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

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

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

revision 69 by nigel, Sat Feb 24 21:40:18 2007 UTC revision 182 by ph10, Wed Jun 13 15:09:54 2007 UTC
# Line 1  Line 1 
1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
# Line 5  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
15    
16    
17  DESCRIPTION  INTRODUCTION
18    
19       The PCRE library is a set of functions that implement  regu-         The  PCRE  library is a set of functions that implement regular expres-
20       lar  expression  pattern  matching using the same syntax and         sion pattern matching using the same syntax and semantics as Perl, with
21       semantics as Perl, with just a few differences. The  current         just  a  few differences. (Certain features that appeared in Python and
22       implementation  of  PCRE  (release 4.x) corresponds approxi-         PCRE before they appeared in Perl are also available using  the  Python
23       mately with Perl 5.8, including support  for  UTF-8  encoded         syntax.)
24       strings.    However,  this  support  has  to  be  explicitly  
25       enabled; it is not the default.         The  current  implementation of PCRE (release 7.x) corresponds approxi-
26           mately with Perl 5.10, including support for UTF-8 encoded strings  and
27       PCRE is written in C and released as a C library. However, a         Unicode general category properties. However, UTF-8 and Unicode support
28       number  of  people  have  written wrappers and interfaces of         has to be explicitly enabled; it is not the default. The Unicode tables
29       various kinds. A C++ class is included  in  these  contribu-         correspond to Unicode release 5.0.0.
30       tions,  which  can  be found in the Contrib directory at the  
31       primary FTP site, which is:         In  addition to the Perl-compatible matching function, PCRE contains an
32           alternative matching function that matches the same  compiled  patterns
33       ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre         in  a different way. In certain circumstances, the alternative function
34           has some advantages. For a discussion of the two  matching  algorithms,
35       Details of exactly which Perl  regular  expression  features         see the pcrematching page.
36       are  and  are  not  supported  by PCRE are given in separate  
37       documents. See the pcrepattern and pcrecompat pages.         PCRE  is  written  in C and released as a C library. A number of people
38           have written wrappers and interfaces of various kinds.  In  particular,
39       Some features of PCRE can be included, excluded, or  changed         Google  Inc.   have  provided  a comprehensive C++ wrapper. This is now
40       when  the library is built. The pcre_config() function makes         included as part of the PCRE distribution. The pcrecpp page has details
41       it possible for a client  to  discover  which  features  are         of  this  interface.  Other  people's contributions can be found in the
42       available.  Documentation  about  building  PCRE for various         Contrib directory at the primary FTP site, which is:
43       operating systems can be found in the  README  file  in  the  
44       source distribution.         ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
45    
46           Details of exactly which Perl regular expression features are  and  are
47           not supported by PCRE are given in separate documents. See the pcrepat-
48           tern and pcrecompat pages.
49    
50           Some features of PCRE can be included, excluded, or  changed  when  the
51           library  is  built.  The pcre_config() function makes it possible for a
52           client to discover which features are  available.  The  features  them-
53           selves  are described in the pcrebuild page. Documentation about build-
54           ing PCRE for various operating systems can be found in the README  file
55           in the source distribution.
56    
57           The  library  contains  a number of undocumented internal functions and
58           data tables that are used by more than one  of  the  exported  external
59           functions,  but  which  are  not  intended for use by external callers.
60           Their names all begin with "_pcre_", which hopefully will  not  provoke
61           any name clashes. In some environments, it is possible to control which
62           external symbols are exported when a shared library is  built,  and  in
63           these cases the undocumented symbols are not exported.
64    
65    
66  USER DOCUMENTATION  USER DOCUMENTATION
67    
68       The user documentation for PCRE has been  split  up  into  a         The  user  documentation  for PCRE comprises a number of different sec-
69       number  of  different sections. In the "man" format, each of         tions. In the "man" format, each of these is a separate "man page".  In
70       these is a separate "man page". In the HTML format, each  is         the  HTML  format, each is a separate page, linked from the index page.
71       a  separate  page,  linked from the index page. In the plain         In the plain text format, all the sections are concatenated,  for  ease
72       text format, all the sections are concatenated, for ease  of         of searching. The sections are as follows:
73       searching. The sections are as follows:  
74             pcre              this document
75         pcre              this document           pcre-config       show PCRE installation configuration information
76         pcreapi           details of PCRE's native API           pcreapi           details of PCRE's native C API
77         pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
78         pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
79         pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
80         pcregrep          description of the pcregrep command           pcrecpp           details of the C++ wrapper
81         pcrepattern       syntax and semantics of supported           pcregrep          description of the pcregrep command
82                             regular expressions           pcrematching      discussion of the two matching algorithms
83         pcreperform       discussion of performance issues           pcrepartial       details of the partial matching facility
84         pcreposix         the POSIX-compatible API           pcrepattern       syntax and semantics of supported
85         pcresample        discussion of the sample program                               regular expressions
86         pcretest          the pcretest testing command           pcreperform       discussion of performance issues
87             pcreposix         the POSIX-compatible C API
88       In addition, in the "man" and HTML formats, there is a short           pcreprecompile    details of saving and re-using precompiled patterns
89       page  for  each  library function, listing its arguments and           pcresample        discussion of the sample program
90       results.           pcrestack         discussion of stack usage
91             pcretest          description of the pcretest testing command
92    
93           In addition, in the "man" and HTML formats, there is a short  page  for
94           each C library function, listing its arguments and results.
95    
96    
97  LIMITATIONS  LIMITATIONS
98    
99       There are some size limitations in PCRE but it is hoped that         There  are some size limitations in PCRE but it is hoped that they will
100       they will never in practice be relevant.         never in practice be relevant.
101    
102       The maximum length of a  compiled  pattern  is  65539  (sic)         The maximum length of a compiled pattern is 65539 (sic) bytes  if  PCRE
103       bytes  if PCRE is compiled with the default internal linkage         is compiled with the default internal linkage size of 2. If you want to
104       size of 2. If you want to process regular  expressions  that         process regular expressions that are truly enormous,  you  can  compile
105       are  truly  enormous,  you can compile PCRE with an internal         PCRE  with  an  internal linkage size of 3 or 4 (see the README file in
106       linkage size of 3 or 4 (see the README file  in  the  source         the source distribution and the pcrebuild documentation  for  details).
107       distribution  and  the pcrebuild documentation for details).         In  these  cases the limit is substantially larger.  However, the speed
108       If these cases the limit is substantially larger.   However,         of execution is slower.
109       the speed of execution will be slower.  
110           All values in repeating quantifiers must be less than 65536. The  maxi-
111       All values in repeating quantifiers must be less than 65536.         mum  compiled  length  of  subpattern  with an explicit repeat count is
112       The maximum number of capturing subpatterns is 65535.         30000 bytes. The maximum number of capturing subpatterns is 65535.
113    
114       There is no limit to the  number  of  non-capturing  subpat-         There is no limit to the number of parenthesized subpatterns, but there
115       terns,  but  the  maximum  depth  of nesting of all kinds of         can be no more than 65535 capturing subpatterns.
116       parenthesized subpattern, including  capturing  subpatterns,  
117       assertions, and other types of subpattern, is 200.         The maximum length of name for a named subpattern is 32 characters, and
118           the maximum number of named subpatterns is 10000.
119       The maximum length of a subject string is the largest  posi-  
120       tive number that an integer variable can hold. However, PCRE         The maximum length of a subject string is the largest  positive  number
121       uses recursion to handle subpatterns and indefinite  repeti-         that  an integer variable can hold. However, when using the traditional
122       tion.  This  means  that the available stack space may limit         matching function, PCRE uses recursion to handle subpatterns and indef-
123       the size of a subject string that can be processed  by  cer-         inite  repetition.  This means that the available stack space may limit
124       tain patterns.         the size of a subject string that can be processed by certain patterns.
125           For a discussion of stack issues, see the pcrestack documentation.
126    
127    
128    UTF-8 AND UNICODE PROPERTY SUPPORT
129    
130           From  release  3.3,  PCRE  has  had  some support for character strings
131           encoded in the UTF-8 format. For release 4.0 this was greatly  extended
132           to  cover  most common requirements, and in release 5.0 additional sup-
133           port for Unicode general category properties was added.
134    
135           In order process UTF-8 strings, you must build PCRE  to  include  UTF-8
136           support  in  the  code,  and, in addition, you must call pcre_compile()
137           with the PCRE_UTF8 option flag. When you do this, both the pattern  and
138           any  subject  strings  that are matched against it are treated as UTF-8
139           strings instead of just strings of bytes.
140    
141           If you compile PCRE with UTF-8 support, but do not use it at run  time,
142           the  library will be a bit bigger, but the additional run time overhead
143           is limited to testing the PCRE_UTF8 flag occasionally, so should not be
144           very big.
145    
146           If PCRE is built with Unicode character property support (which implies
147           UTF-8 support), the escape sequences \p{..}, \P{..}, and  \X  are  sup-
148           ported.  The available properties that can be tested are limited to the
149           general category properties such as Lu for an upper case letter  or  Nd
150           for  a  decimal number, the Unicode script names such as Arabic or Han,
151           and the derived properties Any and L&. A full  list  is  given  in  the
152           pcrepattern documentation. Only the short names for properties are sup-
153           ported. For example, \p{L} matches a letter. Its Perl synonym,  \p{Let-
154           ter},  is  not  supported.   Furthermore,  in Perl, many properties may
155           optionally be prefixed by "Is", for compatibility with Perl  5.6.  PCRE
156           does not support this.
157    
158           The following comments apply when PCRE is running in UTF-8 mode:
159    
160           1.  When you set the PCRE_UTF8 flag, the strings passed as patterns and
161           subjects are checked for validity on entry to the  relevant  functions.
162           If an invalid UTF-8 string is passed, an error return is given. In some
163           situations, you may already know  that  your  strings  are  valid,  and
164           therefore want to skip these checks in order to improve performance. If
165           you set the PCRE_NO_UTF8_CHECK flag at compile time  or  at  run  time,
166           PCRE  assumes  that  the  pattern or subject it is given (respectively)
167           contains only valid UTF-8 codes. In this case, it does not diagnose  an
168           invalid  UTF-8 string. If you pass an invalid UTF-8 string to PCRE when
169           PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program  may
170           crash.
171    
172           2.  An  unbraced  hexadecimal  escape sequence (such as \xb3) matches a
173           two-byte UTF-8 character if the value is greater than 127.
174    
175           3. Octal numbers up to \777 are recognized, and  match  two-byte  UTF-8
176           characters for values greater than \177.
177    
178           4.  Repeat quantifiers apply to complete UTF-8 characters, not to indi-
179           vidual bytes, for example: \x{100}{3}.
180    
181           5. The dot metacharacter matches one UTF-8 character instead of a  sin-
182           gle byte.
183    
184           6.  The  escape sequence \C can be used to match a single byte in UTF-8
185           mode, but its use can lead to some strange effects.  This  facility  is
186           not available in the alternative matching function, pcre_dfa_exec().
187    
188           7.  The  character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
189           test characters of any code value, but the characters that PCRE  recog-
190           nizes  as  digits,  spaces,  or  word characters remain the same set as
191           before, all with values less than 256. This remains true even when PCRE
192           includes  Unicode  property support, because to do otherwise would slow
193           down PCRE in many common cases. If you really want to test for a  wider
194           sense  of,  say,  "digit",  you must use Unicode property tests such as
195           \p{Nd}.
196    
197           8. Similarly, characters that match the POSIX named  character  classes
198           are all low-valued characters.
199    
200           9.  However,  the Perl 5.10 horizontal and vertical whitespace matching
201           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
202           acters.
203    
204           10.  Case-insensitive  matching applies only to characters whose values
205           are less than 128, unless PCRE is built with Unicode property  support.
206           Even  when  Unicode  property support is available, PCRE still uses its
207           own character tables when checking the case of  low-valued  characters,
208           so  as not to degrade performance.  The Unicode property information is
209           used only for characters with higher values. Even when Unicode property
210           support is available, PCRE supports case-insensitive matching only when
211           there is a one-to-one mapping between a letter's  cases.  There  are  a
212           small  number  of  many-to-one  mappings in Unicode; these are not sup-
213           ported by PCRE.
214    
215    
216  UTF-8 SUPPORT  AUTHOR
217    
218       Starting at release 3.3, PCRE has had some support for char-         Philip Hazel
219       acter  strings  encoded in the UTF-8 format. For release 4.0         University Computing Service
220       this has been greatly extended to cover most common require-         Cambridge CB2 3QH, England.
      ments.  
   
      In order process UTF-8  strings,  you  must  build  PCRE  to  
      include  UTF-8  support  in  the code, and, in addition, you  
      must call pcre_compile() with  the  PCRE_UTF8  option  flag.  
      When  you  do this, both the pattern and any subject strings  
      that are matched against it are  treated  as  UTF-8  strings  
      instead of just strings of bytes.  
   
      If you compile PCRE with UTF-8 support, but do not use it at  
      run  time,  the  library will be a bit bigger, but the addi-  
      tional run time overhead is limited to testing the PCRE_UTF8  
      flag in several places, so should not be very large.  
   
      The following comments apply when PCRE is running  in  UTF-8  
      mode:  
   
      1. PCRE assumes that the strings it is given  contain  valid  
      UTF-8  codes. It does not diagnose invalid UTF-8 strings. If  
      you pass invalid UTF-8 strings  to  PCRE,  the  results  are  
      undefined.  
   
      2. In a pattern, the escape sequence \x{...}, where the con-  
      tents  of  the  braces is a string of hexadecimal digits, is  
      interpreted as a UTF-8 character whose code  number  is  the  
      given  hexadecimal  number, for example: \x{1234}. If a non-  
      hexadecimal digit appears between the braces,  the  item  is  
      not  recognized.  This escape sequence can be used either as  
      a literal, or within a character class.  
   
      3. The original hexadecimal escape sequence, \xhh, matches a  
      two-byte UTF-8 character if the value is greater than 127.  
   
      4. Repeat quantifiers apply to  complete  UTF-8  characters,  
      not to individual bytes, for example: \x{100}{3}.  
   
      5. The dot metacharacter matches one UTF-8 character instead  
      of a single byte.  
   
      6. The escape sequence \C can be used to match a single byte  
      in UTF-8 mode, but its use can lead to some strange effects.  
   
      7. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  
      correctly test characters of any code value, but the charac-  
      ters that PCRE recognizes as digits, spaces, or word charac-  
      ters  remain  the  same  set as before, all with values less  
      than 256.  
   
