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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.  There is also some support for certain .NET and Oniguruma syn-
24       strings.    However,  this  support  has  to  be  explicitly         tax items, and there is an option for  requesting  some  minor  changes
25       enabled; it is not the default.         that give better JavaScript compatibility.
26    
27       PCRE is written in C and released as a C library. However, a         The  current  implementation of PCRE (release 7.x) corresponds approxi-
28       number  of  people  have  written wrappers and interfaces of         mately with Perl 5.10, including support for UTF-8 encoded strings  and
29       various kinds. A C++ class is included  in  these  contribu-         Unicode general category properties. However, UTF-8 and Unicode support
30       tions,  which  can  be found in the Contrib directory at the         has to be explicitly enabled; it is not the default. The Unicode tables
31       primary FTP site, which is:         correspond to Unicode release 5.0.0.
32    
33       ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         In  addition to the Perl-compatible matching function, PCRE contains an
34           alternative matching function that matches the same  compiled  patterns
35       Details of exactly which Perl  regular  expression  features         in  a different way. In certain circumstances, the alternative function
36       are  and  are  not  supported  by PCRE are given in separate         has some advantages. For a discussion of the two  matching  algorithms,
37       documents. See the pcrepattern and pcrecompat pages.         see the pcrematching page.
38    
39       Some features of PCRE can be included, excluded, or  changed         PCRE  is  written  in C and released as a C library. A number of people
40       when  the library is built. The pcre_config() function makes         have written wrappers and interfaces of various kinds.  In  particular,
41       it possible for a client  to  discover  which  features  are         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
42       available.  Documentation  about  building  PCRE for various         included as part of the PCRE distribution. The pcrecpp page has details
43       operating systems can be found in the  README  file  in  the         of  this  interface.  Other  people's contributions can be found in the
44       source distribution.         Contrib directory at the primary FTP site, which is:
45    
46           ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
47    
48           Details of exactly which Perl regular expression features are  and  are
49           not supported by PCRE are given in separate documents. See the pcrepat-
50           tern and pcrecompat pages. There is a syntax summary in the  pcresyntax
51           page.
52    
53           Some  features  of  PCRE can be included, excluded, or changed when the
54           library is built. The pcre_config() function makes it  possible  for  a
55           client  to  discover  which  features are available. The features them-
56           selves are described in the pcrebuild page. Documentation about  build-
57           ing  PCRE for various operating systems can be found in the README file
58           in the source distribution.
59    
60           The library contains a number of undocumented  internal  functions  and
61           data  tables  that  are  used by more than one of the exported external
62           functions, but which are not intended  for  use  by  external  callers.
63           Their  names  all begin with "_pcre_", which hopefully will not provoke
64           any name clashes. In some environments, it is possible to control which
65           external  symbols  are  exported when a shared library is built, and in
66           these cases the undocumented symbols are not exported.
67    
68    
69  USER DOCUMENTATION  USER DOCUMENTATION
70    
71       The user documentation for PCRE has been  split  up  into  a         The user documentation for PCRE comprises a number  of  different  sec-
72       number  of  different sections. In the "man" format, each of         tions.  In the "man" format, each of these is a separate "man page". In
73       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.
74       a  separate  page,  linked from the index page. In the plain         In  the  plain text format, all the sections are concatenated, for ease
75       text format, all the sections are concatenated, for ease  of         of searching. The sections are as follows:
76       searching. The sections are as follows:  
77             pcre              this document
78         pcre              this document           pcre-config       show PCRE installation configuration information
79         pcreapi           details of PCRE's native API           pcreapi           details of PCRE's native C API
80         pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
81         pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
82         pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
83         pcregrep          description of the pcregrep command           pcrecpp           details of the C++ wrapper
84         pcrepattern       syntax and semantics of supported           pcregrep          description of the pcregrep command
85                             regular expressions           pcrematching      discussion of the two matching algorithms
86         pcreperform       discussion of performance issues           pcrepartial       details of the partial matching facility
87         pcreposix         the POSIX-compatible API           pcrepattern       syntax and semantics of supported
88         pcresample        discussion of the sample program                               regular expressions
89         pcretest          the pcretest testing command           pcresyntax        quick syntax reference
90             pcreperform       discussion of performance issues
91       In addition, in the "man" and HTML formats, there is a short           pcreposix         the POSIX-compatible C API
92       page  for  each  library function, listing its arguments and           pcreprecompile    details of saving and re-using precompiled patterns
93       results.           pcresample        discussion of the sample program
94             pcrestack         discussion of stack usage
95             pcretest          description of the pcretest testing command
96    
97           In  addition,  in the "man" and HTML formats, there is a short page for
98           each C library function, listing its arguments and results.
99    
100    
101  LIMITATIONS  LIMITATIONS
102    
103       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
104       they will never in practice be relevant.         never in practice be relevant.
105    
106       The maximum length of a  compiled  pattern  is  65539  (sic)         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
107       bytes  if PCRE is compiled with the default internal linkage         is compiled with the default internal linkage size of 2. If you want to
108       size of 2. If you want to process regular  expressions  that         process  regular  expressions  that are truly enormous, you can compile
109       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
110       linkage size of 3 or 4 (see the README file  in  the  source         the  source  distribution and the pcrebuild documentation for details).
111       distribution  and  the pcrebuild documentation for details).         In these cases the limit is substantially larger.  However,  the  speed
112       If these cases the limit is substantially larger.   However,         of execution is slower.
113       the speed of execution will be slower.  
114           All values in repeating quantifiers must be less than 65536.
115       All values in repeating quantifiers must be less than 65536.  
116       The maximum number of capturing subpatterns is 65535.         There is no limit to the number of parenthesized subpatterns, but there
117           can be no more than 65535 capturing subpatterns.
118       There is no limit to the  number  of  non-capturing  subpat-  
119       terns,  but  the  maximum  depth  of nesting of all kinds of         The maximum length of name for a named subpattern is 32 characters, and
120       parenthesized subpattern, including  capturing  subpatterns,         the maximum number of named subpatterns is 10000.
121       assertions, and other types of subpattern, is 200.  
122           The  maximum  length of a subject string is the largest positive number
123       The maximum length of a subject string is the largest  posi-         that an integer variable can hold. However, when using the  traditional
124       tive number that an integer variable can hold. However, PCRE         matching function, PCRE uses recursion to handle subpatterns and indef-
125       uses recursion to handle subpatterns and indefinite  repeti-         inite repetition.  This means that the available stack space may  limit
126       tion.  This  means  that the available stack space may limit         the size of a subject string that can be processed by certain patterns.
127       the size of a subject string that can be processed  by  cer-         For a discussion of stack issues, see the pcrestack documentation.
128       tain patterns.  
129    
130    UTF-8 AND UNICODE PROPERTY SUPPORT
131    
132           From release 3.3, PCRE has  had  some  support  for  character  strings
133           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
134           to cover most common requirements, and in release 5.0  additional  sup-
135           port for Unicode general category properties was added.
136    
137           In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
138           support in the code, and, in addition,  you  must  call  pcre_compile()
139           with  the PCRE_UTF8 option flag. When you do this, both the pattern and
140           any subject strings that are matched against it are  treated  as  UTF-8
141           strings instead of just strings of bytes.
142    
143           If  you compile PCRE with UTF-8 support, but do not use it at run time,
144           the library will be a bit bigger, but the additional run time  overhead
145           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
146           very big.
147    
148           If PCRE is built with Unicode character property support (which implies
149           UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
150           ported.  The available properties that can be tested are limited to the
151           general  category  properties such as Lu for an upper case letter or Nd
152           for a decimal number, the Unicode script names such as Arabic  or  Han,
153           and  the  derived  properties  Any  and L&. A full list is given in the
154           pcrepattern documentation. Only the short names for properties are sup-
155           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
156           ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
157           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
158           does not support this.
159    
160       Validity of UTF-8 strings
161    
162           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
163           subjects are (by default) checked for validity on entry to the relevant
164           functions. From release 7.3 of PCRE, the check is according  the  rules
165           of  RFC  3629, which are themselves derived from the Unicode specifica-
166           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
167           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
168           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
169           to U+DFFF.
170    
171           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
172           which the Unicode Standard says this: "The Low Surrogate Area does  not
173           contain  any  character  assignments,  consequently  no  character code
174           charts or namelists are provided for this area. Surrogates are reserved
175           for  use  with  UTF-16 and then must be used in pairs." The code points
176           that are encoded by UTF-16 pairs  are  available  as  independent  code
177           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
178           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
179    
180           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
181           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
182           that your strings are valid, and therefore want to skip these checks in
183           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
184           compile time or at run time, PCRE assumes that the pattern  or  subject
185           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
186           case, it does not diagnose an invalid UTF-8 string.
187    
188           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
189           what  happens  depends on why the string is invalid. If the string con-
190           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
191           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
192           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
193           strings  according  to  the more liberal rules of RFC 2279. However, if
194           the string does not even conform to RFC 2279, the result is  undefined.
195           Your program may crash.
196    
197           If  you  want  to  process  strings  of  values  in the full range 0 to
198           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
199           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
200           this situation, you will have to apply your own validity check.
201    
202       General comments about UTF-8 mode
203    
204           1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
205           two-byte UTF-8 character if the value is greater than 127.
206    
207           2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
208           characters for values greater than \177.
209    
210           3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
211           vidual bytes, for example: \x{100}{3}.
212    
213           4.  The dot metacharacter matches one UTF-8 character instead of a sin-
214           gle byte.
215    
216           5. The escape sequence \C can be used to match a single byte  in  UTF-8
217           mode,  but  its  use can lead to some strange effects. This facility is
218           not available in the alternative matching function, pcre_dfa_exec().
219    
220           6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
221           test  characters of any code value, but the characters that PCRE recog-
222           nizes as digits, spaces, or word characters  remain  the  same  set  as
223           before, all with values less than 256. This remains true even when PCRE
224           includes Unicode property support, because to do otherwise  would  slow
225           down  PCRE in many common cases. If you really want to test for a wider
226           sense of, say, "digit", you must use Unicode  property  tests  such  as
227           \p{Nd}.
228    
229           7.  Similarly,  characters that match the POSIX named character classes
230           are all low-valued characters.
231    
232           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
233           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
234           acters.
235    
236           9. Case-insensitive matching applies only to  characters  whose  values
237           are  less than 128, unless PCRE is built with Unicode property support.
238           Even when Unicode property support is available, PCRE  still  uses  its
239           own  character  tables when checking the case of low-valued characters,
240           so as not to degrade performance.  The Unicode property information  is
241           used only for characters with higher values. Even when Unicode property
242           support is available, PCRE supports case-insensitive matching only when
243           there  is  a  one-to-one  mapping between a letter's cases. There are a
244           small number of many-to-one mappings in Unicode;  these  are  not  sup-
245           ported by PCRE.
246    
247    
248  UTF-8 SUPPORT  AUTHOR
249    
250       Starting at release 3.3, PCRE has had some support for char-         Philip Hazel
251       acter  strings  encoded in the UTF-8 format. For release 4.0         University Computing Service
252       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. When you set the PCRE_UTF8 flag, the  strings  passed  as  
      patterns  and  subjects are checked for validity on entry to  
      the relevant  functions.  If  an  invalid  UTF-8  string  is  
      passed,  an  error  return is given. In some situations, you  
      may already know that your strings are valid, and  therefore  
      want  to  skip these checks in order to improve performance.  
      If you set the PCRE_NO_UTF8_CHECK flag at compile time or at  
      run  time,  PCRE  assumes  that the pattern or subject it is  
      given (respectively) contains only  valid  UTF-8  codes.  In  
      this  case, it does not diagnose an invalid UTF-8 string. If  
      you  pass   an   invalid   UTF-8   string   to   PCRE   when  
      PCRE_NO_UTF8_CHECK  is  set, the results are undefined. Your  
      program may crash.  
   
      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.  
253    
254       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,
255       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,
256           followed by the two digits 10, at the domain cam.ac.uk.
257    
258    
259  AUTHOR  REVISION
260    
261       Philip Hazel <ph10@cam.ac.uk>         Last updated: 12 April 2008
262       University Computing Service,         Copyright (c) 1997-2008 University of Cambridge.
263       Cambridge CB2 3QG, England.  ------------------------------------------------------------------------------
264       Phone: +44 1223 334714  
265    
266    PCREBUILD(3)                                                      PCREBUILD(3)
267    
 Last updated: 20 August 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
268    
269  NAME  NAME
270       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
271    
272    
273  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
274    
275       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
276       can  be  selected when the library is compiled. They are all         selected when the library is compiled. It assumes use of the  configure
277       selected, or deselected, by providing options to the config-         script,  where the optional features are selected or deselected by pro-
278       ure  script  which  is run before the make command. The com-         viding options to configure before running the make  command.  However,
279       plete list of options  for  configure  (which  includes  the         the  same  options  can be selected in both Unix-like and non-Unix-like
280       standard  ones  such  as  the  selection of the installation         environments using the GUI facility of  CMakeSetup  if  you  are  using
281       directory) can be obtained by running         CMake instead of configure to build PCRE.
282    
283         ./configure --help         The complete list of options for configure (which includes the standard
284           ones such as the  selection  of  the  installation  directory)  can  be
285       The following sections describe certain options whose  names         obtained by running
286       begin  with  --enable  or  --disable. These settings specify  
287       changes to the defaults for the configure  command.  Because           ./configure --help
288       of  the  way  that  configure  works, --enable and --disable  
289       always come in pairs, so  the  complementary  option  always         The  following  sections  include  descriptions  of options whose names
290       exists  as  well, but as it specifies the default, it is not         begin with --enable or --disable. These settings specify changes to the
291       described.         defaults  for  the configure command. Because of the way that configure
292           works, --enable and --disable always come in pairs, so  the  complemen-
293           tary  option always exists as well, but as it specifies the default, it
294           is not described.
295    
296    
297    C++ SUPPORT
298    
299           By default, the configure script will search for a C++ compiler and C++
300           header files. If it finds them, it automatically builds the C++ wrapper
301           library for PCRE. You can disable this by adding
302    
303             --disable-cpp
304    
305           to the configure command.
306    
307    
308  UTF-8 SUPPORT  UTF-8 SUPPORT
309    
310       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
311    
312             --enable-utf8
313    
314           to the configure command. Of itself, this  does  not  make  PCRE  treat
315           strings  as UTF-8. As well as compiling PCRE with this option, you also
316           have have to set the PCRE_UTF8 option when you call the  pcre_compile()
317           function.
318    
319    
320    UNICODE CHARACTER PROPERTY SUPPORT
321    
322         --enable-utf8         UTF-8  support allows PCRE to process character values greater than 255
323           in the strings that it handles. On its own, however, it does  not  pro-
324           vide any facilities for accessing the properties of such characters. If
325           you want to be able to use the pattern escapes \P, \p,  and  \X,  which
326           refer to Unicode character properties, you must add
327    
328       to the configure command. Of itself, this does not make PCRE           --enable-unicode-properties
329       treat  strings as UTF-8. As well as compiling PCRE with this  
330       option, you also have have to set the PCRE_UTF8 option  when         to  the configure command. This implies UTF-8 support, even if you have
331       you call the pcre_compile() function.         not explicitly requested it.
332    
333           Including Unicode property support adds around 30K  of  tables  to  the
334           PCRE  library.  Only  the general category properties such as Lu and Nd
335           are supported. Details are given in the pcrepattern documentation.
336    
337    
338  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
339    
340       By default, PCRE treats character 10 (linefeed) as the  new-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
341       line  character.  This  is  the  normal newline character on         the  end  of  a line. This is the normal newline character on Unix-like
342       Unix-like systems. You can compile PCRE to use character  13         systems. You can compile PCRE to use character 13 (carriage return, CR)
343       (carriage return) instead by adding         instead, by adding
344    
345         --enable-newline-is-cr           --enable-newline-is-cr
346    
347       to the configure command. For completeness there is  also  a         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
348       --enable-newline-is-lf  option,  which  explicitly specifies         option, which explicitly specifies linefeed as the newline character.
349       linefeed as the newline character.  
350           Alternatively, you can specify that line endings are to be indicated by
351           the two character sequence CRLF. If you want this, add
352    
353             --enable-newline-is-crlf
354    
355           to the configure command. There is a fourth option, specified by
356    
357             --enable-newline-is-anycrlf
358    
359           which  causes  PCRE  to recognize any of the three sequences CR, LF, or
360           CRLF as indicating a line ending. Finally, a fifth option, specified by
361    
362             --enable-newline-is-any
363    
364           causes PCRE to recognize any Unicode newline sequence.
365    
366           Whatever  line  ending convention is selected when PCRE is built can be
367           overridden when the library functions are called. At build time  it  is
368           conventional to use the standard for your operating system.
