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