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