369    
370    
371    WHAT \R MATCHES
372    
373           By  default,  the  sequence \R in a pattern matches any Unicode newline
374           sequence, whatever has been selected as the line  ending  sequence.  If
375           you specify
376    
377             --enable-bsr-anycrlf
378    
379           the  default  is changed so that \R matches only CR, LF, or CRLF. What-
380           ever is selected when PCRE is built can be overridden when the  library
381           functions are called.
382    
383    
384  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
385    
386       The PCRE building process uses libtool to build both  shared         The  PCRE building process uses libtool to build both shared and static
387       and  static  Unix libraries by default. You can suppress one         Unix libraries by default. You can suppress one of these by adding  one
388       of these by adding one of         of
389    
390         --disable-shared           --disable-shared
391         --disable-static           --disable-static
392    
393       to the configure command, as required.         to the configure command, as required.
394    
395    
396  POSIX MALLOC USAGE  POSIX MALLOC USAGE
397    
398       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
399       pcreposix  documentation),  additional  working  storage  is         umentation), additional working storage is  required  for  holding  the
400       required for holding the pointers  to  capturing  substrings         pointers  to capturing substrings, because PCRE requires three integers
401       because  PCRE requires three integers per substring, whereas         per substring, whereas the POSIX interface provides only  two.  If  the
402       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
403       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
404       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
405       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
406       stack is no longer used is 10; it can be changed by adding a  
407       setting such as           --with-posix-malloc-threshold=20
408    
409           to the configure command.
410    
411    
412         --with-posix-malloc-threshold=20  HANDLING VERY LARGE PATTERNS
413    
414       to the configure command.         Within a compiled pattern, offset values are used  to  point  from  one
415           part  to another (for example, from an opening parenthesis to an alter-
416           nation metacharacter). By default, two-byte values are used  for  these
417           offsets,  leading  to  a  maximum size for a compiled pattern of around
418           64K. This is sufficient to handle all but the most  gigantic  patterns.
419           Nevertheless,  some  people do want to process enormous patterns, so it
420           is possible to compile PCRE to use three-byte or four-byte  offsets  by
421           adding a setting such as
422    
423             --with-link-size=3
424    
425           to  the  configure  command.  The value given must be 2, 3, or 4. Using
426           longer offsets slows down the operation of PCRE because it has to  load
427           additional bytes when handling them.
428    
429    
430    AVOIDING EXCESSIVE STACK USAGE
431    
432           When matching with the pcre_exec() function, PCRE implements backtrack-
433           ing by making recursive calls to an internal function  called  match().
434           In  environments  where  the size of the stack is limited, this can se-
435           verely limit PCRE's operation. (The Unix environment does  not  usually
436           suffer from this problem, but it may sometimes be necessary to increase
437           the maximum stack size.  There is a discussion in the  pcrestack  docu-
438           mentation.)  An alternative approach to recursion that uses memory from
439           the heap to remember data, instead of using recursive  function  calls,
440           has  been  implemented to work round the problem of limited stack size.
441           If you want to build a version of PCRE that works this way, add
442    
443             --disable-stack-for-recursion
444    
445           to the configure command. With this configuration, PCRE  will  use  the
446           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
447           ment functions. By default these point to malloc() and free(), but  you
448           can replace the pointers so that your own functions are used.
449    
450           Separate  functions  are  provided  rather  than  using pcre_malloc and
451           pcre_free because the  usage  is  very  predictable:  the  block  sizes
452           requested  are  always  the  same,  and  the blocks are always freed in
453           reverse order. A calling program might be able to  implement  optimized
454           functions  that  perform  better  than  malloc()  and free(). PCRE runs
455           noticeably more slowly when built in this way. This option affects only
456           the   pcre_exec()   function;   it   is   not   relevant  for  the  the
457           pcre_dfa_exec() function.
458    
459    
460  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
461    
462       Internally, PCRE has a  function  called  match()  which  it         Internally, PCRE has a function called match(), which it calls  repeat-
463       calls  repeatedly  (possibly  recursively) when performing a         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
464       matching operation. By limiting the  number  of  times  this         pcre_exec() function. By controlling the maximum number of  times  this
465       function  may  be  called,  a  limit  can  be  placed on the         function  may be called during a single matching operation, a limit can
466       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
467       can  be  changed  at  run  time, as described in the pcreapi         limit  can be changed at run time, as described in the pcreapi documen-
468       documentation. The default is 10 million, but  this  can  be         tation. The default is 10 million, but this can be changed by adding  a
469       changed by adding a setting such as         setting such as
470    
471         --with-match-limit=500000           --with-match-limit=500000
472    
473       to the configure command.         to   the   configure  command.  This  setting  has  no  effect  on  the
474           pcre_dfa_exec() matching function.
475    
476           In some environments it is desirable to limit the  depth  of  recursive
477           calls of match() more strictly than the total number of calls, in order
478           to restrict the maximum amount of stack (or heap,  if  --disable-stack-
479           for-recursion is specified) that is used. A second limit controls this;
480           it defaults to the value that  is  set  for  --with-match-limit,  which
481           imposes  no  additional constraints. However, you can set a lower limit
482           by adding, for example,
483    
484  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
485    
486       Within a compiled pattern, offset values are used  to  point         to the configure command. This value can  also  be  overridden  at  run
487       from  one  part  to  another  (for  example, from an opening         time.
488       parenthesis to an  alternation  metacharacter).  By  default  
489       two-byte  values  are  used  for these offsets, leading to a  
490       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
491       sufficient  to  handle  all  but the most gigantic patterns.  
492       Nevertheless, some people do want to process  enormous  pat-         PCRE  uses fixed tables for processing characters whose code values are
493       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
494       or four-byte offsets by adding a setting such as         distributed  in  the  file pcre_chartables.c.dist. These tables are for
495           ASCII codes only. If you add
496         --with-link-size=3  
497             --enable-rebuild-chartables
498       to the configure command. The value given must be 2,  3,  or  
499       4.  Using  longer  offsets  slows down the operation of PCRE         to the configure command, the distributed tables are  no  longer  used.
500       because it has to load additional bytes when handling them.         Instead,  a  program  called dftables is compiled and run. This outputs
501           the source for new set of tables, created in the default locale of your
502       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
503       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
504       of these tests is a representation of the compiled  pattern,         you  need  to  create alternative tables when cross compiling, you will
505       and this changes with the link size.         have to do so "by hand".)
506    
507    
508    USING EBCDIC CODE
509    
510           PCRE assumes by default that it will run in an  environment  where  the
511           character  code  is  ASCII  (or Unicode, which is a superset of ASCII).
512           This is the case for most computer operating systems.  PCRE  can,  how-
513           ever, be compiled to run in an EBCDIC environment by adding
514    
515             --enable-ebcdic
516    
517           to the configure command. This setting implies --enable-rebuild-charta-
518           bles. You should only use it if you know that  you  are  in  an  EBCDIC
519           environment (for example, an IBM mainframe operating system).
520    
521    
522    PCREGREP OPTIONS FOR COMPRESSED FILE SUPPORT
523    
524           By default, pcregrep reads all files as plain text. You can build it so
525           that it recognizes files whose names end in .gz or .bz2, and reads them
526           with libz or libbz2, respectively, by adding one or both of
527    
528             --enable-pcregrep-libz
529             --enable-pcregrep-libbz2
530    
531           to the configure command. These options naturally require that the rel-
532           evant libraries are installed on your system. Configuration  will  fail
533           if they are not.
534    
535    
536    PCRETEST OPTION FOR LIBREADLINE SUPPORT
537    
538           If you add
539    
540             --enable-pcretest-libreadline
541    
542           to  the  configure  command,  pcretest  is  linked with the libreadline
543           library, and when its input is from a terminal, it reads it  using  the
544           readline() function. This provides line-editing and history facilities.
545           Note that libreadline is GPL-licenced, so if you distribute a binary of
546           pcretest linked in this way, there may be licensing issues.
547    
548           Setting  this  option  causes  the -lreadline option to be added to the
549           pcretest build. In many operating environments with  a  sytem-installed
550           libreadline this is sufficient. However, in some environments (e.g.  if
551           an unmodified distribution version of readline is in use),  some  extra
552           configuration  may  be necessary. The INSTALL file for libreadline says
553           this:
554    
555             "Readline uses the termcap functions, but does not link with the
556             termcap or curses library itself, allowing applications which link
557             with readline the to choose an appropriate library."
558    
559           If your environment has not been set up so that an appropriate  library
560           is automatically included, you may need to add something like
561    
562             LIBS="-ncurses"
563    
564           immediately before the configure command.
565    
566    
567    SEE ALSO
568    
569           pcreapi(3), pcre_config(3).
570    
571    
572    AUTHOR
573    
574           Philip Hazel
575           University Computing Service
576           Cambridge CB2 3QH, England.
577    
578    
579    REVISION
580    
581           Last updated: 13 April 2008
582           Copyright (c) 1997-2008 University of Cambridge.
583    ------------------------------------------------------------------------------
584    
585    
586    PCREMATCHING(3)                                                PCREMATCHING(3)
587    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
588    
589  NAME  NAME
590       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
591    
592    
593    PCRE MATCHING ALGORITHMS
594    
595           This document describes the two different algorithms that are available
596           in PCRE for matching a compiled regular expression against a given sub-
597           ject  string.  The  "standard"  algorithm  is  the  one provided by the
598           pcre_exec() function.  This works in the same was  as  Perl's  matching
599           function, and provides a Perl-compatible matching operation.
600    
601           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
602           this operates in a different way, and is not  Perl-compatible.  It  has
603           advantages  and disadvantages compared with the standard algorithm, and
604           these are described below.
605    
606           When there is only one possible way in which a given subject string can
607           match  a pattern, the two algorithms give the same answer. A difference
608           arises, however, when there are multiple possibilities. For example, if
609           the pattern
610    
611             ^<.*>
612    
613           is matched against the string
614    
615             <something> <something else> <something further>
616    
617           there are three possible answers. The standard algorithm finds only one
618           of them, whereas the alternative algorithm finds all three.
619    
620    
621    REGULAR EXPRESSIONS AS TREES
622    
623           The set of strings that are matched by a regular expression can be rep-
624           resented  as  a  tree structure. An unlimited repetition in the pattern
625           makes the tree of infinite size, but it is still a tree.  Matching  the
626           pattern  to a given subject string (from a given starting point) can be
627           thought of as a search of the tree.  There are two  ways  to  search  a
628           tree:  depth-first  and  breadth-first, and these correspond to the two
629           matching algorithms provided by PCRE.
630    
631    
632  SYNOPSIS OF PCRE API  THE STANDARD MATCHING ALGORITHM
633    
634       #include <pcre.h>         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
635           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
636           depth-first search of the pattern tree. That is, it  proceeds  along  a
637           single path through the tree, checking that the subject matches what is
638           required. When there is a mismatch, the algorithm  tries  any  alterna-
639           tives  at  the  current point, and if they all fail, it backs up to the
640           previous branch point in the  tree,  and  tries  the  next  alternative
641           branch  at  that  level.  This often involves backing up (moving to the
642           left) in the subject string as well.  The  order  in  which  repetition
643           branches  are  tried  is controlled by the greedy or ungreedy nature of
644           the quantifier.
645    
646       pcre *pcre_compile(const char *pattern, int options,         If a leaf node is reached, a matching string has  been  found,  and  at
647            const char **errptr, int *erroffset,         that  point the algorithm stops. Thus, if there is more than one possi-
648            const unsigned char *tableptr);         ble match, this algorithm returns the first one that it finds.  Whether
649           this  is the shortest, the longest, or some intermediate length depends
650           on the way the greedy and ungreedy repetition quantifiers are specified
651           in the pattern.
652    
653       pcre_extra *pcre_study(const pcre *code, int options,         Because  it  ends  up  with a single path through the tree, it is rela-
654            const char **errptr);         tively straightforward for this algorithm to keep  track  of  the  sub-
655           strings  that  are  matched  by portions of the pattern in parentheses.
656           This provides support for capturing parentheses and back references.
657    
      int pcre_exec(const pcre *code, const pcre_extra *extra,  
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
658    
659       int pcre_copy_named_substring(const pcre *code,  THE ALTERNATIVE MATCHING ALGORITHM
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
660    
661       int pcre_copy_substring(const char *subject, int *ovector,         This algorithm conducts a breadth-first search of  the  tree.  Starting
662            int stringcount, int stringnumber, char *buffer,         from  the  first  matching  point  in the subject, it scans the subject
663            int buffersize);         string from left to right, once, character by character, and as it does
664           this,  it remembers all the paths through the tree that represent valid
665           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
666           though  it is not implemented as a traditional finite state machine (it
667           keeps multiple states active simultaneously).
668    
669       int pcre_get_named_substring(const pcre *code,         The scan continues until either the end of the subject is  reached,  or
670            const char *subject, int *ovector,         there  are  no more unterminated paths. At this point, terminated paths
671            int stringcount, const char *stringname,         represent the different matching possibilities (if there are none,  the
672            const char **stringptr);         match  has  failed).   Thus,  if there is more than one possible match,
673           this algorithm finds all of them, and in particular, it finds the long-
674           est.  In PCRE, there is an option to stop the algorithm after the first
675           match (which is necessarily the shortest) has been found.
676    
677       int pcre_get_stringnumber(const pcre *code,         Note that all the matches that are found start at the same point in the
678            const char *name);         subject. If the pattern
679    
680       int pcre_get_substring(const char *subject, int *ovector,           cat(er(pillar)?)
           int stringcount, int stringnumber,  
           const char **stringptr);  
681    
682       int pcre_get_substring_list(const char *subject,         is  matched  against the string "the caterpillar catchment", the result
683            int *ovector, int stringcount, const char ***listptr);         will be the three strings "cat", "cater", and "caterpillar" that  start
684           at the fourth character of the subject. The algorithm does not automat-
685           ically move on to find matches that start at later positions.
686    
687       void pcre_free_substring(const char *stringptr);         There are a number of features of PCRE regular expressions that are not
688           supported by the alternative matching algorithm. They are as follows:
689    
690       void pcre_free_substring_list(const char **stringptr);         1.  Because  the  algorithm  finds  all possible matches, the greedy or
691           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
692           ungreedy quantifiers are treated in exactly the same way. However, pos-
693           sessive quantifiers can make a difference when what follows could  also
694           match what is quantified, for example in a pattern like this:
695    
696       const unsigned char *pcre_maketables(void);           ^a++\w!
697    
698       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         This  pattern matches "aaab!" but not "aaa!", which would be matched by
699            int what, void *where);         a non-possessive quantifier. Similarly, if an atomic group is  present,
700           it  is matched as if it were a standalone pattern at the current point,
701           and the longest match is then "locked in" for the rest of  the  overall
702           pattern.
703    
704           2. When dealing with multiple paths through the tree simultaneously, it
705           is not straightforward to keep track of  captured  substrings  for  the
706           different  matching  possibilities,  and  PCRE's implementation of this
707           algorithm does not attempt to do this. This means that no captured sub-
708           strings are available.
709    
710       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         3.  Because no substrings are captured, back references within the pat-
711           tern are not supported, and cause errors if encountered.
712    
713       int pcre_config(int what, void *where);         4. For the same reason, conditional expressions that use  a  backrefer-
714           ence  as  the  condition or test for a specific group recursion are not
715           supported.
716    
717       char *pcre_version(void);         5. Because many paths through the tree may be  active,  the  \K  escape
718           sequence, which resets the start of the match when encountered (but may
719           be on some paths and not on others), is not  supported.  It  causes  an
720           error if encountered.
721    
722       void *(*pcre_malloc)(size_t);         6.  Callouts  are  supported, but the value of the capture_top field is
723           always 1, and the value of the capture_last field is always -1.
724    
725       void (*pcre_free)(void *);         7. The \C escape sequence, which (in the standard algorithm) matches  a
726           single  byte, even in UTF-8 mode, is not supported because the alterna-
727           tive algorithm moves through the subject  string  one  character  at  a
728           time, for all active paths through the tree.
729    
730       int (*pcre_callout)(pcre_callout_block *);         8.  Except for (*FAIL), the backtracking control verbs such as (*PRUNE)
731           are not supported. (*FAIL) is supported, and  behaves  like  a  failing
732           negative assertion.
733    
734    
735  PCRE API  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
736    
737       PCRE has its own native API,  which  is  described  in  this         Using  the alternative matching algorithm provides the following advan-
738       document.  There  is  also  a  set of wrapper functions that         tages:
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
739    
740       The native API function prototypes are defined in the header         1. All possible matches (at a single point in the subject) are automat-
741       file  pcre.h,  and  on  Unix  systems  the library itself is         ically  found,  and  in particular, the longest match is found. To find
742       called libpcre.a, so can be accessed by adding -lpcre to the         more than one match using the standard algorithm, you have to do kludgy
743       command  for  linking  an  application  which  calls it. The         things with callouts.
      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.  
