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