/[pcre]/code/trunk/doc/pcre.txt
ViewVC logotype

Diff of /code/trunk/doc/pcre.txt

Parent Directory Parent Directory | Revision Log Revision Log | View Patch Patch

revision 69 by nigel, Sat Feb 24 21:40:18 2007 UTC revision 91 by nigel, Sat Feb 24 21:41:34 2007 UTC
# Line 1  Line 1 
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.  The current implementation of PCRE (release
22       implementation  of  PCRE  (release 4.x) corresponds approxi-         6.x) corresponds approximately with Perl  5.8,  including  support  for
23       mately with Perl 5.8, including support  for  UTF-8  encoded         UTF-8 encoded strings and Unicode general category properties. However,
24       strings.    However,  this  support  has  to  be  explicitly         this support has to be explicitly enabled; it is not the default.
25       enabled; it is not the default.  
26           In addition to the Perl-compatible matching function,  PCRE  also  con-
27       PCRE is written in C and released as a C library. However, a         tains  an  alternative matching function that matches the same compiled
28       number  of  people  have  written wrappers and interfaces of         patterns in a different way. In certain circumstances, the  alternative
29       various kinds. A C++ class is included  in  these  contribu-         function  has  some  advantages.  For  a discussion of the two matching
30       tions,  which  can  be found in the Contrib directory at the         algorithms, see the pcrematching page.
31       primary FTP site, which is:  
32           PCRE is written in C and released as a C library. A  number  of  people
33       ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         have  written  wrappers and interfaces of various kinds. In particular,
34           Google Inc.  have provided a comprehensive C++  wrapper.  This  is  now
35       Details of exactly which Perl  regular  expression  features         included as part of the PCRE distribution. The pcrecpp page has details
36       are  and  are  not  supported  by PCRE are given in separate         of this interface. Other people's contributions can  be  found  in  the
37       documents. See the pcrepattern and pcrecompat pages.         Contrib directory at the primary FTP site, which is:
38    
39       Some features of PCRE can be included, excluded, or  changed         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
40       when  the library is built. The pcre_config() function makes  
41       it possible for a client  to  discover  which  features  are         Details  of  exactly which Perl regular expression features are and are
42       available.  Documentation  about  building  PCRE for various         not supported by PCRE are given in separate documents. See the pcrepat-
43       operating systems can be found in the  README  file  in  the         tern and pcrecompat pages.
44       source distribution.  
45           Some  features  of  PCRE can be included, excluded, or changed when the
46           library is built. The pcre_config() function makes it  possible  for  a
47           client  to  discover  which  features are available. The features them-
48           selves are described in the pcrebuild page. Documentation about  build-
49           ing  PCRE for various operating systems can be found in the README file
50           in the source distribution.
51    
52           The library contains a number of undocumented  internal  functions  and
53           data  tables  that  are  used by more than one of the exported external
54           functions, but which are not intended  for  use  by  external  callers.
55           Their  names  all begin with "_pcre_", which hopefully will not provoke
56           any name clashes. In some environments, it is possible to control which
57           external  symbols  are  exported when a shared library is built, and in
58           these cases the undocumented symbols are not exported.
59    
60    
61  USER DOCUMENTATION  USER DOCUMENTATION
62    
63       The user documentation for PCRE has been  split  up  into  a         The user documentation for PCRE comprises a number  of  different  sec-
64       number  of  different sections. In the "man" format, each of         tions.  In the "man" format, each of these is a separate "man page". In
65       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.
66       a  separate  page,  linked from the index page. In the plain         In  the  plain text format, all the sections are concatenated, for ease
67       text format, all the sections are concatenated, for ease  of         of searching. The sections are as follows:
68       searching. The sections are as follows:  
69             pcre              this document
70         pcre              this document           pcreapi           details of PCRE's native C API
71         pcreapi           details of PCRE's native API           pcrebuild         options for building PCRE
72         pcrebuild         options for building PCRE           pcrecallout       details of the callout feature
73         pcrecallout       details of the callout feature           pcrecompat        discussion of Perl compatibility
74         pcrecompat        discussion of Perl compatibility           pcrecpp           details of the C++ wrapper
75         pcregrep          description of the pcregrep command           pcregrep          description of the pcregrep command
76         pcrepattern       syntax and semantics of supported           pcrematching      discussion of the two matching algorithms
77                             regular expressions           pcrepartial       details of the partial matching facility
78         pcreperform       discussion of performance issues           pcrepattern       syntax and semantics of supported
79         pcreposix         the POSIX-compatible API                               regular expressions
80         pcresample        discussion of the sample program           pcreperform       discussion of performance issues
81         pcretest          the pcretest testing command           pcreposix         the POSIX-compatible C API
82             pcreprecompile    details of saving and re-using precompiled patterns
83       In addition, in the "man" and HTML formats, there is a short           pcresample        discussion of the sample program
84       page  for  each  library function, listing its arguments and           pcrestack         discussion of stack usage
85       results.           pcretest          description of the pcretest testing command
86    
87           In  addition,  in the "man" and HTML formats, there is a short page for
88           each C library function, listing its arguments and results.
89    
90    
91  LIMITATIONS  LIMITATIONS
92    
93       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
94       they will never in practice be relevant.         never in practice be relevant.
95    
96       The maximum length of a  compiled  pattern  is  65539  (sic)         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
97       bytes  if PCRE is compiled with the default internal linkage         is compiled with the default internal linkage size of 2. If you want to
98       size of 2. If you want to process regular  expressions  that         process  regular  expressions  that are truly enormous, you can compile
99       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
100       linkage size of 3 or 4 (see the README file  in  the  source         the  source  distribution and the pcrebuild documentation for details).
101       distribution  and  the pcrebuild documentation for details).         In these cases the limit is substantially larger.  However,  the  speed
102       If these cases the limit is substantially larger.   However,         of execution will be slower.
103       the speed of execution will be slower.  
104           All  values in repeating quantifiers must be less than 65536. The maxi-
105       All values in repeating quantifiers must be less than 65536.         mum compiled length of subpattern with  an  explicit  repeat  count  is
106       The maximum number of capturing subpatterns is 65535.         30000 bytes. The maximum number of capturing subpatterns is 65535.
107    
108       There is no limit to the  number  of  non-capturing  subpat-         There  is  no limit to the number of non-capturing subpatterns, but the
109       terns,  but  the  maximum  depth  of nesting of all kinds of         maximum depth of nesting of  all  kinds  of  parenthesized  subpattern,
110       parenthesized subpattern, including  capturing  subpatterns,         including capturing subpatterns, assertions, and other types of subpat-
111       assertions, and other types of subpattern, is 200.         tern, is 200.
112    
113       The maximum length of a subject string is the largest  posi-         The maximum length of name for a named subpattern is 32, and the  maxi-
114       tive number that an integer variable can hold. However, PCRE         mum number of named subpatterns is 10000.
115       uses recursion to handle subpatterns and indefinite  repeti-  
116       tion.  This  means  that the available stack space may limit         The  maximum  length of a subject string is the largest positive number
117       the size of a subject string that can be processed  by  cer-         that an integer variable can hold. However, when using the  traditional
118       tain patterns.         matching function, PCRE uses recursion to handle subpatterns and indef-
119           inite repetition.  This means that the available stack space may  limit
120           the size of a subject string that can be processed by certain patterns.
121           For a discussion of stack issues, see the pcrestack documentation.
122    
123    
124    UTF-8 AND UNICODE PROPERTY SUPPORT
125    
126           From release 3.3, PCRE has  had  some  support  for  character  strings
127           encoded  in the UTF-8 format. For release 4.0 this was greatly extended
128           to cover most common requirements, and in release 5.0  additional  sup-
129           port for Unicode general category properties was added.
130    
131           In  order  process  UTF-8 strings, you must build PCRE to include UTF-8
132           support in the code, and, in addition,  you  must  call  pcre_compile()
133           with  the PCRE_UTF8 option flag. When you do this, both the pattern and
134           any subject strings that are matched against it are  treated  as  UTF-8
135           strings instead of just strings of bytes.
136    
137           If  you compile PCRE with UTF-8 support, but do not use it at run time,
138           the library will be a bit bigger, but the additional run time  overhead
139           is  limited  to testing the PCRE_UTF8 flag in several places, so should
140           not be very large.
141    
142           If PCRE is built with Unicode character property support (which implies
143           UTF-8  support),  the  escape sequences \p{..}, \P{..}, and \X are sup-
144           ported.  The available properties that can be tested are limited to the
145           general  category  properties such as Lu for an upper case letter or Nd
146           for a decimal number, the Unicode script names such as Arabic  or  Han,
147           and  the  derived  properties  Any  and L&. A full list is given in the
148           pcrepattern documentation. Only the short names for properties are sup-
149           ported.  For example, \p{L} matches a letter. Its Perl synonym, \p{Let-
150           ter}, is not supported.  Furthermore,  in  Perl,  many  properties  may
151           optionally  be  prefixed by "Is", for compatibility with Perl 5.6. PCRE
152           does not support this.
153    
154           The following comments apply when PCRE is running in UTF-8 mode:
155    
156           1. When you set the PCRE_UTF8 flag, the strings passed as patterns  and
157           subjects  are  checked for validity on entry to the relevant functions.
158           If an invalid UTF-8 string is passed, an error return is given. In some
159           situations,  you  may  already  know  that  your strings are valid, and
160           therefore want to skip these checks in order to improve performance. If
161           you  set  the  PCRE_NO_UTF8_CHECK  flag at compile time or at run time,
162           PCRE assumes that the pattern or subject  it  is  given  (respectively)
163           contains  only valid UTF-8 codes. In this case, it does not diagnose an
164           invalid UTF-8 string. If you pass an invalid UTF-8 string to PCRE  when
165           PCRE_NO_UTF8_CHECK  is set, the results are undefined. Your program may
166           crash.
167    
168           2. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
169           two-byte UTF-8 character if the value is greater than 127.
170    
171           3.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
172           characters for values greater than \177.
173    
174           4. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
175           vidual bytes, for example: \x{100}{3}.
176    
177           5.  The dot metacharacter matches one UTF-8 character instead of a sin-
178           gle byte.
179    
180           6. The escape sequence \C can be used to match a single byte  in  UTF-8
181           mode,  but  its  use can lead to some strange effects. This facility is
182           not available in the alternative matching function, pcre_dfa_exec().
183    
184           7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
185           test  characters of any code value, but the characters that PCRE recog-
186           nizes as digits, spaces, or word characters  remain  the  same  set  as
187           before, all with values less than 256. This remains true even when PCRE
188           includes Unicode property support, because to do otherwise  would  slow
189           down  PCRE in many common cases. If you really want to test for a wider
190           sense of, say, "digit", you must use Unicode  property  tests  such  as
191           \p{Nd}.
192    
193           8.  Similarly,  characters that match the POSIX named character classes
194           are all low-valued characters.
195    
196           9. Case-insensitive matching applies only to  characters  whose  values
197           are  less than 128, unless PCRE is built with Unicode property support.
198           Even when Unicode property support is available, PCRE  still  uses  its
199           own  character  tables when checking the case of low-valued characters,
200           so as not to degrade performance.  The Unicode property information  is
201           used only for characters with higher values. Even when Unicode property
202           support is available, PCRE supports case-insensitive matching only when
203           there  is  a  one-to-one  mapping between a letter's cases. There are a
204           small number of many-to-one mappings in Unicode;  these  are  not  sup-
205           ported by PCRE.
206    
207    
208  UTF-8 SUPPORT  AUTHOR
209    
210       Starting at release 3.3, PCRE has had some support for char-         Philip Hazel
211       acter  strings  encoded in the UTF-8 format. For release 4.0         University Computing Service,
212       this has been greatly extended to cover most common require-         Cambridge CB2 3QG, England.
      ments.  
   
      In order process UTF-8  strings,  you  must  build  PCRE  to  
      include  UTF-8  support  in  the code, and, in addition, you  
      must call pcre_compile() with  the  PCRE_UTF8  option  flag.  
      When  you  do this, both the pattern and any subject strings  
      that are matched against it are  treated  as  UTF-8  strings  
      instead of just strings of bytes.  
   
      If you compile PCRE with UTF-8 support, but do not use it at  
      run  time,  the  library will be a bit bigger, but the addi-  
      tional run time overhead is limited to testing the PCRE_UTF8  
      flag in several places, so should not be very large.  
   
      The following comments apply when PCRE is running  in  UTF-8  
      mode:  
   
      1. PCRE assumes that the strings it is given  contain  valid  
      UTF-8  codes. It does not diagnose invalid UTF-8 strings. If  
      you pass invalid UTF-8 strings  to  PCRE,  the  results  are  
      undefined.  
   
      2. In a pattern, the escape sequence \x{...}, where the con-  
      tents  of  the  braces is a string of hexadecimal digits, is  
      interpreted as a UTF-8 character whose code  number  is  the  
      given  hexadecimal  number, for example: \x{1234}. If a non-  
      hexadecimal digit appears between the braces,  the  item  is  
      not  recognized.  This escape sequence can be used either as  
      a literal, or within a character class.  
   
      3. The original hexadecimal escape sequence, \xhh, matches a  
      two-byte UTF-8 character if the value is greater than 127.  
   
      4. Repeat quantifiers apply to  complete  UTF-8  characters,  
      not to individual bytes, for example: \x{100}{3}.  
   
      5. The dot metacharacter matches one UTF-8 character instead  
      of a single byte.  
   
      6. The escape sequence \C can be used to match a single byte  
      in UTF-8 mode, but its use can lead to some strange effects.  
   
      7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  
      correctly test characters of any code value, but the charac-  
      ters that PCRE recognizes as digits, spaces, or word charac-  
      ters  remain  the  same  set as before, all with values less  
      than 256.  
   