744    
745       The functions pcre_compile(), pcre_study(), and  pcre_exec()         2.  There is much better support for partial matching. The restrictions
746       are  used  for compiling and matching regular expressions. A         on the content of the pattern that apply when using the standard  algo-
747       sample program that demonstrates the simplest way  of  using         rithm  for  partial matching do not apply to the alternative algorithm.
748       them  is  given in the file pcredemo.c. The pcresample docu-         For non-anchored patterns, the starting position of a partial match  is
749       mentation describes how to run it.         available.
750    
751       There are convenience functions for extracting captured sub-         3.  Because  the  alternative  algorithm  scans the subject string just
752       strings from a matched subject string. They are:         once, and never needs to backtrack, it is possible to  pass  very  long
753           subject  strings  to  the matching function in several pieces, checking
754           for partial matching each time.
755    
        pcre_copy_substring()  
        pcre_copy_named_substring()  
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
756    
757       pcre_free_substring()  and  pcre_free_substring_list()   are  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      also  provided,  to  free  the  memory  used  for  extracted  
      strings.  
758    
759       The function pcre_maketables() is used (optionally) to build         The alternative algorithm suffers from a number of disadvantages:
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
760    
761       The function pcre_fullinfo() is used to find out information         1. It is substantially slower than  the  standard  algorithm.  This  is
762       about a compiled pattern; pcre_info() is an obsolete version         partly  because  it has to search for all possible matches, but is also
763       which returns only some of the available information, but is         because it is less susceptible to optimization.
      retained   for   backwards   compatibility.    The  function  
      pcre_version() returns a pointer to a string containing  the  
      version of PCRE and its date of release.  
764    
765       The global variables  pcre_malloc  and  pcre_free  initially         2. Capturing parentheses and back references are not supported.
      contain the entry points of the standard malloc() and free()  
      functions respectively. PCRE  calls  the  memory  management  
      functions  via  these  variables,  so  a calling program can  
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
766    
767       The global variable pcre_callout initially contains NULL. It         3. Although atomic groups are supported, their use does not provide the
768       can be set by the caller to a "callout" function, which PCRE         performance advantage that it does for the standard algorithm.
769       will then call at specified points during a matching  opera-  
770       tion. Details are given in the pcrecallout documentation.  
771    AUTHOR
772    
773           Philip Hazel
774           University Computing Service
775           Cambridge CB2 3QH, England.
776    
777    
778    REVISION
779    
780           Last updated: 19 April 2008
781           Copyright (c) 1997-2008 University of Cambridge.
782    ------------------------------------------------------------------------------
783    
784    
785    PCREAPI(3)                                                          PCREAPI(3)
786    
787    
788    NAME
789           PCRE - Perl-compatible regular expressions
790    
791    
792    PCRE NATIVE API
793    
794           #include <pcre.h>
795    
796           pcre *pcre_compile(const char *pattern, int options,
797                const char **errptr, int *erroffset,
798                const unsigned char *tableptr);
799    
800           pcre *pcre_compile2(const char *pattern, int options,
801                int *errorcodeptr,
802                const char **errptr, int *erroffset,
803                const unsigned char *tableptr);
804    
805           pcre_extra *pcre_study(const pcre *code, int options,
806                const char **errptr);
807    
808           int pcre_exec(const pcre *code, const pcre_extra *extra,
809                const char *subject, int length, int startoffset,
810                int options, int *ovector, int ovecsize);
811    
812           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
813                const char *subject, int length, int startoffset,
814                int options, int *ovector, int ovecsize,
815                int *workspace, int wscount);
816    
817           int pcre_copy_named_substring(const pcre *code,
818                const char *subject, int *ovector,
819                int stringcount, const char *stringname,
820                char *buffer, int buffersize);
821    
822           int pcre_copy_substring(const char *subject, int *ovector,
823                int stringcount, int stringnumber, char *buffer,
824                int buffersize);
825    
826           int pcre_get_named_substring(const pcre *code,
827                const char *subject, int *ovector,
828                int stringcount, const char *stringname,
829                const char **stringptr);
830    
831           int pcre_get_stringnumber(const pcre *code,
832                const char *name);
833    
834           int pcre_get_stringtable_entries(const pcre *code,
835                const char *name, char **first, char **last);
836    
837           int pcre_get_substring(const char *subject, int *ovector,
838                int stringcount, int stringnumber,
839                const char **stringptr);
840    
841           int pcre_get_substring_list(const char *subject,
842                int *ovector, int stringcount, const char ***listptr);
843    
844           void pcre_free_substring(const char *stringptr);
845    
846           void pcre_free_substring_list(const char **stringptr);
847    
848           const unsigned char *pcre_maketables(void);
849    
850           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
851                int what, void *where);
852    
853           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
854    
855           int pcre_refcount(pcre *code, int adjust);
856    
857           int pcre_config(int what, void *where);
858    
859           char *pcre_version(void);
860    
861           void *(*pcre_malloc)(size_t);
862    
863           void (*pcre_free)(void *);
864    
865           void *(*pcre_stack_malloc)(size_t);
866    
867           void (*pcre_stack_free)(void *);
868    
869           int (*pcre_callout)(pcre_callout_block *);
870    
871    
872    PCRE API OVERVIEW
873    
874           PCRE has its own native API, which is described in this document. There
875           are also some wrapper functions that correspond to  the  POSIX  regular
876           expression  API.  These  are  described in the pcreposix documentation.
877           Both of these APIs define a set of C function calls. A C++  wrapper  is
878           distributed with PCRE. It is documented in the pcrecpp page.
879    
880           The  native  API  C  function prototypes are defined in the header file
881           pcre.h, and on Unix systems the library itself is called  libpcre.   It
882           can normally be accessed by adding -lpcre to the command for linking an
883           application  that  uses  PCRE.  The  header  file  defines  the  macros
884           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
885           bers for the library.  Applications can use these  to  include  support
886           for different releases of PCRE.
887    
888           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
889           pcre_exec() are used for compiling and matching regular expressions  in
890           a  Perl-compatible  manner. A sample program that demonstrates the sim-
891           plest way of using them is provided in the file  called  pcredemo.c  in
892           the  source distribution. The pcresample documentation describes how to
893           compile and run it.
894    
895           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
896           ble,  is  also provided. This uses a different algorithm for the match-
897           ing. The alternative algorithm finds all possible matches (at  a  given
898           point  in  the subject), and scans the subject just once. However, this
899           algorithm does not return captured substrings. A description of the two
900           matching  algorithms and their advantages and disadvantages is given in
901           the pcrematching documentation.
902    
903           In addition to the main compiling and  matching  functions,  there  are
904           convenience functions for extracting captured substrings from a subject
905           string that is matched by pcre_exec(). They are:
906    
907             pcre_copy_substring()
908             pcre_copy_named_substring()
909             pcre_get_substring()
910             pcre_get_named_substring()
911             pcre_get_substring_list()
912             pcre_get_stringnumber()
913             pcre_get_stringtable_entries()
914    
915           pcre_free_substring() and pcre_free_substring_list() are also provided,
916           to free the memory used for extracted strings.
917    
918           The  function  pcre_maketables()  is  used  to build a set of character
919           tables  in  the  current  locale   for   passing   to   pcre_compile(),
920           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
921           provided for specialist use.  Most  commonly,  no  special  tables  are
922           passed,  in  which case internal tables that are generated when PCRE is
923           built are used.
924    
925           The function pcre_fullinfo() is used to find out  information  about  a
926           compiled  pattern; pcre_info() is an obsolete version that returns only
927           some of the available information, but is retained for  backwards  com-
928           patibility.   The function pcre_version() returns a pointer to a string
929           containing the version of PCRE and its date of release.
930    
931           The function pcre_refcount() maintains a  reference  count  in  a  data
932           block  containing  a compiled pattern. This is provided for the benefit
933           of object-oriented applications.
934    
935           The global variables pcre_malloc and pcre_free  initially  contain  the
936           entry  points  of  the  standard malloc() and free() functions, respec-
937           tively. PCRE calls the memory management functions via these variables,
938           so  a  calling  program  can replace them if it wishes to intercept the
939           calls. This should be done before calling any PCRE functions.
940    
941           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
942           indirections  to  memory  management functions. These special functions
943           are used only when PCRE is compiled to use  the  heap  for  remembering
944           data, instead of recursive function calls, when running the pcre_exec()
945           function. See the pcrebuild documentation for  details  of  how  to  do
946           this.  It  is  a non-standard way of building PCRE, for use in environ-
947           ments that have limited stacks. Because of the greater  use  of  memory
948           management,  it  runs  more  slowly. Separate functions are provided so
949           that special-purpose external code can be  used  for  this  case.  When
950           used,  these  functions  are always called in a stack-like manner (last
951           obtained, first freed), and always for memory blocks of the same  size.
952           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
953           mentation.
954    
955           The global variable pcre_callout initially contains NULL. It can be set
956           by  the  caller  to  a "callout" function, which PCRE will then call at
957           specified points during a matching operation. Details are given in  the
958           pcrecallout documentation.
959    
960    
961    NEWLINES
962    
963           PCRE  supports five different conventions for indicating line breaks in
964           strings: a single CR (carriage return) character, a  single  LF  (line-
965           feed) character, the two-character sequence CRLF, any of the three pre-
966           ceding, or any Unicode newline sequence. The Unicode newline  sequences
967           are  the  three just mentioned, plus the single characters VT (vertical
968           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
969           separator, U+2028), and PS (paragraph separator, U+2029).
970    
971           Each  of  the first three conventions is used by at least one operating
972           system as its standard newline sequence. When PCRE is built, a  default
973           can  be  specified.  The default default is LF, which is the Unix stan-
974           dard. When PCRE is run, the default can be overridden,  either  when  a
975           pattern is compiled, or when it is matched.
976    
977           At compile time, the newline convention can be specified by the options
978           argument of pcre_compile(), or it can be specified by special  text  at
979           the start of the pattern itself; this overrides any other settings. See
980           the pcrepattern page for details of the special character sequences.
981    
982           In the PCRE documentation the word "newline" is used to mean "the char-
983           acter  or pair of characters that indicate a line break". The choice of
984           newline convention affects the handling of  the  dot,  circumflex,  and
985           dollar metacharacters, the handling of #-comments in /x mode, and, when
986           CRLF is a recognized line ending sequence, the match position  advance-
987           ment for a non-anchored pattern. There is more detail about this in the
988           section on pcre_exec() options below.
989    
990           The choice of newline convention does not affect the interpretation  of
991           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
992           which is controlled in a similar way, but by separate options.
993    
994    
995  MULTITHREADING  MULTITHREADING
996    
997       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
998       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
999       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
1000       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
1001       threads.  
1002           The compiled form of a regular expression is not altered during  match-
1003       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
1004       during  matching, so the same compiled pattern can safely be         at once.
1005       used by several threads at once.  
1006    
1007    SAVING PRECOMPILED PATTERNS FOR LATER USE
1008    
1009           The compiled form of a regular expression can be saved and re-used at a
1010           later  time,  possibly by a different program, and even on a host other
1011           than the one on which  it  was  compiled.  Details  are  given  in  the
1012           pcreprecompile  documentation.  However, compiling a regular expression
1013           with one version of PCRE for use with a different version is not  guar-
1014           anteed to work and may cause crashes.
1015    
1016    
1017  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
1018    
1019       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
1020    
1021       The function pcre_config() makes  it  possible  for  a  PCRE         The  function pcre_config() makes it possible for a PCRE client to dis-
1022       client  to  discover  which optional features have been com-         cover which optional features have been compiled into the PCRE library.
1023       piled into the PCRE library. The pcrebuild documentation has         The  pcrebuild documentation has more details about these optional fea-
1024       more details about these optional features.         tures.
1025    
1026       The first argument for pcre_config() is an integer, specify-         The first argument for pcre_config() is an  integer,  specifying  which
1027       ing  which information is required; the second argument is a         information is required; the second argument is a pointer to a variable
1028       pointer to a variable into which the information is  placed.         into which the information is  placed.  The  following  information  is
1029       The following information is available:         available:
1030    
1031         PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
1032    
1033       The output is an integer that is set to one if UTF-8 support         The  output is an integer that is set to one if UTF-8 support is avail-
1034       is available; otherwise it is set to zero.         able; otherwise it is set to zero.
1035    
1036         PCRE_CONFIG_NEWLINE           PCRE_CONFIG_UNICODE_PROPERTIES
1037    
1038       The output is an integer that is set to  the  value  of  the         The output is an integer that is set to  one  if  support  for  Unicode
1039       code  that  is  used for the newline character. It is either         character properties is available; otherwise it is set to zero.
      linefeed (10) or carriage return (13), and  should  normally  
      be the standard character for your operating system.  
1040    
1041         PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_NEWLINE
1042    
1043       The output is an integer that contains the number  of  bytes         The  output  is  an integer whose value specifies the default character
1044       used  for  internal linkage in compiled regular expressions.         sequence that is recognized as meaning "newline". The four values  that
1045       The value is 2, 3, or 4. Larger values allow larger  regular         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
1046       expressions  to be compiled, at the expense of slower match-         and -1 for ANY. The default should normally be  the  standard  sequence
1047       ing. The default value of 2 is sufficient for  all  but  the         for your operating system.
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
1048    
1049         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_BSR
1050    
1051       The output is an integer that contains the  threshold  above         The output is an integer whose value indicates what character sequences
1052       which  the POSIX interface uses malloc() for output vectors.         the \R escape sequence matches by default. A value of 0 means  that  \R
1053       Further details are given in the pcreposix documentation.         matches  any  Unicode  line ending sequence; a value of 1 means that \R
1054           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1055           tern is compiled or matched.
1056    
1057         PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_LINK_SIZE
1058    
1059       The output is an integer that gives the  default  limit  for         The  output  is  an  integer that contains the number of bytes used for
1060       the   number  of  internal  matching  function  calls  in  a         internal linkage in compiled regular expressions. The value is 2, 3, or
1061       pcre_exec()  execution.  Further  details  are  given   with         4.  Larger  values  allow larger regular expressions to be compiled, at
1062       pcre_exec() below.         the expense of slower matching. The default value of  2  is  sufficient
1063           for  all  but  the  most massive patterns, since it allows the compiled
1064           pattern to be up to 64K in size.
1065    
1066             PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1067    
1068           The output is an integer that contains the threshold  above  which  the
1069           POSIX  interface  uses malloc() for output vectors. Further details are
1070           given in the pcreposix documentation.
1071    
1072             PCRE_CONFIG_MATCH_LIMIT
1073    
1074           The output is an integer that gives the default limit for the number of
1075           internal  matching  function  calls in a pcre_exec() execution. Further
1076           details are given with pcre_exec() below.
1077    
1078             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1079    
1080           The output is an integer that gives the default limit for the depth  of
1081           recursion  when calling the internal matching function in a pcre_exec()
1082           execution. Further details are given with pcre_exec() below.
1083    
1084             PCRE_CONFIG_STACKRECURSE
1085    
1086           The output is an integer that is set to one if internal recursion  when
1087           running pcre_exec() is implemented by recursive function calls that use
1088           the stack to remember their state. This is the usual way that  PCRE  is
1089           compiled. The output is zero if PCRE was compiled to use blocks of data
1090           on the  heap  instead  of  recursive  function  calls.  In  this  case,
1091           pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1092           blocks on the heap, thus avoiding the use of the stack.
1093    
1094    
1095  COMPILING A PATTERN  COMPILING A PATTERN
1096    
1097       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
1098            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1099            const unsigned char *tableptr);              const unsigned char *tableptr);
1100    
1101       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
1102       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
1103       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
1104       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
1105       pcre_malloc is returned. This contains the compiled code and  
1106       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
1107       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
1108       not  externally  defined. It is up to the caller to free the         the two interfaces is that pcre_compile2() has an additional  argument,
1109       memory when it is no longer required.         errorcodeptr, via which a numerical error code can be returned.
1110    
1111       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
1112       that is, it does not depend on memory location, the complete         the pattern argument. A pointer to a single block  of  memory  that  is
1113       pcre data block is not fully relocatable,  because  it  con-         obtained  via  pcre_malloc is returned. This contains the compiled code
1114       tains  a  copy of the tableptr argument, which is an address         and related data. The pcre type is defined for the returned block; this
1115       (see below).         is a typedef for a structure whose contents are not externally defined.
1116       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
1117       the  compilation.  It  should  be  zero  if  no  options are         longer required.
1118       required. Some of the options, in particular, those that are  
1119       compatible  with Perl, can also be set and unset from within         Although  the compiled code of a PCRE regex is relocatable, that is, it
1120       the pattern (see the detailed description of regular expres-         does not depend on memory location, the complete pcre data block is not
1121       sions  in the pcrepattern documentation). For these options,         fully  relocatable, because it may contain a copy of the tableptr argu-
1122       the contents of the options argument specifies their initial         ment, which is an address (see below).
