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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    WHAT \R MATCHES
365    
366           By default, the sequence \R in a pattern matches  any  Unicode  newline
367           sequence,  whatever  has  been selected as the line ending sequence. If
368           you specify
369    
370             --enable-bsr-anycrlf
371    
372           the default is changed so that \R matches only CR, LF, or  CRLF.  What-
373           ever  is selected when PCRE is built can be overridden when the library
374           functions are called.
375    
376    
377  BUILDING SHARED AND STATIC LIBRARIES  BUILDING SHARED AND STATIC LIBRARIES
378    
379       The PCRE building process uses libtool to build both  shared         The PCRE building process uses libtool to build both shared and  static
380       and  static  Unix libraries by default. You can suppress one         Unix  libraries by default. You can suppress one of these by adding one
381       of these by adding one of         of
382    
383         --disable-shared           --disable-shared
384         --disable-static           --disable-static
385    
386       to the configure command, as required.         to the configure command, as required.
387    
388    
389  POSIX MALLOC USAGE  POSIX MALLOC USAGE
390    
391       When PCRE is called through the  POSIX  interface  (see  the         When PCRE is called through the POSIX interface (see the pcreposix doc-
392       pcreposix  documentation),  additional  working  storage  is         umentation),  additional  working  storage  is required for holding the
393       required for holding the pointers  to  capturing  substrings         pointers to capturing substrings, because PCRE requires three  integers
394       because  PCRE requires three integers per substring, whereas         per  substring,  whereas  the POSIX interface provides only two. If the
395       the POSIX interface provides only  two.  If  the  number  of         number of expected substrings is small, the wrapper function uses space
396       expected  substrings  is  small,  the  wrapper function uses         on the stack, because this is faster than using malloc() for each call.
397       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
398       loc()  for  each call. The default threshold above which the         can be changed by adding a setting such as
      stack is no longer used is 10; it can be changed by adding a  
      setting such as  
399    
400         --with-posix-malloc-threshold=20           --with-posix-malloc-threshold=20
401    
402       to the configure command.         to the configure command.
403    
404    
405    HANDLING VERY LARGE PATTERNS
406    
407           Within  a  compiled  pattern,  offset values are used to point from one
408           part to another (for example, from an opening parenthesis to an  alter-
409           nation  metacharacter).  By default, two-byte values are used for these
410           offsets, leading to a maximum size for a  compiled  pattern  of  around
411           64K.  This  is sufficient to handle all but the most gigantic patterns.
412           Nevertheless, some people do want to process enormous patterns,  so  it
413           is  possible  to compile PCRE to use three-byte or four-byte offsets by
414           adding a setting such as
415    
416             --with-link-size=3
417    
418           to the configure command. The value given must be 2,  3,  or  4.  Using
419           longer  offsets slows down the operation of PCRE because it has to load
420           additional bytes when handling them.
421    
422    
423    AVOIDING EXCESSIVE STACK USAGE
424    
425           When matching with the pcre_exec() function, PCRE implements backtrack-
426           ing  by  making recursive calls to an internal function called match().
427           In environments where the size of the stack is limited,  this  can  se-
428           verely  limit  PCRE's operation. (The Unix environment does not usually
429           suffer from this problem, but it may sometimes be necessary to increase
430           the  maximum  stack size.  There is a discussion in the pcrestack docu-
431           mentation.) An alternative approach to recursion that uses memory  from
432           the  heap  to remember data, instead of using recursive function calls,
433           has been implemented to work round the problem of limited  stack  size.
434           If you want to build a version of PCRE that works this way, add
435    
436             --disable-stack-for-recursion
437    
438           to  the  configure  command. With this configuration, PCRE will use the
439           pcre_stack_malloc and pcre_stack_free variables to call memory  manage-
440           ment  functions. By default these point to malloc() and free(), but you
441           can replace the pointers so that your own functions are used.
442    
443           Separate functions are  provided  rather  than  using  pcre_malloc  and
444           pcre_free  because  the  usage  is  very  predictable:  the block sizes
445           requested are always the same, and  the  blocks  are  always  freed  in
446           reverse  order.  A calling program might be able to implement optimized
447           functions that perform better  than  malloc()  and  free().  PCRE  runs
448           noticeably more slowly when built in this way. This option affects only
449           the  pcre_exec()  function;  it   is   not   relevant   for   the   the
450           pcre_dfa_exec() function.
451    
452    
453  LIMITING PCRE RESOURCE USAGE  LIMITING PCRE RESOURCE USAGE
454    
455       Internally, PCRE has a  function  called  match()  which  it         Internally,  PCRE has a function called match(), which it calls repeat-
456       calls  repeatedly  (possibly  recursively) when performing a         edly  (sometimes  recursively)  when  matching  a  pattern   with   the
457       matching operation. By limiting the  number  of  times  this         pcre_exec()  function.  By controlling the maximum number of times this
458       function  may  be  called,  a  limit  can  be  placed on the         function may be called during a single matching operation, a limit  can
459       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
460       can  be  changed  at  run  time, as described in the pcreapi         limit can be changed at run time, as described in the pcreapi  documen-
461       documentation. The default is 10 million, but  this  can  be         tation.  The default is 10 million, but this can be changed by adding a
462       changed by adding a setting such as         setting such as
463    
464         --with-match-limit=500000           --with-match-limit=500000
465    
466       to the configure command.         to  the  configure  command.  This  setting  has  no  effect   on   the
467           pcre_dfa_exec() matching function.
468    
469           In  some  environments  it is desirable to limit the depth of recursive
470           calls of match() more strictly than the total number of calls, in order
471           to  restrict  the maximum amount of stack (or heap, if --disable-stack-
472           for-recursion is specified) that is used. A second limit controls this;
473           it  defaults  to  the  value  that is set for --with-match-limit, which
474           imposes no additional constraints. However, you can set a  lower  limit
475           by adding, for example,
476    
477  HANDLING VERY LARGE PATTERNS           --with-match-limit-recursion=10000
478    
479       Within a compiled pattern, offset values are used  to  point         to  the  configure  command.  This  value can also be overridden at run
480       from  one  part  to  another  (for  example, from an opening         time.
481       parenthesis to an  alternation  metacharacter).  By  default  
482       two-byte  values  are  used  for these offsets, leading to a  
483       maximum size for a compiled pattern of around 64K.  This  is  CREATING CHARACTER TABLES AT BUILD TIME
484       sufficient  to  handle  all  but the most gigantic patterns.  
485       Nevertheless, some people do want to process  enormous  pat-         PCRE uses fixed tables for processing characters whose code values  are
486       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
487       or four-byte offsets by adding a setting such as         distributed in the file pcre_chartables.c.dist. These  tables  are  for
488           ASCII codes only. If you add
489         --with-link-size=3  
490             --enable-rebuild-chartables
491       to the configure command. The value given must be 2,  3,  or  
492       4.  Using  longer  offsets  slows down the operation of PCRE         to  the  configure  command, the distributed tables are no longer used.
493       because it has to load additional bytes when handling them.         Instead, a program called dftables is compiled and  run.  This  outputs
494           the source for new set of tables, created in the default locale of your
495       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
496       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
497       of these tests is a representation of the compiled  pattern,         you need to create alternative tables when cross  compiling,  you  will
498       and this changes with the link size.         have to do so "by hand".)
499    
500    
501    USING EBCDIC CODE
502    
503           PCRE  assumes  by  default that it will run in an environment where the
504           character code is ASCII (or Unicode, which is  a  superset  of  ASCII).
505           This  is  the  case for most computer operating systems. PCRE can, how-
506           ever, be compiled to run in an EBCDIC environment by adding
507    
508             --enable-ebcdic
509    
510           to the configure command. This setting implies --enable-rebuild-charta-
511           bles.  You  should  only  use  it if you know that you are in an EBCDIC
512           environment (for example, an IBM mainframe operating system).
513    
514    
515    SEE ALSO
516    
517           pcreapi(3), pcre_config(3).
518    
519    
520    AUTHOR
521    
522           Philip Hazel
523           University Computing Service
524           Cambridge CB2 3QH, England.
525    
526    
527    REVISION
528    
529           Last updated: 11 September 2007
530           Copyright (c) 1997-2007 University of Cambridge.
531    ------------------------------------------------------------------------------
532    
533    
534    PCREMATCHING(3)                                                PCREMATCHING(3)
535    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
536    
537  NAME  NAME
538       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
539    
540    
541    PCRE MATCHING ALGORITHMS
542    
543           This document describes the two different algorithms that are available
544           in PCRE for matching a compiled regular expression against a given sub-
545           ject  string.  The  "standard"  algorithm  is  the  one provided by the
546           pcre_exec() function.  This works in the same was  as  Perl's  matching
547           function, and provides a Perl-compatible matching operation.
548    
549           An  alternative  algorithm is provided by the pcre_dfa_exec() function;
550           this operates in a different way, and is not  Perl-compatible.  It  has
551           advantages  and disadvantages compared with the standard algorithm, and
552           these are described below.
553    
554           When there is only one possible way in which a given subject string can
555           match  a pattern, the two algorithms give the same answer. A difference
556           arises, however, when there are multiple possibilities. For example, if
557           the pattern
558    
559             ^<.*>
560    
561           is matched against the string
562    
563             <something> <something else> <something further>
564    
565           there are three possible answers. The standard algorithm finds only one
566           of them, whereas the alternative algorithm finds all three.
567    
568    
569    REGULAR EXPRESSIONS AS TREES
570    
571           The set of strings that are matched by a regular expression can be rep-
572           resented  as  a  tree structure. An unlimited repetition in the pattern
573           makes the tree of infinite size, but it is still a tree.  Matching  the
574           pattern  to a given subject string (from a given starting point) can be
575           thought of as a search of the tree.  There are two  ways  to  search  a
576           tree:  depth-first  and  breadth-first, and these correspond to the two
577           matching algorithms provided by PCRE.
578    
579    
580  SYNOPSIS OF PCRE API  THE STANDARD MATCHING ALGORITHM
581    
582       #include <pcre.h>         In the terminology of Jeffrey Friedl's book "Mastering Regular  Expres-
583           sions",  the  standard  algorithm  is an "NFA algorithm". It conducts a
584           depth-first search of the pattern tree. That is, it  proceeds  along  a
585           single path through the tree, checking that the subject matches what is
586           required. When there is a mismatch, the algorithm  tries  any  alterna-
587           tives  at  the  current point, and if they all fail, it backs up to the
588           previous branch point in the  tree,  and  tries  the  next  alternative
589           branch  at  that  level.  This often involves backing up (moving to the
590           left) in the subject string as well.  The  order  in  which  repetition
591           branches  are  tried  is controlled by the greedy or ungreedy nature of
592           the quantifier.
593    
594       pcre *pcre_compile(const char *pattern, int options,         If a leaf node is reached, a matching string has  been  found,  and  at
595            const char **errptr, int *erroffset,         that  point the algorithm stops. Thus, if there is more than one possi-
596            const unsigned char *tableptr);         ble match, this algorithm returns the first one that it finds.  Whether
597           this  is the shortest, the longest, or some intermediate length depends
598           on the way the greedy and ungreedy repetition quantifiers are specified
599           in the pattern.
600    
601       pcre_extra *pcre_study(const pcre *code, int options,         Because  it  ends  up  with a single path through the tree, it is rela-
602            const char **errptr);         tively straightforward for this algorithm to keep  track  of  the  sub-
603           strings  that  are  matched  by portions of the pattern in parentheses.
604           This provides support for capturing parentheses and back references.
605    
      int pcre_exec(const pcre *code, const pcre_extra *extra,  
           const char *subject, int length, int startoffset,  
           int options, int *ovector, int ovecsize);  
606    
607       int pcre_copy_named_substring(const pcre *code,  THE ALTERNATIVE MATCHING ALGORITHM
           const char *subject, int *ovector,  
           int stringcount, const char *stringname,  
           char *buffer, int buffersize);  
608    
609       int pcre_copy_substring(const char *subject, int *ovector,         This algorithm conducts a breadth-first search of  the  tree.  Starting
610            int stringcount, int stringnumber, char *buffer,         from  the  first  matching  point  in the subject, it scans the subject
611            int buffersize);         string from left to right, once, character by character, and as it does
612           this,  it remembers all the paths through the tree that represent valid
613           matches. In Friedl's terminology, this is a kind  of  "DFA  algorithm",
614           though  it is not implemented as a traditional finite state machine (it
615           keeps multiple states active simultaneously).
616    
617       int pcre_get_named_substring(const pcre *code,         The scan continues until either the end of the subject is  reached,  or
618            const char *subject, int *ovector,         there  are  no more unterminated paths. At this point, terminated paths
619            int stringcount, const char *stringname,         represent the different matching possibilities (if there are none,  the
620            const char **stringptr);         match  has  failed).   Thus,  if there is more than one possible match,
621           this algorithm finds all of them, and in particular, it finds the long-
622           est.  In PCRE, there is an option to stop the algorithm after the first
623           match (which is necessarily the shortest) has been found.
624    
625       int pcre_get_stringnumber(const pcre *code,         Note that all the matches that are found start at the same point in the
626            const char *name);         subject. If the pattern
627    
628       int pcre_get_substring(const char *subject, int *ovector,           cat(er(pillar)?)
           int stringcount, int stringnumber,  
           const char **stringptr);  
629    
630       int pcre_get_substring_list(const char *subject,         is  matched  against the string "the caterpillar catchment", the result
631            int *ovector, int stringcount, const char ***listptr);         will be the three strings "cat", "cater", and "caterpillar" that  start
632           at the fourth character of the subject. The algorithm does not automat-
633           ically move on to find matches that start at later positions.
634    
635       void pcre_free_substring(const char *stringptr);         There are a number of features of PCRE regular expressions that are not
636           supported by the alternative matching algorithm. They are as follows:
637    
638       void pcre_free_substring_list(const char **stringptr);         1.  Because  the  algorithm  finds  all possible matches, the greedy or
639           ungreedy nature of repetition quantifiers is not relevant.  Greedy  and
640           ungreedy quantifiers are treated in exactly the same way. However, pos-
641           sessive quantifiers can make a difference when what follows could  also
642           match what is quantified, for example in a pattern like this:
643    
644       const unsigned char *pcre_maketables(void);           ^a++\w!
645    
646       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         This  pattern matches "aaab!" but not "aaa!", which would be matched by
647            int what, void *where);         a non-possessive quantifier. Similarly, if an atomic group is  present,
648           it  is matched as if it were a standalone pattern at the current point,
649           and the longest match is then "locked in" for the rest of  the  overall
650           pattern.
651    
652           2. When dealing with multiple paths through the tree simultaneously, it
653           is not straightforward to keep track of  captured  substrings  for  the
654           different  matching  possibilities,  and  PCRE's implementation of this
655           algorithm does not attempt to do this. This means that no captured sub-
656           strings are available.
657    
658       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         3.  Because no substrings are captured, back references within the pat-
659           tern are not supported, and cause errors if encountered.
660    
661       int pcre_config(int what, void *where);         4. For the same reason, conditional expressions that use  a  backrefer-
662           ence  as  the  condition or test for a specific group recursion are not
663           supported.
664    
665       char *pcre_version(void);         5. Because many paths through the tree may be  active,  the  \K  escape
666           sequence, which resets the start of the match when encountered (but may
667           be on some paths and not on others), is not  supported.  It  causes  an
668           error if encountered.
669    
670       void *(*pcre_malloc)(size_t);         6.  Callouts  are  supported, but the value of the capture_top field is
671           always 1, and the value of the capture_last field is always -1.
672    
673       void (*pcre_free)(void *);         7. The \C escape sequence, which (in the standard algorithm) matches  a
674           single  byte, even in UTF-8 mode, is not supported because the alterna-
675           tive algorithm moves through the subject  string  one  character  at  a
676           time, for all active paths through the tree.
677    
678       int (*pcre_callout)(pcre_callout_block *);         8.  None  of  the  backtracking control verbs such as (*PRUNE) are sup-
679           ported.
680    
681    
682  PCRE API  ADVANTAGES OF THE ALTERNATIVE ALGORITHM
683    
684       PCRE has its own native API,  which  is  described  in  this         Using the alternative matching algorithm provides the following  advan-
685       document.  There  is  also  a  set of wrapper functions that         tages:
      correspond to the POSIX regular expression API.   These  are  
      described in the pcreposix documentation.  
686    
687       The native API function prototypes are defined in the header         1. All possible matches (at a single point in the subject) are automat-
688       file  pcre.h,  and  on  Unix  systems  the library itself is         ically found, and in particular, the longest match is  found.  To  find
689       called libpcre.a, so can be accessed by adding -lpcre to the         more than one match using the standard algorithm, you have to do kludgy
690       command  for  linking  an  application  which  calls it. The         things with callouts.
      header file defines the macros PCRE_MAJOR and PCRE_MINOR  to  
      contain the major and minor release numbers for the library.  
      Applications can use these to include support for  different  
      releases.  
691    
692       The functions pcre_compile(), pcre_study(), and  pcre_exec()         2. There is much better support for partial matching. The  restrictions
693       are  used  for compiling and matching regular expressions. A         on  the content of the pattern that apply when using the standard algo-
694       sample program that demonstrates the simplest way  of  using         rithm for partial matching do not apply to the  alternative  algorithm.