      8. Case-insensitive  matching  applies  only  to  characters  
      whose  values  are  less than 256. PCRE does not support the  
      notion of "case" for higher-valued characters.  
221    
222       9. PCRE does not support the use of Unicode tables and  pro-         Putting an actual email address here seems to have been a spam  magnet,
223       perties or the Perl escapes \p, \P, and \X.         so  I've  taken  it away. If you want to email me, use my two initials,
224           followed by the two digits 10, at the domain cam.ac.uk.
225    
226    
227  AUTHOR  REVISION
228    
229       Philip Hazel <ph10@cam.ac.uk>         Last updated: 13 June 2007
230       University Computing Service,         Copyright (c) 1997-2007 University of Cambridge.
231       Cambridge CB2 3QG, England.  ------------------------------------------------------------------------------
232       Phone: +44 1223 334714  
233    
234    PCREBUILD(3)                                                      PCREBUILD(3)
235    
 Last updated: 04 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
236    
237  NAME  NAME
238       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
239    
240    
241  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
242    
243       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
244       can  be  selected when the library is compiled. They are all         selected when the library is compiled. They are all selected, or  dese-
245       selected, or deselected, by providing options to the config-         lected, by providing options to the configure script that is run before
246       ure  script  which  is run before the make command. The com-         the make command. The complete list of  options  for  configure  (which
247       plete list of options  for  configure  (which  includes  the         includes  the  standard  ones such as the selection of the installation
248       standard  ones  such  as  the  selection of the installation         directory) can be obtained by running
249       directory) can be obtained by running  
250             ./configure --help
251         ./configure --help  
252           The following sections include  descriptions  of  options  whose  names
253       The following sections describe certain options whose  names         begin with --enable or --disable. These settings specify changes to the
254       begin  with  --enable  or  --disable. These settings specify         defaults for the configure command. Because of the way  that  configure
255       changes to the defaults for the configure  command.  Because         works,  --enable  and --disable always come in pairs, so the complemen-
256       of  the  way  that  configure  works, --enable and --disable         tary option always exists as well, but as it specifies the default,  it
257       always come in pairs, so  the  complementary  option  always         is not described.
258       exists  as  well, but as it specifies the default, it is not  
259       described.  
260    C++ SUPPORT
261    
262           By default, the configure script will search for a C++ compiler and C++
263           header files. If it finds them, it automatically builds the C++ wrapper
264           library for PCRE. You can disable this by adding
265    
266             --disable-cpp
267    
268           to the configure command.
269    
270    
271  UTF-8 SUPPORT  UTF-8 SUPPORT
272    
273       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
274    
275             --enable-utf8
276    
277           to  the  configure  command.  Of  itself, this does not make PCRE treat
278           strings as UTF-8. As well as compiling PCRE with this option, you  also
279           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
280           function.
281    
282    
283    UNICODE CHARACTER PROPERTY SUPPORT
284    
285           UTF-8 support allows PCRE to process character values greater than  255
286           in  the  strings that it handles. On its own, however, it does not pro-
287           vide any facilities for accessing the properties of such characters. If
288           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
289           refer to Unicode character properties, you must add
290    
291             --enable-unicode-properties
292    
293         --enable-utf8         to the configure command. This implies UTF-8 support, even if you  have
294           not explicitly requested it.
295    
296       to the configure command. Of itself, this does not make PCRE         Including  Unicode  property  support  adds around 30K of tables to the
297       treat  strings as UTF-8. As well as compiling PCRE with this         PCRE library. Only the general category properties such as  Lu  and  Nd
298       option, you also have have to set the PCRE_UTF8 option  when         are supported. Details are given in the pcrepattern documentation.
      you call the pcre_compile() function.  
299    
300    
301  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
302    
303       By default, PCRE treats character 10 (linefeed) as the  new-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
304       line  character.  This  is  the  normal newline character on         the end of a line. This is the normal newline  character  on  Unix-like
305       Unix-like systems. You can compile PCRE to use character  13         systems. You can compile PCRE to use character 13 (carriage return, CR)
306       (carriage return) instead by adding         instead, by adding
307    
308         --enable-newline-is-cr           --enable-newline-is-cr
309    
310       to the configure command. For completeness there is  also  a         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
311       --enable-newline-is-lf  option,  which  explicitly specifies         option, which explicitly specifies linefeed as the newline character.
312       linefeed as the newline character.  
313           Alternatively, you can specify that line endings are to be indicated by
314           the two character sequence CRLF. If you want this, add
315    
316             --enable-newline-is-crlf
317    
318           to the configure command. There is a fourth option, specified by
319    
320             --enable-newline-is-anycrlf
321    
322           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
323           CRLF as indicating a line ending. Finally, a fifth option, specified by
324    
325             --enable-newline-is-any
326    
327           causes PCRE to recognize any Unicode newline sequence.
328    
329           Whatever line ending convention is selected when PCRE is built  can  be
330           overridden  when  the library functions are called. At build time it is
331           conventional to use the standard for your operating system.
332    
333    
334  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
335    
336       The PCRE building process uses libtool to build both  shared         The PCRE building process uses libtool to build both shared and  static
337       and  static  Unix libraries by default. You can suppress one         Unix  libraries by default. You can suppress one of these by adding one
338       of these by adding one of         of
339    
340         --disable-shared           --disable-shared
341         --disable-static           --disable-static
342    
343       to the configure command, as required.         to the configure command, as required.
344    
345    
346  POSIX MALLOC USAGE  POSIX MALLOC USAGE
347    
348       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
349       pcreposix  documentation),  additional  working  storage  is         umentation),  additional  working  storage  is required for holding the
350       required for holding the pointers  to  capturing  substrings         pointers to capturing substrings, because PCRE requires three  integers
351       because  PCRE requires three integers per substring, whereas         per  substring,  whereas  the POSIX interface provides only two. If the
352       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
353       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
354       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
355       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
356       stack is no longer used is 10; it can be changed by adding a  
357       setting such as           --with-posix-malloc-threshold=20
358    
359           to the configure command.
360    
        --with-posix-malloc-threshold=20  
361    
362       to the configure command.  HANDLING VERY LARGE PATTERNS
363    
364           Within  a  compiled  pattern,  offset values are used to point from one
365           part to another (for example, from an opening parenthesis to an  alter-
366           nation  metacharacter).  By default, two-byte values are used for these
367           offsets, leading to a maximum size for a  compiled  pattern  of  around
368           64K.  This  is sufficient to handle all but the most gigantic patterns.
369           Nevertheless, some people do want to process enormous patterns,  so  it
370           is  possible  to compile PCRE to use three-byte or four-byte offsets by
371           adding a setting such as
372    
373             --with-link-size=3
374    
375           to the configure command. The value given must be 2,  3,  or  4.  Using
376           longer  offsets slows down the operation of PCRE because it has to load
377           additional bytes when handling them.
378    
379    
380    AVOIDING EXCESSIVE STACK USAGE
381    
382           When matching with the pcre_exec() function, PCRE implements backtrack-
383           ing  by  making recursive calls to an internal function called match().
384           In environments where the size of the stack is limited,  this  can  se-
385           verely  limit  PCRE's operation. (The Unix environment does not usually
386           suffer from this problem, but it may sometimes be necessary to increase
387           the  maximum  stack size.  There is a discussion in the pcrestack docu-
388           mentation.) An alternative approach to recursion that uses memory  from
389           the  heap  to remember data, instead of using recursive function calls,
390           has been implemented to work round the problem of limited  stack  size.
391           If you want to build a version of PCRE that works this way, add
392    
393             --disable-stack-for-recursion
394    
395           to  the  configure  command. With this configuration, PCRE will use the
396           pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
397           ment  functions. By default these point to malloc() and free(), but you
398           can replace the pointers so that your own functions are used.
399    
400           Separate functions are  provided  rather  than  using  pcre_malloc  and
401           pcre_free  because  the  usage  is  very  predictable:  the block sizes
402           requested are always the same, and  the  blocks  are  always  freed  in
403           reverse  order.  A calling program might be able to implement optimized
404           functions that perform better  than  malloc()  and  free().  PCRE  runs
405           noticeably more slowly when built in this way. This option affects only
406           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
407           pcre_dfa_exec() function.
408    
409    
410  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
411    
412       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
413       calls  repeatedly  (possibly  recursively) when performing a         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
414       matching operation. By limiting the  number  of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
415       function  may  be  called,  a  limit  can  be  placed on the         function may be called during a single matching operation, a limit  can
416       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
417       can  be  changed  at  run  time, as described in the pcreapi         limit can be changed at run time, as described in the pcreapi  documen-
418       documentation. The default is 10 million, but  this  can  be         tation.  The default is 10 million, but this can be changed by adding a
419       changed by adding a setting such as         setting such as
420    
421         --with-match-limit=500000           --with-match-limit=500000
422    
423       to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
424           pcre_dfa_exec() matching function.
425    
426           In  some  environments  it is desirable to limit the depth of recursive
427           calls of match() more strictly than the total number of calls, in order
428           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
429           for-recursion is specified) that is used. A second limit controls this;
430           it  defaults  to  the  value  that is set for --with-match-limit, which
431           imposes no additional constraints. However, you can set a  lower  limit
432           by adding, for example,
433    
434  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
435    
436       Within a compiled pattern, offset values are used  to  point         to  the  configure  command.  This  value can also be overridden at run
437       from  one  part  to  another  (for  example, from an opening         time.
438       parenthesis to an  alternation  metacharacter).  By  default  
439       two-byte  values  are  used  for these offsets, leading to a  
440       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
441       sufficient  to  handle  all  but the most gigantic patterns.  
442       Nevertheless, some people do want to process  enormous  pat-         PCRE uses fixed tables for processing characters whose code values  are
443       terns,  so  it is possible to compile PCRE to use three-byte         less  than 256. By default, PCRE is built with a set of tables that are
444       or four-byte offsets by adding a setting such as         distributed in the file pcre_chartables.c.dist. These  tables  are  for
445           ASCII codes only. If you add
446         --with-link-size=3  
447             --enable-rebuild-chartables
448       to the configure command. The value given must be 2,  3,  or  
449       4.  Using  longer  offsets  slows down the operation of PCRE         to  the  configure  command, the distributed tables are no longer used.
450       because it has to load additional bytes when handling them.         Instead, a program called dftables is compiled and  run.  This  outputs
451           the source for new set of tables, created in the default locale of your
452       If you build PCRE with an increased link size, test  2  (and         C runtime system. (This method of replacing the tables does not work if
453       test 5 if you are using UTF-8) will fail. Part of the output         you  are cross compiling, because dftables is run on the local host. If
454       of these tests is a representation of the compiled  pattern,         you need to create alternative tables when cross  compiling,  you  will
455       and this changes with the link size.         have to do so "by hand".)
456    
457    
458    USING EBCDIC CODE
459    
460           PCRE  assumes  by  default that it will run in an environment where the
461           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
462           PCRE  can,  however,  be  compiled  to  run in an EBCDIC environment by
463           adding
464    
465             --enable-ebcdic
466    
467           to the configure command. This setting implies --enable-rebuild-charta-
468           bles.
469    
470    
471    SEE ALSO
472    
473           pcreapi(3), pcre_config(3).
474    
475    
476    AUTHOR
477    
478           Philip Hazel
479           University Computing Service
480           Cambridge CB2 3QH, England.
481    
482    
483    REVISION
484    
485           Last updated: 05 June 2007
486           Copyright (c) 1997-2007 University of Cambridge.
487    ------------------------------------------------------------------------------
488    
489    
490    PCREMATCHING(3)                                                PCREMATCHING(3)
491    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
492    
493  NAME  NAME
494       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
495    
496    
497    PCRE MATCHING ALGORITHMS
498    
499           This document describes the two different algorithms that are available
500           in PCRE for matching a compiled regular expression against a given sub-
501           ject  string.  The  "standard"  algorithm  is  the  one provided by the
502           pcre_exec() function.  This works in the same was  as  Perl's  matching
503           function, and provides a Perl-compatible matching operation.
504    
505           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
506           this operates in a different way, and is not  Perl-compatible.  It  has
507           advantages  and disadvantages compared with the standard algorithm, and
508           these are described below.
509    
510           When there is only one possible way in which a given subject string can
511           match  a pattern, the two algorithms give the same answer. A difference
512           arises, however, when there are multiple possibilities. For example, if
513           the pattern
514    
515             ^<.*>
516    
517           is matched against the string
518    
519             <something> <something else> <something further>
520    
521           there are three possible answers. The standard algorithm finds only one
522           of them, whereas the alternative algorithm finds all three.
523    
524    
525    REGULAR EXPRESSIONS AS TREES
526    
527           The set of strings that are matched by a regular expression can be rep-
528           resented  as  a  tree structure. An unlimited repetition in the pattern
529           makes the tree of infinite size, but it is still a tree.  Matching  the
530           pattern  to a given subject string (from a given starting point) can be
531           thought of as a search of the tree.  There are two  ways  to  search  a
532           tree:  depth-first  and  breadth-first, and these correspond to the two
533           matching algorithms provided by PCRE.
534    
 SYNOPSIS OF PCRE API  
535    
536       #include <pcre.h>  THE STANDARD MATCHING ALGORITHM
537    
538       pcre *pcre_compile(const char *pattern, int options,         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
539            const char **errptr, int *erroffset,         sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
540            const unsigned char *tableptr);         depth-first search of the pattern tree. That is, it  proceeds  along  a
541           single path through the tree, checking that the subject matches what is
542           required. When there is a mismatch, the algorithm  tries  any  alterna-
543           tives  at  the  current point, and if they all fail, it backs up to the
544           previous branch point in the  tree,  and  tries  the  next  alternative
545           branch  at  that  level.  This often involves backing up (moving to the
546           left) in the subject string as well.  The  order  in  which  repetition
547           branches  are  tried  is controlled by the greedy or ungreedy nature of
548           the quantifier.
549    
550       pcre_extra *pcre_study(const pcre *code, int options,         If a leaf node is reached, a matching string has  been  found,  and  at
551            const char **errptr);         that  point the algorithm stops. Thus, if there is more than one possi-
552           ble match, this algorithm returns the first one that it finds.  Whether
553           this  is the shortest, the longest, or some intermediate length depends
554           on the way the greedy and ungreedy repetition quantifiers are specified
555           in the pattern.
556    
557       int pcre_exec(const pcre *code, const pcre_extra *extra,         Because  it  ends  up  with a single path through the tree, it is rela-
558            const char *subject, int length, int startoffset,         tively straightforward for this algorithm to keep  track  of  the  sub-
559            int options, int *ovector, int ovecsize);         strings  that  are  matched  by portions of the pattern in parentheses.
560           This provides support for capturing parentheses and back references.
561    
      int pcre_copy_named_substring(const pcre *code,  
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
562    
563       int pcre_copy_substring(const char *subject, int *ovector,  THE ALTERNATIVE MATCHING ALGORITHM
           int stringcount, int stringnumber, char *buffer,  
           int buffersize);  
564    
565       int pcre_get_named_substring(const pcre *code,         This algorithm conducts a breadth-first search of  the  tree.  Starting
566            const char *subject, int *ovector,         from  the  first  matching  point  in the subject, it scans the subject
567            int stringcount, const char *stringname,         string from left to right, once, character by character, and as it does
568            const char **stringptr);         this,  it remembers all the paths through the tree that represent valid
569           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
570           though  it is not implemented as a traditional finite state machine (it
571           keeps multiple states active simultaneously).
572    
573       int pcre_get_stringnumber(const pcre *code,         The scan continues until either the end of the subject is  reached,  or
574            const char *name);         there  are  no more unterminated paths. At this point, terminated paths
575           represent the different matching possibilities (if there are none,  the
576           match  has  failed).   Thus,  if there is more than one possible match,
577           this algorithm finds all of them, and in particular, it finds the long-
578           est.  In PCRE, there is an option to stop the algorithm after the first
579           match (which is necessarily the shortest) has been found.
580    
581       int pcre_get_substring(const char *subject, int *ovector,         Note that all the matches that are found start at the same point in the
582            int stringcount, int stringnumber,         subject. If the pattern
           const char **stringptr);  
583    
584       int pcre_get_substring_list(const char *subject,           cat(er(pillar)?)
           int *ovector, int stringcount, const char ***listptr);  
585    
586       void pcre_free_substring(const char *stringptr);         is  matched  against the string "the caterpillar catchment", the result
587           will be the three strings "cat", "cater", and "caterpillar" that  start
588           at the fourth character of the subject. The algorithm does not automat-
589           ically move on to find matches that start at later positions.
590    
591       void pcre_free_substring_list(const char **stringptr);         There are a number of features of PCRE regular expressions that are not
592           supported by the alternative matching algorithm. They are as follows:
593    
594       const unsigned char *pcre_maketables(void);         1.  Because  the  algorithm  finds  all possible matches, the greedy or
595           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
596           ungreedy quantifiers are treated in exactly the same way. However, pos-
597           sessive quantifiers can make a difference when what follows could  also
598           match what is quantified, for example in a pattern like this:
599    
600       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,           ^a++\w!
           int what, void *where);  
601    
602           This  pattern matches "aaab!" but not "aaa!", which would be matched by
603           a non-possessive quantifier. Similarly, if an atomic group is  present,
604           it  is matched as if it were a standalone pattern at the current point,
605           and the longest match is then "locked in" for the rest of  the  overall
606           pattern.
607    
608       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         2. When dealing with multiple paths through the tree simultaneously, it
609           is not straightforward to keep track of  captured  substrings  for  the
610           different  matching  possibilities,  and  PCRE's implementation of this
611           algorithm does not attempt to do this. This means that no captured sub-
612           strings are available.
613    
614       int pcre_config(int what, void *where);         3.  Because no substrings are captured, back references within the pat-
615           tern are not supported, and cause errors if encountered.
616    
617       char *pcre_version(void);         4. For the same reason, conditional expressions that use  a  backrefer-
618           ence  as  the  condition or test for a specific group recursion are not
619           supported.
620    
621       void *(*pcre_malloc)(size_t);         5. Because many paths through the tree may be  active,  the  \K  escape
622           sequence, which resets the start of the match when encountered (but may
623           be on some paths and not on others), is not  supported.  It  causes  an
624           error if encountered.
625    
626       void (*pcre_free)(void *);         6.  Callouts  are  supported, but the value of the capture_top field is
627           always 1, and the value of the capture_last field is always -1.
628    
629       int (*pcre_callout)(pcre_callout_block *);         7.  The \C escape sequence, which (in the standard algorithm) matches a
630           single  byte, even in UTF-8 mode, is not supported because the alterna-
631           tive algorithm moves through the subject  string  one  character  at  a
632           time, for all active paths through the tree.
633    
634    
635  PCRE API  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
636    
637       PCRE has its own native API,  which  is  described  in  this         Using  the alternative matching algorithm provides the following advan-
638       document.  There  is  also  a  set of wrapper functions that         tages:
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
639    
640       The native API function prototypes are defined in the header         1. All possible matches (at a single point in the subject) are automat-
641       file  pcre.h,  and  on  Unix  systems  the library itself is         ically  found,  and  in particular, the longest match is found. To find
642       called libpcre.a, so can be accessed by adding -lpcre to the         more than one match using the standard algorithm, you have to do kludgy
643       command  for  linking  an  application  which  calls it. The         things with callouts.
      header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
644    
645       The functions pcre_compile(), pcre_study(), and  pcre_exec()         2.  There is much better support for partial matching. The restrictions
646       are  used  for compiling and matching regular expressions. A         on the content of the pattern that apply when using the standard  algo-
647       sample program that demonstrates the simplest way  of  using         rithm  for  partial matching do not apply to the alternative algorithm.
648       them  is  given in the file pcredemo.c. The pcresample docu-         For non-anchored patterns, the starting position of a partial match  is
649       mentation describes how to run it.         available.
650    
651       There are convenience functions for extracting captured sub-         3.  Because  the  alternative  algorithm  scans the subject string just
652       strings from a matched subject string. They are:         once, and never needs to backtrack, it is possible to  pass  very  long
653           subject  strings  to  the matching function in several pieces, checking
654           for partial matching each time.
655    
        pcre_copy_substring()  
        pcre_copy_named_substring()  
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
656    
657       pcre_free_substring()  and  pcre_free_substring_list()   are  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
      also  provided,  to  free  the  memory  used  for  extracted  
      strings.  
658    
659       The function pcre_maketables() is used (optionally) to build         The alternative algorithm suffers from a number of disadvantages:
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
660    
661       The function pcre_fullinfo() is used to find out information         1. It is substantially slower than  the  standard  algorithm.  This  is
662       about a compiled pattern; pcre_info() is an obsolete version         partly  because  it has to search for all possible matches, but is also
663       which returns only some of the available information, but is         because it is less susceptible to optimization.
      retained   for   backwards   compatibility.    The  function  
      pcre_version() returns a pointer to a string containing  the  
      version of PCRE and its date of release.  
664    
665       The global variables  pcre_malloc  and  pcre_free  initially         2. Capturing parentheses and back references are not supported.
      contain the entry points of the standard malloc() and free()  
      functions respectively. PCRE  calls  the  memory  management  
      functions  via  these  variables,  so  a calling program can  
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
666    
667       The global variable pcre_callout initially contains NULL. It         3. Although atomic groups are supported, their use does not provide the
668       can be set by the caller to a "callout" function, which PCRE         performance advantage that it does for the standard algorithm.
669       will then call at specified points during a matching  opera-  
670       tion. Details are given in the pcrecallout documentation.  
671    AUTHOR
672    
673           Philip Hazel
674           University Computing Service
675           Cambridge CB2 3QH, England.
676    
677    
678    REVISION
679    
680           Last updated: 29 May 2007
681           Copyright (c) 1997-2007 University of Cambridge.
682    ------------------------------------------------------------------------------
683    
684    
685    PCREAPI(3)                                                          PCREAPI(3)
686    
687    
688    NAME
689           PCRE - Perl-compatible regular expressions
690    
691    
692    PCRE NATIVE API
693    
694           #include <pcre.h>
695    
696           pcre *pcre_compile(const char *pattern, int options,
697                const char **errptr, int *erroffset,
698                const unsigned char *tableptr);
699    
700           pcre *pcre_compile2(const char *pattern, int options,
701                int *errorcodeptr,
702                const char **errptr, int *erroffset,
703                const unsigned char *tableptr);
