  this  
      without PCRE_MULTILINE (at compile time) causes dollar never  
      to match.  
   
        PCRE_NOTEMPTY  
   
      An empty string is not considered to be  a  valid  match  if  
      this  option  is  set. If there are alternatives in the pat-  
      tern, they are tried. If  all  the  alternatives  match  the  
      empty  string,  the  entire match fails. For example, if the  
      pattern  
   
        a?b?  
   
      is applied to a string not beginning with  "a"  or  "b",  it  
      matches  the  empty string at the start of the subject. With  
      PCRE_NOTEMPTY set, this match is not valid, so PCRE searches  
      further into the string for occurrences of "a" or "b".  
   
      Perl has no direct equivalent of PCRE_NOTEMPTY, but it  does  
      make  a  special case of a pattern match of the empty string  
      within its split() function, and when using the /g modifier.  
      It  is possible to emulate Perl's behaviour after matching a  
      null string by first trying the  match  again  at  the  same  
      offset  with  PCRE_NOTEMPTY  set,  and then if that fails by  
      advancing the starting offset  (see  below)  and  trying  an  
      ordinary match again.  
   
      The subject string is passed to pcre_exec() as a pointer  in  
      subject,  a length in length, and a starting offset in star-  
      toffset. Unlike the pattern string, the subject may  contain  
      binary  zero  bytes.  When  the starting offset is zero, the  
      search for a match starts at the beginning of  the  subject,  
      and this is by far the most common case.  
   
      If the pattern was compiled with the PCRE_UTF8  option,  the  
      subject  must  be  a sequence of bytes that is a valid UTF-8  
      string.  If  an  invalid  UTF-8  string  is  passed,  PCRE's  
      behaviour is not defined.  
   
      A non-zero starting offset  is  useful  when  searching  for  
      another  match  in  the  same subject by calling pcre_exec()  
      again after a previous success.  Setting startoffset differs  
      from  just  passing  over  a  shortened  string  and setting  
      PCRE_NOTBOL in the case of a pattern that  begins  with  any  
      kind of lookbehind. For example, consider the pattern  
   
        \Biss\B  
   
      which finds occurrences of "iss" in the middle of words. (\B  
      matches only if the current position in the subject is not a  
      word boundary.) When applied to the string "Mississipi"  the  
      first  call  to  pcre_exec()  finds the first occurrence. If  
      pcre_exec() is called again with just the remainder  of  the  
      subject,  namely  "issipi", it does not match, because \B is  
      always false at the start of the subject, which is deemed to  
      be  a  word  boundary. However, if pcre_exec() is passed the  
      entire string again, but with startoffset set to 4, it finds  
      the  second  occurrence  of "iss" because it is able to look  
      behind the starting point to discover that it is preceded by  
      a letter.  
   
      If a non-zero starting offset is passed when the pattern  is  
      anchored, one attempt to match at the given offset is tried.  
      This can only succeed if the pattern does  not  require  the  
      match to be at the start of the subject.  
   
      In general, a pattern matches a certain portion of the  sub-  
      ject,  and  in addition, further substrings from the subject  
      may be picked out by parts of  the  pattern.  Following  the  
      usage  in  Jeffrey Friedl's book, this is called "capturing"  
      in what follows, and the phrase  "capturing  subpattern"  is  
      used for a fragment of a pattern that picks out a substring.  
      PCRE supports several other kinds of  parenthesized  subpat-  
      tern that do not cause substrings to be captured.  
   
      Captured substrings are returned to the caller via a  vector  
      of  integer  offsets whose address is passed in ovector. The  
      number of elements in the vector is passed in ovecsize.  The  
      first two-thirds of the vector is used to pass back captured  
      substrings, each substring using a  pair  of  integers.  The  
      remaining  third  of  the  vector  is  used  as workspace by  
      pcre_exec() while matching capturing subpatterns, and is not  
      available for passing back information. The length passed in  
      ovecsize should always be a multiple of three. If it is not,  
      it is rounded down.  
   
      When a match has been successful, information about captured  
      substrings is returned in pairs of integers, starting at the  
      beginning of ovector, and continuing up to two-thirds of its  
      length  at  the  most. The first element of a pair is set to  
      the offset of the first character in a  substring,  and  the  
      second is set to the offset of the first character after the  
      end of a substring. The first  pair,  ovector[0]  and  ovec-  
      tor[1],  identify  the portion of the subject string matched  
      by the entire pattern. The next pair is used for  the  first  
      capturing  subpattern,  and  so  on.  The  value returned by  
      pcre_exec() is the number of pairs that have  been  set.  If  
      there  are no capturing subpatterns, the return value from a  
      successful match is 1, indicating that just the  first  pair  
      of offsets has been set.  
   
      Some convenience functions are provided for  extracting  the  
      captured substrings as separate strings. These are described  
      in the following section.  
   
      It is possible for an capturing  subpattern  number  n+1  to  
      match  some  part  of  the subject when subpattern n has not  
      been used at all.  For  example,  if  the  string  "abc"  is  
      matched  against the pattern (a|(z))(bc) subpatterns 1 and 3  
      are matched, but 2 is not. When this  happens,  both  offset  
      values corresponding to the unused subpattern are set to -1.  
   
      If a capturing subpattern is matched repeatedly, it  is  the  
      last  portion  of  the  string  that  it  matched  that gets  
      returned.  
   
      If the vector is too small to hold  all  the  captured  sub-  
      strings,  it is used as far as possible (up to two-thirds of  
      its length), and the function returns a value  of  zero.  In  
      particular,  if  the  substring offsets are not of interest,  
      pcre_exec() may be called with ovector passed  as  NULL  and  
      ovecsize  as  zero.  However,  if  the pattern contains back  
      references and the ovector isn't big enough to remember  the  
      related  substrings,  PCRE  has to get additional memory for  
      use during matching. Thus it is usually advisable to  supply  
      an ovector.  
   
