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1    -----------------------------------------------------------------------------
2  This file contains a concatenation of the PCRE man pages, converted to plain  This file contains a concatenation of the PCRE man pages, converted to plain
3  text format for ease of searching with a text editor, or for use on systems  text format for ease of searching with a text editor, or for use on systems
4  that do not have a man page processor. The small individual files that give  that do not have a man page processor. The small individual files that give
# Line 5  synopses of each function in the library Line 6  synopses of each function in the library
6  separate text files for the pcregrep and pcretest commands.  separate text files for the pcregrep and pcretest commands.
7  -----------------------------------------------------------------------------  -----------------------------------------------------------------------------
8    
9    
10    PCRE(3)                                                                PCRE(3)
11    
12    
13  NAME  NAME
14       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
15    
16    
17  DESCRIPTION  INTRODUCTION
18    
19       The PCRE library is a set of functions that implement  regu-         The  PCRE  library is a set of functions that implement regular expres-
20       lar  expression  pattern  matching using the same syntax and         sion pattern matching using the same syntax and semantics as Perl, with
21       semantics as Perl, with just a few differences. The  current         just  a  few differences. (Certain features that appeared in Python and
22       implementation  of  PCRE  (release 4.x) corresponds approxi-         PCRE before they appeared in Perl are also available using  the  Python
23       mately with Perl 5.8, including support  for  UTF-8  encoded         syntax.)
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. There is a syntax summary in the  pcresyntax
49           page.
50    
51           Some  features  of  PCRE can be included, excluded, or changed when the
52           library is built. The pcre_config() function makes it  possible  for  a
53           client  to  discover  which  features are available. The features them-
54           selves are described in the pcrebuild page. Documentation about  build-
55           ing  PCRE for various operating systems can be found in the README file
56           in the source distribution.
57    
58           The library contains a number of undocumented  internal  functions  and
59           data  tables  that  are  used by more than one of the exported external
60           functions, but which are not intended  for  use  by  external  callers.
61           Their  names  all begin with "_pcre_", which hopefully will not provoke
62           any name clashes. In some environments, it is possible to control which
63           external  symbols  are  exported when a shared library is built, and in
64           these cases the undocumented symbols are not exported.
65    
66    
67  USER DOCUMENTATION  USER DOCUMENTATION
68    
69       The user documentation for PCRE has been  split  up  into  a         The user documentation for PCRE comprises a number  of  different  sec-
70       number  of  different sections. In the "man" format, each of         tions.  In the "man" format, each of these is a separate "man page". In
71       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.
72       a  separate  page,  linked from the index page. In the plain         In  the  plain text format, all the sections are concatenated, for ease
73       text format, all the sections are concatenated, for ease  of         of searching. The sections are as follows:
74       searching. The sections are as follows:  
75             pcre              this document
76         pcre              this document           pcre-config       show PCRE installation configuration information
77         pcreapi           details of PCRE's native API           pcreapi           details of PCRE's native C API
78         pcrebuild         options for building PCRE           pcrebuild         options for building PCRE
79         pcrecallout       details of the callout feature           pcrecallout       details of the callout feature
80         pcrecompat        discussion of Perl compatibility           pcrecompat        discussion of Perl compatibility
81         pcregrep          description of the pcregrep command           pcrecpp           details of the C++ wrapper
82         pcrepattern       syntax and semantics of supported           pcregrep          description of the pcregrep command
83                             regular expressions           pcrematching      discussion of the two matching algorithms
84         pcreperform       discussion of performance issues           pcrepartial       details of the partial matching facility
85         pcreposix         the POSIX-compatible API           pcrepattern       syntax and semantics of supported
86         pcresample        discussion of the sample program                               regular expressions
87         pcretest          the pcretest testing command           pcresyntax        quick syntax reference
88             pcreperform       discussion of performance issues
89       In addition, in the "man" and HTML formats, there is a short           pcreposix         the POSIX-compatible C API
90       page  for  each  library function, listing its arguments and           pcreprecompile    details of saving and re-using precompiled patterns
91       results.           pcresample        discussion of the sample program
92             pcrestack         discussion of stack usage
93             pcretest          description of the pcretest testing command
94    
95           In  addition,  in the "man" and HTML formats, there is a short page for
96           each C library function, listing its arguments and results.
97    
98    
99  LIMITATIONS  LIMITATIONS
100    
101       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
102       they will never in practice be relevant.         never in practice be relevant.
103    
104       The maximum length of a  compiled  pattern  is  65539  (sic)         The  maximum  length of a compiled pattern is 65539 (sic) bytes if PCRE
105       bytes  if PCRE is compiled with the default internal linkage         is compiled with the default internal linkage size of 2. If you want to
106       size of 2. If you want to process regular  expressions  that         process  regular  expressions  that are truly enormous, you can compile
107       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
108       linkage size of 3 or 4 (see the README file  in  the  source         the  source  distribution and the pcrebuild documentation for details).
109       distribution  and  the pcrebuild documentation for details).         In these cases the limit is substantially larger.  However,  the  speed
110       If these cases the limit is substantially larger.   However,         of execution is slower.
111       the speed of execution will be slower.  
112           All values in repeating quantifiers must be less than 65536.
113       All values in repeating quantifiers must be less than 65536.  
114       The maximum number of capturing subpatterns is 65535.         There is no limit to the number of parenthesized subpatterns, but there
115           can be no more than 65535 capturing subpatterns.
116       There is no limit to the  number  of  non-capturing  subpat-  
117       terns,  but  the  maximum  depth  of nesting of all kinds of         The maximum length of name for a named subpattern is 32 characters, and
118       parenthesized subpattern, including  capturing  subpatterns,         the maximum number of named subpatterns is 10000.
119       assertions, and other types of subpattern, is 200.  
120           The  maximum  length of a subject string is the largest positive number
121       The maximum length of a subject string is the largest  posi-         that an integer variable can hold. However, when using the  traditional
122       tive number that an integer variable can hold. However, PCRE         matching function, PCRE uses recursion to handle subpatterns and indef-
123       uses recursion to handle subpatterns and indefinite  repeti-         inite repetition.  This means that the available stack space may  limit
124       tion.  This  means  that the available stack space may limit         the size of a subject string that can be processed by certain patterns.
125       the size of a subject string that can be processed  by  cer-         For a discussion of stack issues, see the pcrestack documentation.
126       tain patterns.  
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       Validity of UTF-8 strings
159    
160           When you set the PCRE_UTF8 flag, the strings  passed  as  patterns  and
161           subjects are (by default) checked for validity on entry to the relevant
162           functions. From release 7.3 of PCRE, the check is according  the  rules
163           of  RFC  3629, which are themselves derived from the Unicode specifica-
164           tion. Earlier releases of PCRE followed the rules of  RFC  2279,  which
165           allows  the  full range of 31-bit values (0 to 0x7FFFFFFF). The current
166           check allows only values in the range U+0 to U+10FFFF, excluding U+D800
167           to U+DFFF.
168    
169           The  excluded  code  points are the "Low Surrogate Area" of Unicode, of
170           which the Unicode Standard says this: "The Low Surrogate Area does  not
171           contain  any  character  assignments,  consequently  no  character code
172           charts or namelists are provided for this area. Surrogates are reserved
173           for  use  with  UTF-16 and then must be used in pairs." The code points
174           that are encoded by UTF-16 pairs  are  available  as  independent  code
175           points  in  the  UTF-8  encoding.  (In other words, the whole surrogate
176           thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
177    
178           If an  invalid  UTF-8  string  is  passed  to  PCRE,  an  error  return
179           (PCRE_ERROR_BADUTF8) is given. In some situations, you may already know
180           that your strings are valid, and therefore want to skip these checks in
181           order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag at
182           compile time or at run time, PCRE assumes that the pattern  or  subject
183           it  is  given  (respectively)  contains only valid UTF-8 codes. In this
184           case, it does not diagnose an invalid UTF-8 string.
185    
186           If you pass an invalid UTF-8 string  when  PCRE_NO_UTF8_CHECK  is  set,
187           what  happens  depends on why the string is invalid. If the string con-
188           forms to the "old" definition of UTF-8 (RFC 2279), it is processed as a
189           string  of  characters  in  the  range 0 to 0x7FFFFFFF. In other words,
190           apart from the initial validity test, PCRE (when in UTF-8 mode) handles
191           strings  according  to  the more liberal rules of RFC 2279. However, if
192           the string does not even conform to RFC 2279, the result is  undefined.
193           Your program may crash.
194    
195           If  you  want  to  process  strings  of  values  in the full range 0 to
196           0x7FFFFFFF, encoded in a UTF-8-like manner as per the old RFC, you  can
197           set PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in
198           this situation, you will have to apply your own validity check.
199    
200       General comments about UTF-8 mode
201    
202           1. An unbraced hexadecimal escape sequence (such  as  \xb3)  matches  a
203           two-byte UTF-8 character if the value is greater than 127.
204    
205           2.  Octal  numbers  up to \777 are recognized, and match two-byte UTF-8
206           characters for values greater than \177.
207    
208           3. Repeat quantifiers apply to complete UTF-8 characters, not to  indi-
209           vidual bytes, for example: \x{100}{3}.
210    
211           4.  The dot metacharacter matches one UTF-8 character instead of a sin-
212           gle byte.
213    
214           5. The escape sequence \C can be used to match a single byte  in  UTF-8
215           mode,  but  its  use can lead to some strange effects. This facility is
216           not available in the alternative matching function, pcre_dfa_exec().
217    
218           6. The character escapes \b, \B, \d, \D, \s, \S, \w, and  \W  correctly
219           test  characters of any code value, but the characters that PCRE recog-
220           nizes as digits, spaces, or word characters  remain  the  same  set  as
221           before, all with values less than 256. This remains true even when PCRE
222           includes Unicode property support, because to do otherwise  would  slow
223           down  PCRE in many common cases. If you really want to test for a wider
224           sense of, say, "digit", you must use Unicode  property  tests  such  as
225           \p{Nd}.
226    
227           7.  Similarly,  characters that match the POSIX named character classes
228           are all low-valued characters.
229    
230           8. However, the Perl 5.10 horizontal and vertical  whitespace  matching
231           escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
232           acters.
233    
234           9. Case-insensitive matching applies only to  characters  whose  values
235           are  less than 128, unless PCRE is built with Unicode property support.
236           Even when Unicode property support is available, PCRE  still  uses  its
237           own  character  tables when checking the case of low-valued characters,
238           so as not to degrade performance.  The Unicode property information  is
239           used only for characters with higher values. Even when Unicode property
240           support is available, PCRE supports case-insensitive matching only when
241           there  is  a  one-to-one  mapping between a letter's cases. There are a
242           small number of many-to-one mappings in Unicode;  these  are  not  sup-
243           ported by PCRE.
244    
245    
246  UTF-8 SUPPORT  AUTHOR
247    
248       Starting at release 3.3, PCRE has had some support for char-         Philip Hazel
249       acter  strings  encoded in the UTF-8 format. For release 4.0         University Computing Service
250       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.  
251    
252       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,
253       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,
254           followed by the two digits 10, at the domain cam.ac.uk.
255    
256    
257  AUTHOR  REVISION
258    
259       Philip Hazel <ph10@cam.ac.uk>         Last updated: 09 August 2007
260       University Computing Service,         Copyright (c) 1997-2007 University of Cambridge.
261       Cambridge CB2 3QG, England.  ------------------------------------------------------------------------------
262       Phone: +44 1223 334714  
263    
264    PCREBUILD(3)                                                      PCREBUILD(3)
265    
 Last updated: 04 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
266    
267  NAME  NAME
268       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
269    
270    
271  PCRE BUILD-TIME OPTIONS  PCRE BUILD-TIME OPTIONS
272    
273       This document describes the optional features of  PCRE  that         This  document  describes  the  optional  features  of PCRE that can be
274       can  be  selected when the library is compiled. They are all         selected when the library is compiled. They are all selected, or  dese-
275       selected, or deselected, by providing options to the config-         lected, by providing options to the configure script that is run before
276       ure  script  which  is run before the make command. The com-         the make command. The complete list of  options  for  configure  (which
277       plete list of options  for  configure  (which  includes  the         includes  the  standard  ones such as the selection of the installation
278       standard  ones  such  as  the  selection of the installation         directory) can be obtained by running
279       directory) can be obtained by running  
280             ./configure --help
281         ./configure --help  
282           The following sections include  descriptions  of  options  whose  names
283       The following sections describe certain options whose  names         begin with --enable or --disable. These settings specify changes to the
284       begin  with  --enable  or  --disable. These settings specify         defaults for the configure command. Because of the way  that  configure
285       changes to the defaults for the configure  command.  Because         works,  --enable  and --disable always come in pairs, so the complemen-
286       of  the  way  that  configure  works, --enable and --disable         tary option always exists as well, but as it specifies the default,  it
287       always come in pairs, so  the  complementary  option  always         is not described.
288       exists  as  well, but as it specifies the default, it is not  
289       described.  
290    C++ SUPPORT
291    
292           By default, the configure script will search for a C++ compiler and C++
293           header files. If it finds them, it automatically builds the C++ wrapper
294           library for PCRE. You can disable this by adding
295    
296             --disable-cpp
297    
298           to the configure command.
299    
300    
301  UTF-8 SUPPORT  UTF-8 SUPPORT
302    
303       To build PCRE with support for UTF-8 character strings, add         To build PCRE with support for UTF-8 character strings, add
304    
305             --enable-utf8
306    
307           to  the  configure  command.  Of  itself, this does not make PCRE treat
308           strings as UTF-8. As well as compiling PCRE with this option, you  also
309           have  have to set the PCRE_UTF8 option when you call the pcre_compile()
310           function.
311    
312    
313    UNICODE CHARACTER PROPERTY SUPPORT
314    
315           UTF-8 support allows PCRE to process character values greater than  255
316           in  the  strings that it handles. On its own, however, it does not pro-
317           vide any facilities for accessing the properties of such characters. If
318           you  want  to  be able to use the pattern escapes \P, \p, and \X, which
319           refer to Unicode character properties, you must add
320    
321         --enable-utf8           --enable-unicode-properties
322    
323       to the configure command. Of itself, this does not make PCRE         to the configure command. This implies UTF-8 support, even if you  have
324       treat  strings as UTF-8. As well as compiling PCRE with this         not explicitly requested it.
325       option, you also have have to set the PCRE_UTF8 option  when  
326       you call the pcre_compile() function.         Including  Unicode  property  support  adds around 30K of tables to the
327           PCRE library. Only the general category properties such as  Lu  and  Nd
328           are supported. Details are given in the pcrepattern documentation.
329    
330    
331  CODE VALUE OF NEWLINE  CODE VALUE OF NEWLINE
332    
333       By default, PCRE treats character 10 (linefeed) as the  new-         By  default,  PCRE interprets character 10 (linefeed, LF) as indicating
334       line  character.  This  is  the  normal newline character on         the end of a line. This is the normal newline  character  on  Unix-like
335       Unix-like systems. You can compile PCRE to use character  13         systems. You can compile PCRE to use character 13 (carriage return, CR)
336       (carriage return) instead by adding         instead, by adding
337    
338         --enable-newline-is-cr           --enable-newline-is-cr
339    
340       to the configure command. For completeness there is  also  a         to the  configure  command.  There  is  also  a  --enable-newline-is-lf
341       --enable-newline-is-lf  option,  which  explicitly specifies         option, which explicitly specifies linefeed as the newline character.
342       linefeed as the newline character.  
343           Alternatively, you can specify that line endings are to be indicated by
344           the two character sequence CRLF. If you want this, add
345    
346             --enable-newline-is-crlf
347    
348           to the configure command. There is a fourth option, specified by
349    
350             --enable-newline-is-anycrlf
351    
352           which causes PCRE to recognize any of the three sequences  CR,  LF,  or
353           CRLF as indicating a line ending. Finally, a fifth option, specified by
354    
355             --enable-newline-is-any
356    
357           causes PCRE to recognize any Unicode newline sequence.
358    
359           Whatever line ending convention is selected when PCRE is built  can  be
360           overridden  when  the library functions are called. At build time it is
361           conventional to use the standard for your operating system.
362    
363    
364  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
365    
366       The PCRE building process uses libtool to build both  shared         The PCRE building process uses libtool to build both shared and  static
367       and  static  Unix libraries by default. You can suppress one         Unix  libraries by default. You can suppress one of these by adding one
368       of these by adding one of         of
369    
370         --disable-shared           --disable-shared
371         --disable-static           --disable-static
372    
373       to the configure command, as required.         to the configure command, as required.