704    
705           pcre_extra *pcre_study(const pcre *code, int options,
706                const char **errptr);
707    
708           int pcre_exec(const pcre *code, const pcre_extra *extra,
709                const char *subject, int length, int startoffset,
710                int options, int *ovector, int ovecsize);
711    
712           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
713                const char *subject, int length, int startoffset,
714                int options, int *ovector, int ovecsize,
715                int *workspace, int wscount);
716    
717           int pcre_copy_named_substring(const pcre *code,
718                const char *subject, int *ovector,
719                int stringcount, const char *stringname,
720                char *buffer, int buffersize);
721    
722           int pcre_copy_substring(const char *subject, int *ovector,
723                int stringcount, int stringnumber, char *buffer,
724                int buffersize);
725    
726           int pcre_get_named_substring(const pcre *code,
727                const char *subject, int *ovector,
728                int stringcount, const char *stringname,
729                const char **stringptr);
730    
731           int pcre_get_stringnumber(const pcre *code,
732                const char *name);
733    
734           int pcre_get_stringtable_entries(const pcre *code,
735                const char *name, char **first, char **last);
736    
737           int pcre_get_substring(const char *subject, int *ovector,
738                int stringcount, int stringnumber,
739                const char **stringptr);
740    
741           int pcre_get_substring_list(const char *subject,
742                int *ovector, int stringcount, const char ***listptr);
743    
744           void pcre_free_substring(const char *stringptr);
745    
746           void pcre_free_substring_list(const char **stringptr);
747    
748           const unsigned char *pcre_maketables(void);
749    
750           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
751                int what, void *where);
752    
753           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
754    
755           int pcre_refcount(pcre *code, int adjust);
756    
757           int pcre_config(int what, void *where);
758    
759           char *pcre_version(void);
760    
761           void *(*pcre_malloc)(size_t);
762    
763           void (*pcre_free)(void *);
764    
765           void *(*pcre_stack_malloc)(size_t);
766    
767           void (*pcre_stack_free)(void *);
768    
769           int (*pcre_callout)(pcre_callout_block *);
770    
771    
772    PCRE API OVERVIEW
773    
774           PCRE has its own native API, which is described in this document. There
775           are also some wrapper functions that correspond to  the  POSIX  regular
776           expression  API.  These  are  described in the pcreposix documentation.
777           Both of these APIs define a set of C function calls. A C++  wrapper  is
778           distributed with PCRE. It is documented in the pcrecpp page.
779    
780           The  native  API  C  function prototypes are defined in the header file
781           pcre.h, and on Unix systems the library itself is called  libpcre.   It
782           can normally be accessed by adding -lpcre to the command for linking an
783           application  that  uses  PCRE.  The  header  file  defines  the  macros
784           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
785           bers for the library.  Applications can use these  to  include  support
786           for different releases of PCRE.
787    
788           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
789           pcre_exec() are used for compiling and matching regular expressions  in
790           a  Perl-compatible  manner. A sample program that demonstrates the sim-
791           plest way of using them is provided in the file  called  pcredemo.c  in
792           the  source distribution. The pcresample documentation describes how to
793           run it.
794    
795           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
796           ble,  is  also provided. This uses a different algorithm for the match-
797           ing. The alternative algorithm finds all possible matches (at  a  given
798           point  in  the subject), and scans the subject just once. However, this
799           algorithm does not return captured substrings. A description of the two
800           matching  algorithms and their advantages and disadvantages is given in
801           the pcrematching documentation.
802    
803           In addition to the main compiling and  matching  functions,  there  are
804           convenience functions for extracting captured substrings from a subject
805           string that is matched by pcre_exec(). They are:
806    
807             pcre_copy_substring()
808             pcre_copy_named_substring()
809             pcre_get_substring()
810             pcre_get_named_substring()
811             pcre_get_substring_list()
812             pcre_get_stringnumber()
813             pcre_get_stringtable_entries()
814    
815           pcre_free_substring() and pcre_free_substring_list() are also provided,
816           to free the memory used for extracted strings.
817    
818           The  function  pcre_maketables()  is  used  to build a set of character
819           tables  in  the  current  locale   for   passing   to   pcre_compile(),
820           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
821           provided for specialist use.  Most  commonly,  no  special  tables  are
822           passed,  in  which case internal tables that are generated when PCRE is
823           built are used.
824    
825           The function pcre_fullinfo() is used to find out  information  about  a
826           compiled  pattern; pcre_info() is an obsolete version that returns only
827           some of the available information, but is retained for  backwards  com-
828           patibility.   The function pcre_version() returns a pointer to a string
829           containing the version of PCRE and its date of release.
830    
831           The function pcre_refcount() maintains a  reference  count  in  a  data
832           block  containing  a compiled pattern. This is provided for the benefit
833           of object-oriented applications.
834    
835           The global variables pcre_malloc and pcre_free  initially  contain  the
836           entry  points  of  the  standard malloc() and free() functions, respec-
837           tively. PCRE calls the memory management functions via these variables,
838           so  a  calling  program  can replace them if it wishes to intercept the
839           calls. This should be done before calling any PCRE functions.
840    
841           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
842           indirections  to  memory  management functions. These special functions
843           are used only when PCRE is compiled to use  the  heap  for  remembering
844           data, instead of recursive function calls, when running the pcre_exec()
845           function. See the pcrebuild documentation for  details  of  how  to  do
846           this.  It  is  a non-standard way of building PCRE, for use in environ-
847           ments that have limited stacks. Because of the greater  use  of  memory
848           management,  it  runs  more  slowly. Separate functions are provided so
849           that special-purpose external code can be  used  for  this  case.  When
850           used,  these  functions  are always called in a stack-like manner (last
851           obtained, first freed), and always for memory blocks of the same  size.
852           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
853           mentation.
854    
855           The global variable pcre_callout initially contains NULL. It can be set
856           by  the  caller  to  a "callout" function, which PCRE will then call at
857           specified points during a matching operation. Details are given in  the
858           pcrecallout documentation.
859    
860    
861    NEWLINES
862    
863           PCRE  supports five different conventions for indicating line breaks in
864           strings: a single CR (carriage return) character, a  single  LF  (line-
865           feed) character, the two-character sequence CRLF, any of the three pre-
866           ceding, or any Unicode newline sequence. The Unicode newline  sequences
867           are  the  three just mentioned, plus the single characters VT (vertical
868           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
869           separator, U+2028), and PS (paragraph separator, U+2029).
870    
871           Each  of  the first three conventions is used by at least one operating
872           system as its standard newline sequence. When PCRE is built, a  default
873           can  be  specified.  The default default is LF, which is the Unix stan-
874           dard. When PCRE is run, the default can be overridden,  either  when  a
875           pattern is compiled, or when it is matched.
876    
877           In the PCRE documentation the word "newline" is used to mean "the char-
878           acter or pair of characters that indicate a line break". The choice  of
879           newline  convention  affects  the  handling of the dot, circumflex, and
880           dollar metacharacters, the handling of #-comments in /x mode, and, when
881           CRLF  is a recognized line ending sequence, the match position advance-
882           ment for a non-anchored pattern. The choice of newline convention  does
883           not affect the interpretation of the \n or \r escape sequences.
884    
885    
886  MULTITHREADING  MULTITHREADING
887    
888       The PCRE functions can be used in  multi-threading  applica-         The  PCRE  functions  can be used in multi-threading applications, with
889       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
890       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
891       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
892       threads.  
893           The  compiled form of a regular expression is not altered during match-
894       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
895       during  matching, so the same compiled pattern can safely be         at once.
896       used by several threads at once.  
897    
898    SAVING PRECOMPILED PATTERNS FOR LATER USE
899    
900           The compiled form of a regular expression can be saved and re-used at a
901           later time, possibly by a different program, and even on a  host  other
902           than  the  one  on  which  it  was  compiled.  Details are given in the
903           pcreprecompile documentation. However, compiling a  regular  expression
904           with  one version of PCRE for use with a different version is not guar-
905           anteed to work and may cause crashes.
906    
907    
908  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
909    
910       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
911    
912           The function pcre_config() makes it possible for a PCRE client to  dis-
913           cover which optional features have been compiled into the PCRE library.
914           The pcrebuild documentation has more details about these optional  fea-
915           tures.
916    
917           The  first  argument  for pcre_config() is an integer, specifying which
918           information is required; the second argument is a pointer to a variable
919           into  which  the  information  is  placed. The following information is
920           available:
921    
922       The function pcre_config() makes  it  possible  for  a  PCRE           PCRE_CONFIG_UTF8
      client  to  discover  which optional features have been com-  
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
923    
924       The first argument for pcre_config() is an integer, specify-         The output is an integer that is set to one if UTF-8 support is  avail-
925       ing  which information is required; the second argument is a         able; otherwise it is set to zero.
      pointer to a variable into which the information is  placed.  
      The following information is available:  
926    
927         PCRE_CONFIG_UTF8           PCRE_CONFIG_UNICODE_PROPERTIES
928    
929       The output is an integer that is set to one if UTF-8 support         The  output  is  an  integer  that is set to one if support for Unicode
930       is available; otherwise it is set to zero.         character properties is available; otherwise it is set to zero.
931    
932         PCRE_CONFIG_NEWLINE           PCRE_CONFIG_NEWLINE
933    
934       The output is an integer that is set to  the  value  of  the         The output is an integer whose value specifies  the  default  character
935       code  that  is  used for the newline character. It is either         sequence  that is recognized as meaning "newline". The four values that
936       linefeed (10) or carriage return (13), and  should  normally         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
937       be the standard character for your operating system.         and  -1  for  ANY. The default should normally be the standard sequence
938           for your operating system.
939    
940         PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_LINK_SIZE
941    
942       The output is an integer that contains the number  of  bytes         The output is an integer that contains the number  of  bytes  used  for
943       used  for  internal linkage in compiled regular expressions.         internal linkage in compiled regular expressions. The value is 2, 3, or
944       The value is 2, 3, or 4. Larger values allow larger  regular         4. Larger values allow larger regular expressions to  be  compiled,  at
945       expressions  to be compiled, at the expense of slower match-         the  expense  of  slower matching. The default value of 2 is sufficient
946       ing. The default value of 2 is sufficient for  all  but  the         for all but the most massive patterns, since  it  allows  the  compiled
947       most  massive patterns, since it allows the compiled pattern         pattern to be up to 64K in size.
      to be up to 64K in size.  
948    
949         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
950    
951       The output is an integer that contains the  threshold  above         The  output  is  an integer that contains the threshold above which the
952       which  the POSIX interface uses malloc() for output vectors.         POSIX interface uses malloc() for output vectors. Further  details  are
953       Further details are given in the pcreposix documentation.         given in the pcreposix documentation.
954    
955         PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_MATCH_LIMIT
956    
957       The output is an integer that gives the  default  limit  for         The output is an integer that gives the default limit for the number of
958       the   number  of  internal  matching  function  calls  in  a         internal matching function calls in a  pcre_exec()  execution.  Further
959       pcre_exec()  execution.  Further  details  are  given   with         details are given with pcre_exec() below.
960       pcre_exec() below.  
961             PCRE_CONFIG_MATCH_LIMIT_RECURSION
962    
963           The  output is an integer that gives the default limit for the depth of
964           recursion when calling the internal matching function in a  pcre_exec()
965           execution. Further details are given with pcre_exec() below.
966    
967             PCRE_CONFIG_STACKRECURSE
968    
969           The  output is an integer that is set to one if internal recursion when
970           running pcre_exec() is implemented by recursive function calls that use
971           the  stack  to remember their state. This is the usual way that PCRE is
972           compiled. The output is zero if PCRE was compiled to use blocks of data
973           on  the  heap  instead  of  recursive  function  calls.  In  this case,
974           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
975           blocks on the heap, thus avoiding the use of the stack.
976    
977    
978  COMPILING A PATTERN  COMPILING A PATTERN
979    
980       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
981            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
982            const unsigned char *tableptr);              const unsigned char *tableptr);
983    
984       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
985       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
986       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
987       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
988       pcre_malloc is returned. This contains the compiled code and  
989       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
990       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
991       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
992       memory when it is no longer required.         errorcodeptr, via which a numerical error code can be returned.
993    
994       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
995       that is, it does not depend on memory location, the complete         the  pattern  argument.  A  pointer to a single block of memory that is
996       pcre data block is not fully relocatable,  because  it  con-         obtained via pcre_malloc is returned. This contains the  compiled  code
997       tains  a  copy of the tableptr argument, which is an address         and related data. The pcre type is defined for the returned block; this
998       (see below).         is a typedef for a structure whose contents are not externally defined.
999       The options argument contains independent bits  that  affect         It is up to the caller to free the memory (via pcre_free) when it is no
1000       the  compilation.  It  should  be  zero  if  no  options are         longer required.
1001       required. Some of the options, in particular, those that are  
1002       compatible  with Perl, can also be set and unset from within         Although the compiled code of a PCRE regex is relocatable, that is,  it
1003       the pattern (see the detailed description of regular expres-         does not depend on memory location, the complete pcre data block is not
1004       sions  in the pcrepattern documentation). For these options,         fully relocatable, because it may contain a copy of the tableptr  argu-
1005       the contents of the options argument specifies their initial         ment, which is an address (see below).
1006       settings  at  the  start  of  compilation and execution. The  
1007       PCRE_ANCHORED option can be set at the time of  matching  as         The options argument contains various bit settings that affect the com-
1008       well as at compile time.         pilation. It should be zero if no options are required.  The  available
1009           options  are  described  below. Some of them, in particular, those that
1010       If errptr is NULL, pcre_compile() returns NULL  immediately.         are compatible with Perl, can also be set and  unset  from  within  the
1011       Otherwise, if compilation of a pattern fails, pcre_compile()         pattern  (see  the  detailed  description in the pcrepattern documenta-
1012       returns NULL, and sets the variable pointed to by errptr  to         tion). For these options, the contents of the options  argument  speci-
1013       point  to a textual error message. The offset from the start         fies  their initial settings at the start of compilation and execution.
1014       of  the  pattern  to  the  character  where  the  error  was         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
1015       discovered   is   placed  in  the  variable  pointed  to  by         of matching as well as at compile time.
1016       erroffset, which must not be NULL. If it  is,  an  immediate  
1017       error is given.         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1018           if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1019       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         sets the variable pointed to by errptr to point to a textual error mes-
1020       default  set  of character tables which are built when it is         sage. This is a static string that is part of the library. You must not
1021       compiled, using the default C  locale.  Otherwise,  tableptr         try to free it. The offset from the start of the pattern to the charac-
1022       must  be  the result of a call to pcre_maketables(). See the         ter where the error was discovered is placed in the variable pointed to
1023       section on locale support below.         by  erroffset,  which must not be NULL. If it is, an immediate error is
1024           given.
1025       This code fragment shows a typical straightforward  call  to  
1026       pcre_compile():         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
1027           codeptr  argument is not NULL, a non-zero error code number is returned
1028         pcre *re;         via this argument in the event of an error. This is in addition to  the
1029         const char *error;         textual error message. Error codes and messages are listed below.
1030         int erroffset;  
1031         re = pcre_compile(         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
1032           "^A.*Z",          /* the pattern */         character tables that are  built  when  PCRE  is  compiled,  using  the
1033           0,                /* default options */         default  C  locale.  Otherwise, tableptr must be an address that is the
1034           &error,           /* for error message */         result of a call to pcre_maketables(). This value is  stored  with  the
1035           &erroffset,       /* for error offset */         compiled  pattern,  and used again by pcre_exec(), unless another table
1036           NULL);            /* use default character tables */         pointer is passed to it. For more discussion, see the section on locale
1037           support below.
1038       The following option bits are defined:  
1039           This  code  fragment  shows a typical straightforward call to pcre_com-
1040         PCRE_ANCHORED         pile():
1041    
1042       If this bit is set, the pattern is forced to be  "anchored",           pcre *re;
1043       that is, it is constrained to match only at the first match-           const char *error;
1044       ing point in the string which is being searched  (the  "sub-           int erroffset;
1045       ject string"). This effect can also be achieved by appropri-           re = pcre_compile(
1046       ate constructs in the pattern itself, which is the only  way             "^A.*Z",          /* the pattern */
1047       to do it in Perl.             0,                /* default options */
1048               &error,           /* for error message */
1049         PCRE_CASELESS             &erroffset,       /* for error offset */
1050               NULL);            /* use default character tables */
1051       If this bit is set, letters in the pattern match both  upper  
1052       and  lower  case  letters.  It  is  equivalent  to Perl's /i         The following names for option bits are defined in  the  pcre.h  header
1053       option, and it can be changed within a  pattern  by  a  (?i)         file:
1054       option setting.  
1055             PCRE_ANCHORED
1056         PCRE_DOLLAR_ENDONLY  
1057           If this bit is set, the pattern is forced to be "anchored", that is, it
1058       If this bit is set, a dollar metacharacter  in  the  pattern         is constrained to match only at the first matching point in the  string
1059       matches  only at the end of the subject string. Without this         that  is being searched (the "subject string"). This effect can also be
1060       option, a dollar also matches immediately before  the  final         achieved by appropriate constructs in the pattern itself, which is  the
1061       character  if it is a newline (but not before any other new-         only way to do it in Perl.
1062       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
1063       PCRE_MULTILINE is set. There is no equivalent to this option           PCRE_AUTO_CALLOUT
1064       in Perl, and no way to set it within a pattern.  
1065           If this bit is set, pcre_compile() automatically inserts callout items,
1066         PCRE_DOTALL         all with number 255, before each pattern item. For  discussion  of  the
1067           callout facility, see the pcrecallout documentation.
1068       If this bit is  set,  a  dot  metacharater  in  the  pattern  
1069       matches all characters, including newlines. Without it, new-           PCRE_CASELESS
1070       lines are excluded. This option is equivalent to  Perl's  /s  
1071       option,  and  it  can  be changed within a pattern by a (?s)         If  this  bit is set, letters in the pattern match both upper and lower
1072       option setting. A negative class such as [^a] always matches         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
1073       a  newline  character,  independent  of  the setting of this         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1074       option.         always understands the concept of case for characters whose values  are
1075           less  than 128, so caseless matching is always possible. For characters
1076         PCRE_EXTENDED         with higher values, the concept of case is supported if  PCRE  is  com-
1077           piled  with Unicode property support, but not otherwise. If you want to
1078       If this bit is set, whitespace data characters in  the  pat-         use caseless matching for characters 128 and  above,  you  must  ensure
1079       tern  are  totally  ignored  except when escaped or inside a         that  PCRE  is  compiled  with Unicode property support as well as with
1080       character class. Whitespace does not include the VT  charac-         UTF-8 support.
1081       ter  (code 11). In addition, characters between an unescaped  
1082       # outside a character class and the next newline  character,           PCRE_DOLLAR_ENDONLY
1083       inclusive, are also ignored. This is equivalent to Perl's /x  
1084       option, and it can be changed within a  pattern  by  a  (?x)         If this bit is set, a dollar metacharacter in the pattern matches  only
1085       option setting.         at  the  end  of the subject string. Without this option, a dollar also
1086           matches immediately before a newline at the end of the string (but  not
1087       This option makes it possible  to  include  comments  inside         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1088       complicated patterns.  Note, however, that this applies only         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
1089       to data characters. Whitespace characters may  never  appear         Perl, and no way to set it within a pattern.
1090       within special character sequences in a pattern, for example  
1091       within the sequence (?( which introduces a conditional  sub-           PCRE_DOTALL
1092       pattern.  
1093           If this bit is set, a dot metacharater in the pattern matches all char-
1094         PCRE_EXTRA         acters, including those that indicate newline. Without it, a  dot  does
1095           not  match  when  the  current position is at a newline. This option is
1096       This option was invented in  order  to  turn  on  additional         equivalent to Perl's /s option, and it can be changed within a  pattern
1097       functionality of PCRE that is incompatible with Perl, but it         by  a (?s) option setting. A negative class such as [^a] always matches
1098       is currently of very little use. When set, any backslash  in         newline characters, independent of the setting of this option.
1099       a  pattern  that is followed by a letter that has no special  
1100       meaning causes an error, thus reserving  these  combinations           PCRE_DUPNAMES
1101       for  future  expansion.  By default, as in Perl, a backslash  
1102       followed by a letter with no special meaning is treated as a         If this bit is set, names used to identify capturing  subpatterns  need
1103       literal.  There  are at present no other features controlled         not be unique. This can be helpful for certain types of pattern when it
1104       by this option. It can also be set by a (?X) option  setting         is known that only one instance of the named  subpattern  can  ever  be
1105       within a pattern.         matched.  There  are  more details of named subpatterns below; see also
1106           the pcrepattern documentation.
1107         PCRE_MULTILINE  
1108             PCRE_EXTENDED
1109       By default, PCRE treats the subject string as consisting  of  
1110       a  single "line" of characters (even if it actually contains         If this bit is set, whitespace  data  characters  in  the  pattern  are
1111       several newlines). The "start  of  line"  metacharacter  (^)         totally ignored except when escaped or inside a character class. White-
1112       matches  only  at the start of the string, while the "end of         space does not include the VT character (code 11). In addition, charac-
1113       line" metacharacter ($) matches  only  at  the  end  of  the         ters between an unescaped # outside a character class and the next new-
1114       string,    or   before   a   terminating   newline   (unless         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1115       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.         option,  and  it  can be changed within a pattern by a (?x) option set-
1116           ting.
1117       When PCRE_MULTILINE it is set, the "start of line" and  "end  
1118       of  line"  constructs match immediately following or immedi-         This option makes it possible to include  comments  inside  complicated
1119       ately before any newline  in  the  subject  string,  respec-         patterns.   Note,  however,  that this applies only to data characters.
1120       tively,  as  well  as  at  the  very  start and end. This is         Whitespace  characters  may  never  appear  within  special   character
1121       equivalent to Perl's /m option, and it can be changed within         sequences  in  a  pattern,  for  example  within the sequence (?( which
1122       a  pattern  by  a  (?m) option setting. If there are no "\n"         introduces a conditional subpattern.
1123       characters in a subject string, or no occurrences of ^ or  $  
1124       in a pattern, setting PCRE_MULTILINE has no effect.           PCRE_EXTRA
1125    
1126         PCRE_NO_AUTO_CAPTURE         This option was invented in order to turn on  additional  functionality
1127           of  PCRE  that  is  incompatible with Perl, but it is currently of very
1128       If this option is set, it disables the use of numbered  cap-         little use. When set, any backslash in a pattern that is followed by  a