695       them  is  given in the file pcredemo.c. The pcresample docu-         For  non-anchored patterns, the starting position of a partial match is
696       mentation describes how to run it.         available.
697    
698       There are convenience functions for extracting captured sub-         3. Because the alternative algorithm  scans  the  subject  string  just
699       strings from a matched subject string. They are:         once,  and  never  needs to backtrack, it is possible to pass very long
700           subject strings to the matching function in  several  pieces,  checking
701           for partial matching each time.
702    
        pcre_copy_substring()  
        pcre_copy_named_substring()  
        pcre_get_substring()  
        pcre_get_named_substring()  
        pcre_get_substring_list()  
703    
704       pcre_free_substring()  and  pcre_free_substring_list()   are  DISADVANTAGES OF THE ALTERNATIVE ALGORITHM
705       also  provided,  to  free  the  memory  used  for  extracted  
706       strings.         The alternative algorithm suffers from a number of disadvantages:
707    
708           1.  It  is  substantially  slower  than the standard algorithm. This is
709           partly because it has to search for all possible matches, but  is  also
710           because it is less susceptible to optimization.
711    
712           2. Capturing parentheses and back references are not supported.
713    
714           3. Although atomic groups are supported, their use does not provide the
715           performance advantage that it does for the standard algorithm.
716    
717    
718    AUTHOR
719    
720           Philip Hazel
721           University Computing Service
722           Cambridge CB2 3QH, England.
723    
724    
725    REVISION
726    
727           Last updated: 08 August 2007
728           Copyright (c) 1997-2007 University of Cambridge.
729    ------------------------------------------------------------------------------
730    
731    
732    PCREAPI(3)                                                          PCREAPI(3)
733    
734    
735    NAME
736           PCRE - Perl-compatible regular expressions
737    
      The function pcre_maketables() is used (optionally) to build  
      a  set of character tables in the current locale for passing  
      to pcre_compile().  
738    
739       The function pcre_fullinfo() is used to find out information  PCRE NATIVE API
      about a compiled pattern; pcre_info() is an obsolete version  
      which returns only some of the available information, but is  
      retained   for   backwards   compatibility.    The  function  
      pcre_version() returns a pointer to a string containing  the  
      version of PCRE and its date of release.  
740    
741       The global variables  pcre_malloc  and  pcre_free  initially         #include <pcre.h>
      contain the entry points of the standard malloc() and free()  
      functions respectively. PCRE  calls  the  memory  management  
      functions  via  these  variables,  so  a calling program can  
      replace them if it  wishes  to  intercept  the  calls.  This  
      should be done before calling any PCRE functions.  
742    
743       The global variable pcre_callout initially contains NULL. It         pcre *pcre_compile(const char *pattern, int options,
744       can be set by the caller to a "callout" function, which PCRE              const char **errptr, int *erroffset,
745       will then call at specified points during a matching  opera-              const unsigned char *tableptr);
746       tion. Details are given in the pcrecallout documentation.  
747           pcre *pcre_compile2(const char *pattern, int options,
748                int *errorcodeptr,
749                const char **errptr, int *erroffset,
750                const unsigned char *tableptr);
751    
752           pcre_extra *pcre_study(const pcre *code, int options,
753                const char **errptr);
754    
755           int pcre_exec(const pcre *code, const pcre_extra *extra,
756                const char *subject, int length, int startoffset,
757                int options, int *ovector, int ovecsize);
758    
759           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
760                const char *subject, int length, int startoffset,
761                int options, int *ovector, int ovecsize,
762                int *workspace, int wscount);
763    
764           int pcre_copy_named_substring(const pcre *code,
765                const char *subject, int *ovector,
766                int stringcount, const char *stringname,
767                char *buffer, int buffersize);
768    
769           int pcre_copy_substring(const char *subject, int *ovector,
770                int stringcount, int stringnumber, char *buffer,
771                int buffersize);
772    
773           int pcre_get_named_substring(const pcre *code,
774                const char *subject, int *ovector,
775                int stringcount, const char *stringname,
776                const char **stringptr);
777    
778           int pcre_get_stringnumber(const pcre *code,
779                const char *name);
780    
781           int pcre_get_stringtable_entries(const pcre *code,
782                const char *name, char **first, char **last);
783    
784           int pcre_get_substring(const char *subject, int *ovector,
785                int stringcount, int stringnumber,
786                const char **stringptr);
787    
788           int pcre_get_substring_list(const char *subject,
789                int *ovector, int stringcount, const char ***listptr);
790    
791           void pcre_free_substring(const char *stringptr);
792    
793           void pcre_free_substring_list(const char **stringptr);
794    
795           const unsigned char *pcre_maketables(void);
796    
797           int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
798                int what, void *where);
799    
800           int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
801    
802           int pcre_refcount(pcre *code, int adjust);
803    
804           int pcre_config(int what, void *where);
805    
806           char *pcre_version(void);
807    
808           void *(*pcre_malloc)(size_t);
809    
810           void (*pcre_free)(void *);
811    
812           void *(*pcre_stack_malloc)(size_t);
813    
814           void (*pcre_stack_free)(void *);
815    
816           int (*pcre_callout)(pcre_callout_block *);
817    
818    
819    PCRE API OVERVIEW
820    
821           PCRE has its own native API, which is described in this document. There
822           are also some wrapper functions that correspond to  the  POSIX  regular
823           expression  API.  These  are  described in the pcreposix documentation.
824           Both of these APIs define a set of C function calls. A C++  wrapper  is
825           distributed with PCRE. It is documented in the pcrecpp page.
826    
827           The  native  API  C  function prototypes are defined in the header file
828           pcre.h, and on Unix systems the library itself is called  libpcre.   It
829           can normally be accessed by adding -lpcre to the command for linking an
830           application  that  uses  PCRE.  The  header  file  defines  the  macros
831           PCRE_MAJOR  and  PCRE_MINOR to contain the major and minor release num-
832           bers for the library.  Applications can use these  to  include  support
833           for different releases of PCRE.
834    
835           The   functions   pcre_compile(),  pcre_compile2(),  pcre_study(),  and
836           pcre_exec() are used for compiling and matching regular expressions  in
837           a  Perl-compatible  manner. A sample program that demonstrates the sim-
838           plest way of using them is provided in the file  called  pcredemo.c  in
839           the  source distribution. The pcresample documentation describes how to
840           run it.
841    
842           A second matching function, pcre_dfa_exec(), which is not Perl-compati-
843           ble,  is  also provided. This uses a different algorithm for the match-
844           ing. The alternative algorithm finds all possible matches (at  a  given
845           point  in  the subject), and scans the subject just once. However, this
846           algorithm does not return captured substrings. A description of the two
847           matching  algorithms and their advantages and disadvantages is given in
848           the pcrematching documentation.
849    
850           In addition to the main compiling and  matching  functions,  there  are
851           convenience functions for extracting captured substrings from a subject
852           string that is matched by pcre_exec(). They are:
853    
854             pcre_copy_substring()
855             pcre_copy_named_substring()
856             pcre_get_substring()
857             pcre_get_named_substring()
858             pcre_get_substring_list()
859             pcre_get_stringnumber()
860             pcre_get_stringtable_entries()
861    
862           pcre_free_substring() and pcre_free_substring_list() are also provided,
863           to free the memory used for extracted strings.
864    
865           The  function  pcre_maketables()  is  used  to build a set of character
866           tables  in  the  current  locale   for   passing   to   pcre_compile(),
867           pcre_exec(),  or  pcre_dfa_exec(). This is an optional facility that is
868           provided for specialist use.  Most  commonly,  no  special  tables  are
869           passed,  in  which case internal tables that are generated when PCRE is
870           built are used.
871    
872           The function pcre_fullinfo() is used to find out  information  about  a
873           compiled  pattern; pcre_info() is an obsolete version that returns only
874           some of the available information, but is retained for  backwards  com-
875           patibility.   The function pcre_version() returns a pointer to a string
876           containing the version of PCRE and its date of release.
877    
878           The function pcre_refcount() maintains a  reference  count  in  a  data
879           block  containing  a compiled pattern. This is provided for the benefit
880           of object-oriented applications.
881    
882           The global variables pcre_malloc and pcre_free  initially  contain  the
883           entry  points  of  the  standard malloc() and free() functions, respec-
884           tively. PCRE calls the memory management functions via these variables,
885           so  a  calling  program  can replace them if it wishes to intercept the
886           calls. This should be done before calling any PCRE functions.
887    
888           The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
889           indirections  to  memory  management functions. These special functions
890           are used only when PCRE is compiled to use  the  heap  for  remembering
891           data, instead of recursive function calls, when running the pcre_exec()
892           function. See the pcrebuild documentation for  details  of  how  to  do
893           this.  It  is  a non-standard way of building PCRE, for use in environ-
894           ments that have limited stacks. Because of the greater  use  of  memory
895           management,  it  runs  more  slowly. Separate functions are provided so
896           that special-purpose external code can be  used  for  this  case.  When
897           used,  these  functions  are always called in a stack-like manner (last
898           obtained, first freed), and always for memory blocks of the same  size.
899           There  is  a discussion about PCRE's stack usage in the pcrestack docu-
900           mentation.
901    
902           The global variable pcre_callout initially contains NULL. It can be set
903           by  the  caller  to  a "callout" function, which PCRE will then call at
904           specified points during a matching operation. Details are given in  the
905           pcrecallout documentation.
906    
907    
908    NEWLINES
909    
910           PCRE  supports five different conventions for indicating line breaks in
911           strings: a single CR (carriage return) character, a  single  LF  (line-
912           feed) character, the two-character sequence CRLF, any of the three pre-
913           ceding, or any Unicode newline sequence. The Unicode newline  sequences
914           are  the  three just mentioned, plus the single characters VT (vertical
915           tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS  (line
916           separator, U+2028), and PS (paragraph separator, U+2029).
917    
918           Each  of  the first three conventions is used by at least one operating
919           system as its standard newline sequence. When PCRE is built, a  default
920           can  be  specified.  The default default is LF, which is the Unix stan-
921           dard. When PCRE is run, the default can be overridden,  either  when  a
922           pattern is compiled, or when it is matched.
923    
924           At compile time, the newline convention can be specified by the options
925           argument of pcre_compile(), or it can be specified by special  text  at
926           the start of the pattern itself; this overrides any other settings. See
927           the pcrepattern page for details of the special character sequences.
928    
929           In the PCRE documentation the word "newline" is used to mean "the char-
930           acter  or pair of characters that indicate a line break". The choice of
931           newline convention affects the handling of  the  dot,  circumflex,  and
932           dollar metacharacters, the handling of #-comments in /x mode, and, when
933           CRLF is a recognized line ending sequence, the match position  advance-
934           ment for a non-anchored pattern. There is more detail about this in the
935           section on pcre_exec() options below.
936    
937           The choice of newline convention does not affect the interpretation  of
938           the  \n  or  \r  escape  sequences, nor does it affect what \R matches,
939           which is controlled in a similar way, but by separate options.
940    
941    
942  MULTITHREADING  MULTITHREADING
943    
944       The PCRE functions can be used in  multi-threading  applica-         The PCRE functions can be used in  multi-threading  applications,  with
945       tions, with the proviso that the memory management functions         the  proviso  that  the  memory  management  functions  pointed  to  by
946       pointed to by pcre_malloc and  pcre_free,  and  the  callout         pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
947       function  pointed  to  by  pcre_callout,  are  shared by all         callout function pointed to by pcre_callout, are shared by all threads.
948       threads.  
949           The compiled form of a regular expression is not altered during  match-
950       The compiled form of a regular  expression  is  not  altered         ing, so the same compiled pattern can safely be used by several threads
951       during  matching, so the same compiled pattern can safely be         at once.
952       used by several threads at once.  
953    
954    SAVING PRECOMPILED PATTERNS FOR LATER USE
955    
956           The compiled form of a regular expression can be saved and re-used at a
957           later  time,  possibly by a different program, and even on a host other
958           than the one on which  it  was  compiled.  Details  are  given  in  the
959           pcreprecompile  documentation.  However, compiling a regular expression
960           with one version of PCRE for use with a different version is not  guar-
961           anteed to work and may cause crashes.
962    
963    
964  CHECKING BUILD-TIME OPTIONS  CHECKING BUILD-TIME OPTIONS
965    
966       int pcre_config(int what, void *where);         int pcre_config(int what, void *where);
967    
968       The function pcre_config() makes  it  possible  for  a  PCRE         The  function pcre_config() makes it possible for a PCRE client to dis-
969       client  to  discover  which optional features have been com-         cover which optional features have been compiled into the PCRE library.
970       piled into the PCRE library. The pcrebuild documentation has         The  pcrebuild documentation has more details about these optional fea-
971       more details about these optional features.         tures.
972    
973       The first argument for pcre_config() is an integer, specify-         The first argument for pcre_config() is an  integer,  specifying  which
974       ing  which information is required; the second argument is a         information is required; the second argument is a pointer to a variable
975       pointer to a variable into which the information is  placed.         into which the information is  placed.  The  following  information  is
976       The following information is available:         available:
977    
978         PCRE_CONFIG_UTF8           PCRE_CONFIG_UTF8
979    
980       The output is an integer that is set to one if UTF-8 support         The  output is an integer that is set to one if UTF-8 support is avail-
981       is available; otherwise it is set to zero.         able; otherwise it is set to zero.
982    
983         PCRE_CONFIG_NEWLINE           PCRE_CONFIG_UNICODE_PROPERTIES
984    
985       The output is an integer that is set to  the  value  of  the         The output is an integer that is set to  one  if  support  for  Unicode
986       code  that  is  used for the newline character. It is either         character properties is available; otherwise it is set to zero.
      linefeed (10) or carriage return (13), and  should  normally  
      be the standard character for your operating system.  
987    
988         PCRE_CONFIG_LINK_SIZE           PCRE_CONFIG_NEWLINE
989    
990       The output is an integer that contains the number  of  bytes         The  output  is  an integer whose value specifies the default character
991       used  for  internal linkage in compiled regular expressions.         sequence that is recognized as meaning "newline". The four values  that
992       The value is 2, 3, or 4. Larger values allow larger  regular         are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
993       expressions  to be compiled, at the expense of slower match-         and -1 for ANY. The default should normally be  the  standard  sequence
994       ing. The default value of 2 is sufficient for  all  but  the         for your operating system.
      most  massive patterns, since it allows the compiled pattern  
      to be up to 64K in size.  
995    
996         PCRE_CONFIG_POSIX_MALLOC_THRESHOLD           PCRE_CONFIG_BSR
997    
998       The output is an integer that contains the  threshold  above         The output is an integer whose value indicates what character sequences
999       which  the POSIX interface uses malloc() for output vectors.         the \R escape sequence matches by default. A value of 0 means  that  \R
1000       Further details are given in the pcreposix documentation.         matches  any  Unicode  line ending sequence; a value of 1 means that \R
1001           matches only CR, LF, or CRLF. The default can be overridden when a pat-
1002           tern is compiled or matched.
1003    
1004         PCRE_CONFIG_MATCH_LIMIT           PCRE_CONFIG_LINK_SIZE
1005    
1006       The output is an integer that gives the  default  limit  for         The  output  is  an  integer that contains the number of bytes used for
1007       the   number  of  internal  matching  function  calls  in  a         internal linkage in compiled regular expressions. The value is 2, 3, or
1008       pcre_exec()  execution.  Further  details  are  given   with         4.  Larger  values  allow larger regular expressions to be compiled, at
1009       pcre_exec() below.         the expense of slower matching. The default value of  2  is  sufficient
1010           for  all  but  the  most massive patterns, since it allows the compiled
1011           pattern to be up to 64K in size.
1012    
1013             PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
1014    
1015           The output is an integer that contains the threshold  above  which  the
1016           POSIX  interface  uses malloc() for output vectors. Further details are
1017           given in the pcreposix documentation.
1018    
1019             PCRE_CONFIG_MATCH_LIMIT
1020    
1021           The output is an integer that gives the default limit for the number of
1022           internal  matching  function  calls in a pcre_exec() execution. Further
1023           details are given with pcre_exec() below.
1024    
1025             PCRE_CONFIG_MATCH_LIMIT_RECURSION
1026    
1027           The output is an integer that gives the default limit for the depth  of
1028           recursion  when calling the internal matching function in a pcre_exec()
1029           execution. Further details are given with pcre_exec() below.
1030    
1031             PCRE_CONFIG_STACKRECURSE
1032    
1033           The output is an integer that is set to one if internal recursion  when
1034           running pcre_exec() is implemented by recursive function calls that use
1035           the stack to remember their state. This is the usual way that  PCRE  is
1036           compiled. The output is zero if PCRE was compiled to use blocks of data
1037           on the  heap  instead  of  recursive  function  calls.  In  this  case,
1038           pcre_stack_malloc  and  pcre_stack_free  are  called  to  manage memory
1039           blocks on the heap, thus avoiding the use of the stack.