374    
375    
376  POSIX MALLOC USAGE  POSIX MALLOC USAGE
377    
378       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
379       pcreposix  documentation),  additional  working  storage  is         umentation),  additional  working  storage  is required for holding the
380       required for holding the pointers  to  capturing  substrings         pointers to capturing substrings, because PCRE requires three  integers
381       because  PCRE requires three integers per substring, whereas         per  substring,  whereas  the POSIX interface provides only two. If the
382       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
383       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
384       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
385       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
386       stack is no longer used is 10; it can be changed by adding a  
387       setting such as           --with-posix-malloc-threshold=20
388    
389         --with-posix-malloc-threshold=20         to the configure command.
390    
391       to the configure command.  
392    HANDLING VERY LARGE PATTERNS
393    
394           Within  a  compiled  pattern,  offset values are used to point from one
395           part to another (for example, from an opening parenthesis to an  alter-
396           nation  metacharacter).  By default, two-byte values are used for these
397           offsets, leading to a maximum size for a  compiled  pattern  of  around
398           64K.  This  is sufficient to handle all but the most gigantic patterns.
399           Nevertheless, some people do want to process enormous patterns,  so  it
400           is  possible  to compile PCRE to use three-byte or four-byte offsets by
401           adding a setting such as
402    
403             --with-link-size=3
404    
405           to the configure command. The value given must be 2,  3,  or  4.  Using
406           longer  offsets slows down the operation of PCRE because it has to load
407           additional bytes when handling them.
408    
409    
410    AVOIDING EXCESSIVE STACK USAGE
411    
412           When matching with the pcre_exec() function, PCRE implements backtrack-
413           ing  by  making recursive calls to an internal function called match().
414           In environments where the size of the stack is limited,  this  can  se-
415           verely  limit  PCRE's operation. (The Unix environment does not usually
416           suffer from this problem, but it may sometimes be necessary to increase
417           the  maximum  stack size.  There is a discussion in the pcrestack docu-
418           mentation.) An alternative approach to recursion that uses memory  from
419           the  heap  to remember data, instead of using recursive function calls,
420           has been implemented to work round the problem of limited  stack  size.
421           If you want to build a version of PCRE that works this way, add
422    
423             --disable-stack-for-recursion
424    
425           to  the  configure  command. With this configuration, PCRE will use the
426           pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
427           ment  functions. By default these point to malloc() and free(), but you
428           can replace the pointers so that your own functions are used.
429    
430           Separate functions are  provided  rather  than  using  pcre_malloc  and
431           pcre_free  because  the  usage  is  very  predictable:  the block sizes
432           requested are always the same, and  the  blocks  are  always  freed  in
433           reverse  order.  A calling program might be able to implement optimized
434           functions that perform better  than  malloc()  and  free().  PCRE  runs
435           noticeably more slowly when built in this way. This option affects only
436           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
437           pcre_dfa_exec() function.
438    
439    
440  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
441    
442       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
443       calls  repeatedly  (possibly  recursively) when performing a         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
444       matching operation. By limiting the  number  of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
445       function  may  be  called,  a  limit  can  be  placed on the         function may be called during a single matching operation, a limit  can
446       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
447       can  be  changed  at  run  time, as described in the pcreapi         limit can be changed at run time, as described in the pcreapi  documen-
448       documentation. The default is 10 million, but  this  can  be         tation.  The default is 10 million, but this can be changed by adding a
449       changed by adding a setting such as         setting such as
450    
451         --with-match-limit=500000           --with-match-limit=500000
452    
453       to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
454           pcre_dfa_exec() matching function.
455    
456           In  some  environments  it is desirable to limit the depth of recursive
457           calls of match() more strictly than the total number of calls, in order
458           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
459           for-recursion is specified) that is used. A second limit controls this;
460           it  defaults  to  the  value  that is set for --with-match-limit, which
461           imposes no additional constraints. However, you can set a  lower  limit
462           by adding, for example,
463    
464  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
465    
466       Within a compiled pattern, offset values are used  to  point         to  the  configure  command.  This  value can also be overridden at run
467       from  one  part  to  another  (for  example, from an opening         time.
468       parenthesis to an  alternation  metacharacter).  By  default  
469       two-byte  values  are  used  for these offsets, leading to a  
470       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
471       sufficient  to  handle  all  but the most gigantic patterns.  
472       Nevertheless, some people do want to process  enormous  pat-         PCRE uses fixed tables for processing characters whose code values  are
473       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
474       or four-byte offsets by adding a setting such as         distributed in the file pcre_chartables.c.dist. These  tables  are  for
475           ASCII codes only. If you add
476         --with-link-size=3  
477             --enable-rebuild-chartables
478       to the configure command. The value given must be 2,  3,  or  
479       4.  Using  longer  offsets  slows down the operation of PCRE         to  the  configure  command, the distributed tables are no longer used.
480       because it has to load additional bytes when handling them.         Instead, a program called dftables is compiled and  run.  This  outputs
481           the source for new set of tables, created in the default locale of your
482       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
483       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
484       of these tests is a representation of the compiled  pattern,         you need to create alternative tables when cross  compiling,  you  will
485       and this changes with the link size.         have to do so "by hand".)
486    
487    
488    USING EBCDIC CODE
489    
490           PCRE  assumes  by  default that it will run in an environment where the
491           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
492           This  is  the  case for most computer operating systems. PCRE can, how-
493           ever, be compiled to run in an EBCDIC environment by adding
494    
495             --enable-ebcdic
496    
497           to the configure command. This setting implies --enable-rebuild-charta-
498           bles.  You  should  only  use  it if you know that you are in an EBCDIC
499           environment (for example, an IBM mainframe operating system).
500    
501    
502    SEE ALSO
503    
504           pcreapi(3), pcre_config(3).
505    
506    
507    AUTHOR
508    
509           Philip Hazel
510           University Computing Service
511           Cambridge CB2 3QH, England.
512    
513    
514    REVISION
515    
516           Last updated: 30 July 2007
517           Copyright (c) 1997-2007 University of Cambridge.
518    ------------------------------------------------------------------------------
519    
520    
521    PCREMATCHING(3)                                                PCREMATCHING(3)
522    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
523    
524  NAME  NAME
525       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
526    
527    
528    PCRE MATCHING ALGORITHMS
529    
530  SYNOPSIS OF PCRE API         This document describes the two different algorithms that are available
531           in PCRE for matching a compiled regular expression against a given sub-
532           ject  string.  The  "standard"  algorithm  is  the  one provided by the
533           pcre_exec() function.  This works in the same was  as  Perl's  matching
534           function, and provides a Perl-compatible matching operation.
535    
536       #include <pcre.h>         An  alternative  algorithm is provided by the pcre_dfa_exec() function;
537           this operates in a different way, and is not  Perl-compatible.  It  has
538           advantages  and disadvantages compared with the standard algorithm, and
539           these are described below.
540    
541       pcre *pcre_compile(const char *pattern, int options,         When there is only one possible way in which a given subject string can
542            const char **errptr, int *erroffset,         match  a pattern, the two algorithms give the same answer. A difference
543            const unsigned char *tableptr);         arises, however, when there are multiple possibilities. For example, if
544           the pattern
545    
546       pcre_extra *pcre_study(const pcre *code, int options,           ^<.*>
           const char **errptr);  
547    
548       int pcre_exec(const pcre *code, const pcre_extra *extra,         is matched against the string
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
549    
550       int pcre_copy_named_substring(const pcre *code,           <something> <something else> <something further>
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
551    
552       int pcre_copy_substring(const char *subject, int *ovector,         there are three possible answers. The standard algorithm finds only one
553            int stringcount, int stringnumber, char *buffer,         of them, whereas the alternative algorithm finds all three.
           int buffersize);  
554    
      int pcre_get_named_substring(const pcre *code,  
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           const char **stringptr);  
555    
556       int pcre_get_stringnumber(const pcre *code,  REGULAR EXPRESSIONS AS TREES
           const char *name);  
557    
558       int pcre_get_substring(const char *subject, int *ovector,         The set of strings that are matched by a regular expression can be rep-
559            int stringcount, int stringnumber,         resented  as  a  tree structure. An unlimited repetition in the pattern
560            const char **stringptr);         makes the tree of infinite size, but it is still a tree.  Matching  the
561           pattern  to a given subject string (from a given starting point) can be
562           thought of as a search of the tree.  There are two  ways  to  search  a
563           tree:  depth-first  and  breadth-first, and these correspond to the two
564           matching algorithms provided by PCRE.
565    
      int pcre_get_substring_list(const char *subject,  
           int *ovector, int stringcount, const char ***listptr);  
566    
567       void pcre_free_substring(const char *stringptr);  THE STANDARD MATCHING ALGORITHM
568    
569       void pcre_free_substring_list(const char **stringptr);         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
570           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
571           depth-first search of the pattern tree. That is, it  proceeds  along  a
572           single path through the tree, checking that the subject matches what is
573           required. When there is a mismatch, the algorithm  tries  any  alterna-
574           tives  at  the  current point, and if they all fail, it backs up to the
575           previous branch point in the  tree,  and  tries  the  next  alternative
576           branch  at  that  level.  This often involves backing up (moving to the
577           left) in the subject string as well.  The  order  in  which  repetition
578           branches  are  tried  is controlled by the greedy or ungreedy nature of
579           the quantifier.
580    
581       const unsigned char *pcre_maketables(void);         If a leaf node is reached, a matching string has  been  found,  and  at
582           that  point the algorithm stops. Thus, if there is more than one possi-
583           ble match, this algorithm returns the first one that it finds.  Whether
584           this  is the shortest, the longest, or some intermediate length depends
585           on the way the greedy and ungreedy repetition quantifiers are specified
586           in the pattern.
587    
588       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         Because  it  ends  up  with a single path through the tree, it is rela-
589            int what, void *where);         tively straightforward for this algorithm to keep  track  of  the  sub-
590           strings  that  are  matched  by portions of the pattern in parentheses.
591           This provides support for capturing parentheses and back references.
592    
593    
594       int pcre_info(const pcre *code, int *optptr, *firstcharptr);  THE ALTERNATIVE MATCHING ALGORITHM
595    
596       int pcre_config(int what, void *where);         This algorithm conducts a breadth-first search of  the  tree.  Starting
597           from  the  first  matching  point  in the subject, it scans the subject
598           string from left to right, once, character by character, and as it does
599           this,  it remembers all the paths through the tree that represent valid
600           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
601           though  it is not implemented as a traditional finite state machine (it
602           keeps multiple states active simultaneously).
603    
604       char *pcre_version(void);         The scan continues until either the end of the subject is  reached,  or
605           there  are  no more unterminated paths. At this point, terminated paths
606           represent the different matching possibilities (if there are none,  the
607           match  has  failed).   Thus,  if there is more than one possible match,
608           this algorithm finds all of them, and in particular, it finds the long-
609           est.  In PCRE, there is an option to stop the algorithm after the first
610           match (which is necessarily the shortest) has been found.
611    
612       void *(*pcre_malloc)(size_t);         Note that all the matches that are found start at the same point in the
613           subject. If the pattern
614    
615       void (*pcre_free)(void *);           cat(er(pillar)?)
616    
617       int (*pcre_callout)(pcre_callout_block *);         is  matched  against the string "the caterpillar catchment", the result
618           will be the three strings "cat", "cater", and "caterpillar" that  start
619           at the fourth character of the subject. The algorithm does not automat-
620           ically move on to find matches that start at later positions.
621    
622           There are a number of features of PCRE regular expressions that are not
623           supported by the alternative matching algorithm. They are as follows:
624    
625  PCRE API         1.  Because  the  algorithm  finds  all possible matches, the greedy or
626           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
627           ungreedy quantifiers are treated in exactly the same way. However, pos-
628           sessive quantifiers can make a difference when what follows could  also
629           match what is quantified, for example in a pattern like this:
630    
631       PCRE has its own native API,  which  is  described  in  this           ^a++\w!
      document.  There  is  also  a  set of wrapper functions that  
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
632    
633       The native API function prototypes are defined in the header         This  pattern matches "aaab!" but not "aaa!", which would be matched by
634       file  pcre.h,  and  on  Unix  systems  the library itself is         a non-possessive quantifier. Similarly, if an atomic group is  present,
635       called libpcre.a, so can be accessed by adding -lpcre to the         it  is matched as if it were a standalone pattern at the current point,
636       command  for  linking  an  application  which  calls it. The         and the longest match is then "locked in" for the rest of  the  overall
637       header file defines the macros PCRE_MAJOR and PCRE_MINOR  to         pattern.
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
638    
639       The functions pcre_compile(), pcre_study(), and  pcre_exec()         2. When dealing with multiple paths through the tree simultaneously, it
640       are  used  for compiling and matching regular expressions. A         is not straightforward to keep track of  captured  substrings  for  the
641       sample program that demonstrates the simplest way  of  using         different  matching  possibilities,  and  PCRE's implementation of this
642       them  is  given in the file pcredemo.c. The pcresample docu-         algorithm does not attempt to do this. This means that no captured sub-
643       mentation describes how to run it.         strings are available.
644    
645       There are convenience functions for extracting captured sub-         3.  Because no substrings are captured, back references within the pat-
646       strings from a matched subject string. They are:         tern are not supported, and cause errors if encountered.
647    
648         pcre_copy_substring()         4. For the same reason, conditional expressions that use  a  backrefer-
649         pcre_copy_named_substring()         ence  as  the  condition or test for a specific group recursion are not
650         pcre_get_substring()         supported.
        pcre_get_named_substring()  
        pcre_get_substring_list()  
651    
652       pcre_free_substring()  and  pcre_free_substring_list()   are         5. Because many paths through the tree may be  active,  the  \K  escape
653       also  provided,  to  free  the  memory  used  for  extracted         sequence, which resets the start of the match when encountered (but may
654       strings.         be on some paths and not on others), is not  supported.  It  causes  an
655           error if encountered.
656    
657       The function pcre_maketables() is used (optionally) to build         6.  Callouts  are  supported, but the value of the capture_top field is
658       a  set of character tables in the current locale for passing         always 1, and the value of the capture_last field is always -1.
      to pcre_compile().  
659    
660       The function pcre_fullinfo() is used to find out information         7. The \C escape sequence, which (in the standard algorithm) matches  a
661       about a compiled pattern; pcre_info() is an obsolete version         single  byte, even in UTF-8 mode, is not supported because the alterna-
662       which returns only some of the available information, but is         tive algorithm moves through the subject  string  one  character  at  a
663       retained   for   backwards   compatibility.    The  function         time, for all active paths through the tree.
      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         8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
666       contain the entry points of the standard malloc() and free()         ported.
      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.  
667    
668       The global variable pcre_callout initially contains NULL. It  
669       can be set by the caller to a "callout" function, which PCRE  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
670       will then call at specified points during a matching  opera-  
671       tion. Details are given in the pcrecallout documentation.         Using the alternative matching algorithm provides the following  advan-
672           tages:
673    
674           1. All possible matches (at a single point in the subject) are automat-
675           ically found, and in particular, the longest match is  found.  To  find
676           more than one match using the standard algorithm, you have to do kludgy
677           things with callouts.
678    
679           2. There is much better support for partial matching. The  restrictions
680           on  the content of the pattern that apply when using the standard algo-
681           rithm for partial matching do not apply to the  alternative  algorithm.
682           For  non-anchored patterns, the starting position of a partial match is
683           available.
684    
685           3. Because the alternative algorithm  scans  the  subject  string  just
686           once,  and  never  needs to backtrack, it is possible to pass very long
687           subject strings to the matching function in  several  pieces,  checking
688           for partial matching each time.
689    
690    
691    DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
692    
693           The alternative algorithm suffers from a number of disadvantages:
694    
695           1.  It  is  substantially  slower  than the standard algorithm. This is
696           partly because it has to search for all possible matches, but  is  also
697           because it is less susceptible to optimization.
698    
699           2. Capturing parentheses and back references are not supported.
700    
701           3. Although atomic groups are supported, their use does not provide the
702           performance advantage that it does for the standard algorithm.