1129       turing  parentheses  in the pattern. Any opening parenthesis         letter  that  has  no  special  meaning causes an error, thus reserving
1130       that is not followed by ? behaves as if it were followed  by         these combinations for future expansion. By  default,  as  in  Perl,  a
1131       ?:  but  named  parentheses  can still be used for capturing         backslash  followed by a letter with no special meaning is treated as a
1132       (and they acquire numbers in the usual  way).  There  is  no         literal. (Perl can, however, be persuaded to give a warning for  this.)
1133       equivalent of this option in Perl.         There  are  at  present no other features controlled by this option. It
1134           can also be set by a (?X) option setting within a pattern.
1135         PCRE_UNGREEDY  
1136             PCRE_FIRSTLINE
1137       This option inverts the "greediness" of the  quantifiers  so  
1138       that  they  are  not greedy by default, but become greedy if         If this option is set, an  unanchored  pattern  is  required  to  match
1139       followed by "?". It is not compatible with Perl. It can also         before  or  at  the  first  newline  in  the subject string, though the
1140       be set by a (?U) option setting within the pattern.         matched text may continue over the newline.
1141    
1142         PCRE_UTF8           PCRE_MULTILINE
1143    
1144       This option causes PCRE to regard both the pattern  and  the         By default, PCRE treats the subject string as consisting  of  a  single
1145       subject  as  strings  of UTF-8 characters instead of single-         line  of characters (even if it actually contains newlines). The "start
1146       byte character strings. However, it  is  available  only  if         of line" metacharacter (^) matches only at the  start  of  the  string,
1147       PCRE  has  been  built to include UTF-8 support. If not, the         while  the  "end  of line" metacharacter ($) matches only at the end of
1148       use of this option provokes an error. Details  of  how  this         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1149       option  changes  the behaviour of PCRE are given in the sec-         is set). This is the same as Perl.
1150       tion on UTF-8 support in the main pcre page.  
1151           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1152           constructs match immediately following or immediately  before  internal
1153           newlines  in  the  subject string, respectively, as well as at the very
1154           start and end. This is equivalent to Perl's /m option, and  it  can  be
1155           changed within a pattern by a (?m) option setting. If there are no new-
1156           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1157           setting PCRE_MULTILINE has no effect.
1158    
1159             PCRE_NEWLINE_CR
1160             PCRE_NEWLINE_LF
1161             PCRE_NEWLINE_CRLF
1162             PCRE_NEWLINE_ANYCRLF
1163             PCRE_NEWLINE_ANY
1164    
1165           These  options  override the default newline definition that was chosen
1166           when PCRE was built. Setting the first or the second specifies  that  a
1167           newline  is  indicated  by a single character (CR or LF, respectively).
1168           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1169           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1170           that any of the three preceding sequences should be recognized. Setting
1171           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1172           recognized. The Unicode newline sequences are the three just mentioned,
1173           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1174           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1175           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1176           UTF-8 mode.
1177    
1178           The newline setting in the  options  word  uses  three  bits  that  are
1179           treated as a number, giving eight possibilities. Currently only six are
1180           used (default plus the five values above). This means that if  you  set
1181           more  than one newline option, the combination may or may not be sensi-
1182           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1183           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1184           cause an error.
1185    
1186           The only time that a line break is specially recognized when  compiling
1187           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1188           character class is encountered. This indicates  a  comment  that  lasts
1189           until  after the next line break sequence. In other circumstances, line
1190           break  sequences  are  treated  as  literal  data,   except   that   in
1191           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1192           and are therefore ignored.
1193    
1194           The newline option that is set at compile time becomes the default that
1195           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1196    
1197             PCRE_NO_AUTO_CAPTURE
1198    
1199           If this option is set, it disables the use of numbered capturing paren-
1200           theses  in the pattern. Any opening parenthesis that is not followed by
1201           ? behaves as if it were followed by ?: but named parentheses can  still
1202           be  used  for  capturing  (and  they acquire numbers in the usual way).
1203           There is no equivalent of this option in Perl.
1204    
1205             PCRE_UNGREEDY
1206    
1207           This option inverts the "greediness" of the quantifiers  so  that  they
1208           are  not greedy by default, but become greedy if followed by "?". It is
1209           not compatible with Perl. It can also be set by a (?U)  option  setting
1210           within the pattern.
1211    
1212             PCRE_UTF8
1213    
1214           This  option  causes PCRE to regard both the pattern and the subject as
1215           strings of UTF-8 characters instead of single-byte  character  strings.
1216           However,  it is available only when PCRE is built to include UTF-8 sup-
1217           port. If not, the use of this option provokes an error. Details of  how
1218           this  option  changes the behaviour of PCRE are given in the section on
1219           UTF-8 support in the main pcre page.
1220    
1221             PCRE_NO_UTF8_CHECK
1222    
1223           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1224           automatically  checked. If an invalid UTF-8 sequence of bytes is found,
1225           pcre_compile() returns an error. If you already know that your  pattern
1226           is  valid, and you want to skip this check for performance reasons, you
1227           can set the PCRE_NO_UTF8_CHECK option. When it is set,  the  effect  of
1228           passing an invalid UTF-8 string as a pattern is undefined. It may cause
1229           your program to crash.  Note that this option can  also  be  passed  to
1230           pcre_exec()  and pcre_dfa_exec(), to suppress the UTF-8 validity check-
1231           ing of subject strings.
1232    
1233    
1234    COMPILATION ERROR CODES
1235    
1236           The following table lists the error  codes  than  may  be  returned  by
1237           pcre_compile2(),  along with the error messages that may be returned by
1238           both compiling functions. As PCRE has developed, some error codes  have
1239           fallen out of use. To avoid confusion, they have not been re-used.
1240    
1241              0  no error
1242              1  \ at end of pattern
1243              2  \c at end of pattern
1244              3  unrecognized character follows \
1245              4  numbers out of order in {} quantifier
1246              5  number too big in {} quantifier
1247              6  missing terminating ] for character class
1248              7  invalid escape sequence in character class
1249              8  range out of order in character class
1250              9  nothing to repeat
1251             10  [this code is not in use]
1252             11  internal error: unexpected repeat
1253             12  unrecognized character after (?
1254             13  POSIX named classes are supported only within a class
1255             14  missing )
1256             15  reference to non-existent subpattern
1257             16  erroffset passed as NULL
1258             17  unknown option bit(s) set
1259             18  missing ) after comment
1260             19  [this code is not in use]
1261             20  regular expression too large
1262             21  failed to get memory
1263             22  unmatched parentheses
1264             23  internal error: code overflow
1265             24  unrecognized character after (?<
1266             25  lookbehind assertion is not fixed length
1267             26  malformed number or name after (?(
1268             27  conditional group contains more than two branches
1269             28  assertion expected after (?(
1270             29  (?R or (?[+-]digits must be followed by )
1271             30  unknown POSIX class name
1272             31  POSIX collating elements are not supported
1273             32  this version of PCRE is not compiled with PCRE_UTF8 support
1274             33  [this code is not in use]
1275             34  character value in \x{...} sequence is too large
1276             35  invalid condition (?(0)
1277             36  \C not allowed in lookbehind assertion
1278             37  PCRE does not support \L, \l, \N, \U, or \u
1279             38  number after (?C is > 255
1280             39  closing ) for (?C expected
1281             40  recursive call could loop indefinitely
1282             41  unrecognized character after (?P
1283             42  syntax error in subpattern name (missing terminator)
1284             43  two named subpatterns have the same name
1285             44  invalid UTF-8 string
1286             45  support for \P, \p, and \X has not been compiled
1287             46  malformed \P or \p sequence
1288             47  unknown property name after \P or \p
1289             48  subpattern name is too long (maximum 32 characters)
1290             49  too many named subpatterns (maximum 10,000)
1291             50  repeated subpattern is too long
1292             51  octal value is greater than \377 (not in UTF-8 mode)
1293             52  internal error: overran compiling workspace
1294             53   internal  error:  previously-checked  referenced  subpattern not
1295           found
1296             54  DEFINE group contains more than one branch
1297             55  repeating a DEFINE group is not allowed
1298             56  inconsistent NEWLINE options"
1299             57  \g is not followed by a braced name or an optionally braced
1300                   non-zero number
1301             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1302    
1303    
1304  STUDYING A PATTERN  STUDYING A PATTERN
1305    
1306       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1307            const char **errptr);              const char **errptr);
1308    
1309       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
1310       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
1311       the time taken for matching. The function pcre_study() takes         matching. The function pcre_study() takes a pointer to a compiled  pat-
1312       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1313       studing the pattern  produces  additional  information  that         information that will help speed up matching,  pcre_study()  returns  a
1314       will  help speed up matching, pcre_study() returns a pointer         pointer  to a pcre_extra block, in which the study_data field points to
1315       to a pcre_extra block, in which the study_data field  points         the results of the study.
1316       to the results of the study.  
1317           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1318       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1319       directly  to pcre_exec(). However, the pcre_extra block also         that can be set by the caller before the block  is  passed;  these  are
1320       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
1321       the  block is passed; these are described below. If studying  
1322       the pattern does not  produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1323       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1324       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
1325       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
1326    
1327       The second argument contains option  bits.  At  present,  no         The second argument of pcre_study() contains option bits.  At  present,
1328       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1329       should always be zero.  
1330           The  third argument for pcre_study() is a pointer for an error message.
1331       The third argument for pcre_study()  is  a  pointer  for  an         If studying succeeds (even if no data is  returned),  the  variable  it
1332       error  message.  If  studying  succeeds  (even if no data is         points  to  is  set  to NULL. Otherwise it is set to point to a textual
1333       returned), the variable it points to is set to NULL.  Other-         error message. This is a static string that is part of the library. You
1334       wise it points to a textual error message. You should there-         must  not  try  to  free it. You should test the error pointer for NULL
1335       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1336       pcre_study(), to be sure that it has run successfully.  
1337           This is a typical call to pcre_study():
1338       This is a typical call to pcre_study():  
1339             pcre_extra *pe;
1340         pcre_extra *pe;           pe = pcre_study(
1341         pe = pcre_study(             re,             /* result of pcre_compile() */
1342           re,             /* result of pcre_compile() */             0,              /* no options exist */
1343           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1344           &error);        /* set to NULL or points to a message */  
1345           At present, studying a pattern is useful only for non-anchored patterns
1346       At present, studying a  pattern  is  useful  only  for  non-         that  do not have a single fixed starting character. A bitmap of possi-
1347       anchored  patterns  that do not have a single fixed starting         ble starting bytes is created.
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1348    
1349    
1350  LOCALE SUPPORT  LOCALE SUPPORT
1351    
1352       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1353       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
1354       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
1355       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
1356       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
1357       locale  when  PCRE  is compiled. This is used when the final         with  Unicode  character property support. The use of locales with Uni-
1358       argument of pcre_compile() is NULL, and  is  sufficient  for         code is discouraged. If you are handling characters with codes  greater
1359       many applications.         than  128, you should either use UTF-8 and Unicode, or use locales, but
1360           not try to mix the two.
1361       An alternative set of tables can, however, be supplied. Such  
1362       tables  are built by calling the pcre_maketables() function,         PCRE contains an internal set of tables that are used  when  the  final
1363       which has no arguments, in the relevant locale.  The  result         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1364       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1365       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1366       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1367       greater than 128 are treated as letters), the following code         which may cause them to be different.
1368       could be used:  
1369           The  internal tables can always be overridden by tables supplied by the
1370         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1371         tables = pcre_maketables();         from  the  default.  As more and more applications change to using Uni-
1372         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1373    
1374       The  tables  are  built  in  memory  that  is  obtained  via         External tables are built by calling  the  pcre_maketables()  function,
1375       pcre_malloc.  The  pointer that is passed to pcre_compile is         which  has no arguments, in the relevant locale. The result can then be
1376       saved with the compiled pattern, and  the  same  tables  are         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1377       used via this pointer by pcre_study() and pcre_exec(). Thus,         example,  to  build  and use tables that are appropriate for the French
1378       for any single pattern, compilation, studying  and  matching         locale (where accented characters with  values  greater  than  128  are
1379       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1380       compiled in different locales. It is the caller's  responsi-  
1381       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1382       remains available for as long as it is needed.           tables = pcre_maketables();
1383             re = pcre_compile(..., tables);
1384    
1385           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1386           if you are using Windows, the name for the French locale is "french".
1387    
1388           When pcre_maketables() runs, the tables are built  in  memory  that  is
1389           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1390           that the memory containing the tables remains available for as long  as
1391           it is needed.
1392    
1393           The pointer that is passed to pcre_compile() is saved with the compiled
1394           pattern, and the same tables are used via this pointer by  pcre_study()
1395           and normally also by pcre_exec(). Thus, by default, for any single pat-
1396           tern, compilation, studying and matching all happen in the same locale,
1397           but different patterns can be compiled in different locales.
1398    
1399           It  is  possible to pass a table pointer or NULL (indicating the use of
1400           the internal tables) to pcre_exec(). Although  not  intended  for  this
1401           purpose,  this facility could be used to match a pattern in a different
1402           locale from the one in which it was compiled. Passing table pointers at
1403           run time is discussed below in the section on matching a pattern.
1404    
1405    
1406  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1407    
1408       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1409            int what, void *where);              int what, void *where);
1410    
1411       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1412       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1413       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1414       ity (and is documented below).  
1415           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1416       The first argument for pcre_fullinfo() is a pointer  to  the         pattern. The second argument is the result of pcre_study(), or NULL  if
1417       compiled  pattern.  The  second  argument  is  the result of         the  pattern  was not studied. The third argument specifies which piece
1418       pcre_study(), or NULL if the pattern was  not  studied.  The         of information is required, and the fourth argument is a pointer  to  a
1419       third  argument  specifies  which  piece  of  information is         variable  to  receive  the  data. The yield of the function is zero for
1420       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1421       to  receive  the data. The yield of the function is zero for  
1422       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1423                                   the argument where was NULL
1424         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1425                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1426         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1427         PCRE_ERROR_BADOPTION  the value of what was invalid         The "magic number" is placed at the start of each compiled  pattern  as
1428           an  simple check against passing an arbitrary memory pointer. Here is a
1429       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1430       length of the compiled pattern:         pattern:
1431    
1432         int rc;           int rc;
1433         unsigned long int length;           size_t length;
1434         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1435           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1436           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1437           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1438           &length);         /* where to put the data */             &length);         /* where to put the data */
1439    
1440       The possible values for the third argument  are  defined  in         The  possible  values for the third argument are defined in pcre.h, and
1441       pcre.h, and are as follows:         are as follows:
1442    
1443         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1444    
1445       Return the number of the highest back reference in the  pat-         Return the number of the highest back reference  in  the  pattern.  The
1446       tern.  The  fourth argument should point to an int variable.         fourth  argument  should  point to an int variable. Zero is returned if
1447       Zero is returned if there are no back references.         there are no back references.
1448    
1449         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1450    
1451       Return the number of capturing subpatterns in  the  pattern.         Return the number of capturing subpatterns in the pattern.  The  fourth
1452       The fourth argument should point to an int variable.         argument should point to an int variable.
1453    
1454         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1455    
1456       Return information about  the  first  byte  of  any  matched         Return  a pointer to the internal default character tables within PCRE.
1457       string,  for a non-anchored pattern. (This option used to be         The fourth argument should point to an unsigned char *  variable.  This
1458       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1459       for backwards compatibility.)         tion. External callers can cause PCRE to use  its  internal  tables  by
1460           passing a NULL table pointer.
1461       If there is a fixed first byte, e.g. from a pattern such  as  
1462       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1463       by where. Otherwise, if either  
1464           Return  information  about  the first byte of any matched string, for a
1465       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored pattern. The fourth argument should point to an int  vari-
1466       and every branch starts with "^", or         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1467           is still recognized for backwards compatibility.)
1468       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1469       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
1470       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1471    
1472       -1 is returned, indicating that the pattern matches only  at         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1473       the  start  of  a subject string or after any newline within         branch starts with "^", or
1474       the string. Otherwise -2 is returned. For anchored patterns,  
1475       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1476           set (if it were set, the pattern would be anchored),
1477         PCRE_INFO_FIRSTTABLE  
1478           -1  is  returned, indicating that the pattern matches only at the start
1479       If the pattern was studied, and this resulted  in  the  con-         of a subject string or after any newline within the  string.  Otherwise
1480       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1481       for the first byte in any matching string, a pointer to  the  
1482       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1483       argument should point to an unsigned char * variable.  
1484           If  the pattern was studied, and this resulted in the construction of a
1485         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1486           matching  string, a pointer to the table is returned. Otherwise NULL is
1487       Return the value of the rightmost  literal  byte  that  must         returned. The fourth argument should point to an unsigned char *  vari-
1488       exist  in  any  matched  string, other than at its start, if         able.
1489       such a byte has been recorded. The  fourth  argument  should  
1490       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_JCHANGED
1491       returned. For anchored patterns,  a  last  literal  byte  is  
1492       recorded  only  if  it follows something of variable length.         Return  1  if the (?J) option setting is used in the pattern, otherwise
1493       For example, for the pattern /^a\d+z\d+/ the returned  value         0. The fourth argument should point to an int variable. The (?J) inter-
1494       is "z", but for /^a\dz\d/ the returned value is -1.         nal option setting changes the local PCRE_DUPNAMES option.
1495    
1496         PCRE_INFO_NAMECOUNT           PCRE_INFO_LASTLITERAL
1497         PCRE_INFO_NAMEENTRYSIZE  
1498         PCRE_INFO_NAMETABLE         Return  the  value of the rightmost literal byte that must exist in any
1499           matched string, other than at its  start,  if  such  a  byte  has  been
1500       PCRE supports the use of named as well as numbered capturing         recorded. The fourth argument should point to an int variable. If there
1501       parentheses. The names are just an additional way of identi-         is no such byte, -1 is returned. For anchored patterns, a last  literal
1502       fying the parentheses,  which  still  acquire  a  number.  A         byte  is  recorded only if it follows something of variable length. For
1503       caller  that  wants  to extract data from a named subpattern         example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1504       must convert the name to a number in  order  to  access  the         /^a\dz\d/ the returned value is -1.
1505       correct  pointers  in  the  output  vector  (described  with  
1506       pcre_exec() below). In order to do this, it must  first  use           PCRE_INFO_NAMECOUNT
1507       these  three  values  to  obtain  the name-to-number mapping           PCRE_INFO_NAMEENTRYSIZE
1508       table for the pattern.           PCRE_INFO_NAMETABLE
1509    
1510       The  map  consists  of  a  number  of  fixed-size   entries.         PCRE  supports the use of named as well as numbered capturing parenthe-
1511       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         ses. The names are just an additional way of identifying the  parenthe-
1512       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both         ses, which still acquire numbers. Several convenience functions such as
1513       of  these return an int value. The entry size depends on the         pcre_get_named_substring() are provided for  extracting  captured  sub-
1514       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a         strings  by  name. It is also possible to extract the data directly, by
1515       pointer to the first entry of the table (a pointer to char).         first converting the name to a number in order to  access  the  correct
1516       The first two bytes of each entry are the number of the cap-         pointers in the output vector (described with pcre_exec() below). To do
1517       turing parenthesis, most significant byte first. The rest of         the conversion, you need  to  use  the  name-to-number  map,  which  is
1518       the entry is the corresponding name,  zero  terminated.  The         described by these three values.
1519       names  are  in alphabetical order. For example, consider the  
1520       following pattern (assume PCRE_EXTENDED  is  set,  so  white         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1521       space - including newlines - is ignored):         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1522           of  each  entry;  both  of  these  return  an int value. The entry size
1523         (?P<date> (?P<year>(\d\d)?\d\d) -         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1524         (?P<month>\d\d) - (?P<day>\d\d) )         a  pointer  to  the  first  entry of the table (a pointer to char). The
1525           first two bytes of each entry are the number of the capturing parenthe-
1526       There are four named subpatterns,  so  the  table  has  four         sis,  most  significant byte first. The rest of the entry is the corre-
1527       entries,  and  each  entry in the table is eight bytes long.         sponding name, zero terminated. The names are  in  alphabetical  order.
1528       The table is as follows, with non-printing  bytes  shows  in         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1529       hex, and undefined bytes shown as ??:         theses numbers. For example, consider  the  following  pattern  (assume
1530           PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1531         00 01 d  a  t  e  00 ??         ignored):
1532         00 05 d  a  y  00 ?? ??  
1533         00 04 m  o  n  t  h  00           (?<date> (?<year>(\d\d)?\d\d) -
1534         00 02 y  e  a  r  00 ??           (?<month>\d\d) - (?<day>\d\d) )
1535    
1536       When writing code to extract data  from  named  subpatterns,         There are four named subpatterns, so the table has  four  entries,  and
1537       remember  that the length of each entry may be different for         each  entry  in the table is eight bytes long. The table is as follows,
1538       each compiled pattern.         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1539           as ??:
1540         PCRE_INFO_OPTIONS  
1541             00 01 d  a  t  e  00 ??
1542       Return a copy of the options with which the pattern was com-           00 05 d  a  y  00 ?? ??
1543       piled.  The fourth argument should point to an unsigned long           00 04 m  o  n  t  h  00
1544       int variable. These option bits are those specified  in  the           00 02 y  e  a  r  00 ??
1545       call  to  pcre_compile(),  modified  by any top-level option  
1546       settings within the pattern itself.         When  writing  code  to  extract  data from named subpatterns using the