      Note that pcre_info() can be used to find out how many  cap-  
      turing  subpatterns  there  are  in  a compiled pattern. The  
      smallest size for ovector that will  allow  for  n  captured  
      substrings,  in  addition  to  the  offsets of the substring  
      matched by the whole pattern, is (n+1)*3.  
   
      If pcre_exec() fails, it returns a negative number. The fol-  
      lowing are defined in the header file:  
   
        PCRE_ERROR_NOMATCH        (-1)  
   
      The subject string did not match the pattern.  
   
        PCRE_ERROR_NULL           (-2)  
   
      Either code or subject was passed as NULL,  or  ovector  was  
      NULL and ovecsize was not zero.  
   
        PCRE_ERROR_BADOPTION      (-3)  
   
      An unrecognized bit was set in the options argument.  
   
        PCRE_ERROR_BADMAGIC       (-4)  
   
      PCRE stores a 4-byte "magic number" at the start of the com-  
      piled  code,  to  catch  the  case  when it is passed a junk  
      pointer. This is the error it gives when  the  magic  number  
      isn't present.  
   
        PCRE_ERROR_UNKNOWN_NODE   (-5)  
   
      While running the pattern match, an unknown item was encoun-  
      tered in the compiled pattern. This error could be caused by  
      a bug in PCRE or by overwriting of the compiled pattern.  
   
        PCRE_ERROR_NOMEMORY       (-6)  
   
      If a pattern contains back references, but the ovector  that  
      is  passed  to pcre_exec() is not big enough to remember the  
      referenced substrings, PCRE gets a block of  memory  at  the  
      start  of  matching to use for this purpose. If the call via  
      pcre_malloc() fails, this error  is  given.  The  memory  is  
      freed at the end of matching.  
   
        PCRE_ERROR_NOSUBSTRING    (-7)  
   
      This   error   is   used   by   the   pcre_copy_substring(),  
      pcre_get_substring(),  and  pcre_get_substring_list()  func-  
      tions (see below). It is never returned by pcre_exec().  
   
        PCRE_ERROR_MATCHLIMIT     (-8)  
   
      The recursion and backtracking limit, as  specified  by  the  
      match_limit  field  in a pcre_extra structure (or defaulted)  
      was reached. See the description above.  
   
        PCRE_ERROR_CALLOUT        (-9)  
   