703    
704    
705    AUTHOR
706    
707           Philip Hazel
708           University Computing Service
709           Cambridge CB2 3QH, England.
710    
711    
712    REVISION
713    
714           Last updated: 08 August 2007
715           Copyright (c) 1997-2007 University of Cambridge.
716    ------------------------------------------------------------------------------
717    
718    
719    PCREAPI(3)                                                          PCREAPI(3)
720    
721    
722    NAME
723           PCRE - Perl-compatible regular expressions
724    
725    
726    PCRE NATIVE API
727    
728           #include <pcre.h>
729    
730           pcre *pcre_compile(const char *pattern, int options,
731                const char **errptr, int *erroffset,
732                const unsigned char *tableptr);
733    
734           pcre *pcre_compile2(const char *pattern, int options,
735                int *errorcodeptr,
736                const char **errptr, int *erroffset,
737                const unsigned char *tableptr);
738    
739           pcre_extra *pcre_study(const pcre *code, int options,
740                const char **errptr);
741    
742           int pcre_exec(const pcre *code, const pcre_extra *extra,
743                const char *subject, int length, int startoffset,
744                int options, int *ovector, int ovecsize);
745    
746           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
747                const char *subject, int length, int startoffset,
748                int options, int *ovector, int ovecsize,
749                int *workspace, int wscount);
750    
751           int pcre_copy_named_substring(const pcre *code,
752                const char *subject, int *ovector,
753                int stringcount, const char *stringname,
754                char *buffer, int buffersize);
755    
756           int pcre_copy_substring(const char *subject, int *ovector,
757                int stringcount, int stringnumber, char *buffer,
758                int buffersize);
759    
760           int pcre_get_named_substring(const pcre *code,
761                const char *subject, int *ovector,
762                int stringcount, const char *stringname,
763                const char **stringptr);
764    
765           int pcre_get_stringnumber(const pcre *code,
766                const char *name);
767    
768           int pcre_get_stringtable_entries(const pcre *code,
769                const char *name, char **first, char **last);
770    
771           int pcre_get_substring(const char *subject, int *ovector,
772                int stringcount, int stringnumber,
773                const char **stringptr);
774    
775           int pcre_get_substring_list(const char *subject,
776                int *ovector, int stringcount, const char ***listptr);
777    
778           void pcre_free_substring(const char *stringptr);
779    
780           void pcre_free_substring_list(const char **stringptr);
781    
782           const unsigned char *pcre_maketables(void);
783    
784           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
785                int what, void *where);
786    
787           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
788    
789           int pcre_refcount(pcre *code, int adjust);
790    
791           int pcre_config(int what, void *where);
792    
793           char *pcre_version(void);
794    
795           void *(*pcre_malloc)(size_t);
796    
797           void (*pcre_free)(void *);
798    
799           void *(*pcre_stack_malloc)(size_t);
800    
801           void (*pcre_stack_free)(void *);
802    
803           int (*pcre_callout)(pcre_callout_block *);
804    
805    
806    PCRE API OVERVIEW
807    
808           PCRE has its own native API, which is described in this document. There
809           are also some wrapper functions that correspond to  the  POSIX  regular
810           expression  API.  These  are  described in the pcreposix documentation.
811           Both of these APIs define a set of C function calls. A C++  wrapper  is
812           distributed with PCRE. It is documented in the pcrecpp page.
813    
814           The  native  API  C  function prototypes are defined in the header file
815           pcre.h, and on Unix systems the library itself is called  libpcre.   It
816           can normally be accessed by adding -lpcre to the command for linking an
817           application  that  uses  PCRE.  The  header  file  defines  the  macros
818           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
819           bers for the library.  Applications can use these  to  include  support
820           for different releases of PCRE.
821    
822           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
823           pcre_exec() are used for compiling and matching regular expressions  in
824           a  Perl-compatible  manner. A sample program that demonstrates the sim-
825           plest way of using them is provided in the file  called  pcredemo.c  in
826           the  source distribution. The pcresample documentation describes how to
827           run it.
828    
829           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
830           ble,  is  also provided. This uses a different algorithm for the match-
831           ing. The alternative algorithm finds all possible matches (at  a  given
832           point  in  the subject), and scans the subject just once. However, this
833           algorithm does not return captured substrings. A description of the two
834           matching  algorithms and their advantages and disadvantages is given in
835           the pcrematching documentation.
836    
837           In addition to the main compiling and  matching  functions,  there  are
838           convenience functions for extracting captured substrings from a subject
839           string that is matched by pcre_exec(). They are:
840    
841             pcre_copy_substring()
842             pcre_copy_named_substring()
843             pcre_get_substring()
844             pcre_get_named_substring()
845             pcre_get_substring_list()
846             pcre_get_stringnumber()
847             pcre_get_stringtable_entries()
848    
849           pcre_free_substring() and pcre_free_substring_list() are also provided,
850           to free the memory used for extracted strings.
851    
852           The  function  pcre_maketables()  is  used  to build a set of character
853           tables  in  the  current  locale   for   passing   to   pcre_compile(),
854           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
855           provided for specialist use.  Most  commonly,  no  special  tables  are
856           passed,  in  which case internal tables that are generated when PCRE is
857           built are used.
858    
859           The function pcre_fullinfo() is used to find out  information  about  a
860           compiled  pattern; pcre_info() is an obsolete version that returns only
861           some of the available information, but is retained for  backwards  com-
862           patibility.   The function pcre_version() returns a pointer to a string
863           containing the version of PCRE and its date of release.
864    
865           The function pcre_refcount() maintains a  reference  count  in  a  data
866           block  containing  a compiled pattern. This is provided for the benefit
867           of object-oriented applications.
868    
869           The global variables pcre_malloc and pcre_free  initially  contain  the
870           entry  points  of  the  standard malloc() and free() functions, respec-
871           tively. PCRE calls the memory management functions via these variables,
872           so  a  calling  program  can replace them if it wishes to intercept the
873           calls. This should be done before calling any PCRE functions.
874    
875           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
876           indirections  to  memory  management functions. These special functions
877           are used only when PCRE is compiled to use  the  heap  for  remembering
878           data, instead of recursive function calls, when running the pcre_exec()
879           function. See the pcrebuild documentation for  details  of  how  to  do
880           this.  It  is  a non-standard way of building PCRE, for use in environ-
881           ments that have limited stacks. Because of the greater  use  of  memory
882           management,  it  runs  more  slowly. Separate functions are provided so
883           that special-purpose external code can be  used  for  this  case.  When
884           used,  these  functions  are always called in a stack-like manner (last
885           obtained, first freed), and always for memory blocks of the same  size.
886           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
887           mentation.
888    
889           The global variable pcre_callout initially contains NULL. It can be set
890           by  the  caller  to  a "callout" function, which PCRE will then call at
891           specified points during a matching operation. Details are given in  the
892           pcrecallout documentation.
893    
894    
895    NEWLINES
896    
897           PCRE  supports five different conventions for indicating line breaks in
898           strings: a single CR (carriage return) character, a  single  LF  (line-
899           feed) character, the two-character sequence CRLF, any of the three pre-
900           ceding, or any Unicode newline sequence. The Unicode newline  sequences
901           are  the  three just mentioned, plus the single characters VT (vertical
902           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
903           separator, U+2028), and PS (paragraph separator, U+2029).
904    
905           Each  of  the first three conventions is used by at least one operating
906           system as its standard newline sequence. When PCRE is built, a  default
907           can  be  specified.  The default default is LF, which is the Unix stan-
908           dard. When PCRE is run, the default can be overridden,  either  when  a
909           pattern is compiled, or when it is matched.
910    
911           In the PCRE documentation the word "newline" is used to mean "the char-
912           acter or pair of characters that indicate a line break". The choice  of
913           newline  convention  affects  the  handling of the dot, circumflex, and
914           dollar metacharacters, the handling of #-comments in /x mode, and, when
915           CRLF  is a recognized line ending sequence, the match position advance-
916           ment for a non-anchored pattern. The choice of newline convention  does
917           not affect the interpretation of the \n or \r escape sequences.
918    
919    
920  MULTITHREADING  MULTITHREADING
921    
922       The PCRE functions can be used in  multi-threading  applica-         The  PCRE  functions  can be used in multi-threading applications, with
923       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
924       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
925       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
926       threads.  
927           The  compiled form of a regular expression is not altered during match-
928       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
929       during  matching, so the same compiled pattern can safely be         at once.
930       used by several threads at once.  
931    
932    SAVING PRECOMPILED PATTERNS FOR LATER USE
933    
934           The compiled form of a regular expression can be saved and re-used at a
935           later time, possibly by a different program, and even on a  host  other
936           than  the  one  on  which  it  was  compiled.  Details are given in the
937           pcreprecompile documentation. However, compiling a  regular  expression
938           with  one version of PCRE for use with a different version is not guar-
939           anteed to work and may cause crashes.
940    
941    
942  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
943    
944       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
945    
946           The function pcre_config() makes it possible for a PCRE client to  dis-
947           cover which optional features have been compiled into the PCRE library.
948           The pcrebuild documentation has more details about these optional  fea-
949           tures.
950    
951           The  first  argument  for pcre_config() is an integer, specifying which
952           information is required; the second argument is a pointer to a variable
953           into  which  the  information  is  placed. The following information is
954           available:
955    
956             PCRE_CONFIG_UTF8
957    
958           The output is an integer that is set to one if UTF-8 support is  avail-
959           able; otherwise it is set to zero.
960    
961             PCRE_CONFIG_UNICODE_PROPERTIES
962    
963       The function pcre_config() makes  it  possible  for  a  PCRE         The  output  is  an  integer  that is set to one if support for Unicode
964       client  to  discover  which optional features have been com-         character properties is available; otherwise it is set to zero.
      piled into the PCRE library. The pcrebuild documentation has  
      more details about these optional features.  
965    
966       The first argument for pcre_config() is an integer, specify-           PCRE_CONFIG_NEWLINE
      ing  which information is required; the second argument is a  
      pointer to a variable into which the information is  placed.  
      The following information is available:  
967    
968         PCRE_CONFIG_UTF8         The output is an integer whose value specifies  the  default  character
969           sequence  that is recognized as meaning "newline". The four values that
970           are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
971           and  -1  for  ANY. The default should normally be the standard sequence
972           for your operating system.
973    
974       The output is an integer that is set to one if UTF-8 support           PCRE_CONFIG_LINK_SIZE
      is available; otherwise it is set to zero.  
975    
976         PCRE_CONFIG_NEWLINE         The output is an integer that contains the number  of  bytes  used  for
977           internal linkage in compiled regular expressions. The value is 2, 3, or
978           4. Larger values allow larger regular expressions to  be  compiled,  at
979           the  expense  of  slower matching. The default value of 2 is sufficient
980           for all but the most massive patterns, since  it  allows  the  compiled
981           pattern to be up to 64K in size.
982    
983       The output is an integer that is set to  the  value  of  the           PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
      code  that  is  used for the newline character. It is either  
      linefeed (10) or carriage return (13), and  should  normally  
      be the standard character for your operating system.  
984    
985         PCRE_CONFIG_LINK_SIZE         The  output  is  an integer that contains the threshold above which the
986           POSIX interface uses malloc() for output vectors. Further  details  are
987           given in the pcreposix documentation.
988    
989       The output is an integer that contains the number  of  bytes           PCRE_CONFIG_MATCH_LIMIT
      used  for  internal linkage in compiled regular expressions.  
      The value is 2, 3, or 4. Larger values allow larger  regular  
      expressions  to be compiled, at the expense of slower match-  
      ing. The default value of 2 is sufficient for  all  but  the  
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
990    
991         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD         The output is an integer that gives the default limit for the number of
992           internal matching function calls in a  pcre_exec()  execution.  Further
993           details are given with pcre_exec() below.
994    
995       The output is an integer that contains the  threshold  above           PCRE_CONFIG_MATCH_LIMIT_RECURSION
      which  the POSIX interface uses malloc() for output vectors.  
      Further details are given in the pcreposix documentation.  
996    
997         PCRE_CONFIG_MATCH_LIMIT         The  output is an integer that gives the default limit for the depth of
998           recursion when calling the internal matching function in a  pcre_exec()
999           execution. Further details are given with pcre_exec() below.
1000    
1001       The output is an integer that gives the  default  limit  for           PCRE_CONFIG_STACKRECURSE
1002       the   number  of  internal  matching  function  calls  in  a  
1003       pcre_exec()  execution.  Further  details  are  given   with         The  output is an integer that is set to one if internal recursion when
1004       pcre_exec() below.         running pcre_exec() is implemented by recursive function calls that use
1005           the  stack  to remember their state. This is the usual way that PCRE is
1006           compiled. The output is zero if PCRE was compiled to use blocks of data
1007           on  the  heap  instead  of  recursive  function  calls.  In  this case,
1008           pcre_stack_malloc and  pcre_stack_free  are  called  to  manage  memory
1009           blocks on the heap, thus avoiding the use of the stack.
1010    
1011    
1012  COMPILING A PATTERN  COMPILING A PATTERN
1013    
1014       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
1015            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1016            const unsigned char *tableptr);              const unsigned char *tableptr);
1017    
1018       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
1019       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
1020       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
1021       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
1022       pcre_malloc is returned. This contains the compiled code and  
1023       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
1024       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
1025       not  externally  defined. It is up to the caller to free the         the  two interfaces is that pcre_compile2() has an additional argument,
1026       memory when it is no longer required.         errorcodeptr, via which a numerical error code can be returned.
1027    
1028       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
1029       that is, it does not depend on memory location, the complete         the  pattern  argument.  A  pointer to a single block of memory that is
1030       pcre data block is not fully relocatable,  because  it  con-         obtained via pcre_malloc is returned. This contains the  compiled  code
1031       tains  a  copy of the tableptr argument, which is an address         and related data. The pcre type is defined for the returned block; this
1032       (see below).         is a typedef for a structure whose contents are not externally defined.
1033       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
1034       the  compilation.  It  should  be  zero  if  no  options are         longer required.
1035       required. Some of the options, in particular, those that are  
1036       compatible  with Perl, can also be set and unset from within         Although the compiled code of a PCRE regex is relocatable, that is,  it
1037       the pattern (see the detailed description of regular expres-         does not depend on memory location, the complete pcre data block is not
1038       sions  in the pcrepattern documentation). For these options,         fully relocatable, because it may contain a copy of the tableptr  argu-
1039       the contents of the options argument specifies their initial         ment, which is an address (see below).
1040       settings  at  the  start  of  compilation and execution. The  
1041       PCRE_ANCHORED option can be set at the time of  matching  as         The options argument contains various bit settings that affect the com-
1042       well as at compile time.         pilation. It should be zero if no options are required.  The  available
1043           options  are  described  below. Some of them, in particular, those that
1044       If errptr is NULL, pcre_compile() returns NULL  immediately.         are compatible with Perl, can also be set and  unset  from  within  the
1045       Otherwise, if compilation of a pattern fails, pcre_compile()         pattern  (see  the  detailed  description in the pcrepattern documenta-
1046       returns NULL, and sets the variable pointed to by errptr  to         tion). For these options, the contents of the options  argument  speci-
1047       point  to a textual error message. The offset from the start         fies  their initial settings at the start of compilation and execution.
1048       of  the  pattern  to  the  character  where  the  error  was         The PCRE_ANCHORED and PCRE_NEWLINE_xxx options can be set at  the  time
1049       discovered   is   placed  in  the  variable  pointed  to  by         of matching as well as at compile time.
1050       erroffset, which must not be NULL. If it  is,  an  immediate  
1051       error is given.         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1052           if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
1053       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         sets the variable pointed to by errptr to point to a textual error mes-
1054       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
1055       compiled, using the default C  locale.  Otherwise,  tableptr         try to free it. The offset from the start of the pattern to the charac-
1056       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
1057       section on locale support below.         by  erroffset,  which must not be NULL. If it is, an immediate error is
1058           given.
1059       This code fragment shows a typical straightforward  call  to  
1060       pcre_compile():         If pcre_compile2() is used instead of pcre_compile(),  and  the  error-
1061           codeptr  argument is not NULL, a non-zero error code number is returned
1062         pcre *re;         via this argument in the event of an error. This is in addition to  the
1063         const char *error;         textual error message. Error codes and messages are listed below.
1064         int erroffset;  
1065         re = pcre_compile(         If  the  final  argument, tableptr, is NULL, PCRE uses a default set of
1066           "^A.*Z",          /* the pattern */         character tables that are  built  when  PCRE  is  compiled,  using  the
1067           0,                /* default options */         default  C  locale.  Otherwise, tableptr must be an address that is the
1068           &error,           /* for error message */         result of a call to pcre_maketables(). This value is  stored  with  the
1069           &erroffset,       /* for error offset */         compiled  pattern,  and used again by pcre_exec(), unless another table
1070           NULL);            /* use default character tables */         pointer is passed to it. For more discussion, see the section on locale
1071           support below.