1547           name-to-number map, remember that the length of the entries  is  likely
1548       A pattern is automatically anchored by PCRE if  all  of  its         to be different for each compiled pattern.
1549       top-level alternatives begin with one of the following:  
1550             PCRE_INFO_OKPARTIAL
1551         ^     unless PCRE_MULTILINE is set  
1552         \A    always         Return  1 if the pattern can be used for partial matching, otherwise 0.
1553         \G    always         The fourth argument should point to an int  variable.  The  pcrepartial
1554         .*    if PCRE_DOTALL is set and there are no back         documentation  lists  the restrictions that apply to patterns when par-
1555                 references to the subpattern in which .* appears         tial matching is used.
1556    
1557       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the           PCRE_INFO_OPTIONS
1558       options returned by pcre_fullinfo().  
1559           Return a copy of the options with which the pattern was  compiled.  The
1560         PCRE_INFO_SIZE         fourth  argument  should  point to an unsigned long int variable. These
1561           option bits are those specified in the call to pcre_compile(), modified
1562       Return the size of the compiled pattern, that is, the  value         by any top-level option settings within the pattern itself.
1563       that  was  passed as the argument to pcre_malloc() when PCRE  
1564       was getting memory in which to place the compiled data.  The         A  pattern  is  automatically  anchored by PCRE if all of its top-level
1565       fourth argument should point to a size_t variable.         alternatives begin with one of the following:
1566    
1567         PCRE_INFO_STUDYSIZE           ^     unless PCRE_MULTILINE is set
1568             \A    always
1569       Returns the size  of  the  data  block  pointed  to  by  the           \G    always
1570       study_data  field  in a pcre_extra block. That is, it is the           .*    if PCRE_DOTALL is set and there are no back
1571       value that was passed to pcre_malloc() when PCRE was getting                   references to the subpattern in which .* appears
1572       memory into which to place the data created by pcre_study().  
1573       The fourth argument should point to a size_t variable.         For such patterns, the PCRE_ANCHORED bit is set in the options returned
1574           by pcre_fullinfo().
1575    
1576             PCRE_INFO_SIZE
1577    
1578           Return  the  size  of the compiled pattern, that is, the value that was
1579           passed as the argument to pcre_malloc() when PCRE was getting memory in
1580           which to place the compiled data. The fourth argument should point to a
1581           size_t variable.
1582    
1583             PCRE_INFO_STUDYSIZE
1584    
1585           Return the size of the data block pointed to by the study_data field in
1586           a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
1587           pcre_malloc() when PCRE was getting memory into which to place the data
1588           created  by  pcre_study(). The fourth argument should point to a size_t
1589           variable.
1590    
1591    
1592  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1593    
1594       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1595    
1596       The pcre_info() function is now obsolete because its  inter-         The pcre_info() function is now obsolete because its interface  is  too
1597       face  is  too  restrictive  to return all the available data         restrictive  to return all the available data about a compiled pattern.
1598       about  a  compiled  pattern.   New   programs   should   use         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1599       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info()  is the number of capturing subpatterns, or one of the fol-
1600       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1601       negative numbers:  
1602             PCRE_ERROR_NULL       the argument code was NULL
1603         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1604         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1605           If the optptr argument is not NULL, a copy of the  options  with  which
1606       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
1607       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1608       it points to (see PCRE_INFO_OPTIONS above).  
1609           If the pattern is not anchored and the  firstcharptr  argument  is  not
1610       If the pattern is not anchored and the firstcharptr argument         NULL,  it is used to pass back information about the first character of
1611       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1612       first    character    of    any    matched    string    (see  
1613       PCRE_INFO_FIRSTBYTE above).  
1614    REFERENCE COUNTS
1615    
1616           int pcre_refcount(pcre *code, int adjust);
1617    
1618           The pcre_refcount() function is used to maintain a reference  count  in
1619           the data block that contains a compiled pattern. It is provided for the
1620           benefit of applications that  operate  in  an  object-oriented  manner,
1621           where different parts of the application may be using the same compiled
1622           pattern, but you want to free the block when they are all done.
1623    
1624           When a pattern is compiled, the reference count field is initialized to
1625           zero.   It is changed only by calling this function, whose action is to
1626           add the adjust value (which may be positive or  negative)  to  it.  The
1627           yield of the function is the new value. However, the value of the count
1628           is constrained to lie between 0 and 65535, inclusive. If the new  value
1629           is outside these limits, it is forced to the appropriate limit value.
1630    
1631           Except  when it is zero, the reference count is not correctly preserved
1632           if a pattern is compiled on one host and then  transferred  to  a  host
1633           whose byte-order is different. (This seems a highly unlikely scenario.)
1634    
1635    
1636    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1637    
1638           int pcre_exec(const pcre *code, const pcre_extra *extra,
1639                const char *subject, int length, int startoffset,
1640                int options, int *ovector, int ovecsize);
1641    
1642           The function pcre_exec() is called to match a subject string against  a
1643           compiled  pattern, which is passed in the code argument. If the pattern
1644           has been studied, the result of the study should be passed in the extra
1645           argument.  This  function is the main matching facility of the library,
1646           and it operates in a Perl-like manner. For specialist use there is also
1647           an  alternative matching function, which is described below in the sec-
1648           tion about the pcre_dfa_exec() function.
1649    
1650           In most applications, the pattern will have been compiled (and  option-
1651           ally  studied)  in the same process that calls pcre_exec(). However, it
1652           is possible to save compiled patterns and study data, and then use them
1653           later  in  different processes, possibly even on different hosts. For a
1654           discussion about this, see the pcreprecompile documentation.
1655    
1656           Here is an example of a simple call to pcre_exec():
1657    
1658             int rc;
1659             int ovector[30];
1660             rc = pcre_exec(
1661               re,             /* result of pcre_compile() */
1662               NULL,           /* we didn't study the pattern */
1663               "some string",  /* the subject string */
1664               11,             /* the length of the subject string */
1665               0,              /* start at offset 0 in the subject */
1666               0,              /* default options */
1667               ovector,        /* vector of integers for substring information */
1668               30);            /* number of elements (NOT size in bytes) */
1669    
1670       Extra data for pcre_exec()
1671    
1672           If the extra argument is not NULL, it must point to a  pcre_extra  data
1673           block.  The pcre_study() function returns such a block (when it doesn't
1674           return NULL), but you can also create one for yourself, and pass  addi-
1675           tional  information  in it. The pcre_extra block contains the following
1676           fields (not necessarily in this order):
1677    
1678             unsigned long int flags;
1679             void *study_data;
1680             unsigned long int match_limit;
1681             unsigned long int match_limit_recursion;
1682             void *callout_data;
1683             const unsigned char *tables;
1684    
1685           The flags field is a bitmap that specifies which of  the  other  fields
1686           are set. The flag bits are:
1687    
1688             PCRE_EXTRA_STUDY_DATA
1689             PCRE_EXTRA_MATCH_LIMIT
1690             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1691             PCRE_EXTRA_CALLOUT_DATA
1692             PCRE_EXTRA_TABLES
1693    
1694           Other  flag  bits should be set to zero. The study_data field is set in
1695           the pcre_extra block that is returned by  pcre_study(),  together  with
1696           the appropriate flag bit. You should not set this yourself, but you may
1697           add to the block by setting the other fields  and  their  corresponding
1698           flag bits.
1699    
1700           The match_limit field provides a means of preventing PCRE from using up
1701           a vast amount of resources when running patterns that are not going  to
1702           match,  but  which  have  a very large number of possibilities in their
1703           search trees. The classic  example  is  the  use  of  nested  unlimited
1704           repeats.
1705    
1706           Internally,  PCRE uses a function called match() which it calls repeat-
1707           edly (sometimes recursively). The limit set by match_limit  is  imposed
1708           on  the  number  of times this function is called during a match, which
1709           has the effect of limiting the amount of  backtracking  that  can  take
1710           place. For patterns that are not anchored, the count restarts from zero
1711           for each position in the subject string.
1712    
1713           The default value for the limit can be set  when  PCRE  is  built;  the
1714           default  default  is 10 million, which handles all but the most extreme
1715           cases. You can override the default  by  suppling  pcre_exec()  with  a
1716           pcre_extra     block    in    which    match_limit    is    set,    and
1717           PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
1718           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1719    
1720           The  match_limit_recursion field is similar to match_limit, but instead
1721           of limiting the total number of times that match() is called, it limits
1722           the  depth  of  recursion. The recursion depth is a smaller number than
1723           the total number of calls, because not all calls to match() are  recur-
1724           sive.  This limit is of use only if it is set smaller than match_limit.
1725    
1726           Limiting the recursion depth limits the amount of  stack  that  can  be
1727           used, or, when PCRE has been compiled to use memory on the heap instead
1728           of the stack, the amount of heap memory that can be used.
1729    
1730           The default value for match_limit_recursion can be  set  when  PCRE  is
1731           built;  the  default  default  is  the  same  value  as the default for
1732           match_limit. You can override the default by suppling pcre_exec()  with
1733           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1734           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1735           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1736    
1737           The  pcre_callout  field is used in conjunction with the "callout" fea-
1738           ture, which is described in the pcrecallout documentation.
1739    
1740           The tables field  is  used  to  pass  a  character  tables  pointer  to
1741           pcre_exec();  this overrides the value that is stored with the compiled
1742           pattern. A non-NULL value is stored with the compiled pattern  only  if
1743           custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1744           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1745           PCRE's  internal  tables  to be used. This facility is helpful when re-
1746           using patterns that have been saved after compiling  with  an  external
1747           set  of  tables,  because  the  external tables might be at a different
1748           address when pcre_exec() is called. See the  pcreprecompile  documenta-
1749           tion for a discussion of saving compiled patterns for later use.
1750    
1751       Option bits for pcre_exec()
1752    
1753           The  unused  bits of the options argument for pcre_exec() must be zero.
1754           The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1755           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1756           PCRE_PARTIAL.
1757    
1758             PCRE_ANCHORED
1759    
1760           The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1761           matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1762           turned out to be anchored by virtue of its contents, it cannot be  made
1763           unachored at matching time.
1764    
1765             PCRE_NEWLINE_CR
1766             PCRE_NEWLINE_LF
1767             PCRE_NEWLINE_CRLF
1768             PCRE_NEWLINE_ANYCRLF
1769             PCRE_NEWLINE_ANY
1770    
1771           These  options  override  the  newline  definition  that  was chosen or
1772           defaulted when the pattern was compiled. For details, see the  descrip-
1773           tion  of  pcre_compile()  above.  During  matching,  the newline choice
1774           affects the behaviour of the dot, circumflex,  and  dollar  metacharac-
1775           ters.  It may also alter the way the match position is advanced after a
1776           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1777           PCRE_NEWLINE_ANYCRLF,  or  PCRE_NEWLINE_ANY is set, and a match attempt
1778           fails when the current position is at a CRLF sequence, the match  posi-
1779           tion  is  advanced by two characters instead of one, in other words, to
1780           after the CRLF.
1781    
1782             PCRE_NOTBOL
1783    
1784           This option specifies that first character of the subject string is not
1785           the  beginning  of  a  line, so the circumflex metacharacter should not
1786           match before it. Setting this without PCRE_MULTILINE (at compile  time)
1787           causes  circumflex  never to match. This option affects only the behav-
1788           iour of the circumflex metacharacter. It does not affect \A.
1789    
1790             PCRE_NOTEOL
1791    
1792           This option specifies that the end of the subject string is not the end
1793           of  a line, so the dollar metacharacter should not match it nor (except
1794           in multiline mode) a newline immediately before it. Setting this  with-
1795           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1796           option affects only the behaviour of the dollar metacharacter. It  does
1797           not affect \Z or \z.
1798    
1799             PCRE_NOTEMPTY
1800    
1801           An empty string is not considered to be a valid match if this option is
1802           set. If there are alternatives in the pattern, they are tried.  If  all
1803           the  alternatives  match  the empty string, the entire match fails. For
1804           example, if the pattern
1805    
1806             a?b?
1807    
1808           is applied to a string not beginning with "a" or "b",  it  matches  the
1809           empty  string at the start of the subject. With PCRE_NOTEMPTY set, this
1810           match is not valid, so PCRE searches further into the string for occur-
1811           rences of "a" or "b".
1812    
1813           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1814           cial case of a pattern match of the empty  string  within  its  split()
1815           function,  and  when  using  the /g modifier. It is possible to emulate
1816           Perl's behaviour after matching a null string by first trying the match
1817           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1818           if that fails by advancing the starting offset (see below)  and  trying
1819           an ordinary match again. There is some code that demonstrates how to do
1820           this in the pcredemo.c sample program.
1821    
1822             PCRE_NO_UTF8_CHECK
1823    
1824           When PCRE_UTF8 is set at compile time, the validity of the subject as a
1825           UTF-8  string is automatically checked when pcre_exec() is subsequently
1826           called.  The value of startoffset is also checked  to  ensure  that  it
1827           points  to the start of a UTF-8 character. If an invalid UTF-8 sequence
1828           of bytes is found, pcre_exec() returns the error PCRE_ERROR_BADUTF8. If
1829           startoffset  contains  an  invalid  value, PCRE_ERROR_BADUTF8_OFFSET is
1830           returned.
1831    
1832           If you already know that your subject is valid, and you  want  to  skip
1833           these    checks    for   performance   reasons,   you   can   set   the
1834           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1835           do  this  for the second and subsequent calls to pcre_exec() if you are
1836           making repeated calls to find all  the  matches  in  a  single  subject
1837           string.  However,  you  should  be  sure  that the value of startoffset
1838           points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1839           set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1840           value of startoffset that does not point to the start of a UTF-8  char-
1841           acter, is undefined. Your program may crash.
1842    
1843             PCRE_PARTIAL
1844    
1845           This  option  turns  on  the  partial  matching feature. If the subject
1846           string fails to match the pattern, but at some point during the  match-
1847           ing  process  the  end of the subject was reached (that is, the subject
1848           partially matches the pattern and the failure to  match  occurred  only
1849           because  there were not enough subject characters), pcre_exec() returns
1850           PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1851           used,  there  are restrictions on what may appear in the pattern. These
1852           are discussed in the pcrepartial documentation.
1853    
1854       The string to be matched by pcre_exec()
1855    
1856           The subject string is passed to pcre_exec() as a pointer in subject,  a
1857           length  in  length, and a starting byte offset in startoffset. In UTF-8
1858           mode, the byte offset must point to the start  of  a  UTF-8  character.
1859           Unlike  the  pattern string, the subject may contain binary zero bytes.
1860           When the starting offset is zero, the search for a match starts at  the
1861           beginning of the subject, and this is by far the most common case.
1862    
1863           A  non-zero  starting offset is useful when searching for another match
1864           in the same subject by calling pcre_exec() again after a previous  suc-
1865           cess.   Setting  startoffset differs from just passing over a shortened
1866           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1867           with any kind of lookbehind. For example, consider the pattern
1868    
1869             \Biss\B
1870    
1871           which  finds  occurrences  of "iss" in the middle of words. (\B matches
1872           only if the current position in the subject is not  a  word  boundary.)
1873           When  applied  to the string "Mississipi" the first call to pcre_exec()
1874           finds the first occurrence. If pcre_exec() is called  again  with  just
1875           the  remainder  of  the  subject,  namely  "issipi", it does not match,
1876           because \B is always false at the start of the subject, which is deemed
1877           to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1878           string again, but with startoffset set to 4, it finds the second occur-
1879           rence  of "iss" because it is able to look behind the starting point to
1880           discover that it is preceded by a letter.
1881    
1882           If a non-zero starting offset is passed when the pattern  is  anchored,
1883           one attempt to match at the given offset is made. This can only succeed
1884           if the pattern does not require the match to be at  the  start  of  the
1885           subject.
1886    
1887       How pcre_exec() returns captured substrings
1888    
1889           In  general, a pattern matches a certain portion of the subject, and in
1890           addition, further substrings from the subject  may  be  picked  out  by
1891           parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1892           this is called "capturing" in what follows, and the  phrase  "capturing
1893           subpattern"  is  used for a fragment of a pattern that picks out a sub-
1894           string. PCRE supports several other kinds of  parenthesized  subpattern
1895           that do not cause substrings to be captured.
1896    
1897           Captured  substrings are returned to the caller via a vector of integer
1898           offsets whose address is passed in ovector. The number of  elements  in
1899           the  vector is passed in ovecsize, which must be a non-negative number.
1900           Note: this argument is NOT the size of ovector in bytes.
1901    
1902           The first two-thirds of the vector is used to pass back  captured  sub-
1903           strings,  each  substring using a pair of integers. The remaining third
1904           of the vector is used as workspace by pcre_exec() while  matching  cap-
1905           turing  subpatterns, and is not available for passing back information.
1906           The length passed in ovecsize should always be a multiple of three.  If
1907           it is not, it is rounded down.
1908    
1909           When  a  match  is successful, information about captured substrings is
1910           returned in pairs of integers, starting at the  beginning  of  ovector,
1911           and  continuing  up  to two-thirds of its length at the most. The first
1912           element of a pair is set to the offset of the first character in a sub-
1913           string,  and  the  second  is  set to the offset of the first character
1914           after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1915           tor[1],  identify  the  portion  of  the  subject string matched by the
1916           entire pattern. The next pair is used for the first  capturing  subpat-
1917           tern, and so on. The value returned by pcre_exec() is one more than the
1918           highest numbered pair that has been set. For example, if two substrings
1919           have  been captured, the returned value is 3. If there are no capturing
1920           subpatterns, the return value from a successful match is 1,  indicating
1921           that just the first pair of offsets has been set.
1922    
1923           If a capturing subpattern is matched repeatedly, it is the last portion
1924           of the string that it matched that is returned.
1925    
1926           If the vector is too small to hold all the captured substring  offsets,
1927           it is used as far as possible (up to two-thirds of its length), and the
1928           function returns a value of zero. In particular, if the substring  off-
1929           sets are not of interest, pcre_exec() may be called with ovector passed
1930           as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1931           references  and  the  ovector is not big enough to remember the related
1932           substrings, PCRE has to get additional memory for use during  matching.
1933           Thus it is usually advisable to supply an ovector.
1934    
1935           The  pcre_info()  function  can  be used to find out how many capturing
1936           subpatterns there are in a compiled  pattern.  The  smallest  size  for
1937           ovector  that  will allow for n captured substrings, in addition to the
1938           offsets of the substring matched by the whole pattern, is (n+1)*3.
1939    
1940           It is possible for capturing subpattern number n+1 to match  some  part
1941           of the subject when subpattern n has not been used at all. For example,
1942           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1943           return from the function is 4, and subpatterns 1 and 3 are matched, but
1944           2 is not. When this happens, both values in  the  offset  pairs  corre-
1945           sponding to unused subpatterns are set to -1.
1946    
1947           Offset  values  that correspond to unused subpatterns at the end of the
1948           expression are also set to -1. For example,  if  the  string  "abc"  is
1949           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1950           matched. The return from the function is 2, because  the  highest  used
1951           capturing subpattern number is 1. However, you can refer to the offsets
1952           for the second and third capturing subpatterns if  you  wish  (assuming
1953           the vector is large enough, of course).
1954    
1955           Some  convenience  functions  are  provided for extracting the captured
1956           substrings as separate strings. These are described below.
1957    
1958       Error return values from pcre_exec()
1959    
1960           If pcre_exec() fails, it returns a negative number. The  following  are
1961           defined in the header file:
1962    
1963             PCRE_ERROR_NOMATCH        (-1)
1964    
1965           The subject string did not match the pattern.
1966    
1967             PCRE_ERROR_NULL           (-2)
1968    
1969           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
1970           ovecsize was not zero.
1971    
1972             PCRE_ERROR_BADOPTION      (-3)
1973    
1974           An unrecognized bit was set in the options argument.
1975    
1976             PCRE_ERROR_BADMAGIC       (-4)
1977    
1978           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
1979           to catch the case when it is passed a junk pointer and to detect when a
1980           pattern that was compiled in an environment of one endianness is run in
1981           an  environment  with the other endianness. This is the error that PCRE
1982           gives when the magic number is not present.
1983    
1984             PCRE_ERROR_UNKNOWN_OPCODE (-5)
1985    
1986           While running the pattern match, an unknown item was encountered in the
1987           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
1988           overwriting of the compiled pattern.
1989    
1990             PCRE_ERROR_NOMEMORY       (-6)
1991    
1992           If a pattern contains back references, but the ovector that  is  passed
1993           to pcre_exec() is not big enough to remember the referenced substrings,
1994           PCRE gets a block of memory at the start of matching to  use  for  this
1995           purpose.  If the call via pcre_malloc() fails, this error is given. The
1996           memory is automatically freed at the end of matching.
1997    
1998             PCRE_ERROR_NOSUBSTRING    (-7)
1999    
2000           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2001           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2002           returned by pcre_exec().
2003    
2004             PCRE_ERROR_MATCHLIMIT     (-8)
2005    
2006           The backtracking limit, as specified by  the  match_limit  field  in  a
2007           pcre_extra  structure  (or  defaulted) was reached. See the description
2008           above.
2009    
2010             PCRE_ERROR_CALLOUT        (-9)
2011    
2012           This error is never generated by pcre_exec() itself. It is provided for
2013           use  by  callout functions that want to yield a distinctive error code.
2014           See the pcrecallout documentation for details.
2015    
2016             PCRE_ERROR_BADUTF8        (-10)
2017    
2018           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2019           subject.
2020    
2021             PCRE_ERROR_BADUTF8_OFFSET (-11)
2022    
2023           The UTF-8 byte sequence that was passed as a subject was valid, but the
2024           value of startoffset did not point to the beginning of a UTF-8  charac-
2025           ter.
2026    
2027             PCRE_ERROR_PARTIAL        (-12)
2028    
2029           The  subject  string did not match, but it did match partially. See the
2030           pcrepartial documentation for details of partial matching.
2031    
2032             PCRE_ERROR_BADPARTIAL     (-13)
2033    
2034           The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2035           items  that are not supported for partial matching. See the pcrepartial
2036           documentation for details of partial matching.
2037    
2038             PCRE_ERROR_INTERNAL       (-14)
2039    
2040           An unexpected internal error has occurred. This error could  be  caused
2041           by a bug in PCRE or by overwriting of the compiled pattern.
2042    
2043             PCRE_ERROR_BADCOUNT       (-15)
2044    
2045           This  error is given if the value of the ovecsize argument is negative.
2046    
2047             PCRE_ERROR_RECURSIONLIMIT (-21)
2048    
2049           The internal recursion limit, as specified by the match_limit_recursion
2050           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2051           description above.
2052    
2053             PCRE_ERROR_NULLWSLIMIT    (-22)
2054    
2055           When a group that can match an empty  substring  is  repeated  with  an
2056           unbounded  upper  limit, the subject position at the start of the group
2057           must be remembered, so that a test for an empty string can be made when
2058           the  end  of the group is reached. Some workspace is required for this;
2059           if it runs out, this error is given.
2060    
2061             PCRE_ERROR_BADNEWLINE     (-23)
2062    
2063  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2064    
2065       int pcre_exec(const pcre *code, const pcre_extra *extra,         Error numbers -16 to -20 are not used by pcre_exec().
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
   