1123       settings  at  the  start  of  compilation and execution. The  
1124       PCRE_ANCHORED option can be set at the time of  matching  as         The options argument contains various bit settings that affect the com-
1125       well as at compile time.         pilation.  It  should be zero if no options are required. The available
1126           options are described below. Some of them, in  particular,  those  that
1127       If errptr is NULL, pcre_compile() returns NULL  immediately.         are  compatible  with  Perl,  can also be set and unset from within the
1128       Otherwise, if compilation of a pattern fails, pcre_compile()         pattern (see the detailed description  in  the  pcrepattern  documenta-
1129       returns NULL, and sets the variable pointed to by errptr  to         tion).  For  these options, the contents of the options argument speci-
1130       point  to a textual error message. The offset from the start         fies their initial settings at the start of compilation and  execution.
1131       of  the  pattern  to  the  character  where  the  error  was         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1132       discovered   is   placed  in  the  variable  pointed  to  by         of matching as well as at compile time.
1133       erroffset, which must not be NULL. If it  is,  an  immediate  
1134       error is given.         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1135           if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1136       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         sets the variable pointed to by errptr to point to a textual error mes-
1137       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
1138       compiled, using the default C  locale.  Otherwise,  tableptr         try to free it. The offset from the start of the pattern to the charac-
1139       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
1140       section on locale support below.         by erroffset, which must not be NULL. If it is, an immediate  error  is
1141           given.
1142       This code fragment shows a typical straightforward  call  to  
1143       pcre_compile():         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1144           codeptr argument is not NULL, a non-zero error code number is  returned
1145         pcre *re;         via  this argument in the event of an error. This is in addition to the
1146         const char *error;         textual error message. Error codes and messages are listed below.
1147         int erroffset;  
1148         re = pcre_compile(         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1149           "^A.*Z",          /* the pattern */         character  tables  that  are  built  when  PCRE  is compiled, using the
1150           0,                /* default options */         default C locale. Otherwise, tableptr must be an address  that  is  the
1151           &error,           /* for error message */         result  of  a  call to pcre_maketables(). This value is stored with the
1152           &erroffset,       /* for error offset */         compiled pattern, and used again by pcre_exec(), unless  another  table
1153           NULL);            /* use default character tables */         pointer is passed to it. For more discussion, see the section on locale
1154           support below.
1155       The following option bits are defined:  
1156           This code fragment shows a typical straightforward  call  to  pcre_com-
1157         PCRE_ANCHORED         pile():
1158    
1159       If this bit is set, the pattern is forced to be  "anchored",           pcre *re;
1160       that is, it is constrained to match only at the first match-           const char *error;
1161       ing point in the string which is being searched  (the  "sub-           int erroffset;
1162       ject string"). This effect can also be achieved by appropri-           re = pcre_compile(
1163       ate constructs in the pattern itself, which is the only  way             "^A.*Z",          /* the pattern */
1164       to do it in Perl.             0,                /* default options */
1165               &error,           /* for error message */
1166         PCRE_CASELESS             &erroffset,       /* for error offset */
1167               NULL);            /* use default character tables */
1168       If this bit is set, letters in the pattern match both  upper  
1169       and  lower  case  letters.  It  is  equivalent  to Perl's /i         The  following  names  for option bits are defined in the pcre.h header
1170       option, and it can be changed within a  pattern  by  a  (?i)         file:
1171       option setting.  
1172             PCRE_ANCHORED
1173         PCRE_DOLLAR_ENDONLY  
1174           If this bit is set, the pattern is forced to be "anchored", that is, it
1175       If this bit is set, a dollar metacharacter  in  the  pattern         is  constrained to match only at the first matching point in the string
1176       matches  only at the end of the subject string. Without this         that is being searched (the "subject string"). This effect can also  be
1177       option, a dollar also matches immediately before  the  final         achieved  by appropriate constructs in the pattern itself, which is the
1178       character  if it is a newline (but not before any other new-         only way to do it in Perl.
1179       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
1180       PCRE_MULTILINE is set. There is no equivalent to this option           PCRE_AUTO_CALLOUT
1181       in Perl, and no way to set it within a pattern.  
1182           If this bit is set, pcre_compile() automatically inserts callout items,
1183         PCRE_DOTALL         all  with  number  255, before each pattern item. For discussion of the
1184           callout facility, see the pcrecallout documentation.
1185       If this bit is  set,  a  dot  metacharater  in  the  pattern  
1186       matches all characters, including newlines. Without it, new-           PCRE_BSR_ANYCRLF
1187       lines are excluded. This option is equivalent to  Perl's  /s           PCRE_BSR_UNICODE
1188       option,  and  it  can  be changed within a pattern by a (?s)  
1189       option setting. A negative class such as [^a] always matches         These options (which are mutually exclusive) control what the \R escape
1190       a  newline  character,  independent  of  the setting of this         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1191       option.         or to match any Unicode newline sequence. The default is specified when
1192           PCRE is built. It can be overridden from within the pattern, or by set-
1193         PCRE_EXTENDED         ting an option when a compiled pattern is matched.
1194    
1195       If this bit is set, whitespace data characters in  the  pat-           PCRE_CASELESS
1196       tern  are  totally  ignored  except when escaped or inside a  
1197       character class. Whitespace does not include the VT  charac-         If this bit is set, letters in the pattern match both upper  and  lower
1198       ter  (code 11). In addition, characters between an unescaped         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1199       # outside a character class and the next newline  character,         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1200       inclusive, are also ignored. This is equivalent to Perl's /x         always  understands the concept of case for characters whose values are
1201       option, and it can be changed within a  pattern  by  a  (?x)         less than 128, so caseless matching is always possible. For  characters
1202       option setting.         with  higher  values,  the concept of case is supported if PCRE is com-
1203           piled with Unicode property support, but not otherwise. If you want  to
1204       This option makes it possible  to  include  comments  inside         use  caseless  matching  for  characters 128 and above, you must ensure
1205       complicated patterns.  Note, however, that this applies only         that PCRE is compiled with Unicode property support  as  well  as  with
1206       to data characters. Whitespace characters may  never  appear         UTF-8 support.
1207       within special character sequences in a pattern, for example  
1208       within the sequence (?( which introduces a conditional  sub-           PCRE_DOLLAR_ENDONLY
1209       pattern.  
1210           If  this bit is set, a dollar metacharacter in the pattern matches only
1211         PCRE_EXTRA         at the end of the subject string. Without this option,  a  dollar  also
1212           matches  immediately before a newline at the end of the string (but not
1213       This option was invented in  order  to  turn  on  additional         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1214       functionality of PCRE that is incompatible with Perl, but it         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1215       is currently of very little use. When set, any backslash  in         Perl, and no way to set it within a pattern.
1216       a  pattern  that is followed by a letter that has no special  
1217       meaning causes an error, thus reserving  these  combinations           PCRE_DOTALL
1218       for  future  expansion.  By default, as in Perl, a backslash  
1219       followed by a letter with no special meaning is treated as a         If this bit is set, a dot metacharater in the pattern matches all char-
1220       literal.  There  are at present no other features controlled         acters,  including  those that indicate newline. Without it, a dot does
1221       by this option. It can also be set by a (?X) option  setting         not match when the current position is at a  newline.  This  option  is
1222       within a pattern.         equivalent  to Perl's /s option, and it can be changed within a pattern
1223           by a (?s) option setting. A negative class such as [^a] always  matches
1224         PCRE_MULTILINE         newline characters, independent of the setting of this option.
1225    
1226       By default, PCRE treats the subject string as consisting  of           PCRE_DUPNAMES
1227       a  single "line" of characters (even if it actually contains  
1228       several newlines). The "start  of  line"  metacharacter  (^)         If  this  bit is set, names used to identify capturing subpatterns need
1229       matches  only  at the start of the string, while the "end of         not be unique. This can be helpful for certain types of pattern when it
1230       line" metacharacter ($) matches  only  at  the  end  of  the         is  known  that  only  one instance of the named subpattern can ever be
1231       string,    or   before   a   terminating   newline   (unless         matched. There are more details of named subpatterns  below;  see  also
1232       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.         the pcrepattern documentation.
1233    
1234       When PCRE_MULTILINE it is set, the "start of line" and  "end           PCRE_EXTENDED
1235       of  line"  constructs match immediately following or immedi-  
1236       ately before any newline  in  the  subject  string,  respec-         If  this  bit  is  set,  whitespace  data characters in the pattern are
1237       tively,  as  well  as  at  the  very  start and end. This is         totally ignored except when escaped or inside a character class. White-
1238       equivalent to Perl's /m option, and it can be changed within         space does not include the VT character (code 11). In addition, charac-
1239       a  pattern  by  a  (?m) option setting. If there are no "\n"         ters between an unescaped # outside a character class and the next new-
1240       characters in a subject string, or no occurrences of ^ or  $         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1241       in a pattern, setting PCRE_MULTILINE has no effect.         option, and it can be changed within a pattern by a  (?x)  option  set-
1242           ting.
1243         PCRE_NO_AUTO_CAPTURE  
1244           This  option  makes  it possible to include comments inside complicated
1245       If this option is set, it disables the use of numbered  cap-         patterns.  Note, however, that this applies only  to  data  characters.
1246       turing  parentheses  in the pattern. Any opening parenthesis         Whitespace   characters  may  never  appear  within  special  character
1247       that is not followed by ? behaves as if it were followed  by         sequences in a pattern, for  example  within  the  sequence  (?(  which
1248       ?:  but  named  parentheses  can still be used for capturing         introduces a conditional subpattern.
1249       (and they acquire numbers in the usual  way).  There  is  no  
1250       equivalent of this option in Perl.           PCRE_EXTRA
1251    
1252         PCRE_UNGREEDY         This  option  was invented in order to turn on additional functionality
1253           of PCRE that is incompatible with Perl, but it  is  currently  of  very
1254       This option inverts the "greediness" of the  quantifiers  so         little  use. When set, any backslash in a pattern that is followed by a
1255       that  they  are  not greedy by default, but become greedy if         letter that has no special meaning  causes  an  error,  thus  reserving
1256       followed by "?". It is not compatible with Perl. It can also         these  combinations  for  future  expansion.  By default, as in Perl, a
1257       be set by a (?U) option setting within the pattern.         backslash followed by a letter with no special meaning is treated as  a
1258           literal.  (Perl can, however, be persuaded to give a warning for this.)
1259         PCRE_UTF8         There are at present no other features controlled by  this  option.  It
1260           can also be set by a (?X) option setting within a pattern.
1261       This option causes PCRE to regard both the pattern  and  the  
1262       subject  as  strings  of UTF-8 characters instead of single-           PCRE_FIRSTLINE
1263       byte character strings. However, it  is  available  only  if  
1264       PCRE  has  been  built to include UTF-8 support. If not, the         If  this  option  is  set,  an  unanchored pattern is required to match
1265       use of this option provokes an error. Details  of  how  this         before or at the first  newline  in  the  subject  string,  though  the
1266       option  changes  the behaviour of PCRE are given in the sec-         matched text may continue over the newline.
1267       tion on UTF-8 support in the main pcre page.  
1268             PCRE_JAVASCRIPT_COMPAT
1269         PCRE_NO_UTF8_CHECK  
1270           If this option is set, PCRE's behaviour is changed in some ways so that
1271       When PCRE_UTF8 is set, the validity  of  the  pattern  as  a         it is compatible with JavaScript rather than Perl. The changes  are  as
1272       UTF-8  string  is automatically checked. If an invalid UTF-8         follows:
1273       sequence of bytes is found, pcre_compile() returns an error.  
1274       If you already know that your pattern is valid, and you want         (1)  A  lone  closing square bracket in a pattern causes a compile-time
1275       to skip this check for performance reasons, you can set  the         error, because this is illegal in JavaScript (by default it is  treated
1276       PCRE_NO_UTF8_CHECK  option.  When  it  is set, the effect of         as a data character). Thus, the pattern AB]CD becomes illegal when this
1277       passing an invalid UTF-8 string as a pattern  is  undefined.         option is set.
1278       It  may  cause  your program to crash.  Note that there is a  
1279       similar option  for  suppressing  the  checking  of  subject         (2) At run time, a back reference to an unset subpattern group  matches
1280       strings passed to pcre_exec().         an  empty  string (by default this causes the current matching alterna-
1281           tive to fail). A pattern such as (\1)(a) succeeds when this  option  is
1282           set  (assuming  it can find an "a" in the subject), whereas it fails by
1283           default, for Perl compatibility.
1284    
1285             PCRE_MULTILINE
1286    
1287           By default, PCRE treats the subject string as consisting  of  a  single
1288           line  of characters (even if it actually contains newlines). The "start
1289           of line" metacharacter (^) matches only at the  start  of  the  string,
1290           while  the  "end  of line" metacharacter ($) matches only at the end of
1291           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1292           is set). This is the same as Perl.
1293    
1294           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1295           constructs match immediately following or immediately  before  internal
1296           newlines  in  the  subject string, respectively, as well as at the very
1297           start and end. This is equivalent to Perl's /m option, and  it  can  be
1298           changed within a pattern by a (?m) option setting. If there are no new-
1299           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1300           setting PCRE_MULTILINE has no effect.
1301    
1302             PCRE_NEWLINE_CR
1303             PCRE_NEWLINE_LF
1304             PCRE_NEWLINE_CRLF
1305             PCRE_NEWLINE_ANYCRLF
1306             PCRE_NEWLINE_ANY
1307    
1308           These  options  override the default newline definition that was chosen
1309           when PCRE was built. Setting the first or the second specifies  that  a
1310           newline  is  indicated  by a single character (CR or LF, respectively).
1311           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1312           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1313           that any of the three preceding sequences should be recognized. Setting
1314           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1315           recognized. The Unicode newline sequences are the three just mentioned,
1316           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1317           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1318           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1319           UTF-8 mode.
1320    
1321           The newline setting in the  options  word  uses  three  bits  that  are
1322           treated as a number, giving eight possibilities. Currently only six are
1323           used (default plus the five values above). This means that if  you  set
1324           more  than one newline option, the combination may or may not be sensi-
1325           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1326           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1327           cause an error.
1328    
1329           The only time that a line break is specially recognized when  compiling
1330           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1331           character class is encountered. This indicates  a  comment  that  lasts
1332           until  after the next line break sequence. In other circumstances, line
1333           break  sequences  are  treated  as  literal  data,   except   that   in
1334           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1335           and are therefore ignored.
1336    
1337           The newline option that is set at compile time becomes the default that
1338           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1339    
1340             PCRE_NO_AUTO_CAPTURE
1341    
1342           If this option is set, it disables the use of numbered capturing paren-
1343           theses  in the pattern. Any opening parenthesis that is not followed by
1344           ? behaves as if it were followed by ?: but named parentheses can  still
1345           be  used  for  capturing  (and  they acquire numbers in the usual way).
1346           There is no equivalent of this option in Perl.
1347    
1348             PCRE_UNGREEDY
1349    
1350           This option inverts the "greediness" of the quantifiers  so  that  they
1351           are  not greedy by default, but become greedy if followed by "?". It is
1352           not compatible with Perl. It can also be set by a (?U)  option  setting
1353           within the pattern.
1354    
1355             PCRE_UTF8
1356    
1357           This  option  causes PCRE to regard both the pattern and the subject as
1358           strings of UTF-8 characters instead of single-byte  character  strings.
1359           However,  it is available only when PCRE is built to include UTF-8 sup-
1360           port. If not, the use of this option provokes an error. Details of  how
1361           this  option  changes the behaviour of PCRE are given in the section on
1362           UTF-8 support in the main pcre page.
1363    
1364             PCRE_NO_UTF8_CHECK
1365    
1366           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1367           automatically  checked.  There  is  a  discussion about the validity of
1368           UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1369           bytes  is  found,  pcre_compile() returns an error. If you already know
1370           that your pattern is valid, and you want to skip this check for perfor-
1371           mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1372           set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1373           undefined.  It  may  cause your program to crash. Note that this option
1374           can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1375           UTF-8 validity checking of subject strings.
1376    
1377    
1378    COMPILATION ERROR CODES
1379    
1380           The  following  table  lists  the  error  codes than may be returned by
1381           pcre_compile2(), along with the error messages that may be returned  by
1382           both  compiling functions. As PCRE has developed, some error codes have
1383           fallen out of use. To avoid confusion, they have not been re-used.