1072       The following option bits are defined:  
1073           This  code  fragment  shows a typical straightforward call to pcre_com-
1074         PCRE_ANCHORED         pile():
1075    
1076       If this bit is set, the pattern is forced to be  "anchored",           pcre *re;
1077       that is, it is constrained to match only at the first match-           const char *error;
1078       ing point in the string which is being searched  (the  "sub-           int erroffset;
1079       ject string"). This effect can also be achieved by appropri-           re = pcre_compile(
1080       ate constructs in the pattern itself, which is the only  way             "^A.*Z",          /* the pattern */
1081       to do it in Perl.             0,                /* default options */
1082               &error,           /* for error message */
1083         PCRE_CASELESS             &erroffset,       /* for error offset */
1084               NULL);            /* use default character tables */
1085       If this bit is set, letters in the pattern match both  upper  
1086       and  lower  case  letters.  It  is  equivalent  to Perl's /i         The following names for option bits are defined in  the  pcre.h  header
1087       option, and it can be changed within a  pattern  by  a  (?i)         file:
1088       option setting.  
1089             PCRE_ANCHORED
1090         PCRE_DOLLAR_ENDONLY  
1091           If this bit is set, the pattern is forced to be "anchored", that is, it
1092       If this bit is set, a dollar metacharacter  in  the  pattern         is constrained to match only at the first matching point in the  string
1093       matches  only at the end of the subject string. Without this         that  is being searched (the "subject string"). This effect can also be
1094       option, a dollar also matches immediately before  the  final         achieved by appropriate constructs in the pattern itself, which is  the
1095       character  if it is a newline (but not before any other new-         only way to do it in Perl.
1096       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
1097       PCRE_MULTILINE is set. There is no equivalent to this option           PCRE_AUTO_CALLOUT
1098       in Perl, and no way to set it within a pattern.  
1099           If this bit is set, pcre_compile() automatically inserts callout items,
1100         PCRE_DOTALL         all with number 255, before each pattern item. For  discussion  of  the
1101           callout facility, see the pcrecallout documentation.
1102       If this bit is  set,  a  dot  metacharater  in  the  pattern  
1103       matches all characters, including newlines. Without it, new-           PCRE_CASELESS
1104       lines are excluded. This option is equivalent to  Perl's  /s  
1105       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
1106       option setting. A negative class such as [^a] always matches         case letters. It is equivalent to Perl's  /i  option,  and  it  can  be
1107       a  newline  character,  independent  of  the setting of this         changed  within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
1108       option.         always understands the concept of case for characters whose values  are
1109           less  than 128, so caseless matching is always possible. For characters
1110         PCRE_EXTENDED         with higher values, the concept of case is supported if  PCRE  is  com-
1111           piled  with Unicode property support, but not otherwise. If you want to
1112       If this bit is set, whitespace data characters in  the  pat-         use caseless matching for characters 128 and  above,  you  must  ensure
1113       tern  are  totally  ignored  except when escaped or inside a         that  PCRE  is  compiled  with Unicode property support as well as with
1114       character class. Whitespace does not include the VT  charac-         UTF-8 support.
1115       ter  (code 11). In addition, characters between an unescaped  
1116       # outside a character class and the next newline  character,           PCRE_DOLLAR_ENDONLY
1117       inclusive, are also ignored. This is equivalent to Perl's /x  
1118       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
1119       option setting.         at  the  end  of the subject string. Without this option, a dollar also
1120           matches immediately before a newline at the end of the string (but  not
1121       This option makes it possible  to  include  comments  inside         before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
1122       complicated patterns.  Note, however, that this applies only         if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
1123       to data characters. Whitespace characters may  never  appear         Perl, and no way to set it within a pattern.
1124       within special character sequences in a pattern, for example  
1125       within the sequence (?( which introduces a conditional  sub-           PCRE_DOTALL
1126       pattern.  
1127           If this bit is set, a dot metacharater in the pattern matches all char-
1128         PCRE_EXTRA         acters, including those that indicate newline. Without it, a  dot  does
1129           not  match  when  the  current position is at a newline. This option is
1130       This option was invented in  order  to  turn  on  additional         equivalent to Perl's /s option, and it can be changed within a  pattern
1131       functionality of PCRE that is incompatible with Perl, but it         by  a (?s) option setting. A negative class such as [^a] always matches
1132       is currently of very little use. When set, any backslash  in         newline characters, independent of the setting of this option.
1133       a  pattern  that is followed by a letter that has no special  
1134       meaning causes an error, thus reserving  these  combinations           PCRE_DUPNAMES
1135       for  future  expansion.  By default, as in Perl, a backslash  
1136       followed by a letter with no special meaning is treated as a         If this bit is set, names used to identify capturing  subpatterns  need
1137       literal.  There  are at present no other features controlled         not be unique. This can be helpful for certain types of pattern when it
1138       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
1139       within a pattern.         matched.  There  are  more details of named subpatterns below; see also
1140           the pcrepattern documentation.
1141         PCRE_MULTILINE  
1142             PCRE_EXTENDED
1143       By default, PCRE treats the subject string as consisting  of  
1144       a  single "line" of characters (even if it actually contains         If this bit is set, whitespace  data  characters  in  the  pattern  are
1145       several newlines). The "start  of  line"  metacharacter  (^)         totally ignored except when escaped or inside a character class. White-
1146       matches  only  at the start of the string, while the "end of         space does not include the VT character (code 11). In addition, charac-
1147       line" metacharacter ($) matches  only  at  the  end  of  the         ters between an unescaped # outside a character class and the next new-
1148       string,    or   before   a   terminating   newline   (unless         line, inclusive, are also ignored. This  is  equivalent  to  Perl's  /x
1149       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-
1150           ting.
1151       When PCRE_MULTILINE it is set, the "start of line" and  "end  
1152       of  line"  constructs match immediately following or immedi-         This option makes it possible to include  comments  inside  complicated
1153       ately before any newline  in  the  subject  string,  respec-         patterns.   Note,  however,  that this applies only to data characters.
1154       tively,  as  well  as  at  the  very  start and end. This is         Whitespace  characters  may  never  appear  within  special   character
1155       equivalent to Perl's /m option, and it can be changed within         sequences  in  a  pattern,  for  example  within the sequence (?( which
1156       a  pattern  by  a  (?m) option setting. If there are no "\n"         introduces a conditional subpattern.
1157       characters in a subject string, or no occurrences of ^ or  $  
1158       in a pattern, setting PCRE_MULTILINE has no effect.           PCRE_EXTRA
1159    
1160         PCRE_NO_AUTO_CAPTURE         This option was invented in order to turn on  additional  functionality
1161           of  PCRE  that  is  incompatible with Perl, but it is currently of very
1162       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
1163       turing  parentheses  in the pattern. Any opening parenthesis         letter  that  has  no  special  meaning causes an error, thus reserving
1164       that is not followed by ? behaves as if it were followed  by         these combinations for future expansion. By  default,  as  in  Perl,  a
1165       ?:  but  named  parentheses  can still be used for capturing         backslash  followed by a letter with no special meaning is treated as a
1166       (and they acquire numbers in the usual  way).  There  is  no         literal. (Perl can, however, be persuaded to give a warning for  this.)
1167       equivalent of this option in Perl.         There  are  at  present no other features controlled by this option. It
1168           can also be set by a (?X) option setting within a pattern.
1169         PCRE_UNGREEDY  
1170             PCRE_FIRSTLINE
1171       This option inverts the "greediness" of the  quantifiers  so  
1172       that  they  are  not greedy by default, but become greedy if         If this option is set, an  unanchored  pattern  is  required  to  match
1173       followed by "?". It is not compatible with Perl. It can also         before  or  at  the  first  newline  in  the subject string, though the
1174       be set by a (?U) option setting within the pattern.         matched text may continue over the newline.
1175    
1176         PCRE_UTF8           PCRE_MULTILINE
1177    
1178       This option causes PCRE to regard both the pattern  and  the         By default, PCRE treats the subject string as consisting  of  a  single
1179       subject  as  strings  of UTF-8 characters instead of single-         line  of characters (even if it actually contains newlines). The "start
1180       byte character strings. However, it  is  available  only  if         of line" metacharacter (^) matches only at the  start  of  the  string,
1181       PCRE  has  been  built to include UTF-8 support. If not, the         while  the  "end  of line" metacharacter ($) matches only at the end of
1182       use of this option provokes an error. Details  of  how  this         the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1183       option  changes  the behaviour of PCRE are given in the sec-         is set). This is the same as Perl.
1184       tion on UTF-8 support in the main pcre page.  
1185           When  PCRE_MULTILINE  it  is set, the "start of line" and "end of line"
1186           constructs match immediately following or immediately  before  internal
1187           newlines  in  the  subject string, respectively, as well as at the very
1188           start and end. This is equivalent to Perl's /m option, and  it  can  be
1189           changed within a pattern by a (?m) option setting. If there are no new-
1190           lines in a subject string, or no occurrences of ^ or $  in  a  pattern,
1191           setting PCRE_MULTILINE has no effect.
1192    
1193             PCRE_NEWLINE_CR
1194             PCRE_NEWLINE_LF
1195             PCRE_NEWLINE_CRLF
1196             PCRE_NEWLINE_ANYCRLF
1197             PCRE_NEWLINE_ANY
1198    
1199           These  options  override the default newline definition that was chosen
1200           when PCRE was built. Setting the first or the second specifies  that  a
1201           newline  is  indicated  by a single character (CR or LF, respectively).
1202           Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by  the
1203           two-character  CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF specifies
1204           that any of the three preceding sequences should be recognized. Setting
1205           PCRE_NEWLINE_ANY  specifies that any Unicode newline sequence should be
1206           recognized. The Unicode newline sequences are the three just mentioned,
1207           plus  the  single  characters  VT (vertical tab, U+000B), FF (formfeed,
1208           U+000C), NEL (next line, U+0085), LS (line separator, U+2028),  and  PS
1209           (paragraph  separator,  U+2029).  The  last  two are recognized only in
1210           UTF-8 mode.
1211    
1212           The newline setting in the  options  word  uses  three  bits  that  are
1213           treated as a number, giving eight possibilities. Currently only six are
1214           used (default plus the five values above). This means that if  you  set
1215           more  than one newline option, the combination may or may not be sensi-
1216           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1217           PCRE_NEWLINE_CRLF,  but other combinations may yield unused numbers and
1218           cause an error.
1219    
1220           The only time that a line break is specially recognized when  compiling
1221           a  pattern  is  if  PCRE_EXTENDED  is set, and an unescaped # outside a
1222           character class is encountered. This indicates  a  comment  that  lasts
1223           until  after the next line break sequence. In other circumstances, line
1224           break  sequences  are  treated  as  literal  data,   except   that   in
1225           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1226           and are therefore ignored.
1227    
1228           The newline option that is set at compile time becomes the default that
1229           is  used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
1230    
1231             PCRE_NO_AUTO_CAPTURE
1232    
1233           If this option is set, it disables the use of numbered capturing paren-
1234           theses  in the pattern. Any opening parenthesis that is not followed by
1235           ? behaves as if it were followed by ?: but named parentheses can  still
1236           be  used  for  capturing  (and  they acquire numbers in the usual way).
1237           There is no equivalent of this option in Perl.
1238    
1239             PCRE_UNGREEDY
1240    
1241           This option inverts the "greediness" of the quantifiers  so  that  they
1242           are  not greedy by default, but become greedy if followed by "?". It is
1243           not compatible with Perl. It can also be set by a (?U)  option  setting
1244           within the pattern.
1245    
1246             PCRE_UTF8
1247    
1248           This  option  causes PCRE to regard both the pattern and the subject as
1249           strings of UTF-8 characters instead of single-byte  character  strings.
1250           However,  it is available only when PCRE is built to include UTF-8 sup-
1251           port. If not, the use of this option provokes an error. Details of  how
1252           this  option  changes the behaviour of PCRE are given in the section on
1253           UTF-8 support in the main pcre page.
1254    
1255             PCRE_NO_UTF8_CHECK
1256    
1257           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1258           automatically  checked.  There  is  a  discussion about the validity of
1259           UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
1260           bytes  is  found,  pcre_compile() returns an error. If you already know
1261           that your pattern is valid, and you want to skip this check for perfor-
1262           mance  reasons,  you  can set the PCRE_NO_UTF8_CHECK option. When it is
1263           set, the effect of passing an invalid UTF-8  string  as  a  pattern  is
1264           undefined.  It  may  cause your program to crash. Note that this option
1265           can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
1266           UTF-8 validity checking of subject strings.
1267    
1268    
1269    COMPILATION ERROR CODES
1270    
1271           The  following  table  lists  the  error  codes than may be returned by
1272           pcre_compile2(), along with the error messages that may be returned  by
1273           both  compiling functions. As PCRE has developed, some error codes have
1274           fallen out of use. To avoid confusion, they have not been re-used.
1275    
1276              0  no error
1277              1  \ at end of pattern
1278              2  \c at end of pattern
1279              3  unrecognized character follows \
1280              4  numbers out of order in {} quantifier
1281              5  number too big in {} quantifier
1282              6  missing terminating ] for character class
1283              7  invalid escape sequence in character class
1284              8  range out of order in character class
1285              9  nothing to repeat
1286             10  [this code is not in use]
1287             11  internal error: unexpected repeat
1288             12  unrecognized character after (?
1289             13  POSIX named classes are supported only within a class
1290             14  missing )
1291             15  reference to non-existent subpattern
1292             16  erroffset passed as NULL
1293             17  unknown option bit(s) set
1294             18  missing ) after comment
1295             19  [this code is not in use]
1296             20  regular expression too large
1297             21  failed to get memory
1298             22  unmatched parentheses
1299             23  internal error: code overflow
1300             24  unrecognized character after (?<
1301             25  lookbehind assertion is not fixed length
1302             26  malformed number or name after (?(
1303             27  conditional group contains more than two branches
1304             28  assertion expected after (?(
1305             29  (?R or (?[+-]digits must be followed by )
1306             30  unknown POSIX class name
1307             31  POSIX collating elements are not supported
1308             32  this version of PCRE is not compiled with PCRE_UTF8 support
1309             33  [this code is not in use]
1310             34  character value in \x{...} sequence is too large
1311             35  invalid condition (?(0)
1312             36  \C not allowed in lookbehind assertion
1313             37  PCRE does not support \L, \l, \N, \U, or \u
1314             38  number after (?C is > 255
1315             39  closing ) for (?C expected
1316             40  recursive call could loop indefinitely
1317             41  unrecognized character after (?P
1318             42  syntax error in subpattern name (missing terminator)
1319             43  two named subpatterns have the same name
1320             44  invalid UTF-8 string
1321             45  support for \P, \p, and \X has not been compiled
1322             46  malformed \P or \p sequence
1323             47  unknown property name after \P or \p
1324             48  subpattern name is too long (maximum 32 characters)
1325             49  too many named subpatterns (maximum 10,000)
1326             50  [this code is not in use]
1327             51  octal value is greater than \377 (not in UTF-8 mode)
1328             52  internal error: overran compiling workspace
1329             53  internal  error:  previously-checked  referenced  subpattern  not
1330           found
1331             54  DEFINE group contains more than one branch
1332             55  repeating a DEFINE group is not allowed
1333             56  inconsistent NEWLINE options"
1334             57  \g is not followed by a braced name or an optionally braced
1335                   non-zero number
1336             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1337    
1338    
1339  STUDYING A PATTERN  STUDYING A PATTERN
1340    
1341       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1342            const char **errptr);              const char **errptr);
1343    
1344       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
1345       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
1346       the time taken for matching. The function pcre_study() takes         matching.  The function pcre_study() takes a pointer to a compiled pat-
1347       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1348       studing the pattern  produces  additional  information  that         information  that  will  help speed up matching, pcre_study() returns a
1349       will  help speed up matching, pcre_study() returns a pointer         pointer to a pcre_extra block, in which the study_data field points  to
1350       to a pcre_extra block, in which the study_data field  points         the results of the study.
1351       to the results of the study.  
1352           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1353       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec(). However, a pcre_extra block  also  contains  other  fields
1354       directly  to pcre_exec(). However, the pcre_extra block also         that  can  be  set  by the caller before the block is passed; these are
1355       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
1356       the  block is passed; these are described below. If studying  
1357       the pattern does not  produce  any  additional  information,         If studying the pattern does not  produce  any  additional  information
1358       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1359       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
1360       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
1361    
1362       The second argument contains option  bits.  At  present,  no         The  second  argument of pcre_study() contains option bits. At present,
1363       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1364       should always be zero.  
1365           The third argument for pcre_study() is a pointer for an error  message.
1366       The third argument for pcre_study()  is  a  pointer  for  an         If  studying  succeeds  (even  if no data is returned), the variable it
1367       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
1368       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
1369       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
1370       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1371       pcre_study(), to be sure that it has run successfully.  
