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