1384    
1385              0  no error
1386              1  \ at end of pattern
1387              2  \c at end of pattern
1388              3  unrecognized character follows \
1389              4  numbers out of order in {} quantifier
1390              5  number too big in {} quantifier
1391              6  missing terminating ] for character class
1392              7  invalid escape sequence in character class
1393              8  range out of order in character class
1394              9  nothing to repeat
1395             10  [this code is not in use]
1396             11  internal error: unexpected repeat
1397             12  unrecognized character after (? or (?-
1398             13  POSIX named classes are supported only within a class
1399             14  missing )
1400             15  reference to non-existent subpattern
1401             16  erroffset passed as NULL
1402             17  unknown option bit(s) set
1403             18  missing ) after comment
1404             19  [this code is not in use]
1405             20  regular expression is too large
1406             21  failed to get memory
1407             22  unmatched parentheses
1408             23  internal error: code overflow
1409             24  unrecognized character after (?<
1410             25  lookbehind assertion is not fixed length
1411             26  malformed number or name after (?(
1412             27  conditional group contains more than two branches
1413             28  assertion expected after (?(
1414             29  (?R or (?[+-]digits must be followed by )
1415             30  unknown POSIX class name
1416             31  POSIX collating elements are not supported
1417             32  this version of PCRE is not compiled with PCRE_UTF8 support
1418             33  [this code is not in use]
1419             34  character value in \x{...} sequence is too large
1420             35  invalid condition (?(0)
1421             36  \C not allowed in lookbehind assertion
1422             37  PCRE does not support \L, \l, \N, \U, or \u
1423             38  number after (?C is > 255
1424             39  closing ) for (?C expected
1425             40  recursive call could loop indefinitely
1426             41  unrecognized character after (?P
1427             42  syntax error in subpattern name (missing terminator)
1428             43  two named subpatterns have the same name
1429             44  invalid UTF-8 string
1430             45  support for \P, \p, and \X has not been compiled
1431             46  malformed \P or \p sequence
1432             47  unknown property name after \P or \p
1433             48  subpattern name is too long (maximum 32 characters)
1434             49  too many named subpatterns (maximum 10000)
1435             50  [this code is not in use]
1436             51  octal value is greater than \377 (not in UTF-8 mode)
1437             52  internal error: overran compiling workspace
1438             53  internal  error:  previously-checked  referenced  subpattern  not
1439           found
1440             54  DEFINE group contains more than one branch
1441             55  repeating a DEFINE group is not allowed
1442             56  inconsistent NEWLINE options
1443             57  \g is not followed by a braced, angle-bracketed, or quoted
1444                   name/number or by a plain number
1445             58  a numbered reference must not be zero
1446             59  (*VERB) with an argument is not supported
1447             60  (*VERB) not recognized
1448             61  number is too big
1449             62  subpattern name expected
1450             63  digit expected after (?+
1451             64  ] is an invalid data character in JavaScript compatibility mode
1452    
1453           The  numbers  32  and 10000 in errors 48 and 49 are defaults; different
1454           values may be used if the limits were changed when PCRE was built.
1455    
1456    
1457  STUDYING A PATTERN  STUDYING A PATTERN
1458    
1459       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1460            const char **errptr);              const char **errptr);
1461    
1462       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
1463       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
1464       the time taken for matching. The function pcre_study() takes         matching. The function pcre_study() takes a pointer to a compiled  pat-
1465       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1466       studing the pattern  produces  additional  information  that         information that will help speed up matching,  pcre_study()  returns  a
1467       will  help speed up matching, pcre_study() returns a pointer         pointer  to a pcre_extra block, in which the study_data field points to
1468       to a pcre_extra block, in which the study_data field  points         the results of the study.
1469       to the results of the study.  
1470           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1471       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1472       directly  to pcre_exec(). However, the pcre_extra block also         that can be set by the caller before the block  is  passed;  these  are
1473       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
1474       the  block is passed; these are described below. If studying  
1475       the pattern does not  produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1476       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1477       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
1478       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
1479    
1480       The second argument contains option  bits.  At  present,  no         The second argument of pcre_study() contains option bits.  At  present,
1481       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1482       should always be zero.  
1483           The  third argument for pcre_study() is a pointer for an error message.
1484       The third argument for pcre_study()  is  a  pointer  for  an         If studying succeeds (even if no data is  returned),  the  variable  it
1485       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
1486       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
1487       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
1488       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1489       pcre_study(), to be sure that it has run successfully.  
1490           This is a typical call to pcre_study():
1491       This is a typical call to pcre_study():  
1492             pcre_extra *pe;
1493         pcre_extra *pe;           pe = pcre_study(
1494         pe = pcre_study(             re,             /* result of pcre_compile() */
1495           re,             /* result of pcre_compile() */             0,              /* no options exist */
1496           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1497           &error);        /* set to NULL or points to a message */  
1498           At present, studying a pattern is useful only for non-anchored patterns
1499       At present, studying a  pattern  is  useful  only  for  non-         that  do not have a single fixed starting character. A bitmap of possi-
1500       anchored  patterns  that do not have a single fixed starting         ble starting bytes is created.
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1501    
1502    
1503  LOCALE SUPPORT  LOCALE SUPPORT
1504    
1505       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1506       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
1507       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
1508       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
1509       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
1510       locale  when  PCRE  is compiled. This is used when the final         with  Unicode  character property support. The use of locales with Uni-
1511       argument of pcre_compile() is NULL, and  is  sufficient  for         code is discouraged. If you are handling characters with codes  greater
1512       many applications.         than  128, you should either use UTF-8 and Unicode, or use locales, but
1513           not try to mix the two.
1514       An alternative set of tables can, however, be supplied. Such  
1515       tables  are built by calling the pcre_maketables() function,         PCRE contains an internal set of tables that are used  when  the  final
1516       which has no arguments, in the relevant locale.  The  result         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1517       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1518       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1519       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1520       greater than 128 are treated as letters), the following code         which may cause them to be different.
1521       could be used:  
1522           The  internal tables can always be overridden by tables supplied by the
1523         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1524         tables = pcre_maketables();         from  the  default.  As more and more applications change to using Uni-
1525         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1526    
1527       The  tables  are  built  in  memory  that  is  obtained  via         External tables are built by calling  the  pcre_maketables()  function,
1528       pcre_malloc.  The  pointer that is passed to pcre_compile is         which  has no arguments, in the relevant locale. The result can then be
1529       saved with the compiled pattern, and  the  same  tables  are         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1530       used via this pointer by pcre_study() and pcre_exec(). Thus,         example,  to  build  and use tables that are appropriate for the French
1531       for any single pattern, compilation, studying  and  matching         locale (where accented characters with  values  greater  than  128  are
1532       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1533       compiled in different locales. It is the caller's  responsi-  
1534       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1535       remains available for as long as it is needed.           tables = pcre_maketables();
1536             re = pcre_compile(..., tables);
1537    
1538           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1539           if you are using Windows, the name for the French locale is "french".
1540    
1541           When pcre_maketables() runs, the tables are built  in  memory  that  is
1542           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1543           that the memory containing the tables remains available for as long  as
1544           it is needed.
1545    
1546           The pointer that is passed to pcre_compile() is saved with the compiled
1547           pattern, and the same tables are used via this pointer by  pcre_study()
1548           and normally also by pcre_exec(). Thus, by default, for any single pat-
1549           tern, compilation, studying and matching all happen in the same locale,
1550           but different patterns can be compiled in different locales.
1551    
1552           It  is  possible to pass a table pointer or NULL (indicating the use of
1553           the internal tables) to pcre_exec(). Although  not  intended  for  this
1554           purpose,  this facility could be used to match a pattern in a different
1555           locale from the one in which it was compiled. Passing table pointers at
1556           run time is discussed below in the section on matching a pattern.
1557    
1558    
1559  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1560    
1561       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1562            int what, void *where);              int what, void *where);
1563    
1564       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1565       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1566       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1567       ity (and is documented below).  
1568       The first argument for pcre_fullinfo() is a pointer  to  the         The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1569       compiled  pattern.  The  second  argument  is  the result of         pattern. The second argument is the result of pcre_study(), or NULL  if
1570       pcre_study(), or NULL if the pattern was  not  studied.  The         the  pattern  was not studied. The third argument specifies which piece
1571       third  argument  specifies  which  piece  of  information is         of information is required, and the fourth argument is a pointer  to  a
1572       required, and the fourth argument is a pointer to a variable         variable  to  receive  the  data. The yield of the function is zero for
1573       to  receive  the data. The yield of the function is zero for         success, or one of the following negative numbers:
1574       success, or one of the following negative numbers:  
1575             PCRE_ERROR_NULL       the argument code was NULL
1576         PCRE_ERROR_NULL       the argument code was NULL                                 the argument where was NULL
1577                               the argument where was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1578         PCRE_ERROR_BADMAGIC   the "magic number" was not found           PCRE_ERROR_BADOPTION  the value of what was invalid
1579         PCRE_ERROR_BADOPTION  the value of what was invalid  
1580           The "magic number" is placed at the start of each compiled  pattern  as
1581       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         an  simple check against passing an arbitrary memory pointer. Here is a
1582       length of the compiled pattern:         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1583           pattern:
1584         int rc;  
1585         unsigned long int length;           int rc;
1586         rc = pcre_fullinfo(           size_t length;
1587           re,               /* result of pcre_compile() */           rc = pcre_fullinfo(
1588           pe,               /* result of pcre_study(), or NULL */             re,               /* result of pcre_compile() */
1589           PCRE_INFO_SIZE,   /* what is required */             pe,               /* result of pcre_study(), or NULL */
1590           &length);         /* where to put the data */             PCRE_INFO_SIZE,   /* what is required */
1591               &length);         /* where to put the data */
1592       The possible values for the third argument  are  defined  in  
1593       pcre.h, and are as follows:         The  possible  values for the third argument are defined in pcre.h, and
1594           are as follows:
1595         PCRE_INFO_BACKREFMAX  
1596             PCRE_INFO_BACKREFMAX
1597       Return the number of the highest back reference in the  pat-  
1598       tern.  The  fourth argument should point to an int variable.         Return the number of the highest back reference  in  the  pattern.  The
1599       Zero is returned if there are no back references.         fourth  argument  should  point to an int variable. Zero is returned if
1600           there are no back references.
1601         PCRE_INFO_CAPTURECOUNT  
1602             PCRE_INFO_CAPTURECOUNT
1603       Return the number of capturing subpatterns in  the  pattern.  
1604       The fourth argument should point to an int variable.         Return the number of capturing subpatterns in the pattern.  The  fourth
1605           argument should point to an int variable.
1606         PCRE_INFO_FIRSTBYTE  
1607             PCRE_INFO_DEFAULT_TABLES
1608       Return information about  the  first  byte  of  any  matched  
1609       string,  for a non-anchored pattern. (This option used to be         Return  a pointer to the internal default character tables within PCRE.
1610       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         The fourth argument should point to an unsigned char *  variable.  This
1611       for backwards compatibility.)         information call is provided for internal use by the pcre_study() func-
1612           tion. External callers can cause PCRE to use  its  internal  tables  by
1613       If there is a fixed first byte, e.g. from a pattern such  as         passing a NULL table pointer.
1614       (cat|cow|coyote),  it  is returned in the integer pointed to  
1615       by where. Otherwise, if either           PCRE_INFO_FIRSTBYTE
1616    
1617       (a) the pattern was compiled with the PCRE_MULTILINE option,         Return  information  about  the first byte of any matched string, for a
1618       and every branch starts with "^", or         non-anchored pattern. The fourth argument should point to an int  vari-
1619           able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1620       (b) every  branch  of  the  pattern  starts  with  ".*"  and         is still recognized for backwards compatibility.)
1621       PCRE_DOTALL is not set (if it were set, the pattern would be  
1622       anchored),         If there is a fixed first byte, for example, from  a  pattern  such  as
1623           (cat|cow|coyote), its value is returned. Otherwise, if either
1624       -1 is returned, indicating that the pattern matches only  at  
1625       the  start  of  a subject string or after any newline within         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1626       the string. Otherwise -2 is returned. For anchored patterns,         branch starts with "^", or
1627       -2 is returned.  
1628           (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1629         PCRE_INFO_FIRSTTABLE         set (if it were set, the pattern would be anchored),
1630    
1631       If the pattern was studied, and this resulted  in  the  con-         -1  is  returned, indicating that the pattern matches only at the start
1632       struction of a 256-bit table indicating a fixed set of bytes         of a subject string or after any newline within the  string.  Otherwise
1633       for the first byte in any matching string, a pointer to  the         -2 is returned. For anchored patterns, -2 is returned.
1634       table  is  returned.  Otherwise NULL is returned. The fourth  
1635       argument should point to an unsigned char * variable.           PCRE_INFO_FIRSTTABLE
1636    
1637         PCRE_INFO_LASTLITERAL         If  the pattern was studied, and this resulted in the construction of a
1638           256-bit table indicating a fixed set of bytes for the first byte in any
1639       Return the value of the rightmost  literal  byte  that  must         matching  string, a pointer to the table is returned. Otherwise NULL is
1640       exist  in  any  matched  string, other than at its start, if         returned. The fourth argument should point to an unsigned char *  vari-
1641       such a byte has been recorded. The  fourth  argument  should         able.
1642       point  to  an  int variable. If there is no such byte, -1 is  
1643       returned. For anchored patterns,  a  last  literal  byte  is           PCRE_INFO_HASCRORLF
1644       recorded  only  if  it follows something of variable length.  
1645       For example, for the pattern /^a\d+z\d+/ the returned  value         Return  1  if  the  pattern  contains any explicit matches for CR or LF
1646       is "z", but for /^a\dz\d/ the returned value is -1.         characters, otherwise 0. The fourth argument should  point  to  an  int
1647           variable.  An explicit match is either a literal CR or LF character, or
1648         PCRE_INFO_NAMECOUNT         \r or \n.
1649         PCRE_INFO_NAMEENTRYSIZE  
1650         PCRE_INFO_NAMETABLE           PCRE_INFO_JCHANGED
1651    
1652       PCRE supports the use of named as well as numbered capturing         Return 1 if the (?J) or (?-J) option setting is used  in  the  pattern,
1653       parentheses. The names are just an additional way of identi-         otherwise  0. The fourth argument should point to an int variable. (?J)
1654       fying the parentheses,  which  still  acquire  a  number.  A         and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1655       caller  that  wants  to extract data from a named subpattern  
1656       must convert the name to a number in  order  to  access  the           PCRE_INFO_LASTLITERAL
1657       correct  pointers  in  the  output  vector  (described  with  
1658       pcre_exec() below). In order to do this, it must  first  use         Return the value of the rightmost literal byte that must exist  in  any
1659       these  three  values  to  obtain  the name-to-number mapping         matched  string,  other  than  at  its  start,  if such a byte has been
1660       table for the pattern.         recorded. The fourth argument should point to an int variable. If there
1661           is  no such byte, -1 is returned. For anchored patterns, a last literal
1662       The  map  consists  of  a  number  of  fixed-size   entries.         byte is recorded only if it follows something of variable  length.  For
1663       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1664       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both         /^a\dz\d/ the returned value is -1.
1665       of  these return an int value. The entry size depends on the  
1666       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a           PCRE_INFO_NAMECOUNT
1667       pointer to the first entry of the table (a pointer to char).           PCRE_INFO_NAMEENTRYSIZE
1668       The first two bytes of each entry are the number of the cap-           PCRE_INFO_NAMETABLE
1669       turing parenthesis, most significant byte first. The rest of  
1670       the entry is the corresponding name,  zero  terminated.  The         PCRE supports the use of named as well as numbered capturing  parenthe-
1671       names  are  in alphabetical order. For example, consider the         ses.  The names are just an additional way of identifying the parenthe-
1672       following pattern (assume PCRE_EXTENDED  is  set,  so  white         ses, which still acquire numbers. Several convenience functions such as
1673       space - including newlines - is ignored):         pcre_get_named_substring()  are  provided  for extracting captured sub-
1674           strings by name. It is also possible to extract the data  directly,  by
1675         (?P<date> (?P<year>(\d\d)?\d\d) -         first  converting  the  name to a number in order to access the correct
1676         (?P<month>\d\d) - (?P<day>\d\d) )         pointers in the output vector (described with pcre_exec() below). To do
1677           the  conversion,  you  need  to  use  the  name-to-number map, which is
1678       There are four named subpatterns,  so  the  table  has  four         described by these three values.
1679       entries,  and  each  entry in the table is eight bytes long.  
1680       The table is as follows, with non-printing  bytes  shows  in         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1681       hex, and undefined bytes shown as ??:         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1682           of each entry; both of these  return  an  int  value.  The  entry  size
1683         00 01 d  a  t  e  00 ??         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1684         00 05 d  a  y  00 ?? ??         a pointer to the first entry of the table  (a  pointer  to  char).  The
1685         00 04 m  o  n  t  h  00         first two bytes of each entry are the number of the capturing parenthe-
1686         00 02 y  e  a  r  00 ??         sis, most significant byte first. The rest of the entry is  the  corre-
1687           sponding  name,  zero  terminated. The names are in alphabetical order.