1040    
1041    
1042  COMPILING A PATTERN  COMPILING A PATTERN
1043    
1044       pcre *pcre_compile(const char *pattern, int options,         pcre *pcre_compile(const char *pattern, int options,
1045            const char **errptr, int *erroffset,              const char **errptr, int *erroffset,
1046            const unsigned char *tableptr);              const unsigned char *tableptr);
1047    
1048       The function pcre_compile() is called to compile  a  pattern         pcre *pcre_compile2(const char *pattern, int options,
1049       into  an internal form. The pattern is a C string terminated              int *errorcodeptr,
1050       by a binary zero, and is passed in the argument  pattern.  A              const char **errptr, int *erroffset,
1051       pointer  to  a  single  block of memory that is obtained via              const unsigned char *tableptr);
1052       pcre_malloc is returned. This contains the compiled code and  
1053       related  data.  The  pcre  type  is defined for the returned         Either of the functions pcre_compile() or pcre_compile2() can be called
1054       block; this is a typedef for a structure whose contents  are         to compile a pattern into an internal form. The only difference between
1055       not  externally  defined. It is up to the caller to free the         the two interfaces is that pcre_compile2() has an additional  argument,
1056       memory when it is no longer required.         errorcodeptr, via which a numerical error code can be returned.
1057    
1058       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
1059       that is, it does not depend on memory location, the complete         the pattern argument. A pointer to a single block  of  memory  that  is
1060       pcre data block is not fully relocatable,  because  it  con-         obtained  via  pcre_malloc is returned. This contains the compiled code
1061       tains  a  copy of the tableptr argument, which is an address         and related data. The pcre type is defined for the returned block; this
1062       (see below).         is a typedef for a structure whose contents are not externally defined.
1063       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
1064       the  compilation.  It  should  be  zero  if  no  options are         longer required.
1065       required. Some of the options, in particular, those that are  
1066       compatible  with Perl, can also be set and unset from within         Although  the compiled code of a PCRE regex is relocatable, that is, it
1067       the pattern (see the detailed description of regular expres-         does not depend on memory location, the complete pcre data block is not
1068       sions  in the pcrepattern documentation). For these options,         fully  relocatable, because it may contain a copy of the tableptr argu-
1069       the contents of the options argument specifies their initial         ment, which is an address (see below).
1070       settings  at  the  start  of  compilation and execution. The  
1071       PCRE_ANCHORED option can be set at the time of  matching  as         The options argument contains various bit settings that affect the com-
1072       well as at compile time.         pilation.  It  should be zero if no options are required. The available
1073           options are described below. Some of them, in  particular,  those  that
1074       If errptr is NULL, pcre_compile() returns NULL  immediately.         are  compatible  with  Perl,  can also be set and unset from within the
1075       Otherwise, if compilation of a pattern fails, pcre_compile()         pattern (see the detailed description  in  the  pcrepattern  documenta-
1076       returns NULL, and sets the variable pointed to by errptr  to         tion).  For  these options, the contents of the options argument speci-
1077       point  to a textual error message. The offset from the start         fies their initial settings at the start of compilation and  execution.
1078       of  the  pattern  to  the  character  where  the  error  was         The  PCRE_ANCHORED  and PCRE_NEWLINE_xxx options can be set at the time
1079       discovered   is   placed  in  the  variable  pointed  to  by         of matching as well as at compile time.
1080       erroffset, which must not be NULL. If it  is,  an  immediate  
1081       error is given.         If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
1082           if  compilation  of  a  pattern fails, pcre_compile() returns NULL, and
1083       If the final  argument,  tableptr,  is  NULL,  PCRE  uses  a         sets the variable pointed to by errptr to point to a textual error mes-
1084       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
1085       compiled, using the default C  locale.  Otherwise,  tableptr         try to free it. The offset from the start of the pattern to the charac-
1086       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
1087       section on locale support below.         by erroffset, which must not be NULL. If it is, an immediate  error  is
1088           given.
1089       This code fragment shows a typical straightforward  call  to  
1090       pcre_compile():         If  pcre_compile2()  is  used instead of pcre_compile(), and the error-
1091           codeptr argument is not NULL, a non-zero error code number is  returned
1092         pcre *re;         via  this argument in the event of an error. This is in addition to the
1093         const char *error;         textual error message. Error codes and messages are listed below.
1094         int erroffset;  
1095         re = pcre_compile(         If the final argument, tableptr, is NULL, PCRE uses a  default  set  of
1096           "^A.*Z",          /* the pattern */         character  tables  that  are  built  when  PCRE  is compiled, using the
1097           0,                /* default options */         default C locale. Otherwise, tableptr must be an address  that  is  the
1098           &error,           /* for error message */         result  of  a  call to pcre_maketables(). This value is stored with the
1099           &erroffset,       /* for error offset */         compiled pattern, and used again by pcre_exec(), unless  another  table
1100           NULL);            /* use default character tables */         pointer is passed to it. For more discussion, see the section on locale
1101           support below.
1102       The following option bits are defined:  
1103           This code fragment shows a typical straightforward  call  to  pcre_com-
1104         PCRE_ANCHORED         pile():
1105    
1106       If this bit is set, the pattern is forced to be  "anchored",           pcre *re;
1107       that is, it is constrained to match only at the first match-           const char *error;
1108       ing point in the string which is being searched  (the  "sub-           int erroffset;
1109       ject string"). This effect can also be achieved by appropri-           re = pcre_compile(
1110       ate constructs in the pattern itself, which is the only  way             "^A.*Z",          /* the pattern */
1111       to do it in Perl.             0,                /* default options */
1112               &error,           /* for error message */
1113         PCRE_CASELESS             &erroffset,       /* for error offset */
1114               NULL);            /* use default character tables */
1115       If this bit is set, letters in the pattern match both  upper  
1116       and  lower  case  letters.  It  is  equivalent  to Perl's /i         The  following  names  for option bits are defined in the pcre.h header
1117       option, and it can be changed within a  pattern  by  a  (?i)         file:
1118       option setting.  
1119             PCRE_ANCHORED
1120         PCRE_DOLLAR_ENDONLY  
1121           If this bit is set, the pattern is forced to be "anchored", that is, it
1122       If this bit is set, a dollar metacharacter  in  the  pattern         is  constrained to match only at the first matching point in the string
1123       matches  only at the end of the subject string. Without this         that is being searched (the "subject string"). This effect can also  be
1124       option, a dollar also matches immediately before  the  final         achieved  by appropriate constructs in the pattern itself, which is the
1125       character  if it is a newline (but not before any other new-         only way to do it in Perl.
1126       lines).  The  PCRE_DOLLAR_ENDONLY  option  is   ignored   if  
1127       PCRE_MULTILINE is set. There is no equivalent to this option           PCRE_AUTO_CALLOUT
1128       in Perl, and no way to set it within a pattern.  
1129           If this bit is set, pcre_compile() automatically inserts callout items,
1130         PCRE_DOTALL         all  with  number  255, before each pattern item. For discussion of the
1131           callout facility, see the pcrecallout documentation.
1132       If this bit is  set,  a  dot  metacharater  in  the  pattern  
1133       matches all characters, including newlines. Without it, new-           PCRE_BSR_ANYCRLF
1134       lines are excluded. This option is equivalent to  Perl's  /s           PCRE_BSR_UNICODE
1135       option,  and  it  can  be changed within a pattern by a (?s)  
1136       option setting. A negative class such as [^a] always matches         These options (which are mutually exclusive) control what the \R escape
1137       a  newline  character,  independent  of  the setting of this         sequence  matches.  The choice is either to match only CR, LF, or CRLF,
1138       option.         or to match any Unicode newline sequence. The default is specified when
1139           PCRE is built. It can be overridden from within the pattern, or by set-
1140         PCRE_EXTENDED         ting an option when a compiled pattern is matched.
1141    
1142       If this bit is set, whitespace data characters in  the  pat-           PCRE_CASELESS
1143       tern  are  totally  ignored  except when escaped or inside a  
1144       character class. Whitespace does not include the VT  charac-         If this bit is set, letters in the pattern match both upper  and  lower
1145       ter  (code 11). In addition, characters between an unescaped         case  letters.  It  is  equivalent  to  Perl's /i option, and it can be
1146       # outside a character class and the next newline  character,         changed within a pattern by a (?i) option setting. In UTF-8 mode,  PCRE
1147       inclusive, are also ignored. This is equivalent to Perl's /x         always  understands the concept of case for characters whose values are
1148       option, and it can be changed within a  pattern  by  a  (?x)         less than 128, so caseless matching is always possible. For  characters
1149       option setting.         with  higher  values,  the concept of case is supported if PCRE is com-
1150           piled with Unicode property support, but not otherwise. If you want  to
1151       This option makes it possible  to  include  comments  inside         use  caseless  matching  for  characters 128 and above, you must ensure
1152       complicated patterns.  Note, however, that this applies only         that PCRE is compiled with Unicode property support  as  well  as  with
1153       to data characters. Whitespace characters may  never  appear         UTF-8 support.
1154       within special character sequences in a pattern, for example  
1155       within the sequence (?( which introduces a conditional  sub-           PCRE_DOLLAR_ENDONLY
1156       pattern.  
1157           If  this bit is set, a dollar metacharacter in the pattern matches only
1158         PCRE_EXTRA         at the end of the subject string. Without this option,  a  dollar  also
1159           matches  immediately before a newline at the end of the string (but not
1160       This option was invented in  order  to  turn  on  additional         before any other newlines). The PCRE_DOLLAR_ENDONLY option  is  ignored
1161       functionality of PCRE that is incompatible with Perl, but it         if  PCRE_MULTILINE  is  set.   There is no equivalent to this option in
1162       is currently of very little use. When set, any backslash  in         Perl, and no way to set it within a pattern.
1163       a  pattern  that is followed by a letter that has no special  
1164       meaning causes an error, thus reserving  these  combinations           PCRE_DOTALL
1165       for  future  expansion.  By default, as in Perl, a backslash  
1166       followed by a letter with no special meaning is treated as a         If this bit is set, a dot metacharater in the pattern matches all char-
1167       literal.  There  are at present no other features controlled         acters,  including  those that indicate newline. Without it, a dot does
1168       by this option. It can also be set by a (?X) option  setting         not match when the current position is at a  newline.  This  option  is
1169       within a pattern.         equivalent  to Perl's /s option, and it can be changed within a pattern
1170           by a (?s) option setting. A negative class such as [^a] always  matches
1171         PCRE_MULTILINE         newline characters, independent of the setting of this option.
1172    
1173       By default, PCRE treats the subject string as consisting  of           PCRE_DUPNAMES
1174       a  single "line" of characters (even if it actually contains  
1175       several newlines). The "start  of  line"  metacharacter  (^)         If  this  bit is set, names used to identify capturing subpatterns need
1176       matches  only  at the start of the string, while the "end of         not be unique. This can be helpful for certain types of pattern when it
1177       line" metacharacter ($) matches  only  at  the  end  of  the         is  known  that  only  one instance of the named subpattern can ever be
1178       string,    or   before   a   terminating   newline   (unless         matched. There are more details of named subpatterns  below;  see  also
1179       PCRE_DOLLAR_ENDONLY is set). This is the same as Perl.         the pcrepattern documentation.
1180    
1181       When PCRE_MULTILINE it is set, the "start of line" and  "end           PCRE_EXTENDED
1182       of  line"  constructs match immediately following or immedi-  
1183       ately before any newline  in  the  subject  string,  respec-         If  this  bit  is  set,  whitespace  data characters in the pattern are
1184       tively,  as  well  as  at  the  very  start and end. This is         totally ignored except when escaped or inside a character class. White-
1185       equivalent to Perl's /m option, and it can be changed within         space does not include the VT character (code 11). In addition, charac-
1186       a  pattern  by  a  (?m) option setting. If there are no "\n"         ters between an unescaped # outside a character class and the next new-
1187       characters in a subject string, or no occurrences of ^ or  $         line,  inclusive,  are  also  ignored.  This is equivalent to Perl's /x
1188       in a pattern, setting PCRE_MULTILINE has no effect.         option, and it can be changed within a pattern by a  (?x)  option  set-
1189           ting.
1190         PCRE_NO_AUTO_CAPTURE  
1191           This  option  makes  it possible to include comments inside complicated
1192       If this option is set, it disables the use of numbered  cap-         patterns.  Note, however, that this applies only  to  data  characters.
1193       turing  parentheses  in the pattern. Any opening parenthesis         Whitespace   characters  may  never  appear  within  special  character
1194       that is not followed by ? behaves as if it were followed  by         sequences in a pattern, for  example  within  the  sequence  (?(  which
1195       ?:  but  named  parentheses  can still be used for capturing         introduces a conditional subpattern.
1196       (and they acquire numbers in the usual  way).  There  is  no  
1197       equivalent of this option in Perl.           PCRE_EXTRA
1198    
1199         PCRE_UNGREEDY         This  option  was invented in order to turn on additional functionality
1200           of PCRE that is incompatible with Perl, but it  is  currently  of  very
1201       This option inverts the "greediness" of the  quantifiers  so         little  use. When set, any backslash in a pattern that is followed by a
1202       that  they  are  not greedy by default, but become greedy if         letter that has no special meaning  causes  an  error,  thus  reserving
1203       followed by "?". It is not compatible with Perl. It can also         these  combinations  for  future  expansion.  By default, as in Perl, a
1204       be set by a (?U) option setting within the pattern.         backslash followed by a letter with no special meaning is treated as  a
1205           literal.  (Perl can, however, be persuaded to give a warning for this.)
1206         PCRE_UTF8         There are at present no other features controlled by  this  option.  It
1207           can also be set by a (?X) option setting within a pattern.
1208       This option causes PCRE to regard both the pattern  and  the  
1209       subject  as  strings  of UTF-8 characters instead of single-           PCRE_FIRSTLINE
1210       byte character strings. However, it  is  available  only  if  
1211       PCRE  has  been  built to include UTF-8 support. If not, the         If  this  option  is  set,  an  unanchored pattern is required to match
1212       use of this option provokes an error. Details  of  how  this         before or at the first  newline  in  the  subject  string,  though  the
1213       option  changes  the behaviour of PCRE are given in the sec-         matched text may continue over the newline.
1214       tion on UTF-8 support in the main pcre page.  
1215             PCRE_MULTILINE
1216    
1217           By  default,  PCRE  treats the subject string as consisting of a single
1218           line of characters (even if it actually contains newlines). The  "start
1219           of  line"  metacharacter  (^)  matches only at the start of the string,
1220           while the "end of line" metacharacter ($) matches only at  the  end  of
1221           the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
1222           is set). This is the same as Perl.
1223    
1224           When PCRE_MULTILINE it is set, the "start of line" and  "end  of  line"
1225           constructs  match  immediately following or immediately before internal
1226           newlines in the subject string, respectively, as well as  at  the  very
1227           start  and  end.  This is equivalent to Perl's /m option, and it can be
1228           changed within a pattern by a (?m) option setting. If there are no new-
1229           lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
1230           setting PCRE_MULTILINE has no effect.
1231    
1232             PCRE_NEWLINE_CR
1233             PCRE_NEWLINE_LF
1234             PCRE_NEWLINE_CRLF
1235             PCRE_NEWLINE_ANYCRLF
1236             PCRE_NEWLINE_ANY
1237    
1238           These options override the default newline definition that  was  chosen
1239           when  PCRE  was built. Setting the first or the second specifies that a
1240           newline is indicated by a single character (CR  or  LF,  respectively).
1241           Setting  PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
1242           two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
1243           that any of the three preceding sequences should be recognized. Setting
1244           PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
1245           recognized. The Unicode newline sequences are the three just mentioned,
1246           plus the single characters VT (vertical  tab,  U+000B),  FF  (formfeed,
1247           U+000C),  NEL  (next line, U+0085), LS (line separator, U+2028), and PS
1248           (paragraph separator, U+2029). The last  two  are  recognized  only  in
1249           UTF-8 mode.
1250    
1251           The  newline  setting  in  the  options  word  uses three bits that are
1252           treated as a number, giving eight possibilities. Currently only six are
1253           used  (default  plus the five values above). This means that if you set
1254           more than one newline option, the combination may or may not be  sensi-
1255           ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
1256           PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
1257           cause an error.
1258    
1259           The  only time that a line break is specially recognized when compiling
1260           a pattern is if PCRE_EXTENDED is set, and  an  unescaped  #  outside  a
1261           character  class  is  encountered.  This indicates a comment that lasts
1262           until after the next line break sequence. In other circumstances,  line
1263           break   sequences   are   treated  as  literal  data,  except  that  in
1264           PCRE_EXTENDED mode, both CR and LF are treated as whitespace characters
1265           and are therefore ignored.
1266    
1267           The newline option that is set at compile time becomes the default that
1268           is used for pcre_exec() and pcre_dfa_exec(), but it can be  overridden.
1269    
1270             PCRE_NO_AUTO_CAPTURE
1271    
1272           If this option is set, it disables the use of numbered capturing paren-
1273           theses in the pattern. Any opening parenthesis that is not followed  by
1274           ?  behaves as if it were followed by ?: but named parentheses can still
1275           be used for capturing (and they acquire  numbers  in  the  usual  way).
1276           There is no equivalent of this option in Perl.
1277    
1278             PCRE_UNGREEDY
1279    
1280           This  option  inverts  the "greediness" of the quantifiers so that they
1281           are not greedy by default, but become greedy if followed by "?". It  is
1282           not  compatible  with Perl. It can also be set by a (?U) option setting
1283           within the pattern.
1284    
1285             PCRE_UTF8
1286    
1287           This option causes PCRE to regard both the pattern and the  subject  as
1288           strings  of  UTF-8 characters instead of single-byte character strings.