      The function pcre_exec() is called to match a subject string  
      against  a pre-compiled pattern, which is passed in the code  
      argument. If the pattern has been studied, the result of the  
      study should be passed in the extra argument.  
   
      Here is an example of a simple call to pcre_exec():  
   
        int rc;  
        int ovector[30];  
        rc = pcre_exec(  
          re,             /* result of pcre_compile() */  
          NULL,           /* we didn't study the pattern */  
          "some string",  /* the subject string */  
          11,             /* the length of the subject string */  
          0,              /* start at offset 0 in the subject */  
          0,              /* default options */  
          ovector,        /* vector for substring information */  
          30);            /* number of elements in the vector */  
   
      If the extra argument is  not  NULL,  it  must  point  to  a  
      pcre_extra  data  block.  The  pcre_study() function returns  
      such a block (when it doesn't return NULL), but you can also  
      create  one for yourself, and pass additional information in  
      it. The fields in the block are as follows:  
   
        unsigned long int flags;  
        void *study_data;  
        unsigned long int match_limit;  
        void *callout_data;  
   
      The flags field is a bitmap  that  specifies  which  of  the  
      other fields are set. The flag bits are:  
   
        PCRE_EXTRA_STUDY_DATA  
        PCRE_EXTRA_MATCH_LIMIT  
        PCRE_EXTRA_CALLOUT_DATA  
   
      Other flag bits should be set to zero. The study_data  field  
      is   set  in  the  pcre_extra  block  that  is  returned  by  
      pcre_study(), together with the appropriate  flag  bit.  You  
      should  not  set this yourself, but you can add to the block  
      by setting the other fields.  
   
      The match_limit field provides a means  of  preventing  PCRE  
      from  using  up a vast amount of resources when running pat-  
      terns that are not going to match, but  which  have  a  very  
      large  number  of  possibilities  in their search trees. The  
      classic example is the  use  of  nested  unlimited  repeats.  
      Internally,  PCRE  uses  a  function called match() which it  
      calls  repeatedly  (sometimes  recursively).  The  limit  is  
      imposed  on the number of times this function is called dur-  
      ing a match, which has the effect of limiting the amount  of  
      recursion and backtracking that can take place. For patterns  
      that are not anchored, the count starts from zero  for  each  
      position in the subject string.  
   
      The default limit for the library can be set  when  PCRE  is  
      built;  the default default is 10 million, which handles all  
      but the most extreme cases. You can reduce  the  default  by  
      suppling  pcre_exec()  with  a  pcre_extra  block  in  which  
      match_limit   is   set   to    a    smaller    value,    and  
      PCRE_EXTRA_MATCH_LIMIT  is  set  in  the flags field. If the  
      limit      is      exceeded,       pcre_exec()       returns  
      PCRE_ERROR_MATCHLIMIT.  
   
      The pcre_callout field is used in conjunction with the "cal-  
      lout"  feature,  which is described in the pcrecallout docu-  
      mentation.  
   
      The PCRE_ANCHORED option can be passed in the options  argu-  
      ment,   whose   unused   bits  must  be  zero.  This  limits  
      pcre_exec() to matching at the first matching position. How-  
      ever,  if  a  pattern  was  compiled  with PCRE_ANCHORED, or  
      turned out to be anchored by virtue of its contents, it can-  
      not be made unachored at matching time.  
   
      There are also three further options that can be set only at  
      matching time:  
   
        PCRE_NOTBOL  
   
      The first character of the string is not the beginning of  a  
      line,  so  the  circumflex  metacharacter  should  not match  
      before it. Setting this without PCRE_MULTILINE  (at  compile  
      time) causes circumflex never to match.  
   
        PCRE_NOTEOL  
   
      The end of the string is not the end of a line, so the  dol-  
      lar  metacharacter should not match it nor (except in multi-  
      line mode) a newline immediately  before  it.  Setting  this  
      without PCRE_MULTILINE (at compile time) causes dollar never  
      to match.  
   
        PCRE_NOTEMPTY  
   
      An empty string is not considered to be  a  valid  match  if  
      this  option  is  set. If there are alternatives in the pat-  
      tern, they are tried. If  all  the  alternatives  match  the  
      empty  string,  the  entire match fails. For example, if the  
      pattern  
   
        a?b?  
   
      is applied to a string not beginning with  "a"  or  "b",  it  
      matches  the  empty string at the start of the subject. With  
      PCRE_NOTEMPTY set, this match is not valid, so PCRE searches  
      further into the string for occurrences of "a" or "b".  
   
      Perl has no direct equivalent of PCRE_NOTEMPTY, but it  does  
      make  a  special case of a pattern match of the empty string  
      within its split() function, and when using the /g modifier.  
      It  is possible to emulate Perl's behaviour after matching a  
      null string by first trying the  match  again  at  the  same  
      offset  with  PCRE_NOTEMPTY  set,  and then if that fails by  
      advancing the starting offset  (see  below)  and  trying  an  
      ordinary match again.  
   
      The subject string is passed to pcre_exec() as a pointer  in  
      subject,  a length in length, and a starting offset in star-  
      toffset. Unlike the pattern string, the subject may  contain  
      binary  zero  bytes.  When  the starting offset is zero, the  
      search for a match starts at the beginning of  the  subject,  
      and this is by far the most common case.  
   
      If the pattern was compiled with the PCRE_UTF8  option,  the  
      subject  must  be  a sequence of bytes that is a valid UTF-8  
      string.  If  an  invalid  UTF-8  string  is  passed,  PCRE's  
      behaviour is not defined.  
   
      A non-zero starting offset  is  useful  when  searching  for  
      another  match  in  the  same subject by calling pcre_exec()  
      again after a previous success.  Setting startoffset differs  
      from  just  passing  over  a  shortened  string  and setting  
      PCRE_NOTBOL in the case of a pattern that  begins  with  any  
      kind of lookbehind. For example, consider the pattern  
   
        \Biss\B  
   
      which finds occurrences of "iss" in the middle of words. (\B  
      matches only if the current position in the subject is not a  
      word boundary.) When applied to the string "Mississipi"  the  
      first  call  to  pcre_exec()  finds the first occurrence. If  
      pcre_exec() is called again with just the remainder  of  the  
      subject,  namely  "issipi", it does not match, because \B is  
      always false at the start of the subject, which is deemed to  
      be  a  word  boundary. However, if pcre_exec() is passed the  
      entire string again, but with startoffset set to 4, it finds  
      the  second  occurrence  of "iss" because it is able to look  
      behind the starting point to discover that it is preceded by  
      a letter.  
   
      If a non-zero starting offset is passed when the pattern  is  
      anchored, one attempt to match at the given offset is tried.  
      This can only succeed if the pattern does  not  require  the  
      match to be at the start of the subject.  
   
      In general, a pattern matches a certain portion of the  sub-  
      ject,  and  in addition, further substrings from the subject  
      may be picked out by parts of  the  pattern.  Following  the  
      usage  in  Jeffrey Friedl's book, this is called "capturing"  
      in what follows, and the phrase  "capturing  subpattern"  is  
      used for a fragment of a pattern that picks out a substring.  
      PCRE supports several other kinds of  parenthesized  subpat-  
      tern that do not cause substrings to be captured.  
   
      Captured substrings are returned to the caller via a  vector  
      of  integer  offsets whose address is passed in ovector. The  
      number of elements in the vector is passed in ovecsize.  The  
      first two-thirds of the vector is used to pass back captured  
      substrings, each substring using a  pair  of  integers.  The  
      remaining  third  of  the  vector  is  used  as workspace by  
      pcre_exec() while matching capturing subpatterns, and is not  
      available for passing back information. The length passed in  
      ovecsize should always be a multiple of three. If it is not,  
      it is rounded down.  
   
      When a match has been successful, information about captured  
      substrings is returned in pairs of integers, starting at the  
      beginning of ovector, and continuing up to two-thirds of its  
      length  at  the  most. The first element of a pair is set to  
      the offset of the first character in a  substring,  and  the  
      second is set to the offset of the first character after the  
      end of a substring. The first  pair,  ovector[0]  and  ovec-  
      tor[1],  identify  the portion of the subject string matched  
      by the entire pattern. The next pair is used for  the  first  
      capturing  subpattern,  and  so  on.  The  value returned by  
      pcre_exec() is the number of pairs that have  been  set.  If  
      there  are no capturing subpatterns, the return value from a  
      successful match is 1, indicating that just the  first  pair  
      of offsets has been set.  
   