      8. Case-insensitive  matching  applies  only  to  characters  
      whose  values  are  less than 256. PCRE does not support the  
      notion of "case" for higher-valued characters.  
213    
214       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,
215       perties or the Perl escapes \p, \P, and \X.         so I've taken it away. If you want to email me, use my initial and sur-
216           name, separated by a dot, at the domain ucs.cam.ac.uk.
217    
218    Last updated: 05 June 2006
219    Copyright (c) 1997-2006 University of Cambridge.
220    ------------------------------------------------------------------------------
221    
 AUTHOR  
222    
223       Philip Hazel <ph10@cam.ac.uk>  PCREBUILD(3)                                                      PCREBUILD(3)
      University Computing Service,  
      Cambridge CB2 3QG, England.  
      Phone: +44 1223 334714  
224    
 Last updated: 04 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
225    
226  NAME  NAME
227       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
228    
229    
230  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
231    
232       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
233       can  be  selected when the library is compiled. They are all         selected when the library is compiled. They are all selected, or  dese-
234       selected, or deselected, by providing options to the config-         lected, by providing options to the configure script that is run before
235       ure  script  which  is run before the make command. The com-         the make command. The complete list of  options  for  configure  (which
236       plete list of options  for  configure  (which  includes  the         includes  the  standard  ones such as the selection of the installation
237       standard  ones  such  as  the  selection of the installation         directory) can be obtained by running
238       directory) can be obtained by running  
239             ./configure --help
240         ./configure --help  
241           The following sections describe certain options whose names begin  with
242       The following sections describe certain options whose  names         --enable  or  --disable. These settings specify changes to the defaults
243       begin  with  --enable  or  --disable. These settings specify         for the configure command. Because of the  way  that  configure  works,
244       changes to the defaults for the configure  command.  Because         --enable  and  --disable  always  come  in  pairs, so the complementary
245       of  the  way  that  configure  works, --enable and --disable         option always exists as well, but as it specifies the  default,  it  is
246       always come in pairs, so  the  complementary  option  always         not described.
247       exists  as  well, but as it specifies the default, it is not  
248       described.  
249    C++ SUPPORT
250    
251           By default, the configure script will search for a C++ compiler and C++
252           header files. If it finds them, it automatically builds the C++ wrapper
253           library for PCRE. You can disable this by adding
254    
255             --disable-cpp
256    
257           to the configure command.
258    
259    
260  UTF-8 SUPPORT  UTF-8 SUPPORT
261    
262       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
263    
264             --enable-utf8
265    
266           to  the  configure  command.  Of  itself, this does not make PCRE treat
267           strings as UTF-8. As well as compiling PCRE with this option, you  also
268           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
269           function.
270    
271    
272         --enable-utf8  UNICODE CHARACTER PROPERTY SUPPORT
273    
274       to the configure command. Of itself, this does not make PCRE         UTF-8 support allows PCRE to process character values greater than  255
275       treat  strings as UTF-8. As well as compiling PCRE with this         in  the  strings that it handles. On its own, however, it does not pro-
276       option, you also have have to set the PCRE_UTF8 option  when         vide any facilities for accessing the properties of such characters. If
277       you call the pcre_compile() function.         you  want  to  be able to use the pattern escapes \P, \p, and \X, which
278           refer to Unicode character properties, you must add
279    
280             --enable-unicode-properties
281    
282           to the configure command. This implies UTF-8 support, even if you  have
283           not explicitly requested it.
284    
285           Including  Unicode  property  support  adds around 90K of tables to the
286           PCRE library, approximately doubling its size. Only the  general  cate-
287           gory  properties  such as Lu and Nd are supported. Details are given in
288           the pcrepattern documentation.
289    
290    
291  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
292    
293       By default, PCRE treats character 10 (linefeed) as the  new-         By default, PCRE interprets character 10 (linefeed, LF)  as  indicating
294       line  character.  This  is  the  normal newline character on         the  end  of  a line. This is the normal newline character on Unix-like
295       Unix-like systems. You can compile PCRE to use character  13         systems. You can compile PCRE to use character 13 (carriage return, CR)
296       (carriage return) instead by adding         instead, by adding
297    
298         --enable-newline-is-cr           --enable-newline-is-cr
299    
300       to the configure command. For completeness there is  also  a         to  the  configure  command.  There  is  also  a --enable-newline-is-lf
301       --enable-newline-is-lf  option,  which  explicitly specifies         option, which explicitly specifies linefeed as the newline character.
302       linefeed as the newline character.  
303           Alternatively, you can specify that line endings are to be indicated by
304           the two character sequence CRLF. If you want this, add
305    
306             --enable-newline-is-crlf
307    
308           to  the  configure command. Whatever line ending convention is selected
309           when PCRE is built can be overridden when  the  library  functions  are
310           called.  At  build time it is conventional to use the standard for your
311           operating system.
312    
313    
314  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
315    
316       The PCRE building process uses libtool to build both  shared         The PCRE building process uses libtool to build both shared and  static
317       and  static  Unix libraries by default. You can suppress one         Unix  libraries by default. You can suppress one of these by adding one
318       of these by adding one of         of
319    
320         --disable-shared           --disable-shared
321         --disable-static           --disable-static
322    
323       to the configure command, as required.         to the configure command, as required.
324    
325    
326  POSIX MALLOC USAGE  POSIX MALLOC USAGE
327    
328       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
329       pcreposix  documentation),  additional  working  storage  is         umentation),  additional  working  storage  is required for holding the
330       required for holding the pointers  to  capturing  substrings         pointers to capturing substrings, because PCRE requires three  integers
331       because  PCRE requires three integers per substring, whereas         per  substring,  whereas  the POSIX interface provides only two. If the
332       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
333       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
334       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
335       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
336       stack is no longer used is 10; it can be changed by adding a  
337       setting such as           --with-posix-malloc-threshold=20
338    
339           to the configure command.
340    
        --with-posix-malloc-threshold=20  
341    
342       to the configure command.  HANDLING VERY LARGE PATTERNS
343    
344           Within  a  compiled  pattern,  offset values are used to point from one
345           part to another (for example, from an opening parenthesis to an  alter-
346           nation  metacharacter).  By default, two-byte values are used for these
347           offsets, leading to a maximum size for a  compiled  pattern  of  around
348           64K.  This  is sufficient to handle all but the most gigantic patterns.
349           Nevertheless, some people do want to process enormous patterns,  so  it
350           is  possible  to compile PCRE to use three-byte or four-byte offsets by
351           adding a setting such as
352    
353             --with-link-size=3
354    
355           to the configure command. The value given must be 2,  3,  or  4.  Using
356           longer  offsets slows down the operation of PCRE because it has to load
357           additional bytes when handling them.
358    
359           If you build PCRE with an increased link size, test 2 (and  test  5  if
360           you  are using UTF-8) will fail. Part of the output of these tests is a
361           representation of the compiled pattern, and this changes with the  link
362           size.
363    
364    
365    AVOIDING EXCESSIVE STACK USAGE
366    
367           When matching with the pcre_exec() function, PCRE implements backtrack-
368           ing by making recursive calls to an internal function  called  match().
369           In  environments  where  the size of the stack is limited, this can se-
370           verely limit PCRE's operation. (The Unix environment does  not  usually
371           suffer from this problem, but it may sometimes be necessary to increase
372           the maximum stack size.  There is a discussion in the  pcrestack  docu-
373           mentation.)  An alternative approach to recursion that uses memory from
374           the heap to remember data, instead of using recursive  function  calls,
375           has  been  implemented to work round the problem of limited stack size.
376           If you want to build a version of PCRE that works this way, add
377    
378             --disable-stack-for-recursion
379    
380           to the configure command. With this configuration, PCRE  will  use  the
381           pcre_stack_malloc  and pcre_stack_free variables to call memory manage-
382           ment functions. Separate functions are provided because  the  usage  is
383           very  predictable:  the  block sizes requested are always the same, and
384           the blocks are always freed in reverse order. A calling  program  might
385           be  able  to implement optimized functions that perform better than the
386           standard malloc() and  free()  functions.  PCRE  runs  noticeably  more
387           slowly when built in this way. This option affects only the pcre_exec()
388           function; it is not relevant for the the pcre_dfa_exec() function.
389    
390    
391  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
392    
393       Internally, PCRE has a  function  called  match()  which  it         Internally, PCRE has a function called match(), which it calls  repeat-
394       calls  repeatedly  (possibly  recursively) when performing a         edly   (sometimes   recursively)  when  matching  a  pattern  with  the
395       matching operation. By limiting the  number  of  times  this         pcre_exec() function. By controlling the maximum number of  times  this
396       function  may  be  called,  a  limit  can  be  placed on the         function  may be called during a single matching operation, a limit can
397       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
398       can  be  changed  at  run  time, as described in the pcreapi         limit  can be changed at run time, as described in the pcreapi documen-
399       documentation. The default is 10 million, but  this  can  be         tation. The default is 10 million, but this can be changed by adding  a
400       changed by adding a setting such as         setting such as
401    
402         --with-match-limit=500000           --with-match-limit=500000
403    
404       to the configure command.         to   the   configure  command.  This  setting  has  no  effect  on  the
405           pcre_dfa_exec() matching function.
406    
407           In some environments it is desirable to limit the  depth  of  recursive
408           calls of match() more strictly than the total number of calls, in order
409           to restrict the maximum amount of stack (or heap,  if  --disable-stack-
410           for-recursion is specified) that is used. A second limit controls this;
411           it defaults to the value that  is  set  for  --with-match-limit,  which
412           imposes  no  additional constraints. However, you can set a lower limit
413           by adding, for example,
414    
415  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
416    
417       Within a compiled pattern, offset values are used  to  point         to the configure command. This value can  also  be  overridden  at  run
418       from  one  part  to  another  (for  example, from an opening         time.
419       parenthesis to an  alternation  metacharacter).  By  default  
420       two-byte  values  are  used  for these offsets, leading to a  
421       maximum size for a compiled pattern of around 64K.  This  is  USING EBCDIC CODE
422       sufficient  to  handle  all  but the most gigantic patterns.  
423       Nevertheless, some people do want to process  enormous  pat-         PCRE  assumes  by  default that it will run in an environment where the
424       terns,  so  it is possible to compile PCRE to use three-byte         character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
425       or four-byte offsets by adding a setting such as         PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
426           adding
427         --with-link-size=3  
428             --enable-ebcdic
429       to the configure command. The value given must be 2,  3,  or  
430       4.  Using  longer  offsets  slows down the operation of PCRE         to the configure command.
431       because it has to load additional bytes when handling them.  
432    Last updated: 06 June 2006
433       If you build PCRE with an increased link size, test  2  (and  Copyright (c) 1997-2006 University of Cambridge.
434       test 5 if you are using UTF-8) will fail. Part of the output  ------------------------------------------------------------------------------
435       of these tests is a representation of the compiled  pattern,  
436       and this changes with the link size.  
437    PCREMATCHING(3)                                                PCREMATCHING(3)
438    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
439    
440  NAME  NAME
441       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
442    
443    
444    PCRE MATCHING ALGORITHMS
445    
446           This document describes the two different algorithms that are available
447           in PCRE for matching a compiled regular expression against a given sub-
448           ject  string.  The  "standard"  algorithm  is  the  one provided by the
449           pcre_exec() function.  This works in the same was  as  Perl's  matching
450           function, and provides a Perl-compatible matching operation.
451    
452           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
453           this operates in a different way, and is not  Perl-compatible.  It  has
454           advantages  and disadvantages compared with the standard algorithm, and
455           these are described below.
456    
457           When there is only one possible way in which a given subject string can
458           match  a pattern, the two algorithms give the same answer. A difference
459           arises, however, when there are multiple possibilities. For example, if
460           the pattern
461    
462             ^<.*>
463    
464           is matched against the string
465    
466             <something> <something else> <something further>
467    
468           there are three possible answers. The standard algorithm finds only one
469           of them, whereas the DFA algorithm finds all three.
470    
471    
472    REGULAR EXPRESSIONS AS TREES
473    
474           The set of strings that are matched by a regular expression can be rep-
475           resented  as  a  tree structure. An unlimited repetition in the pattern
476           makes the tree of infinite size, but it is still a tree.  Matching  the
477           pattern  to a given subject string (from a given starting point) can be
478           thought of as a search of the tree.  There are two  ways  to  search  a
479           tree:  depth-first  and  breadth-first, and these correspond to the two
480           matching algorithms provided by PCRE.
481    
482    
483    THE STANDARD MATCHING ALGORITHM
484    
485           In the terminology of Jeffrey Friedl's book Mastering  Regular  Expres-
486           sions,  the  standard  algorithm  is  an "NFA algorithm". It conducts a
487           depth-first search of the pattern tree. That is, it  proceeds  along  a
488           single path through the tree, checking that the subject matches what is
489           required. When there is a mismatch, the algorithm  tries  any  alterna-
490           tives  at  the  current point, and if they all fail, it backs up to the
491           previous branch point in the  tree,  and  tries  the  next  alternative
492           branch  at  that  level.  This often involves backing up (moving to the
493           left) in the subject string as well.  The  order  in  which  repetition
494           branches  are  tried  is controlled by the greedy or ungreedy nature of
495           the quantifier.
496    
497           If a leaf node is reached, a matching string has  been  found,  and  at
498           that  point the algorithm stops. Thus, if there is more than one possi-
499           ble match, this algorithm returns the first one that it finds.  Whether
500           this  is the shortest, the longest, or some intermediate length depends
501           on the way the greedy and ungreedy repetition quantifiers are specified
502           in the pattern.
503    
504           Because  it  ends  up  with a single path through the tree, it is rela-
505           tively straightforward for this algorithm to keep  track  of  the  sub-
506           strings  that  are  matched  by portions of the pattern in parentheses.
507           This provides support for capturing parentheses and back references.
508    
509    
510    THE DFA MATCHING ALGORITHM
511    
512  SYNOPSIS OF PCRE API         DFA stands for "deterministic finite automaton", but you do not need to
513           understand the origins of that name. This algorithm conducts a breadth-
514           first search of the tree. Starting from the first matching point in the
515           subject,  it scans the subject string from left to right, once, charac-
516           ter by character, and as it does  this,  it  remembers  all  the  paths
517           through the tree that represent valid matches.
518    
519       #include <pcre.h>         The  scan  continues until either the end of the subject is reached, or
520           there are no more unterminated paths. At this point,  terminated  paths
521           represent  the different matching possibilities (if there are none, the
522           match has failed).  Thus, if there is more  than  one  possible  match,
523           this algorithm finds all of them, and in particular, it finds the long-
524           est. In PCRE, there is an option to stop the algorithm after the  first
525           match (which is necessarily the shortest) has been found.
526    
527       pcre *pcre_compile(const char *pattern, int options,         Note that all the matches that are found start at the same point in the
528            const char **errptr, int *erroffset,         subject. If the pattern
           const unsigned char *tableptr);  
529    
530       pcre_extra *pcre_study(const pcre *code, int options,           cat(er(pillar)?)
           const char **errptr);  
531    
532       int pcre_exec(const pcre *code, const pcre_extra *extra,         is matched against the string "the caterpillar catchment",  the  result
533            const char *subject, int length, int startoffset,         will  be the three strings "cat", "cater", and "caterpillar" that start
534            int options, int *ovector, int ovecsize);         at the fourth character of the subject. The algorithm does not automat-
535           ically move on to find matches that start at later positions.
536    
537       int pcre_copy_named_substring(const pcre *code,         There are a number of features of PCRE regular expressions that are not
538            const char *subject, int *ovector,         supported by the DFA matching algorithm. They are as follows:
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
539    
540       int pcre_copy_substring(const char *subject, int *ovector,         1. Because the algorithm finds all  possible  matches,  the  greedy  or
541            int stringcount, int stringnumber, char *buffer,         ungreedy  nature  of repetition quantifiers is not relevant. Greedy and
542            int buffersize);         ungreedy quantifiers are treated in exactly the same way.
543    
544       int pcre_get_named_substring(const pcre *code,         2. When dealing with multiple paths through the tree simultaneously, it
545            const char *subject, int *ovector,         is  not  straightforward  to  keep track of captured substrings for the
546            int stringcount, const char *stringname,         different matching possibilities, and  PCRE's  implementation  of  this
547            const char **stringptr);         algorithm does not attempt to do this. This means that no captured sub-
548           strings are available.
549    
550       int pcre_get_stringnumber(const pcre *code,         3. Because no substrings are captured, back references within the  pat-
551            const char *name);         tern are not supported, and cause errors if encountered.
552    
553       int pcre_get_substring(const char *subject, int *ovector,         4.  For  the same reason, conditional expressions that use a backrefer-
554            int stringcount, int stringnumber,         ence as the condition are not supported.
555            const char **stringptr);  
556           5. Callouts are supported, but the value of the  capture_top  field  is
557           always 1, and the value of the capture_last field is always -1.
558    
559           6.  The \C escape sequence, which (in the standard algorithm) matches a
560           single byte, even in UTF-8 mode, is not supported because the DFA algo-
561           rithm moves through the subject string one character at a time, for all
562           active paths through the tree.
563    
564    
565    ADVANTAGES OF THE DFA ALGORITHM
566    
567           Using the DFA matching algorithm provides the following advantages:
568    
569           1. All possible matches (at a single point in the subject) are automat-
570           ically  found,  and  in particular, the longest match is found. To find
571           more than one match using the standard algorithm, you have to do kludgy
572           things with callouts.
573    
574           2.  There is much better support for partial matching. The restrictions
575           on the content of the pattern that apply when using the standard  algo-
576           rithm  for partial matching do not apply to the DFA algorithm. For non-
577           anchored patterns, the starting position of a partial match  is  avail-
578           able.
579    
580           3.  Because  the  DFA algorithm scans the subject string just once, and
581           never needs to backtrack, it is possible  to  pass  very  long  subject
582           strings  to  the matching function in several pieces, checking for par-
583           tial matching each time.
584    
585    
586    DISADVANTAGES OF THE DFA ALGORITHM
587    
588           The DFA algorithm suffers from a number of disadvantages:
589    
590           1. It is substantially slower than  the  standard  algorithm.  This  is
591           partly  because  it has to search for all possible matches, but is also
592           because it is less susceptible to optimization.
593    
594           2. Capturing parentheses and back references are not supported.
595    
596           3. The "atomic group" feature of PCRE regular expressions is supported,
597           but  does not provide the advantage that it does for the standard algo-
598           rithm.
599    
600    Last updated: 06 June 2006
601    Copyright (c) 1997-2006 University of Cambridge.
602    ------------------------------------------------------------------------------
603    
604    
605    PCREAPI(3)                                                          PCREAPI(3)
606    
607    
608    NAME
609           PCRE - Perl-compatible regular expressions
610    
      int pcre_get_substring_list(const char *subject,  
           int *ovector, int stringcount, const char ***listptr);  
611    
612       void pcre_free_substring(const char *stringptr);  PCRE NATIVE API
613    
614       void pcre_free_substring_list(const char **stringptr);         #include <pcre.h>
615    
616       const unsigned char *pcre_maketables(void);         pcre *pcre_compile(const char *pattern, int options,
617                const char **errptr, int *erroffset,
618                const unsigned char *tableptr);
619    
620       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         pcre *pcre_compile2(const char *pattern, int options,
621            int what, void *where);              int *errorcodeptr,
622                const char **errptr, int *erroffset,
623                const unsigned char *tableptr);
624    
625           pcre_extra *pcre_study(const pcre *code, int options,
626                const char **errptr);
627    
628       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_exec(const pcre *code, const pcre_extra *extra,
629                const char *subject, int length, int startoffset,
630                int options, int *ovector, int ovecsize);
631    
632       int pcre_config(int what, void *where);         int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
633                const char *subject, int length, int startoffset,
634                int options, int *ovector, int ovecsize,
635                int *workspace, int wscount);
636    
637       char *pcre_version(void);         int pcre_copy_named_substring(const pcre *code,
638                const char *subject, int *ovector,
639                int stringcount, const char *stringname,
640                char *buffer, int buffersize);
641    
642       void *(*pcre_malloc)(size_t);         int pcre_copy_substring(const char *subject, int *ovector,
643                int stringcount, int stringnumber, char *buffer,
644                int buffersize);
645    
646       void (*pcre_free)(void *);         int pcre_get_named_substring(const pcre *code,
647                const char *subject, int *ovector,
648                int stringcount, const char *stringname,
649                const char **stringptr);
650    
651       int (*pcre_callout)(pcre_callout_block *);         int pcre_get_stringnumber(const pcre *code,
652                const char *name);
653    
654           int pcre_get_stringtable_entries(const pcre *code,
655                const char *name, char **first, char **last);
656    
657  PCRE API         int pcre_get_substring(const char *subject, int *ovector,
658                int stringcount, int stringnumber,
659                const char **stringptr);
660    
661       PCRE has its own native API,  which  is  described  in  this         int pcre_get_substring_list(const char *subject,
662       document.  There  is  also  a  set of wrapper functions that              int *ovector, int stringcount, const char ***listptr);
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
663    
664       The native API function prototypes are defined in the header         void pcre_free_substring(const char *stringptr);
      file  pcre.h,  and  on  Unix  systems  the library itself is  
      called libpcre.a, so can be accessed by adding -lpcre to the  
      command  for  linking  an  application  which  calls it. The  
      header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
665    
666       The functions pcre_compile(), pcre_study(), and  pcre_exec()         void pcre_free_substring_list(const char **stringptr);
      are  used  for compiling and matching regular expressions. A  
      sample program that demonstrates the simplest way  of  using  
      them  is  given in the file pcredemo.c. The pcresample docu-  
      mentation describes how to run it.  
667    
668       There are convenience functions for extracting captured sub-         const unsigned char *pcre_maketables(void);
      strings from a matched subject string. They are:  
669    
670         pcre_copy_substring()         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
671         pcre_copy_named_substring()              int what, void *where);
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
672    
673       pcre_free_substring()  and  pcre_free_substring_list()   are         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
      also  provided,  to  free  the  memory  used  for  extracted  
      strings.  
674    
675       The function pcre_maketables() is used (optionally) to build         int pcre_refcount(pcre *code, int adjust);
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
676    
677       The function pcre_fullinfo() is used to find out information         int pcre_config(int what, void *where);
      about a compiled pattern; pcre_info() is an obsolete version  
      which returns only some of the available information, but is  
      retained   for   backwards   compatibility.    The  function  
      pcre_version() returns a pointer to a string containing  the  
      version of PCRE and its date of release.  
678    
679       The global variables  pcre_malloc  and  pcre_free  initially         char *pcre_version(void);
      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.  
680    
681       The global variable pcre_callout initially contains NULL. It         void *(*pcre_malloc)(size_t);
682       can be set by the caller to a "callout" function, which PCRE  
683       will then call at specified points during a matching  opera-         void (*pcre_free)(void *);
684       tion. Details are given in the pcrecallout documentation.  
685           void *(*pcre_stack_malloc)(size_t);
686    
687           void (*pcre_stack_free)(void *);
688    
689           int (*pcre_callout)(pcre_callout_block *);
690    
691    
692    PCRE API OVERVIEW
693    
694           PCRE has its own native API, which is described in this document. There
695           is also a set of wrapper functions that correspond to the POSIX regular
696           expression  API.  These  are  described in the pcreposix documentation.
697           Both of these APIs define a set of C function calls. A C++  wrapper  is
698           distributed with PCRE. It is documented in the pcrecpp page.
699    
700           The  native  API  C  function prototypes are defined in the header file
701           pcre.h, and on Unix systems the library itself is called  libpcre.   It
702           can normally be accessed by adding -lpcre to the command for linking an
703           application  that  uses  PCRE.  The  header  file  defines  the  macros
704           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
705           bers for the library.  Applications can use these  to  include  support
706           for different releases of PCRE.
707    
708           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
709           pcre_exec() are used for compiling and matching regular expressions  in
710           a  Perl-compatible  manner. A sample program that demonstrates the sim-
711           plest way of using them is provided in the file  called  pcredemo.c  in
712           the  source distribution. The pcresample documentation describes how to
713           run it.
714    
715           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
716           ble,  is  also provided. This uses a different algorithm for the match-
717           ing. The alternative algorithm finds all possible matches (at  a  given
718           point in the subject). However, this algorithm does not return captured
719           substrings. A description of the  two  matching  algorithms  and  their
720           advantages  and  disadvantages  is given in the pcrematching documenta-
721           tion.
722    
723           In addition to the main compiling and  matching  functions,  there  are
724           convenience functions for extracting captured substrings from a subject
725           string that is matched by pcre_exec(). They are:
726    
727             pcre_copy_substring()
728             pcre_copy_named_substring()
729             pcre_get_substring()
730             pcre_get_named_substring()
731             pcre_get_substring_list()
732             pcre_get_stringnumber()
733             pcre_get_stringtable_entries()
734    
735           pcre_free_substring() and pcre_free_substring_list() are also provided,
736           to free the memory used for extracted strings.
737    
738           The  function  pcre_maketables()  is  used  to build a set of character
739           tables  in  the  current  locale   for   passing   to   pcre_compile(),
740           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
741           provided for specialist use.  Most  commonly,  no  special  tables  are
742           passed,  in  which case internal tables that are generated when PCRE is
743           built are used.
744    
745           The function pcre_fullinfo() is used to find out  information  about  a
746           compiled  pattern; pcre_info() is an obsolete version that returns only
747           some of the available information, but is retained for  backwards  com-
748           patibility.   The function pcre_version() returns a pointer to a string
749           containing the version of PCRE and its date of release.
750    
751           The function pcre_refcount() maintains a  reference  count  in  a  data
752           block  containing  a compiled pattern. This is provided for the benefit
753           of object-oriented applications.
754    
755           The global variables pcre_malloc and pcre_free  initially  contain  the
756           entry  points  of  the  standard malloc() and free() functions, respec-
757           tively. PCRE calls the memory management functions via these variables,
758           so  a  calling  program  can replace them if it wishes to intercept the
759           calls. This should be done before calling any PCRE functions.
760    
761           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
762           indirections  to  memory  management functions. These special functions
763           are used only when PCRE is compiled to use  the  heap  for  remembering
764           data, instead of recursive function calls, when running the pcre_exec()
765           function. See the pcrebuild documentation for  details  of  how  to  do
766           this.  It  is  a non-standard way of building PCRE, for use in environ-
767           ments that have limited stacks. Because of the greater  use  of  memory
768           management,  it  runs  more  slowly. Separate functions are provided so
769           that special-purpose external code can be  used  for  this  case.  When
770           used,  these  functions  are always called in a stack-like manner (last
771           obtained, first freed), and always for memory blocks of the same  size.
772           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
773           mentation.
774    
775           The global variable pcre_callout initially contains NULL. It can be set
776           by  the  caller  to  a "callout" function, which PCRE will then call at
777           specified points during a matching operation. Details are given in  the
778           pcrecallout documentation.
779    
780    
781    NEWLINES
782           PCRE supports three different conventions for indicating line breaks in
783           strings: a single CR character, a single LF character, or the two-char-
784           acter  sequence  CRLF.  All  three  are used as "standard" by different
785           operating systems.  When PCRE is built, a default can be specified. The
786           default  default  is  LF, which is the Unix standard. When PCRE is run,
787           the default can be overridden, either when a pattern  is  compiled,  or
788           when it is matched.
789    
790           In the PCRE documentation the word "newline" is used to mean "the char-
791           acter or pair of characters that indicate a line break".
792    
793    
794  MULTITHREADING  MULTITHREADING
795    
796       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
797       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
798       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
799       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
800       threads.  
801           The compiled form of a regular expression is not altered during  match-
802       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
803       during  matching, so the same compiled pattern can safely be         at once.
804       used by several threads at once.  
805    
806    SAVING PRECOMPILED PATTERNS FOR LATER USE
807    
808           The compiled form of a regular expression can be saved and re-used at a
809           later  time,  possibly by a different program, and even on a host other
810           than the one on which  it  was  compiled.  Details  are  given  in  the
811           pcreprecompile documentation.
812    
813    
814  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
815    
816       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
817    
818           The  function pcre_config() makes it possible for a PCRE client to dis-
819           cover which optional features have been compiled into the PCRE library.
820           The  pcrebuild documentation has more details about these optional fea-
821           tures.
822    
823           The first argument for pcre_config() is an  integer,  specifying  which
824           information is required; the second argument is a pointer to a variable