      This error is never generated by pcre_exec() itself.  It  is  
      provided  for  use by callout functions that want to yield a  
      distinctive error code. See  the  pcrecallout  documentation  
      for details.  
2035    
2036    
2037  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2038    
2039       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2040            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2041            int buffersize);              int buffersize);
2042    
2043       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2044            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2045            const char **stringptr);              const char **stringptr);
2046    
2047       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2048            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2049    
2050       Captured substrings can be accessed directly  by  using  the         Captured  substrings  can  be  accessed  directly  by using the offsets
2051       offsets returned by pcre_exec() in ovector. For convenience,         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2052       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2053       and  pcre_get_substring_list()  are  provided for extracting         string_list() are provided for extracting captured substrings  as  new,
2054       captured  substrings  as  new,   separate,   zero-terminated         separate,  zero-terminated strings. These functions identify substrings
2055       strings.  These functions identify substrings by number. The         by number. The next section describes functions  for  extracting  named
2056       next section describes functions for extracting  named  sub-         substrings.
2057       strings.   A  substring  that  contains  a  binary  zero  is  
2058       correctly extracted and has a further zero added on the end,         A  substring that contains a binary zero is correctly extracted and has
2059       but the result is not, of course, a C string.         a further zero added on the end, but the result is not, of course, a  C
2060           string.   However,  you  can  process such a string by referring to the
2061       The first three arguments are the  same  for  all  three  of         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2062       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2063       just been successfully matched, ovector is a pointer to  the         not adequate for handling strings containing binary zeros, because  the
2064       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2065       and stringcount is the number of substrings that  were  cap-  
2066       tured by the match, including the substring that matched the         The  first  three  arguments  are the same for all three of these func-
2067       entire regular expression. This is  the  value  returned  by         tions: subject is the subject string that has  just  been  successfully
2068       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2069       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2070       tor,  the  value passed as stringcount should be the size of         were  captured  by  the match, including the substring that matched the
2071       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2072           it  is greater than zero. If pcre_exec() returned zero, indicating that
2073       The functions pcre_copy_substring() and pcre_get_substring()         it ran out of space in ovector, the value passed as stringcount  should
2074       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2075       number. A value of zero extracts the substring that  matched  
2076       the entire pattern, while higher values extract the captured         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2077       substrings. For pcre_copy_substring(), the string is  placed         single substring, whose number is given as  stringnumber.  A  value  of
2078       in  buffer,  whose  length is given by buffersize, while for         zero  extracts  the  substring that matched the entire pattern, whereas
2079       pcre_get_substring() a new block of memory is  obtained  via         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2080       pcre_malloc,  and its address is returned via stringptr. The         string(),  the  string  is  placed  in buffer, whose length is given by
2081       yield of the function is  the  length  of  the  string,  not         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2082       including the terminating zero, or one of         obtained  via  pcre_malloc,  and its address is returned via stringptr.
2083           The yield of the function is the length of the  string,  not  including
2084         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2085    
2086       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2087       attempt to get memory failed for pcre_get_substring().  
2088           The  buffer  was too small for pcre_copy_substring(), or the attempt to
2089         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2090    
2091       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2092    
2093       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2094       able  substrings  and builds a list of pointers to them. All  
2095       this is done in a single block of memory which  is  obtained         The pcre_get_substring_list()  function  extracts  all  available  sub-
2096       via pcre_malloc. The address of the memory block is returned         strings  and  builds  a list of pointers to them. All this is done in a
2097       via listptr, which is also the start of the list  of  string         single block of memory that is obtained via pcre_malloc. The address of
2098       pointers.  The  end of the list is marked by a NULL pointer.         the  memory  block  is returned via listptr, which is also the start of
2099       The yield of the function is zero if all went well, or         the list of string pointers. The end of the list is marked  by  a  NULL
2100           pointer.  The  yield  of  the function is zero if all went well, or the
2101         PCRE_ERROR_NOMEMORY       (-6)         error code
2102    
2103       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2104    
2105       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2106       unset, which can happen when capturing subpattern number n+1  
2107       matches some part of the subject, but subpattern n  has  not         When any of these functions encounter a substring that is unset,  which
2108       been  used  at all, they return an empty string. This can be         can  happen  when  capturing subpattern number n+1 matches some part of
2109       distinguished  from  a  genuine  zero-length  substring   by         the subject, but subpattern n has not been used at all, they return  an
2110       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2111       tive for unset substrings.         string by inspecting the appropriate offset in ovector, which is  nega-
2112           tive for unset substrings.
2113       The  two  convenience  functions  pcre_free_substring()  and  
2114       pcre_free_substring_list()  can  be  used to free the memory         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2115       returned by  a  previous  call  of  pcre_get_substring()  or         string_list() can be used to free the memory  returned  by  a  previous
2116       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2117       more than call the function pointed to by  pcre_free,  which         tively. They do nothing more than  call  the  function  pointed  to  by
2118       of  course  could  be called directly from a C program. How-         pcre_free,  which  of course could be called directly from a C program.
2119       ever, PCRE is used in some situations where it is linked via         However, PCRE is used in some situations where it is linked via a  spe-
2120       a  special  interface  to another programming language which         cial   interface  to  another  programming  language  that  cannot  use
2121       cannot use pcre_free directly; it is for  these  cases  that         pcre_free directly; it is for these cases that the functions  are  pro-
2122       the functions are provided.         vided.
2123    
2124    
2125  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2126    
2127       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2128            const char *subject, int *ovector,              const char *name);
2129            int stringcount, const char *stringname,  
2130            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2131                const char *subject, int *ovector,
2132       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2133            const char *name);              char *buffer, int buffersize);
2134    
2135       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2136            const char *subject, int *ovector,              const char *subject, int *ovector,
2137            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2138            const char **stringptr);              const char **stringptr);
2139    
2140       To extract a substring by name, you first have to find asso-         To  extract a substring by name, you first have to find associated num-
2141       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2142       pcre_get_stringnumber(). The first argument is the  compiled  
2143       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2144       pattern  
2145           the number of the subpattern called "xxx" is 2. If the name is known to
2146         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2147           name by calling pcre_get_stringnumber(). The first argument is the com-
2148       the number of the subpattern called "xxx" is  1.  Given  the         piled pattern, and the second is the name. The yield of the function is
2149       number,  you can then extract the substring directly, or use         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2150       one of the functions described in the previous section.  For         subpattern of that name.
2151       convenience,  there are also two functions that do the whole  
2152       job.         Given the number, you can extract the substring directly, or use one of
2153           the functions described in the previous section. For convenience, there
2154       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2155       pcre_get_named_substring()  are  the  same  as those for the  
2156       functions that  extract  by  number,  and  so  are  not  re-         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2157       described here. There are just two differences.         pcre_get_named_substring() are the same  as  those  for  the  similarly
2158           named  functions  that extract by number. As these are described in the
2159       First, instead of a substring number, a  substring  name  is         previous section, they are not re-described here. There  are  just  two
2160       given.  Second,  there  is  an  extra argument, given at the         differences:
2161       start, which is a pointer to the compiled pattern.  This  is  
2162       needed  in order to gain access to the name-to-number trans-         First,  instead  of a substring number, a substring name is given. Sec-
2163       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2164           to  the compiled pattern. This is needed in order to gain access to the
2165       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2166       succeeds,    they   then   call   pcre_copy_substring()   or  
2167       pcre_get_substring(), as appropriate.         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2168           then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2169           ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2170           behaviour may not be what you want (see the next section).