1372           This is a typical call to pcre_study():
1373       This is a typical call to pcre_study():  
1374             pcre_extra *pe;
1375         pcre_extra *pe;           pe = pcre_study(
1376         pe = pcre_study(             re,             /* result of pcre_compile() */
1377           re,             /* result of pcre_compile() */             0,              /* no options exist */
1378           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1379           &error);        /* set to NULL or points to a message */  
1380           At present, studying a pattern is useful only for non-anchored patterns
1381       At present, studying a  pattern  is  useful  only  for  non-         that do not have a single fixed starting character. A bitmap of  possi-
1382       anchored  patterns  that do not have a single fixed starting         ble starting bytes is created.
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1383    
1384    
1385  LOCALE SUPPORT  LOCALE SUPPORT
1386    
1387       PCRE handles caseless matching, and determines whether char-         PCRE  handles  caseless matching, and determines whether characters are
1388       acters  are  letters, digits, or whatever, by reference to a         letters, digits, or whatever, by reference to a set of tables,  indexed
1389       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
1390       to characters with codes less than 256. The library contains         characters with codes less than 128. Higher-valued  codes  never  match
1391       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
1392       locale  when  PCRE  is compiled. This is used when the final         with Unicode character property support. The use of locales  with  Uni-
1393       argument of pcre_compile() is NULL, and  is  sufficient  for         code  is discouraged. If you are handling characters with codes greater
1394       many applications.         than 128, you should either use UTF-8 and Unicode, or use locales,  but
1395           not try to mix the two.
1396       An alternative set of tables can, however, be supplied. Such  
1397       tables  are built by calling the pcre_maketables() function,         PCRE  contains  an  internal set of tables that are used when the final
1398       which has no arguments, in the relevant locale.  The  result         argument of pcre_compile() is  NULL.  These  are  sufficient  for  many
1399       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1400       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1401       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1402       greater than 128 are treated as letters), the following code         which may cause them to be different.
1403       could be used:  
1404           The internal tables can always be overridden by tables supplied by  the
1405         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1406         tables = pcre_maketables();         from the default. As more and more applications change  to  using  Uni-
1407         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1408    
1409       The  tables  are  built  in  memory  that  is  obtained  via         External  tables  are  built by calling the pcre_maketables() function,
1410       pcre_malloc.  The  pointer that is passed to pcre_compile is         which has no arguments, in the relevant locale. The result can then  be
1411       saved with the compiled pattern, and  the  same  tables  are         passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
1412       used via this pointer by pcre_study() and pcre_exec(). Thus,         example, to build and use tables that are appropriate  for  the  French
1413       for any single pattern, compilation, studying  and  matching         locale  (where  accented  characters  with  values greater than 128 are
1414       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1415       compiled in different locales. It is the caller's  responsi-  
1416       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1417       remains available for as long as it is needed.           tables = pcre_maketables();
1418             re = pcre_compile(..., tables);
1419    
1420           The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
1421           if you are using Windows, the name for the French locale is "french".
1422    
1423           When  pcre_maketables()  runs,  the  tables are built in memory that is
1424           obtained via pcre_malloc. It is the caller's responsibility  to  ensure
1425           that  the memory containing the tables remains available for as long as
1426           it is needed.
1427    
1428           The pointer that is passed to pcre_compile() is saved with the compiled
1429           pattern,  and the same tables are used via this pointer by pcre_study()
1430           and normally also by pcre_exec(). Thus, by default, for any single pat-
1431           tern, compilation, studying and matching all happen in the same locale,
1432           but different patterns can be compiled in different locales.
1433    
1434           It is possible to pass a table pointer or NULL (indicating the  use  of
1435           the  internal  tables)  to  pcre_exec(). Although not intended for this
1436           purpose, this facility could be used to match a pattern in a  different
1437           locale from the one in which it was compiled. Passing table pointers at
1438           run time is discussed below in the section on matching a pattern.
1439    
1440    
1441  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1442    
1443       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1444            int what, void *where);              int what, void *where);
1445    
1446       The pcre_fullinfo() function  returns  information  about  a         The pcre_fullinfo() function returns information about a compiled  pat-
1447       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1448       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1449       ity (and is documented below).  
1450           The first argument for pcre_fullinfo() is a  pointer  to  the  compiled
1451       The first argument for pcre_fullinfo() is a pointer  to  the         pattern.  The second argument is the result of pcre_study(), or NULL if
1452       compiled  pattern.  The  second  argument  is  the result of         the pattern was not studied. The third argument specifies  which  piece
1453       pcre_study(), or NULL if the pattern was  not  studied.  The         of  information  is required, and the fourth argument is a pointer to a
1454       third  argument  specifies  which  piece  of  information is         variable to receive the data. The yield of the  function  is  zero  for
1455       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1456       to  receive  the data. The yield of the function is zero for  
1457       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1458                                   the argument where was NULL
1459         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1460                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1461         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1462         PCRE_ERROR_BADOPTION  the value of what was invalid         The  "magic  number" is placed at the start of each compiled pattern as
1463           an simple check against passing an arbitrary memory pointer. Here is  a
1464       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical  call  of pcre_fullinfo(), to obtain the length of the compiled
1465       length of the compiled pattern:         pattern:
1466    
1467         int rc;           int rc;
1468         unsigned long int length;           size_t length;
1469         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1470           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1471           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1472           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1473           &length);         /* where to put the data */             &length);         /* where to put the data */
1474    
1475       The possible values for the third argument  are  defined  in         The possible values for the third argument are defined in  pcre.h,  and
1476       pcre.h, and are as follows:         are as follows:
1477    
1478         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1479    
1480       Return the number of the highest back reference in the  pat-         Return  the  number  of  the highest back reference in the pattern. The
1481       tern.  The  fourth argument should point to an int variable.         fourth argument should point to an int variable. Zero  is  returned  if
1482       Zero is returned if there are no back references.         there are no back references.
1483    
1484         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1485    
1486       Return the number of capturing subpatterns in  the  pattern.         Return  the  number of capturing subpatterns in the pattern. The fourth
1487       The fourth argument should point to an int variable.         argument should point to an int variable.
1488    
1489         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1490    
1491       Return information about  the  first  byte  of  any  matched         Return a pointer to the internal default character tables within  PCRE.
1492       string,  for a non-anchored pattern. (This option used to be         The  fourth  argument should point to an unsigned char * variable. This
1493       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1494       for backwards compatibility.)         tion.  External  callers  can  cause PCRE to use its internal tables by
1495           passing a NULL table pointer.
1496       If there is a fixed first byte, e.g. from a pattern such  as  
1497       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1498       by where. Otherwise, if either  
1499           Return information about the first byte of any matched  string,  for  a
1500       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored  pattern. The fourth argument should point to an int vari-
1501       and every branch starts with "^", or         able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
1502           is still recognized for backwards compatibility.)
1503       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1504       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
1505       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1506    
1507       -1 is returned, indicating that the pattern matches only  at         (a) the pattern was compiled with the PCRE_MULTILINE option, and  every
1508       the  start  of  a subject string or after any newline within         branch starts with "^", or
1509       the string. Otherwise -2 is returned. For anchored patterns,  
1510       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1511           set (if it were set, the pattern would be anchored),
1512         PCRE_INFO_FIRSTTABLE  
1513           -1 is returned, indicating that the pattern matches only at  the  start
1514       If the pattern was studied, and this resulted  in  the  con-         of  a  subject string or after any newline within the string. Otherwise
1515       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1516       for the first byte in any matching string, a pointer to  the  
1517       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1518       argument should point to an unsigned char * variable.  
1519           If the pattern was studied, and this resulted in the construction of  a
1520         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1521           matching string, a pointer to the table is returned. Otherwise NULL  is
1522       Return the value of the rightmost  literal  byte  that  must         returned.  The fourth argument should point to an unsigned char * vari-
1523       exist  in  any  matched  string, other than at its start, if         able.
1524       such a byte has been recorded. The  fourth  argument  should  
1525       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_JCHANGED
1526       returned. For anchored patterns,  a  last  literal  byte  is  
1527       recorded  only  if  it follows something of variable length.         Return 1 if the (?J) option setting is used in the  pattern,  otherwise
1528       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-
1529       is "z", but for /^a\dz\d/ the returned value is -1.         nal option setting changes the local PCRE_DUPNAMES option.
1530    
1531         PCRE_INFO_NAMECOUNT           PCRE_INFO_LASTLITERAL
1532         PCRE_INFO_NAMEENTRYSIZE  
1533         PCRE_INFO_NAMETABLE         Return the value of the rightmost literal byte that must exist  in  any
1534           matched  string,  other  than  at  its  start,  if such a byte has been
1535       PCRE supports the use of named as well as numbered capturing         recorded. The fourth argument should point to an int variable. If there
1536       parentheses. The names are just an additional way of identi-         is  no such byte, -1 is returned. For anchored patterns, a last literal
1537       fying the parentheses,  which  still  acquire  a  number.  A         byte is recorded only if it follows something of variable  length.  For
1538       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
1539       must convert the name to a number in  order  to  access  the         /^a\dz\d/ the returned value is -1.
1540       correct  pointers  in  the  output  vector  (described  with  
1541       pcre_exec() below). In order to do this, it must  first  use           PCRE_INFO_NAMECOUNT
1542       these  three  values  to  obtain  the name-to-number mapping           PCRE_INFO_NAMEENTRYSIZE
1543       table for the pattern.           PCRE_INFO_NAMETABLE
1544    
1545       The  map  consists  of  a  number  of  fixed-size   entries.         PCRE supports the use of named as well as numbered capturing  parenthe-
1546       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and         ses.  The names are just an additional way of identifying the parenthe-
1547       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both         ses, which still acquire numbers. Several convenience functions such as
1548       of  these return an int value. The entry size depends on the         pcre_get_named_substring()  are  provided  for extracting captured sub-
1549       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a         strings by name. It is also possible to extract the data  directly,  by
1550       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
1551       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
1552       turing parenthesis, most significant byte first. The rest of         the  conversion,  you  need  to  use  the  name-to-number map, which is
1553       the entry is the corresponding name,  zero  terminated.  The         described by these three values.
1554       names  are  in alphabetical order. For example, consider the  
1555       following pattern (assume PCRE_EXTENDED  is  set,  so  white         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1556       space - including newlines - is ignored):         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1557           of each entry; both of these  return  an  int  value.  The  entry  size
1558         (?P<date> (?P<year>(\d\d)?\d\d) -         depends  on the length of the longest name. PCRE_INFO_NAMETABLE returns
1559         (?P<month>\d\d) - (?P<day>\d\d) )         a pointer to the first entry of the table  (a  pointer  to  char).  The
1560           first two bytes of each entry are the number of the capturing parenthe-
1561       There are four named subpatterns,  so  the  table  has  four         sis, most significant byte first. The rest of the entry is  the  corre-
1562       entries,  and  each  entry in the table is eight bytes long.         sponding  name,  zero  terminated. The names are in alphabetical order.
1563       The table is as follows, with non-printing  bytes  shows  in         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1564       hex, and undefined bytes shown as ??:         theses  numbers.  For  example,  consider the following pattern (assume
1565           PCRE_EXTENDED is  set,  so  white  space  -  including  newlines  -  is
1566         00 01 d  a  t  e  00 ??         ignored):
1567         00 05 d  a  y  00 ?? ??  
1568         00 04 m  o  n  t  h  00           (?<date> (?<year>(\d\d)?\d\d) -
1569         00 02 y  e  a  r  00 ??           (?<month>\d\d) - (?<day>\d\d) )
1570    
1571       When writing code to extract data  from  named  subpatterns,         There  are  four  named subpatterns, so the table has four entries, and
1572       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,
1573       each compiled pattern.         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1574           as ??:
1575         PCRE_INFO_OPTIONS  
1576             00 01 d  a  t  e  00 ??
1577       Return a copy of the options with which the pattern was com-           00 05 d  a  y  00 ?? ??
1578       piled.  The fourth argument should point to an unsigned long           00 04 m  o  n  t  h  00
1579       int variable. These option bits are those specified  in  the           00 02 y  e  a  r  00 ??
1580       call  to  pcre_compile(),  modified  by any top-level option  
1581       settings within the pattern itself.         When writing code to extract data  from  named  subpatterns  using  the
1582           name-to-number  map,  remember that the length of the entries is likely
1583       A pattern is automatically anchored by PCRE if  all  of  its         to be different for each compiled pattern.
1584       top-level alternatives begin with one of the following:  
1585             PCRE_INFO_OKPARTIAL
1586         ^     unless PCRE_MULTILINE is set  
1587         \A    always         Return 1 if the pattern can be used for partial matching, otherwise  0.
1588         \G    always         The  fourth  argument  should point to an int variable. The pcrepartial
1589         .*    if PCRE_DOTALL is set and there are no back         documentation lists the restrictions that apply to patterns  when  par-
1590                 references to the subpattern in which .* appears         tial matching is used.
1591    
1592       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the           PCRE_INFO_OPTIONS
1593       options returned by pcre_fullinfo().  
1594           Return  a  copy of the options with which the pattern was compiled. The
1595         PCRE_INFO_SIZE         fourth argument should point to an unsigned long  int  variable.  These
1596           option bits are those specified in the call to pcre_compile(), modified
1597       Return the size of the compiled pattern, that is, the  value         by any top-level option settings at the start of the pattern itself. In
1598       that  was  passed as the argument to pcre_malloc() when PCRE         other  words,  they are the options that will be in force when matching
1599       was getting memory in which to place the compiled data.  The         starts. For example, if the pattern /(?im)abc(?-i)d/ is  compiled  with
1600       fourth argument should point to a size_t variable.         the  PCRE_EXTENDED option, the result is PCRE_CASELESS, PCRE_MULTILINE,
1601           and PCRE_EXTENDED.
1602         PCRE_INFO_STUDYSIZE  
1603           A pattern is automatically anchored by PCRE if  all  of  its  top-level
1604       Returns the size  of  the  data  block  pointed  to  by  the         alternatives begin with one of the following:
1605       study_data  field  in a pcre_extra block. That is, it is the  
1606       value that was passed to pcre_malloc() when PCRE was getting           ^     unless PCRE_MULTILINE is set
1607       memory into which to place the data created by pcre_study().           \A    always
1608       The fourth argument should point to a size_t variable.           \G    always
1609             .*    if PCRE_DOTALL is set and there are no back
1610                     references to the subpattern in which .* appears
1611    
1612           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1613           by pcre_fullinfo().
1614    
1615             PCRE_INFO_SIZE
1616    
1617           Return the size of the compiled pattern, that is, the  value  that  was
1618           passed as the argument to pcre_malloc() when PCRE was getting memory in
1619           which to place the compiled data. The fourth argument should point to a
1620           size_t variable.
1621    
1622             PCRE_INFO_STUDYSIZE
1623    
1624           Return the size of the data block pointed to by the study_data field in
1625           a pcre_extra block. That is,  it  is  the  value  that  was  passed  to
1626           pcre_malloc() when PCRE was getting memory into which to place the data
1627           created by pcre_study(). The fourth argument should point to  a  size_t
1628           variable.
1629    
1630    
1631  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1632    
1633       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1634    
1635       The pcre_info() function is now obsolete because its  inter-         The  pcre_info()  function is now obsolete because its interface is too
1636       face  is  too  restrictive  to return all the available data         restrictive to return all the available data about a compiled  pattern.
1637       about  a  compiled  pattern.   New   programs   should   use         New   programs   should  use  pcre_fullinfo()  instead.  The  yield  of
1638       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info() is the number of capturing subpatterns, or one of the  fol-
1639       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1640       negative numbers:  
1641             PCRE_ERROR_NULL       the argument code was NULL
1642         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1643         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1644           If  the  optptr  argument is not NULL, a copy of the options with which
1645       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
1646       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1647       it points to (see PCRE_INFO_OPTIONS above).  
1648           If  the  pattern  is  not anchored and the firstcharptr argument is not
1649       If the pattern is not anchored and the firstcharptr argument         NULL, it is used to pass back information about the first character  of
1650       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1651       first    character    of    any    matched    string    (see  
1652       PCRE_INFO_FIRSTBYTE above).  
1653    REFERENCE COUNTS
1654    
1655           int pcre_refcount(pcre *code, int adjust);
1656    
1657           The  pcre_refcount()  function is used to maintain a reference count in
1658           the data block that contains a compiled pattern. It is provided for the
1659           benefit  of  applications  that  operate  in an object-oriented manner,
1660           where different parts of the application may be using the same compiled
1661           pattern, but you want to free the block when they are all done.
1662    
1663           When a pattern is compiled, the reference count field is initialized to
1664           zero.  It is changed only by calling this function, whose action is  to
1665           add  the  adjust  value  (which may be positive or negative) to it. The
1666           yield of the function is the new value. However, the value of the count
1667           is  constrained to lie between 0 and 65535, inclusive. If the new value
1668           is outside these limits, it is forced to the appropriate limit value.