825           into which the information is  placed.  The  following  information  is
826           available:
827    
828             PCRE_CONFIG_UTF8
829    
830       The function pcre_config() makes  it  possible  for  a  PCRE         The  output is an integer that is set to one if UTF-8 support is avail-
831       client  to  discover  which optional features have been com-         able; otherwise it is set to zero.
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
832    
833       The first argument for pcre_config() is an integer, specify-           PCRE_CONFIG_UNICODE_PROPERTIES
      ing  which information is required; the second argument is a  
      pointer to a variable into which the information is  placed.  
      The following information is available:  
834    
835         PCRE_CONFIG_UTF8         The output is an integer that is set to  one  if  support  for  Unicode
836           character properties is available; otherwise it is set to zero.
837    
838       The output is an integer that is set to one if UTF-8 support           PCRE_CONFIG_NEWLINE
      is available; otherwise it is set to zero.  
839    
840         PCRE_CONFIG_NEWLINE         The  output  is  an integer whose value specifies the default character
841           sequence that is recognized as meaning "newline". The three values that
842           are supported are: 10 for LF, 13 for CR, and 3338 for CRLF. The default
843           should normally be the standard sequence for your operating system.
844    
845       The output is an integer that is set to  the  value  of  the           PCRE_CONFIG_LINK_SIZE
      code  that  is  used for the newline character. It is either  
      linefeed (10) or carriage return (13), and  should  normally  
      be the standard character for your operating system.  
846    
847         PCRE_CONFIG_LINK_SIZE         The output is an integer that contains the number  of  bytes  used  for
848           internal linkage in compiled regular expressions. The value is 2, 3, or
849           4. Larger values allow larger regular expressions to  be  compiled,  at
850           the  expense  of  slower matching. The default value of 2 is sufficient
851           for all but the most massive patterns, since  it  allows  the  compiled
852           pattern to be up to 64K in size.
853    
854       The output is an integer that contains the number  of  bytes           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
      used  for  internal linkage in compiled regular expressions.  
      The value is 2, 3, or 4. Larger values allow larger  regular  
      expressions  to be compiled, at the expense of slower match-  
      ing. The default value of 2 is sufficient for  all  but  the  
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
855    
856         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD         The  output  is  an integer that contains the threshold above which the
857           POSIX interface uses malloc() for output vectors. Further  details  are
858           given in the pcreposix documentation.
859    
860       The output is an integer that contains the  threshold  above           PCRE_CONFIG_MATCH_LIMIT
      which  the POSIX interface uses malloc() for output vectors.  
      Further details are given in the pcreposix documentation.  
861    
862         PCRE_CONFIG_MATCH_LIMIT         The output is an integer that gives the default limit for the number of
863           internal matching function calls in a  pcre_exec()  execution.  Further
864           details are given with pcre_exec() below.
865    
866       The output is an integer that gives the  default  limit  for           PCRE_CONFIG_MATCH_LIMIT_RECURSION
867       the   number  of  internal  matching  function  calls  in  a  
868       pcre_exec()  execution.  Further  details  are  given   with         The  output is an integer that gives the default limit for the depth of
869       pcre_exec() below.         recursion when calling the internal matching function in a  pcre_exec()
870           execution. Further details are given with pcre_exec() below.
871    
872             PCRE_CONFIG_STACKRECURSE
873    
874           The  output is an integer that is set to one if internal recursion when
875           running pcre_exec() is implemented by recursive function calls that use
876           the  stack  to remember their state. This is the usual way that PCRE is
877           compiled. The output is zero if PCRE was compiled to use blocks of data
878           on  the  heap  instead  of  recursive  function  calls.  In  this case,
879           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
880           blocks on the heap, thus avoiding the use of the stack.
881    
882    
883  COMPILING A PATTERN  COMPILING A PATTERN
884    
885       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
886            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
887            const unsigned char *tableptr);              const unsigned char *tableptr);
888    
889       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
890       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
891       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
892       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
893       pcre_malloc is returned. This contains the compiled code and  
894       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
895       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
896       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
897       memory when it is no longer required.         errorcodeptr, via which a numerical error code can be returned.
898    
899       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
900       that is, it does not depend on memory location, the complete         the  pattern  argument.  A  pointer to a single block of memory that is
901       pcre data block is not fully relocatable,  because  it  con-         obtained via pcre_malloc is returned. This contains the  compiled  code
902       tains  a  copy of the tableptr argument, which is an address         and related data. The pcre type is defined for the returned block; this
903       (see below).         is a typedef for a structure whose contents are not externally defined.
904       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
905       the  compilation.  It  should  be  zero  if  no  options are         longer required.
906       required. Some of the options, in particular, those that are  
907       compatible  with Perl, can also be set and unset from within         Although the compiled code of a PCRE regex is relocatable, that is,  it
908       the pattern (see the detailed description of regular expres-         does not depend on memory location, the complete pcre data block is not
909       sions  in the pcrepattern documentation). For these options,         fully relocatable, because it may contain a copy of the tableptr  argu-
910       the contents of the options argument specifies their initial         ment, which is an address (see below).
911       settings  at  the  start  of  compilation and execution. The  
912       PCRE_ANCHORED option can be set at the time of  matching  as         The options argument contains independent bits that affect the compila-
913       well as at compile time.         tion. It should be zero if  no  options  are  required.  The  available
914           options  are  described  below. Some of them, in particular, those that
915       If errptr is NULL, pcre_compile() returns NULL  immediately.         are compatible with Perl, can also be set and  unset  from  within  the
916       Otherwise, if compilation of a pattern fails, pcre_compile()         pattern  (see  the  detailed  description in the pcrepattern documenta-
917       returns NULL, and sets the variable pointed to by errptr  to         tion). For these options, the contents of the options  argument  speci-
918       point  to a textual error message. The offset from the start         fies  their initial settings at the start of compilation and execution.
919       of  the  pattern  to  the  character  where  the  error  was         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
920       discovered   is   placed  in  the  variable  pointed  to  by         of matching as well as at compile time.
921       erroffset, which must not be NULL. If it  is,  an  immediate  
922       error is given.         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
923           if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
924       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         sets the variable pointed to by errptr to point to a textual error mes-
925       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
926       compiled, using the default C  locale.  Otherwise,  tableptr         try to free it. The offset from the start of the pattern to the charac-
927       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
928       section on locale support below.         by  erroffset,  which must not be NULL. If it is, an immediate error is
929           given.
930       This code fragment shows a typical straightforward  call  to  
931       pcre_compile():         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
932           codeptr  argument is not NULL, a non-zero error code number is returned
933         pcre *re;         via this argument in the event of an error. This is in addition to  the
934         const char *error;         textual error message. Error codes and messages are listed below.
935         int erroffset;  
936         re = pcre_compile(         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
937           "^A.*Z",          /* the pattern */         character tables that are  built  when  PCRE  is  compiled,  using  the
938           0,                /* default options */         default  C  locale.  Otherwise, tableptr must be an address that is the
939           &error,           /* for error message */         result of a call to pcre_maketables(). This value is  stored  with  the
940           &erroffset,       /* for error offset */         compiled  pattern,  and used again by pcre_exec(), unless another table
941           NULL);            /* use default character tables */         pointer is passed to it. For more discussion, see the section on locale
942           support below.
943       The following option bits are defined:  
944           This  code  fragment  shows a typical straightforward call to pcre_com-
945         PCRE_ANCHORED         pile():
946    
947       If this bit is set, the pattern is forced to be  "anchored",           pcre *re;
948       that is, it is constrained to match only at the first match-           const char *error;
949       ing point in the string which is being searched  (the  "sub-           int erroffset;
950       ject string"). This effect can also be achieved by appropri-           re = pcre_compile(
951       ate constructs in the pattern itself, which is the only  way             "^A.*Z",          /* the pattern */
952       to do it in Perl.             0,                /* default options */
953               &error,           /* for error message */
954         PCRE_CASELESS             &erroffset,       /* for error offset */
955               NULL);            /* use default character tables */
956       If this bit is set, letters in the pattern match both  upper  
957       and  lower  case  letters.  It  is  equivalent  to Perl's /i         The following names for option bits are defined in  the  pcre.h  header
958       option, and it can be changed within a  pattern  by  a  (?i)         file:
959       option setting.  
960             PCRE_ANCHORED
961         PCRE_DOLLAR_ENDONLY  
962           If this bit is set, the pattern is forced to be "anchored", that is, it
963       If this bit is set, a dollar metacharacter  in  the  pattern         is constrained to match only at the first matching point in the  string
964       matches  only at the end of the subject string. Without this         that  is being searched (the "subject string"). This effect can also be
965       option, a dollar also matches immediately before  the  final         achieved by appropriate constructs in the pattern itself, which is  the
966       character  if it is a newline (but not before any other new-         only way to do it in Perl.
967       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
968       PCRE_MULTILINE is set. There is no equivalent to this option           PCRE_AUTO_CALLOUT
969       in Perl, and no way to set it within a pattern.  
970           If this bit is set, pcre_compile() automatically inserts callout items,
971         PCRE_DOTALL         all with number 255, before each pattern item. For  discussion  of  the
972           callout facility, see the pcrecallout documentation.
973       If this bit is  set,  a  dot  metacharater  in  the  pattern  
974       matches all characters, including newlines. Without it, new-           PCRE_CASELESS
975       lines are excluded. This option is equivalent to  Perl's  /s  
976       option,  and  it  can  be changed within a pattern by a (?s)         If  this  bit is set, letters in the pattern match both upper and lower
977       option setting. A negative class such as [^a] always matches         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
978       a  newline  character,  independent  of  the setting of this         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
979       option.         always understands the concept of case for characters whose values  are
980           less  than 128, so caseless matching is always possible. For characters
981         PCRE_EXTENDED         with higher values, the concept of case is supported if  PCRE  is  com-
982           piled  with Unicode property support, but not otherwise. If you want to
983       If this bit is set, whitespace data characters in  the  pat-         use caseless matching for characters 128 and  above,  you  must  ensure
984       tern  are  totally  ignored  except when escaped or inside a         that  PCRE  is  compiled  with Unicode property support as well as with
985       character class. Whitespace does not include the VT  charac-         UTF-8 support.
986       ter  (code 11). In addition, characters between an unescaped  
987       # outside a character class and the next newline  character,           PCRE_DOLLAR_ENDONLY
988       inclusive, are also ignored. This is equivalent to Perl's /x  
989       option, and it can be changed within a  pattern  by  a  (?x)         If this bit is set, a dollar metacharacter in the pattern matches  only
990       option setting.         at  the  end  of the subject string. Without this option, a dollar also
991           matches immediately before a newline at the end of the string (but  not
992       This option makes it possible  to  include  comments  inside         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
993       complicated patterns.  Note, however, that this applies only         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
994       to data characters. Whitespace characters may  never  appear         Perl, and no way to set it within a pattern.
995       within special character sequences in a pattern, for example  
996       within the sequence (?( which introduces a conditional  sub-           PCRE_DOTALL
997       pattern.  
998           If this bit is set, a dot metacharater in the pattern matches all char-
999         PCRE_EXTRA         acters, including those that indicate newline. Without it, a  dot  does
1000           not  match  when  the  current position is at a newline. This option is
1001       This option was invented in  order  to  turn  on  additional         equivalent to Perl's /s option, and it can be changed within a  pattern
1002       functionality of PCRE that is incompatible with Perl, but it         by  a (?s) option setting. A negative class such as [^a] always matches
1003       is currently of very little use. When set, any backslash  in         newlines, independent of the setting of this option.
1004       a  pattern  that is followed by a letter that has no special  
1005       meaning causes an error, thus reserving  these  combinations           PCRE_DUPNAMES
1006       for  future  expansion.  By default, as in Perl, a backslash  
1007       followed by a letter with no special meaning is treated as a         If this bit is set, names used to identify capturing  subpatterns  need
1008       literal.  There  are at present no other features controlled         not be unique. This can be helpful for certain types of pattern when it
1009       by this option. It can also be set by a (?X) option  setting         is known that only one instance of the named  subpattern  can  ever  be
1010       within a pattern.         matched.  There  are  more details of named subpatterns below; see also
1011           the pcrepattern documentation.
1012         PCRE_MULTILINE  
1013             PCRE_EXTENDED
1014       By default, PCRE treats the subject string as consisting  of  
1015       a  single "line" of characters (even if it actually contains         If this bit is set, whitespace  data  characters  in  the  pattern  are
1016       several newlines). The "start  of  line"  metacharacter  (^)         totally ignored except when escaped or inside a character class. White-
1017       matches  only  at the start of the string, while the "end of         space does not include the VT character (code 11). In addition, charac-
1018       line" metacharacter ($) matches  only  at  the  end  of  the         ters between an unescaped # outside a character class and the next new-
1019       string,    or   before   a   terminating   newline   (unless         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1020       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.         option,  and  it  can be changed within a pattern by a (?x) option set-
1021           ting.
1022       When PCRE_MULTILINE it is set, the "start of line" and  "end  
1023       of  line"  constructs match immediately following or immedi-         This option makes it possible to include  comments  inside  complicated
1024       ately before any newline  in  the  subject  string,  respec-         patterns.   Note,  however,  that this applies only to data characters.
1025       tively,  as  well  as  at  the  very  start and end. This is         Whitespace  characters  may  never  appear  within  special   character
1026       equivalent to Perl's /m option, and it can be changed within         sequences  in  a  pattern,  for  example  within the sequence (?( which
1027       a  pattern  by  a  (?m) option setting. If there are no "\n"         introduces a conditional subpattern.
1028       characters in a subject string, or no occurrences of ^ or  $  
1029       in a pattern, setting PCRE_MULTILINE has no effect.           PCRE_EXTRA
1030    
1031         PCRE_NO_AUTO_CAPTURE         This option was invented in order to turn on  additional  functionality
1032           of  PCRE  that  is  incompatible with Perl, but it is currently of very
1033       If this option is set, it disables the use of numbered  cap-         little use. When set, any backslash in a pattern that is followed by  a
1034       turing  parentheses  in the pattern. Any opening parenthesis         letter  that  has  no  special  meaning causes an error, thus reserving
1035       that is not followed by ? behaves as if it were followed  by         these combinations for future expansion. By  default,  as  in  Perl,  a
1036       ?:  but  named  parentheses  can still be used for capturing         backslash  followed by a letter with no special meaning is treated as a
1037       (and they acquire numbers in the usual  way).  There  is  no         literal. (Perl can, however, be persuaded to give a warning for  this.)
1038       equivalent of this option in Perl.         There  are  at  present no other features controlled by this option. It
1039           can also be set by a (?X) option setting within a pattern.
1040         PCRE_UNGREEDY  
1041             PCRE_FIRSTLINE
1042       This option inverts the "greediness" of the  quantifiers  so  
1043       that  they  are  not greedy by default, but become greedy if         If this option is set, an  unanchored  pattern  is  required  to  match
1044       followed by "?". It is not compatible with Perl. It can also         before  or  at  the  first  newline  in  the subject string, though the
1045       be set by a (?U) option setting within the pattern.         matched text may continue over the newline.
1046    
1047         PCRE_UTF8           PCRE_MULTILINE
1048    
1049       This option causes PCRE to regard both the pattern  and  the         By default, PCRE treats the subject string as consisting  of  a  single
1050       subject  as  strings  of UTF-8 characters instead of single-         line  of characters (even if it actually contains newlines). The "start
1051       byte character strings. However, it  is  available  only  if         of line" metacharacter (^) matches only at the  start  of  the  string,
1052       PCRE  has  been  built to include UTF-8 support. If not, the         while  the  "end  of line" metacharacter ($) matches only at the end of
1053       use of this option provokes an error. Details  of  how  this         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1054       option  changes  the behaviour of PCRE are given in the sec-         is set). This is the same as Perl.
1055       tion on UTF-8 support in the main pcre page.  
1056           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1057           constructs match immediately following or immediately  before  internal
1058           newlines  in  the  subject string, respectively, as well as at the very
1059           start and end. This is equivalent to Perl's /m option, and  it  can  be
1060           changed within a pattern by a (?m) option setting. If there are no new-
1061           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1062           setting PCRE_MULTILINE has no effect.
1063    
1064             PCRE_NEWLINE_CR
1065             PCRE_NEWLINE_LF
1066             PCRE_NEWLINE_CRLF
1067    
1068           These  options  override the default newline definition that was chosen
1069           when PCRE was built. Setting the first or the second specifies  that  a
1070           newline  is  indicated  by a single character (CR or LF, respectively).
1071           Setting both of them specifies that a newline is indicated by the  two-
1072           character  CRLF sequence. For convenience, PCRE_NEWLINE_CRLF is defined
1073           to contain both bits. The only time that a line break is relevant  when
1074           compiling a pattern is if PCRE_EXTENDED is set, and an unescaped # out-
1075           side a character class is encountered. This indicates  a  comment  that
1076           lasts until after the next newline.
1077    
1078           The newline option set at compile time becomes the default that is used
1079           for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1080    
1081             PCRE_NO_AUTO_CAPTURE
1082    
1083           If this option is set, it disables the use of numbered capturing paren-
1084           theses  in the pattern. Any opening parenthesis that is not followed by
1085           ? behaves as if it were followed by ?: but named parentheses can  still
1086           be  used  for  capturing  (and  they acquire numbers in the usual way).
1087           There is no equivalent of this option in Perl.
1088    
1089             PCRE_UNGREEDY
1090    
1091           This option inverts the "greediness" of the quantifiers  so  that  they
1092           are  not greedy by default, but become greedy if followed by "?". It is
1093           not compatible with Perl. It can also be set by a (?U)  option  setting
1094           within the pattern.
1095    
1096             PCRE_UTF8
1097    
1098           This  option  causes PCRE to regard both the pattern and the subject as
1099           strings of UTF-8 characters instead of single-byte  character  strings.
1100           However,  it is available only when PCRE is built to include UTF-8 sup-
1101           port. If not, the use of this option provokes an error. Details of  how
1102           this  option  changes the behaviour of PCRE are given in the section on
1103           UTF-8 support in the main pcre page.
1104    
1105             PCRE_NO_UTF8_CHECK
1106    
1107           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1108           automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1109           pcre_compile() returns an error. If you already know that your  pattern
1110           is  valid, and you want to skip this check for performance reasons, you
1111           can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1112           passing an invalid UTF-8 string as a pattern is undefined. It may cause
1113           your program to crash.  Note that this option can  also  be  passed  to
1114           pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1115           ing of subject strings.
1116    
1117    
1118    COMPILATION ERROR CODES
1119    
1120           The following table lists the error  codes  than  may  be  returned  by
1121           pcre_compile2(),  along with the error messages that may be returned by
1122           both compiling functions.
1123    
1124              0  no error
1125              1  \ at end of pattern
1126              2  \c at end of pattern
1127              3  unrecognized character follows \
1128              4  numbers out of order in {} quantifier
1129              5  number too big in {} quantifier
1130              6  missing terminating ] for character class
1131              7  invalid escape sequence in character class
1132              8  range out of order in character class
1133              9  nothing to repeat
1134             10  operand of unlimited repeat could match the empty string
1135             11  internal error: unexpected repeat
1136             12  unrecognized character after (?
1137             13  POSIX named classes are supported only within a class
1138             14  missing )
1139             15  reference to non-existent subpattern
1140             16  erroffset passed as NULL
1141             17  unknown option bit(s) set
1142             18  missing ) after comment
1143             19  parentheses nested too deeply
1144             20  regular expression too large
1145             21  failed to get memory
1146             22  unmatched parentheses
1147             23  internal error: code overflow
1148             24  unrecognized character after (?<
1149             25  lookbehind assertion is not fixed length
1150             26  malformed number or name after (?(
1151             27  conditional group contains more than two branches
1152             28  assertion expected after (?(
1153             29  (?R or (?digits must be followed by )
1154             30  unknown POSIX class name
1155             31  POSIX collating elements are not supported
1156             32  this version of PCRE is not compiled with PCRE_UTF8 support
1157             33  spare error
1158             34  character value in \x{...} sequence is too large
1159             35  invalid condition (?(0)
1160             36  \C not allowed in lookbehind assertion
1161             37  PCRE does not support \L, \l, \N, \U, or \u
1162             38  number after (?C is > 255
1163             39  closing ) for (?C expected
1164             40  recursive call could loop indefinitely
1165             41  unrecognized character after (?P
1166             42  syntax error after (?P
1167             43  two named subpatterns have the same name
1168             44  invalid UTF-8 string
1169             45  support for \P, \p, and \X has not been compiled
1170             46  malformed \P or \p sequence
1171             47  unknown property name after \P or \p
1172             48  subpattern name is too long (maximum 32 characters)
1173             49  too many named subpatterns (maximum 10,000)
1174             50  repeated subpattern is too long
1175             51  octal value is greater than \377 (not in UTF-8 mode)
1176    
1177    
1178  STUDYING A PATTERN  STUDYING A PATTERN
1179    
1180       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1181            const char **errptr);              const char **errptr);
1182    
1183       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
1184       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
1185       the time taken for matching. The function pcre_study() takes         matching. The function pcre_study() takes a pointer to a compiled  pat-
1186       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1187       studing the pattern  produces  additional  information  that         information that will help speed up matching,  pcre_study()  returns  a
1188       will  help speed up matching, pcre_study() returns a pointer         pointer  to a pcre_extra block, in which the study_data field points to
1189       to a pcre_extra block, in which the study_data field  points         the results of the study.
1190       to the results of the study.  
1191           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1192       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1193       directly  to pcre_exec(). However, the pcre_extra block also         that can be set by the caller before the block  is  passed;  these  are
1194       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
1195       the  block is passed; these are described below. If studying  
1196       the pattern does not  produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1197       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1198       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
1199       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
1200    
1201       The second argument contains option  bits.  At  present,  no         The second argument of pcre_study() contains option bits.  At  present,
1202       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1203       should always be zero.  
1204           The  third argument for pcre_study() is a pointer for an error message.
1205       The third argument for pcre_study()  is  a  pointer  for  an         If studying succeeds (even if no data is  returned),  the  variable  it
1206       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
1207       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
1208       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
1209       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1210       pcre_study(), to be sure that it has run successfully.  
1211           This is a typical call to pcre_study():
1212       This is a typical call to pcre_study():  
1213             pcre_extra *pe;
1214         pcre_extra *pe;           pe = pcre_study(
1215         pe = pcre_study(             re,             /* result of pcre_compile() */
1216           re,             /* result of pcre_compile() */             0,              /* no options exist */
1217           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1218           &error);        /* set to NULL or points to a message */  
1219           At present, studying a pattern is useful only for non-anchored patterns
1220       At present, studying a  pattern  is  useful  only  for  non-         that  do not have a single fixed starting character. A bitmap of possi-
1221       anchored  patterns  that do not have a single fixed starting         ble starting bytes is created.
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1222    
1223    
1224  LOCALE SUPPORT  LOCALE SUPPORT
1225    
1226       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1227       acters  are  letters, digits, or whatever, by reference to a         letters  digits,  or whatever, by reference to a set of tables, indexed
1228       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
1229       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
1230       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
1231       locale  when  PCRE  is compiled. This is used when the final         with  Unicode  character property support. The use of locales with Uni-
1232       argument of pcre_compile() is NULL, and  is  sufficient  for         code is discouraged.
1233       many applications.  
1234           An internal set of tables is created in the default C locale when  PCRE
1235       An alternative set of tables can, however, be supplied. Such         is  built.  This  is  used when the final argument of pcre_compile() is
1236       tables  are built by calling the pcre_maketables() function,         NULL, and is sufficient for many applications. An  alternative  set  of
1237       which has no arguments, in the relevant locale.  The  result         tables  can,  however, be supplied. These may be created in a different
1238       can  then be passed to pcre_compile() as often as necessary.         locale from the default. As more and more applications change to  using
1239       For example, to build and use tables  that  are  appropriate         Unicode, the need for this locale support is expected to die away.
1240       for  the French locale (where accented characters with codes  
1241       greater than 128 are treated as letters), the following code         External  tables  are  built by calling the pcre_maketables() function,
1242       could be used:         which has no arguments, in the relevant locale. The result can then  be
1243           passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1244         setlocale(LC_CTYPE, "fr");         example, to build and use tables that are appropriate  for  the  French
1245         tables = pcre_maketables();         locale  (where  accented  characters  with  values greater than 128 are
1246         re = pcre_compile(..., tables);         treated as letters), the following code could be used:
1247    
1248       The  tables  are  built  in  memory  that  is  obtained  via           setlocale(LC_CTYPE, "fr_FR");
1249       pcre_malloc.  The  pointer that is passed to pcre_compile is           tables = pcre_maketables();
1250       saved with the compiled pattern, and  the  same  tables  are           re = pcre_compile(..., tables);
1251       used via this pointer by pcre_study() and pcre_exec(). Thus,  
1252       for any single pattern, compilation, studying  and  matching         When pcre_maketables() runs, the tables are built  in  memory  that  is
1253       all happen in the same locale, but different patterns can be         obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1254       compiled in different locales. It is the caller's  responsi-         that the memory containing the tables remains available for as long  as
1255       bility  to  ensure  that  the  memory  containing the tables         it is needed.
1256       remains available for as long as it is needed.  
1257           The pointer that is passed to pcre_compile() is saved with the compiled
1258           pattern, and the same tables are used via this pointer by  pcre_study()
1259           and normally also by pcre_exec(). Thus, by default, for any single pat-
1260           tern, compilation, studying and matching all happen in the same locale,
1261           but different patterns can be compiled in different locales.
1262    
1263           It  is  possible to pass a table pointer or NULL (indicating the use of
1264           the internal tables) to pcre_exec(). Although  not  intended  for  this
1265           purpose,  this facility could be used to match a pattern in a different
1266           locale from the one in which it was compiled. Passing table pointers at
1267           run time is discussed below in the section on matching a pattern.
1268    
1269    
1270  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1271    
1272       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1273            int what, void *where);              int what, void *where);
1274    
1275       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1276       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1277       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1278       ity (and is documented below).  
1279           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1280       The first argument for pcre_fullinfo() is a pointer  to  the         pattern. The second argument is the result of pcre_study(), or NULL  if
1281       compiled  pattern.  The  second  argument  is  the result of         the  pattern  was not studied. The third argument specifies which piece
1282       pcre_study(), or NULL if the pattern was  not  studied.  The         of information is required, and the fourth argument is a pointer  to  a
1283       third  argument  specifies  which  piece  of  information is         variable  to  receive  the  data. The yield of the function is zero for
1284       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1285       to  receive  the data. The yield of the function is zero for  
1286       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1287                                   the argument where was NULL
1288         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1289                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1290         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1291         PCRE_ERROR_BADOPTION  the value of what was invalid         The "magic number" is placed at the start of each compiled  pattern  as
1292           an  simple check against passing an arbitrary memory pointer. Here is a
1293       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1294       length of the compiled pattern:         pattern:
1295    
1296         int rc;           int rc;
1297         unsigned long int length;           size_t length;
1298         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1299           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1300           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1301           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1302           &length);         /* where to put the data */             &length);         /* where to put the data */
1303    
1304       The possible values for the third argument  are  defined  in         The  possible  values for the third argument are defined in pcre.h, and
1305       pcre.h, and are as follows:         are as follows:
1306    
1307         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1308    
1309       Return the number of the highest back reference in the  pat-         Return the number of the highest back reference  in  the  pattern.  The