      Some convenience functions are provided for  extracting  the  
      captured substrings as separate strings. These are described  
      in the following section.  
   
      It is possible for an capturing  subpattern  number  n+1  to  
      match  some  part  of  the subject when subpattern n has not  
      been used at all.  For  example,  if  the  string  "abc"  is  
      matched  against the pattern (a|(z))(bc) subpatterns 1 and 3  
      are matched, but 2 is not. When this  happens,  both  offset  
      values corresponding to the unused subpattern are set to -1.  
   
      If a capturing subpattern is matched repeatedly, it  is  the  
      last  portion  of  the  string  that  it  matched  that gets  
      returned.  
   
      If the vector is too small to hold  all  the  captured  sub-  
      strings,  it is used as far as possible (up to two-thirds of  
      its length), and the function returns a value  of  zero.  In  
      particular,  if  the  substring offsets are not of interest,  
      pcre_exec() may be called with ovector passed  as  NULL  and  
      ovecsize  as  zero.  However,  if  the pattern contains back  
      references and the ovector isn't big enough to remember  the  
      related  substrings,  PCRE  has to get additional memory for  
      use during matching. Thus it is usually advisable to  supply  
      an ovector.  
   
      Note that pcre_info() can be used to find out how many  cap-  
      turing  subpatterns  there  are  in  a compiled pattern. The  
      smallest size for ovector that will  allow  for  n  captured  
      substrings,  in  addition  to  the  offsets of the substring  
      matched by the whole pattern, is (n+1)*3.  
   
      If pcre_exec() fails, it returns a negative number. The fol-  
      lowing are defined in the header file:  
   
        PCRE_ERROR_NOMATCH        (-1)  
   
      The subject string did not match the pattern.  
   
        PCRE_ERROR_NULL           (-2)  
   
      Either code or subject was passed as NULL,  or  ovector  was  
      NULL and ovecsize was not zero.  
   
        PCRE_ERROR_BADOPTION      (-3)  
   
      An unrecognized bit was set in the options argument.  
   
        PCRE_ERROR_BADMAGIC       (-4)  
   
      PCRE stores a 4-byte "magic number" at the start of the com-  
      piled  code,  to  catch  the  case  when it is passed a junk  
      pointer. This is the error it gives when  the  magic  number  
      isn't present.  
   
        PCRE_ERROR_UNKNOWN_NODE   (-5)  
   
      While running the pattern match, an unknown item was encoun-  
      tered in the compiled pattern. This error could be caused by  
      a bug in PCRE or by overwriting of the compiled pattern.  
   
        PCRE_ERROR_NOMEMORY       (-6)  
   
      If a pattern contains back references, but the ovector  that  
      is  passed  to pcre_exec() is not big enough to remember the  
      referenced substrings, PCRE gets a block of  memory  at  the  
      start  of  matching to use for this purpose. If the call via  
      pcre_malloc() fails, this error  is  given.  The  memory  is  
      freed at the end of matching.  
   
        PCRE_ERROR_NOSUBSTRING    (-7)  
   
      This   error   is   used   by   the   pcre_copy_substring(),  
      pcre_get_substring(),  and  pcre_get_substring_list()  func-  
      tions (see below). It is never returned by pcre_exec().  
   
        PCRE_ERROR_MATCHLIMIT     (-8)  
   
      The recursion and backtracking limit, as  specified  by  the  
      match_limit  field  in a pcre_extra structure (or defaulted)  
      was reached. See the description above.  
   
        PCRE_ERROR_CALLOUT        (-9)  
   