1289           However, it is available only when PCRE is built to include UTF-8  sup-
1290           port.  If not, the use of this option provokes an error. Details of how
1291           this option changes the behaviour of PCRE are given in the  section  on
1292           UTF-8 support in the main pcre page.
1293    
1294             PCRE_NO_UTF8_CHECK
1295    
1296           When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
1297           automatically checked. There is a  discussion  about  the  validity  of
1298           UTF-8  strings  in  the main pcre page. If an invalid UTF-8 sequence of
1299           bytes is found, pcre_compile() returns an error. If  you  already  know
1300           that your pattern is valid, and you want to skip this check for perfor-
1301           mance reasons, you can set the PCRE_NO_UTF8_CHECK option.  When  it  is
1302           set,  the  effect  of  passing  an invalid UTF-8 string as a pattern is
1303           undefined. It may cause your program to crash. Note  that  this  option
1304           can  also be passed to pcre_exec() and pcre_dfa_exec(), to suppress the
1305           UTF-8 validity checking of subject strings.
1306    
1307    
1308    COMPILATION ERROR CODES
1309    
1310           The following table lists the error  codes  than  may  be  returned  by
1311           pcre_compile2(),  along with the error messages that may be returned by
1312           both compiling functions. As PCRE has developed, some error codes  have
1313           fallen out of use. To avoid confusion, they have not been re-used.
1314    
1315              0  no error
1316              1  \ at end of pattern
1317              2  \c at end of pattern
1318              3  unrecognized character follows \
1319              4  numbers out of order in {} quantifier
1320              5  number too big in {} quantifier
1321              6  missing terminating ] for character class
1322              7  invalid escape sequence in character class
1323              8  range out of order in character class
1324              9  nothing to repeat
1325             10  [this code is not in use]
1326             11  internal error: unexpected repeat
1327             12  unrecognized character after (?
1328             13  POSIX named classes are supported only within a class
1329             14  missing )
1330             15  reference to non-existent subpattern
1331             16  erroffset passed as NULL
1332             17  unknown option bit(s) set
1333             18  missing ) after comment
1334             19  [this code is not in use]
1335             20  regular expression too large
1336             21  failed to get memory
1337             22  unmatched parentheses
1338             23  internal error: code overflow
1339             24  unrecognized character after (?<
1340             25  lookbehind assertion is not fixed length
1341             26  malformed number or name after (?(
1342             27  conditional group contains more than two branches
1343             28  assertion expected after (?(
1344             29  (?R or (?[+-]digits must be followed by )
1345             30  unknown POSIX class name
1346             31  POSIX collating elements are not supported
1347             32  this version of PCRE is not compiled with PCRE_UTF8 support
1348             33  [this code is not in use]
1349             34  character value in \x{...} sequence is too large
1350             35  invalid condition (?(0)
1351             36  \C not allowed in lookbehind assertion
1352             37  PCRE does not support \L, \l, \N, \U, or \u
1353             38  number after (?C is > 255
1354             39  closing ) for (?C expected
1355             40  recursive call could loop indefinitely
1356             41  unrecognized character after (?P
1357             42  syntax error in subpattern name (missing terminator)
1358             43  two named subpatterns have the same name
1359             44  invalid UTF-8 string
1360             45  support for \P, \p, and \X has not been compiled
1361             46  malformed \P or \p sequence
1362             47  unknown property name after \P or \p
1363             48  subpattern name is too long (maximum 32 characters)
1364             49  too many named subpatterns (maximum 10,000)
1365             50  [this code is not in use]
1366             51  octal value is greater than \377 (not in UTF-8 mode)
1367             52  internal error: overran compiling workspace
1368             53   internal  error:  previously-checked  referenced  subpattern not
1369           found
1370             54  DEFINE group contains more than one branch
1371             55  repeating a DEFINE group is not allowed
1372             56  inconsistent NEWLINE options
1373             57  \g is not followed by a braced name or an optionally braced
1374                   non-zero number
1375             58  (?+ or (?- or (?(+ or (?(- must be followed by a non-zero number
1376    
1377    
1378  STUDYING A PATTERN  STUDYING A PATTERN
1379    
1380       pcre_extra *pcre_study(const pcre *code, int options,         pcre_extra *pcre_study(const pcre *code, int options
1381            const char **errptr);              const char **errptr);
1382    
1383       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
1384       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
1385       the time taken for matching. The function pcre_study() takes         matching. The function pcre_study() takes a pointer to a compiled  pat-
1386       a  pointer  to  a compiled pattern as its first argument. If         tern as its first argument. If studying the pattern produces additional
1387       studing the pattern  produces  additional  information  that         information that will help speed up matching,  pcre_study()  returns  a
1388       will  help speed up matching, pcre_study() returns a pointer         pointer  to a pcre_extra block, in which the study_data field points to
1389       to a pcre_extra block, in which the study_data field  points         the results of the study.
1390       to the results of the study.  
1391           The  returned  value  from  pcre_study()  can  be  passed  directly  to
1392       The  returned  value  from  a  pcre_study()  can  be  passed         pcre_exec().  However,  a  pcre_extra  block also contains other fields
1393       directly  to pcre_exec(). However, the pcre_extra block also         that can be set by the caller before the block  is  passed;  these  are
1394       contains other fields that can be set by the  caller  before         described below in the section on matching a pattern.
1395       the  block is passed; these are described below. If studying  
1396       the pattern does not  produce  any  additional  information,         If  studying  the  pattern  does not produce any additional information
1397       pcre_study() returns NULL. In that circumstance, if the cal-         pcre_study() returns NULL. In that circumstance, if the calling program
1398       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
1399       pcre_exec(), it must set up its own pcre_extra block.         its own pcre_extra block.
1400    
1401       The second argument contains option  bits.  At  present,  no         The second argument of pcre_study() contains option bits.  At  present,
1402       options  are  defined  for  pcre_study(),  and this argument         no options are defined, and this argument should always be zero.
1403       should always be zero.  
1404           The  third argument for pcre_study() is a pointer for an error message.
1405       The third argument for pcre_study()  is  a  pointer  for  an         If studying succeeds (even if no data is  returned),  the  variable  it
1406       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
1407       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
1408       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
1409       fore  test  the  error  pointer  for  NULL   after   calling         after calling pcre_study(), to be sure that it has run successfully.
1410       pcre_study(), to be sure that it has run successfully.  
1411           This is a typical call to pcre_study():
1412       This is a typical call to pcre_study():  
1413             pcre_extra *pe;
1414         pcre_extra *pe;           pe = pcre_study(
1415         pe = pcre_study(             re,             /* result of pcre_compile() */
1416           re,             /* result of pcre_compile() */             0,              /* no options exist */
1417           0,              /* no options exist */             &error);        /* set to NULL or points to a message */
1418           &error);        /* set to NULL or points to a message */  
1419           At present, studying a pattern is useful only for non-anchored patterns
1420       At present, studying a  pattern  is  useful  only  for  non-         that  do not have a single fixed starting character. A bitmap of possi-
1421       anchored  patterns  that do not have a single fixed starting         ble starting bytes is created.
      character. A  bitmap  of  possible  starting  characters  is  
      created.  
1422    
1423    
1424  LOCALE SUPPORT  LOCALE SUPPORT
1425    
1426       PCRE handles caseless matching, and determines whether char-         PCRE handles caseless matching, and determines whether  characters  are
1427       acters  are  letters, digits, or whatever, by reference to a         letters,  digits, or whatever, by reference to a set of tables, indexed
1428       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
1429       to characters with codes less than 256. The library contains         characters  with  codes  less than 128. Higher-valued codes never match
1430       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
1431       locale  when  PCRE  is compiled. This is used when the final         with  Unicode  character property support. The use of locales with Uni-
1432       argument of pcre_compile() is NULL, and  is  sufficient  for         code is discouraged. If you are handling characters with codes  greater
1433       many applications.         than  128, you should either use UTF-8 and Unicode, or use locales, but
1434           not try to mix the two.
1435       An alternative set of tables can, however, be supplied. Such  
1436       tables  are built by calling the pcre_maketables() function,         PCRE contains an internal set of tables that are used  when  the  final
1437       which has no arguments, in the relevant locale.  The  result         argument  of  pcre_compile()  is  NULL.  These  are sufficient for many
1438       can  then be passed to pcre_compile() as often as necessary.         applications.  Normally, the internal tables recognize only ASCII char-
1439       For example, to build and use tables  that  are  appropriate         acters. However, when PCRE is built, it is possible to cause the inter-
1440       for  the French locale (where accented characters with codes         nal tables to be rebuilt in the default "C" locale of the local system,
1441       greater than 128 are treated as letters), the following code         which may cause them to be different.
1442       could be used:  
1443           The  internal tables can always be overridden by tables supplied by the
1444         setlocale(LC_CTYPE, "fr");         application that calls PCRE. These may be created in a different locale
1445         tables = pcre_maketables();         from  the  default.  As more and more applications change to using Uni-
1446         re = pcre_compile(..., tables);         code, the need for this locale support is expected to die away.
1447    
1448       The  tables  are  built  in  memory  that  is  obtained  via         External tables are built by calling  the  pcre_maketables()  function,
1449       pcre_malloc.  The  pointer that is passed to pcre_compile is         which  has no arguments, in the relevant locale. The result can then be
1450       saved with the compiled pattern, and  the  same  tables  are         passed to pcre_compile() or pcre_exec()  as  often  as  necessary.  For
1451       used via this pointer by pcre_study() and pcre_exec(). Thus,         example,  to  build  and use tables that are appropriate for the French
1452       for any single pattern, compilation, studying  and  matching         locale (where accented characters with  values  greater  than  128  are
1453       all happen in the same locale, but different patterns can be         treated as letters), the following code could be used:
1454       compiled in different locales. It is the caller's  responsi-  
1455       bility  to  ensure  that  the  memory  containing the tables           setlocale(LC_CTYPE, "fr_FR");
1456       remains available for as long as it is needed.           tables = pcre_maketables();
1457             re = pcre_compile(..., tables);
1458    
1459           The  locale  name "fr_FR" is used on Linux and other Unix-like systems;
1460           if you are using Windows, the name for the French locale is "french".
1461    
1462           When pcre_maketables() runs, the tables are built  in  memory  that  is
1463           obtained  via  pcre_malloc. It is the caller's responsibility to ensure
1464           that the memory containing the tables remains available for as long  as
1465           it is needed.
1466    
1467           The pointer that is passed to pcre_compile() is saved with the compiled
1468           pattern, and the same tables are used via this pointer by  pcre_study()
1469           and normally also by pcre_exec(). Thus, by default, for any single pat-
1470           tern, compilation, studying and matching all happen in the same locale,
1471           but different patterns can be compiled in different locales.
1472    
1473           It  is  possible to pass a table pointer or NULL (indicating the use of
1474           the internal tables) to pcre_exec(). Although  not  intended  for  this
1475           purpose,  this facility could be used to match a pattern in a different
1476           locale from the one in which it was compiled. Passing table pointers at
1477           run time is discussed below in the section on matching a pattern.
1478    
1479    
1480  INFORMATION ABOUT A PATTERN  INFORMATION ABOUT A PATTERN
1481    
1482       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,         int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
1483            int what, void *where);              int what, void *where);
1484    
1485       The pcre_fullinfo() function  returns  information  about  a         The  pcre_fullinfo() function returns information about a compiled pat-
1486       compiled pattern. It replaces the obsolete pcre_info() func-         tern. It replaces the obsolete pcre_info() function, which is neverthe-
1487       tion, which is nevertheless retained for backwards compabil-         less retained for backwards compability (and is documented below).
1488       ity (and is documented below).  
1489           The  first  argument  for  pcre_fullinfo() is a pointer to the compiled
1490       The first argument for pcre_fullinfo() is a pointer  to  the         pattern. The second argument is the result of pcre_study(), or NULL  if
1491       compiled  pattern.  The  second  argument  is  the result of         the  pattern  was not studied. The third argument specifies which piece
1492       pcre_study(), or NULL if the pattern was  not  studied.  The         of information is required, and the fourth argument is a pointer  to  a
1493       third  argument  specifies  which  piece  of  information is         variable  to  receive  the  data. The yield of the function is zero for
1494       required, and the fourth argument is a pointer to a variable         success, or one of the following negative numbers:
1495       to  receive  the data. The yield of the function is zero for  
1496       success, or one of the following negative numbers:           PCRE_ERROR_NULL       the argument code was NULL
1497                                   the argument where was NULL
1498         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1499                               the argument where was NULL           PCRE_ERROR_BADOPTION  the value of what was invalid
1500         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1501         PCRE_ERROR_BADOPTION  the value of what was invalid         The "magic number" is placed at the start of each compiled  pattern  as
1502           an  simple check against passing an arbitrary memory pointer. Here is a
1503       Here is a typical call of  pcre_fullinfo(),  to  obtain  the         typical call of pcre_fullinfo(), to obtain the length of  the  compiled
1504       length of the compiled pattern:         pattern:
1505    
1506         int rc;           int rc;
1507         unsigned long int length;           size_t length;
1508         rc = pcre_fullinfo(           rc = pcre_fullinfo(
1509           re,               /* result of pcre_compile() */             re,               /* result of pcre_compile() */
1510           pe,               /* result of pcre_study(), or NULL */             pe,               /* result of pcre_study(), or NULL */
1511           PCRE_INFO_SIZE,   /* what is required */             PCRE_INFO_SIZE,   /* what is required */
1512           &length);         /* where to put the data */             &length);         /* where to put the data */
1513    
1514       The possible values for the third argument  are  defined  in         The  possible  values for the third argument are defined in pcre.h, and
1515       pcre.h, and are as follows:         are as follows:
1516    
1517         PCRE_INFO_BACKREFMAX           PCRE_INFO_BACKREFMAX
1518    
1519       Return the number of the highest back reference in the  pat-         Return the number of the highest back reference  in  the  pattern.  The
1520       tern.  The  fourth argument should point to an int variable.         fourth  argument  should  point to an int variable. Zero is returned if
1521       Zero is returned if there are no back references.         there are no back references.
1522    
1523         PCRE_INFO_CAPTURECOUNT           PCRE_INFO_CAPTURECOUNT
1524    
1525       Return the number of capturing subpatterns in  the  pattern.         Return the number of capturing subpatterns in the pattern.  The  fourth
1526       The fourth argument should point to an int variable.         argument should point to an int variable.
1527    
1528         PCRE_INFO_FIRSTBYTE           PCRE_INFO_DEFAULT_TABLES
1529    
1530       Return information about  the  first  byte  of  any  matched         Return  a pointer to the internal default character tables within PCRE.
1531       string,  for a non-anchored pattern. (This option used to be         The fourth argument should point to an unsigned char *  variable.  This
1532       called PCRE_INFO_FIRSTCHAR; the old name is still recognized         information call is provided for internal use by the pcre_study() func-
1533       for backwards compatibility.)         tion. External callers can cause PCRE to use  its  internal  tables  by
1534           passing a NULL table pointer.
1535       If there is a fixed first byte, e.g. from a pattern such  as  
1536       (cat|cow|coyote),  it  is returned in the integer pointed to           PCRE_INFO_FIRSTBYTE
1537       by where. Otherwise, if either  
1538           Return  information  about  the first byte of any matched string, for a
1539       (a) the pattern was compiled with the PCRE_MULTILINE option,         non-anchored pattern. The fourth argument should point to an int  vari-
1540       and every branch starts with "^", or         able.  (This option used to be called PCRE_INFO_FIRSTCHAR; the old name
1541           is still recognized for backwards compatibility.)
1542       (b) every  branch  of  the  pattern  starts  with  ".*"  and  
1543       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
1544       anchored),         (cat|cow|coyote), its value is returned. Otherwise, if either
1545    
1546       -1 is returned, indicating that the pattern matches only  at         (a)  the pattern was compiled with the PCRE_MULTILINE option, and every
1547       the  start  of  a subject string or after any newline within         branch starts with "^", or
1548       the string. Otherwise -2 is returned. For anchored patterns,  
1549       -2 is returned.         (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
1550           set (if it were set, the pattern would be anchored),
1551         PCRE_INFO_FIRSTTABLE  
1552           -1  is  returned, indicating that the pattern matches only at the start
1553       If the pattern was studied, and this resulted  in  the  con-         of a subject string or after any newline within the  string.  Otherwise
1554       struction of a 256-bit table indicating a fixed set of bytes         -2 is returned. For anchored patterns, -2 is returned.
1555       for the first byte in any matching string, a pointer to  the  
1556       table  is  returned.  Otherwise NULL is returned. The fourth           PCRE_INFO_FIRSTTABLE
1557       argument should point to an unsigned char * variable.  
1558           If  the pattern was studied, and this resulted in the construction of a
1559         PCRE_INFO_LASTLITERAL         256-bit table indicating a fixed set of bytes for the first byte in any
1560           matching  string, a pointer to the table is returned. Otherwise NULL is
1561       Return the value of the rightmost  literal  byte  that  must         returned. The fourth argument should point to an unsigned char *  vari-
1562       exist  in  any  matched  string, other than at its start, if         able.
1563       such a byte has been recorded. The  fourth  argument  should  
1564       point  to  an  int variable. If there is no such byte, -1 is           PCRE_INFO_HASCRORLF
1565       returned. For anchored patterns,  a  last  literal  byte  is  
1566       recorded  only  if  it follows something of variable length.         Return  1  if  the  pattern  contains any explicit matches for CR or LF
1567       For example, for the pattern /^a\d+z\d+/ the returned  value         characters, otherwise 0. The fourth argument should  point  to  an  int
1568       is "z", but for /^a\dz\d/ the returned value is -1.         variable.