1310       tern.  The  fourth argument should point to an int variable.         fourth  argument  should  point to an int variable. Zero is returned if
1311       Zero is returned if there are no back references.         there are no back references.
1312    
1313         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1314    
1315       Return the number of capturing subpatterns in  the  pattern.         Return the number of capturing subpatterns in the pattern.  The  fourth
1316       The fourth argument should point to an int variable.         argument should point to an int variable.
1317    
1318         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1319    
1320       Return information about  the  first  byte  of  any  matched         Return  a pointer to the internal default character tables within PCRE.
1321       string,  for a non-anchored pattern. (This option used to be         The fourth argument should point to an unsigned char *  variable.  This
1322       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1323       for backwards compatibility.)         tion. External callers can cause PCRE to use  its  internal  tables  by
1324           passing a NULL table pointer.
1325       If there is a fixed first byte, e.g. from a pattern such  as  
1326       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1327       by where. Otherwise, if either  
1328           Return  information  about  the first byte of any matched string, for a
1329       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored pattern. The fourth argument should point to an int  vari-
1330       and every branch starts with "^", or         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1331           is still recognized for backwards compatibility.)
1332       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1333       PCRE_DOTALL is not set (if it were set, the pattern would be         If there is a fixed first byte, for example, from  a  pattern  such  as
1334       anchored),         (cat|cow|coyote). Otherwise, if either
1335    
1336       -1 is returned, indicating that the pattern matches only  at         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1337       the  start  of  a subject string or after any newline within         branch starts with "^", or
1338       the string. Otherwise -2 is returned. For anchored patterns,  
1339       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1340           set (if it were set, the pattern would be anchored),
1341         PCRE_INFO_FIRSTTABLE  
1342           -1  is  returned, indicating that the pattern matches only at the start
1343       If the pattern was studied, and this resulted  in  the  con-         of a subject string or after any newline within the  string.  Otherwise
1344       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1345       for the first byte in any matching string, a pointer to  the  
1346       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1347       argument should point to an unsigned char * variable.  
1348           If  the pattern was studied, and this resulted in the construction of a
1349         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1350           matching  string, a pointer to the table is returned. Otherwise NULL is
1351       Return the value of the rightmost  literal  byte  that  must         returned. The fourth argument should point to an unsigned char *  vari-
1352       exist  in  any  matched  string, other than at its start, if         able.
1353       such a byte has been recorded. The  fourth  argument  should  
1354       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_LASTLITERAL
1355       returned. For anchored patterns,  a  last  literal  byte  is  
1356       recorded  only  if  it follows something of variable length.         Return  the  value of the rightmost literal byte that must exist in any
1357       For example, for the pattern /^a\d+z\d+/ the returned  value         matched string, other than at its  start,  if  such  a  byte  has  been
1358       is "z", but for /^a\dz\d/ the returned value is -1.         recorded. The fourth argument should point to an int variable. If there
1359           is no such byte, -1 is returned. For anchored patterns, a last  literal
1360         PCRE_INFO_NAMECOUNT         byte  is  recorded only if it follows something of variable length. For
1361         PCRE_INFO_NAMEENTRYSIZE         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1362         PCRE_INFO_NAMETABLE         /^a\dz\d/ the returned value is -1.
1363    
1364       PCRE supports the use of named as well as numbered capturing           PCRE_INFO_NAMECOUNT
1365       parentheses. The names are just an additional way of identi-           PCRE_INFO_NAMEENTRYSIZE
1366       fying the parentheses,  which  still  acquire  a  number.  A           PCRE_INFO_NAMETABLE
1367       caller  that  wants  to extract data from a named subpattern  
1368       must convert the name to a number in  order  to  access  the         PCRE  supports the use of named as well as numbered capturing parenthe-
1369       correct  pointers  in  the  output  vector  (described  with         ses. The names are just an additional way of identifying the  parenthe-
1370       pcre_exec() below). In order to do this, it must  first  use         ses, which still acquire numbers. Several convenience functions such as
1371       these  three  values  to  obtain  the name-to-number mapping         pcre_get_named_substring() are provided for  extracting  captured  sub-
1372       table for the pattern.         strings  by  name. It is also possible to extract the data directly, by
1373           first converting the name to a number in order to  access  the  correct
1374       The  map  consists  of  a  number  of  fixed-size   entries.         pointers in the output vector (described with pcre_exec() below). To do
1375       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         the conversion, you need  to  use  the  name-to-number  map,  which  is
1376       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both         described by these three values.
1377       of  these return an int value. The entry size depends on the  
1378       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1379       pointer to the first entry of the table (a pointer to char).         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1380       The first two bytes of each entry are the number of the cap-         of  each  entry;  both  of  these  return  an int value. The entry size
1381       turing parenthesis, most significant byte first. The rest of         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1382       the entry is the corresponding name,  zero  terminated.  The         a  pointer  to  the  first  entry of the table (a pointer to char). The
1383       names  are  in alphabetical order. For example, consider the         first two bytes of each entry are the number of the capturing parenthe-
1384       following pattern (assume PCRE_EXTENDED  is  set,  so  white         sis,  most  significant byte first. The rest of the entry is the corre-
1385       space - including newlines - is ignored):         sponding name, zero terminated. The names are  in  alphabetical  order.
1386           When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1387         (?P<date> (?P<year>(\d\d)?\d\d) -         theses numbers. For example, consider  the  following  pattern  (assume
1388         (?P<month>\d\d) - (?P<day>\d\d) )         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1389           ignored):
1390       There are four named subpatterns,  so  the  table  has  four  
1391       entries,  and  each  entry in the table is eight bytes long.           (?P<date> (?P<year>(\d\d)?\d\d) -
1392       The table is as follows, with non-printing  bytes  shows  in           (?P<month>\d\d) - (?P<day>\d\d) )
1393       hex, and undefined bytes shown as ??:  
1394           There are four named subpatterns, so the table has  four  entries,  and
1395         00 01 d  a  t  e  00 ??         each  entry  in the table is eight bytes long. The table is as follows,
1396         00 05 d  a  y  00 ?? ??         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1397         00 04 m  o  n  t  h  00         as ??:
1398         00 02 y  e  a  r  00 ??  
1399             00 01 d  a  t  e  00 ??
1400       When writing code to extract data  from  named  subpatterns,           00 05 d  a  y  00 ?? ??
1401       remember  that the length of each entry may be different for           00 04 m  o  n  t  h  00
1402       each compiled pattern.           00 02 y  e  a  r  00 ??
1403    
1404         PCRE_INFO_OPTIONS         When  writing  code  to  extract  data from named subpatterns using the
1405           name-to-number map, remember that the length of the entries  is  likely
1406       Return a copy of the options with which the pattern was com-         to be different for each compiled pattern.
1407       piled.  The fourth argument should point to an unsigned long  
1408       int variable. These option bits are those specified  in  the           PCRE_INFO_OPTIONS
1409       call  to  pcre_compile(),  modified  by any top-level option  
1410       settings within the pattern itself.         Return  a  copy of the options with which the pattern was compiled. The
1411           fourth argument should point to an unsigned long  int  variable.  These
1412       A pattern is automatically anchored by PCRE if  all  of  its         option bits are those specified in the call to pcre_compile(), modified
1413       top-level alternatives begin with one of the following:         by any top-level option settings within the pattern itself.
1414    
1415         ^     unless PCRE_MULTILINE is set         A pattern is automatically anchored by PCRE if  all  of  its  top-level
1416         \A    always         alternatives begin with one of the following:
1417         \G    always  
1418         .*    if PCRE_DOTALL is set and there are no back           ^     unless PCRE_MULTILINE is set
1419                 references to the subpattern in which .* appears           \A    always
1420             \G    always
1421       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the           .*    if PCRE_DOTALL is set and there are no back
1422       options returned by pcre_fullinfo().                   references to the subpattern in which .* appears
1423    
1424         PCRE_INFO_SIZE         For such patterns, the PCRE_ANCHORED bit is set in the options returned
1425           by pcre_fullinfo().
1426       Return the size of the compiled pattern, that is, the  value  
1427       that  was  passed as the argument to pcre_malloc() when PCRE           PCRE_INFO_SIZE
1428       was getting memory in which to place the compiled data.  The  
1429       fourth argument should point to a size_t variable.         Return the size of the compiled pattern, that is, the  value  that  was
1430           passed as the argument to pcre_malloc() when PCRE was getting memory in
1431         PCRE_INFO_STUDYSIZE         which to place the compiled data. The fourth argument should point to a
1432           size_t variable.
1433       Returns the size  of  the  data  block  pointed  to  by  the  
1434       study_data  field  in a pcre_extra block. That is, it is the           PCRE_INFO_STUDYSIZE
1435       value that was passed to pcre_malloc() when PCRE was getting  
1436       memory into which to place the data created by pcre_study().         Return the size of the data block pointed to by the study_data field in
1437       The fourth argument should point to a size_t variable.         a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1438           pcre_malloc() when PCRE was getting memory into which to place the data
1439           created by pcre_study(). The fourth argument should point to  a  size_t
1440           variable.
1441    
1442    
1443  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1444    
1445       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1446    
1447       The pcre_info() function is now obsolete because its  inter-         The  pcre_info()  function is now obsolete because its interface is too
1448       face  is  too  restrictive  to return all the available data         restrictive to return all the available data about a compiled  pattern.
1449       about  a  compiled  pattern.   New   programs   should   use         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1450       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1451       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1452       negative numbers:  
1453             PCRE_ERROR_NULL       the argument code was NULL
1454         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1455         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1456           If  the  optptr  argument is not NULL, a copy of the options with which
1457       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
1458       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1459       it points to (see PCRE_INFO_OPTIONS above).  
1460           If  the  pattern  is  not anchored and the firstcharptr argument is not
1461       If the pattern is not anchored and the firstcharptr argument         NULL, it is used to pass back information about the first character  of
1462       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1463       first    character    of    any    matched    string    (see  
1464       PCRE_INFO_FIRSTBYTE above).  
1465    REFERENCE COUNTS
1466    
1467           int pcre_refcount(pcre *code, int adjust);
1468    
1469           The  pcre_refcount()  function is used to maintain a reference count in
1470           the data block that contains a compiled pattern. It is provided for the
1471           benefit  of  applications  that  operate  in an object-oriented manner,
1472           where different parts of the application may be using the same compiled
1473           pattern, but you want to free the block when they are all done.
1474    
1475           When a pattern is compiled, the reference count field is initialized to
1476           zero.  It is changed only by calling this function, whose action is  to
1477           add  the  adjust  value  (which may be positive or negative) to it. The
1478           yield of the function is the new value. However, the value of the count
1479           is  constrained to lie between 0 and 65535, inclusive. If the new value
1480           is outside these limits, it is forced to the appropriate limit value.
1481    
1482           Except when it is zero, the reference count is not correctly  preserved
1483           if  a  pattern  is  compiled on one host and then transferred to a host
1484           whose byte-order is different. (This seems a highly unlikely scenario.)
1485    
1486    
1487    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1488    
1489           int pcre_exec(const pcre *code, const pcre_extra *extra,
1490                const char *subject, int length, int startoffset,
1491                int options, int *ovector, int ovecsize);
1492    
1493           The  function pcre_exec() is called to match a subject string against a
1494           compiled pattern, which is passed in the code argument. If the  pattern
1495           has been studied, the result of the study should be passed in the extra
1496           argument. This function is the main matching facility of  the  library,
1497           and it operates in a Perl-like manner. For specialist use there is also
1498           an alternative matching function, which is described below in the  sec-
1499           tion about the pcre_dfa_exec() function.
1500    
1501           In  most applications, the pattern will have been compiled (and option-
1502           ally studied) in the same process that calls pcre_exec().  However,  it
1503           is possible to save compiled patterns and study data, and then use them
1504           later in different processes, possibly even on different hosts.  For  a
1505           discussion about this, see the pcreprecompile documentation.
1506    
1507           Here is an example of a simple call to pcre_exec():
1508    
1509             int rc;
1510             int ovector[30];
1511             rc = pcre_exec(
1512               re,             /* result of pcre_compile() */
1513               NULL,           /* we didn't study the pattern */
1514               "some string",  /* the subject string */
1515               11,             /* the length of the subject string */
1516               0,              /* start at offset 0 in the subject */
1517               0,              /* default options */
1518               ovector,        /* vector of integers for substring information */
1519               30);            /* number of elements (NOT size in bytes) */
1520    
1521       Extra data for pcre_exec()
1522    
1523           If  the  extra argument is not NULL, it must point to a pcre_extra data
1524           block. The pcre_study() function returns such a block (when it  doesn't
1525           return  NULL), but you can also create one for yourself, and pass addi-
1526           tional information in it. The pcre_extra block contains  the  following
1527           fields (not necessarily in this order):
1528    
1529             unsigned long int flags;
1530             void *study_data;
1531             unsigned long int match_limit;
1532             unsigned long int match_limit_recursion;
1533             void *callout_data;
1534             const unsigned char *tables;
1535    
1536           The  flags  field  is a bitmap that specifies which of the other fields
1537           are set. The flag bits are:
1538    
1539             PCRE_EXTRA_STUDY_DATA
1540             PCRE_EXTRA_MATCH_LIMIT
1541             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1542             PCRE_EXTRA_CALLOUT_DATA
1543             PCRE_EXTRA_TABLES
1544    
1545           Other flag bits should be set to zero. The study_data field is  set  in
1546           the  pcre_extra  block  that is returned by pcre_study(), together with
1547           the appropriate flag bit. You should not set this yourself, but you may
1548           add  to  the  block by setting the other fields and their corresponding
1549           flag bits.
1550    
1551           The match_limit field provides a means of preventing PCRE from using up
1552           a  vast amount of resources when running patterns that are not going to
1553           match, but which have a very large number  of  possibilities  in  their
1554           search  trees.  The  classic  example  is  the  use of nested unlimited
1555           repeats.
1556    
1557           Internally, PCRE uses a function called match() which it calls  repeat-
1558           edly  (sometimes  recursively). The limit set by match_limit is imposed
1559           on the number of times this function is called during  a  match,  which
1560           has  the  effect  of  limiting the amount of backtracking that can take
1561           place. For patterns that are not anchored, the count restarts from zero
1562           for each position in the subject string.
1563    
1564           The  default  value  for  the  limit can be set when PCRE is built; the
1565           default default is 10 million, which handles all but the  most  extreme
1566           cases.  You  can  override  the  default by suppling pcre_exec() with a
1567           pcre_extra    block    in    which    match_limit    is    set,     and
1568           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1569           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1570    
1571           The match_limit_recursion field is similar to match_limit, but  instead
1572           of limiting the total number of times that match() is called, it limits
1573           the depth of recursion. The recursion depth is a  smaller  number  than
1574           the  total number of calls, because not all calls to match() are recur-
1575           sive.  This limit is of use only if it is set smaller than match_limit.
1576    
1577           Limiting  the  recursion  depth  limits the amount of stack that can be
1578           used, or, when PCRE has been compiled to use memory on the heap instead
1579           of the stack, the amount of heap memory that can be used.
1580    
1581           The  default  value  for  match_limit_recursion can be set when PCRE is
1582           built; the default default  is  the  same  value  as  the  default  for
1583           match_limit.  You can override the default by suppling pcre_exec() with
1584           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1585           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1586           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1587    
1588           The pcre_callout field is used in conjunction with the  "callout"  fea-
1589           ture, which is described in the pcrecallout documentation.
1590    
1591           The  tables  field  is  used  to  pass  a  character  tables pointer to
1592           pcre_exec(); this overrides the value that is stored with the  compiled
1593           pattern.  A  non-NULL value is stored with the compiled pattern only if
1594           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1595           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1596           PCRE's internal tables to be used. This facility is  helpful  when  re-
1597           using  patterns  that  have been saved after compiling with an external
1598           set of tables, because the external tables  might  be  at  a  different
1599           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1600           tion for a discussion of saving compiled patterns for later use.
1601    
1602       Option bits for pcre_exec()
1603    
1604           The unused bits of the options argument for pcre_exec() must  be  zero.
1605           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1606           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1607           PCRE_PARTIAL.
1608    
1609             PCRE_ANCHORED
1610    
1611           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1612           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1613           turned  out to be anchored by virtue of its contents, it cannot be made
1614           unachored at matching time.
1615    
1616             PCRE_NEWLINE_CR
1617             PCRE_NEWLINE_LF
1618             PCRE_NEWLINE_CRLF
1619    
1620           These options override  the  newline  definition  that  was  chosen  or
1621           defaulted  when the pattern was compiled. For details, see the descrip-
1622           tion pcre_compile() above. During matching, the newline choice  affects
1623           the behaviour of the dot, circumflex, and dollar metacharacters.
1624    
1625             PCRE_NOTBOL
1626    
1627           This option specifies that first character of the subject string is not
1628           the beginning of a line, so the  circumflex  metacharacter  should  not
1629           match  before it. Setting this without PCRE_MULTILINE (at compile time)
1630           causes circumflex never to match. This option affects only  the  behav-
1631           iour of the circumflex metacharacter. It does not affect \A.
1632    
1633             PCRE_NOTEOL
1634    
1635           This option specifies that the end of the subject string is not the end
1636           of a line, so the dollar metacharacter should not match it nor  (except
1637           in  multiline mode) a newline immediately before it. Setting this with-
1638           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1639           option  affects only the behaviour of the dollar metacharacter. It does
1640           not affect \Z or \z.
1641    
1642             PCRE_NOTEMPTY
1643    
1644           An empty string is not considered to be a valid match if this option is
1645           set.  If  there are alternatives in the pattern, they are tried. If all
1646           the alternatives match the empty string, the entire  match  fails.  For
1647           example, if the pattern
1648    
1649             a?b?
1650    
1651           is  applied  to  a string not beginning with "a" or "b", it matches the
1652           empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1653           match is not valid, so PCRE searches further into the string for occur-
1654           rences of "a" or "b".
1655    
1656           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1657           cial  case  of  a  pattern match of the empty string within its split()
1658           function, and when using the /g modifier. It  is  possible  to  emulate
1659           Perl's behaviour after matching a null string by first trying the match
1660           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1661           if  that  fails by advancing the starting offset (see below) and trying
1662           an ordinary match again. There is some code that demonstrates how to do
1663           this in the pcredemo.c sample program.
1664    
1665             PCRE_NO_UTF8_CHECK
1666    
1667           When PCRE_UTF8 is set at compile time, the validity of the subject as a
1668           UTF-8 string is automatically checked when pcre_exec() is  subsequently
1669           called.   The  value  of  startoffset is also checked to ensure that it
1670           points to the start of a UTF-8 character. If an invalid UTF-8  sequence
1671           of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1672           startoffset contains an  invalid  value,  PCRE_ERROR_BADUTF8_OFFSET  is
1673           returned.
1674    
1675           If  you  already  know that your subject is valid, and you want to skip
1676           these   checks   for   performance   reasons,   you   can    set    the
1677           PCRE_NO_UTF8_CHECK  option  when calling pcre_exec(). You might want to
1678           do this for the second and subsequent calls to pcre_exec() if  you  are
1679           making  repeated  calls  to  find  all  the matches in a single subject
1680           string. However, you should be  sure  that  the  value  of  startoffset
1681           points  to  the  start of a UTF-8 character. When PCRE_NO_UTF8_CHECK is
1682           set, the effect of passing an invalid UTF-8 string as a subject,  or  a
1683           value  of startoffset that does not point to the start of a UTF-8 char-
1684           acter, is undefined. Your program may crash.
1685    
1686             PCRE_PARTIAL
1687    
1688           This option turns on the  partial  matching  feature.  If  the  subject
1689           string  fails to match the pattern, but at some point during the match-
1690           ing process the end of the subject was reached (that  is,  the  subject
1691           partially  matches  the  pattern and the failure to match occurred only
1692           because there were not enough subject characters), pcre_exec()  returns
1693           PCRE_ERROR_PARTIAL  instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is
1694           used, there are restrictions on what may appear in the  pattern.  These
1695           are discussed in the pcrepartial documentation.
1696    
1697       The string to be matched by pcre_exec()
1698    
1699           The  subject string is passed to pcre_exec() as a pointer in subject, a
1700           length in length, and a starting byte offset in startoffset.  In  UTF-8
1701           mode,  the  byte  offset  must point to the start of a UTF-8 character.
1702           Unlike the pattern string, the subject may contain binary  zero  bytes.
1703           When  the starting offset is zero, the search for a match starts at the
1704           beginning of the subject, and this is by far the most common case.
1705    
1706           A non-zero starting offset is useful when searching for  another  match
1707           in  the same subject by calling pcre_exec() again after a previous suc-
1708           cess.  Setting startoffset differs from just passing over  a  shortened
1709           string  and  setting  PCRE_NOTBOL  in the case of a pattern that begins
1710           with any kind of lookbehind. For example, consider the pattern
1711    
1712             \Biss\B
1713    
1714           which finds occurrences of "iss" in the middle of  words.  (\B  matches
1715           only  if  the  current position in the subject is not a word boundary.)
1716           When applied to the string "Mississipi" the first call  to  pcre_exec()
1717           finds  the  first  occurrence. If pcre_exec() is called again with just
1718           the remainder of the subject,  namely  "issipi",  it  does  not  match,
1719           because \B is always false at the start of the subject, which is deemed
1720           to be a word boundary. However, if pcre_exec()  is  passed  the  entire
1721           string again, but with startoffset set to 4, it finds the second occur-
1722           rence of "iss" because it is able to look behind the starting point  to
1723           discover that it is preceded by a letter.
1724    
1725           If  a  non-zero starting offset is passed when the pattern is anchored,
1726           one attempt to match at the given offset is made. This can only succeed
1727           if  the  pattern  does  not require the match to be at the start of the
1728           subject.
1729    
1730       How pcre_exec() returns captured substrings
1731    
1732           In general, a pattern matches a certain portion of the subject, and  in
1733           addition,  further  substrings  from  the  subject may be picked out by
1734           parts of the pattern. Following the usage  in  Jeffrey  Friedl's  book,
1735           this  is  called "capturing" in what follows, and the phrase "capturing
1736           subpattern" is used for a fragment of a pattern that picks out  a  sub-
1737           string.  PCRE  supports several other kinds of parenthesized subpattern
1738           that do not cause substrings to be captured.
1739    
1740           Captured substrings are returned to the caller via a vector of  integer
1741           offsets  whose  address is passed in ovector. The number of elements in
1742           the vector is passed in ovecsize, which must be a non-negative  number.
1743           Note: this argument is NOT the size of ovector in bytes.
1744    
1745           The  first  two-thirds of the vector is used to pass back captured sub-
1746           strings, each substring using a pair of integers. The  remaining  third
1747           of  the  vector is used as workspace by pcre_exec() while matching cap-
1748           turing subpatterns, and is not available for passing back  information.
1749           The  length passed in ovecsize should always be a multiple of three. If
1750           it is not, it is rounded down.
1751    
1752           When a match is successful, information about  captured  substrings  is
1753           returned  in  pairs  of integers, starting at the beginning of ovector,
1754           and continuing up to two-thirds of its length at the  most.  The  first
1755           element of a pair is set to the offset of the first character in a sub-
1756           string, and the second is set to the  offset  of  the  first  character
1757           after  the  end  of  a  substring. The first pair, ovector[0] and ovec-
1758           tor[1], identify the portion of  the  subject  string  matched  by  the
1759           entire  pattern.  The next pair is used for the first capturing subpat-
1760           tern, and so on. The value returned by pcre_exec() is one more than the
1761           highest numbered pair that has been set. For example, if two substrings
1762           have been captured, the returned value is 3. If there are no  capturing
1763           subpatterns,  the return value from a successful match is 1, indicating
1764           that just the first pair of offsets has been set.
1765    
1766           If a capturing subpattern is matched repeatedly, it is the last portion
1767           of the string that it matched that is returned.
1768    
1769           If  the vector is too small to hold all the captured substring offsets,
1770           it is used as far as possible (up to two-thirds of its length), and the
1771           function  returns a value of zero. In particular, if the substring off-
1772           sets are not of interest, pcre_exec() may be called with ovector passed
1773           as  NULL  and  ovecsize  as zero. However, if the pattern contains back
1774           references and the ovector is not big enough to  remember  the  related
1775           substrings,  PCRE has to get additional memory for use during matching.
1776           Thus it is usually advisable to supply an ovector.
1777    
1778           The pcre_info() function can be used to find  out  how  many  capturing
1779           subpatterns  there  are  in  a  compiled pattern. The smallest size for
1780           ovector that will allow for n captured substrings, in addition  to  the
1781           offsets of the substring matched by the whole pattern, is (n+1)*3.
1782    
1783           It  is  possible for capturing subpattern number n+1 to match some part
1784           of the subject when subpattern n has not been used at all. For example,
1785           if  the  string  "abc"  is  matched against the pattern (a|(z))(bc) the
1786           return from the function is 4, and subpatterns 1 and 3 are matched, but
1787           2  is  not.  When  this happens, both values in the offset pairs corre-
1788           sponding to unused subpatterns are set to -1.
1789    
1790           Offset values that correspond to unused subpatterns at the end  of  the
1791           expression  are  also  set  to  -1. For example, if the string "abc" is
1792           matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are  not
1793           matched.  The  return  from the function is 2, because the highest used
1794           capturing subpattern number is 1. However, you can refer to the offsets
1795           for  the  second  and third capturing subpatterns if you wish (assuming
1796           the vector is large enough, of course).
1797    
1798           Some convenience functions are provided  for  extracting  the  captured
1799           substrings as separate strings. These are described below.
1800    
1801       Error return values from pcre_exec()
1802    
1803           If  pcre_exec()  fails, it returns a negative number. The following are
1804           defined in the header file:
1805    
1806             PCRE_ERROR_NOMATCH        (-1)
1807    
1808           The subject string did not match the pattern.
1809    
1810             PCRE_ERROR_NULL           (-2)
1811    
1812           Either code or subject was passed as NULL,  or  ovector  was  NULL  and
1813           ovecsize was not zero.
1814    
1815             PCRE_ERROR_BADOPTION      (-3)
1816    
1817           An unrecognized bit was set in the options argument.
1818    
1819             PCRE_ERROR_BADMAGIC       (-4)
1820    
1821           PCRE  stores a 4-byte "magic number" at the start of the compiled code,
1822           to catch the case when it is passed a junk pointer and to detect when a
1823           pattern that was compiled in an environment of one endianness is run in
1824           an environment with the other endianness. This is the error  that  PCRE
1825           gives when the magic number is not present.
1826    
1827             PCRE_ERROR_UNKNOWN_NODE   (-5)
1828    
1829           While running the pattern match, an unknown item was encountered in the
1830           compiled pattern. This error could be caused by a bug  in  PCRE  or  by
1831           overwriting of the compiled pattern.
1832    
1833             PCRE_ERROR_NOMEMORY       (-6)
1834    
1835           If  a  pattern contains back references, but the ovector that is passed
1836           to pcre_exec() is not big enough to remember the referenced substrings,
1837           PCRE  gets  a  block of memory at the start of matching to use for this
1838           purpose. If the call via pcre_malloc() fails, this error is given.  The
1839           memory is automatically freed at the end of matching.
1840    
1841             PCRE_ERROR_NOSUBSTRING    (-7)
1842    
1843           This  error is used by the pcre_copy_substring(), pcre_get_substring(),
1844           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
1845           returned by pcre_exec().
1846    
1847             PCRE_ERROR_MATCHLIMIT     (-8)
1848    
1849           The  backtracking  limit,  as  specified  by the match_limit field in a
1850           pcre_extra structure (or defaulted) was reached.  See  the  description
1851           above.
1852    
1853             PCRE_ERROR_RECURSIONLIMIT (-21)
1854    
1855           The internal recursion limit, as specified by the match_limit_recursion
1856           field in a pcre_extra structure (or defaulted)  was  reached.  See  the
1857           description above.
1858    
1859             PCRE_ERROR_CALLOUT        (-9)
1860    
1861           This error is never generated by pcre_exec() itself. It is provided for
1862           use by callout functions that want to yield a distinctive  error  code.
1863           See the pcrecallout documentation for details.
1864    
1865             PCRE_ERROR_BADUTF8        (-10)
1866    
1867           A  string  that contains an invalid UTF-8 byte sequence was passed as a
1868           subject.
1869    
1870             PCRE_ERROR_BADUTF8_OFFSET (-11)
1871    
1872           The UTF-8 byte sequence that was passed as a subject was valid, but the
1873           value  of startoffset did not point to the beginning of a UTF-8 charac-
1874           ter.
1875    
1876             PCRE_ERROR_PARTIAL        (-12)
1877    
1878           The subject string did not match, but it did match partially.  See  the
1879           pcrepartial documentation for details of partial matching.
1880    
1881             PCRE_ERROR_BADPARTIAL     (-13)
1882    
1883           The  PCRE_PARTIAL  option  was  used with a compiled pattern containing
1884           items that are not supported for partial matching. See the  pcrepartial
1885           documentation for details of partial matching.
1886    
1887             PCRE_ERROR_INTERNAL       (-14)
1888    
1889  MATCHING A PATTERN         An  unexpected  internal error has occurred. This error could be caused
1890           by a bug in PCRE or by overwriting of the compiled pattern.
1891    
1892             PCRE_ERROR_BADCOUNT       (-15)
1893    
1894       int pcre_exec(const pcre *code, const pcre_extra *extra,         This error is given if the value of the ovecsize argument is  negative.
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
   