1688       When writing code to extract data  from  named  subpatterns,         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1689       remember  that the length of each entry may be different for         theses  numbers.  For  example,  consider the following pattern (assume
1690       each compiled pattern.         PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1691           ignored):
1692         PCRE_INFO_OPTIONS  
1693             (?<date> (?<year>(\d\d)?\d\d) -
1694       Return a copy of the options with which the pattern was com-           (?<month>\d\d) - (?<day>\d\d) )
1695       piled.  The fourth argument should point to an unsigned long  
1696       int variable. These option bits are those specified  in  the         There  are  four  named subpatterns, so the table has four entries, and
1697       call  to  pcre_compile(),  modified  by any top-level option         each entry in the table is eight bytes long. The table is  as  follows,
1698       settings within the pattern itself.         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1699           as ??:
1700       A pattern is automatically anchored by PCRE if  all  of  its  
1701       top-level alternatives begin with one of the following:           00 01 d  a  t  e  00 ??
1702             00 05 d  a  y  00 ?? ??
1703         ^     unless PCRE_MULTILINE is set           00 04 m  o  n  t  h  00
1704         \A    always           00 02 y  e  a  r  00 ??
1705         \G    always  
1706         .*    if PCRE_DOTALL is set and there are no back         When writing code to extract data  from  named  subpatterns  using  the
1707                 references to the subpattern in which .* appears         name-to-number  map,  remember that the length of the entries is likely
1708           to be different for each compiled pattern.
1709       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the  
1710       options returned by pcre_fullinfo().           PCRE_INFO_OKPARTIAL
1711    
1712         PCRE_INFO_SIZE         Return 1 if the pattern can be used for partial matching, otherwise  0.
1713           The  fourth  argument  should point to an int variable. The pcrepartial
1714       Return the size of the compiled pattern, that is, the  value         documentation lists the restrictions that apply to patterns  when  par-
1715       that  was  passed as the argument to pcre_malloc() when PCRE         tial matching is used.
1716       was getting memory in which to place the compiled data.  The  
1717       fourth argument should point to a size_t variable.           PCRE_INFO_OPTIONS
1718    
1719         PCRE_INFO_STUDYSIZE         Return  a  copy of the options with which the pattern was compiled. The
1720           fourth argument should point to an unsigned long  int  variable.  These
1721       Returns the size  of  the  data  block  pointed  to  by  the         option bits are those specified in the call to pcre_compile(), modified
1722       study_data  field  in a pcre_extra block. That is, it is the         by any top-level option settings at the start of the pattern itself. In
1723       value that was passed to pcre_malloc() when PCRE was getting         other  words,  they are the options that will be in force when matching
1724       memory into which to place the data created by pcre_study().         starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1725       The fourth argument should point to a size_t variable.         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1726           and PCRE_EXTENDED.
1727    
1728           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1729           alternatives begin with one of the following:
1730    
1731             ^     unless PCRE_MULTILINE is set
1732             \A    always
1733             \G    always
1734             .*    if PCRE_DOTALL is set and there are no back
1735                     references to the subpattern in which .* appears
1736    
1737           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1738           by pcre_fullinfo().
1739    
1740             PCRE_INFO_SIZE
1741    
1742           Return the size of the compiled pattern, that is, the  value  that  was
1743           passed as the argument to pcre_malloc() when PCRE was getting memory in
1744           which to place the compiled data. The fourth argument should point to a
1745           size_t variable.
1746    
1747             PCRE_INFO_STUDYSIZE
1748    
1749           Return the size of the data block pointed to by the study_data field in
1750           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1751           pcre_malloc() when PCRE was getting memory into which to place the data
1752           created by pcre_study(). The fourth argument should point to  a  size_t
1753           variable.
1754    
1755    
1756  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1757    
1758       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1759    
1760       The pcre_info() function is now obsolete because its  inter-         The  pcre_info()  function is now obsolete because its interface is too
1761       face  is  too  restrictive  to return all the available data         restrictive to return all the available data about a compiled  pattern.
1762       about  a  compiled  pattern.   New   programs   should   use         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1763       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1764       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1765       negative numbers:  
1766             PCRE_ERROR_NULL       the argument code was NULL
1767         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1768         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1769           If  the  optptr  argument is not NULL, a copy of the options with which
1770       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
1771       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1772       it points to (see PCRE_INFO_OPTIONS above).  
1773           If  the  pattern  is  not anchored and the firstcharptr argument is not
1774       If the pattern is not anchored and the firstcharptr argument         NULL, it is used to pass back information about the first character  of
1775       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1776       first    character    of    any    matched    string    (see  
1777       PCRE_INFO_FIRSTBYTE above).  
1778    REFERENCE COUNTS
1779    
1780           int pcre_refcount(pcre *code, int adjust);
1781    
1782           The  pcre_refcount()  function is used to maintain a reference count in
1783           the data block that contains a compiled pattern. It is provided for the
1784           benefit  of  applications  that  operate  in an object-oriented manner,
1785           where different parts of the application may be using the same compiled
1786           pattern, but you want to free the block when they are all done.
1787    
1788           When a pattern is compiled, the reference count field is initialized to
1789           zero.  It is changed only by calling this function, whose action is  to
1790           add  the  adjust  value  (which may be positive or negative) to it. The
1791           yield of the function is the new value. However, the value of the count
1792           is  constrained to lie between 0 and 65535, inclusive. If the new value
1793           is outside these limits, it is forced to the appropriate limit value.
1794    
1795           Except when it is zero, the reference count is not correctly  preserved
1796           if  a  pattern  is  compiled on one host and then transferred to a host
1797           whose byte-order is different. (This seems a highly unlikely scenario.)
1798    
1799    
1800    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1801    
1802           int pcre_exec(const pcre *code, const pcre_extra *extra,
1803                const char *subject, int length, int startoffset,
1804                int options, int *ovector, int ovecsize);
1805    
1806           The  function pcre_exec() is called to match a subject string against a
1807           compiled pattern, which is passed in the code argument. If the  pattern
1808           has been studied, the result of the study should be passed in the extra
1809           argument. This function is the main matching facility of  the  library,
1810           and it operates in a Perl-like manner. For specialist use there is also
1811           an alternative matching function, which is described below in the  sec-
1812           tion about the pcre_dfa_exec() function.
1813    
1814           In  most applications, the pattern will have been compiled (and option-
1815           ally studied) in the same process that calls pcre_exec().  However,  it
1816           is possible to save compiled patterns and study data, and then use them
1817           later in different processes, possibly even on different hosts.  For  a
1818           discussion about this, see the pcreprecompile documentation.
1819    
1820           Here is an example of a simple call to pcre_exec():
1821    
1822             int rc;
1823             int ovector[30];
1824             rc = pcre_exec(
1825               re,             /* result of pcre_compile() */
1826               NULL,           /* we didn't study the pattern */
1827               "some string",  /* the subject string */
1828               11,             /* the length of the subject string */
1829               0,              /* start at offset 0 in the subject */
1830               0,              /* default options */
1831               ovector,        /* vector of integers for substring information */
1832               30);            /* number of elements (NOT size in bytes) */
1833    
1834       Extra data for pcre_exec()
1835    
1836           If  the  extra argument is not NULL, it must point to a pcre_extra data
1837           block. The pcre_study() function returns such a block (when it  doesn't
1838           return  NULL), but you can also create one for yourself, and pass addi-
1839           tional information in it. The pcre_extra block contains  the  following
1840           fields (not necessarily in this order):
1841    
1842             unsigned long int flags;
1843             void *study_data;
1844             unsigned long int match_limit;
1845             unsigned long int match_limit_recursion;
1846             void *callout_data;
1847             const unsigned char *tables;
1848    
1849           The  flags  field  is a bitmap that specifies which of the other fields
1850           are set. The flag bits are:
1851    
1852             PCRE_EXTRA_STUDY_DATA
1853             PCRE_EXTRA_MATCH_LIMIT
1854             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1855             PCRE_EXTRA_CALLOUT_DATA
1856             PCRE_EXTRA_TABLES
1857    
1858           Other flag bits should be set to zero. The study_data field is  set  in
1859           the  pcre_extra  block  that is returned by pcre_study(), together with
1860           the appropriate flag bit. You should not set this yourself, but you may
1861           add  to  the  block by setting the other fields and their corresponding
1862           flag bits.
1863    
1864           The match_limit field provides a means of preventing PCRE from using up
1865           a  vast amount of resources when running patterns that are not going to
1866           match, but which have a very large number  of  possibilities  in  their
1867           search  trees.  The  classic  example  is  the  use of nested unlimited
1868           repeats.
1869    
1870           Internally, PCRE uses a function called match() which it calls  repeat-
1871           edly  (sometimes  recursively). The limit set by match_limit is imposed
1872           on the number of times this function is called during  a  match,  which
1873           has  the  effect  of  limiting the amount of backtracking that can take
1874           place. For patterns that are not anchored, the count restarts from zero
1875           for each position in the subject string.
1876    
1877           The  default  value  for  the  limit can be set when PCRE is built; the
1878           default default is 10 million, which handles all but the  most  extreme
1879           cases.  You  can  override  the  default by suppling pcre_exec() with a
1880           pcre_extra    block    in    which    match_limit    is    set,     and
1881           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1882           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1883    
1884           The match_limit_recursion field is similar to match_limit, but  instead
1885           of limiting the total number of times that match() is called, it limits
1886           the depth of recursion. The recursion depth is a  smaller  number  than
1887           the  total number of calls, because not all calls to match() are recur-
1888           sive.  This limit is of use only if it is set smaller than match_limit.
1889    
1890           Limiting  the  recursion  depth  limits the amount of stack that can be
1891           used, or, when PCRE has been compiled to use memory on the heap instead
1892           of the stack, the amount of heap memory that can be used.
1893    
1894           The  default  value  for  match_limit_recursion can be set when PCRE is
1895           built; the default default  is  the  same  value  as  the  default  for
1896           match_limit.  You can override the default by suppling pcre_exec() with
1897           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1898           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1899           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1900    
1901           The pcre_callout field is used in conjunction with the  "callout"  fea-
1902           ture, which is described in the pcrecallout documentation.
1903    
1904           The  tables  field  is  used  to  pass  a  character  tables pointer to
1905           pcre_exec(); this overrides the value that is stored with the  compiled
1906           pattern.  A  non-NULL value is stored with the compiled pattern only if
1907           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1908           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1909           PCRE's internal tables to be used. This facility is  helpful  when  re-
1910           using  patterns  that  have been saved after compiling with an external
1911           set of tables, because the external tables  might  be  at  a  different
1912           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1913           tion for a discussion of saving compiled patterns for later use.
1914    
1915       Option bits for pcre_exec()
1916    
1917           The unused bits of the options argument for pcre_exec() must  be  zero.
1918           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1919           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1920           PCRE_PARTIAL.
1921    
1922             PCRE_ANCHORED
1923    
1924           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1925           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1926           turned  out to be anchored by virtue of its contents, it cannot be made
1927           unachored at matching time.
1928    
1929             PCRE_BSR_ANYCRLF
1930             PCRE_BSR_UNICODE
1931    
1932           These options (which are mutually exclusive) control what the \R escape
1933           sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1934           or to match any Unicode newline sequence. These  options  override  the
1935           choice that was made or defaulted when the pattern was compiled.
1936    
1937             PCRE_NEWLINE_CR
1938             PCRE_NEWLINE_LF
1939             PCRE_NEWLINE_CRLF
1940             PCRE_NEWLINE_ANYCRLF
1941             PCRE_NEWLINE_ANY
1942    
1943           These  options  override  the  newline  definition  that  was chosen or
1944           defaulted when the pattern was compiled. For details, see the  descrip-
1945           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1946           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1947           ters.  It may also alter the way the match position is advanced after a
1948           match failure for an unanchored pattern.
1949    
1950           When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY  is
1951           set,  and a match attempt for an unanchored pattern fails when the cur-
1952           rent position is at a  CRLF  sequence,  and  the  pattern  contains  no
1953           explicit  matches  for  CR  or  LF  characters,  the  match position is
1954           advanced by two characters instead of one, in other words, to after the
1955           CRLF.
1956    
1957           The above rule is a compromise that makes the most common cases work as
1958           expected. For example, if the  pattern  is  .+A  (and  the  PCRE_DOTALL
1959           option is not set), it does not match the string "\r\nA" because, after
1960           failing at the start, it skips both the CR and the LF before  retrying.
1961           However,  the  pattern  [\r\n]A does match that string, because it con-
1962           tains an explicit CR or LF reference, and so advances only by one char-
1963           acter after the first failure.
1964    
1965           An explicit match for CR of LF is either a literal appearance of one of
1966           those characters, or one of the \r or  \n  escape  sequences.  Implicit
1967           matches  such  as [^X] do not count, nor does \s (which includes CR and
1968           LF in the characters that it matches).
1969    
1970           Notwithstanding the above, anomalous effects may still occur when  CRLF
1971           is a valid newline sequence and explicit \r or \n escapes appear in the
1972           pattern.
1973    
1974             PCRE_NOTBOL
1975    
1976           This option specifies that first character of the subject string is not
1977           the  beginning  of  a  line, so the circumflex metacharacter should not
1978           match before it. Setting this without PCRE_MULTILINE (at compile  time)
1979           causes  circumflex  never to match. This option affects only the behav-
1980           iour of the circumflex metacharacter. It does not affect \A.
1981    
1982             PCRE_NOTEOL
1983    
1984           This option specifies that the end of the subject string is not the end
1985           of  a line, so the dollar metacharacter should not match it nor (except
1986           in multiline mode) a newline immediately before it. Setting this  with-
1987           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1988           option affects only the behaviour of the dollar metacharacter. It  does
1989           not affect \Z or \z.
1990    
1991             PCRE_NOTEMPTY
1992    
1993           An empty string is not considered to be a valid match if this option is
1994           set. If there are alternatives in the pattern, they are tried.  If  all
1995           the  alternatives  match  the empty string, the entire match fails. For
1996           example, if the pattern
1997    
1998             a?b?
1999    
2000           is applied to a string not beginning with "a" or "b",  it  matches  the
2001           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
2002           match is not valid, so PCRE searches further into the string for occur-
2003           rences of "a" or "b".
2004    
2005           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
2006           cial case of a pattern match of the empty  string  within  its  split()
2007           function,  and  when  using  the /g modifier. It is possible to emulate
2008           Perl's behaviour after matching a null string by first trying the match
2009           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
2010           if that fails by advancing the starting offset (see below)  and  trying
2011           an ordinary match again. There is some code that demonstrates how to do
2012           this in the pcredemo.c sample program.
2013    
2014             PCRE_NO_UTF8_CHECK
2015    
2016           When PCRE_UTF8 is set at compile time, the validity of the subject as a
2017           UTF-8  string is automatically checked when pcre_exec() is subsequently
2018           called.  The value of startoffset is also checked  to  ensure  that  it
2019           points  to  the start of a UTF-8 character. There is a discussion about
2020           the validity of UTF-8 strings in the section on UTF-8  support  in  the
2021           main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
2022           pcre_exec() returns the error PCRE_ERROR_BADUTF8. If  startoffset  con-
2023           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
2024    
2025           If  you  already  know that your subject is valid, and you want to skip
2026           these   checks   for   performance   reasons,   you   can    set    the
2027           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
2028           do this for the second and subsequent calls to pcre_exec() if  you  are
2029           making  repeated  calls  to  find  all  the matches in a single subject
2030           string. However, you should be  sure  that  the  value  of  startoffset
2031           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
2032           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
2033           value  of startoffset that does not point to the start of a UTF-8 char-
2034           acter, is undefined. Your program may crash.
2035    
2036             PCRE_PARTIAL
2037    
2038           This option turns on the  partial  matching  feature.  If  the  subject
2039           string  fails to match the pattern, but at some point during the match-
2040           ing process the end of the subject was reached (that  is,  the  subject
2041           partially  matches  the  pattern and the failure to match occurred only
2042           because there were not enough subject characters), pcre_exec()  returns
2043           PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
2044           used, there are restrictions on what may appear in the  pattern.  These
2045           are discussed in the pcrepartial documentation.
2046    
2047       The string to be matched by pcre_exec()
2048    
2049           The  subject string is passed to pcre_exec() as a pointer in subject, a
2050           length in length, and a starting byte offset in startoffset.  In  UTF-8
2051           mode,  the  byte  offset  must point to the start of a UTF-8 character.
2052           Unlike the pattern string, the subject may contain binary  zero  bytes.
2053           When  the starting offset is zero, the search for a match starts at the
2054           beginning of the subject, and this is by far the most common case.
2055    
2056           A non-zero starting offset is useful when searching for  another  match
2057           in  the same subject by calling pcre_exec() again after a previous suc-
2058           cess.  Setting startoffset differs from just passing over  a  shortened
2059           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
2060           with any kind of lookbehind. For example, consider the pattern
2061    
2062             \Biss\B
2063    
2064           which finds occurrences of "iss" in the middle of  words.  (\B  matches
2065           only  if  the  current position in the subject is not a word boundary.)