1669    
1670           Except when it is zero, the reference count is not correctly  preserved
1671           if  a  pattern  is  compiled on one host and then transferred to a host
1672           whose byte-order is different. (This seems a highly unlikely scenario.)
1673    
1674    
1675    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1676    
1677           int pcre_exec(const pcre *code, const pcre_extra *extra,
1678                const char *subject, int length, int startoffset,
1679                int options, int *ovector, int ovecsize);
1680    
1681           The  function pcre_exec() is called to match a subject string against a
1682           compiled pattern, which is passed in the code argument. If the  pattern
1683           has been studied, the result of the study should be passed in the extra
1684           argument. This function is the main matching facility of  the  library,
1685           and it operates in a Perl-like manner. For specialist use there is also
1686           an alternative matching function, which is described below in the  sec-
1687           tion about the pcre_dfa_exec() function.
1688    
1689           In  most applications, the pattern will have been compiled (and option-
1690           ally studied) in the same process that calls pcre_exec().  However,  it
1691           is possible to save compiled patterns and study data, and then use them
1692           later in different processes, possibly even on different hosts.  For  a
1693           discussion about this, see the pcreprecompile documentation.
1694    
1695           Here is an example of a simple call to pcre_exec():
1696    
1697             int rc;
1698             int ovector[30];
1699             rc = pcre_exec(
1700               re,             /* result of pcre_compile() */
1701               NULL,           /* we didn't study the pattern */
1702               "some string",  /* the subject string */
1703               11,             /* the length of the subject string */
1704               0,              /* start at offset 0 in the subject */
1705               0,              /* default options */
1706               ovector,        /* vector of integers for substring information */
1707               30);            /* number of elements (NOT size in bytes) */
1708    
1709       Extra data for pcre_exec()
1710    
1711           If  the  extra argument is not NULL, it must point to a pcre_extra data
1712           block. The pcre_study() function returns such a block (when it  doesn't
1713           return  NULL), but you can also create one for yourself, and pass addi-
1714           tional information in it. The pcre_extra block contains  the  following
1715           fields (not necessarily in this order):
1716    
1717             unsigned long int flags;
1718             void *study_data;
1719             unsigned long int match_limit;
1720             unsigned long int match_limit_recursion;
1721             void *callout_data;
1722             const unsigned char *tables;
1723    
1724           The  flags  field  is a bitmap that specifies which of the other fields
1725           are set. The flag bits are:
1726    
1727             PCRE_EXTRA_STUDY_DATA
1728             PCRE_EXTRA_MATCH_LIMIT
1729             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1730             PCRE_EXTRA_CALLOUT_DATA
1731             PCRE_EXTRA_TABLES
1732    
1733           Other flag bits should be set to zero. The study_data field is  set  in
1734           the  pcre_extra  block  that is returned by pcre_study(), together with
1735           the appropriate flag bit. You should not set this yourself, but you may
1736           add  to  the  block by setting the other fields and their corresponding
1737           flag bits.
1738    
1739           The match_limit field provides a means of preventing PCRE from using up
1740           a  vast amount of resources when running patterns that are not going to
1741           match, but which have a very large number  of  possibilities  in  their
1742           search  trees.  The  classic  example  is  the  use of nested unlimited
1743           repeats.
1744    
1745           Internally, PCRE uses a function called match() which it calls  repeat-
1746           edly  (sometimes  recursively). The limit set by match_limit is imposed
1747           on the number of times this function is called during  a  match,  which
1748           has  the  effect  of  limiting the amount of backtracking that can take
1749           place. For patterns that are not anchored, the count restarts from zero
1750           for each position in the subject string.
1751    
1752           The  default  value  for  the  limit can be set when PCRE is built; the
1753           default default is 10 million, which handles all but the  most  extreme
1754           cases.  You  can  override  the  default by suppling pcre_exec() with a
1755           pcre_extra    block    in    which    match_limit    is    set,     and
1756           PCRE_EXTRA_MATCH_LIMIT  is  set  in  the  flags  field. If the limit is
1757           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1758    
1759           The match_limit_recursion field is similar to match_limit, but  instead
1760           of limiting the total number of times that match() is called, it limits
1761           the depth of recursion. The recursion depth is a  smaller  number  than
1762           the  total number of calls, because not all calls to match() are recur-
1763           sive.  This limit is of use only if it is set smaller than match_limit.
1764    
1765           Limiting  the  recursion  depth  limits the amount of stack that can be
1766           used, or, when PCRE has been compiled to use memory on the heap instead
1767           of the stack, the amount of heap memory that can be used.
1768    
1769           The  default  value  for  match_limit_recursion can be set when PCRE is
1770           built; the default default  is  the  same  value  as  the  default  for
1771           match_limit.  You can override the default by suppling pcre_exec() with
1772           a  pcre_extra  block  in  which  match_limit_recursion  is   set,   and
1773           PCRE_EXTRA_MATCH_LIMIT_RECURSION  is  set  in  the  flags field. If the
1774           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1775    
1776           The pcre_callout field is used in conjunction with the  "callout"  fea-
1777           ture, which is described in the pcrecallout documentation.
1778    
1779           The  tables  field  is  used  to  pass  a  character  tables pointer to
1780           pcre_exec(); this overrides the value that is stored with the  compiled
1781           pattern.  A  non-NULL value is stored with the compiled pattern only if
1782           custom tables were supplied to pcre_compile() via  its  tableptr  argu-
1783           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1784           PCRE's internal tables to be used. This facility is  helpful  when  re-
1785           using  patterns  that  have been saved after compiling with an external
1786           set of tables, because the external tables  might  be  at  a  different
1787           address  when  pcre_exec() is called. See the pcreprecompile documenta-
1788           tion for a discussion of saving compiled patterns for later use.
1789    
1790       Option bits for pcre_exec()
1791    
1792           The unused bits of the options argument for pcre_exec() must  be  zero.
1793           The  only  bits  that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
1794           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1795           PCRE_PARTIAL.
1796    
1797             PCRE_ANCHORED
1798    
1799           The  PCRE_ANCHORED  option  limits pcre_exec() to matching at the first
1800           matching position. If a pattern was  compiled  with  PCRE_ANCHORED,  or
1801           turned  out to be anchored by virtue of its contents, it cannot be made
1802           unachored at matching time.
1803    
1804             PCRE_NEWLINE_CR
1805             PCRE_NEWLINE_LF
1806             PCRE_NEWLINE_CRLF
1807             PCRE_NEWLINE_ANYCRLF
1808             PCRE_NEWLINE_ANY
1809    
1810           These options override  the  newline  definition  that  was  chosen  or
1811           defaulted  when the pattern was compiled. For details, see the descrip-
1812           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1813           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1814           ters. It may also alter the way the match position is advanced after  a
1815           match  failure  for  an  unanchored  pattern.  When  PCRE_NEWLINE_CRLF,
1816           PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a  match  attempt
1817           fails  when the current position is at a CRLF sequence, the match posi-
1818           tion is advanced by two characters instead of one, in other  words,  to
1819           after the CRLF.
1820    
1821             PCRE_NOTBOL
1822    
1823           This option specifies that first character of the subject string is not
1824           the beginning of a line, so the  circumflex  metacharacter  should  not
1825           match  before it. Setting this without PCRE_MULTILINE (at compile time)
1826           causes circumflex never to match. This option affects only  the  behav-
1827           iour of the circumflex metacharacter. It does not affect \A.
1828    
1829             PCRE_NOTEOL
1830    
1831           This option specifies that the end of the subject string is not the end
1832           of a line, so the dollar metacharacter should not match it nor  (except
1833           in  multiline mode) a newline immediately before it. Setting this with-
1834           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1835           option  affects only the behaviour of the dollar metacharacter. It does
1836           not affect \Z or \z.
1837    
1838             PCRE_NOTEMPTY
1839    
1840           An empty string is not considered to be a valid match if this option is
1841           set.  If  there are alternatives in the pattern, they are tried. If all
1842           the alternatives match the empty string, the entire  match  fails.  For
1843           example, if the pattern
1844    
1845             a?b?
1846    
1847           is  applied  to  a string not beginning with "a" or "b", it matches the
1848           empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1849           match is not valid, so PCRE searches further into the string for occur-
1850           rences of "a" or "b".
1851    
1852           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1853           cial  case  of  a  pattern match of the empty string within its split()
1854           function, and when using the /g modifier. It  is  possible  to  emulate
1855           Perl's behaviour after matching a null string by first trying the match
1856           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1857           if  that  fails by advancing the starting offset (see below) and trying
1858           an ordinary match again. There is some code that demonstrates how to do
1859           this in the pcredemo.c sample program.
1860    
1861             PCRE_NO_UTF8_CHECK
1862    
1863           When PCRE_UTF8 is set at compile time, the validity of the subject as a
1864           UTF-8 string is automatically checked when pcre_exec() is  subsequently
1865           called.   The  value  of  startoffset is also checked to ensure that it
1866           points to the start of a UTF-8 character. There is a  discussion  about
1867           the  validity  of  UTF-8 strings in the section on UTF-8 support in the
1868           main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
1869           pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
1870           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1871    
1872           If you already know that your subject is valid, and you  want  to  skip
1873           these    checks    for   performance   reasons,   you   can   set   the
1874           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1875           do  this  for the second and subsequent calls to pcre_exec() if you are
1876           making repeated calls to find all  the  matches  in  a  single  subject
1877           string.  However,  you  should  be  sure  that the value of startoffset
1878           points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1879           set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1880           value of startoffset that does not point to the start of a UTF-8  char-
1881           acter, is undefined. Your program may crash.
1882    
1883             PCRE_PARTIAL
1884    
1885           This  option  turns  on  the  partial  matching feature. If the subject
1886           string fails to match the pattern, but at some point during the  match-
1887           ing  process  the  end of the subject was reached (that is, the subject
1888           partially matches the pattern and the failure to  match  occurred  only
1889           because  there were not enough subject characters), pcre_exec() returns
1890           PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1891           used,  there  are restrictions on what may appear in the pattern. These
1892           are discussed in the pcrepartial documentation.
1893    
1894       The string to be matched by pcre_exec()
1895    
1896           The subject string is passed to pcre_exec() as a pointer in subject,  a
1897           length  in  length, and a starting byte offset in startoffset. In UTF-8
1898           mode, the byte offset must point to the start  of  a  UTF-8  character.
1899           Unlike  the  pattern string, the subject may contain binary zero bytes.
1900           When the starting offset is zero, the search for a match starts at  the
1901           beginning of the subject, and this is by far the most common case.
1902    
1903           A  non-zero  starting offset is useful when searching for another match
1904           in the same subject by calling pcre_exec() again after a previous  suc-
1905           cess.   Setting  startoffset differs from just passing over a shortened
1906           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1907           with any kind of lookbehind. For example, consider the pattern
1908    
1909             \Biss\B
1910    
1911           which  finds  occurrences  of "iss" in the middle of words. (\B matches
1912           only if the current position in the subject is not  a  word  boundary.)
1913           When  applied  to the string "Mississipi" the first call to pcre_exec()
1914           finds the first occurrence. If pcre_exec() is called  again  with  just
1915           the  remainder  of  the  subject,  namely  "issipi", it does not match,
1916           because \B is always false at the start of the subject, which is deemed
1917           to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1918           string again, but with startoffset set to 4, it finds the second occur-
1919           rence  of "iss" because it is able to look behind the starting point to
1920           discover that it is preceded by a letter.
1921    
1922           If a non-zero starting offset is passed when the pattern  is  anchored,
1923           one attempt to match at the given offset is made. This can only succeed
1924           if the pattern does not require the match to be at  the  start  of  the
1925           subject.
1926    
1927       How pcre_exec() returns captured substrings
1928    
1929           In  general, a pattern matches a certain portion of the subject, and in
1930           addition, further substrings from the subject  may  be  picked  out  by
1931           parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
1932           this is called "capturing" in what follows, and the  phrase  "capturing
1933           subpattern"  is  used for a fragment of a pattern that picks out a sub-
1934           string. PCRE supports several other kinds of  parenthesized  subpattern
1935           that do not cause substrings to be captured.
1936    
1937           Captured  substrings are returned to the caller via a vector of integer
1938           offsets whose address is passed in ovector. The number of  elements  in
1939           the  vector is passed in ovecsize, which must be a non-negative number.
1940           Note: this argument is NOT the size of ovector in bytes.
1941    
1942           The first two-thirds of the vector is used to pass back  captured  sub-
1943           strings,  each  substring using a pair of integers. The remaining third
1944           of the vector is used as workspace by pcre_exec() while  matching  cap-
1945           turing  subpatterns, and is not available for passing back information.
1946           The length passed in ovecsize should always be a multiple of three.  If
1947           it is not, it is rounded down.
1948    
1949           When  a  match  is successful, information about captured substrings is
1950           returned in pairs of integers, starting at the  beginning  of  ovector,
1951           and  continuing  up  to two-thirds of its length at the most. The first
1952           element of a pair is set to the offset of the first character in a sub-
1953           string,  and  the  second  is  set to the offset of the first character
1954           after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
1955           tor[1],  identify  the  portion  of  the  subject string matched by the
1956           entire pattern. The next pair is used for the first  capturing  subpat-
1957           tern, and so on. The value returned by pcre_exec() is one more than the
1958           highest numbered pair that has been set. For example, if two substrings
1959           have  been captured, the returned value is 3. If there are no capturing
1960           subpatterns, the return value from a successful match is 1,  indicating
1961           that just the first pair of offsets has been set.
1962    
1963           If a capturing subpattern is matched repeatedly, it is the last portion
1964           of the string that it matched that is returned.
1965    
1966           If the vector is too small to hold all the captured substring  offsets,
1967           it is used as far as possible (up to two-thirds of its length), and the
1968           function returns a value of zero. In particular, if the substring  off-
1969           sets are not of interest, pcre_exec() may be called with ovector passed
1970           as NULL and ovecsize as zero. However, if  the  pattern  contains  back
1971           references  and  the  ovector is not big enough to remember the related
1972           substrings, PCRE has to get additional memory for use during  matching.
1973           Thus it is usually advisable to supply an ovector.
1974    
1975           The  pcre_info()  function  can  be used to find out how many capturing
1976           subpatterns there are in a compiled  pattern.  The  smallest  size  for
1977           ovector  that  will allow for n captured substrings, in addition to the
1978           offsets of the substring matched by the whole pattern, is (n+1)*3.
1979    
1980           It is possible for capturing subpattern number n+1 to match  some  part
1981           of the subject when subpattern n has not been used at all. For example,
1982           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
1983           return from the function is 4, and subpatterns 1 and 3 are matched, but
1984           2 is not. When this happens, both values in  the  offset  pairs  corre-
1985           sponding to unused subpatterns are set to -1.
1986    
1987           Offset  values  that correspond to unused subpatterns at the end of the
1988           expression are also set to -1. For example,  if  the  string  "abc"  is
1989           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
1990           matched. The return from the function is 2, because  the  highest  used
1991           capturing subpattern number is 1. However, you can refer to the offsets
1992           for the second and third capturing subpatterns if  you  wish  (assuming
1993           the vector is large enough, of course).
1994    
1995           Some  convenience  functions  are  provided for extracting the captured
1996           substrings as separate strings. These are described below.
1997    
1998       Error return values from pcre_exec()
1999    
2000           If pcre_exec() fails, it returns a negative number. The  following  are
2001           defined in the header file:
2002    
2003             PCRE_ERROR_NOMATCH        (-1)
2004    
2005           The subject string did not match the pattern.
2006    
2007             PCRE_ERROR_NULL           (-2)
2008    
2009           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2010           ovecsize was not zero.
2011    
2012             PCRE_ERROR_BADOPTION      (-3)
2013    
2014           An unrecognized bit was set in the options argument.
2015    
2016             PCRE_ERROR_BADMAGIC       (-4)
2017    
2018           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2019           to catch the case when it is passed a junk pointer and to detect when a
2020           pattern that was compiled in an environment of one endianness is run in
2021           an  environment  with the other endianness. This is the error that PCRE
2022           gives when the magic number is not present.
2023    
2024             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2025    
2026           While running the pattern match, an unknown item was encountered in the
2027           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2028           overwriting of the compiled pattern.
2029    
2030             PCRE_ERROR_NOMEMORY       (-6)
2031    
2032           If a pattern contains back references, but the ovector that  is  passed
2033           to pcre_exec() is not big enough to remember the referenced substrings,
2034           PCRE gets a block of memory at the start of matching to  use  for  this
2035           purpose.  If the call via pcre_malloc() fails, this error is given. The
2036           memory is automatically freed at the end of matching.