      The function pcre_exec() is called to match a subject string  
      against  a pre-compiled pattern, which is passed in the code  
      argument. If the pattern has been studied, the result of the  
      study should be passed in the extra argument.  
   
      Here is an example of a simple call to pcre_exec():  
   
        int rc;  
        int ovector[30];  
        rc = pcre_exec(  
          re,             /* result of pcre_compile() */  
          NULL,           /* we didn't study the pattern */  
          "some string",  /* the subject string */  
          11,             /* the length of the subject string */  
          0,              /* start at offset 0 in the subject */  
          0,              /* default options */  
          ovector,        /* vector for substring information */  
          30);            /* number of elements in the vector */  
   
      If the extra argument is  not  NULL,  it  must  point  to  a  
      pcre_extra  data  block.  The  pcre_study() function returns  
      such a block (when it doesn't return NULL), but you can also  
      create  one for yourself, and pass additional information in  
      it. The fields in the block are as follows:  
   
        unsigned long int flags;  
        void *study_data;  
        unsigned long int match_limit;  
        void *callout_data;  
   
      The flags field is a bitmap  that  specifies  which  of  the  
      other fields are set. The flag bits are:  
   
        PCRE_EXTRA_STUDY_DATA  
        PCRE_EXTRA_MATCH_LIMIT  
        PCRE_EXTRA_CALLOUT_DATA  
   
      Other flag bits should be set to zero. The study_data  field  
      is   set  in  the  pcre_extra  block  that  is  returned  by  
      pcre_study(), together with the appropriate  flag  bit.  You  
      should  not  set this yourself, but you can add to the block  
      by setting the other fields.  
   