1569    
1570         PCRE_INFO_NAMECOUNT           PCRE_INFO_JCHANGED
1571         PCRE_INFO_NAMEENTRYSIZE  
1572         PCRE_INFO_NAMETABLE         Return  1  if the (?J) option setting is used in the pattern, otherwise
1573           0. The fourth argument should point to an int variable. The (?J) inter-
1574       PCRE supports the use of named as well as numbered capturing         nal option setting changes the local PCRE_DUPNAMES option.
1575       parentheses. The names are just an additional way of identi-  
1576       fying the parentheses,  which  still  acquire  a  number.  A           PCRE_INFO_LASTLITERAL
1577       caller  that  wants  to extract data from a named subpattern  
1578       must convert the name to a number in  order  to  access  the         Return  the  value of the rightmost literal byte that must exist in any
1579       correct  pointers  in  the  output  vector  (described  with         matched string, other than at its  start,  if  such  a  byte  has  been
1580       pcre_exec() below). In order to do this, it must  first  use         recorded. The fourth argument should point to an int variable. If there
1581       these  three  values  to  obtain  the name-to-number mapping         is no such byte, -1 is returned. For anchored patterns, a last  literal
1582       table for the pattern.         byte  is  recorded only if it follows something of variable length. For
1583           example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
1584       The  map  consists  of  a  number  of  fixed-size   entries.         /^a\dz\d/ the returned value is -1.
1585       PCRE_INFO_NAMECOUNT   gives   the  number  of  entries,  and  
1586       PCRE_INFO_NAMEENTRYSIZE gives the size of each  entry;  both           PCRE_INFO_NAMECOUNT
1587       of  these return an int value. The entry size depends on the           PCRE_INFO_NAMEENTRYSIZE
1588       length of the longest name.  PCRE_INFO_NAMETABLE  returns  a           PCRE_INFO_NAMETABLE
1589       pointer to the first entry of the table (a pointer to char).  
1590       The first two bytes of each entry are the number of the cap-         PCRE  supports the use of named as well as numbered capturing parenthe-
1591       turing parenthesis, most significant byte first. The rest of         ses. The names are just an additional way of identifying the  parenthe-
1592       the entry is the corresponding name,  zero  terminated.  The         ses, which still acquire numbers. Several convenience functions such as
1593       names  are  in alphabetical order. For example, consider the         pcre_get_named_substring() are provided for  extracting  captured  sub-
1594       following pattern (assume PCRE_EXTENDED  is  set,  so  white         strings  by  name. It is also possible to extract the data directly, by
1595       space - including newlines - is ignored):         first converting the name to a number in order to  access  the  correct
1596           pointers in the output vector (described with pcre_exec() below). To do
1597         (?P<date> (?P<year>(\d\d)?\d\d) -         the conversion, you need  to  use  the  name-to-number  map,  which  is
1598         (?P<month>\d\d) - (?P<day>\d\d) )         described by these three values.
1599    
1600       There are four named subpatterns,  so  the  table  has  four         The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
1601       entries,  and  each  entry in the table is eight bytes long.         gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
1602       The table is as follows, with non-printing  bytes  shows  in         of  each  entry;  both  of  these  return  an int value. The entry size
1603       hex, and undefined bytes shown as ??:         depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
1604           a  pointer  to  the  first  entry of the table (a pointer to char). The
1605         00 01 d  a  t  e  00 ??         first two bytes of each entry are the number of the capturing parenthe-
1606         00 05 d  a  y  00 ?? ??         sis,  most  significant byte first. The rest of the entry is the corre-
1607         00 04 m  o  n  t  h  00         sponding name, zero terminated. The names are  in  alphabetical  order.
1608         00 02 y  e  a  r  00 ??         When PCRE_DUPNAMES is set, duplicate names are in order of their paren-
1609           theses numbers. For example, consider  the  following  pattern  (assume
1610       When writing code to extract data  from  named  subpatterns,         PCRE_EXTENDED  is  set,  so  white  space  -  including  newlines  - is
1611       remember  that the length of each entry may be different for         ignored):
1612       each compiled pattern.  
1613             (?<date> (?<year>(\d\d)?\d\d) -
1614         PCRE_INFO_OPTIONS           (?<month>\d\d) - (?<day>\d\d) )
1615    
1616       Return a copy of the options with which the pattern was com-         There are four named subpatterns, so the table has  four  entries,  and
1617       piled.  The fourth argument should point to an unsigned long         each  entry  in the table is eight bytes long. The table is as follows,
1618       int variable. These option bits are those specified  in  the         with non-printing bytes shows in hexadecimal, and undefined bytes shown
1619       call  to  pcre_compile(),  modified  by any top-level option         as ??:
1620       settings within the pattern itself.  
1621             00 01 d  a  t  e  00 ??
1622       A pattern is automatically anchored by PCRE if  all  of  its           00 05 d  a  y  00 ?? ??
1623       top-level alternatives begin with one of the following:           00 04 m  o  n  t  h  00
1624             00 02 y  e  a  r  00 ??
1625         ^     unless PCRE_MULTILINE is set  
1626         \A    always         When  writing  code  to  extract  data from named subpatterns using the
1627         \G    always         name-to-number map, remember that the length of the entries  is  likely
1628         .*    if PCRE_DOTALL is set and there are no back         to be different for each compiled pattern.
1629                 references to the subpattern in which .* appears  
1630             PCRE_INFO_OKPARTIAL
1631       For such patterns, the  PCRE_ANCHORED  bit  is  set  in  the  
1632       options returned by pcre_fullinfo().         Return  1 if the pattern can be used for partial matching, otherwise 0.
1633           The fourth argument should point to an int  variable.  The  pcrepartial
1634         PCRE_INFO_SIZE         documentation  lists  the restrictions that apply to patterns when par-
1635           tial matching is used.
1636       Return the size of the compiled pattern, that is, the  value  
1637       that  was  passed as the argument to pcre_malloc() when PCRE           PCRE_INFO_OPTIONS
1638       was getting memory in which to place the compiled data.  The  
1639       fourth argument should point to a size_t variable.         Return a copy of the options with which the pattern was  compiled.  The
1640           fourth  argument  should  point to an unsigned long int variable. These
1641         PCRE_INFO_STUDYSIZE         option bits are those specified in the call to pcre_compile(), modified
1642           by any top-level option settings at the start of the pattern itself. In
1643       Returns the size  of  the  data  block  pointed  to  by  the         other words, they are the options that will be in force  when  matching
1644       study_data  field  in a pcre_extra block. That is, it is the         starts.  For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
1645       value that was passed to pcre_malloc() when PCRE was getting         the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
1646       memory into which to place the data created by pcre_study().         and PCRE_EXTENDED.
1647       The fourth argument should point to a size_t variable.  
1648           A  pattern  is  automatically  anchored by PCRE if all of its top-level
1649           alternatives begin with one of the following:
1650    
1651             ^     unless PCRE_MULTILINE is set
1652             \A    always
1653             \G    always
1654             .*    if PCRE_DOTALL is set and there are no back
1655                     references to the subpattern in which .* appears
1656    
1657           For such patterns, the PCRE_ANCHORED bit is set in the options returned
1658           by pcre_fullinfo().
1659    
1660             PCRE_INFO_SIZE
1661    
1662           Return  the  size  of the compiled pattern, that is, the value that was
1663           passed as the argument to pcre_malloc() when PCRE was getting memory in
1664           which to place the compiled data. The fourth argument should point to a
1665           size_t variable.
1666    
1667             PCRE_INFO_STUDYSIZE
1668    
1669           Return the size of the data block pointed to by the study_data field in
1670           a  pcre_extra  block.  That  is,  it  is  the  value that was passed to
1671           pcre_malloc() when PCRE was getting memory into which to place the data
1672           created  by  pcre_study(). The fourth argument should point to a size_t
1673           variable.
1674    
1675    
1676  OBSOLETE INFO FUNCTION  OBSOLETE INFO FUNCTION
1677    
1678       int pcre_info(const pcre *code, int *optptr, *firstcharptr);         int pcre_info(const pcre *code, int *optptr, int *firstcharptr);
1679    
1680       The pcre_info() function is now obsolete because its  inter-         The pcre_info() function is now obsolete because its interface  is  too
1681       face  is  too  restrictive  to return all the available data         restrictive  to return all the available data about a compiled pattern.
1682       about  a  compiled  pattern.   New   programs   should   use         New  programs  should  use  pcre_fullinfo()  instead.  The   yield   of
1683       pcre_fullinfo()  instead.  The  yield  of pcre_info() is the         pcre_info()  is the number of capturing subpatterns, or one of the fol-
1684       number of capturing subpatterns, or  one  of  the  following         lowing negative numbers:
1685       negative numbers:  
1686             PCRE_ERROR_NULL       the argument code was NULL
1687         PCRE_ERROR_NULL       the argument code was NULL           PCRE_ERROR_BADMAGIC   the "magic number" was not found
1688         PCRE_ERROR_BADMAGIC   the "magic number" was not found  
1689           If the optptr argument is not NULL, a copy of the  options  with  which
1690       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
1691       with which the pattern was compiled is placed in the integer         PCRE_INFO_OPTIONS above).
1692       it points to (see PCRE_INFO_OPTIONS above).  
1693           If the pattern is not anchored and the  firstcharptr  argument  is  not
1694       If the pattern is not anchored and the firstcharptr argument         NULL,  it is used to pass back information about the first character of
1695       is  not  NULL, it is used to pass back information about the         any matched string (see PCRE_INFO_FIRSTBYTE above).
1696       first    character    of    any    matched    string    (see  
1697       PCRE_INFO_FIRSTBYTE above).  
1698    REFERENCE COUNTS
1699    
1700           int pcre_refcount(pcre *code, int adjust);
1701    
1702           The pcre_refcount() function is used to maintain a reference  count  in
1703           the data block that contains a compiled pattern. It is provided for the
1704           benefit of applications that  operate  in  an  object-oriented  manner,
1705           where different parts of the application may be using the same compiled
1706           pattern, but you want to free the block when they are all done.
1707    
1708           When a pattern is compiled, the reference count field is initialized to
1709           zero.   It is changed only by calling this function, whose action is to
1710           add the adjust value (which may be positive or  negative)  to  it.  The
1711           yield of the function is the new value. However, the value of the count
1712           is constrained to lie between 0 and 65535, inclusive. If the new  value
1713           is outside these limits, it is forced to the appropriate limit value.
1714    
1715           Except  when it is zero, the reference count is not correctly preserved
1716           if a pattern is compiled on one host and then  transferred  to  a  host
1717           whose byte-order is different. (This seems a highly unlikely scenario.)
1718    
1719    
1720    MATCHING A PATTERN: THE TRADITIONAL FUNCTION
1721    
1722           int pcre_exec(const pcre *code, const pcre_extra *extra,
1723                const char *subject, int length, int startoffset,
1724                int options, int *ovector, int ovecsize);
1725    
1726           The function pcre_exec() is called to match a subject string against  a
1727           compiled  pattern, which is passed in the code argument. If the pattern
1728           has been studied, the result of the study should be passed in the extra
1729           argument.  This  function is the main matching facility of the library,
1730           and it operates in a Perl-like manner. For specialist use there is also
1731           an  alternative matching function, which is described below in the sec-
1732           tion about the pcre_dfa_exec() function.
1733    
1734           In most applications, the pattern will have been compiled (and  option-
1735           ally  studied)  in the same process that calls pcre_exec(). However, it
1736           is possible to save compiled patterns and study data, and then use them
1737           later  in  different processes, possibly even on different hosts. For a
1738           discussion about this, see the pcreprecompile documentation.
1739    
1740           Here is an example of a simple call to pcre_exec():
1741    
1742             int rc;
1743             int ovector[30];
1744             rc = pcre_exec(
1745               re,             /* result of pcre_compile() */
1746               NULL,           /* we didn't study the pattern */
1747               "some string",  /* the subject string */
1748               11,             /* the length of the subject string */
1749               0,              /* start at offset 0 in the subject */
1750               0,              /* default options */
1751               ovector,        /* vector of integers for substring information */
1752               30);            /* number of elements (NOT size in bytes) */
1753    
1754       Extra data for pcre_exec()
1755    
1756           If the extra argument is not NULL, it must point to a  pcre_extra  data
1757           block.  The pcre_study() function returns such a block (when it doesn't
1758           return NULL), but you can also create one for yourself, and pass  addi-
1759           tional  information  in it. The pcre_extra block contains the following
1760           fields (not necessarily in this order):
1761    
1762             unsigned long int flags;
1763             void *study_data;
1764             unsigned long int match_limit;
1765             unsigned long int match_limit_recursion;
1766             void *callout_data;
1767             const unsigned char *tables;
1768    
1769           The flags field is a bitmap that specifies which of  the  other  fields
1770           are set. The flag bits are:
1771    
1772             PCRE_EXTRA_STUDY_DATA
1773             PCRE_EXTRA_MATCH_LIMIT
1774             PCRE_EXTRA_MATCH_LIMIT_RECURSION
1775             PCRE_EXTRA_CALLOUT_DATA
1776             PCRE_EXTRA_TABLES
1777    
1778           Other  flag  bits should be set to zero. The study_data field is set in
1779           the pcre_extra block that is returned by  pcre_study(),  together  with
1780           the appropriate flag bit. You should not set this yourself, but you may
1781           add to the block by setting the other fields  and  their  corresponding
1782           flag bits.
1783    
1784           The match_limit field provides a means of preventing PCRE from using up
1785           a vast amount of resources when running patterns that are not going  to
1786           match,  but  which  have  a very large number of possibilities in their
1787           search trees. The classic  example  is  the  use  of  nested  unlimited
1788           repeats.
1789    
1790           Internally,  PCRE uses a function called match() which it calls repeat-
1791           edly (sometimes recursively). The limit set by match_limit  is  imposed
1792           on  the  number  of times this function is called during a match, which
1793           has the effect of limiting the amount of  backtracking  that  can  take
1794           place. For patterns that are not anchored, the count restarts from zero
1795           for each position in the subject string.
1796    
1797           The default value for the limit can be set  when  PCRE  is  built;  the
1798           default  default  is 10 million, which handles all but the most extreme
1799           cases. You can override the default  by  suppling  pcre_exec()  with  a
1800           pcre_extra     block    in    which    match_limit    is    set,    and
1801           PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If  the  limit  is
1802           exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
1803    
1804           The  match_limit_recursion field is similar to match_limit, but instead
1805           of limiting the total number of times that match() is called, it limits
1806           the  depth  of  recursion. The recursion depth is a smaller number than
1807           the total number of calls, because not all calls to match() are  recur-
1808           sive.  This limit is of use only if it is set smaller than match_limit.
1809    
1810           Limiting the recursion depth limits the amount of  stack  that  can  be
1811           used, or, when PCRE has been compiled to use memory on the heap instead
1812           of the stack, the amount of heap memory that can be used.
1813    
1814           The default value for match_limit_recursion can be  set  when  PCRE  is
1815           built;  the  default  default  is  the  same  value  as the default for
1816           match_limit. You can override the default by suppling pcre_exec()  with
1817           a   pcre_extra   block  in  which  match_limit_recursion  is  set,  and
1818           PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in  the  flags  field.  If  the
1819           limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
1820    
1821           The  pcre_callout  field is used in conjunction with the "callout" fea-
1822           ture, which is described in the pcrecallout documentation.
1823    
1824           The tables field  is  used  to  pass  a  character  tables  pointer  to
1825           pcre_exec();  this overrides the value that is stored with the compiled
1826           pattern. A non-NULL value is stored with the compiled pattern  only  if
1827           custom  tables  were  supplied to pcre_compile() via its tableptr argu-
1828           ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
1829           PCRE's  internal  tables  to be used. This facility is helpful when re-
1830           using patterns that have been saved after compiling  with  an  external
1831           set  of  tables,  because  the  external tables might be at a different
1832           address when pcre_exec() is called. See the  pcreprecompile  documenta-
1833           tion for a discussion of saving compiled patterns for later use.
1834    
1835       Option bits for pcre_exec()
1836    
1837           The  unused  bits of the options argument for pcre_exec() must be zero.
1838           The only bits that may  be  set  are  PCRE_ANCHORED,  PCRE_NEWLINE_xxx,
1839           PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   PCRE_NO_UTF8_CHECK   and
1840           PCRE_PARTIAL.
1841    
1842             PCRE_ANCHORED
1843    
1844           The PCRE_ANCHORED option limits pcre_exec() to matching  at  the  first
1845           matching  position.  If  a  pattern was compiled with PCRE_ANCHORED, or
1846           turned out to be anchored by virtue of its contents, it cannot be  made
1847           unachored at matching time.
1848    
1849             PCRE_BSR_ANYCRLF
1850             PCRE_BSR_UNICODE
1851    
1852           These options (which are mutually exclusive) control what the \R escape
1853           sequence matches. The choice is either to match only CR, LF,  or  CRLF,
1854           or  to  match  any Unicode newline sequence. These options override the
1855           choice that was made or defaulted when the pattern was compiled.