2037    
2038             PCRE_ERROR_NOSUBSTRING    (-7)
2039    
2040           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2041           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2042           returned by pcre_exec().
2043    
2044             PCRE_ERROR_MATCHLIMIT     (-8)
2045    
2046           The backtracking limit, as specified by  the  match_limit  field  in  a
2047           pcre_extra  structure  (or  defaulted) was reached. See the description
2048           above.
2049    
2050             PCRE_ERROR_CALLOUT        (-9)
2051    
2052           This error is never generated by pcre_exec() itself. It is provided for
2053           use  by  callout functions that want to yield a distinctive error code.
2054           See the pcrecallout documentation for details.
2055    
2056             PCRE_ERROR_BADUTF8        (-10)
2057    
2058           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2059           subject.
2060    
2061             PCRE_ERROR_BADUTF8_OFFSET (-11)
2062    
2063           The UTF-8 byte sequence that was passed as a subject was valid, but the
2064           value of startoffset did not point to the beginning of a UTF-8  charac-
2065           ter.
2066    
2067             PCRE_ERROR_PARTIAL        (-12)
2068    
2069           The  subject  string did not match, but it did match partially. See the
2070           pcrepartial documentation for details of partial matching.
2071    
2072             PCRE_ERROR_BADPARTIAL     (-13)
2073    
2074           The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2075           items  that are not supported for partial matching. See the pcrepartial
2076           documentation for details of partial matching.
2077    
2078             PCRE_ERROR_INTERNAL       (-14)
2079    
2080           An unexpected internal error has occurred. This error could  be  caused
2081           by a bug in PCRE or by overwriting of the compiled pattern.
2082    
2083             PCRE_ERROR_BADCOUNT       (-15)
2084    
2085           This  error is given if the value of the ovecsize argument is negative.
2086    
2087             PCRE_ERROR_RECURSIONLIMIT (-21)
2088    
2089           The internal recursion limit, as specified by the match_limit_recursion
2090           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2091           description above.
2092    
2093             PCRE_ERROR_BADNEWLINE     (-23)
2094    
2095  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2096    
2097       int pcre_exec(const pcre *code, const pcre_extra *extra,         Error numbers -16 to -20 and -22 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.  
2098    
2099    
2100  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2101    
2102       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2103            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2104            int buffersize);              int buffersize);
2105    
2106       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2107            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2108            const char **stringptr);              const char **stringptr);
2109    
2110       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2111            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2112    
2113       Captured substrings can be accessed directly  by  using  the         Captured substrings can be  accessed  directly  by  using  the  offsets
2114       offsets returned by pcre_exec() in ovector. For convenience,         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2115       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2116       and  pcre_get_substring_list()  are  provided for extracting         string_list()  are  provided for extracting captured substrings as new,
2117       captured  substrings  as  new,   separate,   zero-terminated         separate, zero-terminated strings. These functions identify  substrings
2118       strings.  These functions identify substrings by number. The         by  number.  The  next section describes functions for extracting named
2119       next section describes functions for extracting  named  sub-         substrings.
2120       strings.   A  substring  that  contains  a  binary  zero  is  
2121       correctly extracted and has a further zero added on the end,         A substring that contains a binary zero is correctly extracted and  has
2122       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
2123           string.  However, you can process such a string  by  referring  to  the
2124       The first three arguments are the  same  for  all  three  of         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2125       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2126       just been successfully matched, ovector is a pointer to  the         not  adequate for handling strings containing binary zeros, because the
2127       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2128       and stringcount is the number of substrings that  were  cap-  
2129       tured by the match, including the substring that matched the         The first three arguments are the same for all  three  of  these  func-
2130       entire regular expression. This is  the  value  returned  by         tions:  subject  is  the subject string that has just been successfully
2131       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2132       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2133       tor,  the  value passed as stringcount should be the size of         were captured by the match, including the substring  that  matched  the
2134       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2135           it is greater than zero. If pcre_exec() returned zero, indicating  that
2136       The functions pcre_copy_substring() and pcre_get_substring()         it  ran out of space in ovector, the value passed as stringcount should
2137       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2138       number. A value of zero extracts the substring that  matched  
2139       the entire pattern, while higher values extract the captured         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2140       substrings. For pcre_copy_substring(), the string is  placed         single  substring,  whose  number  is given as stringnumber. A value of
2141       in  buffer,  whose  length is given by buffersize, while for         zero extracts the substring that matched the  entire  pattern,  whereas
2142       pcre_get_substring() a new block of memory is  obtained  via         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2143       pcre_malloc,  and its address is returned via stringptr. The         string(), the string is placed in buffer,  whose  length  is  given  by
2144       yield of the function is  the  length  of  the  string,  not         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2145       including the terminating zero, or one of         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2146           The  yield  of  the function is the length of the string, not including
2147         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2148    
2149       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2150       attempt to get memory failed for pcre_get_substring().  
2151           The buffer was too small for pcre_copy_substring(), or the  attempt  to
2152         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2153    
2154       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2155    
2156       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2157       able  substrings  and builds a list of pointers to them. All  
2158       this is done in a single block of memory which  is  obtained         The  pcre_get_substring_list()  function  extracts  all  available sub-
2159       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
2160       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
2161       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
2162       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
2163           pointer. The yield of the function is zero if all  went  well,  or  the
2164         PCRE_ERROR_NOMEMORY       (-6)         error code
2165    
2166       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2167    
2168       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2169       unset, which can happen when capturing subpattern number n+1  
2170       matches some part of the subject, but subpattern n  has  not         When  any of these functions encounter a substring that is unset, which
2171       been  used  at all, they return an empty string. This can be         can happen when capturing subpattern number n+1 matches  some  part  of
2172       distinguished  from  a  genuine  zero-length  substring   by         the  subject, but subpattern n has not been used at all, they return an
2173       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2174       tive for unset substrings.         string  by inspecting the appropriate offset in ovector, which is nega-
2175           tive for unset substrings.
2176       The  two  convenience  functions  pcre_free_substring()  and  
2177       pcre_free_substring_list()  can  be  used to free the memory         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2178       returned by  a  previous  call  of  pcre_get_substring()  or         string_list()  can  be  used  to free the memory returned by a previous
2179       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2180       more than call the function pointed to by  pcre_free,  which         tively.  They  do  nothing  more  than  call the function pointed to by
2181       of  course  could  be called directly from a C program. How-         pcre_free, which of course could be called directly from a  C  program.
2182       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-
2183       a  special  interface  to another programming language which         cial  interface  to  another  programming  language  that  cannot   use
2184       cannot use pcre_free directly; it is for  these  cases  that         pcre_free  directly;  it is for these cases that the functions are pro-
2185       the functions are provided.         vided.
2186    
2187    
2188  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2189    
2190       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2191            const char *subject, int *ovector,              const char *name);
2192            int stringcount, const char *stringname,  
2193            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2194                const char *subject, int *ovector,
2195       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2196            const char *name);              char *buffer, int buffersize);
2197    
2198       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2199            const char *subject, int *ovector,              const char *subject, int *ovector,
2200            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2201            const char **stringptr);              const char **stringptr);
2202    
2203       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-
2204       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2205       pcre_get_stringnumber(). The first argument is the  compiled  
2206       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2207       pattern  
2208           the number of the subpattern called "xxx" is 2. If the name is known to
2209         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2210           name by calling pcre_get_stringnumber(). The first argument is the com-
2211       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
2212       number,  you can then extract the substring directly, or use         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2213       one of the functions described in the previous section.  For         subpattern of that name.
2214       convenience,  there are also two functions that do the whole  
2215       job.         Given the number, you can extract the substring directly, or use one of
2216           the functions described in the previous section. For convenience, there
2217       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2218       pcre_get_named_substring()  are  the  same  as those for the  
2219       functions that  extract  by  number,  and  so  are  not  re-         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2220       described here. There are just two differences.         pcre_get_named_substring()  are  the  same  as  those for the similarly
2221           named functions that extract by number. As these are described  in  the
2222       First, instead of a substring number, a  substring  name  is         previous  section,  they  are not re-described here. There are just two
2223       given.  Second,  there  is  an  extra argument, given at the         differences:
2224       start, which is a pointer to the compiled pattern.  This  is  
2225       needed  in order to gain access to the name-to-number trans-         First, instead of a substring number, a substring name is  given.  Sec-
2226       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2227           to the compiled pattern. This is needed in order to gain access to  the
2228       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2229       succeeds,    they   then   call   pcre_copy_substring()   or  
2230       pcre_get_substring(), as appropriate.         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2231           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2232           ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2233           behaviour may not be what you want (see the next section).
2234    
2235    
2236    DUPLICATE SUBPATTERN NAMES
2237    
2238           int pcre_get_stringtable_entries(const pcre *code,
2239                const char *name, char **first, char **last);
2240    
2241           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2242           subpatterns  are  not  required  to  be unique. Normally, patterns with
2243           duplicate names are such that in any one match, only one of  the  named
2244           subpatterns  participates. An example is shown in the pcrepattern docu-
2245           mentation.
2246    
2247           When   duplicates   are   present,   pcre_copy_named_substring()    and
2248           pcre_get_named_substring()  return the first substring corresponding to
2249           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2250           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2251           function returns one of the numbers that are associated with the  name,
2252           but it is not defined which it is.
2253    
2254           If  you want to get full details of all captured substrings for a given
2255           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2256           first argument is the compiled pattern, and the second is the name. The
2257           third and fourth are pointers to variables which  are  updated  by  the
2258           function. After it has run, they point to the first and last entries in
2259           the name-to-number table  for  the  given  name.  The  function  itself
2260           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2261           there are none. The format of the table is described above in the  sec-
2262           tion  entitled  Information  about  a  pattern.  Given all the relevant
2263           entries for the name, you can extract each of their numbers, and  hence
2264           the captured data, if any.
2265    
2266    
2267    FINDING ALL POSSIBLE MATCHES
2268    
2269           The  traditional  matching  function  uses a similar algorithm to Perl,
2270           which stops when it finds the first match, starting at a given point in
2271           the  subject.  If you want to find all possible matches, or the longest
2272           possible match, consider using the alternative matching  function  (see
2273           below)  instead.  If you cannot use the alternative function, but still
2274           need to find all possible matches, you can kludge it up by  making  use
2275           of the callout facility, which is described in the pcrecallout documen-
2276           tation.
2277    
2278           What you have to do is to insert a callout right at the end of the pat-
2279           tern.   When your callout function is called, extract and save the cur-
2280           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2281           backtrack  and  try other alternatives. Ultimately, when it runs out of
2282           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2283    
2284    
2285    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2286    
2287           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2288                const char *subject, int length, int startoffset,
2289                int options, int *ovector, int ovecsize,
2290                int *workspace, int wscount);
2291    
2292           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2293           against  a  compiled pattern, using a matching algorithm that scans the
2294           subject string just once, and does not backtrack.  This  has  different
2295           characteristics  to  the  normal  algorithm, and is not compatible with
2296           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2297           theless,  there are times when this kind of matching can be useful. For
2298           a discussion of the two matching algorithms, see the pcrematching docu-
2299           mentation.
2300    
2301           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2302           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2303           ent  way,  and  this is described below. The other common arguments are
2304           used in the same way as for pcre_exec(), so their  description  is  not
2305           repeated here.
2306    
2307           The  two  additional  arguments provide workspace for the function. The
2308           workspace vector should contain at least 20 elements. It  is  used  for
2309           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2310           workspace will be needed for patterns and subjects where  there  are  a
2311           lot of potential matches.
2312    
2313           Here is an example of a simple call to pcre_dfa_exec():
2314    
2315             int rc;
2316             int ovector[10];
2317             int wspace[20];
2318             rc = pcre_dfa_exec(
2319               re,             /* result of pcre_compile() */
2320               NULL,           /* we didn't study the pattern */
2321               "some string",  /* the subject string */
2322               11,             /* the length of the subject string */
2323               0,              /* start at offset 0 in the subject */
2324               0,              /* default options */
2325               ovector,        /* vector of integers for substring information */
2326               10,             /* number of elements (NOT size in bytes) */
2327               wspace,         /* working space vector */
2328               20);            /* number of elements (NOT size in bytes) */
2329    
2330       Option bits for pcre_dfa_exec()
2331    
2332           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2333           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2334           LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2335           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2336           three of these are the same as for pcre_exec(), so their description is
2337           not repeated here.
2338    
2339             PCRE_PARTIAL
2340    
2341           This has the same general effect as it does for  pcre_exec(),  but  the
2342           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2343           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2344           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2345           been no complete matches, but there is still at least one matching pos-
2346           sibility.  The portion of the string that provided the partial match is
2347           set as the first matching string.
2348    
2349             PCRE_DFA_SHORTEST
2350    
2351           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2352           stop as soon as it has found one match. Because of the way the alterna-
2353           tive algorithm works, this is necessarily the shortest  possible  match
2354           at the first possible matching point in the subject string.
2355    
2356             PCRE_DFA_RESTART
2357    
2358           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2359           returns a partial match, it is possible to call it  again,  with  addi-
2360           tional  subject  characters,  and have it continue with the same match.
2361           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2362           workspace  and wscount options must reference the same vector as before
2363           because data about the match so far is left in  them  after  a  partial
2364           match.  There  is  more  discussion of this facility in the pcrepartial
2365           documentation.
2366    
2367       Successful returns from pcre_dfa_exec()
2368    
2369           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2370           string in the subject. Note, however, that all the matches from one run
2371           of the function start at the same point in  the  subject.  The  shorter
2372           matches  are all initial substrings of the longer matches. For example,
2373           if the pattern
2374    
2375             <.*>
2376    
2377           is matched against the string
2378    
2379             This is <something> <something else> <something further> no more
2380    
2381           the three matched strings are
2382    
2383             <something>
2384             <something> <something else>
2385             <something> <something else> <something further>
2386    
2387           On success, the yield of the function is a number  greater  than  zero,
2388           which  is  the  number of matched substrings. The substrings themselves
2389           are returned in ovector. Each string uses two elements;  the  first  is
2390           the  offset  to  the start, and the second is the offset to the end. In
2391           fact, all the strings have the same start  offset.  (Space  could  have
2392           been  saved by giving this only once, but it was decided to retain some
2393           compatibility with the way pcre_exec() returns data,  even  though  the
2394           meaning of the strings is different.)
2395    
2396           The strings are returned in reverse order of length; that is, the long-
2397           est matching string is given first. If there were too many  matches  to
2398           fit  into ovector, the yield of the function is zero, and the vector is
2399           filled with the longest matches.
2400    
2401       Error returns from pcre_dfa_exec()
2402    
2403           The pcre_dfa_exec() function returns a negative number when  it  fails.
2404           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2405           described above.  There are in addition the following errors  that  are
2406           specific to pcre_dfa_exec():
2407    
2408             PCRE_ERROR_DFA_UITEM      (-16)
2409    
2410           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2411           tern that it does not support, for instance, the use of \C  or  a  back
2412           reference.
2413    
2414             PCRE_ERROR_DFA_UCOND      (-17)
2415    
2416           This  return  is  given  if pcre_dfa_exec() encounters a condition item
2417           that uses a back reference for the condition, or a test  for  recursion
2418           in a specific group. These are not supported.
2419    
2420             PCRE_ERROR_DFA_UMLIMIT    (-18)
2421    
2422           This  return  is given if pcre_dfa_exec() is called with an extra block
2423           that contains a setting of the match_limit field. This is not supported
2424           (it is meaningless).
2425    
2426             PCRE_ERROR_DFA_WSSIZE     (-19)
2427    
2428           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2429           workspace vector.
2430    
2431             PCRE_ERROR_DFA_RECURSE    (-20)
2432    
2433           When a recursive subpattern is processed, the matching  function  calls
2434           itself  recursively,  using  private vectors for ovector and workspace.
2435           This error is given if the output vector  is  not  large  enough.  This
2436           should be extremely rare, as a vector of size 1000 is used.
2437    
2438    
2439    SEE ALSO
2440    
2441           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2442           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2443    
2444    
2445    AUTHOR
2446    
2447           Philip Hazel
2448           University Computing Service
2449           Cambridge CB2 3QH, England.
2450    
2451    
2452    REVISION
2453    
2454           Last updated: 09 August 2007
2455           Copyright (c) 1997-2007 University of Cambridge.
2456    ------------------------------------------------------------------------------
2457    
2458    
2459    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2460    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2461    
2462  NAME  NAME
2463       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2464    
2465    
2466  PCRE CALLOUTS  PCRE CALLOUTS
2467    
2468       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.  