2171    
2172    
2173    DUPLICATE SUBPATTERN NAMES
2174    
2175           int pcre_get_stringtable_entries(const pcre *code,
2176                const char *name, char **first, char **last);
2177    
2178           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2179           subpatterns are not required to  be  unique.  Normally,  patterns  with
2180           duplicate  names  are such that in any one match, only one of the named
2181           subpatterns participates. An example is shown in the pcrepattern  docu-
2182           mentation. When duplicates are present, pcre_copy_named_substring() and
2183           pcre_get_named_substring() return the first substring corresponding  to
2184           the  given  name  that  is  set.  If  none  are set, an empty string is
2185           returned.  The pcre_get_stringnumber() function returns one of the num-
2186           bers  that are associated with the name, but it is not defined which it
2187           is.
2188    
2189           If you want to get full details of all captured substrings for a  given
2190           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2191           first argument is the compiled pattern, and the second is the name. The
2192           third  and  fourth  are  pointers to variables which are updated by the
2193           function. After it has run, they point to the first and last entries in
2194           the  name-to-number  table  for  the  given  name.  The function itself
2195           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2196           there  are none. The format of the table is described above in the sec-
2197           tion entitled Information about a  pattern.   Given  all  the  relevant
2198           entries  for the name, you can extract each of their numbers, and hence
2199           the captured data, if any.
2200    
2201    
2202    FINDING ALL POSSIBLE MATCHES
2203    
2204           The traditional matching function uses a  similar  algorithm  to  Perl,
2205           which stops when it finds the first match, starting at a given point in
2206           the subject. If you want to find all possible matches, or  the  longest
2207           possible  match,  consider using the alternative matching function (see
2208           below) instead. If you cannot use the alternative function,  but  still
2209           need  to  find all possible matches, you can kludge it up by making use
2210           of the callout facility, which is described in the pcrecallout documen-
2211           tation.
2212    
2213           What you have to do is to insert a callout right at the end of the pat-
2214           tern.  When your callout function is called, extract and save the  cur-
2215           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2216           backtrack and try other alternatives. Ultimately, when it runs  out  of
2217           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2218    
2219    
2220    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2221    
2222           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2223                const char *subject, int length, int startoffset,
2224                int options, int *ovector, int ovecsize,
2225                int *workspace, int wscount);
2226    
2227           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2228           against a compiled pattern, using a matching algorithm that  scans  the
2229           subject  string  just  once, and does not backtrack. This has different
2230           characteristics to the normal algorithm, and  is  not  compatible  with
2231           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2232           theless, there are times when this kind of matching can be useful.  For
2233           a discussion of the two matching algorithms, see the pcrematching docu-
2234           mentation.
2235    
2236           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2237           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2238           ent way, and this is described below. The other  common  arguments  are
2239           used  in  the  same way as for pcre_exec(), so their description is not
2240           repeated here.
2241    
2242           The two additional arguments provide workspace for  the  function.  The
2243           workspace  vector  should  contain at least 20 elements. It is used for
2244           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2245           workspace  will  be  needed for patterns and subjects where there are a
2246           lot of potential matches.
2247    
2248           Here is an example of a simple call to pcre_dfa_exec():
2249    
2250             int rc;
2251             int ovector[10];
2252             int wspace[20];
2253             rc = pcre_dfa_exec(
2254               re,             /* result of pcre_compile() */
2255               NULL,           /* we didn't study the pattern */
2256               "some string",  /* the subject string */
2257               11,             /* the length of the subject string */
2258               0,              /* start at offset 0 in the subject */
2259               0,              /* default options */
2260               ovector,        /* vector of integers for substring information */
2261               10,             /* number of elements (NOT size in bytes) */
2262               wspace,         /* working space vector */
2263               20);            /* number of elements (NOT size in bytes) */
2264    
2265       Option bits for pcre_dfa_exec()
2266    
2267           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2268           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2269           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2270           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2271           three of these are the same as for pcre_exec(), so their description is
2272           not repeated here.
2273    
2274             PCRE_PARTIAL
2275    
2276           This  has  the  same general effect as it does for pcre_exec(), but the
2277           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2278           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2279           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2280           been no complete matches, but there is still at least one matching pos-
2281           sibility. The portion of the string that provided the partial match  is
2282           set as the first matching string.
2283    
2284             PCRE_DFA_SHORTEST
2285    
2286           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2287           stop as soon as it has found one match. Because of the way the alterna-
2288           tive  algorithm  works, this is necessarily the shortest possible match
2289           at the first possible matching point in the subject string.
2290    
2291             PCRE_DFA_RESTART
2292    
2293           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2294           returns  a  partial  match, it is possible to call it again, with addi-
2295           tional subject characters, and have it continue with  the  same  match.
2296           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2297           workspace and wscount options must reference the same vector as  before
2298           because  data  about  the  match so far is left in them after a partial
2299           match. There is more discussion of this  facility  in  the  pcrepartial
2300           documentation.
2301    
2302       Successful returns from pcre_dfa_exec()
2303    
2304           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2305           string in the subject. Note, however, that all the matches from one run
2306           of  the  function  start  at the same point in the subject. The shorter
2307           matches are all initial substrings of the longer matches. For  example,
2308           if the pattern
2309    
2310             <.*>
2311    
2312           is matched against the string
2313    
2314             This is <something> <something else> <something further> no more
2315    
2316           the three matched strings are
2317    
2318             <something>
2319             <something> <something else>
2320             <something> <something else> <something further>
2321    
2322           On  success,  the  yield of the function is a number greater than zero,
2323           which is the number of matched substrings.  The  substrings  themselves
2324           are  returned  in  ovector. Each string uses two elements; the first is
2325           the offset to the start, and the second is the offset to  the  end.  In
2326           fact,  all  the  strings  have the same start offset. (Space could have
2327           been saved by giving this only once, but it was decided to retain  some
2328           compatibility  with  the  way pcre_exec() returns data, even though the
2329           meaning of the strings is different.)
2330    
2331           The strings are returned in reverse order of length; that is, the long-
2332           est  matching  string is given first. If there were too many matches to
2333           fit into ovector, the yield of the function is zero, and the vector  is
2334           filled with the longest matches.
2335    
2336       Error returns from pcre_dfa_exec()
2337    
2338           The  pcre_dfa_exec()  function returns a negative number when it fails.
2339           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2340           described  above.   There are in addition the following errors that are
2341           specific to pcre_dfa_exec():
2342    
2343             PCRE_ERROR_DFA_UITEM      (-16)
2344    
2345           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2346           tern  that  it  does not support, for instance, the use of \C or a back
2347           reference.
2348    
2349             PCRE_ERROR_DFA_UCOND      (-17)
2350    
2351           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2352           that  uses  a back reference for the condition, or a test for recursion
2353           in a specific group. These are not supported.
2354    
2355             PCRE_ERROR_DFA_UMLIMIT    (-18)
2356    
2357           This return is given if pcre_dfa_exec() is called with an  extra  block
2358           that contains a setting of the match_limit field. This is not supported
2359           (it is meaningless).
2360    
2361             PCRE_ERROR_DFA_WSSIZE     (-19)
2362    
2363           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2364           workspace vector.
2365    
2366             PCRE_ERROR_DFA_RECURSE    (-20)
2367    
2368           When  a  recursive subpattern is processed, the matching function calls
2369           itself recursively, using private vectors for  ovector  and  workspace.
2370           This  error  is  given  if  the output vector is not large enough. This
2371           should be extremely rare, as a vector of size 1000 is used.
2372    
2373    
2374    SEE ALSO
2375    
2376           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2377           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2378    
2379    
2380    AUTHOR
2381    
2382           Philip Hazel
2383           University Computing Service
2384           Cambridge CB2 3QH, England.
2385    
2386    
2387    REVISION
2388    
2389           Last updated: 16 April 2007
2390           Copyright (c) 1997-2007 University of Cambridge.
2391    ------------------------------------------------------------------------------
2392    
2393    
2394    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2395    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2396    
2397  NAME  NAME
2398       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2399    
2400    
2401  PCRE CALLOUTS  PCRE CALLOUTS
2402    
2403       int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
   