1856    
1857             PCRE_NEWLINE_CR
1858             PCRE_NEWLINE_LF
1859             PCRE_NEWLINE_CRLF
1860             PCRE_NEWLINE_ANYCRLF
1861             PCRE_NEWLINE_ANY
1862    
1863           These options override  the  newline  definition  that  was  chosen  or
1864           defaulted  when the pattern was compiled. For details, see the descrip-
1865           tion of pcre_compile()  above.  During  matching,  the  newline  choice
1866           affects  the  behaviour  of the dot, circumflex, and dollar metacharac-
1867           ters. It may also alter the way the match position is advanced after  a
1868           match failure for an unanchored pattern.
1869    
1870           When  PCRE_NEWLINE_CRLF,  PCRE_NEWLINE_ANYCRLF,  or PCRE_NEWLINE_ANY is
1871           set, and a match attempt for an unanchored pattern fails when the  cur-
1872           rent  position  is  at  a  CRLF  sequence,  and the pattern contains no
1873           explicit matches for  CR  or  LF  characters,  the  match  position  is
1874           advanced by two characters instead of one, in other words, to after the
1875           CRLF.
1876    
1877           The above rule is a compromise that makes the most common cases work as
1878           expected.  For  example,  if  the  pattern  is .+A (and the PCRE_DOTALL
1879           option is not set), it does not match the string "\r\nA" because, after
1880           failing  at the start, it skips both the CR and the LF before retrying.
1881           However, the pattern [\r\n]A does match that string,  because  it  con-
1882           tains an explicit CR or LF reference, and so advances only by one char-
1883           acter after the first failure.
1884    
1885           An explicit match for CR of LF is either a literal appearance of one of
1886           those  characters,  or  one  of the \r or \n escape sequences. Implicit
1887           matches such as [^X] do not count, nor does \s (which includes  CR  and
1888           LF in the characters that it matches).
1889    
1890           Notwithstanding  the above, anomalous effects may still occur when CRLF
1891           is a valid newline sequence and explicit \r or \n escapes appear in the
1892           pattern.
1893    
1894             PCRE_NOTBOL
1895    
1896           This option specifies that first character of the subject string is not
1897           the beginning of a line, so the  circumflex  metacharacter  should  not
1898           match  before it. Setting this without PCRE_MULTILINE (at compile time)
1899           causes circumflex never to match. This option affects only  the  behav-
1900           iour of the circumflex metacharacter. It does not affect \A.
1901    
1902             PCRE_NOTEOL
1903    
1904           This option specifies that the end of the subject string is not the end
1905           of a line, so the dollar metacharacter should not match it nor  (except
1906           in  multiline mode) a newline immediately before it. Setting this with-
1907           out PCRE_MULTILINE (at compile time) causes dollar never to match. This
1908           option  affects only the behaviour of the dollar metacharacter. It does
1909           not affect \Z or \z.
1910    
1911             PCRE_NOTEMPTY
1912    
1913           An empty string is not considered to be a valid match if this option is
1914           set.  If  there are alternatives in the pattern, they are tried. If all
1915           the alternatives match the empty string, the entire  match  fails.  For
1916           example, if the pattern
1917    
1918             a?b?
1919    
1920           is  applied  to  a string not beginning with "a" or "b", it matches the
1921           empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
1922           match is not valid, so PCRE searches further into the string for occur-
1923           rences of "a" or "b".
1924    
1925           Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a spe-
1926           cial  case  of  a  pattern match of the empty string within its split()
1927           function, and when using the /g modifier. It  is  possible  to  emulate
1928           Perl's behaviour after matching a null string by first trying the match
1929           again at the same offset with PCRE_NOTEMPTY and PCRE_ANCHORED, and then
1930           if  that  fails by advancing the starting offset (see below) and trying
1931           an ordinary match again. There is some code that demonstrates how to do
1932           this in the pcredemo.c sample program.
1933    
1934             PCRE_NO_UTF8_CHECK
1935    
1936           When PCRE_UTF8 is set at compile time, the validity of the subject as a
1937           UTF-8 string is automatically checked when pcre_exec() is  subsequently
1938           called.   The  value  of  startoffset is also checked to ensure that it
1939           points to the start of a UTF-8 character. There is a  discussion  about
1940           the  validity  of  UTF-8 strings in the section on UTF-8 support in the
1941           main pcre page. If  an  invalid  UTF-8  sequence  of  bytes  is  found,
1942           pcre_exec()  returns  the error PCRE_ERROR_BADUTF8. If startoffset con-
1943           tains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
1944    
1945           If you already know that your subject is valid, and you  want  to  skip
1946           these    checks    for   performance   reasons,   you   can   set   the
1947           PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
1948           do  this  for the second and subsequent calls to pcre_exec() if you are
1949           making repeated calls to find all  the  matches  in  a  single  subject
1950           string.  However,  you  should  be  sure  that the value of startoffset
1951           points to the start of a UTF-8 character.  When  PCRE_NO_UTF8_CHECK  is
1952           set,  the  effect of passing an invalid UTF-8 string as a subject, or a
1953           value of startoffset that does not point to the start of a UTF-8  char-
1954           acter, is undefined. Your program may crash.
1955    
1956             PCRE_PARTIAL
1957    
1958           This  option  turns  on  the  partial  matching feature. If the subject
1959           string fails to match the pattern, but at some point during the  match-
1960           ing  process  the  end of the subject was reached (that is, the subject
1961           partially matches the pattern and the failure to  match  occurred  only
1962           because  there were not enough subject characters), pcre_exec() returns
1963           PCRE_ERROR_PARTIAL instead of PCRE_ERROR_NOMATCH. When PCRE_PARTIAL  is
1964           used,  there  are restrictions on what may appear in the pattern. These
1965           are discussed in the pcrepartial documentation.
1966    
1967       The string to be matched by pcre_exec()
1968    
1969           The subject string is passed to pcre_exec() as a pointer in subject,  a
1970           length  in  length, and a starting byte offset in startoffset. In UTF-8
1971           mode, the byte offset must point to the start  of  a  UTF-8  character.
1972           Unlike  the  pattern string, the subject may contain binary zero bytes.
1973           When the starting offset is zero, the search for a match starts at  the
1974           beginning of the subject, and this is by far the most common case.
1975    
1976           A  non-zero  starting offset is useful when searching for another match
1977           in the same subject by calling pcre_exec() again after a previous  suc-
1978           cess.   Setting  startoffset differs from just passing over a shortened
1979           string and setting PCRE_NOTBOL in the case of  a  pattern  that  begins
1980           with any kind of lookbehind. For example, consider the pattern
1981    
1982             \Biss\B
1983    
1984           which  finds  occurrences  of "iss" in the middle of words. (\B matches
1985           only if the current position in the subject is not  a  word  boundary.)
1986           When  applied  to the string "Mississipi" the first call to pcre_exec()
1987           finds the first occurrence. If pcre_exec() is called  again  with  just
1988           the  remainder  of  the  subject,  namely  "issipi", it does not match,
1989           because \B is always false at the start of the subject, which is deemed
1990           to  be  a  word  boundary. However, if pcre_exec() is passed the entire
1991           string again, but with startoffset set to 4, it finds the second occur-
1992           rence  of "iss" because it is able to look behind the starting point to
1993           discover that it is preceded by a letter.
1994    
1995           If a non-zero starting offset is passed when the pattern  is  anchored,
1996           one attempt to match at the given offset is made. This can only succeed
1997           if the pattern does not require the match to be at  the  start  of  the
1998           subject.
1999    
2000       How pcre_exec() returns captured substrings
2001    
2002           In  general, a pattern matches a certain portion of the subject, and in
2003           addition, further substrings from the subject  may  be  picked  out  by
2004           parts  of  the  pattern.  Following the usage in Jeffrey Friedl's book,
2005           this is called "capturing" in what follows, and the  phrase  "capturing
2006           subpattern"  is  used for a fragment of a pattern that picks out a sub-
2007           string. PCRE supports several other kinds of  parenthesized  subpattern
2008           that do not cause substrings to be captured.
2009    
2010           Captured  substrings are returned to the caller via a vector of integer
2011           offsets whose address is passed in ovector. The number of  elements  in
2012           the  vector is passed in ovecsize, which must be a non-negative number.
2013           Note: this argument is NOT the size of ovector in bytes.
2014    
2015           The first two-thirds of the vector is used to pass back  captured  sub-
2016           strings,  each  substring using a pair of integers. The remaining third
2017           of the vector is used as workspace by pcre_exec() while  matching  cap-
2018           turing  subpatterns, and is not available for passing back information.
2019           The length passed in ovecsize should always be a multiple of three.  If
2020           it is not, it is rounded down.
2021    
2022           When  a  match  is successful, information about captured substrings is
2023           returned in pairs of integers, starting at the  beginning  of  ovector,
2024           and  continuing  up  to two-thirds of its length at the most. The first
2025           element of a pair is set to the offset of the first character in a sub-
2026           string,  and  the  second  is  set to the offset of the first character
2027           after the end of a substring. The  first  pair,  ovector[0]  and  ovec-
2028           tor[1],  identify  the  portion  of  the  subject string matched by the
2029           entire pattern. The next pair is used for the first  capturing  subpat-
2030           tern, and so on. The value returned by pcre_exec() is one more than the
2031           highest numbered pair that has been set. For example, if two substrings
2032           have  been captured, the returned value is 3. If there are no capturing
2033           subpatterns, the return value from a successful match is 1,  indicating
2034           that just the first pair of offsets has been set.
2035    
2036           If a capturing subpattern is matched repeatedly, it is the last portion
2037           of the string that it matched that is returned.
2038    
2039           If the vector is too small to hold all the captured substring  offsets,
2040           it is used as far as possible (up to two-thirds of its length), and the
2041           function returns a value of zero. In particular, if the substring  off-
2042           sets are not of interest, pcre_exec() may be called with ovector passed
2043           as NULL and ovecsize as zero. However, if  the  pattern  contains  back
2044           references  and  the  ovector is not big enough to remember the related
2045           substrings, PCRE has to get additional memory for use during  matching.
2046           Thus it is usually advisable to supply an ovector.
2047    
2048           The  pcre_info()  function  can  be used to find out how many capturing
2049           subpatterns there are in a compiled  pattern.  The  smallest  size  for
2050           ovector  that  will allow for n captured substrings, in addition to the
2051           offsets of the substring matched by the whole pattern, is (n+1)*3.
2052    
2053           It is possible for capturing subpattern number n+1 to match  some  part
2054           of the subject when subpattern n has not been used at all. For example,
2055           if the string "abc" is matched  against  the  pattern  (a|(z))(bc)  the
2056           return from the function is 4, and subpatterns 1 and 3 are matched, but
2057           2 is not. When this happens, both values in  the  offset  pairs  corre-
2058           sponding to unused subpatterns are set to -1.
2059    
2060           Offset  values  that correspond to unused subpatterns at the end of the
2061           expression are also set to -1. For example,  if  the  string  "abc"  is
2062           matched  against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
2063           matched. The return from the function is 2, because  the  highest  used
2064           capturing subpattern number is 1. However, you can refer to the offsets
2065           for the second and third capturing subpatterns if  you  wish  (assuming
2066           the vector is large enough, of course).
2067    
2068           Some  convenience  functions  are  provided for extracting the captured
2069           substrings as separate strings. These are described below.
2070    
2071       Error return values from pcre_exec()
2072    
2073           If pcre_exec() fails, it returns a negative number. The  following  are
2074           defined in the header file:
2075    
2076             PCRE_ERROR_NOMATCH        (-1)
2077    
2078           The subject string did not match the pattern.
2079    
2080             PCRE_ERROR_NULL           (-2)
2081    
2082           Either  code  or  subject  was  passed as NULL, or ovector was NULL and
2083           ovecsize was not zero.
2084    
2085             PCRE_ERROR_BADOPTION      (-3)
2086    
2087           An unrecognized bit was set in the options argument.
2088    
2089             PCRE_ERROR_BADMAGIC       (-4)
2090    
2091           PCRE stores a 4-byte "magic number" at the start of the compiled  code,
2092           to catch the case when it is passed a junk pointer and to detect when a
2093           pattern that was compiled in an environment of one endianness is run in
2094           an  environment  with the other endianness. This is the error that PCRE
2095           gives when the magic number is not present.
2096    
2097             PCRE_ERROR_UNKNOWN_OPCODE (-5)
2098    
2099           While running the pattern match, an unknown item was encountered in the
2100           compiled  pattern.  This  error  could be caused by a bug in PCRE or by
2101           overwriting of the compiled pattern.
2102    
2103             PCRE_ERROR_NOMEMORY       (-6)
2104    
2105           If a pattern contains back references, but the ovector that  is  passed
2106           to pcre_exec() is not big enough to remember the referenced substrings,
2107           PCRE gets a block of memory at the start of matching to  use  for  this
2108           purpose.  If the call via pcre_malloc() fails, this error is given. The
2109           memory is automatically freed at the end of matching.
2110    
2111             PCRE_ERROR_NOSUBSTRING    (-7)
2112    
2113           This error is used by the pcre_copy_substring(),  pcre_get_substring(),
2114           and  pcre_get_substring_list()  functions  (see  below).  It  is  never
2115           returned by pcre_exec().
2116    
2117             PCRE_ERROR_MATCHLIMIT     (-8)
2118    
2119           The backtracking limit, as specified by  the  match_limit  field  in  a
2120           pcre_extra  structure  (or  defaulted) was reached. See the description
2121           above.
2122    
2123             PCRE_ERROR_CALLOUT        (-9)
2124    
2125           This error is never generated by pcre_exec() itself. It is provided for
2126           use  by  callout functions that want to yield a distinctive error code.
2127           See the pcrecallout documentation for details.
2128    
2129             PCRE_ERROR_BADUTF8        (-10)
2130    
2131           A string that contains an invalid UTF-8 byte sequence was passed  as  a
2132           subject.
2133    
2134             PCRE_ERROR_BADUTF8_OFFSET (-11)
2135    
2136           The UTF-8 byte sequence that was passed as a subject was valid, but the
2137           value of startoffset did not point to the beginning of a UTF-8  charac-
2138           ter.
2139    
2140             PCRE_ERROR_PARTIAL        (-12)
2141    
2142           The  subject  string did not match, but it did match partially. See the
2143           pcrepartial documentation for details of partial matching.
2144    
2145             PCRE_ERROR_BADPARTIAL     (-13)
2146    
2147           The PCRE_PARTIAL option was used with  a  compiled  pattern  containing
2148           items  that are not supported for partial matching. See the pcrepartial
2149           documentation for details of partial matching.
2150    
2151             PCRE_ERROR_INTERNAL       (-14)
2152    
2153           An unexpected internal error has occurred. This error could  be  caused
2154           by a bug in PCRE or by overwriting of the compiled pattern.
2155    
2156             PCRE_ERROR_BADCOUNT       (-15)
2157    
2158           This  error is given if the value of the ovecsize argument is negative.
2159    
2160             PCRE_ERROR_RECURSIONLIMIT (-21)
2161    
2162           The internal recursion limit, as specified by the match_limit_recursion
2163           field  in  a  pcre_extra  structure (or defaulted) was reached. See the
2164           description above.
2165    
2166             PCRE_ERROR_BADNEWLINE     (-23)
2167    
2168  MATCHING A PATTERN         An invalid combination of PCRE_NEWLINE_xxx options was given.
2169    
2170       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.  
2171    
2172    
2173  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER  EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
2174    
2175       int pcre_copy_substring(const char *subject, int *ovector,         int pcre_copy_substring(const char *subject, int *ovector,
2176            int stringcount, int stringnumber, char *buffer,              int stringcount, int stringnumber, char *buffer,
2177            int buffersize);              int buffersize);
2178    
2179       int pcre_get_substring(const char *subject, int *ovector,         int pcre_get_substring(const char *subject, int *ovector,
2180            int stringcount, int stringnumber,              int stringcount, int stringnumber,
2181            const char **stringptr);              const char **stringptr);
2182    
2183       int pcre_get_substring_list(const char *subject,         int pcre_get_substring_list(const char *subject,
2184            int *ovector, int stringcount, const char ***listptr);              int *ovector, int stringcount, const char ***listptr);
2185    
2186       Captured substrings can be accessed directly  by  using  the         Captured substrings can be  accessed  directly  by  using  the  offsets
2187       offsets returned by pcre_exec() in ovector. For convenience,         returned  by  pcre_exec()  in  ovector.  For convenience, the functions
2188       the functions  pcre_copy_substring(),  pcre_get_substring(),         pcre_copy_substring(),    pcre_get_substring(),    and    pcre_get_sub-
2189       and  pcre_get_substring_list()  are  provided for extracting         string_list()  are  provided for extracting captured substrings as new,
2190       captured  substrings  as  new,   separate,   zero-terminated         separate, zero-terminated strings. These functions identify  substrings
2191       strings.  These functions identify substrings by number. The         by  number.  The  next section describes functions for extracting named
2192       next section describes functions for extracting  named  sub-         substrings.
2193       strings.   A  substring  that  contains  a  binary  zero  is  
2194       correctly extracted and has a further zero added on the end,         A substring that contains a binary zero is correctly extracted and  has
2195       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
2196           string.  However, you can process such a string  by  referring  to  the
2197       The first three arguments are the  same  for  all  three  of         length  that  is  returned  by  pcre_copy_substring() and pcre_get_sub-
2198       these  functions:   subject  is the subject string which has         string().  Unfortunately, the interface to pcre_get_substring_list() is
2199       just been successfully matched, ovector is a pointer to  the         not  adequate for handling strings containing binary zeros, because the
2200       vector  of  integer  offsets that was passed to pcre_exec(),         end of the final string is not independently indicated.