      The match_limit field provides a means  of  preventing  PCRE  
      from  using  up a vast amount of resources when running pat-  
      terns that are not going to match, but  which  have  a  very  
      large  number  of  possibilities  in their search trees. The  
      classic example is the  use  of  nested  unlimited  repeats.  
      Internally,  PCRE  uses  a  function called match() which it  
      calls  repeatedly  (sometimes  recursively).  The  limit  is  
      imposed  on the number of times this function is called dur-  
      ing a match, which has the effect of limiting the amount  of  
      recursion and backtracking that can take place. For patterns  
      that are not anchored, the count starts from zero  for  each  
      position in the subject string.  
   
      The default limit for the library can be set  when  PCRE  is  
      built;  the default default is 10 million, which handles all  
      but the most extreme cases. You can reduce  the  default  by  
      suppling  pcre_exec()  with  a  pcre_extra  block  in  which  
      match_limit   is   set   to    a    smaller    value,    and  
      PCRE_EXTRA_MATCH_LIMIT  is  set  in  the flags field. If the  
      limit      is      exceeded,       pcre_exec()       returns  
      PCRE_ERROR_MATCHLIMIT.  
   
      The pcre_callout field is used in conjunction with the "cal-  
      lout"  feature,  which is described in the pcrecallout docu-  
      mentation.  
   
      The PCRE_ANCHORED option can be passed in the options  argu-  
      ment,   whose   unused   bits  must  be  zero.  This  limits  
      pcre_exec() to matching at the first matching position. How-  
      ever,  if  a  pattern  was  compiled  with PCRE_ANCHORED, or  
      turned out to be anchored by virtue of its contents, it can-  
      not be made unachored at matching time.  
   
      There are also three further options that can be set only at  
      matching time:  
   
        PCRE_NOTBOL  
   
      The first character of the string is not the beginning of  a  
      line,  so  the  circumflex  metacharacter  should  not match  
      before it. Setting this without PCRE_MULTILINE  (at  compile  
      time) causes circumflex never to match.  
   
        PCRE_NOTEOL  
   
      The end of the string is not the end of a line, so the  dol-  
      lar  metacharacter should not match it nor (except in multi-  
      line mode) a newline immediately  before  it.  Setting  this  
      without PCRE_MULTILINE (at compile time) causes dollar never  
      to match.  
   
        PCRE_NOTEMPTY  
   
      An empty string is not considered to be  a  valid  match  if  
      this  option  is  set. If there are alternatives in the pat-  
      tern, they are tried. If  all  the  alternatives  match  the  
      empty  string,  the  entire match fails. For example, if the  
      pattern  
   
        a?b?  
   
      is applied to a string not beginning with  "a"  or  "b",  it  
      matches  the  empty string at the start of the subject. With  
      PCRE_NOTEMPTY set, this match is not valid, so PCRE searches  
      further into the string for occurrences of "a" or "b".  
   
      Perl has no direct equivalent of PCRE_NOTEMPTY, but it  does  
      make  a  special case of a pattern match of the empty string  
      within its split() function, and when using the /g modifier.  
      It  is possible to emulate Perl's behaviour after matching a  
      null string by first trying the  match  again  at  the  same  
      offset  with  PCRE_NOTEMPTY  set,  and then if that fails by  
      advancing the starting offset  (see  below)  and  trying  an  
      ordinary match again.  
   
      The subject string is passed to pcre_exec() as a pointer  in  
      subject,  a length in length, and a starting offset in star-  
      toffset. Unlike the pattern string, the subject may  contain  
      binary  zero  bytes.  When  the starting offset is zero, the  
      search for a match starts at the beginning of  the  subject,  
      and this is by far the most common case.  
   
      If the pattern was compiled with the PCRE_UTF8  option,  the  
      subject  must  be  a sequence of bytes that is a valid UTF-8  
      string.  If  an  invalid  UTF-8  string  is  passed,  PCRE's  
      behaviour is not defined.  
   
      A non-zero starting offset  is  useful  when  searching  for  
      another  match  in  the  same subject by calling pcre_exec()  
      again after a previous success.  Setting startoffset differs  
      from  just  passing  over  a  shortened  string  and setting  
      PCRE_NOTBOL in the case of a pattern that  begins  with  any  
      kind of lookbehind. For example, consider the pattern  
   
        \Biss\B  
   
      which finds occurrences of "iss" in the middle of words. (\B  
      matches only if the current position in the subject is not a  
      word boundary.) When applied to the string "Mississipi"  the  
      first  call  to  pcre_exec()  finds the first occurrence. If  
      pcre_exec() is called again with just the remainder  of  the  
      subject,  namely  "issipi", it does not match, because \B is  
      always false at the start of the subject, which is deemed to  
      be  a  word  boundary. However, if pcre_exec() is passed the  
      entire string again, but with startoffset set to 4, it finds  
      the  second  occurrence  of "iss" because it is able to look  
      behind the starting point to discover that it is preceded by  
      a letter.  
   
      If a non-zero starting offset is passed when the pattern  is  
      anchored, one attempt to match at the given offset is tried.  
      This can only succeed if the pattern does  not  require  the  
      match to be at the start of the subject.  
   
      In general, a pattern matches a certain portion of the  sub-  
      ject,  and  in addition, further substrings from the subject  
      may be picked out by parts of  the  pattern.  Following  the  
      usage  in  Jeffrey Friedl's book, this is called "capturing"  
      in what follows, and the phrase  "capturing  subpattern"  is  
      used for a fragment of a pattern that picks out a substring.  
      PCRE supports several other kinds of  parenthesized  subpat-  
      tern that do not cause substrings to be captured.  
   
      Captured substrings are returned to the caller via a  vector  
      of  integer  offsets whose address is passed in ovector. The  
      number of elements in the vector is passed in ovecsize.  The  
      first two-thirds of the vector is used to pass back captured  
      substrings, each substring using a  pair  of  integers.  The  
      remaining  third  of  the  vector  is  used  as workspace by  
      pcre_exec() while matching capturing subpatterns, and is not  
      available for passing back information. The length passed in  
      ovecsize should always be a multiple of three. If it is not,  
      it is rounded down.  
   
      When a match has been successful, information about captured  
      substrings is returned in pairs of integers, starting at the  
      beginning of ovector, and continuing up to two-thirds of its  
      length  at  the  most. The first element of a pair is set to  
      the offset of the first character in a  substring,  and  the  
      second is set to the offset of the first character after the  
      end of a substring. The first  pair,  ovector[0]  and  ovec-  
      tor[1],  identify  the portion of the subject string matched  
      by the entire pattern. The next pair is used for  the  first  
      capturing  subpattern,  and  so  on.  The  value returned by  
      pcre_exec() is the number of pairs that have  been  set.  If  
      there  are no capturing subpatterns, the return value from a  
      successful match is 1, indicating that just the  first  pair  
      of offsets has been set.  
   
      Some convenience functions are provided for  extracting  the  
      captured substrings as separate strings. These are described  
      in the following section.  
   
      It is possible for an capturing  subpattern  number  n+1  to  
      match  some  part  of  the subject when subpattern n has not  
      been used at all.  For  example,  if  the  string  "abc"  is  
      matched  against the pattern (a|(z))(bc) subpatterns 1 and 3  
      are matched, but 2 is not. When this  happens,  both  offset  
      values corresponding to the unused subpattern are set to -1.  
   
      If a capturing subpattern is matched repeatedly, it  is  the  
      last  portion  of  the  string  that  it  matched  that gets  
      returned.  
   
      If the vector is too small to hold  all  the  captured  sub-  
      strings,  it is used as far as possible (up to two-thirds of  
      its length), and the function returns a value  of  zero.  In  
      particular,  if  the  substring offsets are not of interest,  
      pcre_exec() may be called with ovector passed  as  NULL  and  
      ovecsize  as  zero.  However,  if  the pattern contains back  
      references and the ovector isn't big enough to remember  the  
      related  substrings,  PCRE  has to get additional memory for  
      use during matching. Thus it is usually advisable to  supply  
      an ovector.  
   
      Note that pcre_info() can be used to find out how many  cap-  
      turing  subpatterns  there  are  in  a compiled pattern. The  
      smallest size for ovector that will  allow  for  n  captured  
      substrings,  in  addition  to  the  offsets of the substring  
      matched by the whole pattern, is (n+1)*3.  
   
      If pcre_exec() fails, it returns a negative number. The fol-  
      lowing are defined in the header file:  
   
        PCRE_ERROR_NOMATCH        (-1)  
   
      The subject string did not match the pattern.  
   
        PCRE_ERROR_NULL           (-2)  
   
      Either code or subject was passed as NULL,  or  ovector  was  
      NULL and ovecsize was not zero.  
   
        PCRE_ERROR_BADOPTION      (-3)  
   
      An unrecognized bit was set in the options argument.  
   
        PCRE_ERROR_BADMAGIC       (-4)  
   
      PCRE stores a 4-byte "magic number" at the start of the com-  
      piled  code,  to  catch  the  case  when it is passed a junk  
      pointer. This is the error it gives when  the  magic  number  
      isn't present.  
   
        PCRE_ERROR_UNKNOWN_NODE   (-5)  
   
      While running the pattern match, an unknown item was encoun-  
      tered in the compiled pattern. This error could be caused by  
      a bug in PCRE or by overwriting of the compiled pattern.  
   
        PCRE_ERROR_NOMEMORY       (-6)  
   
      If a pattern contains back references, but the ovector  that  
      is  passed  to pcre_exec() is not big enough to remember the  
      referenced substrings, PCRE gets a block of  memory  at  the  
      start  of  matching to use for this purpose. If the call via  
      pcre_malloc() fails, this error  is  given.  The  memory  is  
      freed at the end of matching.  
   
        PCRE_ERROR_NOSUBSTRING    (-7)  
   
      This   error   is   used   by   the   pcre_copy_substring(),  
      pcre_get_substring(),  and  pcre_get_substring_list()  func-  
      tions (see below). It is never returned by pcre_exec().  
   
        PCRE_ERROR_MATCHLIMIT     (-8)  
   
      The recursion and backtracking limit, as  specified  by  the  
      match_limit  field  in a pcre_extra structure (or defaulted)  
      was reached. See the description above.  
   
        PCRE_ERROR_CALLOUT        (-9)  
   
      This error is never generated by pcre_exec() itself.  It  is  
      provided  for  use by callout functions that want to yield a  
      distinctive error code. See  the  pcrecallout  documentation  
      for details.  
1895    
1896    
1897  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
1898    
1899       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
1900            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
1901            int buffersize);              int buffersize);
1902    
1903       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
1904            int stringcount, int stringnumber,              int stringcount, int stringnumber,
1905            const char **stringptr);              const char **stringptr);
1906    
1907       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
1908            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
1909    
1910       Captured substrings can be accessed directly  by  using  the         Captured  substrings  can  be  accessed  directly  by using the offsets
1911       offsets returned by pcre_exec() in ovector. For convenience,         returned by pcre_exec() in  ovector.  For  convenience,  the  functions
1912       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
1913       and  pcre_get_substring_list()  are  provided for extracting         string_list() are provided for extracting captured substrings  as  new,
1914       captured  substrings  as  new,   separate,   zero-terminated         separate,  zero-terminated strings. These functions identify substrings
1915       strings.  These functions identify substrings by number. The         by number. The next section describes functions  for  extracting  named
1916       next section describes functions for extracting  named  sub-         substrings.
1917       strings.   A  substring  that  contains  a  binary  zero  is  
1918       correctly extracted and has a further zero added on the end,         A  substring that contains a binary zero is correctly extracted and has
1919       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
1920           string.   However,  you  can  process such a string by referring to the
1921       The first three arguments are the  same  for  all  three  of         length that is  returned  by  pcre_copy_substring()  and  pcre_get_sub-
1922       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
1923       just been successfully matched, ovector is a pointer to  the         not adequate for handling strings containing binary zeros, because  the
1924       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
1925       and stringcount is the number of substrings that  were  cap-  
1926       tured by the match, including the substring that matched the         The  first  three  arguments  are the same for all three of these func-
1927       entire regular expression. This is  the  value  returned  by         tions: subject is the subject string that has  just  been  successfully
1928       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
1929       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
1930       tor,  the  value passed as stringcount should be the size of         were  captured  by  the match, including the substring that matched the
1931       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
1932           it  is greater than zero. If pcre_exec() returned zero, indicating that
1933       The functions pcre_copy_substring() and pcre_get_substring()         it ran out of space in ovector, the value passed as stringcount  should
1934       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
1935       number. A value of zero extracts the substring that  matched  
1936       the entire pattern, while higher values extract the captured         The  functions pcre_copy_substring() and pcre_get_substring() extract a
1937       substrings. For pcre_copy_substring(), the string is  placed         single substring, whose number is given as  stringnumber.  A  value  of
1938       in  buffer,  whose  length is given by buffersize, while for         zero  extracts  the  substring that matched the entire pattern, whereas
1939       pcre_get_substring() a new block of memory is  obtained  via         higher values  extract  the  captured  substrings.  For  pcre_copy_sub-
1940       pcre_malloc,  and its address is returned via stringptr. The         string(),  the  string  is  placed  in buffer, whose length is given by
1941       yield of the function is  the  length  of  the  string,  not         buffersize, while for pcre_get_substring() a new  block  of  memory  is
1942       including the terminating zero, or one of         obtained  via  pcre_malloc,  and its address is returned via stringptr.
1943           The yield of the function is the length of the  string,  not  including
1944         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of
1945    
1946       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
1947       attempt to get memory failed for pcre_get_substring().  
1948           The  buffer  was too small for pcre_copy_substring(), or the attempt to
1949         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
1950    
1951       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
1952    
1953       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
1954       able  substrings  and builds a list of pointers to them. All  
1955       this is done in a single block of memory which  is  obtained         The pcre_get_substring_list()  function  extracts  all  available  sub-
1956       via pcre_malloc. The address of the memory block is returned         strings  and  builds  a list of pointers to them. All this is done in a
1957       via listptr, which is also the start of the list  of  string         single block of memory that is obtained via pcre_malloc. The address of
1958       pointers.  The  end of the list is marked by a NULL pointer.         the  memory  block  is returned via listptr, which is also the start of
1959       The yield of the function is zero if all went well, or         the list of string pointers. The end of the list is marked  by  a  NULL
1960           pointer. The yield of the function is zero if all went well, or
1961         PCRE_ERROR_NOMEMORY       (-6)  
1962             PCRE_ERROR_NOMEMORY       (-6)
1963       if the attempt to get the memory block failed.  
1964           if the attempt to get the memory block failed.
1965       When any of these functions encounter a  substring  that  is  
1966       unset, which can happen when capturing subpattern number n+1         When  any of these functions encounter a substring that is unset, which
1967       matches some part of the subject, but subpattern n  has  not         can happen when capturing subpattern number n+1 matches  some  part  of
1968       been  used  at all, they return an empty string. This can be         the  subject, but subpattern n has not been used at all, they return an
1969       distinguished  from  a  genuine  zero-length  substring   by         empty string. This can be distinguished from a genuine zero-length sub-
1970       inspecting the appropriate offset in ovector, which is nega-         string  by inspecting the appropriate offset in ovector, which is nega-
1971       tive for unset substrings.         tive for unset substrings.
1972    
1973       The  two  convenience  functions  pcre_free_substring()  and         The two convenience functions pcre_free_substring() and  pcre_free_sub-
1974       pcre_free_substring_list()  can  be  used to free the memory         string_list()  can  be  used  to free the memory returned by a previous
1975       returned by  a  previous  call  of  pcre_get_substring()  or         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
1976       pcre_get_substring_list(),  respectively.  They  do  nothing         tively.  They  do  nothing  more  than  call the function pointed to by
1977       more than call the function pointed to by  pcre_free,  which         pcre_free, which of course could be called directly from a  C  program.
1978       of  course  could  be called directly from a C program. How-         However,  PCRE is used in some situations where it is linked via a spe-
1979       ever, PCRE is used in some situations where it is linked via         cial  interface  to  another  programming  language  that  cannot   use
1980       a  special  interface  to another programming language which         pcre_free  directly;  it is for these cases that the functions are pro-
1981       cannot use pcre_free directly; it is for  these  cases  that         vided.
      the functions are provided.  
1982    
1983    
1984  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
1985    
1986       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
1987            const char *subject, int *ovector,              const char *name);
1988            int stringcount, const char *stringname,  
1989            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
1990                const char *subject, int *ovector,
1991       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
1992            const char *name);              char *buffer, int buffersize);
1993    
1994       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
1995            const char *subject, int *ovector,              const char *subject, int *ovector,
1996            int stringcount, const char *stringname,              int stringcount, const char *stringname,
1997            const char **stringptr);              const char **stringptr);
1998    
1999       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-
2000       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2001       pcre_get_stringnumber(). The first argument is the  compiled  
2002       pattern,  and  the second is the name. For example, for this           (a+)b(?P<xxx>\d+)...
2003       pattern  
2004           the number of the subpattern called "xxx" is 2. If the name is known to
2005         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2006           name by calling pcre_get_stringnumber(). The first argument is the com-
2007       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
2008       number,  you can then extract the substring directly, or use         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2009       one of the functions described in the previous section.  For         subpattern of that name.
2010       convenience,  there are also two functions that do the whole  
2011       job.         Given the number, you can extract the substring directly, or use one of
2012           the functions described in the previous section. For convenience, there
2013       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2014       pcre_get_named_substring()  are  the  same  as those for the  
2015       functions that  extract  by  number,  and  so  are  not  re-         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2016       described here. There are just two differences.         pcre_get_named_substring()  are  the  same  as  those for the similarly
2017           named functions that extract by number. As these are described  in  the
2018       First, instead of a substring number, a  substring  name  is         previous  section,  they  are not re-described here. There are just two
2019       given.  Second,  there  is  an  extra argument, given at the         differences:
2020       start, which is a pointer to the compiled pattern.  This  is  
2021       needed  in order to gain access to the name-to-number trans-         First, instead of a substring number, a substring name is  given.  Sec-
2022       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2023           to the compiled pattern. This is needed in order to gain access to  the
2024       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2025       succeeds,    they   then   call   pcre_copy_substring()   or  
2026       pcre_get_substring(), as appropriate.         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2027           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2028           ate.
2029    
2030    
2031    DUPLICATE SUBPATTERN NAMES
2032    
2033           int pcre_get_stringtable_entries(const pcre *code,
2034                const char *name, char **first, char **last);
2035    
2036           When  a  pattern  is  compiled with the PCRE_DUPNAMES option, names for
2037           subpatterns are not required to  be  unique.  Normally,  patterns  with
2038           duplicate  names  are such that in any one match, only one of the named
2039           subpatterns participates. An example is shown in the pcrepattern  docu-
2040           mentation. When duplicates are present, pcre_copy_named_substring() and
2041           pcre_get_named_substring() return the first substring corresponding  to
2042           the  given  name  that  is  set.  If  none  are set, an empty string is
2043           returned.  The pcre_get_stringnumber() function returns one of the num-
2044           bers  that are associated with the name, but it is not defined which it
2045           is.
2046    
2047           If you want to get full details of all captured substrings for a  given
2048           name,  you  must  use  the pcre_get_stringtable_entries() function. The
2049           first argument is the compiled pattern, and the second is the name. The
2050           third  and  fourth  are  pointers to variables which are updated by the
2051           function. After it has run, they point to the first and last entries in
2052           the  name-to-number  table  for  the  given  name.  The function itself
2053           returns the length of each entry, or  PCRE_ERROR_NOSUBSTRING  if  there
2054           are  none.  The  format  of the table is described above in the section
2055           entitled Information about a pattern. Given all  the  relevant  entries
2056           for the name, you can extract each of their numbers, and hence the cap-
2057           tured data, if any.
2058    
2059    
2060    FINDING ALL POSSIBLE MATCHES
2061    
2062           The traditional matching function uses a  similar  algorithm  to  Perl,
2063           which stops when it finds the first match, starting at a given point in
2064           the subject. If you want to find all possible matches, or  the  longest
2065           possible  match,  consider using the alternative matching function (see
2066           below) instead. If you cannot use the alternative function,  but  still
2067           need  to  find all possible matches, you can kludge it up by making use
2068           of the callout facility, which is described in the pcrecallout documen-
2069           tation.
2070    
2071           What you have to do is to insert a callout right at the end of the pat-
2072           tern.  When your callout function is called, extract and save the  cur-
2073           rent  matched  substring.  Then  return  1, which forces pcre_exec() to
2074           backtrack and try other alternatives. Ultimately, when it runs  out  of
2075           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2076    
2077    
2078    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2079    
2080           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2081                const char *subject, int length, int startoffset,
2082                int options, int *ovector, int ovecsize,
2083                int *workspace, int wscount);
2084    
2085           The  function  pcre_dfa_exec()  is  called  to  match  a subject string
2086           against a compiled pattern, using a "DFA" matching algorithm. This  has
2087           different  characteristics to the normal algorithm, and is not compati-
2088           ble with Perl. Some of the features of PCRE patterns are not supported.
2089           Nevertheless, there are times when this kind of matching can be useful.
2090           For a discussion of the two matching algorithms, see  the  pcrematching
2091           documentation.
2092    
2093           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2094           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2095           ent  way,  and  this is described below. The other common arguments are
2096           used in the same way as for pcre_exec(), so their  description  is  not
2097           repeated here.
2098    
2099           The  two  additional  arguments provide workspace for the function. The
2100           workspace vector should contain at least 20 elements. It  is  used  for
2101           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2102           workspace will be needed for patterns and subjects where  there  are  a
2103           lot of potential matches.
2104    
2105           Here is an example of a simple call to pcre_dfa_exec():
2106    
2107             int rc;
2108             int ovector[10];
2109             int wspace[20];
2110             rc = pcre_dfa_exec(
2111               re,             /* result of pcre_compile() */
2112               NULL,           /* we didn't study the pattern */
2113               "some string",  /* the subject string */
2114               11,             /* the length of the subject string */
2115               0,              /* start at offset 0 in the subject */
2116               0,              /* default options */
2117               ovector,        /* vector of integers for substring information */
2118               10,             /* number of elements (NOT size in bytes) */
2119               wspace,         /* working space vector */
2120               20);            /* number of elements (NOT size in bytes) */
2121    
2122       Option bits for pcre_dfa_exec()
2123    
2124           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2125           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2126           LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2127           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2128           three of these are the same as for pcre_exec(), so their description is
2129           not repeated here.
2130    
2131             PCRE_PARTIAL
2132    
2133           This has the same general effect as it does for  pcre_exec(),  but  the
2134           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2135           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2136           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2137           been no complete matches, but there is still at least one matching pos-
2138           sibility.  The portion of the string that provided the partial match is
2139           set as the first matching string.
2140    
2141             PCRE_DFA_SHORTEST
2142    
2143           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2144           stop  as  soon  as  it  has found one match. Because of the way the DFA
2145           algorithm works, this is necessarily the shortest possible match at the
2146           first possible matching point in the subject string.
2147    
2148             PCRE_DFA_RESTART
2149    
2150           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2151           returns a partial match, it is possible to call it  again,  with  addi-
2152           tional  subject  characters,  and have it continue with the same match.
2153           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2154           workspace  and wscount options must reference the same vector as before
2155           because data about the match so far is left in  them  after  a  partial
2156           match.  There  is  more  discussion of this facility in the pcrepartial
2157           documentation.
2158    
2159       Successful returns from pcre_dfa_exec()
2160    
2161           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2162           string in the subject. Note, however, that all the matches from one run
2163           of the function start at the same point in  the  subject.  The  shorter
2164           matches  are all initial substrings of the longer matches. For example,
2165           if the pattern
2166    
2167             <.*>
2168    
2169           is matched against the string
2170    
2171             This is <something> <something else> <something further> no more
2172    
2173           the three matched strings are
2174    
2175             <something>
2176             <something> <something else>
2177             <something> <something else> <something further>
2178    
2179           On success, the yield of the function is a number  greater  than  zero,
2180           which  is  the  number of matched substrings. The substrings themselves
2181           are returned in ovector. Each string uses two elements;  the  first  is
2182           the  offset  to the start, and the second is the offset to the end. All
2183           the strings have the same start offset. (Space could have been saved by
2184           giving  this only once, but it was decided to retain some compatibility
2185           with the way pcre_exec() returns data, even though the meaning  of  the
2186           strings is different.)
2187    
2188           The strings are returned in reverse order of length; that is, the long-
2189           est matching string is given first. If there were too many  matches  to
2190           fit  into ovector, the yield of the function is zero, and the vector is
2191           filled with the longest matches.
2192    
2193       Error returns from pcre_dfa_exec()
2194    
2195           The pcre_dfa_exec() function returns a negative number when  it  fails.
2196           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2197           described above.  There are in addition the following errors  that  are
2198           specific to pcre_dfa_exec():
2199    
2200             PCRE_ERROR_DFA_UITEM      (-16)
2201    
2202           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2203           tern that it does not support, for instance, the use of \C  or  a  back
2204           reference.
2205    
2206             PCRE_ERROR_DFA_UCOND      (-17)
2207    
2208           This  return is given if pcre_dfa_exec() encounters a condition item in
2209           a pattern that uses a back reference for the  condition.  This  is  not
2210           supported.
2211    
2212             PCRE_ERROR_DFA_UMLIMIT    (-18)
2213    
2214           This  return  is given if pcre_dfa_exec() is called with an extra block
2215           that contains a setting of the match_limit field. This is not supported
2216           (it is meaningless).
2217    
2218             PCRE_ERROR_DFA_WSSIZE     (-19)
2219    
2220           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2221           workspace vector.
2222    
2223             PCRE_ERROR_DFA_RECURSE    (-20)
2224    
2225           When a recursive subpattern is processed, the matching  function  calls
2226           itself  recursively,  using  private vectors for ovector and workspace.
2227           This error is given if the output vector  is  not  large  enough.  This
2228           should be extremely rare, as a vector of size 1000 is used.
2229    
2230    Last updated: 08 June 2006
2231    Copyright (c) 1997-2006 University of Cambridge.
2232    ------------------------------------------------------------------------------
2233    
2234    
2235    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2236    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2237    
2238  NAME  NAME
2239       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2240    
2241    
2242  PCRE CALLOUTS  PCRE CALLOUTS
2243    
2244       int (*pcre_callout)(pcre_callout_block *);         int (*pcre_callout)(pcre_callout_block *);
   