      PCRE provides a feature called "callout", which is  a  means  
      of  temporarily passing control to the caller of PCRE in the  
      middle of pattern matching. The caller of PCRE  provides  an  
      external  function  by putting its entry point in the global  
      variable pcre_callout. By default,  this  variable  contains  
      NULL, which disables all calling out.  
   
      Within a regular expression, (?C) indicates  the  points  at  
      which  the external function is to be called. Different cal-  
      lout points can be identified by putting a number less  than  
      256  after  the  letter  C.  The default value is zero.  For  
      example, this pattern has two callout points:  
   
        (?C1)9abc(?C2)def  
   
      During matching, when PCRE  reaches  a  callout  point  (and  
      pcre_callout  is  set), the external function is called. Its  
      only argument is a pointer to  a  pcre_callout  block.  This  
      contains the following variables:  
   
        int          version;  
        int          callout_number;  
        int         *offset_vector;  
        const char  *subject;  
        int          subject_length;  
        int          start_match;  
        int          current_position;  
        int          capture_top;  
        int          capture_last;  
        void        *callout_data;  
   
      The version field  is  an  integer  containing  the  version  
      number of the block format. The current version is zero. The  
      version number may change in future if additional fields are  
      added,  but  the  intention  is  never  to remove any of the  
      existing fields.  
   
      The callout_number field contains the number of the callout,  
      as compiled into the pattern (that is, the number after ?C).  
   
      The offset_vector field  is  a  pointer  to  the  vector  of  
      offsets  that  was  passed by the caller to pcre_exec(). The  
      contents can be inspected in  order  to  extract  substrings  
      that  have  been  matched  so  far,  in  the same way as for  
      extracting substrings after a match has completed.  
      The subject and subject_length  fields  contain  copies  the  
      values that were passed to pcre_exec().  
   
      The start_match field contains the offset within the subject  
      at  which  the current match attempt started. If the pattern  
      is not anchored, the callout function may be called  several  
      times for different starting points.  
   
      The current_position field contains the  offset  within  the  
      subject of the current match pointer.  
   
      The capture_top field contains the  number  of  the  highest  
      captured substring so far.  
   
      The capture_last field  contains  the  number  of  the  most  
      recently captured substring.  
   