2201       and stringcount is the number of substrings that  were  cap-  
2202       tured by the match, including the substring that matched the         The first three arguments are the same for all  three  of  these  func-
2203       entire regular expression. This is  the  value  returned  by         tions:  subject  is  the subject string that has just been successfully
2204       pcre_exec  if  it  is  greater  than  zero.  If  pcre_exec()         matched, ovector is a pointer to the vector of integer offsets that was
2205       returned zero, indicating that it ran out of space in  ovec-         passed to pcre_exec(), and stringcount is the number of substrings that
2206       tor,  the  value passed as stringcount should be the size of         were captured by the match, including the substring  that  matched  the
2207       the vector divided by three.         entire regular expression. This is the value returned by pcre_exec() if
2208           it is greater than zero. If pcre_exec() returned zero, indicating  that
2209       The functions pcre_copy_substring() and pcre_get_substring()         it  ran out of space in ovector, the value passed as stringcount should
2210       extract a single substring, whose number is given as string-         be the number of elements in the vector divided by three.
2211       number. A value of zero extracts the substring that  matched  
2212       the entire pattern, while higher values extract the captured         The functions pcre_copy_substring() and pcre_get_substring() extract  a
2213       substrings. For pcre_copy_substring(), the string is  placed         single  substring,  whose  number  is given as stringnumber. A value of
2214       in  buffer,  whose  length is given by buffersize, while for         zero extracts the substring that matched the  entire  pattern,  whereas
2215       pcre_get_substring() a new block of memory is  obtained  via         higher  values  extract  the  captured  substrings.  For pcre_copy_sub-
2216       pcre_malloc,  and its address is returned via stringptr. The         string(), the string is placed in buffer,  whose  length  is  given  by
2217       yield of the function is  the  length  of  the  string,  not         buffersize,  while  for  pcre_get_substring()  a new block of memory is
2218       including the terminating zero, or one of         obtained via pcre_malloc, and its address is  returned  via  stringptr.
2219           The  yield  of  the function is the length of the string, not including
2220         PCRE_ERROR_NOMEMORY       (-6)         the terminating zero, or one of these error codes:
2221    
2222       The buffer was too small for pcre_copy_substring(),  or  the           PCRE_ERROR_NOMEMORY       (-6)
2223       attempt to get memory failed for pcre_get_substring().  
2224           The buffer was too small for pcre_copy_substring(), or the  attempt  to
2225         PCRE_ERROR_NOSUBSTRING    (-7)         get memory failed for pcre_get_substring().
2226    
2227       There is no substring whose number is stringnumber.           PCRE_ERROR_NOSUBSTRING    (-7)
2228    
2229       The pcre_get_substring_list() function extracts  all  avail-         There is no substring whose number is stringnumber.
2230       able  substrings  and builds a list of pointers to them. All  
2231       this is done in a single block of memory which  is  obtained         The  pcre_get_substring_list()  function  extracts  all  available sub-
2232       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
2233       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
2234       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
2235       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
2236           pointer. The yield of the function is zero if all  went  well,  or  the
2237         PCRE_ERROR_NOMEMORY       (-6)         error code
2238    
2239       if the attempt to get the memory block failed.           PCRE_ERROR_NOMEMORY       (-6)
2240    
2241       When any of these functions encounter a  substring  that  is         if the attempt to get the memory block failed.
2242       unset, which can happen when capturing subpattern number n+1  
2243       matches some part of the subject, but subpattern n  has  not         When  any of these functions encounter a substring that is unset, which
2244       been  used  at all, they return an empty string. This can be         can happen when capturing subpattern number n+1 matches  some  part  of
2245       distinguished  from  a  genuine  zero-length  substring   by         the  subject, but subpattern n has not been used at all, they return an
2246       inspecting the appropriate offset in ovector, which is nega-         empty string. This can be distinguished from a genuine zero-length sub-
2247       tive for unset substrings.         string  by inspecting the appropriate offset in ovector, which is nega-
2248           tive for unset substrings.
2249       The  two  convenience  functions  pcre_free_substring()  and  
2250       pcre_free_substring_list()  can  be  used to free the memory         The two convenience functions pcre_free_substring() and  pcre_free_sub-
2251       returned by  a  previous  call  of  pcre_get_substring()  or         string_list()  can  be  used  to free the memory returned by a previous
2252       pcre_get_substring_list(),  respectively.  They  do  nothing         call  of  pcre_get_substring()  or  pcre_get_substring_list(),  respec-
2253       more than call the function pointed to by  pcre_free,  which         tively.  They  do  nothing  more  than  call the function pointed to by
2254       of  course  could  be called directly from a C program. How-         pcre_free, which of course could be called directly from a  C  program.
2255       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-
2256       a  special  interface  to another programming language which         cial  interface  to  another  programming  language  that  cannot   use
2257       cannot use pcre_free directly; it is for  these  cases  that         pcre_free  directly;  it is for these cases that the functions are pro-
2258       the functions are provided.         vided.
2259    
2260    
2261  EXTRACTING CAPTURED SUBSTRINGS BY NAME  EXTRACTING CAPTURED SUBSTRINGS BY NAME
2262    
2263       int pcre_copy_named_substring(const pcre *code,         int pcre_get_stringnumber(const pcre *code,
2264            const char *subject, int *ovector,              const char *name);
2265            int stringcount, const char *stringname,  
2266            char *buffer, int buffersize);         int pcre_copy_named_substring(const pcre *code,
2267                const char *subject, int *ovector,
2268       int pcre_get_stringnumber(const pcre *code,              int stringcount, const char *stringname,
2269            const char *name);              char *buffer, int buffersize);
2270    
2271       int pcre_get_named_substring(const pcre *code,         int pcre_get_named_substring(const pcre *code,
2272            const char *subject, int *ovector,              const char *subject, int *ovector,
2273            int stringcount, const char *stringname,              int stringcount, const char *stringname,
2274            const char **stringptr);              const char **stringptr);
2275    
2276       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-
2277       ciated    number.    This    can    be   done   by   calling         ber.  For example, for this pattern
2278       pcre_get_stringnumber(). The first argument is the  compiled  
2279       pattern,  and  the second is the name. For example, for this           (a+)b(?<xxx>\d+)...
2280       pattern  
2281           the number of the subpattern called "xxx" is 2. If the name is known to
2282         ab(?<xxx>\d+)...         be unique (PCRE_DUPNAMES was not set), you can find the number from the
2283           name by calling pcre_get_stringnumber(). The first argument is the com-
2284       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
2285       number,  you can then extract the substring directly, or use         the  subpattern  number,  or PCRE_ERROR_NOSUBSTRING (-7) if there is no
2286       one of the functions described in the previous section.  For         subpattern of that name.
2287       convenience,  there are also two functions that do the whole  
2288       job.         Given the number, you can extract the substring directly, or use one of
2289           the functions described in the previous section. For convenience, there
2290       Most of the  arguments  of  pcre_copy_named_substring()  and         are also two functions that do the whole job.
2291       pcre_get_named_substring()  are  the  same  as those for the  
2292       functions that  extract  by  number,  and  so  are  not  re-         Most   of   the   arguments    of    pcre_copy_named_substring()    and
2293       described here. There are just two differences.         pcre_get_named_substring()  are  the  same  as  those for the similarly
2294           named functions that extract by number. As these are described  in  the
2295       First, instead of a substring number, a  substring  name  is         previous  section,  they  are not re-described here. There are just two
2296       given.  Second,  there  is  an  extra argument, given at the         differences:
2297       start, which is a pointer to the compiled pattern.  This  is  
2298       needed  in order to gain access to the name-to-number trans-         First, instead of a substring number, a substring name is  given.  Sec-
2299       lation table.         ond, there is an extra argument, given at the start, which is a pointer
2300           to the compiled pattern. This is needed in order to gain access to  the
2301       These functions  call  pcre_get_stringnumber(),  and  if  it         name-to-number translation table.
2302       succeeds,    they   then   call   pcre_copy_substring()   or  
2303       pcre_get_substring(), as appropriate.         These  functions call pcre_get_stringnumber(), and if it succeeds, they
2304           then call pcre_copy_substring() or pcre_get_substring(),  as  appropri-
2305           ate.  NOTE:  If PCRE_DUPNAMES is set and there are duplicate names, the
2306           behaviour may not be what you want (see the next section).
2307    
2308    
2309    DUPLICATE SUBPATTERN NAMES
2310    
2311           int pcre_get_stringtable_entries(const pcre *code,
2312                const char *name, char **first, char **last);
2313    
2314           When a pattern is compiled with the  PCRE_DUPNAMES  option,  names  for
2315           subpatterns  are  not  required  to  be unique. Normally, patterns with
2316           duplicate names are such that in any one match, only one of  the  named
2317           subpatterns  participates. An example is shown in the pcrepattern docu-
2318           mentation.
2319    
2320           When   duplicates   are   present,   pcre_copy_named_substring()    and
2321           pcre_get_named_substring()  return the first substring corresponding to
2322           the given name that is set. If  none  are  set,  PCRE_ERROR_NOSUBSTRING
2323           (-7)  is  returned;  no  data  is returned. The pcre_get_stringnumber()
2324           function returns one of the numbers that are associated with the  name,
2325           but it is not defined which it is.
2326    
2327           If  you want to get full details of all captured substrings for a given
2328           name, you must use  the  pcre_get_stringtable_entries()  function.  The
2329           first argument is the compiled pattern, and the second is the name. The
2330           third and fourth are pointers to variables which  are  updated  by  the
2331           function. After it has run, they point to the first and last entries in
2332           the name-to-number table  for  the  given  name.  The  function  itself
2333           returns  the  length  of  each entry, or PCRE_ERROR_NOSUBSTRING (-7) if
2334           there are none. The format of the table is described above in the  sec-
2335           tion  entitled  Information  about  a  pattern.  Given all the relevant
2336           entries for the name, you can extract each of their numbers, and  hence
2337           the captured data, if any.
2338    
2339    
2340    FINDING ALL POSSIBLE MATCHES
2341    
2342           The  traditional  matching  function  uses a similar algorithm to Perl,
2343           which stops when it finds the first match, starting at a given point in
2344           the  subject.  If you want to find all possible matches, or the longest
2345           possible match, consider using the alternative matching  function  (see
2346           below)  instead.  If you cannot use the alternative function, but still
2347           need to find all possible matches, you can kludge it up by  making  use
2348           of the callout facility, which is described in the pcrecallout documen-
2349           tation.
2350    
2351           What you have to do is to insert a callout right at the end of the pat-
2352           tern.   When your callout function is called, extract and save the cur-
2353           rent matched substring. Then return  1,  which  forces  pcre_exec()  to
2354           backtrack  and  try other alternatives. Ultimately, when it runs out of
2355           matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.
2356    
2357    
2358    MATCHING A PATTERN: THE ALTERNATIVE FUNCTION
2359    
2360           int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
2361                const char *subject, int length, int startoffset,
2362                int options, int *ovector, int ovecsize,
2363                int *workspace, int wscount);
2364    
2365           The function pcre_dfa_exec()  is  called  to  match  a  subject  string
2366           against  a  compiled pattern, using a matching algorithm that scans the
2367           subject string just once, and does not backtrack.  This  has  different
2368           characteristics  to  the  normal  algorithm, and is not compatible with
2369           Perl. Some of the features of PCRE patterns are not  supported.  Never-
2370           theless,  there are times when this kind of matching can be useful. For
2371           a discussion of the two matching algorithms, see the pcrematching docu-
2372           mentation.
2373    
2374           The  arguments  for  the  pcre_dfa_exec()  function are the same as for
2375           pcre_exec(), plus two extras. The ovector argument is used in a differ-
2376           ent  way,  and  this is described below. The other common arguments are
2377           used in the same way as for pcre_exec(), so their  description  is  not
2378           repeated here.
2379    
2380           The  two  additional  arguments provide workspace for the function. The
2381           workspace vector should contain at least 20 elements. It  is  used  for
2382           keeping  track  of  multiple  paths  through  the  pattern  tree.  More
2383           workspace will be needed for patterns and subjects where  there  are  a
2384           lot of potential matches.
2385    
2386           Here is an example of a simple call to pcre_dfa_exec():
2387    
2388             int rc;
2389             int ovector[10];
2390             int wspace[20];
2391             rc = pcre_dfa_exec(
2392               re,             /* result of pcre_compile() */
2393               NULL,           /* we didn't study the pattern */
2394               "some string",  /* the subject string */
2395               11,             /* the length of the subject string */
2396               0,              /* start at offset 0 in the subject */
2397               0,              /* default options */
2398               ovector,        /* vector of integers for substring information */
2399               10,             /* number of elements (NOT size in bytes) */
2400               wspace,         /* working space vector */
2401               20);            /* number of elements (NOT size in bytes) */
2402    
2403       Option bits for pcre_dfa_exec()
2404    
2405           The  unused  bits  of  the options argument for pcre_dfa_exec() must be
2406           zero. The only bits  that  may  be  set  are  PCRE_ANCHORED,  PCRE_NEW-
2407           LINE_xxx,  PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK,
2408           PCRE_PARTIAL, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART. All but the last
2409           three of these are the same as for pcre_exec(), so their description is
2410           not repeated here.
2411    
2412             PCRE_PARTIAL
2413    
2414           This has the same general effect as it does for  pcre_exec(),  but  the
2415           details   are   slightly   different.  When  PCRE_PARTIAL  is  set  for
2416           pcre_dfa_exec(), the return code PCRE_ERROR_NOMATCH is  converted  into
2417           PCRE_ERROR_PARTIAL  if  the  end  of the subject is reached, there have
2418           been no complete matches, but there is still at least one matching pos-
2419           sibility.  The portion of the string that provided the partial match is
2420           set as the first matching string.
2421    
2422             PCRE_DFA_SHORTEST
2423    
2424           Setting the PCRE_DFA_SHORTEST option causes the matching  algorithm  to
2425           stop as soon as it has found one match. Because of the way the alterna-
2426           tive algorithm works, this is necessarily the shortest  possible  match
2427           at the first possible matching point in the subject string.
2428    
2429             PCRE_DFA_RESTART
2430    
2431           When  pcre_dfa_exec()  is  called  with  the  PCRE_PARTIAL  option, and
2432           returns a partial match, it is possible to call it  again,  with  addi-
2433           tional  subject  characters,  and have it continue with the same match.
2434           The PCRE_DFA_RESTART option requests this action; when it is  set,  the
2435           workspace  and wscount options must reference the same vector as before
2436           because data about the match so far is left in  them  after  a  partial
2437           match.  There  is  more  discussion of this facility in the pcrepartial
2438           documentation.
2439    
2440       Successful returns from pcre_dfa_exec()
2441    
2442           When pcre_dfa_exec() succeeds, it may have matched more than  one  sub-
2443           string in the subject. Note, however, that all the matches from one run
2444           of the function start at the same point in  the  subject.  The  shorter
2445           matches  are all initial substrings of the longer matches. For example,
2446           if the pattern
2447    
2448             <.*>
2449    
2450           is matched against the string
2451    
2452             This is <something> <something else> <something further> no more
2453    
2454           the three matched strings are
2455    
2456             <something>
2457             <something> <something else>
2458             <something> <something else> <something further>
2459    
2460           On success, the yield of the function is a number  greater  than  zero,
2461           which  is  the  number of matched substrings. The substrings themselves
2462           are returned in ovector. Each string uses two elements;  the  first  is
2463           the  offset  to  the start, and the second is the offset to the end. In
2464           fact, all the strings have the same start  offset.  (Space  could  have
2465           been  saved by giving this only once, but it was decided to retain some
2466           compatibility with the way pcre_exec() returns data,  even  though  the
2467           meaning of the strings is different.)
2468    
2469           The strings are returned in reverse order of length; that is, the long-
2470           est matching string is given first. If there were too many  matches  to
2471           fit  into ovector, the yield of the function is zero, and the vector is
2472           filled with the longest matches.
2473    
2474       Error returns from pcre_dfa_exec()
2475    
2476           The pcre_dfa_exec() function returns a negative number when  it  fails.
2477           Many  of  the  errors  are  the  same as for pcre_exec(), and these are
2478           described above.  There are in addition the following errors  that  are
2479           specific to pcre_dfa_exec():
2480    
2481             PCRE_ERROR_DFA_UITEM      (-16)
2482    
2483           This  return is given if pcre_dfa_exec() encounters an item in the pat-
2484           tern that it does not support, for instance, the use of \C  or  a  back
2485           reference.
2486    
2487             PCRE_ERROR_DFA_UCOND      (-17)
2488    
2489           This  return  is  given  if pcre_dfa_exec() encounters a condition item
2490           that uses a back reference for the condition, or a test  for  recursion
2491           in a specific group. These are not supported.
2492    
2493             PCRE_ERROR_DFA_UMLIMIT    (-18)
2494    
2495           This  return  is given if pcre_dfa_exec() is called with an extra block
2496           that contains a setting of the match_limit field. This is not supported
2497           (it is meaningless).