2066           When applied to the string "Mississipi" the first call  to  pcre_exec()
2067           finds  the  first  occurrence. If pcre_exec() is called again with just
2068           the remainder of the subject,  namely  "issipi",  it  does  not  match,
2069           because \B is always false at the start of the subject, which is deemed
2070           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
2071           string again, but with startoffset set to 4, it finds the second occur-
2072           rence of "iss" because it is able to look behind the starting point  to
2073           discover that it is preceded by a letter.
2074    
2075           If  a  non-zero starting offset is passed when the pattern is anchored,
2076           one attempt to match at the given offset is made. This can only succeed
2077           if  the  pattern  does  not require the match to be at the start of the
2078           subject.
2079    
2080       How pcre_exec() returns captured substrings
2081    
2082           In general, a pattern matches a certain portion of the subject, and  in
2083           addition,  further  substrings  from  the  subject may be picked out by
2084           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
2085           this  is  called "capturing" in what follows, and the phrase "capturing
2086           subpattern" is used for a fragment of a pattern that picks out  a  sub-
2087           string.  PCRE  supports several other kinds of parenthesized subpattern
2088           that do not cause substrings to be captured.
2089    
2090           Captured substrings are returned to the caller via a vector of  integer
2091           offsets  whose  address is passed in ovector. The number of elements in
2092           the vector is passed in ovecsize, which must be a non-negative  number.
2093           Note: this argument is NOT the size of ovector in bytes.
2094    
2095           The  first  two-thirds of the vector is used to pass back captured sub-
2096           strings, each substring using a pair of integers. The  remaining  third
2097           of  the  vector is used as workspace by pcre_exec() while matching cap-
2098           turing subpatterns, and is not available for passing back  information.
2099           The  length passed in ovecsize should always be a multiple of three. If
2100           it is not, it is rounded down.
2101    
2102           When a match is successful, information about  captured  substrings  is
2103           returned  in  pairs  of integers, starting at the beginning of ovector,
2104           and continuing up to two-thirds of its length at the  most.  The  first
2105           element of a pair is set to the offset of the first character in a sub-
2106           string, and the second is set to the  offset  of  the  first  character
2107           after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
2108           tor[1], identify the portion of  the  subject  string  matched  by  the
2109           entire  pattern.  The next pair is used for the first capturing subpat-
2110           tern, and so on. The value returned by pcre_exec() is one more than the
2111           highest numbered pair that has been set. For example, if two substrings
2112           have been captured, the returned value is 3. If there are no  capturing
2113           subpatterns,  the return value from a successful match is 1, indicating
2114           that just the first pair of offsets has been set.
2115    
2116           If a capturing subpattern is matched repeatedly, it is the last portion
2117           of the string that it matched that is returned.
2118    
2119           If  the vector is too small to hold all the captured substring offsets,
2120           it is used as far as possible (up to two-thirds of its length), and the
2121           function  returns a value of zero. In particular, if the substring off-
2122           sets are not of interest, pcre_exec() may be called with ovector passed
2123           as  NULL  and  ovecsize  as zero. However, if the pattern contains back
2124           references and the ovector is not big enough to  remember  the  related
2125           substrings,  PCRE has to get additional memory for use during matching.
2126           Thus it is usually advisable to supply an ovector.
2127    
2128           The pcre_info() function can be used to find  out  how  many  capturing
2129           subpatterns  there  are  in  a  compiled pattern. The smallest size for
2130           ovector that will allow for n captured substrings, in addition  to  the
2131           offsets of the substring matched by the whole pattern, is (n+1)*3.
2132    
2133           It  is  possible for capturing subpattern number n+1 to match some part
2134           of the subject when subpattern n has not been used at all. For example,
2135           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
2136           return from the function is 4, and subpatterns 1 and 3 are matched, but
2137           2  is  not.  When  this happens, both values in the offset pairs corre-
2138           sponding to unused subpatterns are set to -1.
2139    
2140           Offset values that correspond to unused subpatterns at the end  of  the
2141           expression  are  also  set  to  -1. For example, if the string "abc" is
2142           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
2143           matched.  The  return  from the function is 2, because the highest used
2144           capturing subpattern number is 1. However, you can refer to the offsets
2145           for  the  second  and third capturing subpatterns if you wish (assuming
2146           the vector is large enough, of course).
2147    
2148           Some convenience functions are provided  for  extracting  the  captured
2149           substrings as separate strings. These are described below.
2150    
2151       Error return values from pcre_exec()
2152    
2153           If  pcre_exec()  fails, it returns a negative number. The following are
2154           defined in the header file:
2155    
2156             PCRE_ERROR_NOMATCH        (-1)
2157    
2158           The subject string did not match the pattern.
2159    
2160             PCRE_ERROR_NULL           (-2)
2161    
2162           Either code or subject was passed as NULL,  or  ovector  was  NULL  and
2163           ovecsize was not zero.
2164    
2165             PCRE_ERROR_BADOPTION      (-3)
2166    
2167           An unrecognized bit was set in the options argument.
2168    
2169             PCRE_ERROR_BADMAGIC       (-4)
2170    
2171           PCRE  stores a 4-byte "magic number" at the start of the compiled code,
2172           to catch the case when it is passed a junk pointer and to detect when a
2173           pattern that was compiled in an environment of one endianness is run in
2174           an environment with the other endianness. This is the error  that  PCRE
2175           gives when the magic number is not present.
2176    
2177             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2178    
2179           While running the pattern match, an unknown item was encountered in the
2180           compiled pattern. This error could be caused by a bug  in  PCRE  or  by
2181           overwriting of the compiled pattern.
2182    
2183             PCRE_ERROR_NOMEMORY       (-6)
2184    
2185           If  a  pattern contains back references, but the ovector that is passed
2186           to pcre_exec() is not big enough to remember the referenced substrings,
2187           PCRE  gets  a  block of memory at the start of matching to use for this
2188           purpose. If the call via pcre_malloc() fails, this error is given.  The
2189           memory is automatically freed at the end of matching.
2190    
2191             PCRE_ERROR_NOSUBSTRING    (-7)
2192    
2193           This  error is used by the pcre_copy_substring(), pcre_get_substring(),
2194           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2195           returned by pcre_exec().
2196    
2197             PCRE_ERROR_MATCHLIMIT     (-8)
2198    
2199           The  backtracking  limit,  as  specified  by the match_limit field in a
2200           pcre_extra structure (or defaulted) was reached.  See  the  description
2201           above.
2202    
2203             PCRE_ERROR_CALLOUT        (-9)
2204    
2205           This error is never generated by pcre_exec() itself. It is provided for
2206           use by callout functions that want to yield a distinctive  error  code.
2207           See the pcrecallout documentation for details.
2208    
2209             PCRE_ERROR_BADUTF8        (-10)
2210    
2211           A  string  that contains an invalid UTF-8 byte sequence was passed as a
2212           subject.
2213    
2214             PCRE_ERROR_BADUTF8_OFFSET (-11)
2215    
2216           The UTF-8 byte sequence that was passed as a subject was valid, but the
2217           value  of startoffset did not point to the beginning of a UTF-8 charac-
2218           ter.
2219    
2220             PCRE_ERROR_PARTIAL        (-12)
2221    
2222           The subject string did not match, but it did match partially.  See  the
2223           pcrepartial documentation for details of partial matching.
2224    
2225             PCRE_ERROR_BADPARTIAL     (-13)
2226    
2227           The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
2228           items that are not supported for partial matching. See the  pcrepartial
2229           documentation for details of partial matching.
2230    
2231             PCRE_ERROR_INTERNAL       (-14)
2232    
2233           An  unexpected  internal error has occurred. This error could be caused
2234           by a bug in PCRE or by overwriting of the compiled pattern.
2235    
2236             PCRE_ERROR_BADCOUNT       (-15)
2237    
2238           This error is given if the value of the ovecsize argument is  negative.
2239    
2240             PCRE_ERROR_RECURSIONLIMIT (-21)
2241    
2242           The internal recursion limit, as specified by the match_limit_recursion
2243           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
2244           description above.
2245    
2246             PCRE_ERROR_BADNEWLINE     (-23)
2247    
2248  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
   
      int pcre_exec(const pcre *code, const pcre_extra *extra,  
           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.  
   
      When PCRE_UTF8 was set at compile time, the validity of  the  
      subject  as  a  UTF-8 string is automatically checked. If an  
      invalid  UTF-8  sequence  of  bytes  is  found,  pcre_exec()  
      returns  the  error  PCRE_ERROR_BADUTF8. If you already know  
      that your subject is valid, and you want to skip this  check  
      for  performance reasons, you can set the PCRE_NO_UTF8_CHECK  
      option when calling pcre_exec(). When this  option  is  set,  
      the  effect  of passing an invalid UTF-8 string as a subject  
      is undefined. It may cause your program to crash.  
   
      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.  
2249    
2250         PCRE_ERROR_BADUTF8       (-10)         Error numbers -16 to -20 and -22 are not used by pcre_exec().
   
      A string that contains an invalid UTF-8  byte  sequence  was  
      passed as a subject.  
2251    
2252    
2253  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2254    
2255       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2256            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2257            int buffersize);              int buffersize);
2258    
2259       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2260            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2261            const char **stringptr);              const char **stringptr);
2262    
2263       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2264            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2265    
2266       Captured substrings can be accessed directly  by  using  the         Captured  substrings  can  be  accessed  directly  by using the offsets
2267       offsets returned by pcre_exec() in ovector. For convenience,         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
2268       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2269       and  pcre_get_substring_list()  are  provided for extracting         string_list() are provided for extracting captured substrings  as  new,
2270       captured  substrings  as  new,   separate,   zero-terminated         separate,  zero-terminated strings. These functions identify substrings
2271       strings.  These functions identify substrings by number. The         by number. The next section describes functions  for  extracting  named
2272       next section describes functions for extracting  named  sub-         substrings.
2273       strings.   A  substring  that  contains  a  binary  zero  is  
2274       correctly extracted and has a further zero added on the end,         A  substring that contains a binary zero is correctly extracted and has
2275       but the result is not, of course, a C string.         a further zero added on the end, but the result is not, of course, a  C
2276           string.   However,  you  can  process such a string by referring to the
2277       The first three arguments are the  same  for  all  three  of         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
2278       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2279       just been successfully matched, ovector is a pointer to  the         not adequate for handling strings containing binary zeros, because  the
2280       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2281       and stringcount is the number of substrings that  were  cap-  
2282       tured by the match, including the substring that matched the         The  first  three  arguments  are the same for all three of these func-
2283       entire regular expression. This is  the  value  returned  by         tions: subject is the subject string that has  just  been  successfully
2284       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2285       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2286       tor,  the  value passed as stringcount should be the size of         were  captured  by  the match, including the substring that matched the
2287       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2288       The functions pcre_copy_substring() and pcre_get_substring()         it  is greater than zero. If pcre_exec() returned zero, indicating that
2289       extract a single substring, whose number is given as string-         it ran out of space in ovector, the value passed as stringcount  should
2290       number. A value of zero extracts the substring that  matched         be the number of elements in the vector divided by three.
2291       the entire pattern, while higher values extract the captured  
2292       substrings. For pcre_copy_substring(), the string is  placed         The  functions pcre_copy_substring() and pcre_get_substring() extract a
2293       in  buffer,  whose  length is given by buffersize, while for         single substring, whose number is given as  stringnumber.  A  value  of
2294       pcre_get_substring() a new block of memory is  obtained  via         zero  extracts  the  substring that matched the entire pattern, whereas
2295       pcre_malloc,  and its address is returned via stringptr. The         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
2296       yield of the function is  the  length  of  the  string,  not         string(),  the  string  is  placed  in buffer, whose length is given by
2297       including the terminating zero, or one of         buffersize, while for pcre_get_substring() a new  block  of  memory  is
2298           obtained  via  pcre_malloc,  and its address is returned via stringptr.
2299         PCRE_ERROR_NOMEMORY       (-6)         The yield of the function is the length of the  string,  not  including
2300           the terminating zero, or one of these error codes:
2301       The buffer was too small for pcre_copy_substring(),  or  the  
2302       attempt to get memory failed for pcre_get_substring().           PCRE_ERROR_NOMEMORY       (-6)
2303    
2304         PCRE_ERROR_NOSUBSTRING    (-7)         The  buffer  was too small for pcre_copy_substring(), or the attempt to
2305           get memory failed for pcre_get_substring().
2306       There is no substring whose number is stringnumber.  
2307             PCRE_ERROR_NOSUBSTRING    (-7)
2308       The pcre_get_substring_list() function extracts  all  avail-  
2309       able  substrings  and builds a list of pointers to them. All         There is no substring whose number is stringnumber.
2310       this is done in a single block of memory which  is  obtained  
2311       via pcre_malloc. The address of the memory block is returned         The pcre_get_substring_list()  function  extracts  all  available  sub-
2312       via listptr, which is also the start of the list  of  string         strings  and  builds  a list of pointers to them. All this is done in a
2313       pointers.  The  end of the list is marked by a NULL pointer.         single block of memory that is obtained via pcre_malloc. The address of
2314       The yield of the function is zero if all went well, or         the  memory  block  is returned via listptr, which is also the start of
2315           the list of string pointers. The end of the list is marked  by  a  NULL
2316         PCRE_ERROR_NOMEMORY       (-6)         pointer.  The  yield  of  the function is zero if all went well, or the
2317           error code
2318       if the attempt to get the memory block failed.  
2319             PCRE_ERROR_NOMEMORY       (-6)
2320       When any of these functions encounter a  substring  that  is  
2321       unset, which can happen when capturing subpattern number n+1         if the attempt to get the memory block failed.
2322       matches some part of the subject, but subpattern n  has  not  
2323       been  used  at all, they return an empty string. This can be         When any of these functions encounter a substring that is unset,  which
2324       distinguished  from  a  genuine  zero-length  substring   by         can  happen  when  capturing subpattern number n+1 matches some part of
2325       inspecting the appropriate offset in ovector, which is nega-         the subject, but subpattern n has not been used at all, they return  an
2326       tive for unset substrings.         empty string. This can be distinguished from a genuine zero-length sub-
2327           string by inspecting the appropriate offset in ovector, which is  nega-
2328       The  two  convenience  functions  pcre_free_substring()  and         tive for unset substrings.
2329       pcre_free_substring_list()  can  be  used to free the memory  
2330       returned by  a  previous  call  of  pcre_get_substring()  or         The  two convenience functions pcre_free_substring() and pcre_free_sub-
2331       pcre_get_substring_list(),  respectively.  They  do  nothing         string_list() can be used to free the memory  returned  by  a  previous
2332       more than call the function pointed to by  pcre_free,  which         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2333       of  course  could  be called directly from a C program. How-         tively. They do nothing more than  call  the  function  pointed  to  by
2334       ever, PCRE is used in some situations where it is linked via         pcre_free,  which  of course could be called directly from a C program.
2335       a  special  interface  to another programming language which         However, PCRE is used in some situations where it is linked via a  spe-
2336       cannot use pcre_free directly; it is for  these  cases  that         cial   interface  to  another  programming  language  that  cannot  use
2337       the functions are provided.         pcre_free directly; it is for these cases that the functions  are  pro-
2338           vided.
2339    
2340    
2341  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2342    
2343       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2344            const char *subject, int *ovector,              const char *name);
2345            int stringcount, const char *stringname,  
2346            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2347                const char *subject, int *ovector,
2348       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2349            const char *name);              char *buffer, int buffersize);
2350    
2351       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2352            const char *subject, int *ovector,              const char *subject, int *ovector,
2353            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2354            const char **stringptr);              const char **stringptr);
2355    
2356       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-
2357       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2358       pcre_get_stringnumber(). The first argument is the  compiled  
2359       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2360       pattern  
2361           the number of the subpattern called "xxx" is 2. If the name is known to
2362         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2363           name by calling pcre_get_stringnumber(). The first argument is the com-
2364       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
2365       number,  you can then extract the substring directly, or use         the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if  there  is  no
2366       one of the functions described in the previous section.  For         subpattern of that name.
2367       convenience,  there are also two functions that do the whole  
2368       job.         Given the number, you can extract the substring directly, or use one of
2369           the functions described in the previous section. For convenience, there
2370       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2371       pcre_get_named_substring()  are  the  same  as those for the  
2372       functions that  extract  by  number,  and  so  are  not  re-         Most    of    the    arguments   of   pcre_copy_named_substring()   and
2373       described here. There are just two differences.         pcre_get_named_substring() are the same  as  those  for  the  similarly
2374           named  functions  that extract by number. As these are described in the
2375       First, instead of a substring number, a  substring  name  is         previous section, they are not re-described here. There  are  just  two
2376       given.  Second,  there  is  an  extra argument, given at the         differences:
2377       start, which is a pointer to the compiled pattern.  This  is  
2378       needed  in order to gain access to the name-to-number trans-         First,  instead  of a substring number, a substring name is given. Sec-
2379       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2380           to  the compiled pattern. This is needed in order to gain access to the
2381       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2382       succeeds,    they   then   call   pcre_copy_substring()   or  
2383       pcre_get_substring(), as appropriate.         These functions call pcre_get_stringnumber(), and if it succeeds,  they
2384           then  call  pcre_copy_substring() or pcre_get_substring(), as appropri-
2385           ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
2386           behaviour may not be what you want (see the next section).