      The callout_data field contains a value that  is  passed  to  
      pcre_exec()  by  the  caller  specifically so that it can be  
      passed back in callouts. It is passed  in  the  pcre_callout  
      field  of the pcre_extra data structure. If no such data was  
      passed, the value of callout_data in a pcre_callout block is  
      NULL.  There is a description of the pcre_extra structure in  
      the pcreapi documentation.  
2404    
2405           PCRE provides a feature called "callout", which is a means of temporar-
2406           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2407           matching.  The  caller of PCRE provides an external function by putting
2408           its entry point in the global variable pcre_callout. By  default,  this
2409           variable contains NULL, which disables all calling out.
2410    
2411           Within  a  regular  expression,  (?C) indicates the points at which the
2412           external function is to be called.  Different  callout  points  can  be
2413           identified  by  putting  a number less than 256 after the letter C. The
2414           default value is zero.  For  example,  this  pattern  has  two  callout
2415           points:
2416    
2417             (?C1)eabc(?C2)def
2418    
2419           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2420           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2421           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2422           used with the pattern
2423    
2424             A(\d{2}|--)
2425    
2426           it is processed as if it were
2427    
2428           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2429    
2430           Notice that there is a callout before and after  each  parenthesis  and
2431           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2432           progress of pattern matching. The pcretest command has an  option  that
2433           sets  automatic callouts; when it is used, the output indicates how the
2434           pattern is matched. This is useful information when you are  trying  to
2435           optimize the performance of a particular pattern.
2436    
2437    
2438    MISSING CALLOUTS
2439    
2440           You  should  be  aware  that,  because of optimizations in the way PCRE
2441           matches patterns, callouts sometimes do not happen. For example, if the
2442           pattern is
2443    
2444             ab(?C4)cd
2445    
2446           PCRE knows that any matching string must contain the letter "d". If the
2447           subject string is "abyz", the lack of "d" means that  matching  doesn't
2448           ever  start,  and  the  callout is never reached. However, with "abyd",
2449           though the result is still no match, the callout is obeyed.
2450    
2451    
2452    THE CALLOUT INTERFACE
2453    
2454           During matching, when PCRE reaches a callout point, the external  func-
2455           tion  defined by pcre_callout is called (if it is set). This applies to
2456           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2457           only  argument  to  the callout function is a pointer to a pcre_callout
2458           block. This structure contains the following fields:
2459    
2460             int          version;
2461             int          callout_number;
2462             int         *offset_vector;
2463             const char  *subject;
2464             int          subject_length;
2465             int          start_match;
2466             int          current_position;
2467             int          capture_top;
2468             int          capture_last;
2469             void        *callout_data;
2470             int          pattern_position;
2471             int          next_item_length;
2472    
2473           The version field is an integer containing the version  number  of  the
2474           block  format. The initial version was 0; the current version is 1. The
2475           version number will change again in future  if  additional  fields  are
2476           added, but the intention is never to remove any of the existing fields.
2477    
2478           The callout_number field contains the number of the  callout,  as  com-
2479           piled  into  the pattern (that is, the number after ?C for manual call-
2480           outs, and 255 for automatically generated callouts).
2481    
2482           The offset_vector field is a pointer to the vector of offsets that  was
2483           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2484           pcre_exec() is used, the contents can be inspected in order to  extract
2485           substrings  that  have  been  matched  so  far,  in the same way as for
2486           extracting substrings after a match has completed. For  pcre_dfa_exec()
2487           this field is not useful.
2488    
2489           The subject and subject_length fields contain copies of the values that
2490           were passed to pcre_exec().
2491    
2492           The start_match field contains the offset within the subject  at  which
2493           the  current match attempt started. If the pattern is not anchored, the
2494           callout function may be called several times from the same point in the
2495           pattern for different starting points in the subject.
2496    
2497           The  current_position  field  contains the offset within the subject of
2498           the current match pointer.
2499    
2500           When the pcre_exec() function is used, the capture_top  field  contains
2501           one  more than the number of the highest numbered captured substring so
2502           far. If no substrings have been captured, the value of  capture_top  is
2503           one.  This  is always the case when pcre_dfa_exec() is used, because it
2504           does not support captured substrings.
2505    
2506           The capture_last field contains the number of the  most  recently  cap-
2507           tured  substring. If no substrings have been captured, its value is -1.
2508           This is always the case when pcre_dfa_exec() is used.
2509    
2510           The callout_data field contains a value that is passed  to  pcre_exec()
2511           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2512           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2513           structure.  If  no such data was passed, the value of callout_data in a
2514           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2515           structure in the pcreapi documentation.
2516    
2517           The  pattern_position field is present from version 1 of the pcre_call-
2518           out structure. It contains the offset to the next item to be matched in
2519           the pattern string.
2520    
2521           The  next_item_length field is present from version 1 of the pcre_call-
2522           out structure. It contains the length of the next item to be matched in
2523           the  pattern  string. When the callout immediately precedes an alterna-
2524           tion bar, a closing parenthesis, or the end of the pattern, the  length
2525           is  zero.  When the callout precedes an opening parenthesis, the length
2526           is that of the entire subpattern.
2527    
2528           The pattern_position and next_item_length fields are intended  to  help
2529           in  distinguishing between different automatic callouts, which all have
2530           the same callout number. However, they are set for all callouts.
2531    
2532    
2533  RETURN VALUES  RETURN VALUES
2534    
2535       The callout function returns an integer.  If  the  value  is         The external callout function returns an integer to PCRE. If the  value
2536       zero,  matching  proceeds as normal. If the value is greater         is  zero,  matching  proceeds  as  normal. If the value is greater than
2537       than zero, matching fails at the current  point,  but  back-         zero, matching fails at the current point, but  the  testing  of  other
2538       tracking  to test other possibilities goes ahead, just as if         matching possibilities goes ahead, just as if a lookahead assertion had
2539       a lookahead assertion had failed. If the value is less  than         failed. If the value is less than zero, the  match  is  abandoned,  and
2540       zero,  the  match  is abandoned, and pcre_exec() returns the         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2541       value.  
2542           Negative   values   should   normally   be   chosen  from  the  set  of
2543       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2544       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2545       forces a standard "no  match"  failure.   The  error  number         reserved for use by callout functions; it will never be  used  by  PCRE
2546       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
2547       it will never be used by PCRE itself.  
2548    
2549    AUTHOR
2550    
2551           Philip Hazel
2552           University Computing Service
2553           Cambridge CB2 3QH, England.
2554    
2555    
2556    REVISION
2557    
2558           Last updated: 06 March 2007
2559           Copyright (c) 1997-2007 University of Cambridge.
2560    ------------------------------------------------------------------------------
2561    
2562    
2563    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2564    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2565    
2566  NAME  NAME
2567       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2568    
2569    
2570  DIFFERENCES FROM PERL  DIFFERENCES BETWEEN PCRE AND PERL
2571    
2572       This document describes the differences  in  the  ways  that         This  document describes the differences in the ways that PCRE and Perl
2573       PCRE  and  Perl  handle regular expressions. The differences         handle regular expressions. The differences described here  are  mainly
2574       described here are with respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE version 7.0 contains some fea-
2575           tures that are expected to be in the forthcoming Perl 5.10.