2498    
2499             PCRE_ERROR_DFA_WSSIZE     (-19)
2500    
2501           This  return  is  given  if  pcre_dfa_exec()  runs  out of space in the
2502           workspace vector.
2503    
2504             PCRE_ERROR_DFA_RECURSE    (-20)
2505    
2506           When a recursive subpattern is processed, the matching  function  calls
2507           itself  recursively,  using  private vectors for ovector and workspace.
2508           This error is given if the output vector  is  not  large  enough.  This
2509           should be extremely rare, as a vector of size 1000 is used.
2510    
2511    
2512    SEE ALSO
2513    
2514           pcrebuild(3),  pcrecallout(3), pcrecpp(3)(3), pcrematching(3), pcrepar-
2515           tial(3), pcreposix(3), pcreprecompile(3), pcresample(3),  pcrestack(3).
2516    
2517    
2518    AUTHOR
2519    
2520           Philip Hazel
2521           University Computing Service
2522           Cambridge CB2 3QH, England.
2523    
2524    
2525    REVISION
2526    
2527           Last updated: 11 September 2007
2528           Copyright (c) 1997-2007 University of Cambridge.
2529    ------------------------------------------------------------------------------
2530    
2531    
2532    PCRECALLOUT(3)                                                  PCRECALLOUT(3)
2533    
 Last updated: 03 February 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2534    
2535  NAME  NAME
2536       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2537    
2538    
2539  PCRE CALLOUTS  PCRE CALLOUTS
2540    
2541       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.  
2542    
2543           PCRE provides a feature called "callout", which is a means of temporar-
2544           ily passing control to the caller of PCRE  in  the  middle  of  pattern
2545           matching.  The  caller of PCRE provides an external function by putting
2546           its entry point in the global variable pcre_callout. By  default,  this
2547           variable contains NULL, which disables all calling out.
2548    
2549           Within  a  regular  expression,  (?C) indicates the points at which the
2550           external function is to be called.  Different  callout  points  can  be
2551           identified  by  putting  a number less than 256 after the letter C. The
2552           default value is zero.  For  example,  this  pattern  has  two  callout
2553           points:
2554    
2555             (?C1)abc(?C2)def
2556    
2557           If  the  PCRE_AUTO_CALLOUT  option  bit  is  set when pcre_compile() is
2558           called, PCRE automatically  inserts  callouts,  all  with  number  255,
2559           before  each  item in the pattern. For example, if PCRE_AUTO_CALLOUT is
2560           used with the pattern
2561    
2562             A(\d{2}|--)
2563    
2564           it is processed as if it were
2565    
2566           (?C255)A(?C255)((?C255)\d{2}(?C255)|(?C255)-(?C255)-(?C255))(?C255)
2567    
2568           Notice that there is a callout before and after  each  parenthesis  and
2569           alternation  bar.  Automatic  callouts  can  be  used  for tracking the
2570           progress of pattern matching. The pcretest command has an  option  that
2571           sets  automatic callouts; when it is used, the output indicates how the
2572           pattern is matched. This is useful information when you are  trying  to
2573           optimize the performance of a particular pattern.
2574    
2575    
2576    MISSING CALLOUTS
2577    
2578           You  should  be  aware  that,  because of optimizations in the way PCRE
2579           matches patterns, callouts sometimes do not happen. For example, if the
2580           pattern is
2581    
2582             ab(?C4)cd
2583    
2584           PCRE knows that any matching string must contain the letter "d". If the
2585           subject string is "abyz", the lack of "d" means that  matching  doesn't
2586           ever  start,  and  the  callout is never reached. However, with "abyd",
2587           though the result is still no match, the callout is obeyed.
2588    
2589    
2590    THE CALLOUT INTERFACE
2591    
2592           During matching, when PCRE reaches a callout point, the external  func-
2593           tion  defined by pcre_callout is called (if it is set). This applies to
2594           both the pcre_exec() and the pcre_dfa_exec()  matching  functions.  The
2595           only  argument  to  the callout function is a pointer to a pcre_callout
2596           block. This structure contains the following fields:
2597    
2598             int          version;
2599             int          callout_number;
2600             int         *offset_vector;
2601             const char  *subject;
2602             int          subject_length;
2603             int          start_match;
2604             int          current_position;
2605             int          capture_top;
2606             int          capture_last;
2607             void        *callout_data;
2608             int          pattern_position;
2609             int          next_item_length;
2610    
2611           The version field is an integer containing the version  number  of  the
2612           block  format. The initial version was 0; the current version is 1. The
2613           version number will change again in future  if  additional  fields  are
2614           added, but the intention is never to remove any of the existing fields.
2615    
2616           The callout_number field contains the number of the  callout,  as  com-
2617           piled  into  the pattern (that is, the number after ?C for manual call-
2618           outs, and 255 for automatically generated callouts).
2619    
2620           The offset_vector field is a pointer to the vector of offsets that  was
2621           passed   by   the   caller  to  pcre_exec()  or  pcre_dfa_exec().  When
2622           pcre_exec() is used, the contents can be inspected in order to  extract
2623           substrings  that  have  been  matched  so  far,  in the same way as for
2624           extracting substrings after a match has completed. For  pcre_dfa_exec()
2625           this field is not useful.
2626    
2627           The subject and subject_length fields contain copies of the values that
2628           were passed to pcre_exec().
2629    
2630           The start_match field normally contains the offset within  the  subject
2631           at  which  the  current  match  attempt started. However, if the escape
2632           sequence \K has been encountered, this value is changed to reflect  the
2633           modified  starting  point.  If the pattern is not anchored, the callout
2634           function may be called several times from the same point in the pattern
2635           for different starting points in the subject.
2636    
2637           The  current_position  field  contains the offset within the subject of
2638           the current match pointer.
2639    
2640           When the pcre_exec() function is used, the capture_top  field  contains
2641           one  more than the number of the highest numbered captured substring so
2642           far. If no substrings have been captured, the value of  capture_top  is
2643           one.  This  is always the case when pcre_dfa_exec() is used, because it
2644           does not support captured substrings.
2645    
2646           The capture_last field contains the number of the  most  recently  cap-
2647           tured  substring. If no substrings have been captured, its value is -1.
2648           This is always the case when pcre_dfa_exec() is used.
2649    
2650           The callout_data field contains a value that is passed  to  pcre_exec()
2651           or  pcre_dfa_exec() specifically so that it can be passed back in call-
2652           outs. It is passed in the pcre_callout field  of  the  pcre_extra  data
2653           structure.  If  no such data was passed, the value of callout_data in a
2654           pcre_callout block is NULL. There is a description  of  the  pcre_extra
2655           structure in the pcreapi documentation.
2656    
2657           The  pattern_position field is present from version 1 of the pcre_call-
2658           out structure. It contains the offset to the next item to be matched in
2659           the pattern string.
2660    
2661           The  next_item_length field is present from version 1 of the pcre_call-
2662           out structure. It contains the length of the next item to be matched in
2663           the  pattern  string. When the callout immediately precedes an alterna-
2664           tion bar, a closing parenthesis, or the end of the pattern, the  length
2665           is  zero.  When the callout precedes an opening parenthesis, the length
2666           is that of the entire subpattern.
2667    
2668           The pattern_position and next_item_length fields are intended  to  help
2669           in  distinguishing between different automatic callouts, which all have
2670           the same callout number. However, they are set for all callouts.
2671    
2672    
2673  RETURN VALUES  RETURN VALUES
2674    
2675       The callout function returns an integer.  If  the  value  is         The external callout function returns an integer to PCRE. If the  value
2676       zero,  matching  proceeds as normal. If the value is greater         is  zero,  matching  proceeds  as  normal. If the value is greater than
2677       than zero, matching fails at the current  point,  but  back-         zero, matching fails at the current point, but  the  testing  of  other
2678       tracking  to test other possibilities goes ahead, just as if         matching possibilities goes ahead, just as if a lookahead assertion had
2679       a lookahead assertion had failed. If the value is less  than         failed. If the value is less than zero, the  match  is  abandoned,  and
2680       zero,  the  match  is abandoned, and pcre_exec() returns the         pcre_exec() (or pcre_dfa_exec()) returns the negative value.
2681       value.  
2682           Negative   values   should   normally   be   chosen  from  the  set  of
2683       Negative values should normally be chosen from  the  set  of         PCRE_ERROR_xxx values. In particular, PCRE_ERROR_NOMATCH forces a stan-
2684       PCRE_ERROR_xxx  values.  In  particular,  PCRE_ERROR_NOMATCH         dard  "no  match"  failure.   The  error  number  PCRE_ERROR_CALLOUT is
2685       forces a standard "no  match"  failure.   The  error  number         reserved for use by callout functions; it will never be  used  by  PCRE
2686       PCRE_ERROR_CALLOUT is reserved for use by callout functions;         itself.
2687       it will never be used by PCRE itself.  
2688    
2689    AUTHOR
2690    
2691           Philip Hazel
2692           University Computing Service
2693           Cambridge CB2 3QH, England.
2694    
2695    
2696    REVISION
2697    
2698           Last updated: 29 May 2007
2699           Copyright (c) 1997-2007 University of Cambridge.
2700    ------------------------------------------------------------------------------
2701    
2702    
2703    PCRECOMPAT(3)                                                    PCRECOMPAT(3)
2704    
 Last updated: 21 January 2003  
 Copyright (c) 1997-2003 University of Cambridge.  
 -----------------------------------------------------------------------------  
2705    
2706  NAME  NAME
2707       PCRE - Perl-compatible regular expressions         PCRE - Perl-compatible regular expressions
2708    
2709    
2710  DIFFERENCES FROM PERL  DIFFERENCES BETWEEN PCRE AND PERL
2711    
2712       This document describes the differences  in  the  ways  that         This  document describes the differences in the ways that PCRE and Perl
2713       PCRE  and  Perl  handle regular expressions. The differences         handle regular expressions. The differences described here  are  mainly
2714       described here are with respect to Perl 5.8.         with  respect  to  Perl 5.8, though PCRE versions 7.0 and later contain
2715           some features that are expected to be in the forthcoming Perl 5.10.
2716       1. PCRE does  not  allow  repeat  quantifiers  on  lookahead  
2717       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
2718       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
2719       next  three characters are not "a". It just asserts that the         main pcre page.
2720       next character is not "a" three times.  
2721           2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl
2722       2. Capturing subpatterns that occur inside  negative  looka-         permits  them,  but they do not mean what you might think. For example,
2723       head  assertions  are  counted,  but  their  entries  in the         (?!a){3} does not assert that the next three characters are not "a". It
2724       offsets vector are never set. Perl sets its numerical  vari-         just asserts that the next character is not "a" three times.
2725       ables  from  any  such  patterns that are matched before the  
2726       assertion fails to match something (thereby succeeding), but         3.  Capturing  subpatterns  that occur inside negative lookahead asser-
2727       only  if  the negative lookahead assertion contains just one         tions are counted, but their entries in the offsets  vector  are  never
2728       branch.         set.  Perl sets its numerical variables from any such patterns that are
2729           matched before the assertion fails to match something (thereby succeed-
2730       3. Though binary zero characters are supported in  the  sub-         ing),  but  only  if the negative lookahead assertion contains just one
2731       ject  string,  they  are  not  allowed  in  a pattern string         branch.
2732       because it is passed as a normal  C  string,  terminated  by  
2733       zero. The escape sequence "\0" can be used in the pattern to         4. Though binary zero characters are supported in the  subject  string,
2734       represent a binary zero.         they are not allowed in a pattern string because it is passed as a nor-
2735           mal C string, terminated by zero. The escape sequence \0 can be used in
2736       4. The following Perl escape sequences  are  not  supported:         the pattern to represent a binary zero.
2737       \l,  \u,  \L,  \U,  \P, \p, and \X. In fact these are imple-  
2738       mented by Perl's general string-handling and are not part of         5.  The  following Perl escape sequences are not supported: \l, \u, \L,
2739       its pattern matching engine. If any of these are encountered         \U, and \N. In fact these are implemented by Perl's general string-han-
2740       by PCRE, an error is generated.         dling  and are not part of its pattern matching engine. If any of these
2741           are encountered by PCRE, an error is generated.
2742       5. PCRE does support the \Q...\E  escape  for  quoting  sub-  
2743       strings. Characters in between are treated as literals. This         6. The Perl escape sequences \p, \P, and \X are supported only if  PCRE
2744       is slightly different from Perl in that $  and  @  are  also         is  built  with Unicode character property support. The properties that
2745       handled  as  literals inside the quotes. In Perl, they cause         can be tested with \p and \P are limited to the general category  prop-
2746       variable interpolation (but of course  PCRE  does  not  have         erties  such  as  Lu and Nd, script names such as Greek or Han, and the
2747       variables). Note the following examples:         derived properties Any and L&.
2748    
2749           Pattern            PCRE matches      Perl matches         7. PCRE does support the \Q...\E escape for quoting substrings. Charac-
2750           ters  in  between  are  treated as literals. This is slightly different
2751           \Qabc$xyz\E        abc$xyz           abc followed by the         from Perl in that $ and @ are  also  handled  as  literals  inside  the
2752                                                  contents of $xyz         quotes.  In Perl, they cause variable interpolation (but of course PCRE
2753           \Qabc\$xyz\E       abc\$xyz          abc\$xyz         does not have variables). Note the following examples:
2754           \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz  
2755               Pattern            PCRE matches      Perl matches
2756       In PCRE, the \Q...\E mechanism is not  recognized  inside  a  
2757       character class.             \Qabc$xyz\E        abc$xyz           abc followed by the
2758                                                      contents of $xyz
2759       8. Fairly obviously, PCRE does not support the (?{code}) and             \Qabc\$xyz\E       abc\$xyz          abc\$xyz
2760       (?p{code})  constructions. However, there is some experimen-             \Qabc\E\$\Qxyz\E   abc$xyz           abc$xyz
2761       tal support for recursive patterns using the non-Perl  items  
2762       (?R),  (?number)  and  (?P>name).  Also,  the PCRE "callout"         The \Q...\E sequence is recognized both inside  and  outside  character
2763       feature allows an external function to be called during pat-         classes.
2764       tern matching.  
2765           8. Fairly obviously, PCRE does not support the (?{code}) and (??{code})
2766       9. There are some differences that are  concerned  with  the         constructions. However, there is support for recursive  patterns.  This
2767       settings  of  captured  strings  when  part  of a pattern is         is  not available in Perl 5.8, but will be in Perl 5.10. Also, the PCRE
2768       repeated. For example, matching "aba"  against  the  pattern         "callout" feature allows an external function to be called during  pat-
2769       /^(a(b)?)+$/  in Perl leaves $2 unset, but in PCRE it is set         tern matching. See the pcrecallout documentation for details.
2770       to "b".  
2771           9.  Subpatterns  that  are  called  recursively or as "subroutines" are
2772       10. PCRE  provides  some  extensions  to  the  Perl  regular         always treated as atomic groups in  PCRE.  This  is  like  Python,  but
2773       expression facilities:         unlike Perl.
2774    
2775       (a) Although lookbehind assertions must match  fixed  length         10.  There are some differences that are concerned with the settings of
2776       strings,  each  alternative branch of a lookbehind assertion         captured strings when part of  a  pattern  is  repeated.  For  example,
2777       can match a different length of string. Perl  requires  them         matching  "aba"  against  the  pattern  /^(a(b)?)+$/  in Perl leaves $2
2778       all to have the same length.         unset, but in PCRE it is set to "b".
2779    
2780       (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is  not         11.  PCRE  does  support  Perl  5.10's  backtracking  verbs  (*ACCEPT),
2781       set,  the  $  meta-character matches only at the very end of         (*FAIL),  (*F),  (*COMMIT), (*PRUNE), (*SKIP), and (*THEN), but only in
2782       the string.         the forms without an  argument.  PCRE  does  not  support  (*MARK).  If
2783           (*ACCEPT)  is within capturing parentheses, PCRE does not set that cap-
2784       (c) If PCRE_EXTRA is set, a backslash followed by  a  letter         ture group; this is different to Perl.
2785       with no special meaning is faulted.  
2786           12. PCRE provides some extensions to the Perl regular expression facil-
2787       (d) If PCRE_UNGREEDY is set, the greediness of  the  repeti-         ities.   Perl  5.10  will  include new features that are not in earlier
2788       tion  quantifiers  is inverted, that is, by default they are         versions, some of which (such as named parentheses) have been  in  PCRE
2789       not greedy, but if followed by a question mark they are.         for some time. This list is with respect to Perl 5.10:
2790    
2791       (e) PCRE_ANCHORED can be used to force a pattern to be tried         (a)  Although  lookbehind  assertions  must match fixed length strings,
2792       only at the first matching position in the subject string.         each alternative branch of a lookbehind assertion can match a different
2793           length of string. Perl requires them all to have the same length.
2794       (f)  The  PCRE_NOTBOL,   PCRE_NOTEOL,   PCRE_NOTEMPTY,   and  
2795       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 $
2796       equivalents.         meta-character matches only at the very end of the string.
2797    
2798       (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-
2799       recursive  pattern  matching  (Perl  can  do  this using the         cial meaning is faulted. Otherwise, like Perl, the backslash is quietly
2800       (?p{code}) construct, which PCRE cannot support.)         ignored.  (Perl can be made to issue a warning.)
2801    
2802       (h) PCRE supports  named  capturing  substrings,  using