2469    
2470           PCRE provides a feature called "callout", which is a means of temporar-
2471           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2472           matching.  The  caller of PCRE provides an external function by putting
2473           its entry point in the global variable pcre_callout. By  default,  this
2474           variable contains NULL, which disables all calling out.
2475    
2476           Within  a  regular  expression,  (?C) indicates the points at which the
2477           external function is to be called.  Different  callout  points  can  be
2478           identified  by  putting  a number less than 256 after the letter C. The
2479           default value is zero.  For  example,  this  pattern  has  two  callout
2480           points:
2481    
2482             (?C1)abc(?C2)def
2483    
2484           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2485           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2486           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2487           used with the pattern
2488    
2489             A(\d{2}|--)
2490    
2491           it is processed as if it were
2492    
2493           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2494    
2495           Notice that there is a callout before and after  each  parenthesis  and
2496           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2497           progress of pattern matching. The pcretest command has an  option  that
2498           sets  automatic callouts; when it is used, the output indicates how the
2499           pattern is matched. This is useful information when you are  trying  to
2500           optimize the performance of a particular pattern.
2501    
2502    
2503    MISSING CALLOUTS
2504    
2505           You  should  be  aware  that,  because of optimizations in the way PCRE
2506           matches patterns, callouts sometimes do not happen. For example, if the
2507           pattern is
2508    
2509             ab(?C4)cd
2510    
2511           PCRE knows that any matching string must contain the letter "d". If the
2512           subject string is "abyz", the lack of "d" means that  matching  doesn't
2513           ever  start,  and  the  callout is never reached. However, with "abyd",
2514           though the result is still no match, the callout is obeyed.
2515    
2516    
2517    THE CALLOUT INTERFACE
2518    
2519           During matching, when PCRE reaches a callout point, the external  func-
2520           tion  defined by pcre_callout is called (if it is set). This applies to
2521           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2522           only  argument  to  the callout function is a pointer to a pcre_callout
2523           block. This structure contains the following fields:
2524    
2525             int          version;
2526             int          callout_number;
2527             int         *offset_vector;
2528             const char  *subject;
2529             int          subject_length;
2530             int          start_match;
2531             int          current_position;
2532             int          capture_top;
2533             int          capture_last;
2534             void        *callout_data;
2535             int          pattern_position;
2536             int          next_item_length;
2537    
2538           The version field is an integer containing the version  number  of  the
2539           block  format. The initial version was 0; the current version is 1. The
2540           version number will change again in future  if  additional  fields  are
2541           added, but the intention is never to remove any of the existing fields.
2542    
2543           The callout_number field contains the number of the  callout,  as  com-
2544           piled  into  the pattern (that is, the number after ?C for manual call-
2545           outs, and 255 for automatically generated callouts).
2546    
2547           The offset_vector field is a pointer to the vector of offsets that  was
2548           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2549           pcre_exec() is used, the contents can be inspected in order to  extract
2550           substrings  that  have  been  matched  so  far,  in the same way as for
2551           extracting substrings after a match has completed. For  pcre_dfa_exec()
2552           this field is not useful.
2553    
2554           The subject and subject_length fields contain copies of the values that
2555           were passed to pcre_exec().
2556    
2557           The start_match field normally contains the offset within  the  subject
2558           at  which  the  current  match  attempt started. However, if the escape
2559           sequence \K has been encountered, this value is changed to reflect  the
2560           modified  starting  point.  If the pattern is not anchored, the callout
2561           function may be called several times from the same point in the pattern
2562           for different starting points in the subject.
2563    
2564           The  current_position  field  contains the offset within the subject of
2565           the current match pointer.
2566    
2567           When the pcre_exec() function is used, the capture_top  field  contains
2568           one  more than the number of the highest numbered captured substring so
2569           far. If no substrings have been captured, the value of  capture_top  is
2570           one.  This  is always the case when pcre_dfa_exec() is used, because it
2571           does not support captured substrings.
2572    
2573           The capture_last field contains the number of the  most  recently  cap-
2574           tured  substring. If no substrings have been captured, its value is -1.
2575           This is always the case when pcre_dfa_exec() is used.
2576    
2577           The callout_data field contains a value that is passed  to  pcre_exec()
2578           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2579           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2580           structure.  If  no such data was passed, the value of callout_data in a
2581           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2582           structure in the pcreapi documentation.
2583    
2584           The  pattern_position field is present from version 1 of the pcre_call-
2585           out structure. It contains the offset to the next item to be matched in
2586           the pattern string.
2587    
2588           The  next_item_length field is present from version 1 of the pcre_call-
2589           out structure. It contains the length of the next item to be matched in
2590           the  pattern  string. When the callout immediately precedes an alterna-
2591           tion bar, a closing parenthesis, or the end of the pattern, the  length
2592           is  zero.  When the callout precedes an opening parenthesis, the length
2593           is that of the entire subpattern.
2594    
2595           The pattern_position and next_item_length fields are intended  to  help
2596           in  distinguishing between different automatic callouts, which all have
2597           the same callout number. However, they are set for all callouts.
2598    
2599    
2600  RETURN VALUES  RETURN VALUES
2601    
2602       The callout function returns an integer.  If  the  value  is         The external callout function returns an integer to PCRE. If the  value
2603       zero,  matching  proceeds as normal. If the value is greater         is  zero,  matching  proceeds  as  normal. If the value is greater than
2604       than zero, matching fails at the current  point,  but  back-         zero, matching fails at the current point, but  the  testing  of  other
2605       tracking  to test other possibilities goes ahead, just as if         matching possibilities goes ahead, just as if a lookahead assertion had
2606       a lookahead assertion had failed. If the value is less  than         failed. If the value is less than zero, the  match  is  abandoned,  and
2607       zero,  the  match  is abandoned, and pcre_exec() returns the         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2608       value.  
2609           Negative   values   should   normally   be   chosen  from  the  set  of
2610       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2611       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2612       forces a standard "no  match"  failure.   The  error  number         reserved for use by callout functions; it will never be  used  by  PCRE
2613       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
2614       it will never be used by PCRE itself.  
2615    
2616    AUTHOR
2617    
2618           Philip Hazel
2619           University Computing Service
2620           Cambridge CB2 3QH, England.
2621    
2622    
2623    REVISION
2624    
2625           Last updated: 29 May 2007
2626           Copyright (c) 1997-2007 University of Cambridge.
2627    ------------------------------------------------------------------------------
2628    
2629    
2630    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2631    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2632    
2633  NAME  NAME
2634       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2635    
2636    
2637  DIFFERENCES FROM PERL  DIFFERENCES BETWEEN PCRE AND PERL
2638    
2639       This document describes the differences  in  the  ways  that         This  document describes the differences in the ways that PCRE and Perl
2640       PCRE  and  Perl  handle regular expressions. The differences         handle regular expressions. The differences described here  are  mainly
2641       described here are with respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2642           some features that are expected to be in the forthcoming Perl 5.10.
2643       1. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
2644       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
2645       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
2646       next  three characters are not "a". It just asserts that the         main pcre page.
2647       next character is not "a" three times.  
2648           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2649       2. Capturing subpatterns that occur inside  negative  looka-         permits  them,  but they do not mean what you might think. For example,
2650       head  assertions  are  counted,  but  their  entries  in the         (?!a){3} does not assert that the next three characters are not "a". It
2651       offsets vector are never set. Perl sets its numerical  vari-         just asserts that the next character is not "a" three times.
2652       ables  from  any  such  patterns that are matched before the  
2653       assertion fails to match something (thereby succeeding), but         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2654       only  if  the negative lookahead assertion contains just one         tions are counted, but their entries in the offsets  vector  are  never
2655       branch.         set.  Perl sets its numerical variables from any such patterns that are
2656           matched before the assertion fails to match something (thereby succeed-
2657       3. Though binary zero characters are supported in  the  sub-         ing),  but  only  if the negative lookahead assertion contains just one
2658       ject  string,  they  are  not  allowed  in  a pattern string         branch.
2659       because it is passed as a normal  C  string,  terminated  by  
2660       zero. The escape sequence "\0" can be used in the pattern to         4. Though binary zero characters are supported in the  subject  string,
2661       represent a binary zero.         they are not allowed in a pattern string because it is passed as a nor-
2662           mal C string, terminated by zero. The escape sequence \0 can be used in
2663       4. The following Perl escape sequences  are  not  supported:         the pattern to represent a binary zero.
2664       \l,  \u,  \L,  \U,  \P, \p, and \X. In fact these are imple-  
2665       mented by Perl's general string-handling and are not part of         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2666       its pattern matching engine. If any of these are encountered         \U, and \N. In fact these are implemented by Perl's general string-han-
2667       by PCRE, an error is generated.         dling  and are not part of its pattern matching engine. If any of these
2668           are encountered by PCRE, an error is generated.
2669       5. PCRE does support the \Q...\E  escape  for  quoting  sub-  
2670       strings. Characters in between are treated as literals. This         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2671       is slightly different from Perl in that $  and  @  are  also         is  built  with Unicode character property support. The properties that
2672       handled  as  literals inside the quotes. In Perl, they cause         can be tested with \p and \P are limited to the general category  prop-
2673       variable interpolation (but of course  PCRE  does  not  have         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2674       variables). Note the following examples:         derived properties Any and L&.
2675    
2676           Pattern            PCRE matches      Perl matches         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2677           ters  in  between  are  treated as literals. This is slightly different
2678           \Qabc$xyz\E        abc$xyz           abc followed by the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2679                                                  contents of $xyz         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2680           \Qabc\$xyz\E       abc\$xyz          abc\$xyz         does not have variables). Note the following examples:
2681           \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz  
2682               Pattern            PCRE matches      Perl matches
2683       In PCRE, the \Q...\E mechanism is not  recognized  inside  a  
2684       character class.             \Qabc$xyz\E        abc$xyz           abc followed by the
2685                                                      contents of $xyz
2686       8. Fairly obviously, PCRE does not support the (?{code}) and             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2687       (?p{code})  constructions. However, there is some experimen-             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2688       tal support for recursive patterns using the non-Perl  items  
2689       (?R),  (?number)  and  (?P>name).  Also,  the PCRE "callout"         The \Q...\E sequence is recognized both inside  and  outside  character
2690       feature allows an external function to be called during pat-         classes.
2691       tern matching.  
2692           8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2693       9. There are some differences that are  concerned  with  the         constructions. However, there is support for recursive  patterns.  This
2694       settings  of  captured  strings  when  part  of a pattern is         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2695       repeated. For example, matching "aba"  against  the  pattern         "callout" feature allows an external function to be called during  pat-
2696       /^(a(b)?)+$/  in Perl leaves $2 unset, but in PCRE it is set         tern matching. See the pcrecallout documentation for details.
2697       to "b".  
2698           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2699       10. PCRE  provides  some  extensions  to  the  Perl  regular         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2700       expression facilities:         unlike Perl.
2701    
2702       (a) Although lookbehind assertions must match  fixed  length         10.  There are some differences that are concerned with the settings of
2703       strings,  each  alternative branch of a lookbehind assertion         captured strings when part of  a  pattern  is  repeated.  For  example,
2704       can match a different length of string. Perl  requires  them         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2705       all to have the same length.         unset, but in PCRE it is set to "b".
2706    
2707       (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2708       set,  the  $  meta-character matches only at the very end of         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2709       the string.         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2710           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2711       (c) If PCRE_EXTRA is set, a backslash followed by  a  letter         ture group; this is different to Perl.
2712       with no special meaning is faulted.  
2713           12. PCRE provides some extensions to the Perl regular expression facil-
2714       (d) If PCRE_UNGREEDY is set, the greediness of  the  repeti-         ities.   Perl  5.10  will  include new features that are not in earlier
2715       tion  quantifiers  is inverted, that is, by default they are         versions, some of which (such as named parentheses) have been  in  PCRE
2716       not greedy, but if followed by a question mark they are.         for some time. This list is with respect to Perl 5.10:
2717    
2718       (e) PCRE_ANCHORED can be used to force a pattern to be tried         (a)  Although  lookbehind  assertions  must match fixed length strings,
2719       only at the first matching position in the subject string.         each alternative branch of a lookbehind assertion can match a different
2720           length of string. Perl requires them all to have the same length.
2721       (f)  The  PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   and  
2722       PCRE_NO_AUTO_CAPTURE  options  for  pcre_exec() have no Perl         (b)  If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $
2723       equivalents.         meta-character matches only at the very end of the string.
2724    
2725       (g) The (?R), (?number), and (?P>name) constructs allows for         (c) If PCRE_EXTRA is set, a backslash followed by a letter with no spe-
2726       recursive  pattern  matching  (Perl  can  do  this using the         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2727       (?p{code}) construct, which PCRE cannot support.)         ignored.  (Perl can be made to issue a warning.)
2728    
2729       (h) PCRE supports  named  capturing  substrings,  using  the         (d) If PCRE_UNGREEDY is set, the greediness of the  repetition  quanti-
2730       Python syntax.         fiers is inverted, that is, by default they are not greedy, but if fol-
2731           lowed by a question mark they are.
2732       (i) PCRE supports the  possessive  quantifier  "++"  syntax,  
2733       taken from Sun's Java package.         (e) PCRE_ANCHORED can be used at matching time to force a pattern to be
2734           tried only at the first matching position in the subject string.
2735    
2736           (f)  The PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NO_AUTO_CAP-
2737           TURE options for pcre_exec() have no Perl equivalents.
2738    
2739           (g) The callout facility is PCRE-specific.
2740    
2741       (j) The (R) condition, for  testing  recursion,  is  a  PCRE         (h) The partial matching facility is PCRE-specific.
      extension.  
2742    
2743       (k) The callout facility is PCRE-specific.         (i) Patterns compiled by PCRE can be saved and re-used at a later time,
2744           even on different hosts that have the other endianness.
2745    
2746           (j)  The  alternative  matching function (pcre_dfa_exec()) matches in a
2747           different way and is not Perl-compatible.
2748    
2749    
2750    AUTHOR
2751    
2752           Philip Hazel
2753           University Computing Service
2754           Cambridge CB2 3QH, England.
2755    
2756    
2757    REVISION
2758    
2759           Last updated: 08 August 2007
2760           Copyright (c) 1997-2007 University of Cambridge.
2761    ------------------------------------------------------------------------------
2762    
2763    
2764    PCREPATTERN(3)                                                  PCREPATTERN(3)
2765    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2766    
2767  NAME  NAME
2768       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2769    
2770    
2771  PCRE REGULAR EXPRESSION DETAILS  PCRE REGULAR EXPRESSION DETAILS
2772    
2773       The syntax and semantics of  the  regular  expressions  sup-         The  syntax and semantics of the regular expressions that are supported
2774       ported  by PCRE are described below. Regular expressions are         by PCRE are described in detail below. There is a quick-reference  syn-
2775       also described in the Perl documentation and in a number  of         tax  summary  in  the  pcresyntax  page. Perl's regular expressions are
2776       other  books,  some  of which have copious examples. Jeffrey         described in its own documentation, and regular expressions in  general
2777       Friedl's  "Mastering  Regular  Expressions",  published   by         are  covered in a number of books, some of which have copious examples.
2778       O'Reilly,  covers them in great detail. The description here         Jeffrey  Friedl's  "Mastering  Regular   Expressions",   published   by
2779       is intended as reference documentation.         O'Reilly,  covers regular expressions in great detail. This description
2780           of PCRE's regular expressions is intended as reference material.
2781       The basic operation of PCRE is on strings of bytes. However,  
2782       there  is  also  support for UTF-8 character strings. To use         The original operation of PCRE was on strings of  one-byte  characters.
2783       this support you must build PCRE to include  UTF-8  support,         However,  there is now also support for UTF-8 character strings. To use
2784       and  then call pcre_compile() with the PCRE_UTF8 option. How         this, you must build PCRE to  include  UTF-8  support,  and  then  call
2785       this affects the pattern matching is  mentioned  in  several         pcre_compile()  with  the  PCRE_UTF8  option.  How this affects pattern
2786       places  below.  There is also a summary of UTF-8 features in         matching is mentioned in several places below. There is also a  summary
2787       the section on UTF-8 support in the main pcre page.         of  UTF-8  features  in  the  section on UTF-8 support in the main pcre
2788           page.
2789       A regular expression is a pattern that is matched against  a  
2790       subject string from left to right. Most characters stand for         The remainder of this document discusses the  patterns  that  are  sup-
2791       themselves in a pattern, and match the corresponding charac-         ported  by  PCRE when its main matching function, pcre_exec(), is used.
2792       ters in the subject. As a trivial example, the pattern         From  release  6.0,   PCRE   offers   a   second   matchi