2576       1. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
2577       assertions. Perl permits them, but they do not mean what you         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2578       might think. For example, (?!a){3} does not assert that  the         of  what  it does have are given in the section on UTF-8 support in the
2579       next  three characters are not "a". It just asserts that the         main pcre page.
2580       next character is not "a" three times.  
2581           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2582       2. Capturing subpatterns that occur inside  negative  looka-         permits  them,  but they do not mean what you might think. For example,
2583       head  assertions  are  counted,  but  their  entries  in the         (?!a){3} does not assert that the next three characters are not "a". It
2584       offsets vector are never set. Perl sets its numerical  vari-         just asserts that the next character is not "a" three times.
2585       ables  from  any  such  patterns that are matched before the  
2586       assertion fails to match something (thereby succeeding), but         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2587       only  if  the negative lookahead assertion contains just one         tions are counted, but their entries in the offsets  vector  are  never
2588       branch.         set.  Perl sets its numerical variables from any such patterns that are
2589           matched before the assertion fails to match something (thereby succeed-
2590       3. Though binary zero characters are supported in  the  sub-         ing),  but  only  if the negative lookahead assertion contains just one
2591       ject  string,  they  are  not  allowed  in  a pattern string         branch.
2592       because it is passed as a normal  C  string,  terminated  by  
2593       zero. The escape sequence "\0" can be used in the pattern to         4. Though binary zero characters are supported in the  subject  string,
2594       represent a binary zero.         they are not allowed in a pattern string because it is passed as a nor-
2595           mal C string, terminated by zero. The escape sequence \0 can be used in
2596       4. The following Perl escape sequences  are  not  supported:         the pattern to represent a binary zero.
2597       \l,  \u,  \L,  \U,  \P, \p, and \X. In fact these are imple-  
2598       mented by Perl's general string-handling and are not part of         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2599       its pattern matching engine. If any of these are encountered         \U, and \N. In fact these are implemented by Perl's general string-han-
2600       by PCRE, an error is generated.         dling  and are not part of its pattern matching engine. If any of these
2601           are encountered by PCRE, an error is generated.
2602       5. PCRE does support the \Q...\E  escape  for  quoting  sub-  
2603       strings. Characters in between are treated as literals. This         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2604       is slightly different from Perl in that $  and  @  are  also         is  built  with Unicode character property support. The properties that
2605       handled  as  literals inside the quotes. In Perl, they cause         can be tested with \p and \P are limited to the general category  prop-
2606       variable interpolation (but of course  PCRE  does  not  have         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2607       variables). Note the following examples:         derived properties Any and L&.
2608    
2609           Pattern            PCRE matches      Perl matches         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2610           ters  in  between  are  treated as literals. This is slightly different
2611           \Qabc$xyz\E        abc$xyz           abc followed by the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2612                                                  contents of $xyz         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2613           \Qabc\$xyz\E       abc\$xyz          abc\$xyz         does not have variables). Note the following examples:
2614           \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz  
2615               Pattern            PCRE matches      Perl matches
2616       In PCRE, the \Q...\E mechanism is not  recognized  inside  a  
2617       character class.             \Qabc$xyz\E        abc$xyz           abc followed by the
2618                                                      contents of $xyz
2619       8. Fairly obviously, PCRE does not support the (?{code}) and             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2620       (?p{code})  constructions. However, there is some experimen-             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2621       tal support for recursive patterns using the non-Perl  items  
2622       (?R),  (?number)  and  (?P>name).  Also,  the PCRE "callout"         The \Q...\E sequence is recognized both inside  and  outside  character
2623       feature allows an external function to be called during pat-         classes.
2624       tern matching.  
2625           8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2626       9. There are some differences that are  concerned  with  the         constructions. However, there is support for recursive  patterns.  This
2627       settings  of  captured  strings  when  part  of a pattern is         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2628       repeated. For example, matching "aba"  against  the  pattern         "callout" feature allows an external function to be called during  pat-
2629       /^(a(b)?)+$/  in Perl leaves $2 unset, but in PCRE it is set         tern matching. See the pcrecallout documentation for details.
2630       to "b".  
2631           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2632       10. PCRE  provides  some  extensions  to  the  Perl  regular         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2633       expression facilities:         unlike Perl.
2634    
2635       (a) Although lookbehind assertions must match  fixed  length         10.  There are some differences that are concerned with the settings of
2636       strings,  each  alternative branch of a lookbehind assertion         captured strings when part of  a  pattern  is  repeated.  For  example,
2637       can match a different length of string. Perl  requires  them         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2638       all to have the same length.         unset, but in PCRE it is set to "b".
2639    
2640       (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not         11. PCRE provides some extensions to the Perl regular expression facil-
2641       set,  the  $  meta-character matches only at the very end of         ities.   Perl  5.10  will  include new features that are not in earlier
2642       the string.         versions, some of which (such as named parentheses) have been  in  PCRE
2643           for some time. This list is with respect to Perl 5.10:
2644       (c) If PCRE_EXTRA is set, a backslash followed by  a  letter  
2645       with no special meaning is faulted.         (a)  Although  lookbehind  assertions  must match fixed length strings,
2646           each alternative branch of a lookbehind assertion can match a different
2647       (d) If PCRE_UNGREEDY is set, the greediness of  the  repeti-         length of string. Perl requires them all to have the same length.
2648       tion  quantifiers  is inverted, that is, by default they are  
2649       not greedy, but if followed by a question mark they are.         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2650           meta-character matches only at the very end of the string.
2651       (e) PCRE_ANCHORED can be used to force a pattern to be tried  
2652       only at the first matching position in the subject string.         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2653           cial  meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash is
2654       (f)  The  PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   and         ignored. (Perl can be made to issue a warning.)
2655       PCRE_NO_AUTO_CAPTURE  options  for  pcre_exec() have no Perl  
2656       equivalents.         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2657           fiers is inverted, that is, by default they are not greedy, but if fol-
2658       (g) The (?R), (?number), and (?P>name) constructs allows for         lowed by a question mark they are.
2659       recursive  pattern  matching  (Perl  can  do  this using the  
2660       (?p{code}) construct, which PCRE cannot support.)         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2661           tried only at the first matching position in the subject string.
2662       (h) PCRE supports  named  capturing  substrings,  using  the  
2663       Python syntax.         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2664           TURE options for pcre_exec() have no Perl equivalents.
2665       (i) PCRE supports the  possessive  quantifier  "++"  syntax,  
2666       taken from Sun's Java package.         (g) The callout facility is PCRE-specific.
2667    
2668       (j) The (R) condition, for  testing  recursion,  is  a  PCRE         (h) The partial matching facility is PCRE-specific.
      extension.  
2669    
2670       (k) The callout facility is PCRE-specific.         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2671           even on different hosts that have the other endianness.
2672    
2673           (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2674           different way and is not Perl-compatible.
2675    
2676    
2677    AUTHOR
2678    
2679           Philip Hazel
2680           University Computing Service
2681           Cambridge CB2 3QH, England.
2682    
2683    
2684    REVISION
2685    
2686           Last updated: 06 March 2007
2687           Copyright (c) 1997-2007 University of Cambridge.
2688    ------------------------------------------------------------------------------
2689    
2690    
2691    PCREPATTERN(3)                                                  PCREPATTERN(3)