      PCRE provides a feature called "callout", which is  a  means  
      of  temporarily passing control to the caller of PCRE in the  
      middle of pattern matching. The caller of PCRE  provides  an  
      external  function  by putting its entry point in the global  
      variable pcre_callout. By default,  this  variable  contains  
      NULL, which disables all calling out.  
   
      Within a regular expression, (?C) indicates  the  points  at  
      which  the external function is to be called. Different cal-  
      lout points can be identified by putting a number less  than  
      256  after  the  letter  C.  The default value is zero.  For  
      example, this pattern has two callout points:  
   
        (?C1)9abc(?C2)def  
   
      During matching, when PCRE  reaches  a  callout  point  (and  
      pcre_callout  is  set), the external function is called. Its  
      only argument is a pointer to  a  pcre_callout  block.  This  
      contains the following variables:  
   
        int          version;  
        int          callout_number;  
        int         *offset_vector;  
        const char  *subject;  
        int          subject_length;  
        int          start_match;  
        int          current_position;  
        int          capture_top;  
        int          capture_last;  
        void        *callout_data;  
   
      The version field  is  an  integer  containing  the  version  
      number of the block format. The current version is zero. The  
      version number may change in future if additional fields are  
      added,  but  the  intention  is  never  to remove any of the  
      existing fields.  
   
      The callout_number field contains the number of the callout,  
      as compiled into the pattern (that is, the number after ?C).  
   
      The offset_vector field  is  a  pointer  to  the  vector  of  
      offsets  that  was  passed by the caller to pcre_exec(). The  
      contents can be inspected in  order  to  extract  substrings  
      that  have  been  matched  so  far,  in  the same way as for  
      extracting substrings after a match has completed.  
      The subject and subject_length  fields  contain  copies  the  
      values that were passed to pcre_exec().  
   
      The start_match field contains the offset within the subject  
      at  which  the current match attempt started. If the pattern  
      is not anchored, the callout function may be called  several  
      times for different starting points.  
   
      The current_position field contains the  offset  within  the  
      subject of the current match pointer.  
   
      The capture_top field contains the  number  of  the  highest  
      captured substring so far.  
   
      The capture_last field  contains  the  number  of  the  most  
      recently captured substring.  
   
      The callout_data field contains a value that  is  passed  to  
      pcre_exec()  by  the  caller  specifically so that it can be  
      passed back in callouts. It is passed  in  the  pcre_callout  
      field  of the pcre_extra data structure. If no such data was  
      passed, the value of callout_data in a pcre_callout block is  
      NULL.  There is a description of the pcre_extra structure in  
      the pcreapi documentation.  
2245    
2246           PCRE provides a feature called "callout", which is a means of temporar-
2247           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2248           matching.  The  caller of PCRE provides an external function by putting
2249           its entry point in the global variable pcre_callout. By  default,  this
2250           variable contains NULL, which disables all calling out.
2251    
2252           Within  a  regular  expression,  (?C) indicates the points at which the
2253           external function is to be called.  Different  callout  points  can  be
2254           identified  by  putting  a number less than 256 after the letter C. The
2255           default value is zero.  For  example,  this  pattern  has  two  callout
2256           points:
2257    
2258             (?C1)eabc(?C2)def
2259    
2260           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2261           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2262           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2263           used with the pattern
2264    
2265             A(\d{2}|--)
2266    
2267           it is processed as if it were
2268    
2269           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2270    
2271           Notice that there is a callout before and after  each  parenthesis  and
2272           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2273           progress of pattern matching. The pcretest command has an  option  that
2274           sets  automatic callouts; when it is used, the output indicates how the
2275           pattern is matched. This is useful information when you are  trying  to
2276           optimize the performance of a particular pattern.
2277    
2278    
2279    MISSING CALLOUTS
2280    
2281           You  should  be  aware  that,  because of optimizations in the way PCRE
2282           matches patterns, callouts sometimes do not happen. For example, if the
2283           pattern is
2284    
2285             ab(?C4)cd
2286    
2287           PCRE knows that any matching string must contain the letter "d". If the
2288           subject string is "abyz", the lack of "d" means that  matching  doesn't
2289           ever  start,  and  the  callout is never reached. However, with "abyd",
2290           though the result is still no match, the callout is obeyed.
2291    
2292    
2293    THE CALLOUT INTERFACE
2294    
2295           During matching, when PCRE reaches a callout point, the external  func-
2296           tion  defined by pcre_callout is called (if it is set). This applies to
2297           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2298           only  argument  to  the callout function is a pointer to a pcre_callout
2299           block. This structure contains the following fields:
2300    
2301             int          version;
2302             int          callout_number;
2303             int         *offset_vector;
2304             const char  *subject;
2305             int          subject_length;
2306             int          start_match;
2307             int          current_position;
2308             int          capture_top;
2309             int          capture_last;
2310             void        *callout_data;
2311             int          pattern_position;
2312             int          next_item_length;
2313    
2314           The version field is an integer containing the version  number  of  the
2315           block  format. The initial version was 0; the current version is 1. The
2316           version number will change again in future  if  additional  fields  are
2317           added, but the intention is never to remove any of the existing fields.
2318    
2319           The callout_number field contains the number of the  callout,  as  com-
2320           piled  into  the pattern (that is, the number after ?C for manual call-
2321           outs, and 255 for automatically generated callouts).
2322    
2323           The offset_vector field is a pointer to the vector of offsets that  was
2324           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2325           pcre_exec() is used, the contents can be inspected in order to  extract
2326           substrings  that  have  been  matched  so  far,  in the same way as for
2327           extracting substrings after a match has completed. For  pcre_dfa_exec()
2328           this field is not useful.
2329    
2330           The subject and subject_length fields contain copies of the values that
2331           were passed to pcre_exec().
2332    
2333           The start_match field contains the offset within the subject  at  which
2334           the  current match attempt started. If the pattern is not anchored, the
2335           callout function may be called several times from the same point in the
2336           pattern for different starting points in the subject.
2337    
2338           The  current_position  field  contains the offset within the subject of
2339           the current match pointer.
2340    
2341           When the pcre_exec() function is used, the capture_top  field  contains
2342           one  more than the number of the highest numbered captured substring so
2343           far. If no substrings have been captured, the value of  capture_top  is
2344           one.  This  is always the case when pcre_dfa_exec() is used, because it
2345           does not support captured substrings.
2346    
2347           The capture_last field contains the number of the  most  recently  cap-
2348           tured  substring. If no substrings have been captured, its value is -1.
2349           This is always the case when pcre_dfa_exec() is used.
2350    
2351           The callout_data field contains a value that is passed  to  pcre_exec()
2352           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2353           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2354           structure.  If  no such data was passed, the value of callout_data in a
2355           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2356           structure in the pcreapi documentation.
2357    
2358           The  pattern_position field is present from version 1 of the pcre_call-
2359           out structure. It contains the offset to the next item to be matched in
2360           the pattern string.
2361    
2362           The  next_item_length field is present from version 1 of the pcre_call-
2363           out structure. It contains the length of the next item to be matched in
2364           the  pattern  string. When the callout immediately precedes an alterna-
2365           tion bar, a closing parenthesis, or the end of the pattern, the  length
2366           is  zero.  When the callout precedes an opening parenthesis, the length
2367           is that of the entire subpattern.
2368    
2369           The pattern_position and next_item_length fields are intended  to  help
2370           in  distinguishing between different automatic callouts, which all have
2371           the same callout number. However, they are set for all callouts.
2372    
2373    
2374  RETURN VALUES  RETURN VALUES
2375    
2376       The callout function returns an integer.  If  the  value  is         The external callout function returns an integer to PCRE. If the  value
2377       zero,  matching  proceeds as normal. If the value is greater         is  zero,  matching  proceeds  as  normal. If the value is greater than
2378       than zero, matching fails at the current  point,  but  back-         zero, matching fails at the current point, but  the  testing  of  other
2379       tracking  to test other possibilities goes ahead, just as if         matching possibilities goes ahead, just as if a lookahead assertion had
2380       a lookahead assertion had failed. If the value is less  than         failed. If the value is less than zero, the  match  is  abandoned,  and
2381       zero,  the  match  is abandoned, and pcre_exec() returns the         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2382       value.  
2383           Negative   values   should   normally   be   chosen  from  the  set  of
2384       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2385       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2386       forces a standard "no  match"  failure.   The  error  number         reserved for use by callout functions; it will never be  used  by  PCRE
2387       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
2388       it will never be used by PCRE itself.  
2389    Last updated: 28 February 2005
2390    Copyright (c) 1997-2005 University of Cambridge.
2391    ------------------------------------------------------------------------------
2392    
2393    
2394    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2395    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2396    
2397  NAME  NAME
2398       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2399    
2400    
2401  DIFFERENCES FROM PERL  DIFFERENCES BETWEEN PCRE AND PERL
2402    
2403       This document describes the differences  in  the  ways  that         This  document describes the differences in the ways that PCRE and Perl
2404       PCRE  and  Perl  handle regular expressions. The differences         handle regular expressions. The differences  described  here  are  with
2405       described here are with respect to Perl 5.8.         respect to Perl 5.8.
   
      1. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
      assertions. Perl permits them, but they do not mean what you  
      might think. For example, (?!a){3} does not assert that  the  
      next  three characters are not "a". It just asserts that the  
      next character is not "a" three times.  
   
      2. Capturing subpatterns that occur inside  negative  looka-  
      head  assertions  are  counted,  but  their  entries  in the  
      offsets vector are never set. Perl sets its numerical  vari-  
      ables  from  any  such  patterns that are matched before the  
      assertion fails to match something (thereby succeeding), but  
      only  if  the negative lookahead assertion contains just one  
      branch.  
   
      3. Though binary zero characters are supported in  the  sub-  
      ject  string,  they  are  not  allowed  in  a pattern string  
      because it is passed as a normal  C  string,  terminated  by  
      zero. The escape sequence "\0" can be used in the pattern to  
      represent a binary zero.  
   
      4. The following Perl escape sequences  are  not  supported:  
      \l,  \u,  \L,  \U,  \P, \p, and \X. In fact these are imple-  
      mented by Perl's general string-handling and are not part of  
      its pattern matching engine. If any of these are encountered  
      by PCRE, an error is generated.  
   
      5. PCRE does support the \Q...\E  escape  for  quoting  sub-  
      strings. Characters in between are treated as literals. This  
      is slightly different from Perl in that $  and  @  are  also  
      handled  as  literals inside the quotes. In Perl, they cause  
      variable interpolation (but of course  PCRE  does  not  have  
      variables). Note the following examples:  
   
          Pattern            PCRE matches      Perl matches  
   
          \Qabc$xyz\E        abc$xyz           abc followed by the  
                                                 contents of $xyz  
          \Qabc\$xyz\E       abc\$xyz          abc\$xyz  
          \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz  
   
      In PCRE, the \Q...\E mechanism is not  recognized  inside  a  
      character class.  
   
      8. Fairly obviously, PCRE does not support the (?{code}) and  
      (?p{code})  constructions. However, there is some experimen-  
      tal support for recursive patterns using the non-Perl  items  
      (?R),  (?number)  and  (?P>name).  Also,  the PCRE "callout"  
      feature allows an external function to be called during pat-  
      tern matching.  
   
      9. There are some differences that are  concerned  with  the  
      settings  of  captured  strings  when  part  of a pattern is  
      repeated. For example, matching "aba"  against  the  pattern  
      /^(a(b)?)+$/  in Perl leaves $2 unset, but in PCRE it is set  
      to "b".  
   
      10. PCRE  provides  some  extensions  to  the  Perl  regular  
      expression facilities:  
   
      (a) Although lookbehind assertions must match  fixed  length  
      strings,  each  alternative branch of a lookbehind assertion  
      can match a different length of string. Perl  requires  them  
      all to have the same length.  
   
      (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not  
      set,  the  $  meta-character matches only at the very end of  
      the string.  
   
      (c) If PCRE_EXTRA is set, a backslash followed by  a  letter  
      with no special meaning is faulted.  
   
      (d) If PCRE_UNGREEDY is set, the greediness of  the  repeti-  
      tion  quantifiers  is inverted, that is, by default they are  
      not greedy, but if followed by a question mark they are.  
   
      (e) PCRE_ANCHORED can be used to force a pattern to be tried  
      only at the first matching position in the subject string.  
   
      (f)  The  PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   and  
      PCRE_NO_AUTO_CAPTURE  options  for  pcre_exec() have no Perl  
      equivalents.  
   
      (g) The (?R), (?number), and (?P>name) constructs allows for  
      recursive  pattern  matching  (Perl  can  do  this using the  
      (?p{code}) construct, which PCRE cannot support.)  
   
      (h) PCRE supports  named  capturing  substrings,  using  the  
      Python syntax.  
   