2387    
2388    
2389    DUPLICATE SUBPATTERN NAMES
2390    
2391           int pcre_get_stringtable_entries(const pcre *code,
2392                const char *name, char **first, char **last);
2393    
2394           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2395           subpatterns are not required to  be  unique.  Normally,  patterns  with
2396           duplicate  names  are such that in any one match, only one of the named
2397           subpatterns participates. An example is shown in the pcrepattern  docu-
2398           mentation.
2399    
2400           When    duplicates   are   present,   pcre_copy_named_substring()   and
2401           pcre_get_named_substring() return the first substring corresponding  to
2402           the  given  name  that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
2403           (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
2404           function  returns one of the numbers that are associated with the name,
2405           but it is not defined which it is.
2406    
2407           If you want to get full details of all captured substrings for a  given
2408           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2409           first argument is the compiled pattern, and the second is the name. The
2410           third  and  fourth  are  pointers to variables which are updated by the
2411           function. After it has run, they point to the first and last entries in
2412           the  name-to-number  table  for  the  given  name.  The function itself
2413           returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
2414           there  are none. The format of the table is described above in the sec-
2415           tion entitled Information about a  pattern.   Given  all  the  relevant
2416           entries  for the name, you can extract each of their numbers, and hence
2417           the captured data, if any.
2418    
2419    
2420    FINDING ALL POSSIBLE MATCHES
2421    
2422           The traditional matching function uses a  similar  algorithm  to  Perl,
2423           which stops when it finds the first match, starting at a given point in
2424           the subject. If you want to find all possible matches, or  the  longest
2425           possible  match,  consider using the alternative matching function (see
2426           below) instead. If you cannot use the alternative function,  but  still
2427           need  to  find all possible matches, you can kludge it up by making use
2428           of the callout facility, which is described in the pcrecallout documen-
2429           tation.
2430    
2431           What you have to do is to insert a callout right at the end of the pat-
2432           tern.  When your callout function is called, extract and save the  cur-
2433           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2434           backtrack and try other alternatives. Ultimately, when it runs  out  of
2435           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2436    
2437    
2438    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2439    
2440           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2441                const char *subject, int length, int startoffset,
2442                int options, int *ovector, int ovecsize,
2443                int *workspace, int wscount);
2444    
2445           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2446           against a compiled pattern, using a matching algorithm that  scans  the
2447           subject  string  just  once, and does not backtrack. This has different
2448           characteristics to the normal algorithm, and  is  not  compatible  with
2449           Perl.  Some  of the features of PCRE patterns are not supported. Never-
2450           theless, there are times when this kind of matching can be useful.  For
2451           a discussion of the two matching algorithms, see the pcrematching docu-
2452           mentation.
2453    
2454           The arguments for the pcre_dfa_exec() function  are  the  same  as  for
2455           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2456           ent way, and this is described below. The other  common  arguments  are
2457           used  in  the  same way as for pcre_exec(), so their description is not
2458           repeated here.
2459    
2460           The two additional arguments provide workspace for  the  function.  The
2461           workspace  vector  should  contain at least 20 elements. It is used for
2462           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2463           workspace  will  be  needed for patterns and subjects where there are a
2464           lot of potential matches.
2465    
2466           Here is an example of a simple call to pcre_dfa_exec():
2467    
2468             int rc;
2469             int ovector[10];
2470             int wspace[20];
2471             rc = pcre_dfa_exec(
2472               re,             /* result of pcre_compile() */
2473               NULL,           /* we didn't study the pattern */
2474               "some string",  /* the subject string */
2475               11,             /* the length of the subject string */
2476               0,              /* start at offset 0 in the subject */
2477               0,              /* default options */
2478               ovector,        /* vector of integers for substring information */
2479               10,             /* number of elements (NOT size in bytes) */
2480               wspace,         /* working space vector */
2481               20);            /* number of elements (NOT size in bytes) */
2482    
2483       Option bits for pcre_dfa_exec()
2484    
2485           The unused bits of the options argument  for  pcre_dfa_exec()  must  be
2486           zero.  The  only  bits  that  may  be  set are PCRE_ANCHORED, PCRE_NEW-
2487           LINE_xxx, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY,  PCRE_NO_UTF8_CHECK,
2488           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2489           three of these are the same as for pcre_exec(), so their description is
2490           not repeated here.
2491    
2492             PCRE_PARTIAL
2493    
2494           This  has  the  same general effect as it does for pcre_exec(), but the
2495           details  are  slightly  different.  When  PCRE_PARTIAL   is   set   for
2496           pcre_dfa_exec(),  the  return code PCRE_ERROR_NOMATCH is converted into
2497           PCRE_ERROR_PARTIAL if the end of the subject  is  reached,  there  have
2498           been no complete matches, but there is still at least one matching pos-
2499           sibility. The portion of the string that provided the partial match  is
2500           set as the first matching string.
2501    
2502             PCRE_DFA_SHORTEST
2503    
2504           Setting  the  PCRE_DFA_SHORTEST option causes the matching algorithm to
2505           stop as soon as it has found one match. Because of the way the alterna-
2506           tive  algorithm  works, this is necessarily the shortest possible match
2507           at the first possible matching point in the subject string.
2508    
2509             PCRE_DFA_RESTART
2510    
2511           When pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option,  and
2512           returns  a  partial  match, it is possible to call it again, with addi-
2513           tional subject characters, and have it continue with  the  same  match.
2514           The  PCRE_DFA_RESTART  option requests this action; when it is set, the
2515           workspace and wscount options must reference the same vector as  before
2516           because  data  about  the  match so far is left in them after a partial
2517           match. There is more discussion of this  facility  in  the  pcrepartial
2518           documentation.
2519    
2520       Successful returns from pcre_dfa_exec()
2521    
2522           When  pcre_dfa_exec()  succeeds, it may have matched more than one sub-
2523           string in the subject. Note, however, that all the matches from one run
2524           of  the  function  start  at the same point in the subject. The shorter
2525           matches are all initial substrings of the longer matches. For  example,
2526           if the pattern
2527    
2528             <.*>
2529    
2530           is matched against the string
2531    
2532             This is <something> <something else> <something further> no more
2533    
2534           the three matched strings are
2535    
2536             <something>
2537             <something> <something else>
2538             <something> <something else> <something further>
2539    
2540           On  success,  the  yield of the function is a number greater than zero,
2541           which is the number of matched substrings.  The  substrings  themselves
2542           are  returned  in  ovector. Each string uses two elements; the first is
2543           the offset to the start, and the second is the offset to  the  end.  In
2544           fact,  all  the  strings  have the same start offset. (Space could have
2545           been saved by giving this only once, but it was decided to retain  some
2546           compatibility  with  the  way pcre_exec() returns data, even though the
2547           meaning of the strings is different.)
2548    
2549           The strings are returned in reverse order of length; that is, the long-
2550           est  matching  string is given first. If there were too many matches to
2551           fit into ovector, the yield of the function is zero, and the vector  is
2552           filled with the longest matches.
2553    
2554       Error returns from pcre_dfa_exec()
2555    
2556           The  pcre_dfa_exec()  function returns a negative number when it fails.
2557           Many of the errors are the same  as  for  pcre_exec(),  and  these  are
2558           described  above.   There are in addition the following errors that are
2559           specific to pcre_dfa_exec():
2560    
2561             PCRE_ERROR_DFA_UITEM      (-16)
2562    
2563           This return is given if pcre_dfa_exec() encounters an item in the  pat-
2564           tern  that  it  does not support, for instance, the use of \C or a back
2565           reference.
2566    
2567             PCRE_ERROR_DFA_UCOND      (-17)
2568    
2569           This return is given if pcre_dfa_exec()  encounters  a  condition  item
2570           that  uses  a back reference for the condition, or a test for recursion
2571           in a specific group. These are not supported.
2572    
2573             PCRE_ERROR_DFA_UMLIMIT    (-18)
2574    
2575           This return is given if pcre_dfa_exec() is called with an  extra  block
2576           that contains a setting of the match_limit field. This is not supported
2577           (it is meaningless).
2578    
2579             PCRE_ERROR_DFA_WSSIZE     (-19)
2580    
2581           This return is given if  pcre_dfa_exec()  runs  out  of  space  in  the
2582           workspace vector.
2583    
2584             PCRE_ERROR_DFA_RECURSE    (-20)
2585    
2586           When  a  recursive subpattern is processed, the matching function calls
2587           itself recursively, using private vectors for  ovector  and  workspace.
2588           This  error  is  given  if  the output vector is not large enough. This
2589           should be extremely rare, as a vector of size 1000 is used.
2590    
2591    
2592    SEE ALSO
2593    
2594           pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar-
2595           tial(3),  pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).
2596    
2597    
2598    AUTHOR
2599    
2600           Philip Hazel
2601           University Computing Service
2602           Cambridge CB2 3QH, England.
2603    
2604    
2605    REVISION
2606    
2607           Last updated: 12 April 2008
2608           Copyright (c) 1997-2008 University of Cambridge.
2609    ------------------------------------------------------------------------------
2610    
2611    
2612    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2613    
 Last updated: 20 August 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2614    
2615  NAME  NAME
2616       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2617    
2618    
2619  PCRE CALLOUTS  PCRE CALLOUTS
2620    
2621       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 one more than the  number  of  
      the  highest  numbered captured substring so far. If no sub-  
      strings have been captured, the value of capture_top is one.  
   
      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.  
2622    
2623           PCRE provides a feature called "callout", which is a means of temporar-
2624           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2625           matching.  The  caller of PCRE provides an external function by putting
2626           its entry point in the global variable pcre_callout. By  default,  this
2627           variable contains NULL, which disables all calling out.
2628    
2629           Within  a  regular  expression,  (?C) indicates the points at which the
2630           external function is to be called.  Different  callout  points  can  be
2631           identified  by  putting  a number less than 256 after the letter C. The
2632           default value is zero.  For  example,  this  pattern  has  two  callout
2633           points:
2634    
2635             (?C1)abc(?C2)def
2636    
2637           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2638           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2639           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2640           used with the pattern
2641    
2642             A(\d{2}|--)
2643    
2644           it is processed as if it were
2645    
2646           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2647    
2648           Notice that there is a callout before and after  each  parenthesis  and
2649           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2650           progress of pattern matching. The pcretest command has an  option  that
2651           sets  automatic callouts; when it is used, the output indicates how the
2652           pattern is matched. This is useful information when you are  trying  to
2653           optimize the performance of a particular pattern.
2654    
2655    
2656    MISSING CALLOUTS
2657    
2658           You  should  be  aware  that,  because of optimizations in the way PCRE
2659           matches patterns, callouts sometimes do not happen. For example, if the
2660           pattern is
2661    
2662             ab(?C4)cd
2663    
2664           PCRE knows that any matching string must contain the letter "d". If the
2665           subject string is "abyz", the lack of "d" means that  matching  doesn't
2666           ever  start,  and  the  callout is never reached. However, with "abyd",
2667           though the result is still no match, the callout is obeyed.
2668    
2669    
2670    THE CALLOUT INTERFACE
2671    
2672           During matching, when PCRE reaches a callout point, the external  func-
2673           tion  defined by pcre_callout is called (if it is set). This applies to
2674           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2675           only  argument  to  the callout function is a pointer to a pcre_callout
2676           block. This structure contains the following fields:
2677    
2678             int          version;
2679             int          callout_number;
2680             int         *offset_vector;
2681             const char  *subject;
2682             int          subject_length;
2683             int          start_match;
2684             int          current_position;
2685             int          capture_top;
2686             int          capture_last;
2687             void        *callout_data;
2688             int          pattern_position;
2689             int          next_item_length;
2690    
2691           The version field is an integer containing the version  number  of  the
2692           block  format. The initial version was 0; the current version is 1. The
2693           version number will change again in future  if  additional  fields  are
2694           added, but the intention is never to remove any of the existing fields.
2695    
2696           The callout_number field contains the number of the  callout,  as  com-
2697           piled  into  the pattern (that is, the number after ?C for manual call-
2698           outs, and 255 for automatically generated callouts).
2699    
2700           The offset_vector field is a pointer to the vector of offsets that  was
2701           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2702           pcre_exec() is used, the contents can be inspected in order to  extract
2703           substrings  that  have  been  matched  so  far,  in the same way as for
2704           extracting substrings after a match has completed. For  pcre_dfa_exec()
2705           this field is not useful.
2706    
2707           The subject and subject_length fields contain copies of the values that
2708           were passed to pcre_exec().
2709    
2710           The start_match field normally contains the offset within  the  subject
2711           at  which  the  current  match  attempt started. However, if the escape
2712           sequence \K has been encountered, this value is changed to reflect  the
2713           modified  starting  point.  If the pattern is not anchored, the callout
2714           function may be called several times from the same point in the pattern
2715           for different starting points in the subject.
2716    
2717           The  current_position  field  contains the offset within the subject of
2718           the current match pointer.
2719    
2720           When the pcre_exec() function is used, the capture_top  field  contains
2721           one  more than the number of the highest numbered captured substring so
2722           far. If no substrings have been captured, the value of  capture_top  is
2723           one.  This  is always the case when pcre_dfa_exec() is used, because it
2724           does not support captured substrings.
2725    
2726           The capture_last field contains the number of the  most  recently  cap-
2727           tured  substring. If no substrings have been captured, its value is -1.
2728           This is always the case when pcre_dfa_exec() is used.
2729    
2730           The callout_data field contains a value that is passed  to  pcre_exec()
2731           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2732           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2733           structure.  If  no such data was passed, the value of callout_data in a
2734           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2735           structure in the pcreapi documentation.
2736    
2737           The  pattern_position field is present from version 1 of the pcre_call-
2738           out structure. It contains the offset to the next item to be matched in
2739           the pattern string.
2740    
2741           The  next_item_length field is present from version 1 of the pcre_call-
2742           out structure. It contains the length of the next item to be matched in
2743           the  pattern  string. When the callout immediately precedes an alterna-
2744           tion bar, a closing parenthesis, or the end of the pattern, the  length
2745           is  zero.  When the callout precedes an opening parenthesis, the length
2746           is that of the entire subpattern.
2747    
2748           The pattern_position and next_item_length fields are intended  to  help
2749           in  distinguishing between different automatic callouts, which all have
2750           the same callout number. However, they are set for all callouts.
2751    
2752    
2753  RETURN VALUES  RETURN VALUES
2754    
2755       The callout function returns an integer.  If  the  value  is         The external callout function returns an integer to PCRE. If the  value
2756       zero,  matching  proceeds as normal. If the value is greater         is  zero,  matching  proceeds  as  normal. If the value is greater than
2757       than zero, matching fails at the current  point,  but  back-         zero, matching fails at the current point, but  the  testing  of  other
2758       tracking  to test other possibilities goes ahead, just as if         matching possibilities goes ahead, just as if a lookahead assertion had
2759       a lookahead assertion had failed. If the value is less  than         failed. If the value is less than zero, the  match  is  abandoned,  and
2760       zero,  the  match  is abandoned, and pcre_exec() returns the         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2761       value.  
2762           Negative   values   should   normally   be   chosen  from  the  set  of
2763       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2764       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2765       forces a standard "no  match"  failure.   The  error  number         reserved for use by callout functions; it will never be  used  by  PCRE
2766       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
2767       it will never be used by PCRE itself.  
2768    
2769    AUTHOR
2770    
2771           Philip Hazel
2772           University Computing Service
2773           Cambridge CB2 3QH, England.
2774    
2775    
2776    REVISION
2777    
2778           Last updated: 29 May 2007
2779           Copyright (c) 1997-2007 University of Cambridge.
2780    ------------------------------------------------------------------------------
2781    
2782    
2783    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2784    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2785    
2786  NAME  NAME
2787       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2788    
2789    
2790  DIFFERENCES FROM PERL  DIFFERENCES BETWEEN PCRE AND PERL
2791    
2792       This document describes the differences  in  the  ways  that         This  document describes the differences in the ways that PCRE and Perl
2793       PCRE  and  Perl  handle regular expressions. The differences         handle regular expressions. The differences described here  are  mainly
2794       described here are with respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2795           some features that are expected to be in the forthcoming Perl 5.10.
2796       1. PCRE does  not  allow  repeat  quantifiers  on  lookahead