      This error is never generated by pcre_exec() itself.  It  is  
      provided  for  use by callout functions that want to yield a  
      distinctive error code. See  the  pcrecallout  documentation  
      for details.  
2066    
2067    
2068  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2069    
2070       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2071            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2072            int buffersize);              int buffersize);
2073    
2074       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2075            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2076            const char **stringptr);              const char **stringptr);
2077    
2078       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2079            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2080    
2081       Captured substrings can be accessed directly  by  using  the         Captured substrings can be  accessed  directly  by  using  the  offsets
2082       offsets returned by pcre_exec() in ovector. For convenience,         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2083       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2084       and  pcre_get_substring_list()  are  provided for extracting         string_list()  are  provided for extracting captured substrings as new,
2085       captured  substrings  as  new,   separate,   zero-terminated         separate, zero-terminated strings. These functions identify  substrings
2086       strings.  These functions identify substrings by number. The         by  number.  The  next section describes functions for extracting named
2087       next section describes functions for extracting  named  sub-         substrings.
2088       strings.   A  substring  that  contains  a  binary  zero  is  
2089       correctly extracted and has a further zero added on the end,         A substring that contains a binary zero is correctly extracted and  has
2090       but the result is not, of course, a C string.         a  further zero added on the end, but the result is not, of course, a C
2091           string.  However, you can process such a string  by  referring  to  the
2092       The first three arguments are the  same  for  all  three  of         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2093       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2094       just been successfully matched, ovector is a pointer to  the         not  adequate for handling strings containing binary zeros, because the
2095       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2096       and stringcount is the number of substrings that  were  cap-  
2097       tured by the match, including the substring that matched the         The first three arguments are the same for all  three  of  these  func-
2098       entire regular expression. This is  the  value  returned  by         tions:  subject  is  the subject string that has just been successfully
2099       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2100       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2101       tor,  the  value passed as stringcount should be the size of         were captured by the match, including the substring  that  matched  the
2102       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2103           it is greater than zero. If pcre_exec() returned zero, indicating  that
2104       The functions pcre_copy_substring() and pcre_get_substring()         it  ran out of space in ovector, the value passed as stringcount should
2105       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2106       number. A value of zero extracts the substring that  matched  
2107       the entire pattern, while higher values extract the captured         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2108       substrings. For pcre_copy_substring(), the string is  placed         single  substring,  whose  number  is given as stringnumber. A value of
2109       in  buffer,  whose  length is given by buffersize, while for         zero extracts the substring that matched the  entire  pattern,  whereas
2110       pcre_get_substring() a new block of memory is  obtained  via         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2111       pcre_malloc,  and its address is returned via stringptr. The         string(), the string is placed in buffer,  whose  length  is  given  by
2112       yield of the function is  the  length  of  the  string,  not         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2113       including the terminating zero, or one of         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2114           The  yield  of  the function is the length of the string, not including
2115         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2116    
2117       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2118       attempt to get memory failed for pcre_get_substring().  
2119           The buffer was too small for pcre_copy_substring(), or the  attempt  to
2120         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2121    
2122       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2123    
2124       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2125       able  substrings  and builds a list of pointers to them. All  
2126       this is done in a single block of memory which  is  obtained         The  pcre_get_substring_list()  function  extracts  all  available sub-
2127       via pcre_malloc. The address of the memory block is returned         strings and builds a list of pointers to them. All this is  done  in  a
2128       via listptr, which is also the start of the list  of  string         single block of memory that is obtained via pcre_malloc. The address of
2129       pointers.  The  end of the list is marked by a NULL pointer.         the memory block is returned via listptr, which is also  the  start  of
2130       The yield of the function is zero if all went well, or         the  list  of  string pointers. The end of the list is marked by a NULL
2131           pointer. The yield of the function is zero if all  went  well,  or  the
2132         PCRE_ERROR_NOMEMORY       (-6)         error code
2133    
2134       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2135    
2136       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2137       unset, which can happen when capturing subpattern number n+1  
2138       matches some part of the subject, but subpattern n  has  not         When  any of these functions encounter a substring that is unset, which
2139       been  used  at all, they return an empty string. This can be         can happen when capturing subpattern number n+1 matches  some  part  of
2140       distinguished  from  a  genuine  zero-length  substring   by         the  subject, but subpattern n has not been used at all, they return an
2141       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2142       tive for unset substrings.         string  by inspecting the appropriate offset in ovector, which is nega-
2143           tive for unset substrings.
2144       The  two  convenience  functions  pcre_free_substring()  and  
2145       pcre_free_substring_list()  can  be  used to free the memory         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2146       returned by  a  previous  call  of  pcre_get_substring()  or         string_list()  can  be  used  to free the memory returned by a previous
2147       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2148       more than call the function pointed to by  pcre_free,  which         tively.  They  do  nothing  more  than  call the function pointed to by
2149       of  course  could  be called directly from a C program. How-         pcre_free, which of course could be called directly from a  C  program.
2150       ever, PCRE is used in some situations where it is linked via         However,  PCRE is used in some situations where it is linked via a spe-
2151       a  special  interface  to another programming language which         cial  interface  to  another  programming  language  that  cannot   use
2152       cannot use pcre_free directly; it is for  these  cases  that         pcre_free  directly;  it is for these cases that the functions are pro-
2153       the functions are provided.         vided.
2154    
2155    
2156  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2157    
2158       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2159            const char *subject, int *ovector,              const char *name);
2160            int stringcount, const char *stringname,  
2161            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2162                const char *subject, int *ovector,
2163       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2164            const char *name);              char *buffer, int buffersize);
2165    
2166       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2167            const char *subject, int *ovector,              const char *subject, int *ovector,
2168            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2169            const char **stringptr);              const char **stringptr);
2170    
2171       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-
2172       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2173       pcre_get_stringnumber(). The first argument is the  compiled  
2174       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2175       pattern  
2176           the number of the subpattern called "xxx" is 2. If the name is known to
2177         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2178           name by calling pcre_get_stringnumber(). The first argument is the com-
2179       the number of the subpattern called "xxx" is  1.  Given  the         piled pattern, and the second is the name. The yield of the function is
2180       number,  you can then extract the substring directly, or use         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2181       one of the functions described in the previous section.  For         subpattern of that name.
2182       convenience,  there are also two functions that do the whole  
2183       job.         Given the number, you can extract the substring directly, or use one of
2184           the functions described in the previous section. For convenience, there
2185       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2186       pcre_get_named_substring()  are  the  same  as those for the  
2187       functions that  extract  by  number,  and  so  are  not  re-         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2188       described here. There are just two differences.         pcre_get_named_substring()  are  the  same  as  those for the similarly
2189           named functions that extract by number. As these are described  in  the
2190       First, instead of a substring number, a  substring  name  is         previous  section,  they  are not re-described here. There are just two
2191       given.  Second,  there  is  an  extra argument, given at the         differences:
2192       start, which is a pointer to the compiled pattern.  This  is  
2193       needed  in order to gain access to the name-to-number trans-         First, instead of a substring number, a substring name is  given.  Sec-
2194       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2195           to the compiled pattern. This is needed in order to gain access to  the
2196       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2197       succeeds,    they   then   call   pcre_copy_substring()   or  
2198       pcre_get_substring(), as appropriate.         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2199           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2200           ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2201           behaviour may not be what you want (see the next section).
2202    
2203    
2204    DUPLICATE SUBPATTERN NAMES
2205    
2206           int pcre_get_stringtable_entries(const pcre *code,
2207                const char *name, char **first, char **last);
2208    
2209           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2210           subpatterns  are  not  required  to  be unique. Normally, patterns with
2211           duplicate names are such that in any one match, only one of  the  named
2212           subpatterns  participates. An example is shown in the pcrepattern docu-
2213           mentation. When duplicates are present, pcre_copy_named_substring() and
2214           pcre_get_named_substring()  return the first substring corresponding to
2215           the given name that is set.  If  none  are  set,  an  empty  string  is
2216           returned.  The pcre_get_stringnumber() function returns one of the num-
2217           bers that are associated with the name, but it is not defined which  it
2218           is.
2219    
2220           If  you want to get full details of all captured substrings for a given
2221           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2222           first argument is the compiled pattern, and the second is the name. The
2223           third and fourth are pointers to variables which  are  updated  by  the
2224           function. After it has run, they point to the first and last entries in
2225           the name-to-number table  for  the  given  name.  The  function  itself
2226           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2227           there are none. The format of the table is described above in the  sec-
2228           tion  entitled  Information  about  a  pattern.  Given all the relevant
2229           entries for the name, you can extract each of their numbers, and  hence
2230           the captured data, if any.
2231    
2232    
2233    FINDING ALL POSSIBLE MATCHES
2234    
2235           The  traditional  matching  function  uses a similar algorithm to Perl,
2236           which stops when it finds the first match, starting at a given point in
2237           the  subject.  If you want to find all possible matches, or the longest
2238           possible match, consider using the alternative matching  function  (see
2239           below)  instead.  If you cannot use the alternative function, but still
2240           need to find all possible matches, you can kludge it up by  making  use
2241           of the callout facility, which is described in the pcrecallout documen-
2242           tation.
2243    
2244           What you have to do is to insert a callout right at the end of the pat-
2245           tern.   When your callout function is called, extract and save the cur-
2246           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2247           backtrack  and  try other alternatives. Ultimately, when it runs out of
2248           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2249    
2250    
2251    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2252    
2253           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2254                const char *subject, int length, int startoffset,
2255                int options, int *ovector, int ovecsize,
2256                int *workspace, int wscount);
2257    
2258           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2259           against  a  compiled pattern, using a matching algorithm that scans the
2260           subject string just once, and does not backtrack.  This  has  different
2261           characteristics  to  the  normal  algorithm, and is not compatible with
2262           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2263           theless,  there are times when this kind of matching can be useful. For
2264           a discussion of the two matching algorithms, see the pcrematching docu-
2265           mentation.
2266    
2267           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2268           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2269           ent  way,  and  this is described below. The other common arguments are
2270           used in the same way as for pcre_exec(), so their  description  is  not
2271           repeated here.
2272    
2273           The  two  additional  arguments provide workspace for the function. The
2274           workspace vector should contain at least 20 elements. It  is  used  for
2275           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2276           workspace will be needed for patterns and subjects where  there  are  a
2277           lot of potential matches.
2278    
2279           Here is an example of a simple call to pcre_dfa_exec():
2280    
2281             int rc;
2282             int ovector[10];
2283             int wspace[20];
2284             rc = pcre_dfa_exec(
2285               re,             /* result of pcre_compile() */
2286               NULL,           /* we didn't study the pattern */
2287               "some string",  /* the subject string */
2288               11,             /* the length of the subject string */
2289               0,              /* start at offset 0 in the subject */
2290               0,              /* default options */
2291               ovector,        /* vector of integers for substring information */
2292               10,             /* number of elements (NOT size in bytes) */
2293               wspace,         /* working space vector */
2294               20);            /* number of elements (NOT size in bytes) */
2295    
2296       Option bits for pcre_dfa_exec()
2297    
2298           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2299           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2300           LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2301           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2302           three of these are the same as for pcre_exec(), so their description is
2303           not repeated here.
2304    
2305             PCRE_PARTIAL
2306    
2307           This has the same general effect as it does for  pcre_exec(),  but  the
2308           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2309           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2310           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2311           been no complete matches, but there is still at least one matching pos-
2312           sibility.  The portion of the string that provided the partial match is
2313           set as the first matching string.
2314    
2315             PCRE_DFA_SHORTEST
2316    
2317           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2318           stop as soon as it has found one match. Because of the way the alterna-
2319           tive algorithm works, this is necessarily the shortest  possible  match
2320           at the first possible matching point in the subject string.
2321    
2322             PCRE_DFA_RESTART
2323    
2324           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2325           returns a partial match, it is possible to call it  again,  with  addi-
2326           tional  subject  characters,  and have it continue with the same match.
2327           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2328           workspace  and wscount options must reference the same vector as before
2329           because data about the match so far is left in  them  after  a  partial
2330           match.  There  is  more  discussion of this facility in the pcrepartial
2331           documentation.
2332    
2333       Successful returns from pcre_dfa_exec()
2334    
2335           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2336           string in the subject. Note, however, that all the matches from one run
2337           of the function start at the same point in  the  subject.  The  shorter
2338           matches  are all initial substrings of the longer matches. For example,
2339           if the pattern
2340    
2341             <.*>
2342    
2343           is matched against the string
2344    
2345             This is <something> <something else> <something further> no more
2346    
2347           the three matched strings are
2348    
2349             <something>
2350             <something> <something else>
2351             <something> <something else> <something further>
2352    
2353           On success, the yield of the function is a number  greater  than  zero,
2354           which  is  the  number of matched substrings. The substrings themselves
2355           are returned in ovector. Each string uses two elements;  the  first  is
2356           the  offset  to  the start, and the second is the offset to the end. In
2357           fact, all the strings have the same start  offset.  (Space  could  have
2358           been  saved by giving this only once, but it was decided to retain some
2359           compatibility with the way pcre_exec() returns data,  even  though  the
2360           meaning of the strings is different.)
2361    
2362           The strings are returned in reverse order of length; that is, the long-
2363           est matching string is given first. If there were too many  matches  to
2364           fit  into ovector, the yield of the function is zero, and the vector is
2365           filled with the longest matches.
2366    
2367       Error returns from pcre_dfa_exec()
2368    
2369           The pcre_dfa_exec() function returns a negative number when  it  fails.
2370           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2371           described above.  There are in addition the following errors  that  are
2372           specific to pcre_dfa_exec():
2373    
2374             PCRE_ERROR_DFA_UITEM      (-16)
2375    
2376           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2377           tern that it does not support, for instance, the use of \C  or  a  back
2378           reference.
2379    
2380             PCRE_ERROR_DFA_UCOND      (-17)
2381    
2382           This  return  is  given  if pcre_dfa_exec() encounters a condition item
2383           that uses a back reference for the condition, or a test  for  recursion
2384           in a specific group. These are not supported.
2385    
2386             PCRE_ERROR_DFA_UMLIMIT    (-18)
2387    
2388           This  return  is given if pcre_dfa_exec() is called with an extra block
2389           that contains a setting of the match_limit field. This is not supported
2390           (it is meaningless).
2391    
2392             PCRE_ERROR_DFA_WSSIZE     (-19)
2393    
2394           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2395           workspace vector.
2396    
2397             PCRE_ERROR_DFA_RECURSE    (-20)
2398    
2399           When a recursive subpattern is processed, the matching  function  calls
2400           itself  recursively,  using  private vectors for ovector and workspace.
2401           This error is given if the output vector  is  not  large  enough.  This
2402           should be extremely rare, as a vector of size 1000 is used.
2403    
2404    
2405    SEE ALSO
2406    
2407           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2408           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2409    
2410    
2411    AUTHOR
2412    
2413           Philip Hazel
2414           University Computing Service
2415           Cambridge CB2 3QH, England.
2416    
2417    
2418    REVISION
2419    
2420           Last updated: 13 June 2007
2421           Copyright (c) 1997-2007 University of Cambridge.
2422    ------------------------------------------------------------------------------
2423    
2424    
2425    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2426    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2427    
2428  NAME  NAME
2429       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2430    
2431    
2432  PCRE CALLOUTS  PCRE CALLOUTS
2433    
2434       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.  
2435    
2436           PCRE provides a feature called "callout", which is a means of temporar-
2437           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2438           matching.  The  caller of PCRE provides an external function by putting
2439           its entry point in the global variable pcre_callout. By  default,  this
2440           variable contains NULL, which disables all calling out.
2441    
2442           Within  a  regular  expression,  (?C) indicates the points at which the
2443           external function is to be called.  Different  callout  points  can  be
2444           identified  by  putting  a number less than 256 after the letter C. The
2445           default value is zero.  For  example,  this  pattern  has  two  callout
2446           points:
2447    
2448             (?C1)abc(?C2)def
2449    
2450           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2451           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2452           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2453           used with the pattern
2454    
2455             A(\d{2}|--)
2456    
2457           it is processed as if it were
2458    
2459           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2460    
2461           Notice that there is a callout before and after  each  parenthesis  and
2462           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2463           progress of pattern matching. The pcretest command has an  option  that
2464           sets  automatic callouts; when it is used, the output indicates how the
2465           pattern is matched. This is useful information when you are  trying  to
2466           optimize the performance of a particular pattern.
2467    
2468    
2469    MISSING CALLOUTS
2470    
2471           You  should  be  aware  that,  because of optimizations in the way PCRE
2472           matches patterns, callouts sometimes do not happen. For example, if the
2473           pattern is
2474    
2475             ab(?C4)cd
2476    
2477           PCRE knows that any matching string must contain the letter "d". If the
2478           subject string is "abyz", the lack of "d" means that  matching  doesn't
2479           ever  start,  and  the  callout is never reached. However, with "abyd",
2480           though the result is still no match, the callout is obeyed.
2481    
2482    
2483    THE CALLOUT INTERFACE
2484    
2485           During matching, when PCRE reaches a callout point, the external  func-
2486           tion  defined by pcre_callout is called (if it is set). This applies to
2487           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2488           only  argument  to  the callout function is a pointer to a pcre_callout
2489           block. This structure contains the following fields:
2490    
2491             int          version;
2492             int          callout_number;
2493             int         *offset_vector;
2494             const char  *subject;
2495             int          subject_length;
2496             int          start_match;
2497             int          current_position;
2498             int          capture_top;
2499             int          capture_last;
2500             void        *callout_data;
2501             int          pattern_position;
2502             int          next_item_length;
2503    
2504           The version field is an integer containing the version  number  of  the
2505           block  format. The initial version was 0; the current version is 1. The
2506           version number will change again in future  if  additional  fields  are
2507           added, but the intention is never to remove any of the existing fields.
2508    
2509           The callout_number field contains the number of the  callout,  as  com-
2510           piled  into  the pattern (that is, the number after ?C for manual call-
2511           outs, and 255 for automatically generated callouts).
2512    
2513           The offset_vector field is a pointer to the vector of offsets that  was
2514           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2515           pcre_exec() is used, the contents can be inspected in order to  extract
2516           substrings  that  have  been  matched  so  far,  in the same way as for
2517           extracting substrings after a match has completed. For  pcre_dfa_exec()
2518           this field is not useful.
2519    
2520           The subject and subject_length fields contain copies of the values that
2521           were passed to pcre_exec().
2522    
2523           The start_match field normally contains the offset within  the  subject
2524           at  which  the  current  match  attempt started. However, if the escape
2525           sequence \K has been encountered, this value is changed to reflect  the
2526           modified  starting  point.  If the pattern is not anchored, the callout
2527           function may be called several times from the same point in the pattern
2528           for different starting points in the subject.
2529    
2530           The  current_position  field  contains the offset within the subject of
2531           the current match pointer.
2532    
2533           When the pcre_exec() function is used, the capture_top  field  contains
2534           one  more than the number of the highest numbered captured substring so
2535           far. If no substrings have been captured, the value of  capture_top  is
2536           one.  This  is always the case when pcre_dfa_exec() is used, because it
2537           does not support captured substrings.
2538    
2539           The capture_last field contains the number of the  most  recently  cap-
2540           tured  substring. If no substrings have been captured, its value is -1.
2541           This is always the case when pcre_dfa_exec() is used.
2542    
2543           The callout_data field contains a value that is passed  to  pcre_exec()
2544           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2545           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2546           structure.  If  no such data was passed, the value of callout_data in a
2547           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2548           structure in the pcreapi documentation.
2549    
2550           The  pattern_position field is present from version 1 of the pcre_call-
2551           out structure. It contains the offset to the next item to be matched in
2552           the pattern string.
2553    
2554           The  next_item_length field is present from version 1 of the pcre_call-
2555           out structure. It contains the length of the next item to be matched in
2556           the  pattern  string. When the callout immediately precedes an alterna-
2557           tion bar, a closing parenthesis, or the end of the pattern, the  length
2558           is  zero.  When the callout precedes an opening parenthesis, the length
2559           is that of the entire subpattern.
2560    
2561           The pattern_position and next_item_length fields are intended  to  help
2562           in  distinguishing between different automatic callouts, which all have
2563           the same callout number. However, they are set for all callouts.
2564    
2565    
2566  RETURN VALUES  RETURN VALUES
2567    
2568       The callout function returns an integer.  If  the  value  is         The external callout function returns an integer to PCRE. If the  value
2569       zero,  matching  proceeds as normal. If the value is greater         is  zero,  matching  proceeds  as  normal. If the value is greater than
2570       than zero, matching fails at the current  point,  but  back-         zero, matching fails at the current point, but  the  testing  of  other
2571       tracking  to test other possibilities goes ahead, just as if         matching possibilities goes ahead, just as if a lookahead assertion had
2572       a lookahead assertion had failed. If the value is less  than         failed. If the value is less than zero, the  match  is  abandoned,  and
2573       zero,  the  match  is abandoned, and pcre_exec() returns the         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2574       value.  
2575           Negative   values   should   normally   be   chosen  from  the  set  of
2576       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2577       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2578       forces a standard "no  match"  failure.   The  error  number         reserved for use by callout functions; it will never be  used  by  PCRE
2579       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
2580       it will never be used by PCRE itself.  
2581    
2582    AUTHOR
2583    
2584           Philip Hazel
2585           University Computing Service
2586           Cambridge CB2 3QH, England.
2587    
2588    
2589    REVISION
2590    
2591           Last updated: 29 May 2007
2592           Copyright (c) 1997-2007 University of Cambridge.
2593    ------------------------------------------------------------------------------
2594    
2595    
2596    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2597    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2598    
2599  NAME  NAME
2600       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2601    
2602    
2603  DIFFERENCES FROM PERL  DIFFERENCES BETWEEN PCRE AND PERL
2604    
2605       This document describes the differences  in  the  ways  that         This  document describes the differences in the ways that PCRE and Perl
2606       PCRE  and  Perl  handle regular expressions. The differences         handle regular expressions. The differences described here  are  mainly
2607       described here are with respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2608           some features that are expected to be in the forthcoming Perl 5.10.
2609       1. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
2610       assertions. Perl permits them, but they do not mean what you         1. PCRE has only a subset of Perl's UTF-8 and Unicode support.  Details
2611       might think. For example, (?!a){3} does not assert that  the         of  what  it does have are given in the section on UTF-8 support in the
2612       next  three characters are not "a". It just asserts that the         main pcre page.
2613       next character is not "a" three times.  
2614           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2615       2. Capturing subpatterns that occur inside  negative  looka-         permits  them,  but they do not mean what you might think. For example,
2616       head  assertions  are  counted,  but  their  entries  in the         (?!a){3} does not assert that the next three characters are not "a". It
2617       offsets vector are never set. Perl sets its numerical  vari-         just asserts that the next character is not "a" three times.
2618       ables  from  any  such  patterns that are matched before the  
2619       assertion fails to match something (thereby succeeding), but         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2620       only  if  the negative lookahead assertion contains just one         tions are counted, but their entries in the offsets  vector  are  never
2621       branch.         set.  Perl sets its numerical variables from any such patterns that are
2622           matched before the assertion fails to match something (thereby succeed-
2623       3. Though binary zero characters are supported in  the  sub-         ing),  but  only  if the negative lookahead assertion contains just one
2624       ject  string,  they  are  not  allowed  in  a pattern string         branch.
2625       because it is passed as a normal  C  string,  terminated  by  
2626       zero. The escape sequence "\0" can be used in the pattern to         4. Though binary zero characters are supported in the  subject  string,
2627       represent a binary zero.         they are not allowed in a pattern string because it is passed as a nor-
2628           mal C string, terminated by zero. The escape sequence \0 can be used in
2629       4. The following Perl escape sequences  are  not  supported:         the pattern to represent a binary zero.
2630       \l,  \u,  \L,  \U,  \P, \p, and \X. In fact these are imple-  
2631       mented by Perl's general string-handling and are not part of         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2632       its pattern matching engine. If any of these are encountered         \U, and \N. In fact these are implemented by Perl's general string-han-
2633       by PCRE, an error is generated.         dling  and are not part of its pattern matching engine. If any of these
2634           are encountered by PCRE, an error is generated.
2635       5. PCRE does support the \Q...\E  escape  for  quoting  sub-  
2636       strings. Characters in between are treated as literals. This         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2637       is slightly different from Perl in that $  and  @  are  also         is  built  with Unicode character property support. The properties that
2638       handled  as  literals inside the quotes. In Perl, they cause         can be tested with \p and \P are limited to the general category  prop-
2639       variable interpolation (but of course  PCRE  does  not  have         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2640       variables). Note the following examples:         derived properties Any and L&.
2641    
2642           Pattern            PCRE matches      Perl matches         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2643           ters  in  between  are  treated as literals. This is slightly different
2644           \Qabc$xyz\E        abc$xyz           abc followed by the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2645                                                  contents of $xyz         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2646           \Qabc\$xyz\E       abc\$xyz          abc\$xyz         does not have variables). Note the following examples:
2647           \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz  
2648               Pattern            PCRE matches      Perl matches
2649       In PCRE, the \Q...\E mechanism is not  recognized  inside  a  
2650       character class.             \Qabc$xyz\E        abc$xyz           abc followed by the
2651                                                      contents of $xyz
2652       8. Fairly obviously, PCRE does not support the (?{code}) and             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2653       (?p{code})  constructions. However, there is some experimen-             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2654       tal support for recursive patterns using the non-Perl  items  
2655       (?R),  (?number)  and  (?P>name).  Also,  the PCRE "callout"         The \Q...\E sequence is recognized both inside  and  outside  character
2656       feature allows an external function to be called during pat-         classes.
2657       tern matching.  
2658           8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2659       9. There are some differences that are  concerned  with  the         constructions. However, there is support for recursive  patterns.  This
2660       settings  of  captured  strings  when  part  of a pattern is         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2661       repeated. For example, matching "aba"  against  the  pattern         "callout" feature allows an external function to be called during  pat-
2662       /^(a(b)?)+$/  in Perl leaves $2 unset, but in PCRE it is set         tern matching. See the pcrecallout documentation for details.
2663       to "b".  
2664           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2665       10. PCRE  provides  some  extensions  to  the  Perl  regular         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2666       expression facilities:         unlike Perl.
2667    
2668       (a) Although lookbehind assertions must match  fixed  length         10.  There are some differences that are concerned with the settings of
2669       strings,  each  alternative branch of a lookbehind assertion         captured strings when part of  a  pattern  is  repeated.  For  example,
2670       can match a different length of string. Perl  requires  them         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2671       all to have the same length.         unset, but in PCRE it is set to "b".
2672    
2673       (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not         11. PCRE provides some extensions to the Perl regular expression facil-
2674       set,  the  $  meta-character matches only at the very end of         ities.   Perl  5.10  will  include new features that are not in earlier
2675       the string.         versions, some of which (such as named parentheses) have been  in  PCRE
2676           for some time. This list is with respect to Perl 5.10:
2677       (c) If PCRE_EXTRA is set, a backslash followed by  a  letter  
2678       with no special meaning is faulted.         (a)  Although  lookbehind  assertions  must match fixed length strings,
2679           each alternative branch of a lookbehind assertion can match a different
2680       (d) If PCRE_UNGREEDY is set, the greediness of  the  repeti-         length of string. Perl requires them all to have the same length.
2681       tion  quantifiers  is inverted, that is, by default they are  
2682       not greedy, but if followed by a question mark they are.         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2683           meta-character matches only at the very end of the string.
2684       (e) PCRE_ANCHORED can be used to force a pattern to be tried  
2685       only at the first matching position in the subject string.         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2686           cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2687       (f)  The  PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   and         ignored.  (Perl can be made to issue a warning.)
2688       PCRE_NO_AUTO_CAPTURE  options  for  pcre_exec() have no Perl  
2689       equivalents.         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2690           fiers is inverted, that is, by default they are not greedy, but if fol-
2691       (g) The (?R), (?number), and (?P>name) constructs allows for         lowed by a question mark they are.
2692       recursive  pattern  matching  (Perl  can  do  this using the  
2693       (?p{code}) construct, which PCRE cannot support.)         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2694           tried only at the first matching position in the subject string.
2695       (h) PCRE supports  named  capturing  substrings,  using  the  
2696       Python syntax.         (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2697           TURE options for pcre_exec() have no Perl equivalents.
2698       (i) PCRE supports the  possessive  quantifier  "++"  syntax,  
2699       taken from Sun's Java package.         (g) The callout facility is PCRE-specific.
2700    
2701       (j) The (R) condition, for  testing  recursion,  is  a  PCRE         (h) The partial matching facility is PCRE-specific.
      extension.  
2702    
2703       (k) The callout facility is PCRE-specific.         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2704           even on different hosts that have the other endianness.
2705    
2706           (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2707           different way and is not Perl-compatible.
2708    
2709    
2710    AUTHOR
2711    
2712           Philip Hazel
2713           University Computing Service
2714           Cambridge CB2 3QH, England.
2715    
2716    
2717    REVISION
2718    
2719           Last updated: 13 June 2007
2720           Copyright (c) 1997-2007 University of Cambridge.
2721    ------------------------------------------------------------------------------
2722    
2723    
2724    PCREPATTERN(3)                                                  PCREPATTERN(3)
2725    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2726    
2727  NAME  NAME
2728       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2729    
2730    
2731  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2732    
2733       The syntax and semantics of  the  regular  expressions  sup-         The  syntax  and semantics of the regular expressions supported by PCRE
2734       ported  by PCRE are described below. Regular expressions are         are described below. Regular expressions are also described in the Perl
2735       also described in the Perl documentation and in a number  of         documentation  and  in  a  number  of books, some of which have copious
2736       other  books,  some  of which have copious examples. Jeffrey         examples.  Jeffrey Friedl's "Mastering Regular Expressions",  published
2737       Friedl's  "Mastering  Regular  Expressions",  published   by         by  O'Reilly, covers regular expressions in great detail. This descrip-
2738       O'Reilly,  covers them in great detail. The description here         tion of PCRE's regular expressions is intended as reference material.
2739       is intended as reference documentation.  
2740           The original operation of PCRE was on strings of  one-byte  characters.
2741       The basic operation of PCRE is on strings of bytes. However,         However,  there is now also support for UTF-8 character strings. To use
2742       there  is  also  support for UTF-8 character strings. To use         this, you must build PCRE to  include  UTF-8  support,  and  then  call
2743       this support you must build PCRE to include  UTF-8  support,         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2744       and  then call pcre_compile() with the PCRE_UTF8 option. How         matching is mentioned in several places below. There is also a  summary
2745       this affects the pattern matching is  mentioned  in  several         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2746       places  below.  There is also a summary of UTF-8 features in         page.
2747       the section on UTF-8 support in the main pcre page.  
2748           The remainder of this document discusses the  patterns  that  are  sup-
2749       A regular expression is a pattern that is matched against  a         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2750       subject string from left to right. Most characters stand for         From  release  6.0,   PCRE   offers   a   second   matching   function,
2751       themselves in a pattern, and match the corresponding charac-         pcre_dfa_exec(),  which matches using a different algorithm that is not
2752       ters in the subject. As a trivial example, the pattern         Perl-compatible. Some of the features discussed below are not available
2753           when  pcre_dfa_exec()  is used. The advantages and disadvantages of the
2754         The quick brown fox         alternative function, and how it differs from the normal function,  are
2755           discussed in the pcrematching page.
2756       matches a portion of a subject string that is  identical  to  
2757       itself.  The  power  of  regular  expressions comes from the  
2758       ability to include alternatives and repetitions in the  pat-  CHARACTERS AND METACHARACTERS
2759       tern.  These  are encoded in the pattern by the use of meta-  
2760       characters, which do not stand for  themselves  but  instead         A  regular  expression  is  a pattern that is matched against a subject
2761       are interpreted in some special way.         string from left to right. Most characters stand for  themselves  in  a
2762           pattern,  and  match  the corresponding characters in the subject. As a
2763       There are two different sets of meta-characters: those  that         trivial example, the pattern
2764       are  recognized anywhere in the pattern except within square  
2765       brackets, and those that are recognized in square  brackets.           The quick brown fox
2766       Outside square brackets, the meta-characters are as follows:  
2767           matches a portion of a subject string that is identical to itself. When
2768         \      general escape character with several uses         caseless  matching is specified (the PCRE_CASELESS option), letters are
2769         ^      assert start of string (or line, in multiline mode)         matched independently of case. In UTF-8 mode, PCRE  always  understands
2770         $      assert end of string (or line, in multiline mode)         the  concept  of case for characters whose values are less than 128, so
2771         .      match any character except newline (by default)         caseless matching is always possible. For characters with  higher  val-
2772         [      start character class definition         ues,  the concept of case is supported if PCRE is compiled with Unicode
2773         |      start of alternative branch         property support, but not otherwise.   If  you  want  to  use  caseless
2774         (      start subpattern         matching  for  characters  128  and above, you must ensure that PCRE is
2775         )      end subpattern         compiled with Unicode property support as well as with UTF-8 support.
2776         ?      extends the meaning of (  
2777                also 0 or 1 quantifier         The power of regular expressions comes  from  the  ability  to  include
2778                also quantifier minimizer         alternatives  and  repetitions in the pattern. These are encoded in the
2779         *      0 or more quantifier         pattern by the use of metacharacters, which do not stand for themselves
2780         +      1 or more quantifier         but instead are interpreted in some special way.
2781                also "possessive quantifier"  
2782         {      start min/max quantifier         There  are  two different sets of metacharacters: those that are recog-
2783           nized anywhere in the pattern except within square brackets, and