      (i) PCRE supports the  possessive  quantifier  "++"  syntax,  
      taken from Sun's Java package.  
2406    
2407       (j) The (R) condition, for  testing  recursion,  is  a  PCRE         1.  PCRE has only a subset of Perl's UTF-8 and Unicode support. Details
2408       extension.         of what it does have are given in the section on UTF-8 support  in  the
2409           main pcre page.
2410    
2411       (k) The callout facility is PCRE-specific.         2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2412           permits them, but they do not mean what you might think.  For  example,
2413           (?!a){3} does not assert that the next three characters are not "a". It
2414           just asserts that the next character is not "a" three times.
2415    
2416           3. Capturing subpatterns that occur inside  negative  lookahead  asser-
2417           tions  are  counted,  but their entries in the offsets vector are never
2418           set. Perl sets its numerical variables from any such patterns that  are
2419           matched before the assertion fails to match something (thereby succeed-
2420           ing), but only if the negative lookahead assertion  contains  just  one
2421           branch.
2422    
2423           4.  Though  binary zero characters are supported in the subject string,
2424           they are not allowed in a pattern string because it is passed as a nor-
2425           mal C string, terminated by zero. The escape sequence \0 can be used in
2426           the pattern to represent a binary zero.
2427    
2428           5. The following Perl escape sequences are not supported: \l,  \u,  \L,
2429           \U, and \N. In fact these are implemented by Perl's general string-han-
2430           dling and are not part of its pattern matching engine. If any of  these
2431           are encountered by PCRE, an error is generated.
2432    
2433           6.  The Perl escape sequences \p, \P, and \X are supported only if PCRE
2434           is built with Unicode character property support. The  properties  that
2435           can  be tested with \p and \P are limited to the general category prop-
2436           erties such as Lu and Nd, script names such as Greek or  Han,  and  the
2437           derived properties Any and L&.
2438    
2439           7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2440           ters in between are treated as literals.  This  is  slightly  different
2441           from  Perl  in  that  $  and  @ are also handled as literals inside the
2442           quotes. In Perl, they cause variable interpolation (but of course  PCRE
2443           does not have variables). Note the following examples:
2444    
2445               Pattern            PCRE matches      Perl matches
2446    
2447               \Qabc$xyz\E        abc$xyz           abc followed by the
2448                                                      contents of $xyz
2449               \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2450               \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2451    
2452           The  \Q...\E  sequence  is recognized both inside and outside character
2453           classes.
2454    
2455           8. Fairly obviously, PCRE does not support the (?{code}) and (?p{code})
2456           constructions.  However,  there is support for recursive patterns using
2457           the non-Perl items (?R),  (?number),  and  (?P>name).  Also,  the  PCRE
2458           "callout"  feature allows an external function to be called during pat-
2459           tern matching. See the pcrecallout documentation for details.
2460    
2461           9. There are some differences that are concerned with the  settings  of
2462           captured  strings  when  part  of  a  pattern is repeated. For example,
2463           matching "aba" against the  pattern  /^(a(b)?)+$/  in  Perl  leaves  $2
2464           unset, but in PCRE it is set to "b".
2465    
2466           10. PCRE provides some extensions to the Perl regular expression facil-
2467           ities:
2468    
2469           (a) Although lookbehind assertions must  match  fixed  length  strings,
2470           each alternative branch of a lookbehind assertion can match a different
2471           length of string. Perl requires them all to have the same length.
2472    
2473           (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the  $
2474           meta-character matches only at the very end of the string.
2475    
2476           (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2477           cial meaning  is  faulted.  Otherwise,  like  Perl,  the  backslash  is
2478           ignored. (Perl can be made to issue a warning.)
2479    
2480           (d)  If  PCRE_UNGREEDY is set, the greediness of the repetition quanti-
2481           fiers is inverted, that is, by default they are not greedy, but if fol-
2482           lowed by a question mark they are.
2483    
2484           (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2485           tried only at the first matching position in the subject string.
2486    
2487           (f) The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and  PCRE_NO_AUTO_CAP-
2488           TURE options for pcre_exec() have no Perl equivalents.
2489    
2490           (g)  The (?R), (?number), and (?P>name) constructs allows for recursive
2491           pattern matching (Perl can do  this  using  the  (?p{code})  construct,
2492           which PCRE cannot support.)
2493    
2494           (h)  PCRE supports named capturing substrings, using the Python syntax.
2495    
2496           (i) PCRE supports the possessive quantifier  "++"  syntax,  taken  from
2497           Sun's Java package.
2498    
2499           (j) The (R) condition, for testing recursion, is a PCRE extension.
2500    
2501           (k) The callout facility is PCRE-specific.
2502    
2503           (l) The partial matching facility is PCRE-specific.
2504    
2505           (m) Patterns compiled by PCRE can be saved and re-used at a later time,
2506           even on different hosts that have the other endianness.
2507    
2508           (n) The alternative matching function (pcre_dfa_exec())  matches  in  a
2509           different way and is not Perl-compatible.
2510    
2511    Last updated: 06 June 2006
2512    Copyright (c) 1997-2006 University of Cambridge.
2513    ------------------------------------------------------------------------------
2514    
2515    
2516    PCREPATTERN(3)                                                  PCREPATTERN(3)
2517    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2518    
2519  NAME  NAME
2520       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2521    
2522    
2523  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2524    
2525       The syntax and semantics of  the  regular  expressions  sup-         The  syntax  and semantics of the regular expressions supported by PCRE
2526       ported  by PCRE are described below. Regular expressions are         are described below. Regular expressions are also described in the Perl
2527       also described in the Perl documentation and in a number  of         documentation  and  in  a  number  of books, some of which have copious
2528       other  books,  some  of which have copious examples. Jeffrey         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
2529       Friedl's  "Mastering  Regular  Expressions",  published   by         by  O'Reilly, covers regular expressions in great detail. This descrip-
2530       O'Reilly,  covers them in great detail. The description here         tion of PCRE's regular expressions is intended as reference material.
2531       is intended as reference documentation.  
2532           The original operation of PCRE was on strings of  one-byte  characters.
2533       The basic operation of PCRE is on strings of bytes. However,         However,  there is now also support for UTF-8 character strings. To use
2534       there  is  also  support for UTF-8 character strings. To use         this, you must build PCRE to  include  UTF-8  support,  and  then  call
2535       this support you must build PCRE to include  UTF-8  support,         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2536       and  then call pcre_compile() with the PCRE_UTF8 option. How         matching is mentioned in several places below. There is also a  summary
2537       this affects the pattern matching is  mentioned  in  several         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2538       places  below.  There is also a summary of UTF-8 features in         page.
2539       the section on UTF-8 support in the main pcre page.  
2540           The remainder of this document discusses the  patterns  that  are  sup-
2541       A regular expression is a pattern that is matched against  a         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2542       subject string from left to right. Most characters stand for         From  release  6.0,   PCRE   offers   a   second   matching   function,
2543       themselves in a pattern, and match the corresponding charac-         pcre_dfa_exec(),  which matches using a different algorithm that is not
2544       ters in the subject. As a trivial example, the pattern         Perl-compatible. The advantages and disadvantages  of  the  alternative
2545           function, and how it differs from the normal function, are discussed in
2546         The quick brown fox         the pcrematching page.
2547    
2548       matches a portion of a subject string that is  identical  to         A regular expression is a pattern that is  matched  against  a  subject
2549       itself.  The  power  of  regular  expressions comes from the         string  from  left  to right. Most characters stand for themselves in a
2550       ability to include alternatives and repetitions in the  pat-         pattern, and match the corresponding characters in the  subject.  As  a
2551       tern.  These  are encoded in the pattern by the use of meta-         trivial example, the pattern
2552       characters, which do not stand for  themselves  but  instead  
2553       are interpreted in some special way.           The quick brown fox
2554    
2555       There are two different sets of meta-characters: those  that         matches a portion of a subject string that is identical to itself. When
2556       are  recognized anywhere in the pattern except within square         caseless matching is specified (the PCRE_CASELESS option), letters  are
2557       brackets, and those that are recognized in square  brackets.         matched  independently  of case. In UTF-8 mode, PCRE always understands
2558       Outside square brackets, the meta-characters are as follows:         the concept of case for characters whose values are less than  128,  so
2559           caseless  matching  is always possible. For characters with higher val-
2560         \      general escape character with several uses         ues, the concept of case is supported if PCRE is compiled with  Unicode
2561         ^      assert start of string (or line, in multiline mode)         property  support,  but  not  otherwise.   If  you want to use caseless
2562         $      assert end of string (or line, in multiline mode)         matching for characters 128 and above, you must  ensure  that  PCRE  is
2563         .      match any character except newline (by default)         compiled with Unicode property support as well as with UTF-8 support.
2564         [      start character class definition  
2565         |      start of alternative branch         The  power  of  regular  expressions  comes from the ability to include
2566         (      start subpattern         alternatives and repetitions in the pattern. These are encoded  in  the
2567         )      end subpattern         pattern by the use of metacharacters, which do not stand for themselves
2568         ?      extends the meaning of (         but instead are interpreted in some special way.
2569                also 0 or 1 quantifier  
2570                also quantifier minimizer         There are two different sets of metacharacters: those that  are  recog-
2571         *      0 or more quantifier         nized  anywhere in the pattern except within square brackets, and those
2572         +      1 or more quantifier         that are recognized in square brackets. Outside  square  brackets,  the
2573                also "possessive quantifier"         metacharacters are as follows:
2574         {      start min/max quantifier  
2575             \      general escape character with several uses
2576       Part of a pattern that is in square  brackets  is  called  a           ^      assert start of string (or line, in multiline mode)
2577       "character  class".  In  a  character  class  the only meta-           $      assert end of string (or line, in multiline mode)
2578       characters are:           .      match any character except newline (by default)
2579             [      start character class definition
2580         \      general escape character           |      start of alternative branch
2581         ^      negate the class, but only if the first character           (      start subpattern
2582         -      indicates character range           )      end subpattern
2583         [      POSIX character class (only if followed by POSIX           ?      extends the meaning of (
2584                  syntax)                  also 0 or 1 quantifier
2585         ]      terminates the character class                  also quantifier minimizer
2586             *      0 or more quantifier
2587             +      1 or more quantifier
2588                    also "possessive quantifier"
2589             {      start min/max quantifier
2590    
2591           Part  of  a  pattern  that is in square brackets is called a "character
2592           class". In a character class the only metacharacters are:
2593    
2594             \      general escape character
2595             ^      negate the class, but only if the first character
2596             -      indicates character range
2597             [      POSIX character class (only if followed by POSIX
2598                      syntax)
2599             ]      terminates the character class
2600    
2601       The following sections describe  the  use  of  each  of  the         The following sections describe the use of each of the  metacharacters.
      meta-characters.  
2602    
2603    
2604  BACKSLASH  BACKSLASH
2605    
2606       The backslash character has several uses. Firstly, if it  is         The backslash character has several uses. Firstly, if it is followed by
2607       followed  by  a  non-alphameric character, it takes away any         a non-alphanumeric character, it takes away any  special  meaning  that
2608       special  meaning  that  character  may  have.  This  use  of         character  may  have.  This  use  of  backslash  as an escape character
2609       backslash  as  an  escape  character applies both inside and         applies both inside and outside character classes.
2610       outside character classes.  
2611           For example, if you want to match a * character, you write  \*  in  the
2612       For example, if you want to match a * character,  you  write         pattern.   This  escaping  action  applies whether or not the following
2613       \*  in the pattern.  This escaping action applies whether or         character would otherwise be interpreted as a metacharacter, so  it  is
2614       not the following character would otherwise  be  interpreted         always  safe  to  precede  a non-alphanumeric with backslash to specify
2615       as  a meta-character, so it is always safe to precede a non-         that it stands for itself. In particular, if you want to match a  back-
2616       alphameric with backslash to  specify  that  it  stands  for         slash, you write \\.
2617       itself. In particular, if you want to match a backslash, you  
2618       write \\.         If  a  pattern is compiled with the PCRE_EXTENDED option, whitespace in
2619           the pattern (other than in a character class) and characters between  a
2620       If a pattern is compiled with the PCRE_EXTENDED option, whi-         # outside a character class and the next newline are ignored. An escap-
2621       tespace in the pattern (other than in a character class) and         ing backslash can be used to include a whitespace  or  #  character  as
2622       characters between a # outside a  character  class  and  the         part of the pattern.
2623       next  newline  character  are ignored. An escaping backslash  
2624       can be used to include a whitespace or # character  as  part         If  you  want  to remove the special meaning from a sequence of charac-
2625       of the pattern.         ters, you can do so by putting them between \Q and \E. This is  differ-
2626           ent  from  Perl  in  that  $  and  @ are handled as literals in \Q...\E
2627       If you want to remove the special meaning from a sequence of         sequences in PCRE, whereas in Perl, $ and @ cause  variable  interpola-
2628       characters, you can do so by putting them between \Q and \E.         tion. Note the following examples:
2629       This is different from Perl in that $ and @ are  handled  as  
2630       literals  in  \Q...\E  sequences in PCRE, whereas in Perl, $           Pattern            PCRE matches   Perl matches
2631       and @ cause variable interpolation. Note the following exam-  
2632       ples:           \Qabc$xyz\E        abc$xyz        abc followed by the
2633                                                 contents of $xyz
2634         Pattern            PCRE matches   Perl matches           \Qabc\$xyz\E       abc\$xyz       abc\$xyz
2635             \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz
2636         \Qabc$xyz\E        abc$xyz        abc followed by the  
2637           The  \Q...\E  sequence  is recognized both inside and outside character
2638                                             contents of $xyz         classes.
2639         \Qabc\$xyz\E       abc\$xyz       abc\$xyz  
2640         \Qabc\E\$\Qxyz\E   abc$xyz        abc$xyz     Non-printing characters
2641    
2642       The \Q...\E sequence is recognized both inside  and  outside         A second use of backslash provides a way of encoding non-printing char-
2643       character classes.         acters  in patterns in a visible manner. There is no restriction on the
2644           appearance of non-printing characters, apart from the binary zero  that
2645       A second use of backslash provides a way  of  encoding  non-         terminates  a  pattern,  but  when  a pattern is being prepared by text
2646       printing  characters  in patterns in a visible manner. There         editing, it is usually easier  to  use  one  of  the  following  escape
2647       is no restriction on the appearance of non-printing  charac-         sequences than the binary character it represents:
2648       ters,  apart from the binary zero that terminates a pattern,  
2649       but when a pattern is being prepared by text editing, it  is           \a        alarm, that is, the BEL character (hex 07)
2650       usually  easier to use one of the following escape sequences           \cx       "control-x", where x is any character
2651       than the binary character it represents:           \e        escape (hex 1B)
2652             \f        formfeed (hex 0C)
2653         \a        alarm, that is, the BEL character (hex 07)           \n        newline (hex 0A)
2654         \cx       "control-x", where x is any character           \r        carriage return (hex 0D)
2655         \e        escape (hex 1B)           \t        tab (hex 09)
2656         \f        formfeed (hex 0C)           \ddd      character with octal code ddd, or backreference
2657         \n        newline (hex 0A)           \xhh      character with hex code hh
2658         \r        carriage return (hex 0D)           \x{hhh..} character with hex code hhh..
2659         \t        tab (hex 09)  
2660         \ddd      character with octal code ddd, or backreference         The  precise  effect of \cx is as follows: if x is a lower case letter,
2661         \xhh      character with hex code hh         it is converted to upper case. Then bit 6 of the character (hex 40)  is
2662         \x{hhh..} character with hex code hhh... (UTF-8 mode only)         inverted.   Thus  \cz becomes hex 1A, but \c{ becomes hex 3B, while \c;
2663           becomes hex 7B.
2664       The precise effect of \cx is as follows: if  x  is  a  lower  
2665       case  letter,  it  is converted to upper case. Then bit 6 of         After \x, from zero to two hexadecimal digits are read (letters can  be
2666       the character (hex 40) is inverted.  Thus  \cz  becomes  hex         in  upper  or  lower case). Any number of hexadecimal digits may appear
2667       1A, but \c{ becomes hex 3B, while \c; becomes hex 7B.         between \x{ and }, but the value of the character  code  must  be  less
2668           than 256 in non-UTF-8 mode, and less than 2**31 in UTF-8 mode (that is,
2669       After \x, from zero  to  two  hexadecimal  digits  are  read         the maximum hexadecimal value is 7FFFFFFF). If  characters  other  than
2670       (letters  can be in upper or lower case). In UTF-8 mode, any         hexadecimal  digits  appear between \x{ and }, or if there is no termi-
2671       number of hexadecimal digits may appear between \x{  and  },         nating }, this form of escape is not recognized.  Instead, the  initial
2672       but  the value of the character code must be less than 2**31         \x will be interpreted as a basic hexadecimal escape, with no following
2673       (that is, the maximum hexadecimal  value  is  7FFFFFFF).  If         digits, giving a character whose value is zero.
2674       characters  other than hexadecimal digits appear between \x{  
2675       and }, or if there is no terminating }, this form of  escape         Characters whose value is less than 256 can be defined by either of the
2676       is  not  recognized.  Instead, the initial \x will be inter-         two  syntaxes  for  \x. There is no difference in the way they are han-
2677       preted as a basic  hexadecimal  escape,  with  no  following         dled. For example, \xdc is exactly the same as \x{dc}.
2678       digits, giving a byte whose value is zero.  
2679           After \0 up to two further octal digits are read. If  there  are  fewer
2680       Characters whose value is less than 256 can  be  defined  by         than  two  digits,  just  those  that  are  present  are used. Thus the
2681       either  of  the  two  syntaxes  for \x when PCRE is in UTF-8         sequence \0\x\07 specifies two binary zeros followed by a BEL character
2682       mode. There is no difference in the way  they  are  handled.         (code  value 7). Make sure you supply two digits after the initial zero
2683       For example, \xdc is exactly the same as \x{dc}.         if the pattern character that follows is itself an octal digit.
2684    
2685       After \0 up to two further octal digits are  read.  In  both         The handling of a backslash followed by a digit other than 0 is compli-
2686       cases,  if  there are fewer than two digits, just those that         cated.  Outside a character class, PCRE reads it and any following dig-
2687       are present are used. Thus the  sequence  \0\x\07  specifies         its as a decimal number. If the number is less than  10,  or  if  there
2688       two binary zeros followed by a BEL character (code value 7).         have been at least that many previous capturing left parentheses in the
2689       Make sure you supply two digits after the  initial  zero  if         expression, the entire  sequence  is  taken  as  a  back  reference.  A
2690       the character that follows is itself an octal digit.         description  of how this works is given later, following the discussion
2691           of parenthesized subpatterns.
2692       The handling of a backslash followed by a digit other than 0  
2693       is  complicated.   Outside  a character class, PCRE reads it         Inside a character class, or if the decimal number is  greater  than  9
2694       and any following digits as a decimal number. If the  number         and  there have not been that many capturing subpatterns, PCRE re-reads
2695       is  less  than  10, or if there have been at least that many         up to three octal digits following the backslash, ane uses them to gen-
2696       previous capturing left parentheses in the  expression,  the         erate  a data character. Any subsequent digits stand for themselves. In
2697       entire  sequence is taken as a back reference. A description         non-UTF-8 mode, the value of a character specified  in  octal  must  be
2698       of how this works is given later, following  the  discussion         less  than  \400.  In  UTF-8 mode, values up to \777 are permitted. For
2699       of parenthesized subpatterns.         example:
2700    
2701       Inside a character  class,  or  if  the  decimal  number  is           \040   is another way of writing a space
2702       greater  than  9 and there have not been that many capturing           \40    is the same, provided there are fewer than 40
2703       subpatterns, PCRE re-reads up to three octal digits  follow-                     previous capturing subpatterns
2704       ing  the  backslash,  and  generates  a single byte from the           \7     is always a back reference
2705       least significant 8 bits of the value. Any subsequent digits           \11    might be a back reference, or another way of
2706       stand for themselves.  For example:                     writing a tab
2707             \011   is always a tab
2708         \040   is another way of writing a space           \0113  is a tab followed by the character "3"
2709         \40    is the same, provided there are fewer than 40           \113   might be a back reference, otherwise the
2710                   previous capturing subpatterns                     character with octal code 113
2711         \7     is always a back reference           \377   might be a back reference, otherwise
2712         \11    might be a back reference, or another way of                     the byte consisting entirely of 1 bits
2713                   writing a tab           \81    is either a back reference, or a binary zero
2714         \011   is always a tab                     followed by the two characters "8" and "1"
2715