2692    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2693    
2694  NAME  NAME
2695       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2696    
2697    
2698  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2699    
2700       The syntax and semantics of  the  regular  expressions  sup-         The  syntax  and semantics of the regular expressions supported by PCRE
2701       ported  by PCRE are described below. Regular expressions are         are described below. Regular expressions are also described in the Perl
2702       also described in the Perl documentation and in a number  of         documentation  and  in  a  number  of books, some of which have copious
2703       other  books,  some  of which have copious examples. Jeffrey         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
2704       Friedl's  "Mastering  Regular  Expressions",  published   by         by  O'Reilly, covers regular expressions in great detail. This descrip-
2705       O'Reilly,  covers them in great detail. The description here         tion of PCRE's regular expressions is intended as reference material.
2706       is intended as reference documentation.  
2707           The original operation of PCRE was on strings of  one-byte  characters.
2708       The basic operation of PCRE is on strings of bytes. However,         However,  there is now also support for UTF-8 character strings. To use
2709       there  is  also  support for UTF-8 character strings. To use         this, you must build PCRE to  include  UTF-8  support,  and  then  call
2710       this support you must build PCRE to include  UTF-8  support,         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2711       and  then call pcre_compile() with the PCRE_UTF8 option. How         matching is mentioned in several places below. There is also a  summary
2712       this affects the pattern matching is  mentioned  in  several         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2713       places  below.  There is also a summary of UTF-8 features in         page.
2714       the section on UTF-8 support in the main pcre page.  
2715           The remainder of this document discusses the  patterns  that  are  sup-
2716       A regular expression is a pattern that is matched against  a         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2717       subject string from left to right. Most characters stand for         From  release  6.0,   PCRE   offers   a   second   matching   function,
2718       themselves in a pattern, and match the corresponding charac-         pcre_dfa_exec(),  which matches using a different algorithm that is not
2719       ters in the subject. As a trivial example, the pattern         Perl-compatible. The advantages and disadvantages  of  the  alternative
2720           function, and how it differs from the normal function, are discussed in
2721         The quick brown fox         the pcrematching page.
2722    
2723       matches a portion of a subject string that is  identical  to  
2724       itself.  The  power  of  regular  expressions comes from the  CHARACTERS AND METACHARACTERS
2725       ability to include alternatives and repetitions in the  pat-  
2726       tern.  These  are encoded in the pattern by the use of meta-         A regular expression is a pattern that is  matched  against  a  subject
2727       characters, which do not stand for  themselves  but  instead         string  from  left  to right. Most characters stand for themselves in a
2728       are interpreted in some special way.         pattern, and match the corresponding characters in the  subject.  As  a
2729           trivial example, the pattern
2730       There are two different sets of meta-characters: those  that  
2731       are  recognized anywhere in the pattern except within square           The quick brown fox
2732       brackets, and those that are recognized in square  brackets.  
2733       Outside square brackets, the meta-characters are as follows:         matches a portion of a subject string that is identical to itself. When
2734           caseless matching is specified (the PCRE_CASELESS option), letters  are
2735         \      general escape character with several uses         matched  independently  of case. In UTF-8 mode, PCRE always understands
2736         ^      assert start of string (or line, in multiline mode)         the concept of case for characters whose values are less than  128,  so
2737         $      assert end of string (or line, in multiline mode)         caseless  matching  is always possible. For characters with higher val-
2738         .      match any character except newline (by default)         ues, the concept of case is supported if PCRE is compiled with  Unicode
2739         [      start character class definition         property  support,  but  not  otherwise.   If  you want to use caseless
2740         |      start of alternative branch         matching for characters 128 and above, you must  ensure  that  PCRE  is
2741         (      start subpattern         compiled with Unicode property support as well as with UTF-8 support.
2742         )      end subpattern  
2743         ?      extends the meaning of (         The  power  of  regular  expressions  comes from the ability to include
2744                also 0 or 1 quantifier         alternatives and repetitions in the pattern. These are encoded  in  the
2745                also quantifier minimizer         pattern by the use of metacharacters, which do not stand for themselves
2746         *      0 or more quantifier         but instead are interpreted in some special way.
2747         +      1 or more quantifier  
2748                also "possessive quantifier"         There are two different sets of metacharacters: those that  are  recog-
2749         {      start min/max quantifier         nized  anywhere in the pattern except within square brackets, and those
2750           that are recognized within square brackets.  Outside  square  brackets,
2751       Part of a pattern that is in square  brackets  is  called  a         the metacharacters are as follows:
2752       "character  class".  In  a  character  class  the only meta-  
2753       characters are:           \      general escape character with several uses
2754             ^      assert start of string (or line, in multiline mode)
2755         \      general escape character           $      assert end of string (or line, in multiline mode)
2756         ^      negate the class, but only if the first character           .      match any character except newline (by default)
2757         -      indicates character range           [      start character class definition
2758         [      POSIX character class (only if followed by POSIX           |      start of alternative branch
2759                  syntax)           (      start subpattern
2760         ]      terminates the character class           )      end subpattern
2761             ?      extends the meaning of (
2762                    also 0 or 1 quantifier
2763                    also quantifier minimizer
2764             *      0 or more quantifier
2765             +      1 or more quantifier
2766                    also "possessive quantifier"
2767             {      start min/max quantifier
2768    
2769           Part  of  a  pattern  that is in square brackets is called a "character
2770           class". In a character class the only metacharacters are:
2771    
2772             \      general escape character
2773             ^      negate the class, but only if the first character
2774             -      indicates character range
2775             [      POSIX character class (only if followed by POSIX
2776                      syntax)
2777             ]      terminates the character class
2778    
2779       The following sections describe  the  use  of  each  of  the         The following sections describe the use of each of the  metacharacters.
      meta-characters.  
2780    
2781    
2782  BACKSLASH  BACKSLASH
2783    
2784       The backslash character has several uses. Firstly, if it  is         The backslash character has several uses. Firstly, if it is followed by
2785       followed  by  a  non-alphameric character, it takes away any         a non-alphanumeric character, it takes away any  special  meaning  that
2786       special  meaning  that  character  may  have.  This  use  of         character  may  have.  This  use  of  backslash  as an escape character
2787       backslash  as  an  escape  character applies both inside and         applies both inside and outside character classes.
2788       outside character classes.  
2789           For example, if you want to match a * character, you write  \*  in  the
2790       For example, if you want to match a * character,  you  write         pattern.   This  escaping  action  applies whether or not the following
2791       \*  in the pattern.  This escaping action applies whether or         character would otherwise be interpreted as a metacharacter, so  it  is
2792       not the following character would otherwise  be  interpreted         always  safe  to  precede  a non-alphanumeric with backslash to specify
2793       as  a meta-character, so it is always safe to precede a non-         that it stands for itself. In particular, if you want to match a  back-
2794       alphameric with backslash to  specify  that  it  stands  for         slash, you write \\.
2795       itself. In particular, if you want to match a backslash, you  
2796       write \\.         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2797           the pattern (other than in a character class) and characters between  a
2798       If a pattern is compiled with the PCRE_EXTENDED option, whi-         # outside a character class and the next newline are ignored. An escap-
2799       tespace in the pattern (other than in a character class) and         ing backslash can be used to include a whitespace  or  #  character  as
2800       characters between a # outside a  character  class  and  the         part of the pattern.
2801       next  newline  character  are ignored. An escaping backslash  
2802